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Produced by the NASA Center for Aerospace Information (CASI)
Ir

i 

TRW Electronic Systems One Space Park

Group Redondo Beach, CA 90218

213,535.4321

SN 39042.000

E130.1.83-6404

03 November 1983

National Aeronautics & Space Administration

Goddard Space Flight Center

Greenbelt Road - Building 16

Greenbelt, Maryland 20771

ATTENTION: Mr. Nicholas G. Chrissotimos, Code 727.2

Technical Officer

SUBJECT: Contract Number NAS5-26658

S-Band SBAW Microwave Source - Phase II

FINAL REPORT

In compliance with the subject contract data requirements,

TRW Inc., Electronic Systems. Group, herewith submits ten (10)

copies'of the Final Project Report.

If you have any questions concerning this report, please 

contact me at (213) 535-8637, or Mail Station 138/1460. 

TRW Inc.

Electronic Systems Group

Daniel A. Bush

Contracts Administrator

E1 Military Electronics Division

I

E DAB/jlj

Enclosure - as stated

CC: Graphics Arts Branch (Glossy prints and negatives) - Code 253

Patent Counsel - Code 204 (1 Copy)

Contracting Officer - Code 287 0 copy)

K-F. Lau (letter only)

(NASA-CR-175153) S-BAND SEAW MICROWAVE N84-17432

SOURCE, PHASE 2 Final Report (TRW

Electronic Systems Group) 42 p

HC AO3/MF A01 CSCI 20N unclas

G3/.32 11646

TRW Inc.

r
CONTENTS

Page

1. INTRODUCTION AND SUMMARY 1-1

2. SUMMARY OF PHASE I DEVELOPMENT 2-1

2.1 SBAW in Rotated Y-Cut Quartz 2-1

2.2 1 GHz SBAW Delay Line and Oscillators 2-4

2.3 Other Developments 2-7

3. AGING STUDY OF 1 GHz SBAW OSCILLATORS 3-1

4. 2 GHz SBAW DELAY LINE DEVELOPMENT 4-1

4.1 Devices on 36.250 Rotated Y Cut Quartz 4-1

4.2 Devices on -50.50 Rotated Y Cut Quartz 4-3

4.3 Fabrication and Packaging Techniques 4-6

4.4 Electromagnetic Feedthrough 4-8

5. 2 GHz SBAW OSCILLATOR DEVELOPMENT 5-1

5,1 Detail Design 5-1

5.2 Spurious Output and Phase Noise Characteristics 5-3

5.3 Temperature Stability 5-8

5.4 Long Term Aging Characteristics 5-8

6. REFERENCE SOURCE EVALUATION 6-1

6.1 Comparison Between 1 GHz SAW and SBAW Oscillators 6-1

6.2 Comparison Between 2 Gliz SAW and SBAW Oscillators 6-2

6.3 Trade-Off Between 1 and 2 GHz Refernce Sources 6-2

7. FREQUENCY SELECTABILITY AND SETTABILITY 7-1

7.1 Analysis and Device Design 7-1

7.2 Data Summary 7-3

ii
1. INTRODUCTION AND SUMMARY

This report describes the results of the investigation performed

under NASA Contract NAS5-26656, The primary purpose of this program,

entitled "S-Rand Shallow Bulk Acoustic Wave (SBAW) Microwave Source,"

was to establish techniques necessary to fabricate a high performance

S-band microwave signal source using state-of-the-art SBAW oscillator

technology. The program was divided into two phases, and the present

report deals with the second and final phase of th i s program.

The objectives rf the Phase II effort were:

• Aging study of 1.072 GHz SBAW delay line oscillators.

• Development of 2.143 GHz SBAW delay lines.

• Construction and characterization of 2.143 GHz SBAW

oscillators.

0 Assessment of the compatibility and performance improvement

of SBAW devices in oscillator circuits presently using SAW

devices.

a Demonstration of a cost-effective method to produce SBAW

delay line from the same mask, but operating at different 

frequencies. 

The content of this report will follow the above outline of program objectives. A brief summary of the Phase I effort is in Section 2,

which provides a background summary of the program. The results of the

aging experiments on the 1 GHz SBAW oscillators are described in Section 3.

Section 4 describes the design, fabrication and test of the 2.143 GHz SBAW

delay lines. Two design appproaches were implemented. The third

harmonic transducer on 36 0 rotated Y cut quartz proved to be the most

useful design,whereas the fifth harmonic transducer on - 50.5 0 rotated

Y cut quartz suffered from high insertion loss and poor sidelobe rejection.

