THE ELECTRONICS AND ELECTRICAL

ENGINEERING LABORATORY (EEEL)

One of NISTís seven measurement and standards laboratories,

EEEL conducts research, provides measurement services, and

helps set standards in support of the fundamental electronic

technologies of semiconductors, magnetics, and superconductors; information and communications technologies, such as

fiber optics, photonics, microwaves, electronic displays,

electronics manufacturing supply chain collaboration; forensics

and security measurement instrumentation; fundamental and

practical physical standards and measurement services for

electrical quantities; maintaining the quality and integrity of

electrical power systems; and the development of nanoscale

and microelectromechanical devices. EEEL provides support to

law enforcement, corrections, and criminal justice agencies,

including homeland security.

EEEL consists of six programmatic divisions and two matrixmanaged offices:

Electricity Division

Semiconductor Electronics Division

Radio-Frequency Technology Division

Electromagnetic Technology Division

Optoelectronics Division

Magnetic Technology Division

Office of Microelectronic Programs

Office of Law Enforcement Standards

This publication describes the technical programs of the

Electromagnetic Technology Division. Similar documents

describing the other Divisions and Offices are available.

Contact NIST/EEEL, 100 Bureau Drive, MS 8100,

Gaithersburg, MD 20899-8100, telephone 301-975-2220,

http://www.eeel.nist.gov. These publications are updated

biennially.

On the cover: Against a background of Jim Beall and Maggie Crews working in our yellow-lit

fabrication facility, in the upper left Sae Woo Nam tests room-temperature electronics for fundamental

Johnson noise temperature metrology, while in the lower right Paul Dresselhaus displays a wafer of

Josephson junction arrays fabricated for a quantum-based arbitrary waveform generator.
ELECTRONICS AND ELECTRICAL

ENGINEERING LABORATORY

ELECTROMAGNETIC

TECHNOLOGY

DIVISION

PROGRAMS, ACTIVITIES, AND

ACCOMPLISHMENTS

NISTIR 6626

January 2003

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director
Any mention of commercial products is for information only; it does not imply recommendation

or endorsement by the National Institute of Standards and Technology nor does it imply that the

products mentioned are necessarily the best available for the purpose.
Electromagnetic Technology Division iii

CONTENTS

Welcome ................................................................................................................................ iv

Quantum Standards ................................................................................................................ 1

Quantum Voltage .............................................................................................................. 1

Johnson Noise Thermometry ........................................................................................... 7

Single Electronics for Standards and Metrology ............................................................ 10

Physics of Quantum Hall Resistance Standards ............................................................ 15

Quantum Information ............................................................................................................ 17

Quantum Computing....................................................................................................... 17

Quantum Communication ............................................................................................... 19

Quantum Measurements....................................................................................................... 21

Cryogenic Sensors.......................................................................................................... 21

Terahertz Technology ..................................................................................................... 28

Emerging Electronic Materials ....................................................................................... 31

Nanoscale Fabrication .......................................................................................................... 36

Topics Covered by Organizational Units............................................................................... 37

Appendix A: Experimental Systems and Instruments ........................................................... 38

Appendix B: Post-Doctoral Opportunities ............................................................................ 39

Appendix C: Awards and Recognition .................................................................................. 44

Appendix D: Electromagnetic Technology Division Staff..................................................... 47
iv Electronics and Electrical Engineering Laboratory

WELCOME

The roughly 50 staff and guest scientists in the Electromagnetic Technology Division and I take

great pride in bringing you this brief report on recent progress of our Division. We have a long

history of inventing and disseminating new standards and measurement technology. We focus

on exceptional standards and measurement methods using remarkable quantum effects and low

noise available only at temperatures close to absolute zero or 0 K (ñ460 oF). This publication

describes some of our recent successes.

It has always been our goal to provide U.S. industry with the best metrology in the world. We

began about 35 years ago to bring the unique capabilities of cryogenic electronic technology to

bear on metrology, the science of measurement. In many cases our technology enables measurements that are otherwise impossible. We developed what has become the worldís practical

standard of voltage, based on integrated circuits containing tens of thousands of superconducting Josephson junctions made in our own fabrication facility. We demonstrated the first capacitance standard based on counting of single electrons. For materials analysis, we perfected an

X-ray spectrometer that combines the best features of two types of existing detectors and

promises to be critical in defect analysis of future semiconductor devices. We have also improved our cleanroom facilities, which are critical to all of our efforts and enable us to produce

microfabricated structures smaller than 100 nanometers.

We have a long tradition of excellence dating back to the formation of our organization in 1969.

Our world-leading work has resulted in many prestigious awards to our staff, some of which are

listed in Appendix C.

Whether you are our customer and use the results of our efforts, or are simply interested in the

remarkable progress our technology brings to measurements, we hope you will find this report

exciting. You will find descriptions of our recent work, lists of our publications, and descriptions

of our post-doctoral research opportunities. For the most up-to-date information, please visit

our Web site, http://emtech.boulder.nist.gov. Our website also contains a searchable bibliography of all of our publications.

Thank you for your interest in NISTís Electromagnetic Technology Division.

Richard E. Harris

Division Chief

January 2003

Electromagnetic Technology Division

National Institute of Standards and Technology

325 Broadway

Boulder, Colorado 80305-3328

(303) 497-3678

http://emtech.boulder.nist.gov
Electromagnetic Technology Division 1

QUANTUM STANDARDS

QUANTUM VOLTAGE

GOALS

To develop superconducting electronic circuit and

system technology for fundamental, quantumbased DC and AC voltage standard systems; to

provide improved standards for fundamental metrology; and to support U.S. industryís test and

measurement applications.

Clark Hamilton showing the probe for the 10 V

conventional Josephson voltage standard system

developed at NIST and used throughout the world for

calibration of Zener voltage references.

CUSTOMER NEEDS

The demands of modern technology for accurate

voltage calibrations have exceeded the capability

of classical artifact standards. To meet current

needs, an international agreement signed in 1990

redefined the practical volt in terms of the voltage

generated by a superconductive integrated circuit

developed at NIST and the PhysikalischTechnische Bundesanstalt in Germany. This circuit

contains thousands of superconducting Josephson junctions, all connected in a series array and

biased at a microwave frequency. The voltage developed by each junction depends only on the frequency and a fundamental physical constant; thus,

the circuit never needs to be calibrated. This allows any standards or commercial laboratory to

generate highly accurate voltages without the need

to calibrate an artifact standard. This advance has

improved the uniformity of voltage measurements

around the world by about a hundredfold. These

systems are rapidly becoming essential for meeting legal and accreditation requirements in commercial, governmental, and military activities.

The U.S. electronics instrumentation industry maintains its world position through the development

and deployment of increasingly accurate, flexible,

easy-to-use instruments. Providing U.S. industry

with quantum voltage standard systems gives these

customers, with appropriate assistance from the

NIST Electricity Division, immediate realization of

the highest possible in-house accuracy. These customers also benefit dramatically by eliminating their

dependence on less accurate reference standards

that require frequent calibration.

We also support the standards community by developing voltage standard systems with new capabilities, including lower cost, increased functionality, and ease of use. Other customers are the superconductive electronics community and the U.S.

military, which we support through development

of novel superconductive circuits and high-performance systems, and by providing technical expertise.

A 1 centimeter × 1 centimeter superconducting

integrated circuit with 32 768 SNS Josephson junctions

for the 1 volt programmable voltage standard.

Technical Contact:

Samuel Benz

Staff-Years (FY 2003):

4

The voltage pulse

developed by each

junction depends on

fundamental physical

constants and never

needs to be calibrated.
2 Electronics and Electrical Engineering Laboratory

TECHNICAL STRATEGY

Over the past 20 years, this project has developed

superconductive Josephson junction array technology for quantum voltage standard systems.

Groundbreaking work at NIST led to commercialization of the first practical dc Josephson voltage

standard system. Recent improvements in system

design and operation have led to a traveling Josephson voltage standard system that is compact,

low cost, and transportable for calibration of Zener

reference standards. The technology for this conventional Josephson voltage standard system has

been completely transferred to the private sector,

where systems are produced and supported by a

number of small companies.

A few years ago, we developed a novel superconductor-normal metal-superconductor (SNS) junction technology that adds the features of stability

and programmability to the accuracy of conventional Josephson voltage standards. Programmable

Josephson voltage standard systems based on

these junctions have been delivered to, and installed in, a number of metrology experiments ó

namely the watt-balance experiments at NIST and

Switzerlandís Swiss Federal Office of Metrology

and Accreditation (METAS, formerly OFMET), and

the metrology triangle experiment at Franceís Bureau National de MÈtrologie ó Laboratoire National díEssais (BNM-LNE, formerly LCIE), where

these features should reduce the uncertainty of

the experimental measurements.

EEELís Electricity Division is interested in improving the internal efficiency of its maintenance and

dissemination of the volt through the development

and deployment of an improved one volt programmable voltage standard. We have delivered a programmable Josephson voltage standard to the Electricity Divisionís primary voltage calibration lab in

Gaithersburg, Maryland and we are collaborating

with their staff to integrate the system into the customer calibration chain.

Our present primary goal is to develop the worldís

first quantum-mechanically accurate voltage source

for both ac and dc metrology. This device is essentially a digital-to-analog converter capable of synthesizing arbitrary waveforms and, as for the previously described dc-only systems, exploits the perfectly quantized pulses of Josephson junctions.

The concept for this new device was co-invented

by NIST and Northrop-Grumman researchers in

1996. Present ac voltage calibrations are done using ac-dc thermal voltage converters. A quantumbased ac voltage source would provide an entirely

new instrument and methodology for ac voltage

metrology. Its use as a stable generator of accurate

arbitrary waveforms would also be useful for calibration of other scientific instruments, such as ac

volt-meters, spectrum analyzers, amplifiers, and filters. The major challenge of this technology is to

achieve practical output voltages by developing

improved broadband circuits and novel nano-meterspaced junctions.

Charles Burroughs with the 1 volt programmable

voltage standard system showing (left to right) the low

thermal probe, the microwave and high-speed bias

electronics, and the computer control.

In order to achieve higher output voltages, we have

developed a novel ac-coupled technique that allows multiple arrays to be biased in parallel by

broadband 10 MHz to 20 GHz drive signals, while

connecting the arrays in series for the low-speed,

dc-to-10 MHz output voltage waveforms. This technique, as well as improvements in fabrication and

microwave circuit design, has enabled us for the

first time to increase the peak ac output voltage to

about one-quarter volt. This amplitude will enable

us during the next year to make some of the first

practical calibrations and measurements using the

quantum ac voltage source. However, in order to

reach our desired 1 V goal we are also pursuing

nanoscale junction technology. We can increase

the output voltage of an array by decreasing the

junction spacing to 50 nm and increasing the number of junctions so that the array remains a lumped

microwave element. Stacked junction technology

A quantum-based

ac voltage source would

provide an entirely new

instrument and methodology for ac voltage

metrology.
Electromagnetic Technology Division 3

is one possible approach and this year we have

found a new junction barrier material, molybdenum

di-silicide (MoSi2

), that has shown significant uniformity with a slightly modified fabrication process.

Development of such nanoscale junction technology is critical for the development of future voltage standard systems.

ACCOMPLISHMENTS

# Record One-Quarter AC Volt ñ A dc and ac

Josephson voltage standard system with output

voltages up to one-quarter volt has been demonstrated for the first time. This system, which is capable of synthesizing arbitrary voltage waveforms

from dc to 10 MHz, is based on the perfectly quantized voltage pulses of Josephson junctions, making this the first intrinsic quantum standard for ac

voltage. The heart of the system is a superconducting microwave integrated circuit in which 8200

junctions are placed in two series arrays to increase

the output voltage. The arrays are driven with a 15

GHz sine wave and a high-speed (10 gigabits per

second) pulse train to create the desired waveforms.

The pulse trains correspond to predetermined digital codes in which the placement of zeros and ones

precisely defines all the characteristics (amplitudes,

harmonic frequencies and relative phases) of the

desired synthesized waveforms. Using the perfectly

quantized pulses, the arrays create the desired

waveforms with quantum-mechanical accuracy.

Recent improvements, such as more junctions, improved on-chip rf circuits, and a lower attenuation

cryoprobe, have produced a 2-fold increase in peak

output voltage up to one-quarter volt. This larger

voltage allows this system to be used for the first

time for practical calibrations. DC voltages with

± 0.254 V amplitudes were demonstrated and sine

waves at 3.3 kHz and 33 kHz were synthesized with

0.242 V maximum peak amplitudes. Both synthesized sine waves showed excellent operating margins and stability so that harmonic distortion was

as low as -93 dBc (93 dB below the fundamental).

Precision measurements and comparisons with existing power-detection based ac voltage standards

(e.g., ac-dc transfer standards and thermal voltage

converters) will be completed in 2003. The ability

to synthesize arbitrary waveforms (not just sine

waves) with predetermined precision characteristics will enable advanced calibration of other measurement instruments such as spectrum analyzers,

ac voltmeters, amplifiers, and analog-to-digital converters.

# Uniform Triple-Junction Stacks Demonstrated

ñ Paul Dresselhaus and Yonuk Chong, a guest researcher from South Korea, have succeeded in

making the first 2- and 3-junction stacks using molybdenum di-silicide (MoSi2

) as the normal metal

and niobium as the superconductor for superconductor-normal-metal-superconductor (SNS) Josephson junctions. Precise three-dimensional control of the junctions during fabrication is critical for

achieving uniformity of the electrical characteristics for the junction stacks and large high-density

arrays. These new MoSi2 circuits have demonstrated sufficient uniformity for thousands of junctions to display large quantized-voltage steps at

frequencies up to 20 GHz. For the past few years

the project has been searching for a practical barrier material to allow them to vertically stack junctions in order to make three-dimensional arrays.

Higher junction density is required to increase the

output voltage as well as the operating bandwidth

of both programmable and ac Josephson array circuits. Nanometer control of the barrier thickness,

typically 20 to 30 nanometers, is essential because

junction electrical characteristics depend exponentially on barrier thickness. Reproducibility and uniformity of the fabrication process make MoSi2

 a

leading candidate for future lumped-array Josephson voltage standard circuits and systems. We

plan to demonstrate a record 5-junction stacked

array in 2003.

Paul Dresselhaus holds a silicon wafer containing

superconducting integrated circuits and shows the

current-voltage characteristics of a Josephson junction

array.

The concept of an

arbitrary voltage waveform generator with

quantum-mechanical

accuracy has enabled

the possibility of making

an electronically based

thermometer.

Nanotechnology is

critical for the

development of future

voltage standard

systems.
4 Electronics and Electrical Engineering Laboratory

# Cryoprobe Technology Transferred ñ We have

transferred the technology for constructing

cryoprobes for the 1 Volt programmable Josephson

voltage standard (PJVS) to High Precision Devices

(HPD) in Boulder, CO. HPD has now delivered a

total of seven such probes to NIST and other national metrology labs. Four recent deliveries include

2 probes to the Electricity Division for use in the

electronic kilogram experiment and the voltage calibration lab, and 2 probes to the National Institute

of Advanced Industrial Science and Technology

(AIST) in Japan in support of the AIST-NIST collaboration to develop 10 K voltage standard systems. Charles Burroughs collaborated with HPD to

improve the manufacturing precision of the microwave packaging. The improved packaging increased the uniformity of the 16 GHz microwave

signals that bias all of the superconducting Josephson junction arrays. This allows the superconducting circuits to be operated with only 25 to 50 mW of

rf power, which is 4 to 5 times lower than the power

used in previous cryoprobes. The lower power requirements may decrease the total system costs

for future PJVS systems by eliminating the need for

expensive high-power microwave amplifiers. The

cryoprobes have a 30 to 45 day hold time in a 100-

liter liquid helium storage Dewar.

# Programmable System Delivered to Calibration

Lab ñ Charles Burroughs has delivered a second

1 V programmable voltage standard system to the

Electricity Division (the first system is installed in

the electronic kilogram experiment). This second

system will be used to perform the function of the

Transmission electron microscope (TEM) image of a

two-junction stack with molybdenum di-silicide

barriers and niobium outer and middle electrodes. The

image shows that the MoSi2

 deposits uniformly on the

niobium, even when the niobium is as thin as 20 nm.

(Image by John Bonevich, MSEL, NIST.)

primary standard cell bank, and could eventually

manage much of its workload. He is presently working with Yi-hua Tang to install this system in the

primary voltage calibration lab. In the second quarter, Charlie will assist Yi-hua in evaluating the

systemís ability to perform the function of the primary cell bank. We will fabricate, test and deliver

new 1 V chips with improved operating margins by

March, 2003.

COLLABORATIONS

# With Dr. Shoji and Dr. Yamamori at Japanís

AIST, we are working to develop cryocoolercompatible Josephson junctions for programmable

voltage standards. As a result of our collaboration,

AIST has successfully demonstrated operation of

a 1 V NbN programmable voltage standard at 8.5 K

on a cryocooler refrigeration system. This is the

first time a programmable 1 V system has been demonstrated on a cryocooler.

# We are consulting with Northrop-Grumman on

the development of a pulse-quantized arbitrary

waveform generator for radar applications. This

application uses the same pulse-quantized ac synthesis techniques as the NIST metrology application at radar frequencies. We have fabricated SNS

junction circuits using Northrop-Grumman designs

and demonstrated multiple-tone waveforms at

megahertz frequencies.

# We are collaborating with Ian Robinson of the

National Physical Laboratory (NPL), England, to

provide a programmable 1 V probe and chip for

Two voltage-current characteristics for an array of

1000 stacks, where each stack contains two MoSi2

barriers for a total of 2000 junctions. Good uniformity

of the stacked junctions is demonstrated by the sharp

voltage onset with no microwave bias and by the flat

constant voltage steps when 10 GHz microwave bias is

applied.
Electromagnetic Technology Division 5

their watt-balance experiment. NPL will obtain the

probe from NIST and construct their bias electronics and computer control.

Sam Benz optimizes the operating margins for the

Josephson arbitrary-waveform synthesizer.

RECENT PUBLICATIONS

C.J. Burroughs, S.P. Benz, and P.D. Dresselhaus, ìAC Josephson voltage standard error measurements and analysis,î 2002 Conference on Precision Electromagnetic

Measurements (CPEM) Digest, 16-21 June 2002, Ottawa,

Canada, pp. 430-431 (June 2002).

S. Nam, S. Benz, P.D. Dresselhaus, and J. Martinis, ìA new

approach to Johnson noise thermometry using a quantum

voltage noise source for calibration,î 2002 Conference on

Precision Electromagnetic Measurements (CPEM) Digest,

16-21 June 2002, Ottawa, Canada, pp. 438-439 (June 2002).

S.P. Benz, P.D. Dresselhaus, and J. Martinis, ìAn ac Josephson source for Johnson noise thermometry,î 2002

Conference on Precision Electromagnetic Measurements

(CPEM) Digest, 16-21 June 2002, Ottawa, Canada, pp.

436-437 (June 2002).

S.P. Benz, P.D. Dresselhaus, and C.J. Burroughs,

ìNanotechnology for next generation Josephson voltage

standards,î IEEE Transactions on Instrumentation and

Measurement, Vol. 50, No. 6, pp. 1513-1518 (December

2001).

S.P. Benz, F.L. Walls, P.D. Dresselhaus, and C.J. Burroughs,

ìLow-distortion waveform synthesis with Josephson junction arrays,î Proc. 8th Intíl Superconductive Electronics

Conf. (ISEC í01), 19-22 June 2001, Osaka, Japan, pp.

115-116 (June 2001).

R.H. Hadfield, G. Burnell, M.G. Blamire, P.D. Dresselhaus,

and S.P. Benz, ìNanofabricated SNS junction series arrays

in superconductor-normal metal bilayers,î Proc. 8th Intíl

Superconductive Electronics Conf. (ISEC í01), 19-22 June

2001, Osaka, Japan, pp. 391-392 (June 2001).

H. Yamamori, M. Itoh, H. Sasaki, A. Shoji, S.P. Benz, and

P.D. Dresselhaus, ìFabrication of all-NbN digital-to-analog converters for a programmable voltage standard,î Proc.

8th Intíl Superconductive Electronics Conf. (ISEC í01),

19-22 June 2001, Osaka, Japan, pp. 391-392 (June 2001).
6 Electronics and Electrical Engineering Laboratory
Electromagnetic Technology Division 7

QUANTUM STANDARDS

JOHNSON NOISE

THERMOMETRY

GOALS

To use a quantum-based voltage source to reduce

the uncertainty of Johnson noise thermometers,

with the ultimate goal of creating an intrinsic quantum-based electronic temperature standard.

Sae Woo Nam tests the cross-correlation electronics

for the Johnson noise thermometry system. A gallium

triple-point cell at 302.916 K is behind him.

CUSTOMER NEEDS

Gas-based and fixed-point methods of precision

thermometry are either limited to specific fixed temperatures or require considerable effort to reduce

uncertainties below parts in 105. An electronic quantum-based method would provide another approach as well as advantageous features such as

improved linearity of temperature calibrations. It

would also provide an improved realization of the

Kelvin Thermodynamic Temperature Scale, and a

direct link between temperature and electrical standards, possibly providing a route to a re-determination of the Boltzmann constant. More importantly, this quantum-based Johnson noise thermometry (JNT) method is a new paradigm to realize the

thermodynamic temperature scale through electrical and quantum-based standards. This JNT approach to create an ìelectronic kelvinî is analogous to EEELís watt-balance program to realize an

ìelectronic kilogram.î

Our customers and collaborators include the NIST

Chemical Science and Technology Laboratory

(CSTL), the temperature calibration laboratories of

other national measurement institutes, and industrial users requiring long-term temperature stability

or with temperature sensors in difficult or remote

locations.

In order to meet these needs and to create a quantum-based electronic temperature standard, we

have developed new technology in a number of

different areas. We have constructed low-noise

cross-correlation electronics, developed a quantum voltage noise source (QVNS) specifically for

this application, and performed the first calibrations

of the electronics using the QVNS. We have compared the QVNS synthesized pseudo-noise voltage waveforms with the voltage noise of resistors

in triple-point cells of both gallium and water. We

have also devised a novel ratiometric method that

uses the QVNS to compare the voltage noise of

resistors at different temperatures.

TECHNICAL STRATEGY

In a JNT system, the temperature T is inferred from

a measurement of the Johnson noise voltage VT

across a calibrated resistance R. The mean-squared

voltage noise is given by the Nyquist formula

Technical Contact:

Sae Woo Nam

Samuel Benz

Staff-Years (FY 2003):

1

The concept of a

Josephson arbitrary

voltage waveform

generator with quantummechanical accuracy

has enabled the

possibility of making an

electronically based

thermometer.

 where ƒf is the bandwidth for the

measurement and k is Boltzmannís constant. Crosscorrelation techniques are typically used to measure these extremely small voltages to remove the

error introduced by the noise in amplifiers. In 1999,

we realized that the Josephson Arbitrary Waveform Synthesizer being developed within our Division might be able to provide a stable, accurate,

pseudo-noise voltage to provide a better means of

calibrating the low-noise cross-correlation electronics. A stable, programmable, and intrinsically accurate noise source, such as that provided by the

QVNS, would provide the advantages of direct calibration of the cross-correlation electronics, matching of the calibration voltage noise to that of the

sense resistor, and matching of the source impedance to both the sense resistance and the output

transmission-line impedance. These features reduce

the measurement uncertainty, increase the measurement bandwidth, and decrease the measurement

time for the entire JNT system.

= 4 , 2 V kTR f 〈 T 〉 ∆
8 Electronics and Electrical Engineering Laboratory

Log-log plot showing the measured spectrum of a

QVNS-synthesized pseudo-noise waveform. The

spectrum was measured with the JNT cross-correlated

electronics and shows the power <V2

> spectrum Sxy of

the 1258 tones synthesized by the QVNS. Each bin has

a width of 1 Hz and is an average of 200 samples. The

power spectrum is in arbitrary units.

This JNT approach to

create an ìelectronic

kelvinî is analogous to

the watt-balance

program to realize an

ìelectronic kilogram.î

Using a QVNS we hope to achieve uncertainties of

better than a few parts in 105 for temperatures in the

range of several hundred kelvins. At these temperatures the noise signals are small, on the order

of 1 nV/Hz1⁄2 for a 100 ohm resistor. However, in

order to achieve such small uncertainties for such

low-voltage signals, the noise power spectral density must be integrated for a long time and/or over

a wide bandwidth. Thus the QVNS must be stable

for long integration times but does not need to

generate large voltages. We have devised a special

method of biasing the QVNS that meets these requirements and allows it to be much simpler than

the Josephson arbitrary waveform synthesizer,

where the primary focus has been to obtain the

highest voltages.

NIST has constructed custom cross-correlation

electronics for the JNT program. Two pairs of voltage leads are measured with separate amplifier

channels to perform the cross correlation measurement. Each signal is first measured with an accoupled differential FET, followed by an anti-alias

filter with a cutoff frequency at 2 MHz. The resulting amplified and filtered signals are digitized at 50

MHz by a 14-bit analog-to-digital converter. Fieldprogrammable gate arrays (FPGAs) at the output

of the digitizers then digitally filter the signal with a

low-pass frequency of 100 kHz. The digitally filtered data are transmitted via a 50 megabit/s optical

link into a custom PCI card installed in a computer.

Each channel transmits 2 million samples per second, which is the effective sampling frequency of

the signal. In the present system, a dual-CPU computer is used to calculate two 221-point fast Fourier transforms (FFTs) in real-time (less than one

second). The cross-correlation and auto-correlation power spectra are then calculated, accumulated, and stored for later analysis.

ACCOMPLISHMENTS

# First QVNS-to-Resistor Noise Comparison ñ

Sae Woo Nam, Wes Tew (CSTL), and Sam Benz

performed the first comparisons between the

Johnson noise voltage of a resistor in a gallium cell

and the synthesized pseudo-noise waveforms of

the quantum voltage noise source. Measurements

were made using the recently completed cross-correlation electronic system. The computer-controlled

optically interfaced system demonstrated a 50 MHz

sampling rate and stored and processed the waveforms in real time. These correlation electronics are

different from other systems because we digitally

process the signal in an FPGA before sending it to

a computer. This is necessary to reduce the data

rate to the computer.

# Unipolar QVNS Bias Method Developed ñ Paul

Dresselhaus fabricated a number of circuits specifically for the JNT program. Sam Benz has tested

them with appropriate pseudo-noise waveforms and

demonstrated proper cross-correlation using an

FFT spectrum analyzer. Benz also performed extensive measurements of input-output coupling for

the JNT circuits and devised a novel unipolar bias

method to decrease the coupling by about 40 dB.

These results allowed us to take the next step and

measure the arrays at much smaller voltages and

higher bandwidth using Namís cross-correlation

electronics.

# Improved JNT Uncertainty ñ Sae Woo Nam,

Sam Benz, and Paul Dresselhaus, in collaboration

with Wes Tew of CSTL, have continued development of the Johnson noise thermometry system.

Unwanted distortion was observed when the Josephson signal was measured with the cross-correlation electronics. Nam and Benz were able to

significantly reduce this distortion by using inductive chokes on the input of the electronics. The

cause of the distortion appears to be mixing in the

first FET amplifier stage of 100-400 MHz delta-sigma

modulator tones synthesized by the Josephson

array. With this dramatic improvement, direct comparisons were made between the Josephson-synthesized noise waveform and the gallium and water

triple point cells. We found agreement to 2 parts in

103

 with a 1σ uncertainty of 1x10-3 between the voltage noise of a 100 Ÿ resistor in a triple-point gallium cell (T90 = 302.916) and a pseudo-noise waveform with the same average power that is synthesized by a quantized voltage noise source. We
Electromagnetic Technology Division 9

Sae Woo Nam, Wes Tew, and Sam Benz with the

quantized voltage noise source.

The quantum-based

JNT system provides

a direct link between

temperature and

electrical standards.

estimate the temperature of the resistor to be 302.5

K ± 0.3 K 1 σ (uncertainty based on the uncertainty

from the cross-correlation). With better characterization of our JNT system, we expect to achieve

relative accuracies of parts in 105 for arbitrary temperatures in the range between 270 K and 1000 K.

# Novel Ratiometric Method Demonstrated ñ

Wes Tew proposed using a new ìratiometric

methodî that takes advantage of the linearity of

the Josephson waveforms to make independent

comparisons between different noise powers. Sae

Woo Nam briefly described this approach at the

2002 Conference on Precision Electromagnetic

Measurements (CPEM) and it was explained in detail in a paper given at the 8th Temperature Symposium in Chicago in September 2002. The Johnson

noise power at a known temperature is first balanced with a synthesized noise power from the

QVNS. The process is then repeated by balancing

the noise power from the same resistor at an unknown temperature. When the two noise power

ratios are combined, a thermodynamic temperature

can be derived where the scaling is accomplished

by the ratio of the two QVNS spectral densities.

Using this method, preliminary results of the ratio

between the gallium triple point and the water triple

point were used to demonstrate the accuracy of

the measurement system with a standard uncertainty of 0.04 %. We are planning to perform more

experiments in 2003 and 2004 to understand the

limits of this technique.

COLLABORATIONS

# We are collaborating with Weston Tew of the

Process Measurements Division in the NIST

Chemical Science and Technology Laboratory

(CSTL). The JNT development program has been

supported by a 5-year NIST competence award as

well as with additional funds from both our Division and the Process Measurements Division. In

2003, we expect to deliver a set of JNT correlation

electronics to the Project Measurements Division.

# Dr. D. Rod White from the Measurement Standards Laboratory in Lower Hutt, New Zealand is

also consulting and collaborating with us, based

on his many years of expertise in Johnson noise

thermometry.

RECENT PUBLICATIONS

S. Nam, S. Benz, P.D. Dresselhaus, and J. Martinis, ìJohnson

noise thermometry measurements using a quantized voltage noise source for calibration,î to appear in IEEE Transactions on Instrumentation and Measurement, Vol. 52,

No. 2 (in press).

S. W. Nam, S. P. Benz, J. M. Martinis, P.D. Dresselhaus, W.

L. Tew, and D. R. White, ìA ratiometric method for Johnson

noise thermometry using a quantized voltage noise source,î

to appear in Proc. of 8th Symposium on Temperature: Its

Measurement and Control In Science and Industry, 21-24

Oct 2002, Chicago, IL (in press).

S.P. Benz, P.D. Dresselhaus, and J. Martinis, ìAn ac Josephson source for Johnson noise thermometry,î 2002

Conference on Precision Electromagnetic Measurements

(CPEM) Digest, 16-21 June 2002, Ottawa, Canada, pp.

436-437 (June 2002); also to appear in IEEE Transactions

on Instrumentation and Measurement, Vol. 52, No. 2 (in

press).

S. Nam, S. Benz, P.D. Dresselhaus, and J. Martinis, ìA new

approach to Johnson noise thermometry using a quantum

voltage noise source for calibration,î 2002 Conference on

Precision Electromagnetic Measurements (CPEM) Digest,

16-21 June 2002, Ottawa, Canada, pp. 438-439 (June 2002).

S. P. Benz, J. M. Martinis, S. W. Nam, W. L. Tew, D. R.

White, ìA new approach to Johnson noise thermometry

using a Josephson quantized voltage source for calibration,î to appear in Proc. of TEMPMEKO 2001, 8th Intíl

Symp. on Temperature and Thermal Measurements in Industry and Science, 19-21 June 2001, Berlin, Germany, pp.

39-44 (Apr 2001).
10 Electronics and Electrical Engineering Laboratory

QUANTUM STANDARDS

SINGLE ELECTRONICS FOR

STANDARDS AND METROLOGY

GOALS

To develop novel integrated circuits for standards

and metrology based on the unique properties of

electronic devices that can manipulate and detect

individual electrons.

Atomic force microscope image of an electron counter,

the heart of a new capacitance standard based on

counting electrons. The standard, shown in the

schematic, consists of the electron counter, a capacitor,

and a single-electron electrometer to monitor the

process (not shown). The electron counter, based on

seven nanometer-scale tunnel junctions in series, can

ìpumpî electrons onto the capacitor with an error

rate of less than 1 electron in 108.

Imagine what you could do if you could build circuits that precisely manipulate and detect individual

electrons. Single electronics represents a new class

of electronics that does exactly that. At the core of

this new electronics are nanoscale devices (dimensions less than 100 nm) operating at cryogenic temperatures, usually below 1 K. These new devices

offer unique capabilities that impact electrical standards, fundamental metrology and industrial instrumentation. The goal of this project is to use our

world-leading expertise in this field to create new

quantum-based electrical standards and new measurement techniques applicable to emerging electronics that will operate with very few electrons.

CUSTOMER NEEDS

The U.S. electronics industry continues to seek

improved and more accessible standards for maintaining instrument calibration. NIST is working to

support this need through the development of intrinsic standards based on fundamental physical

principles, such as the volt, based on the Josephson effect, and the ohm, based on the quantum

Hall effect. For capacitance, NISTís primary standard (the calculable capacitor) is a unique instrument that is difficult to replicate, and it currently

provides the best accuracy at only a few fixed frequencies. In this project we have already produced

a prototype capacitance standard based on counting electrons. This standard will provide accurate

calibrations over a wide range of frequencies and

can be replicated to allow customers direct access

to the standard.

This same technology is also being explored for a

variety of other applications. Single electron devices can be used to produce single photons on

demand by the recombination of single electrons

and holes in a semiconductor quantum dot. Such a

single photon source would be used for new optical calibration devices, and could become part of a

quantum communications system. Molecular electronics is another class of electronics that operate

with few or single electrons. The remarkable charge

sensitivity of single electron devices makes them

unique measurement tools to explore the electrical

properties of single molecules. Finally, the superconducting analog of these devices can also be

built. These devices manipulate electrons that are

bound into ìCooper pairsî of charge 2e. These

single Cooper pair devices can in principle be operated at higher speeds to produce large currents

with metrological accuracy. They are also being

considered for application to quantum computing.

TECHNICAL STRATEGY

The creation of electronic devices capable of manipulating and detecting individual electrons has

opened the door to the development of entirely

new standards and metrology tools. The basic electronic device used to create these circuits is the

Single Electron Tunneling (SET) transistor. This

device consists of a nanoscale metal island coupled

to two leads through very small tunnel junctions.

This allows single electrons to be controllably put

on and off the island, as long as thermal fluctuations are small. SET devices are made possible by

Technical Contact:

Mark Keller

David Rudman

Staff-Years (FY 2003):

5

Imagine what you could

do if you could build

circuits that precisely

manipulate and detect

individual electrons.
Electromagnetic Technology Division 11

a combination of state-of-the-art nanolithography

to create the nanometer-scale devices, millikelvin

cryogenics to cool the devices to their operating

temperature, custom low-noise electronics to operate and measure the devices, and fundamental physics to understand and diagnose the operation of

the devices. Maintaining expertise and capabilities

across these fields represents the core technical

strategy of this effort.

At present, the most advanced application for SET

devices within the project is to create a new capacitance standard based on the fundamental definition of capacitance: capacitance is stored charge

per unit voltage, C=Q/V. By placing a known number of electrons on a capacitor, and measuring the

voltage across the capacitor, C can be determined.

A prototype of such a standard has been demonstrated with repeatability on the order of 1 part in

107

. In order to confirm the accuracy of the standard, it must be compared to the SI farad as determined by the calculable capacitor at NISTGaithersburg. Using a new variable-frequency

capacitance bridge and capacitance artifacts calibrated against the calculable capacitor by researchers in EEELís Electricity Division, we will first perform this comparison indirectly in Boulder in early

2003. At the same time, a portable version of the

standard is being developed to allow a direct comparison at NIST-Gaithersburg. This version will

use a commercially available adiabatic demagnetization refrigerator to cool the SET electronics, and

will represent a significant step towards making a

ìuser friendlyî system that could be duplicated for

use in any number of laboratories.

SET devices can also be used as tools to measure

the performance of other devices that operate with

individual electrons. Currently we are focusing on

two different applications utilizing the measurement

capabilities of SET devices: single photon production and molecular electronics. In collaboration with

Richard Mirin from EEELís Optoelectronics Division, work has begun on creating a new class of

electronic devices designed to produce single photons on demand. The principle of operation for the

source is fairly straightforward: individual electrons

and holes are alternately injected onto a single semiconductor quantum dot (QD) using single-electron

tunneling principles. Once on the dot, a single

electron and hole recombine to produce a single

photon. To understand the behavior of these devices, it will be necessary to measure the electrical

currents into the dot at the single electron level.

This can be done only using SET technology. The

first step towards this end requires the development of a process to allow electrical contact to individual QDs, and fabrication of SET devices on the

same substrate as the quantum dots. In 2003 we

will integrate these components on a single chip

with QDs to measure the properties of the QDs and

the neighboring tunnel barriers to learn how to tunnel single charges onto semiconductor QDs.

We have also begun a collaboration with the Departments of Physics and Chemistry at the University of Colorado at Boulder (CU) to apply SET devices to the measurement of single molecules having

interesting electronic properties. Molecules have

been synthesized at CU with large dipole moments

that can rotate on the top of a molecular ìshaft.î

Work is underway at the university to measure the

properties of films made from these molecules. Our

goal in 2003 will be to place a single molecular dipole rotor near an SET electrometer to allow direct

measurement of the properties of a single molecule.

We are currently developing the superconducting

analogs of the various single electron devices described above. Superconducting Single Cooper

Pair Tunneling (SCPT) devices combine the physics of single electron devices and Josephson junctions. Our first application of this new technology

will be to develop a SCPT charge pump. Because

superconducting tunneling is a coherent process,

in principle the SCPT pump should be able to operate at significantly higher frequencies, allowing

larger currents to be produced with metrological

accuracy. If larger currents are available, it may be

possible to perform unique comparisons of the three

intrinsic electrical standards: the volt (based on

the Josephson junction), the ohm (based on the

quantum Hall effect) and the ampere (based on

counting electrons). This test, known as the quantum-metrology triangle, will provide new understanding and confidence in these quantum standards. The experiments will require a significant

increase in current from the electron pump. To build

the SCPT pump will require significant advances in

the fundamental understanding of how these devices work. In 2003 we will continue our research

into SCPT devices. This work will also have direct

impact on worldwide progress towards using these

devices for quantum computing.

ACCOMPLISHMENTS

# Electron Counting Capacitance Standard Demonstrated ñ At present, the most advanced application for SET devices within the project is a new

capacitance standard based on the fundamental

definition of capacitance. The past few years have

brought to fruition the results of a decade of
12 Electronics and Electrical Engineering Laboratory

research aimed at creating this standard. A prototype of an Electron Counting Capacitance Standard (ECCS) has now been demonstrated. The components of the standard are an electron counter, a

capacitor, and an electrometer to monitor the process, as illustrated in the figure at the beginning of

this section. The electron counter is based on seven

nanometer-scale tunnel junctions in series. It can

ìpumpî electrons onto the capacitor with an error

rate of less than one electron in 108. The electron

pumping is monitored with an SET-based electrometer fabricated on the same chip as the pump, with

a charge sensitivity better than 10-2 electrons. The

capacitor, fabricated by Neil Zimmerman from the

Electricity Division, operates at cryogenic temperatures and uses vacuum as the dielectric, resulting

in a frequency-independent capacitance. To operate the ECCS approximately 100 million electrons

are placed, one at a time, on the capacitor. The voltage across the capacitor is then measured, resulting in a calibration of the cryogenic capacitor. This

capacitance can then be transferred to room temperature using a standard ac bridge measurement

technique. The figure below shows the result of

pumping electrons on and off the capacitor, with a

20 second pause when fully charged to measure

the voltage. The result is a value of capacitance

with a repeatability of one part in 107

.

Demonstration of pumping electrons onto and off a

prototype capacitance standard.

# Improved Model of SET Devices Helps Predict Error Rates ñ A thorough understanding of

the physics of SET devices has been necessary to

count electrons with metrological accuracy. The

fundamental error mechanisms in the electron pump

have been the subject of theoretical and experimental investigations in the project for several

years. The development of an experimental technique for characterizing individual junctions in the

pump made possible the first quantitative comparison between experiment and theory in the regime

of very rare errors. Recently, the dependence of

pump errors on voltage across the pump has been

measured for the first time. This directly gives the

operating margin for the feedback that must be

maintained during operation of the capacitance standard, a critical design parameter for the next generation of the standard. This work has led to a new

understanding of the variation in electron temperature within the pump, improving our ability to model

SET device performance. This expanded theory is

a powerful tool for predicting and diagnosing the

performance of the electron pump.

An AFM image of electron-beam lithographicallywritten contact to a single QD. The ëSí indicates where

the QD is located. The lead that approaches the QD

from the bottom is used to capacitively couple the QD

to a single-electron transistor structure. The white lines

coming in from the left side of the micrograph are

alignment marks.

# SET Electronics Developed to Probe GaAs

Quantum Dots for Single Photon Source ñ The past

two years have produced significant progress towards the development of a single-photon turnstile, a device designed to generate single photons

on demand using semiconductor quantum dots

(QD) and single-electron principles. The first step

towards this end requires the development of a

process to allow electrical contact to individual

quantum dots. The process uses a combination of

photolithography, electron-beam lithography,

atomic-force microscopy, etching, and film deposition to allow individual QD, which are only a few

tens of nanometers in diameter, to be located and

connected to nanoscale leads on the same chip.

To evaluate the electron

counting capacitance

standard, we will

compare it with the

present calculable

capacitor.

Work has begun on

creating a new class

of electronic devices

designed to produce

single photons on

demand.
Electromagnetic Technology Division 13

An Atomic Force Microscope (AFM) image of electron-beam lithographically written contacts to a

single quantum dot is shown above. We have also

fabricated SET electrometers on GaAs substrates

in preparation for probing the electronic states of

the quantum dot, shown in an SEM image below.

Two SET electrometers separated by 60 nm on a GaAs

substrate without quantum dots. This device will be

used to probe the electronic states of a quantum dot

located between the SET devices and a buried

conducting layer in a GaAs-based heterostructure.

# Superconducting Single Cooper Pair Devices

Under Investigation as Current Source ñ Superconducting Single Cooper Pair Tunneling (SCPT)

devices represent a new class of single electronics

that operate on single Cooper pairs with charge 2e.

Our first efforts to construct a seven-junction SCPT

pump (shown above right) produced only limited

success. The device did pump Cooper pairs with

charge 2e per cycle, but only against a significant

background of events due to unpaired electrons,

an effect known as ìquasiparticle poisoning.î In

recent years several groups worldwide have been

investigating SCPT devices as possible elements

for quantum computing. These groups have also

reported unexplained quasiparticle poisoning in

their devices, which is highly detrimental to their

performance. To investigate the origin of these

unwanted quasiparticles, we constructed much simpler SCPT devices. We have determined that the

quasiparticle poisoning arises from unintentional

(and usually uncontrolled) differences in the superconducting energy gap between the two Al layers used to make the tunnel junctions. By intentionally varying the gap in the two layers, we have

been able to create devices with either no quasiparticle poisoning or excessive poisoning. These

results, which may also explain the results from

other groups, point the way to a robust recipe for

devices that can realize the promise of superconducting charge transfer for both metrology and

quantum computation. We are currently studying

the behavior of these devices further, and will then

attempt to construct an improved SCPT pump as a

current source for metrology triangle and other experiments.

SEM micrograph of our first 7-junction SCPT pump.

The junctions, which are less than 50 nm on a side, are

too small to be seen in this picture but are located on

the central line near each gate electrode.

RECENT PUBLICATIONS

S. Anders, C. S. Kim, B. Klein, Mark W. Keller, R. P. Mirin,

and A. G. Norman, ìBimodal size distribution of self-assembled InxGa1-xAs quantum dots,î Phys. Rev. B 66,

125309 (2002).

M.W. Keller, ìStandards of current and capacitance based

on single-electron tunneling devices,î Recent Advances in

Metrology and Fundamental Constants ñ FERMI School

CXLVI, Varenna, Italy, ed. T.J. Quinn, S. Leschiutta, and P.

Tavella, IOS Press, Amsterdam, pp. 291-316, (2001).

A.L. Eichenberger, M.W. Keller, J.M. Martinis, and N.M.

Zimmerman, ìFrequency dependence of a cryogenic capacitor measured using single electron tunneling devices,î

J. Low Temp. Physics 188, 317 (2000).

R.L. Kautz, M.W. Keller, and J.M. Martinis, ìNoise-induced leakage and counting errors in the electron pump,î

Phys. Rev. B 62, 1588 (2000).

N.M. Zimmerman, M.W. Keller, ìDynamic input capacitance of single-electron transistors and the effect on chargesensitive electrometers,î J. Appl. Phys. 87, 8570 (2000).

M. Covington, M.W. Keller, R.L. Kautz, J.M. Martinis,

ìPhoton-assisted tunneling in electron pumps,î Phys. Rev.

Lett. 84, 5192 (2000).

M.W. Keller, N.M. Zimmerman, A.L. Eichenberger, J.M.

Martinis, ìA capacitance standard based on counting electrons,î Proc. 2000 Conf. on Precision Electromagnetic

Measurements (CPEM), 14-19 May 2000, Sydney, Australia, pp. 317-318 (2000).
14 Electronics and Electrical Engineering Laboratory

R.L. Kautz, M.W. Keller, J.M. Martinis, ìLeakage and

counting errors in a seven-junction electron pump,î Phys.

Rev. B 60, 8199 (1999).

M.W. Keller, A.L. Eichenberger, J.M. Martinis, N.M.

Zimmerman, ìA capacitance standard based on counting

electrons,î Science, 285, 1706 (1999).
Electromagnetic Technology Division 15

QUANTUM STANDARDS

PHYSICS OF QUANTUM HALL

RESISTANCE STANDARDS

GOALS

To develop applications to metrology of recent

advances in the physics of quantum Hall devices

and to fabricate optimized devices for metrology.

CUSTOMER NEEDS

The quantum Hall effect has been the basis of resistance metrology for a number of years. Metrology laboratories around the world use it routinely

as a practical standard, although the ultimate knowledge of resistance continues to be based on a calculable capacitor. Quantum Hall devices produce

very precise values of resistance of the order 10

parts per billion.

Even though the quantum Hall effect was discovered more than two decades ago, there has not

been a focused effort to produce optimized quantum Hall devices for metrology. The worldwide

lack of a fabrication effort aimed specifically at quantum Hall devices has resulted in a lack of technological progress similar to major advances with the

Josephson array voltage standard over the same

period.

The Electromagnetic Technology Division is therefore initiating a program to remedy these limitations.

TECHNICAL STRATEGY

With the support of the EEEL a program was initiated in 2001. The program will consist of two staff

members and the capability of fabricating twodimensional electron gas (2DEG) samples using a

dedicated molecular beam epitaxy (MBE) machine,

followed by characterizing them at appropriate temperatures and magnetic fields.

The approach to the program will range from relatively straightforward tasks to the development of

new fundamental knowledge that will enhance future electrical metrology. Following that order, the

following are the objectives we foresee at the

present time:

Fabrication of optimized conventional quantum Hall

samples ñ We will undertake a collaborative program with EEELís Electricity Division to produce

optimized quantum Hall samples for that Divisionís

use in resistance calibrations. Using an iterative

approach we will optimize the samples for this application. We hope to reduce occasional unintended noise, to increase the operating temperature, and to reduce the required magnetic field

strength. Ultimately we hope to produce metrology-quality samples that operate at 4.2 kelvin in

magnetic fields of one tesla or less. At this level

the systems would be inexpensive enough that they

could be used by many more laboratories than can

afford quantum Hall resistance standards at present.

Series arrays will be particularly important in EEELís

pursuit of closing the metrology triangle (described

elsewhere in this publication).

Quantum Hall integrated circuits ñ We will fabricate quantum Hall integrated circuits for use in

metrology or physics studies. Inspired by the report of a French group at the 2002 Conference on

Precision Electromagnetic Measurements, we will

produce integrated circuits of quantum Hall devices.

That group fabricated a parallel/series array of devices to enable lower or higher resistance than the

standard resistance of h/e2

 = 25812.807 ohms. Their

significant accomplishment was to reduce the contact resistance between samples to a low enough

value that the overall resistance was accurate to

better than 100 parts per billion. In addition we will

explore the possibility of combined quantum Hall

and superconducting circuits that might permit miniature, or even on-chip, magnetic field generation

to eliminate the need for a bulky external magnet,

further reducing the cost of the overall system. If

this field could be confined to a small region of the

chip, it might be possible to fabricate a Josephson

array voltage standard on the same chip as the

quantum Hall device, creating a monolithic quantum multimeter for the first time. The device would

achieve a voltage and resistance having quantum

accuracy, with the current derived as the ratio of

the two.

New quantum Hall physics for metrology ñ Experiments performed over the last few years at the California Institute of Technology (Caltech) by Professor James P. Eisenstein, his students and collaborators demonstrate new physics having potential

importance to metrology. In these experiments quantum Hall samples are fabricated with two 2DEGs

spaced by less than 100 nm to permit tunneling

between the layers. These remarkable experiments

demonstrate the quantum Hall effect with a filling

factor of 1/2 in each layer, which is not observed in

a single layer. Moreover with a current through

Technical Contact:

Richard Harris

Staff-Years (FY 2003):

0.1

Ö it might be possible to

fabricate a Josephson

array voltage standard

on the same chip as the

quantum Hall device,

creating a monolithic

quantum multimeter for

the first time.
16 Electronics and Electrical Engineering Laboratory

only one of the layers, a voltage is generated in the

other layer that is proportional to the product of

the current and the quantum Hall resistance in the

first layer. While the metrological utility of the second layer is yet to be explored, this effect suggests

opportunities important to practical quantum Hall

metrology.

ACCOMPLISHMENTS

Taking advantage of the refocusing of another program in EEEL, we have acquired an MBE system of

suitable cleanliness to fabricate conventional quantum Hall samples. Based on the experience of researchers at Bell Laboratories, it would also be capable, with modification, of producing very high

mobility samples similar to those presently used in

the Caltech bilayer experiments. We are also searching for two world-class staff members to initiate

and carry out this work.

Molecular beam epitaxy machine prior to shipment to

Electromagnetic Technology Division.

RECENT PUBLICATIONS

Since this program is still being initiated at NIST,

the relevant background is in publications from the

work at Caltech. Two are listed below:

M.Kellogg, J.P. Eisenstein, L.N. Pfeiffer and K.W. West,

ìDouble layer two-dimensional electron systems: probing

the transition from weak to strong coupling with Coulomb

drag,î cond-mat/0211502 (2002).

M.Kellogg, I.B. Spielman, J.P. Eisenstein, L.N. Pfeiffer

and K.W. West, ìObservation of quantized Hall drag in a

strongly correlated bilayer electron system,î Phys. Rev.

Lett. vol. 88, pp. 126804 (2002).
Electromagnetic Technology Division 17

QUANTUM INFORMATION

QUANTUM COMPUTING

USING INTEGRATED CIRCUITS

GOALS

To develop the physical principles essential to quantum computing and other future electronic technologies.

Photograph of current-biased Josephson junction

qubit.

Quantum computing is a radically new approach to

computing. A large part of the scientific community is very excited about this possible application

of very fundamental physics.

In a conventional computer, information is often

stored as an electrical charge on a tiny capacitor.

The presence or absence of charge indicates a

value of 1 or 0. In a quantum computer, information

is stored as a wave function of a quantum bit, or

qubit. Theorists project enormous increases in

computing power if quantum computing can be

made practical.

Many very different quantum systems are being

considered worldwide for possible use in quantum

computing. At NIST, staff in the Physics Laboratory are pursuing single ions and neutral ions. In

EEEL, we are considering superconducting integrated circuits. The potential advantage of our

approach is that we are using lithographic fabrication, which can be scaled from a single first qubit to

an entire integrated circuit, necessary for any actual quantum computer.

CUSTOMER NEEDS

Whether or not quantum computing becomes practical, our work will produce new knowledge of electrical measurements in systems with extremely low

energy levels. This is the direction all computing is

taking. With the current focus on massively integrated nanoscale devices, energy differences between different states in a computer are reduced

because of the ever smaller device sizes, proving

the important practical result of lower power dissipation.

In future systems exceptional care must be taken to

eliminate both external noise and even self-generated noise. Low temperature operation is essential.

While the ultimate success of quantum computing

is still unknown, the measurement techniques that

we will develop will find application in much advanced electronic technology.

TECHNICAL STRATEGY

Our first demonstration of a qubit uses a currentbiased Josephson junction operated at about 20

millikelvin (mK).

Our qubit is based on a current-biased Josephson

junction. The energy levels are shown in the following diagram:

Potential energy of current-biased Josephson junction

showing ground and first excited state wavefunctions

as a function of junction phase difference.

Using a microwave source we can control the population of the first state above the ground state.

Reading out that state is accomplished by applying a second microwave signal to move the system

into the highest state (not shown). Adjusting the

bias permits the system to tunnel through the right

energy barrier into the Josephson voltage state,

which is easily detectable using conventional instrumentation.

This very specialized circuit is fabricated in our

versatile facility, described elsewhere in this publication.

Technical Contact:

John Martinis

Staff-Years (FY 2003):

5
18 Electronics and Electrical Engineering Laboratory

ACCOMPLISHMENTS

# Qubit Demonstrated ñ One important test of

potential qubits is the observation of stimulated

transitions between states, called Rabi oscillations.

These are demonstrated in the figure on the next

page. These and other data reveal a coherence

time of about 10 ns. Calculations suggest that times

as long as about 1 μs should be possible, which is

long enough for experimental quantum communication.

Rabi oscillations demonstrated in plot of measured

probability of occupation p1 of first state as function of

microwave excitation (P01)1/2.

Our results demonstrate an operating qubit. The

next steps in our work, in 2003, are to find ways to

increase the coherence time. Once that is complete

it will be necessary in 2004 to develop methods for

coupling two or more qubits into a logic gate. Following this step we will have to demonstrate quantum computing, beginning with very simple circuits

and learning techniques for increasing the complexity toward circuits, which can perform meaningful computation.

We are vigorously pursuing this fast-moving field

of research and invite interested readers to check

our web site for our latest results.

RECENT PUBLICATIONS

J.M. Martinis, S. Nam, J. Aumentado, K.M. Lang, and C.

Urbina, ìDecoherence of a superconducting qubit from

bias noise,î submitted to Physical Review B (in press).

K.M. Lang, S. Nam, J. Aumentado, C. Urbina, and J.M.

Martinis, ìBanishing quasiparticles from Josephson-junction qubits: why and how to do it,î Proc., 2002 Applied

Superconductivity Conference, 4-9 August 2002, Houston, TX (2002), IEEE Trans. Appl. Supercon. (in press).

J.M. Martinis, S. Nam, J. Aumentado, and C. Urbina, ìRabi

oscillations in a large Josephson-junction qubit,î Phys. Rev.

Lett. 89(11), pp. 117901 1-4 (9 Sept. 2002).

01
Electromagnetic Technology Division 19

QUANTUM INFORMATION

QUANTUM COMMUNICATION

GOALS

To develop and apply single photon detectors (optical/infrared) for metrology and science.

Photograph of a small array of tungsten transition

edge sensors (TES) to detect single photons. The

active areas are the center square and surrounding

rectangular areas. The light colored traces are

aluminum wires to bias the detectors. The light colored

lines are 2 μm wide.

CUSTOMER NEEDS

New quantum-based communication and measurement systems that use single and correlated photons have been developed. However, the current

tools to calibrate the components in these systems

are inadequate for the emerging applications. For

accurate calibration, a detector capable of determining the number of photons in a single pulse of

light is needed. We are developing a high-efficiency detector system with this capability in the

three telecommunication windows (850 nm, 1310

nm, and 1550 nm). This new instrument will also

aid in the understanding and advancement of new

photon sources such as the single photon turnstile (SPT). Our detectors can also be used as a

spectroscopic diagnostic tool or characterization

tool of optical elements, optical materials, and optical systems at ultra-low light levels. This detector

technology will also enable metrology for understanding and evaluating a new class of devices

currently being developed for quantum networks.

In collaboration with Stanford University, we are

also developing arrays of single photon detectors

as spectrophotometers for use in astrophysics and

astronomy. The detectors that have been developed are capable of measuring the energy of the

photon and time stamp the arrival of a photon to

better than 1 microsecond.

TECHNICAL STRATEGY

The technology for counting photons at telecommunication wavelengths or measuring the energy

of a single photon is a refinement of superconducting transition-edge sensor (TES) detector technology that was previously developed by the Division and researchers at Stanford University.

These abilities are achievable due to the low operating temperature (100 mK) of the TES devices. The

photons are detected by exploiting the superconducting properties of tungsten at these low temperatures. At 100 mK the devices become exceedingly sensitive thermometers capable of measuring

the heat deposited into the TES from single optical/infrared photons. The tungsten device absorbs

the photons, heats up a very small amount, and

produces an electrical output signal that is proportional to the energy absorbed by the device.

These TES detectors can be operated in two distinct modes depending on the photon source properties. For single-wavelength (monochromatic)

sources such as lasers and Spontaneous Parameter Down-Conversion (SPDC) crystals (used for

quantum information and metrology) the sensor

response is directly proportional to absorbed photon number (Photon Number Discrimination mode).

For broadband sources (such as white-light or

multiple fluorescence emissions) the energyresolving ability of the TES devices allows

photon-counting spectroscopy to be performed

across the entire near-infrared/optical band (2 microns to 200 nm). In this mode, the photon number

is discarded in favor of determining the energy (i.e.,

color) of the incoming photons (Spectroscopic

mode).

At the present time, our quantum efficiency of detection is ~18 % and is limited by our optical coupling and intrinsic quantum efficiency of absorption of tungsten. Our goal by the end of 2003 is to

develop detectors with a quantum efficiency of at

least 80 % in the telecommunication wavelengths.

Conventional semiconductor-based single-photon

detectors suffer from high rates of ìdark countsî

(false positives), especially at the communication

wavelengths at 1300 nm and 1550 nm, severely limiting the single-photon applications. In principle, our

Technical Contact:

Sae Woo Nam

John Martinis

Staff-Years (FY 2003):

2
20 Electronics and Electrical Engineering Laboratory

detectors do not suffer from dark counts at all. This

simple fact will allow our instrument to be operated

at much lower light levels than any existing metrological instrument. Consequently, these detectors

could be a significant tool in the development of

quantum-based communication protocols. The

multi-photon discrimination metrology will be essential for evaluating the security of such quantum

cryptographic systems.

Comparison of the measured pulse-height distribution

of a pulsed-laser source using a TES calorimetric

photon counter with the expected photon-number

distribution. The source was 100 ns wide pulses of

1550 nm laser light at a repetition rate of 500 Hz

containing an average photon number of ~4. Total

acquisition time was four minutes. Shown are the data

and best fit Poisson distribution convolved with the

measured device response. Inset shows the difference

between measured and fit probability distributions.

Error bars show the expected 1-sigma standard

deviation due to counting statistics.

ACCOMPLISHMENTS

# Operation of Detectors in a Portable Cryostat

ñ Aaron Miller, Sae Woo Nam, and John Martinis

demonstrated the operation of a tungsten TES optical detector in a portable adiabatic demagnetization refrigerator (ADR). Previously, operation of

optical TES detectors has been done in refrigeration systems that were difficult to transport.

# Photon Number Counting Detectors Demonstrated ñ Aaron Miller, Sae Woo Nam, and John

Martinis demonstrated the operation of a tungsten

TES optical detector capable of counting the number of photons in a short pulse of light. The initial

demonstrations were performed with an attenuated

pulsed laser diode.

# Optical Detectors with Photon Number Counting Capabilities Used with a Twin Photon Source ñ

The NIST group and researchers at Boston University have demonstrated the use of the NIST

detectors with a SPDC crystal. Full accounting of

the distribution of all the photons from the SPDC in

simple optical experiments was done for the first

time. The demonstrations included observations

of classical interference and quantum interference.

COLLABORATIONS

# Alan Migdall from NISTís Optical Technology Division (Physics Laboratory) is developing a

single photon source using SPDCs, and we will be

using our detectors to verify the performance of

this type of photon source in 2004.

# With Xiao Tang from the Convergent Information Systems Division (Information Technology

Laboratory), Carl Williams from the Atomic Physics Division (Physics Laboratory), and Alan

Migdall, we are working on installing one of our

detector systems in the quantum communication

testbed being developed at NIST by the end of

2004.

# We collaborate with Prof. Alexander Sergienko,

his colleagues, Prof. Melvin Tesch, and Prof. Baha

Saleh, and their research group at Boston University. Prof. Sergienko is an expert in the use of

SPDCs.

# We work closely with Prof. Blas Cabrera at

Stanford University on the use of tungsten-based

TES detectors for astronomy applications. We work

closely in developing advanced electronics for the

readout and operation of TES detectors

RECENT PUBLICATIONS

S.W. Nam, J. Beyer, G. Hilton, K. Irwin, C. Reintsema, and

J.M. Martinis, ìElectronics for arrays of transition edge

sensors using digital signal processing,î to appear in IEEE

Transactions on Applied Superconductivity vol. 52 no. 2

(in press).

B. Cabrera, J.M. Martinis, A.J. Miller, S.W. Nam, and R.W.

Romani, ìTES spectrophotometers for near IR/optical/

UV,î Proc., 9th Intíl Workshop on Low Temperature Detectors, 22-29 July 2001, Madison, WI, pp. 565-570 (2002).

R.W. Romani, A.J. Miller, B. Cabrera, S.W. Nam, J.M.

Martinis, ìPhase-resolved Crab studies with a cryogenic

transition-edge sensor spectrophotometer,î Astrophysical Journal 563, pp. 221-228 (2001).

R.W. Romani, A.J. Miller, B. Cabrera, E. Figueroa-Feliciano,

S.W. Nam, ìFirst astronomical application of a cryogenic

transition edge sensor spectrophotometer,î Astrophysical

Journal 521, pp. L153-L156 (1999).
Electromagnetic Technology Division 21

QUANTUM MEASUREMENTS

CRYOGENIC SENSORS

GOALS

To develop devices and systems for the measurement of electromagnetic signals using the unique

properties of electronic devices operated at cryogenic temperatures.

Gene Hilton and Steve Deiker standing by an Adiabatic

Demagnetization Refrigerator (ADR). The ADR is

used to cool our transition edge sensor (TES) x-ray

detector down to about 1/10th of a degree above

absolute zero. The TES is used to provide extremely

sensitive x-ray microanalysis of materials.

By operating at temperatures below 1 kelvin, a new

generation of photon detectors is achieving unparalleled sensitivity. Because they operate at such

low temperatures, these detectors are able to measure very small differences in the energy of photons. They also are able to take advantage of extremely low-noise superconducting amplifiers such

as SQUIDs, further enhancing their performance.

The Division has been a world leader in developing these new detector systems. We have developed transition edge sensor (TES) bolometers for

use in a variety of applications. These devices

utilize a strip of superconducting material, biased

in its transition from normal to superconducting

states, as an extremely sensitive thermometer. This

thermometer is attached to an absorber that is isolated from a cold (~100 mK) heat sink by a micromachined structure. The heat deposited by incident photons is then measured to accurately

determine their energy.

Applications include ultra-high-resolution x-ray

spectroscopy for materials analysis for the semiconductor industry and the development of largescale arrays of cryogenic sensors for high-throughput imaging, and spectroscopy of electromagnetic

radiation for materials analysis and astronomy. In

each of these areas the Division is developing detector systems that will redefine the measurement

abilities of currently available technology, often by

orders of magnitude. Our goal is to continue developing groundbreaking detector systems for both

industry and research groups.

CUSTOMER NEEDS

Improved x-ray detector technology has been cited

by International SEMATECHís Analytical Laboratory Managers Working Group (ALMWG, now

ALMC) as one of the most important metrology

needs for the semiconductor industry. In the International Technology Roadmap for Semiconductors,

improved x-ray detector technology is listed as a

key capability that addresses analysis requirements

for small particles and defects. The TES microcalorimeter x-ray detector developed at NIST has been

identified as a primary means of realizing these detector advances, which will greatly improve in-line

and off-line metrology tools that currently use semiconductor energy-dispersive spectrometers (EDS).

At present, these metrology tools fail to provide

fast and unambiguous analysis for particles less

than approximately 0.1 μm to 0.3 μm in diameter.

Improved EDS detectors such as the TES microcalorimeter are necessary to extend the capabilities

of existing SEM-based instruments to meet the analytical requirements for future technology generations. With commercialization and continued development, microcalorimeter EDS should be able to

meet both the near-term and the longer-term requirements of the semiconductor industry for improved particle analysis.

In addition, the astronomy community has an everincreasing need for instruments capable of supplying extremely high energy sensitivity coupled with

large-format arrays for imaging and photon collection. TES detector arrays promise to greatly expand the abilities of astronomers to study objects

Technical Contact:

Kent Irwin

Staff-Years (FY 2003):

14

ì[T]his type of resolution,

very simply, was

something that I thought

was truly, truly a dramatic advance. And I

really would like to

encourage the people

working on this at NIST

and the equipment

industry to get this into

commercialization as

soon as they possibly

can.î

Mark Melliar-Smith,

President and Chief

Executive Officer of

SEMATECH
22 Electronics and Electrical Engineering Laboratory

ranging from solar flares, to supernova remnants,

to the formation of galaxies. The Division has

formed collaborations to transfer our TES technology into astronomical instruments with several institutions, including NASA, Stanford University,

the Lockheed-Martin Solar Astrophysics Laboratory, and the UK Astronomy Technology Center.

X-RAY MICROANALYSIS

The ability to detect photons with high energy resolution and near-unity quantum efficiency promises

to dramatically improve the field of X-ray microanalysis. Improved energy-dispersive X-ray

spectroscopy will be used to solve a wide range of

problems in materials analysis. For instance, in semiconductor manufacturing, improved X-ray materials analysis is needed to identify nanoscale contaminant particles on wafers and to analyze very

thin layers of materials and minor constituents.

To make this technology available to the materials

analysis community, NIST has licensed several

patents to a U.S. company for commercialization.

Additionally, NISTís Chemical Science and Technology Laboratory (CSTL) is using a prototype

microcalorimeter system constructed by our group

to improve its own materials-analysis capability.

TECHNICAL STRATEGY

The TES-based x-ray energy dispersive detector

we developed has been shown to have world-record

energy resolution and to have wide application in

many areas of x-ray microanalysis. In trying to

deliver maximum benefit of this technology to industrial and scientific users of microanalysis, we

are concentrating our efforts in three areas: support of existing demonstration systems and existing licensees; development of improved and simplified single detector pixels; and development of

arrays of detectors as a means of increasing x-ray

collection area and count rate.

The low operation temperature of TES microcalorimeters (~100 mK) necessitates a fairly complex

arrangement of cryogenic and electronic elements

in order to construct a complete x-ray spectrometer. In this case, we have developed superconducting electronics to read out the detectors, compact adiabatic demagnetization refrigerators to

simplify cooling the detectors to millikelvin operating temperatures, and room-temperature electronics to process the output signals.

An important part of our effort is providing support to our existing customers, most notably the

users of the prototype microcalorimeter system at

CSTL in Gaithersburg, MD, and to the current patent

licensees. We continue to provide expertise and

training in detector and SQUID (readout electronic)

operation and optimization, and operation of

millikelvin refrigerators to both CSTL and the licensees, including consultations and site visits.

Additionally we continue to make improvements

to the components in the spectrometer system. We

will continue to provide information on these improvements to our customers.

Our compact adiabatic

demagnetization refrigerator has unique design

features that produce

nearly 24 hours of

continuous operation,

and days of hold time for

liquid helium.

This system holds the

worldís record for

energy resolution for an

EDS detector.

Comparison of resolutions of NIST microcalorimeter

EDS to standard semiconductor EDS.

While the performance of the detectors we have

made is much better than existing energy dispersive detectors, improvements in energy resolution

(particularly at higher energies) are both theoretically possible and desirable by the user community. Improvements in energy resolution require new

understanding of the limitations on performance of

microcalorimeter detectors. We have begun to explore novel detector geometries and materials.

These include annular geometries to reduce edge

effects that may produce some of the noise in detectors, as well as fabricating detectors using magnetic impurities to suppress the transition temperature of superconductors, rather than the bilayer

technique. (The transition temperature of the films

in most TES microcalorimeters is adjusted by depositing a think layer of normal metal on top of the

superconductor to make a bilayer.)

In addition to improving our understanding by

studying new single-pixel designs, we hope to improve and simplify our fabrication methods. One

key advantage of the magnetically doped TES microcalorimeter is that the fabrication would require

approximately half as many steps as the bilayer

TES microcalorimeter. We are exploring this and

other means to make TES microcalorimeters cheap

and reliable to produce.
Electromagnetic Technology Division 23

For many x-ray microanalysis applications, improvements in count-rate and collection area are

far more important than further improvements in

energy resolution. This can be achieved by the

creation of multipixel arrays of detectors. In addition to the fabrication difficulties in making such

arrays, the cold- and room-temperature electronics

to read out the arrays must also be created. The

work on the readout electronics (SQUID multiplexers, high-density wiring and room-temperature signal processing) is discussed in more detail in the

section titled ìSuperconducting Electronics.î We

are currently exploring two means of developing

arrays of Mo/Cu bilayer TES detectors, bulk

micromachining and surface micromachining. These

two methods require different modifications of our

existing process, thus we are exploring both means

of making arrays. We will test both concepts by

June 2003.

ACCOMPLISHMENTS

# Cryogenic X-ray Spectroscopy System Developed ñ We have developed an extremely high energy resolution x-ray detector and demonstrated a

complete x-ray spectroscopy system. This detector and spectrometer have been made possible by

broad expertise within the Division in such fields

as superconductivity, device fabrication including

silicon micromachining, superconducting electronics, cryogenic engineering, and low-noise, roomtemperature electronics. Without expertise in all of

these areas, the complete systems that have provided the compelling demonstrations for the power

of this technology would not have been possible.

# World-Leading Energy Resolution Achieved

ñ This system holds the world record for energy

resolution for an EDS detector of 2.0 eV at 1500 eV,

A microcalorimeter EDS spectrum of 0.7 % by weight

Cu/Al alloy thin film (from Lucent Technologies)

demonstrating the sensitivity of microcalorimeter EDS

for analysis of trace Cu in the semiconductor industry.

which is over 30 times better than the best highresolution semiconductor-based detectors currently

available. The figure on the previous page compares an X-ray spectrum obtained with this system

to that from a semiconductor energy-dispersive

detector, clearly demonstrating the remarkable improvement in resolution. The specimen was a glass

prepared by Dale Newbury of CSTL to use as a test

standard for EDS. We have used the system to

identify submicrometer particles of materials such

as W on Si substrates, an identification problem

that is impossible with standard EDS detectors and

of great importance to the semiconductor industry.

It has also demonstrated energy shifts in the EDS

X-ray spectra of materials such as Al, Fe, and Ti,

depending on their chemical bonding state, thus

allowing differentiation between a particle of Al

and Al2O3, for example.

# Partnerships with Semiconductor Companies

Formed ñ We have completed several effective partnerships with companies in the semiconductor industry to demonstrate the usefulness of the microcalorimeter spectrometer for practical analysis. For

example, in collaboration with researchers at Lucent Technologies in Orlando, Florida, we critically

compared the ability of microcalorimeter-based xray analysis to detect trace Cu with that of other

industrial analytical techniques, including conventional semiconductor Energy-Dispersive Spectrometry (EDS), Auger Electron Spectrometry, and Secondary Ion Mass Spectrometry (SIMS). Although

only SIMS is capable of analysis of trace Cu down

to the ~0.02 % atomic level, microcalorimeter EDS

fared very well in comparison with the other nondestructive analytical techniques.

# Working X-ray Spectroscopy System Delivered to CSTL ñ To enable more advanced applications of this technology to materials-analysis problems requires coupling the spectrometer to

state-of-the-art analytical tools, such as those available in CSTL at NIST-Gaithersburg. To this end, a

working single-pixel spectrometer used in the above

research has been delivered to Gaithersburg. The

system is being used jointly with CSTL to continue

microanalytical work on problems of interest to the

semiconductor and other materials-intensive

industries.

500 1000 1500 2000

0

500

1000

1500

2000

2500

0

50

100

850 900 950 1000

C-K Cu-L O-K W-M

W-M

W-M

Si-K

Counts (0.16 eV/channel)

Energy (eV)

Cu Lβ1

NIST cal EDS

3 keV beam energy

1.3 nA beam current

500 s-1 input rate

1000 s live time

Cu Lα1,2

μ
24 Electronics and Electrical Engineering Laboratory

# New TES Materials Systems Developed ñ We

have demonstrated two new materials systems suitable for a magnetically doped microcalorimeter: Mo

doped with Fe and Al doped with Mn. In both

cases we have demonstrated tenability of the transition temperature of the doped superconductivity

over the range of interest. The iron doped molybdenum is created by ion-implanting Fe ions into

films of Mo. The resulting Tc

 can be controlled

with the ion dose. The Mn-doped Al has been

produced in collaboration with the Magnetic Technology Division of EEEL. Here the films are produced by co-sputtering a highly Mn-doped Al target with a pure Al target. When detectors are

produced using these methods, they should provide new insight into TES detector physics. Additionally these detectors may be simpler and more

reliable to produce than those made by our conventional bilayer methods.

An array of x-ray TES detectors fabricated using a

Deep Reactive Ion Etch (DRIE) process. Each square

pixel is 400 μm on a side.

An 8x8 array of TES x-ray detectors fabricated using a

surface micromachining technique. Each square pixel

is 400 μm on a side.

# New Micromachining Capabilities Developed

ñ In order to produce arrays of TES microcalorimeters, we have developed two micromachining

methods compatible with our existing fabrication

processes. In the first of these, surface micromachining, a sacrificial layer of poly-Si that was fabricated underneath the Si3

N4 membranes and detectors is removed by a XeF2

 ìplasma-lessî etching

technique. Prototype detectors fabricated by this

method are shown at left. The second method, bulk

micromachining, removes all of the substrate Si from

beneath the Si3N4 and pixel using deep-reactive ion

etching. A prototype array fabricated using this

method is also shown at left.

# First ac-dc thermal transfer standard based on

superconducting sensors ó In 1998, we completed

and reported a set of preliminary experiments on

ac-dc transfer using similar transition-edge bolometers. These yielded uncertainties varying from 50

to 150 × 10ñ6 (for frequencies from 100 hertz to

10 kilohertz), limited chiefly by inaccuracy introduced in delivering the ac signal to the cryogenic

reference plane.

ASTRONOMICAL INSTRUMENTATION

The astronomy community has long been the driving force behind improvements in photon detection systems at all wavelengths. Because of TES

detectorsí extremely good sensitivity, they are obvious candidates to solve many problems faced by

this community. The same x-ray detectors used in

our microanalysis efforts, for example, are well

suited to analyzing the x-ray spectra of supernova

remnants and solar flares. By redesigning these

detectors, they may be used as bolometers to measure far infrared and submillimeter radiation on

ground-based telescopes, allowing astronomers to

probe the evolution of galaxies and search for planets around other stars.

The Division has collaborations with several institutions to deploy our detectors for use in astronomical applications. As these collaborations push

the technical abilities of our detectors, they often

drive us to create improvements that are then applied to our more commercial applications, such as

x-ray microanalysis.

TECHNICAL STRATEGY

Many of the requirements for x-ray astronomy are

identical to those for our x-ray microanalysis

project: high energy resolution, large arrays, high

counting rates and multiplexed readout are all desirable. We have two principal collaborators in
Electromagnetic Technology Division 25

this area: NASAís Laboratory for High Energy Astrophysics (LHEA) and the Lockheed-Martin Solar

Astrophysics Laboratory (LMSAL).

NASA has an ongoing program to study x-ray astrophysics as part of its Structure and Evolution of

the Universe theme. Following on its successful

Chandra mission, Constellation-X is the next generation of x-ray astronomy telescopes. To accomplish its goals, Constellation-X will need to have

an imaging array of x-ray spectrometers to place at

the focal plane of an orbiting x-ray telescope.

A similar telescope is planned by LMSAL to study

the mechanisms behind solar flares and coronal

mass ejections (CMEs). CMEs cause significant

financial impact around the world, as they disrupt

satellites in earth orbit and can knock out power

grids on the ground. Scientists hope to understand and possibly predict these solar phenomenon by study the spectra of solar flares, and

LMSAL is working with the Division to develop

TES detectors for this purpose.

In the infrared regime, our TES bolometers have

achieved world-record sensitivity. This impressive

result confirms the utility of TES technology for

this application as well. For several years, we have

been involved in a collaboration with Laboratory

for Astronomy & Solar Physics (LASP), at NASAís

Goddard Space Flight Center, to develop far-infrared bolometers. A result of this collaboration was

the Fabry-Perot Interferometer Bolometer Research

Experiment (FIBRE), an eight-pixel multiplexed TES

bolometer array, which was deployed on the Caltech

Submillimeter Observatory at Mauna Kea, Hawaii.

In addition the Division, in collaboration with the

United Kingdomís Astronomy Technology Center,

is developing both sensors and readout technology for the second Submillimeter Common User

Bolometer Array (SCUBA-2). The SCUBA-2 instrument is designed to detect radiation from astronomical sources at wavelengths of 450 μm and

850 μm, and will be installed on the James Clerk

Maxwell Telescope (JCMT) in Hawaii. This array

will be, by orders of magnitude, the largest bolometer array ever deployed, having 12,800 individual

pixels. It will allow astronomers to map the sky at

speeds over 1,000 times faster than previously accomplished.

ACCOMPLISHMENTS

# Surface Micromachining Techniques Developed

ñ We have developed a surface micromachining

method for producing freestanding pixels above the

surface of a silicon wafer. This process has been

integrated into the x-ray TES fabrication process,

and TES devices have been produced and cooled

down. The surface micromachining process did not

appear to affect the TES process, although further

development is needed to produce working detectors.

# Deep Reactive Ion Etch Techniques Developed

ñ We have used the Divisionís newly acquired Deep

Reactive Ion Etcher (DRIE) to fabricate closely

spaced pixels. This process replaces the anisotropic KOH etch we have used in the past. The KOH

etch, while effective, etched along crystal planes in

silicon wafers, producing sloped sidewalls and forcing a minimum separation between adjacent pixels.

This DRIE etch produces vertical sidewalls, allowing pixels to be more closely spaced, and thus

greater spatial resolution

# X-ray TES Detector Delivered to LMSAL ñ

We have delivered a single pixel x-ray detector and

SQUID to LMSAL. This detector will be used by

LMSAL to develop their own cryogenic facilities

and design a rocket payload for solar observations.

# SCUBA-2 Test Pixel Fabricated ñ We have fabricated a SCUBA-2 test pixel that met or exceeded

all of the design specifications for the SCUBA-2

project.

SUPERCONDUCTING ELECTRONICS

The detector systems discussed above all share a

common technical requirement: large arrays of TES

detectors. This requirement brings with it the complication of reading out such large arrays. These

arrays will all operate at temperatures below 1 K. If

each pixel in the array requires a separate readout

all the way to the room-temperature electronics,

then the heat load on the arrayís refrigeration system will rapidly become unmanageably large. A

system to multiplex the readout of these detectors

at the cold stage of their refrigerator is thus required to reduce the number of wires from the cold

stage to warmer parts of the cryostat.

Fortunately, TES devices are of low impedance,

which allows them to be read out by superconducting SQUIDs. Because SQUIDS, in their unbiased ìoffî state, are superconducting, they may be

effectively multiplexed without adding the noise of

each individual SQUID to the whole.
26 Electronics and Electrical Engineering Laboratory

A photograph of a 32-channel SQUID multiplexer chip

fabricated at NIST. On the chip are 32 first-stage

SQUID amplifiers and one second-stage series-array

SQUID amplifier. The area shown is 4 mm by 6 mm.

TECHNICAL STRATEGY

The Division has been at the forefront of SQUID

multiplexing for several years now. Our first-generation 8-channel SQUID MUX was successfully

deployed with the FIBRE far-infrared bolometer array on the CSO telescope on Mauna Kea, Hawaii.

We have now built upon that success by developing a second generation, 32-channel SQUID MUX

that has better bandwidth and power dissipation

lower by 2 orders of magnitude lower than that of

the first design. The first fabrication run yielded

devices that work at the design specifications.

These MUX chips should have sufficient performance to multiplex x-ray TES detectors, which are

much faster than the infrared bolometers in FIBRE.

ACCOMPLISHMENTS

# SQUID Multiplexer Deployed at the CSO in

Mauna Kea ñ We have demonstrated an 8-channel

multiplexer on the CSO telescope in Mauna Kea,

Hawaii. This is the first astronomical use of SQUID

multiplexing. The multiplexer performed well, and

will be used for further observations.

# Second-Generation SQUID MUX Tested ñ We

have successfully fabricated and tested a secondgeneration SQUID MUX chip, which has significantly improved speed and performance. This chip

will be integrated with a small x-ray detector array

by June 2003.

# Room-Temperature Digital Feedback Electronics Developed ñ We have developed a roomtemperature digital feedback system to read out

the SQUID MUX. This system is critical for deployment of large multiplexed TES systems.

NIS MICROREFRIGERATORS

NIST has a long tradition of exploiting physical

phenomena that occur at ultra low temperatures to

produce electronic devices with properties that

cannot be achieved by conventional electronics.

For instance, NIST has developed TES x-ray sensors, which operate at temperatures near 100 mK

and provide improved analytical capabilities to the

semiconductor industry. The recent development

of two-stage Adiabatic Demagnetization Refrigerators (ADRs) has made these low operating temperatures significantly more accessible. Nonetheless, even a two-stage ADR adds considerable

complexity, size, and expense to an analytical station. To overcome this challenge, NIST has recently begun development of a thin-film refrigerator, which should be capable of cooling sensors

from 300 mK to 100 mK.

TECHNICAL STRATEGY

The refrigerator consists of Normal-InsulatorSuperconductor (NIS) tunnel junctions. Current

flow through the insulating barrier separating the

electrodes preferentially removes the hottest electrons from the normal electrode, thereby producing cooling. When coupled to a helium-3 cryostat,

NIS coolers may provide a significantly smaller,

cheaper, and less complex means of reaching temperatures of 100 mK.

ACCOMPLISHMENTS

# Developed Photolithographic NIS Process ñ

We have recently developed a photolithographic

fabrication process for NIS junctions. This process reliably produces junctions whose smallest

dimensions are 5 μm ñ 10 μm. Junction quality is

extremely high: the leakage current is 0.3 % of the

tunneling current even for barrier transparencies

as low as 1,000 Ÿ (μm)2. We are currently testing

our first set of devices laid out as complete refrigerators.

NEW DIRECTIONS

The Division is currently investigating several new

cryogenic detector applications and technologies.

TECHNICAL STRATEGY

Large arrays of x-ray microcalorimeters will be able

to acquire high-quality spectra in a fraction of a

second. This will make it possible for the first time

to study the evolution of rapidly changing x-ray

spectra at high energy resolution. Such capability

would be revolutionary for in-process monitoring

NIS Microrefrigerators

could make cryogenic

sensors much more

practical to deploy in

industrial and analytical

laboratory settings.
Electromagnetic Technology Division 27

in which, for instance, the evolving materials properties of a film are studied during deposition. We

are exploring this possibility in conjunction with

CSTL at NIST-Gaithersburg.

In addition, two new detector technologies are being investigated. We are developing magnetic calorimeters in conjunction with the Magnetic Technology Division of EEEL. In a magnetic calorimeter,

a SQUID is used to measure the change in magnetization of a sample of material when it is heated by

an incident x-ray photon. Because this type of calorimetry is non-dissipative, it may offer the possibility of greatly improved energy sensitivity. The expertise available in the Division in fabrication and

SQUID readout, combined with the magnetic films

expertise in the Magnetic Technology Division,

makes us ideally suited for exploring this new technology.

Another promising technology is that of kinetic

inductance detectors. In this type of detector,

changes in the inductance of a superconductor are

created by the energy deposited by an incident

photon. This technology has seen a recent revitalization, and may allow for improvements in performance over TES detectors in both speed and array

size. Again, the superconducting fabrication skills

available in the group make this an attractive project

for us.

PATENTS

# ìThe Use of Superconductor-Insulator-Normal (SIN) Tunnel Junctions in Superconducting

Quantum Interference Device (SQUID) Multiplexers,î disclosure submitted, April 2000.

# ìSuperconducting Transition-Edge Sensor

with Weak Links,î issued May 2001.

# ìMechanical Support for a Two Pill Adiabatic

Demagnetization Refrigerator,î issued August 1999.

# ìSuperconducting Transition-Edge Sensor,î

issued March 1999.

# ìMicrocalorimeter X-ray Detectors with X-ray

Lens,î issued March 1999.

# ìParticle Calorimeter with Normal Metal Base

Layer,î issued June 1997.

RECENT PUBLICATIONS

K.D. Irwin, ìSQUID multiplexers for transition-edge sensors (review)î, Physica C, 368, 203 (2002).

R.E. Geer, D. Wu, and D.A. Wollman, ìHigh-resolution

energy-dispersive x-ray spectroscopic analysis of ultrathin

ion diffusion barriers using microcalorimetery,î J. Appl.

Phys., 91, 1099 (2002).

K.D. Irwin, L.R. Vale, N.F. Bergren, S. Deiker, E.N.

Grossman, G.C. Hilton, S.W. Nam, C.D. Reintsema, and

D.A. Rudman, ìTime-division SQUID multiplexers,î Proc.

9th Intíl Workshop on Low-Temperature Detectors, AIP

Conf. Proc. 605, 301 (2002).

R.E. Geer, D. Wu, and D.A. Wollman, ìHigh-resolution

EDS analysis of ultra-thin TaSiN diffusion barriers for Cu

metallization using microcalorimetry,î Proc. IEEE 2001

Intíl Interconnect Tech. Conf., 3-6 June 2001, Burlingame,

CA, pp. 192-194 (2001).

S. Deiker, J. Chervenak, G.C. Hilton, K.D. Irwin, J.M.

Martinis, S. Nam, and D.A. Wollman, ìTransition edge

sensor array development,î IEEE Trans. Appl. Supercond.

11, pp. 469-472 (2001).

G.C. Hilton, J.M. Martinis, K.D. Irwin, N.F. Bergren, D.A.

Wollman, M.E. Huber, and S.W. Nam, ìMicrofabricated

transition-edge x-ray detectors,î IEEE Trans. Appl.

Supercond. 11, pp. 739-742 (2001).

K.D. Irwin, G.C. Hilton, J.M. Martinis, S. Deiker, N.F.

Bergren, S.W. Nam, D.A. Rudman, and D.A. Wollman, ìA

Mo-Cu superconducting transition-edge microcalorimeter

with 4.5 eV energy resolution at 6 keV,î Nuclear Instruments and Methods in Physics Research A 444, pp. 184-

187 (2000).

D.A. Wollman, S.W. Nam, D.E. Newbury, G.C. Hilton,

K.D. Irwin, N.F. Bergren, S. Deiker, D.A. Rudman, and

J.M. Martinis, ìSuperconducting transition-edge-microcalorimeter x-ray spectrometer with 2 eV energy resolution at 1.5 keV,î Nuclear Instruments and Methods in

Physics Research A 444, pp. 145-150 (2000).

J.A. Chervenak, E.N. Grossman, K.D. Irwin, J.M. Martinis, C.D. Reintsema, C.A. Allen, D.I. Bergman, S.H.

Moseley, R. Shafer, ìPerformance of multiplexed SQUID

readout for cryogenic sensor arrays,î Nuclear Instruments

and Methods in Physics Research A 444, 107 (2000).

D.A. Wollman, S.W. Nam, G.C. Hilton, K.D. Irwin, N.F.

Bergren, D.A. Rudman, J.M. Martinis, and D.E. Newbury,

ìMicrocalorimeter energy-dispersive spectrometry using

a low voltage scanning electron microscope,î J. Microscopy 199, pp. 37-44 (2000).

The expertise our group

has in cryogenic detectors and superconducting electronics makes us

ideal to explore new

detector technologies

and applications.
28 Electronics and Electrical Engineering Laboratory

QUANTUM MEASUREMENTS

TERAHERTZ TECHNOLOGY

GOALS

To develop and apply electronic technology, especially cryogenic electronic technology, in the

terahertz spectral range to measurements and standards in support of other NIST organizations and

U.S. industry.

First version of a 120-element antenna-coupled

bolometer array for detection of concealed weapons.

CUSTOMER NEEDS

The U.S. aerospace and defense industries are being pushed toward both higher performance and

faster, less expensive systems. Devices originally

developed for cryogenic electronics, in particular

cryogenic bolometers and tunnel diodes, are often

useful in a wide variety of metrological applications, as well as in other scientific or commercial

applications, not always at cryogenic temperatures.

Atmospheric scientists use satellite-based spectrometers to monitor the worldwide distribution of

species relevant to climate change. Security equipment manufacturers are developing millimeter-wave

imagers for concealed weapons detection. Submillimeter spectroscopy is being developed as a diagnostic tool ó monitoring species concentrations

and temperatures ó for plasma processes in semiconductor manufacturing. The activities of this

project focus on adapting millimeter-wave to IR

technology for the benefit of these industries, either directly through collaborative research and

development programs, or indirectly, by improving

the metrological capabilities of other NIST Divisions, which in turn make the results available to

U.S. industry.

TECHNICAL STRATEGY

The work of this project focuses particularly on

bolometric detectors, initially developed for cryogenic electronic applications, but also useful in the

detection or frequency conversion of radiation from

millimeter to infrared wavelengths.

Some projects do not require the very highest sensitivity but exploit the same antenna-coupled bolometer strategy. An example is millimeter-wave

imaging for the detection of concealed weapons

(clothing is transparent at millimeter wavelengths).

In collaboration with EEELís Electricity Division and

the Office of Law Enforcement Standards (OLES),

we are developing an actively illuminated imaging

system for this application, based on a full waferscale array of several hundred antenna-coupled

bolometers. By early 2003, we will demonstrate realtime readout of our initial 120-element focal plan

array. The technical emphasis in this case is on

development of a practical system, rugged enough

and low enough in cost to allow for field deployment, for example with mobile police units or in

airports.

Millimeter-wave images of a representative handgun

(bottom) compared with optical image (top).

Technical Contact:

Erich Grossman

Staff-Years (FY 2003):

6

Recent advances in

nanoscale fabrication

make the vision of direct

rectification of sunlight

much more realistic.

Our large arrays of

bolometers are applicable to remote sensing

of the earth, atmospheric

spectroscopy, and (by

NASA) astronomy.
Electromagnetic Technology Division 29

In addition, we are working on the application of

uncooled terahertz bolometer arrays to analyze and

diagnose problems in the etching plasmas used for

semiconductor manufacturing. These plasmas typically contain a number of molecular and ionic species, whose concentrations and temperatures can

be accurately monitored by spectroscopy on their

pure rotational transitions, which lie in the terahertz

spectral region. A collaborative program with

NISTís Physics Laboratory, funded by the NIST

Advanced Technology Program (ATP), was started

in 2001 to demonstrate the usefulness of this technique as an industrial plasma diagnostic, and to

develop a practical system that can be applied to it.

A key part of this program is the development of

bolometer arrays with sufficient sensitivity to perform the spectroscopy, but which are not cryogenically cooled, and are therefore practical for industrial use. Based on prior work done for other

programs, a detector system based on uncooled

Nb bolometers has been designed and built; results from an example device are shown in the next

figure. By mid-2003, we will perform a side-by-side

comparison of Nb and semiconducting VO2 based

microbolometers at 0.6 THz.

Uncooled antenna-coupled microbolometer and

spectra of CO, a low concentration reaction product in

an CHF3 plasma, measured in the Gaithersburg

Gaseous Electronics Conference (GEC) reactor.

In most of these programs, the lithographic antenna

forms an important component of the system, frequently requiring as much development as the bolometer or tunnel diode, although its only function

is the efficient coupling of radiation to the device.

We therefore perform significant development work

on lithographic antennas themselves. These are

ubiquitous in wireless telecommunications systems

(e.g., cellular phones) at lower, microwave frequencies. The relentless drive for greater bandwidth in

such telecom systems is driving a push to raise the

operating frequencies to the millimeter-wave range

or beyond, where our present antenna development effort is focused. Moreover, the polarizationspecific nature of antennas can frequently be exploited to provide our devices with additional

functionality. For example, the emittance or reflectance properties of a surface differ for s and p polarizations of obliquely incident radiation. This can

be exploited to resolve the ambiguity of obliquely

incident radiation and to resolve the ambiguity inherent in noncontact thermometry or materials

analysis due to unknown specimen emissivity. In

collaboration with a commercial semiconductor

metrology manufacturer, we are exploring the potential of this technique.

Far-infrared spectroscopy at the highest levels of

sensitivity and spectral resolution has traditionally been accomplished with heterodyne techniques, in which the weak signal to be measured is

combined with a strong ìlocal oscillatorî and focused onto a detector or ìmixer.î The signal at the

difference frequency is then measured with an ultra-low-noise detection system. A program is underway to develop ultra sensitive mixer elements

based on superconducting hot-electron bolometers

(HEBs). As with transition-edge bolometer arrays,

a major application for these mixers lies in spacebased remote sensing. HEBs formed of thin films of

niobium and niobium nitride have already demonstrated sensitivities within a factor of 5 of the fundamental quantum limit. The focus of our research,

and of the most recent progress in the state of the

art, lies in extending the frequency coverage of this

measurement technique above 2 THz, allowing

measurement of a wider variety of species, and in

developing integrated heterodyne arrays.

ACCOMPLISHMENTS

# First Electrical Substitution Radiometer Based

on Superconducting Sensors ó In 1997, we completed a standards-grade, electrical substitution

radiometer for measurement of mid- and far-IR-wavelength blackbody radiation, and delivered it to

NISTís Optical Technology Division, which is responsible for optical and IR power calibration and

metrology. For an extended series of experiments

covering a range of substitution power from 500

picowatts to 5 microwatts, the instrumentís noise

floor could be approximated as 4 picowatts plus 7 ×

10-6 times the measured power. We are now assisting a U.S. manufacturer of cryogenic radiometers

with the incorporation of superconducting sensors

into its products.

Our 300 mK infrared

bolometers have the

best noise equivalent

power ever reported.

Our nano-metalinsulator-metal (MIM)

diodes have clearly

rectified 10 μm infrared

radiation.
30 Electronics and Electrical Engineering Laboratory

# A Novel Slot-Ring Antenna Design for Uncooled Millimeter-wave Bolometer Arrays ñ Imaging applications in the terahertz spectral range require large numbers of pixels, reasonable sensitivity,

and reasonable cost. One approach to achieving

all three goals simultaneously is the use of lithographic antennas to couple the radiation into micrometer-sized detectors. In this case, the antenna

engineering challenge is to develop an array-compatible antenna with the highest possible directivity in a completely planar monolithic structure. This

is the motivation behind a new antenna design we

have developed, in which slot-ring antennas with

finite groundplanes are patterned on electrically

thin substrates. Because the application is imaging, sensitivity to radiation from only one side of

the substrate is desired, so a planar backshort is

employed to reflect radiation from the backside of

the substrate into the forward direction. With the

backshort at the proper position behind the plane

of the slot-ring antenna, constructive interference

occurs between the directly received radiation and

that reflected by the backshort, increasing the directivity. Measured beam patterns are highly circular and exceptionally narrow (22° at -3 dB) from a

completely planar antenna. They can be arrayed at

a spacing of 1.5 wavelengths with negligible measured effect on performance. A 120-element array

for 95 GHz has been fabricated.

# Uncooled Antenna-Coupled Metal-InsulatorMetal (MIM) Junctions for IR Rectification and

Mixing ó The ultra-low-capacitance, fully lithographic diodes have areas as low as 30 × 30 square

nanometers and are fabricated by angled evaporation through a free-standing PMMA resist bridge

defined by electron beam lithography. The diodes

are coupled to planar dipole antennas designed for

resonance at a wavelength of 10 micrometers. We

have successfully fabricated and tested diodes from

Al-AlOx

-Al, Al-AlOx-Pd, and Nb-NbOx-Ag materials. The nonlinear current-voltage characteristics

are accurately predicted by the Brinkman-DynesRowell theory of tunneling through trapezoidal

barriers, both for the nano-MIMs and for separate,

micrometer-sized Nb-NbOx-Ag MIM diodes. The

latter show barrier heights that can be controllably

modified by in-situ Ar-ion milling following the

barrier growth. The optical response of the nanoMIM diodes to CO2

 laser radiation at 10 micrometers was clearly proven to arise from classical rectification. Previous attempts to develop fully

lithographic MIM diodes, on the other hand, all

foundered on the difficulty of separating optical

signals due to rectification from those due to thermal mechanisms. The nonlinearity observed in the

large-area diodes is, according to theory, sufficient

to enable observation of photon-assisted tunneling steps, a phenomenon observed at room temperature only recently in GaAs heterostructures.

RECENT PUBLICATIONS

S. Nolen, C.D. Reintsema, E.N. Grossman, ìSlot-ring antennas with a planar backshort designed for millimeterwave imaging applications,î submitted to IEEE Antennas

and Propagation Lett. (in press).

E.N. Grossman, T.E. Harvey, and C.D. Reintsema, ìControlled barrier modification in Nb/NbOx/Ag metal insulator metal tunnel diodes,î J. Appl. Phys. 91(12), pp.

10134-10139 (Jun. 15, 2002)

E. Gerecht, C.D. Reintsema, E.N. Grossman, A.L. Betz,

and R.T. Boreiko, ìSuperconducting Nb DHEB mixer arrays for far-infrared spectroscopy,î Proc. 12th Intl. Symp.

on Space Terahertz Technology, 12-16 Feb 2001, San Diego, CA, pp. 168-176 (2001).

S. Nolen, T.E. Harvey, C.D. Reintsema, E.N. Grossman

ìProperties of cavity-backed slot-ring antennas at 95 GHz,î

Proc. SPIE v. 4373, 49 (2001)

E.N. Grossman, S. Nolen, N.G. Paulter, C.D. Reintsema,

ìConcealed weapons detection system using uncooled,

pulsed, imaging arrays of millimeter-wave bolometers,î

Proc. SPIE, v. 4373, 7 (2001)

N.G. Paulter, E.N. Grossman, G.N. Stenbakken, B.C. Waltrip,

S. Nolen, C. D. Reintsema, ìDesign of an active mm-wave

concealed object imaging system,î Proc. SPIE. v.4373, 64

(2001).

M.E. MacDonald, A. Alexanian, R.A. York, Z. Popovic,

and E.N. Grossman, ìSpectral transmittance of lossy printed

resonant-grid terahertz bandpass filters,î IEEE Trans. Micro. Theory Tech., 48(4), 712 (2000).

S. Nolen, J.A. Koch, N. Paulter, C.D. Reintsema, and E.N.

Grossman, ìAntenna-coupled niobium bolometers for mmwave imaging arrays,î Proc. SPIE, v. 3795, 279 (1999).

C.D. Reintsema, E. N. Grossman, and J.A. Koch, ìImproved VO2 microbolometers for infrared imaging: operation on the semiconducting-metallic phase transition with

negative electrothermal feedback,î Proc. SPIE v.3698, pp.

190-200 (April 1999).
Electromagnetic Technology Division 31

QUANTUM MEASUREMENTS

EMERGING ELECTRONIC

MATERIALS

GOALS

To develop measurement techniques that aid and

accelerate the incorporation of new thin-film materials and devices in electronic applications.

Pulsed-laser deposition chamber for oriented growth

of complex oxides.

Advances in the microelectronics industry require

a continual supply of new materials with unique

properties that can be exploited to improve device

performance or that enable entirely new devices to

be created. To incorporate these materials into new

technologies requires knowledge of their electronic

properties. Often, full characterization of these

materials requires the development of new measurement techniques, data analysis methods and

material property modeling. The overall goal of

this project is to aid and accelerate the development and incorporation of new thin-film materials

and devices for electronic applications. At present

the focus of the project is on emerging materials of

interest to microwave applications, especially for

the telecommunications industry. We are working

primarily on new high-temperature superconducting (HTS) thin films, tunable ferroelectric thin films,

and microelectromechanical systems (MEMS)

structures. The Division has developed standards

and new measurement methods to characterize and

qualify thin films and devices of these materials for

microwave applications, providing the measurement techniques and engineering parameters necessary to design new devices with these materials.

CUSTOMER NEEDS

This research supports the wireless telecommunications industry through the development of measurement techniques for emerging industries that

are incorporating new materials (such as hightemperature superconductors and tunable ferroelectrics) into new devices and circuits. For hightemperature superconductor microwave standards

development, we actively collaborate with U.S. and

international standards laboratories to exchange

materials and make comparative measurements. We

also work with other NIST divisions that are responsible for standards and measurement techniques in areas such as microwaves and time and

frequency standards. We collaborate with EEELís

Radio-Frequency Technology Division to improve

both linear and nonlinear microwave measurement

and characterization techniques for thin-film materials and devices, particularly at cryogenic temperatures. Our work has attracted the interest of other

U.S. government agencies such as NASA and the

Office of Naval Research (ONR), and we are providing them with research support and direction to

help advance their programs.

TECHNICAL STRATEGY

MICROWAVE MEASUREMENTS

AND DEVICES

Our research projects are selected for their importance for standards improvement and development

and their impact in the commercial sector. We also

look for projects with a strong component of innovative science and technology. Our research has

resulted in the development of fabrication processes, testing capabilities, and theoretical competence for advanced cryogenic materials and devices

at rf, microwave and millimeter-wave frequencies.

We use pulsed laser deposition to grow novel thinfilm materials and take those materials through the

device design and fabrication to final test devices.

We have developed microwave measurement capabilities for unpatterned superconducting films

using a sapphire-loaded dielectric cavity resonator

and for planar devices using a cryogenic microwave probe station (shown on the next page). The

probe station allows us to develop temperaturedependent measurement techniques and provide

test results on new materials in actual devices, rather

than as unpatterned thin films.

Technical Contact:

James Booth

Staff years (FY 2003):

5

We have implemented

a cryogenic microwave

probe station for

broadband (dc to 40 GHz)

characterization of

temperature-dependent

microwave properties.

The rapidly expanding

wireless

communications

industry has begun to

adopt HTS components

in receiver front-ends.
32 Electronics and Electrical Engineering Laboratory

Jim Booth operates the cryogenic microwave probe

station that enables rapid temperature-dependent

measurements of a variety of emerging materials and

devices.

We work with the HTS communications industry

to measure and improve the capabilities of HTS

devices. The rapidly expanding wireless communications industry has begun to adopt HTS components in receiver front-ends. This effort is driven

by the need for more efficient use of a limited spectrum in the face of an increasing amount of interference and signal from other providers. The introduction of third- and fourth-generation technology

for the wireless Internet has created a new market

for improved passive and active devices. Our work

is aimed at addressing some of the unresolved issues in HTS devices that affect their ultimate performance. In particular, the nonlinear response of

HTS-based microwave devices is not well understood and is a serious problem for communications

applications. Our work to characterize and model

the nonlinear response in HTS microwave devices

will continue over the next two years.

By collaborating with EEELís Radio-Frequency

Technology Division, we hope to improve both linear and nonlinear microwave measurement and characterization techniques for thin-film materials and

devices. Our research also includes developing

superconducting devices to be used as model nonlinear elements for detailed evaluation using a Nonlinear Network Measurement System in collaboration with the Nonlinear Device Characterization

Project in the Radio-Frequency Technology Division.

We are participating in developing a new standard

for measuring the surface resistance RS of ultralow-loss superconducting thin films. This is under

the auspices of the International Electrotechnical

Commission (IEC) and the Versailles Agreement on

Advanced Materials and Standards (VAMAS).

Development and improvements in our implementation of the proposed international standard technique will continue in 2003.

In addition, the Division is investigating new materials and device structures for advance microwave

applications. Our development of a superconducting microwave power limiter is of interest to a variety of military applications. We continue to characterize and model low-loss electronically tunable

microwave materials (ferroelectrics). Of particular

interest for these materials are improved broadband

permittivity measurements. We will work with the

Radio-Frequency Technology Division to take advantage of their new 100 GHz network analyzer capabilities for these measurements. In 2003 we will

begin exploring microwave MEMS structures.

MICROMACHINING AND MEMS

MEMS and nanoelectromechanical systems

(NEMS) are the enabling technologies for entire

new generations of electronic systems and measurement devices. Novel sensor and metrology technologies benefit from the ability to use integratedcircuit fabrication paradigms in constructing

mechanical devices. Our work in this area also includes measurement techniques for evaluation of

novel MEMS structures at rf and microwave frequencies. We will continue our research efforts in

support of the NIST Time and Frequency Divisionís

work to develop a fully micromachined ion trap for

time standards and quantum computing. We will

also collaborate with other projects in the Division

to apply MEMS technology to a variety of problems.

ACCOMPLISHMENTS

MICROWAVE MEASUREMENTS AND DEVICES

# International Standard for HTS Surface Resistance Measurement ó Sapphire-loaded dielectric

cavity resonators (shown on the next page) are

under consideration by the IEC as a possible standard for the measurement of the surface resistance

RS of HTS thin films. Previously we have participated in round-robin testing of this technique with

Japan, and good agreement was observed for
Electromagnetic Technology Division 33

values of the superconductor RS and the sapphire

loss tangent. In the past year we have made two

significant improvements in NISTís capability for

determining RS by this technique. We have completed new measurements of the microwave loss

tangent of sapphire at cryogenic temperatures using the HTS resonator with two different length

sapphire rods. While the losses in sapphire are extremely small, the surface resistance of HTS films is

so low that losses in the sapphire are a major source

of error in the current measurement. We have also

implemented an improved method for determining

Qo of the resonator, the Transmission-Mode Q Factor (TMQF) technique. The accuracy of RS

 depends

almost exclusively on the uncertainty in Qo, making

improvements in Qo determination critical. The

TMQF method can provide better than 1 % accuracy in Qo

, an improvement by a factor of 2 over

previous methods.

Sapphire-loaded dielectric resonator for measuring Rs

of HTS films. The sapphire puck is sitting on a black

YBCO thin film.

# Calibration Devices for Nonlinear Phase Measurements ó In collaboration with the Nonlinear

Device Characterization Project in the Radio-Frequency Technology Division, we have succeeded

in measuring for the first time the phase of the nonlinear signal generated by HTS devices at microwave frequencies. The lack of appropriate nonlinear test devices has made it difficult to characterize

the new Nonlinear Network Measurement System,

and this superconducting device is being evaluated for this application. In addition, the value of

the phase of the nonlinear signal provides important information on the origin of the nonlinear response in HTS materials, a limiting problem in HTS

microwave devices. In 2003 we plan on developing

improved circuits with the goal of more accurate

nonlinear phase measurements of HTS-based

devices.

# Superconducting Microwave Power Limiter

Developed ó We have designed, fabricated and

tested an HTS Superconducting Microwave Power

Limiter (SMPL) for the purpose of protecting ultrasensitive analog-to-digital electronics in very-highperformance receivers (such as on military platforms) from over-power conditions such as

lightning strikes. The device makes use of the microwave current-induced transition from the verylow-loss superconducting state to the high-loss

normal state, and has been shown to have extremely

wide bandwidth (> 40 GHz) with constant impedance over the entire band. Reversible operation

(self-resetting) has been demonstrated at microwave powers up to 10 watts, and switching speeds

have been measured to be less than 1 microsecond. Since no other power limiter exists with this

remarkable performance, this device is of interest

for a variety of military applications.

# Dynamic Effects in Tunable Dielectric Thin

Films ó Recent measurements in our project of

ferroelectric thin films have revealed large relaxation effects at high microwave frequencies that

have not been previously observed. Ferroelectric

thin films are potentially valuable because they possess a dielectric permittivity that can be modified

by the application of a relatively modest bias voltage. Such a tunable dielectric material would enable very fast tuning of microwave elements such

as filters, and would also enable cheaper phasedarray antennas. Our measurements have revealed

that the high microwave losses that to date have

limited the application of ferroelectric thin films are

at least in part due to coupling of energy into lattice modes of these materials, and are thus intrinsic

to the class of ferroelectrics being studied (e.g..

SrTiO3

). In collaboration with Radio-Frequency

View of two 40 GHz probes and a sample of YBCO

devices in the probe station. Devices such as these are

used for the nonlinear phase measurements and the

microwave power limiter.

ìDr. Beall has generously

helped us with technical

advice and processing

assistance which in turn

has had a significant

impact on advancing our

prototypes. We hope our

relationship with NIST

will continue.î

- Astralux, Inc.,

Boulder, CO

MEMS and nanoelectromechanical

systems (NEMS) are the

enabling technology for

entire new generations

of electronic systems.
34 Electronics and Electrical Engineering Laboratory

Technology Division we will be extending the frequency for these measurements to above 100 GHz

in early 2003 in an effort to further understand this

behavior.

Pulsed and CW power through a Superconducting

Microwave Power Limiter operating at 76 K and

3 GHz. Onset of limiting behavior is near 20 dBm.

# Tuning Time for Ferroelectric Films ó A major

issue in the application of tunable dielectric thin

films for microwave elements is the response times

over which one can vary the permittivity using an

applied bias field. We have performed nonlinear

harmonic generation measurements as a way of

deducing switching times for these materials on

the nanosecond scale. By comparing the tuning

due to the rf field within the device derived from

such harmonic-generation measurements with the

tuning induced by a dc bias field, we have been

able to show that tuning in these materials is possible on nanosecond time scales or faster. Further

nonlinear measurements are being pursued in order to determine tuning times for different materials

and also as a way of assessing the detrimental nonlinear properties that might arise in a tunable application.

# Measurements of MEMS structures at cryogenic temperatures ó We have modified our cryogenic microwave probe station to allow for the application of large bias voltages in order to enable

measurements of MEMS structures at cryogenic

temperatures. So far, several sets of devices, designed and fabricated by the Electrical Engineering

Department of the University of Colorado at Boulder, have been tested at both room temperature

and cryogenic temperatures. These initial measurements indicate that the MEMS structures will function at cryogenic temperatures, which will allow for

ultra-low-loss MEMS and combination MEMS/

superconductor structures to be designed and

evaluated.

MICROMACHINING AND MEMS

We use our new MEMS facilities to fabricate novel

structures that enable new measurements and devices in a number of different areas.

# Micromachined Structures for Ion Traps ó

We have made micromachined structures for use in

ion traps, in collaboration with the NIST Physics

Laboratoryís Time and Frequency Division, which

has recently demonstrated quantum entanglement

with four ions in one of these traps. Recent traps

made with improved surfaces have had much

smaller anomalous heating, leading to improved ionstorage times. We are proceeding with development of ion traps fabricated from silicon electrodes,

which should have even higher quality.

Cryogenic linear quadrapole Hg ion trap used for

atomic frequency standard experiments.

# Surface Micromachining for Cryogenic Detectors ó Large arrays of cryogenic detectors have

applications to a variety of x-ray and infrared detector projects. One option for creating such large

arrays is to use surface micromachining. Using the

recently developed MEMS capability in the Division, we have demonstrated 64-element thermal isolation platforms above a Si substrate, and have

begun integrating these devices with detectors.

Further details on this project are described elsewhere in this publication.

RECENT PUBLICATIONS

J.C. Booth, S.A. Schima, and R.H. Ono, ìA self-attenuating superconducting transmission line for use as a microwave signal limiter,î to appear in IEEE Trans. Appl.

Supercon. Vol. 13 (in press).
Electromagnetic Technology Division 35

J.C. Booth, S.A. Schima, and D.C. DeGroot, ìPhase-sensitive measurements of the nonlinear microwave response

in YBCO thin film devices,î to appear in IEEE Trans.

Appl. Supercon. Vol. 13 (in press).

J.C. Booth, S.Y. Lee, K.T. Leong, J.H. Lee, J. Lim, H.N.

Lee, S.H. Moon, and B. Oh, ìMicrowave surface impedance and nonlinear properties of MgB2

 films,î to appear in

IEEE Trans. Appl. Supercon. Vol. 13 (in press).

K.T. Leong, J.C. Booth, and S.Y. Lee, ìInfluence of impedance mismatch effects on measurements of unloaded Q

factors of transmission mode dielectric resonators,î to

appear in IEEE Trans. Appl. Supercon. Vol. 13 (in press).

G.C. Hilton, J.A. Beall, S. Deiker, L.R. Vale, C.D. Reintsema,

and K.D. Irwin, ìSurface micromachining for arrays of

transition-edge sensor based detectors,î to appear in IEEE

Trans. Appl. Supercon. Vol. 13 (in press).

J.C. Booth, R.H. Ono, I. Takeuchi, and K.-S. Chang, ìMicrowave frequency tuning and harmonic generation in ferroelectric thin film transmission lines,î Appl. Phys. Lett.

81: pp. 718-720 (2002).

J.C. Booth, L.R. Vale, R.H. Ono, ìComparative studies of

the microwave nonlinearities in high temperature superconducting films and devices,î Physica C Vol. 357-360,

pp. 1516-1520 (2001).

H. Shimakage, R.H. Ono, L.R. Vale, ìInterface engineered

Josephson junctions optimized for high Jc,î IEEE Trans.

Appl. Supercon. 11(2), pp. 4032-4035 (2001).

J.C. Booth, L.R. Vale, R.H. Ono, ìOn-wafer measurements

of nonlinear effects in high temperature superconductors,î

IEEE Trans. Appl. Supercon. 11(1), pp. 1387-1391 (2001).

J.C. Booth, L.R. Vale, R.H. Ono, J.H. Claassen, ìPower

dependent impedance of high temperature superconductors thin films: relation to harmonic generation,î J.

Supercond. 14(1), pp. 65-72 (2001).

R. Rafac, B. Young, J. Beall, W. Itano, D. Wineland, J.

Bergquist, ìSub-Dekahertz ultraviolËt spectroscopy of

199Hg+,î Phys. Rev. Lett. vol. 85, pp. 2462-2465 (2000).

J.C. Booth, J.A. Beall, D.A. Rudman, L.R. Vale, R.H. Ono,

ìGeometry dependence of nonlinear effects in high temperature superconducting transmission lines at microwave

frequencies,î J. Appl. Phys. vol. 86, pp. 1020-1027 (July

1999).
36 Electronics and Electrical Engineering Laboratory

NANOSCALE FABRICATION

Our facilities for fabricating integrated circuits are

essential to nearly all of the work in the Division.

We maintain a research-class facility specialized in

the fabrication of complex superconducting circuits, nanoscale electronics and MEMS structures.

Beginning with computer-aided design, we use electron-beam and optical lithography to make structures smaller than 50 nm and complex circuits containing as many as 32,000 Josephson junctions.

Our tools are housed in 200 m2 of ìclass 100î

cleanroom space, which was improved greatly in

1999. We have recently added tools for fabricating

MEMS that are essential for the creation of many

of our ultra-sensitive instruments, and for

micromachined ion traps for future clocks.

Maggie Crews inspects a mask generated in our new

Optical Pattern Generator.

Our facilities are available as an ìopen-shopî operation. After appropriate training, all of our staff

can personally use them to fabricate the devices

needed for their research. We keep the facility and

the processes flexible and under the control of each

individual user to avoid constraining research and

to allow maximum creativity. Our past accomplishments are testimony to the success of our approach.

In the past year we have upgraded our optical pattern generator (shown above) to a modern instrument capable of making masks with feature sizes of

1.5 micrometers. Having an in-house mask-making

facility allows very rapid turnaround, which improves productivity and encourages creativity. For

patterning at the 1 μm scale, we use optical lithography in an I-line stepper and a deep-UV contact

aligner. Electron-beam lithography enables patterning at less than 50 nm. Our capability in electron

beam lithography is currently being expanded with

the addition of a second scanning electron microscope with wafer-scale stages and load lock.

Our thin-film deposition and etching tools are similar to those found in a semiconductor fabrication

facility, but they have been optimized for normal

and superconducting metal fabrication. We have

general purpose and dedicated sputtering and ebeam systems to deposit multilayers of metals. We

use electron cyclotron resonance (ECR) plasmaenhanced chemical vapor deposition (CVD) of SiO2

for circuit insulation. Dry etching is performed in

standard RIE and plasma etching tools.

Leila Vale examines a 76 mm Nb/Al2O3/Nb trilayer

wafer that will be used for Josephson junction circuit

fabrication.

We have recently installed the tools necessary to

fabricate MEMS structures. We use a set of research-scale tube furnace reactors (5î capable), for

wet and dry silicon oxidation, solid-source diffusion of boron, low-stress silicon nitride/polysilicon

low-pressure chemical vapor deposition (LPCVD),

and LPCVD of low-temperature oxide. We have

added two silicon dry-etch tools for micromachining

of Si. We use xenon difluoride gas to rapidly and

isotropically etch silicon. This year we have also

acquired a deep silicon reactive ion etch system to

allow highly anisotropic etching of Si.

Technical Contact:

James Beall

Staff-Years (FY 2003):

2
Electromagnetic Technology Division 37

TOPICS COVERED BY ORGANIZATIONAL UNITS

The following table shows which organizational unit(s) work on each of the research topics covered in

this book. For information on the staff of the organizational units, please see Appendix D.

Topic Project Name Project Leader

 QUANTUM STANDARDS:

Quantum Voltage Quantum Voltage Samuel Benz

Noise Thermometry Quantum Voltage Samuel Benz

Quantum Information and Richard Harris (acting)

Terahertz Technology

Single Electronics Nanoscale David Rudman

Cryoelectronics

Physics of Quantum Hall Nanoscale Richard Harris (acting)

Resistance Standards Cryoelectronics

 QUANTUM INFORMATION:

Quantum Computing Quantum Information and Richard Harris (acting)

Terahertz Technology

Quantum Communication Quantum Information and Richard Harris (acting)

Terahertz Technology

 QUANTUM MEASUREMENTS:

Cryogenic Sensors Cryogenics Sensors Kent Irwin

Terahertz Technology Quantum Information and Richard Harris (acting)

Terahertz Technology

Emerging Electronic Nanoscale David Rudman

Materials Cryoelectronics
38 Electronics and Electrical Engineering Laboratory

APPENDIX A: EXPERIMENTAL SYSTEMS

AND INSTRUMENTS

Mark Keller (left) and John Martinis with the dilution

refrigerator used for the capacitance standard based

on counting electrons.

The microcalorimeter system connected to an SEM for

x-ray analysis.

A PARTIAL LIST OF OUR MEASUREMENT FACILITIES AND CAPABILITIES:

Experimental environments include two dilution refrigerators (DR) for temperatures down to 30 mK and

7 adiabatic demagnetization refrigerators (ADR) for cooling to 50 mK. The DR cools the capacitance

standard to less than 50 mK and has special filtering to provide a noise-free environment for the standard.

These refrigerators are used to provide cooling for much of the experimental work that takes place in the

Division.

Measurement systems include: high-speed electrical test facilities, an atomic-force microscope, a scanning electron microscope (SEM), high-resolution X-ray materials analysis, X-ray structural analysis, a

high-resolution mass spectrometer with electrospray source, variable-temperature microwave probe station, Josephson voltage standards, and tools for characterizing microwave loss in thin films and detailed

properties of infrared antennas. The figure on the above right is a photograph of an ADR with an x-ray

microcalorimeter spectrometer attached to a commercial SEM.
Electromagnetic Technology Division 39

APPENDIX B: POST-DOCTORAL OPPORTUNITIES

NIST offers post-doctoral associateships in collaboration with the National Research Council

(NRC). Research topics and associated advisers

for the Electromagnetic Technology Division are

listed below. Contact a prospective adviser to discuss details of proposed work and the application

process. If you do not find a topic that exactly

matches your interest, please contact an advisor in

a similar discipline. U.S. citizenship is required for

post-doctoral appointments.

SUPERCONDUCTING AND NANOMETERSCALE DEVICES FOR INFRARED TO

MILLIMETER-WAVE APPLICATIONS

Adviser: Erich N. Grossman

Our goal is to explore the physical mechanisms and

limitations of devices operating in the frequency

range from 0.1 THz to 100 THz, and to develop

novel devices and measurement techniques. For

the short-wavelength end, we use electron-beam

lithography to fabricate the submicron structures

required to minimize parasitic impedances. One specific research area includes mixers and harmonic

mixers for frequency synthesis and high-resolution spectroscopy; another research area involves

IR to millimeter-wave imaging radiometry. Our main

focus is on high-sensitivity bolometers and superconducting multiplexers based on SQUIDS. Other

devices of interest include high-Tc superconducting bolometers; room-temperature, thin-film bolometers; lithographic and/or micromachined coupling

structures, particularly antennas and integrating

cavities; superconducting mixers/rectifiers; and

room-temperature mixers/rectifiers (e.g., lithographic metal-insulator-metal diodes).

APPLICATIONS OF SUPERCONDUCTING

INTEGRATED CIRCUITS AND

JOSEPHSON JUNCTION ARRAYS

Advisers: Samuel P. Benz, Paul D. Dresselhaus

We are developing superconducting integrated

circuit technology and systems using Josephson

junction arrays. These are the most practical

applications of single-flux-quantum-based superconductive electronics, and our project leads the

field in their implementation into systems. Some of

these systems include voltage standards, digitalto-analog converters, and arbitrary waveform synthesizers. We currently focus on the construction

of a pulse-quantized arbitrary waveform synthesizer to be used as an ac and dc voltage standard

source and for other applications that require digitally synthesized waveforms with precise control

of voltage, frequency, and phase. Applicants should

be interested in some or all of the following areas:

nanofabrication, broadband (dc to 20 GHz) circuit

design and construction, digital waveform synthesis, and cryogenic packaging.

FUNCTIONAL MATERIALS AND

SYSTEMS FOR RADIO FREQUENCY/

MICROWAVE/MILLIMETER-WAVE

ELECTRONICS

Advisers: James C. Booth, James A. Beall,

David A. Rudman

Functional materials and systems have key electronic properties that can be manipulated by changing external variables. Examples are voltagetunable dielectric/ferroelectric films (for application

to electronically tuned microwave filters and delay

lines), high-Tc superconductor Josephson junctions (for application to THz-frequency mixers), and

microelectromechanical systems (for application to

radio-frequency and microwave switches and circuit elements). These materials and systems hold

promise for a new generation of high-performance

electronics, enabling new applications because of

their inherent functionality. For all these materials

and systems, the key to optimizing device performance is to understand the intricate connections

between material growth and device fabrication

processes and electronic performance of the resulting structure(s). We exploit our thin-film growth

and fabrication facilities to create novel device

structures that either possess unique properties or

allow for the extraction of the relevant electronic

properties of the constituent materials. A vital part

of this effort is the development of new measurement techniques (such as cryogenic microwave

wafer-probing techniques) to evaluate device performance and obtain fundamental material properties (such as relative permittivity or conductivity)

as a function of frequency, temperature, and applied power. We are also developing novel device

concepts that exploit the unique properties of these

materials and systems, individually, or in combination with each other and with other materials and

systems.
40 Electronics and Electrical Engineering Laboratory

LINEAR AND NONLINEAR MICROWAVE

RESPONSE OF OXIDE THIN FILMS AND

DEVICES

Advisers: James C. Booth, David A. Rudman

Thin-film oxide materials and devices possess extraordinary properties that could revolutionize many

different areas of modern electronics. For example,

the low microwave surface resistance RS of the highTc

 superconductors makes them ideal for a wide

variety of high-performance devices and circuits.

However, fundamental questions still remain with

regard to the origins of losses in these materials at

microwave frequencies, as well as to the origin of

the nonlinear response that is observed under large

signal conditions. We address these fundamental

questions with measurements of the linear properties (surface resistance) as well as the nonlinear

response (third-order intercept and intermodulation) of unpatterned thin films and also patterned

devices at low to moderate power levels. Other

measurements (such as inductive critical-current

measurements and high-power microwave transmission measurements) address the response of

these materials under high-power conditions. In all

of the above measurements, special attention is

paid to the relationship between the electronic properties of interest and film growth and device fabrication processes. Our goals are to understand the

physical origins of both the losses and nonlinearity

in these systems while simultaneously developing

processes to optimize performance of microwave

devices incorporating these materials.

HIGH-TC SUPERCONDUCTORS:

DEVICES, DEVICE PHYSICS, AND

CIRCUITS

Advisers: James C. Booth, David A. Rudman

A major challenge to the development of high-temperature superconducting (HTS) electronics is the

reproducible active device, which is either a Josephson junction or a three-terminal ìtransistorî

analog. Another hurdle is the difficulty in fabricating multilayer circuits where level-to-level epitaxy

is required for insulators and wiring, as well as the

device layers. We have worked on several HTS

Josephson junction approaches and developed

techniques for fabricating multilayer circuits that

incorporate these junctions. Applications of interest include high-frequency mixers and detectors,

voltage standards, and high-speed switching. Integration of active devices into microwave and millimeter-wave monolithic circuits can take advantage of our research on passive applications of HTS

circuits.

MICROMACHINED MATERIALS AND

DEVICES FOR METROLOGICAL

APPLICATIONS

Advisers: James C. Booth, David A. Rudman,

James A. Beall

Recent advances in silicon micromachining techniques have made possible a host of new metrological applications based on microelectromechanical systems. We are currently employing Si

micromachining technologies to fabricate devices

and structures for use in applications such as ion

traps, radiation detectors, bolometers, magnetometers, and microfluidic devices. The breadth of

our Division resources allows metrology solutions

involving high- or low-temperature superconductors, ultra-low-temperature measurements, SQUID

readouts, as well as room-temperature thin-film electronics. Our fabrication facilities include high-temperature furnaces for oxidation, diffusion and

LPCVD of low stress silicon nitride, polysilicon,

and low-temperature oxide as well as optical and

electron beam photolithography, deposition, and

etching equipment (including a deep RIE). In addition to the applications above, we are interested in

applying our Si micromachining technology to a

number of different areas, including radiofrequency and microwave devices.

PHYSICS AND APPLICATIONS OF

SINGLE ELECTRON TUNNELING

DEVICES

Adviser: Mark W. Keller

Single electron tunneling (SET) devices are based

on nanofabricated tunnel junctions operated at temperatures below 1 K, where the charging energy for

a single electron dominates thermal fluctuations.

By using gate voltages to control the charging energy, individual tunneling events can be manipulated very precisely, allowing control of individual

electrons. We have developed and now routinely

operate devices in which the error per tunnel event

is of order 1 part per billion, a worldís best by several orders of magnitude. Our research goals are to

understand the fundamental physics of SET phenomena and to construct practical SET circuits for

applications in metrology and other areas. Examples

include: electron pumps for accurate electron counting, new SET transistors for ultrasensitive electrometry, and SET-based direct measurements of
Electromagnetic Technology Division 41

the properties of single molecules for use in molecular electronics. Facilities include electronbeam lithography, extensive microfabrication,

micromachining and vacuum deposition equipment,

and two dilution refrigerators equipped for measurements up to GHz frequencies.

A CAPACITANCE STANDARD BASED

ON COUNTING ELECTRONS

Adviser: Mark W. Keller

Modern metrology is moving toward quantum measurement standards, such as atomic clocks, that

provide a natural basis for our system of units. In

collaboration with the Electricity Division, we are

currently working toward a method for determining

capacitance in terms of the electron charge. We do

this simply by placing N electrons onto a capacitor,

measuring the resulting voltage V, and thus determining C = Ne/V, where e is the electron charge. We

use a unique cryogenic, vacuum-gap capacitor, and

the electrons are counted using single-electron tunneling (SET) devices operating at temperatures

below 1 K. The current version of the standard has

an estimated uncertainty of less than 1 part-permillion when compared with NISTís primary standard. Future work in this area will focus on determining the ultimate uncertainty of this method, more

direct comparisons with primary standards, and the

construction of a robust, automated version of the

standard. The development of this new standard is

expected to have impacts spanning practical metrology, our knowledge of fundamental constants,

and the fundamental basis of electrical units. Facilities include a clean room for fabricating SET

devices, a custom cryostat for the capacitance standard, and custom capacitance bridges for making

accurate comparisons with other standards.

CHARACTERIZATION OF SINGLE

PHOTON TURNSTILES USING SINGLE

ELECTRON TUNNELING DEVICES

Adviser: Mark W. Keller

NIST is developing a device based on Coulomb

blockade in a self-assembled semiconductor quantum dot (QD) that can generate single photons on

demand. The turnstile operates by applying bias

voltages that inject precisely one electron and one

hole into the QD, which then recombine to produce

one photon. We are using the unique capabilities

of single-electron tunneling (SET) devices to perform electrical characterization of these devices with

unprecedented accuracy. Capacitance spectroscopy performed on an individual QD with an SET

transistor can reveal the single-particle states for

electrons and holes. The accurate current produced

by an SET pump can be compared with the current

flowing through the turnstile to determine if the

turnstile is operating as desired. These measurements allow us to optimize the performance of the

turnstile before mastering the relatively difficult task

of building microstructures to direct the photons

toward an appropriate detector. The QDs are grown

by NISTís Optoelectronics Division, and all facilities for making contacts to individual QDs, fabricating SET devices, and measuring electrical properties are available in our project.

SUPERCONDUCTING DETECTORS

FOR X-RAY THROUGH MILLIMETER

PHOTONS

Advisers: Kent D. Irwin, Carl D. Reintsema,

Gene C. Hilton

Cryogenic detectors and electronics provide unprecedented sensitivity and energy resolution for

the detection of photons. We are developing novel

low-temperature (100 mK) superconducting microcalorimeters and bolometers for the detection of

photons from X rays to millimeter waves. These

devices, fabricated in our state-of-the-art clean

room, consist of superconducting transition-edge

sensors on micromachined structures. They are read

out using unique high-speed, low-noise SQUID

preamplifiers designed and fabricated here. Using

these devices, we have demonstrated the highest

energy resolution achieved with an energy-dispersive x-ray detector, and one of the most sensitive

detectors of incident infrared/submillimeter power.

We are employing these detectors in a system for

x-ray microanalysis of materials on a scanning electron microscope. We are also developing arrays of

x-ray microcalorimeters and infrared/submillimeter

bolometers for astronomy and other applications.

Research opportunities include improving our understanding of the nonequilibrium superconducting processes underlying the performance of

superconducting detectors; developing novel

micromachined structures to integrate detector arrays; developing and testing detector arrays; developing multiplexed superconducting integrated

circuits for the readout of large arrays; and developing the first uses of these detectors in materials

analysis, astronomy and other applications.
42 Electronics and Electrical Engineering Laboratory

HIGH-RESOLUTION

MICROCALORIMETERS FOR X-RAY

MICROANALYSIS

Advisers: Gene C. Hilton, Kent D. Irwin,

Carl D. Reintsema

As the size scale of microelectronics continues to

shrink well below 1 μm, current semiconductorbased energy-dispersive spectrometers (EDS) on

scanning electron microscopes can no longer provide the resolution needed to evaluate these structures. We are developing a high-resolution microcalorimeter-based EDS that provide revolutionary

new capabilities for x-ray microanalysis. Microcalorimeter EDS provides more than an order of magnitude improvement in energy resolution (to 2 eV)

compared to commercial semiconductor EDS, with

good collection area (4 mm2 effective area with the

use of an x-ray polycapillary optic lens) and count

rate (500 s-1). The spectrometer system consists of

a superconducting transition-edge sensor microcalorimeter cooled by a compact adiabatic demagnetization refrigerator and instrumented by a SQUID

current amplifier. These unique superconducting

electronics are fabricated in our state-of-the-art

clean room. Using our microcalorimeter EDS

mounted on a scanning electron microscope, we

have resolved closely spaced x-ray peaks in complicated spectra and have made the first energydispersive chemical shift measurements. The excellent performance of this system enables a wide

range of research opportunities in x-ray microanalysis, including improved particle analysis, chemical

bonding state analysis, and synchrotron-based

measurements. Work is also underway to dramatically increase the collection area and count rate of

the system using arrays of detectors read out with

a superconducting multiplexer, which will dramatically increase throughput and open new applications in real-time in-process monitoring and process-stream monitoring.

SUPERCONDUCTING QUANTUM

INTERFERENCE DEVICE (SQUID)

DEVELOPMENT

Advisers: Kent D. Irwin, Carl D. Reintsema,

Gene C. Hilton

We are developing superconducting electronics for

applications in the measurement of electromagnetic

signals. Our main focus is on the development of

SQUID circuits to multiplex signals from superconducting microcalorimeters and bolometers. SQUID

multiplexers are a practical requirement for the successful deployment of large-format cryogenic detector arrays for x-ray microanalysis and x-ray

through millimeter-wave astronomy. We are also

investigating other novel directions including the

SQUID operational amplifier and the development

of susceptometers for magnetic calorimeters. Research opportunities involve improving the noise

and bandwidth of these devices, fabricating SQUID

circuits in our state-of-the-art superconducting fabrication facility, developing high-performance roomtemperature electronics to drive our superconducting circuits, and exploring the device physics of

SQUID circuits.

THIN-FILM REFRIGERATION USING

NORMAL-INSULATOR

SUPERCONDUCTOR TUNNEL

JUNCTIONS

Adviser: Carl D. Reintsema

We are developing a miniature, solid-state refrigerator using superconducting thin-film technology.

In particular, we use the quantum-mechanical tunneling of electrons through a Normal-InsulatorSuperconductor (NIS) junction to produce cooling. Our goal is to build a refrigerator that can cool

a payload of cryogenic detectors from 0.3 to 0.1

Kelvin. An integrated package of refrigerator and

detectors is desirable for commercial microanalysis. In order to design devices, candidates will acquire a solid understanding of electronic and thermal transport at very low temperatures. In order to

fabricate devices, candidates will master conventional lithographic techniques, the preparation of

unusual substrates, and, possibly, MEMS technology. We are also interested in pursuing the potential of NIS junctions as superconducting transistors.

QUANTUM COMPUTING USING

SUPERCONDUCTING DEVICES

Adviser: John M. Martinis

A new class of powerful computation algorithms

have been proposed based on logic operations in

quantum mechanical systems. Experimental implementation will require a coherence time of the quantum bits of information (qubits) long enough to

perform calculations, a state measurement of the

qubits, and a method to sequence controlled interactions of qubit pairs. While the most dramatic

progress to date has been made with trapped-ion

systems, solid-state quantum devices should in

principle have distinct advantages for the creation
Electromagnetic Technology Division 43

of a practical large-scale ìquantum computerî. The

superconducting state represents a rich system to

explore for this purpose because of its inherently

low dissipation. Using our state-of-the-art superconducting fabrication facility, we have made single

qubit devices based on Josephson junctions. Research opportunities include fabricating novel superconducting qubit devices, exploring the physics of coherence and coupling between qubits, and

engineering multi-qubit devices. Our goal is to build

a 100 to 1000 qubit quantum computer that can

perform 1000 to 10000 logic operations.
44 Electronics and Electrical Engineering Laboratory

APPENDIX C: AWARDS AND RECOGNITION

Note: * indicates a coworker from outside the Electromagnetic Technology Division. Medal awards

are from the U.S. Department of Commerce.

Award Recipient Date Notes

William A. Wildhack

Award

Arnold O. Beckman

Award (ISA)

Gold Medal

Industrial Research-100

Award

NBS Condon Award

NBS Stratton Award

Silver Medal

NBS Condon Award

Silver Medal

Silver Medal

Gold Medal

NBS Fellow

EEEL Outstanding

Paper Award

NBS Stratton Award

Research and Development Magazine

Industrial Research-100

Award

NBS Fellow

NIST Gold Medal

IEEE Fellowship

Robert A. Kamper

Robert A. Kamper

James E. Zimmerman and

Robert A. Kamper

Clark A. Hamilton,

Robert J. Phelan*,

Gordan W. Day*, John

Geist*, and B. McIntosh*

Robert A. Kamper

James E. Zimmerman

Clark A. Hamilton,

Richard E. Harris,

Frances L. Lloyd, and

Robert L. Peterson

Donald G. McDonald

Michael W. Cromar

Richard L. Kautz

Clark A. Hamilton

James E. Zimmerman

Richard L. Kautz

Richard L. Kautz and

Donald B. Sullivan

Clark A. Hamilton,

Richard L. Kautz, and

Frances L. Lloyd

Clark A. Hamilton

Clark A. Hamilton,

Richard L. Kautz, Frances

L. Lloyd, James A. Beall

Robert A. Kamper

October 1972

1974

October 1975

1975

November 1977

1979

November 1980

December 1981

1983

1983

1984

1985

December 1985

1986

1987

October 1989

1989

National Conference of Standards

Laboratories

Instrument Society of America, no

citation

For innovative contributions to practical

precise measurements using superconducting quantum interference device (SQUIDs)

For distinguished achievement in written

exposition

For creative advancement of the state of

the art in ultra-high-speed analog-todigital conversion

For distinguished achievement in written

exposition

For fundamental contributions to the

understanding of chaotic behavior in

Josephson junction devices

For outstanding contributions to the

development of ultra-high-speed Josephson junction microcircuit technology

ìChaos and Thermal Noise in the rfBiased Josephson Junction,î Journal of

Applied Physics, Volume 58, Number 1

(1 July 1985)

For exceptional accomplishments that

established the feasibility of a fundamental

improvement in the Josephson voltage

standard

For development of Josephson series array

voltage standards

For developing the first practical

Josephson-junction series array voltage

standards, at both 1 V and 10 V levels,

including the U.S. primary standard

For leadership and technical contributions

to the application of superconductivity in

instrumentation, measurement, and

standards
Electromagnetic Technology Division 45

Award Recipient Date Notes

EEEL Outstanding

Paper Award

NIST Gold Medal

Silver Medal

Harry Diamond

Memorial Award (IEEE)

EEEL Outstanding

Paper Award

IEEE Electrotechnology

Transfer Award

IEEE Fellow

EEEL Measurement

Services Award

EEEL Outstanding

Paper Award

NIST Stratton Award

Silver Medal

EEEL Outstanding

Authorship Award

Allen V. Astin Award

(National Conference of

Standards Laboratories)

Fellow of American

Physical Society,

Condensed Matter

Physics

Samuel P. Benz and

Charles J. Burroughs

High Temperature

Superconducting

Electronics Team: James

A. Beall, Todd E. Harvey,

Ronald H. Ono, David A.

Rudman, etc

Robert A. Kamper

Robert A. Kamper

John M. Martinis,

Michael Nahum, and

Hans Dalsgaard Jensen

Clark A. Hamilton

Clark A. Hamilton

Clark A. Hamilton

Mark W. Keller, John M.

Martinis, Neil M.

Zimmerman, and Andrew

H. Steinbach

John M. Martinis

John M. Martinis

Mark W. Keller, John M.

Martinis, Neil

Zimmerman, and Andrew

H. Steinbach

Samuel P. Benz, Clark A.

Hamilton, Charles J.

Burroughs, Todd Harvey,

and Lawrence Christian

John M. Martinis

1991

October 1993

1993

1993

1994

1995

1995

February 1995

1996

December 1996

December 1996

February 1997

1997

November 1997

ìCoherent Emission for Two-Dimensional

Josephson Junction Arrays,î Appl. Phys.

Lett. 58(19): 2162-2164, May 1991

For the worldís best Josephson junction

and associated practical technology to put

the U.S. in the lead for superconducting

electronics

For leadership of NISTís Boulder

Laboratories and for excellent negotiating

skills in facilities development

For pioneering the application of

superconducting quantum mechanical

principles to metrology, directing

development of advanced Cryoelectronics

devices, and guiding a metrology program

supporting the lightwave industry

ìMetrological Accuracy of the Electon

Pump,î Physical Review Letters, Volume

72, Number 6, pp. 904-907 (7 February

1994)

For providing services that collectively

have resulted in the practical introduction

of a new voltage standard based on

Josephson-junction arrays into industry

and the general metrology community of

measurement systems.

For his key role in developing the

Josephson voltage standard & other novel

superconducting circuitry.

ìAccuracy for Electron Counting Using a

7-Junction Electron Pump,î Appl. Phys.

Lett. 69 (12), 1804-1806, 16 September

1996

For applying new insights into quantum

phenomena to establish the fundamental

accuracy of Coulomb-blockade circuits for

single-electron counting

For establishing the fundamental accuracy

of Coulomb-blockade circuits for single

electron counting, providing the basis for

new intrinsic standards

ìAccuracy of Electron Counting Using a

7-Junction Electron Pump,î Appl. Phys.

Lett. 69(12), 1804-1806, 16 September

1996

Josephson Standards for AC Voltage

Metrology

For his experimental investigations into

the fundamental quantum behavior of lowtemperature electronic devices
46 Electronics and Electrical Engineering Laboratory

Award Recipient Date Notes

NIST Condon Award

Fellow of the American

Physical Society,

Precision Measurements

and Fundamental

Constants

Fellow of the American

Physical Society,

Precision Measurements

and Fundamental

Constants

EEEL Outstanding

Authorship Award

NIST Applied Research

Award

Gold Medal

EEEL Outstanding

Authorship Award

Presidential Early

Career Award for

Scientists and Engineers

NIST Condon Award

William A. Wildhack

Award

NIST Fellow Award

Symbols, Units,

Nomenclature, Atomic

Masses and Fundamental

Physical Constants

(SUNAMCO) Award

2001 Best Paper Award

ASME International,

Heat Transfer Division

Richard L. Kautz

Richard L. Kautz

Donald G. McDonald

David A. Wollman, Kent

D. Irwin, Gene C. Hilton,

Laura L. Dulcie, Dale E.

Newbury, and John M.

Martinis

Gene C. Hilton, Kent D.

Irwin, John M. Martinis,

and David A. Wollman

Gene C. Hilton, Kent D.

Irwin, John M. Martinis,

and David A. Wollman

Mark W. Keller, Ali L.

Eichenberger, John M.

Martinis, and Neil M.

Zimmerman

Mark W. Keller

Mark W. Keller, John M.

Martinis, Ali

Eichenberger, Neil

Zimmerman

Clark Hamilton

John M. Martinis

Clark Hamilton

David Rudman and Leila

Vale

December 1997

1998

1998

December 1998

December 1998

1999

October 2000

November 2000

October 2001

December 2001

2001

2001

For his extensive review of the physics of

the dc series array voltage standard in the

paper ìNoise, chaos, and the Josephson

voltage standard,î which appeared in

Reports on Progress in Physics, vol. 59,

pp. 935-992, Aug 1996

For experimental and theoretical

investigations of Josephson junctions,

particularly the nonlinear dynamics of

phase locking and chaos, essential to the

development of practical series-array

voltage standards

ìHigh-Resolution, Energy-Dispersive

Microcalorimeter Spectrometer for X-Ray

Microanalysis,î Journal of Microscopy,

Volume 188, Part 3, pp. 196-223,

December 1997

For inventing an x-ray detector, demonstrating its potential to revolutionize xray microanalysis and developing it to the

point of commercialization

For inventing a new x-ray detector,

showing its potential to revolutionize xray microanalysis, and bringing it to the

point of commercialization

ìA Capacitance Standard Based on

Counting Electrons,î Science, Vol. 285,

pp 1706-1709, 10 September 1999

In recognition for his research on using

the fundamental quantum properties of

nature to create new standards and tools

for measurement science

For distinguished achievement in written

exposition

National Conference of Standards

Laboratories

In recognition for his excellence as a

scientist and for the contributions he has

made in both science and technology

International Union of Pure and Applied

Physics (IUPAP)

ìFar-infrared transmittance and reflectance of YBa2

Cu3O7-,î J. Heat Transfer,

vol. 121, p. 844 (1999)
Electromagnetic Technology Division 47

Award Recipient Date Notes

Kurt F.J. Heinrich Award

Gold Medal

David Wollman

Samuel Benz and Charles

Burroughs

August 2002

September 2002

Given by the Microbeam Analysis

Society in recognition of his work

supporting the microcalorimeter project

in the Electromagnetic Technology

Division to develop a high-resolution

microcalorimeter energy-dispersive Xray spectrometer and demonstrate its

usefulness for low-voltage X-ray

microanalysis

In recognition for developing an original

quantum-based dc voltage reference

system that is now being applied to

improve the accuracy and reliability of

NISTís fundamental electrical measurement systems, upon which all U.S.

electrical measurements are based
48 Electronics and Electrical Engineering Laboratory

APPENDIX D: ELECTROMAGNETIC TECHNOLOGY

DIVISION STAFF

(DECEMBER 2002)

DIVISION OFFICE

3776 Harris, Richard E. (Chief)

3678 Metz, Sara E. (Division Secretary)

3812 Schump, Jeanne L. (Admin. Officer)

3811 Copeland, Jill V. (Admin. Asst.)

3988 McCarthy, Sandra E. (Secretary)

5068 Novik, Kristen E. (Secretary)

QUANTUM VOLTAGE

5258 Benz, Samuel P. (Project Leader)

3906 Burroughs, Charles J.

5543 Chong, Yonuk

5211 Dresselhaus, Paul D.

3740 Hamilton, Clark A.

CRYOGENIC SENSORS

5911 Irwin, Kent D. (Project Leader)

4429 Beall, Jonathan

4153 Beyer, Joern

4409 Clark, Anna

3461 Deiker, Steven

4463 Doriese, William (Randy)

4391 Ferreira, Susan (Lisa)

5679 Hilton, Gene C.

3402 Huber, Martin E.

5052 Reintsema, Carl D.

4319 Ruggeiro, Steve

4408 Ullom, Joel N.

5121 Vale, Leila R.

7894 Xu, Yizi

4320 Zink, Barry L.

QUANTUM INFORMATION AND

TERAHERTZ TECHNOLOGY

5344 Bergren, Norman F.

3114 Bhupathiraju, Ashok

4199 Gerecht, Eyal

5102 Grossman, Erich N.

4378 Lang, Kristine

3597 Martinis, John M.

3678 McDermott, Robert

4212 Miller, Aaron J.

3148 Nam, Sae Woo

3021 Rabin, Michael

4464 Rosenberg, Danna

4318 Salminen, Arto

4403 Simmonds, Ray

NANOSCALE CRYOELECTRONICS

5081 Rudman, David A. (Project Leader)

4137 Aumentado, Jose

5989 Beall, James A.

7900 Booth, James C.

5049 Crews, Margaret

4410 Dalberth, Mark

3391 Kautz, Richard L.

5430 Keller, Mark W.

7064 Koch, Jonathan (Jay)

5309 Lee, Sang Young

4369 Leong, Kenneth

5113 McDonald, Donald

4325 Osborn, Kevin

7213 Schima, Susan

Division website:

http://emtech.boulder.nist.gov/

Email addresses for all staff are:

firstname.lastname@boulder.nist.gov

Telephone numbers are: (303) 497-XXXX

(the four-digit extension as indicated).
Division/Office Publication Editor: Sara E. Metz

Publication Coordinator: Gaylen R. Rinaudot

Printing Coordinators: Warren Overman

Verna M. Moore

Document Production: Technology & Management Services, Inc.

Gaithersburg, Maryland
January 2003

For additional information contact:

Telephone: (303) 497-3678

Facsimile: (303) 497-3066

On the Web: http://emtech.boulder.nist.gov/