The construction and characterization of the 2 GHz SBAW oscillator

are described in Section 5. Measurements included phase noise, frequency

dependence on temperature,and 6-month aging. Section 6 described the

comparison of SAW and SBAW oscillators'. Both 1 and 2 GHz oscillators

were compared. The 2 GHz SBAW oscillator showed significant improvement

in phase noise and temperature stability over the 2 GHz SAW oscillator

developed in previous NASA programs.

1-1
r

The final section describes a. tQchnique to produce SBAW delay lines

of different frequencies from a single mask. The five frequencies were

pre-selected within a 2.1 to 2.3 GHz range. The delay lines were incorporated

into oscillator circuits to demonstrate the ability to select the frequency

output of the SBAW oscillator.

1-2

. .. r
2. SUMMARY OF PHASE I DEVELOPMENT

The five main tasks of the Phase I development were:

• Develop 1.072 GNz SBAW delay lines,

• Fabricate five hybrid 1.072 011z SBAW reference oscillators.

0 Investigate SBAW in aluminum nitride on sapphire,AQN/AQ203.

• Perform a design study of the 2.144 GHz SBAW delay lines.

• Investigate SBAW delay line oscillator frequency selectability/settability.

The key element in the SBAW microwave source is the SBAW delay line.

A thorough understanding of wave properties and material selection is the key

to achieving good device performance. A brief discussion of SBAW theory

is thus presented before highlights of the phase I activities are summarized.

2.1 SBAW in Rotated Y-Cut Quartz

Shallow Bulk Acoustic Waves (SBAWs) are essentially bulk waves which

propagate just below the crystal surface. They can be launched and

detected with interdigital transducers. SBAWs have been observed in

quartz, lithium niobate, lithium tantalate and berlinite. Of these

materials, only quartz and berlinite have cuts with a zero first-order

temperature coefficient near the room temperature. Since berlinite is

presently not available commercially, quartz was the only choice for the

present application.

The SBAW in quartz has been extensively searched and characterized.

SBAWs are found to propagate in singly rotated Y-cut quartz with a

propagation direction at 900 off the X-axis.. These SBAWs are pure

shear plane waves with polarization parallel to the surface and

perpendicular to the direction of propagation.

The wave velocity, coupling coeffic tent, and temperature coefficient

of the SBAW as a function of the substrate angle u have been theoretically

calculated and aresummarized in Figures 2-1, 2-2, and 2-3. The angle u

is the angle between the normal to the substrate surface and the negative

crystalline Z axis. The u for the Y cut plate is 90 degrees.

2-1

a
ONGINAL Pzal ,'A-'i !0

OF POOR QUAL17Y

5000

J0

4000

• EXPERIMENTS

30000 90 100

(DEG)

F i gure 2-1. Velocity of SBAW in Rotated Y-Cut Quartz

0102 A vfv

2

xp

asi

U go 100

.w (DEG)

Figure 2-2. Av/v and K p 2 of SBAW in Rotated Y-Cut Quartz

2-2
ORIGINAL PA- 01" M

ne onnR 011AL111

a 100

80

c 60

c 40

h 20 ZW 0

-20

8 -40

W -60

a

-80

a

W -10o

IL

W ^

T

ET

ac

ST

h

μ(DEG)

Figure 2-3. First-Order Temperature Coefficient of Delay

of SBAW in Rotated Y-Cut Quartz

For oscillator applications, the SBAWs are required to be temperature

stable. As shown in Figure 2-3, there are two regions of u where the

first order temperature coefficient of delay is zero at roam temperature.

Specifically, the u's for temperature stable cuts are 125.5 0 and 39.50.

According to conventional nomenclature, such cuts are 35.5 0 and -50.50

rotated Y cuts. In actual devices, the metal loading effect caused by

the metallic fingers shifts the temperature stable cut angles by a few

degrees. The exact magnitude depends on the thickness of the metallization. 

These effects have been quantitatively evaluated and can be incorporated 

into the selection of -"he substrate orientation.

The comparison of thn wave properties of the two temperature

stable orientations is summarized in Table 2-1.

Table 2-1. Comparison of SBAW Properties Between +35.50

and -50.5° Rotated Y-Cut Quartz

j 

+35.5 0 -50.50

Wave Velocity 5100 m/sec 3331 m/sec 

Coupling Coefficient 1.44 x 10-2 0.41 x 10-3 

Mass Loading Effect

(Av/v for t/X =0.01) 0.16% 0.1%

Wave Attenuation 0.83 dB/1,sec 2.0 dB/usec

Temperature Stability

(-55 0C to +85 0 C) +125 ppm +55 ppm

2-3

e .«. ..n . ,... _ ,„s7 -rr^.,.-.^—.-,->...-._n+v..--"z - .r..e a►^ _, ^^ ._.. l..nzui:^ 
OF POOR t^'^^: ^W,6 ^'Yr

From this comparison, it is obvious that the +35,5 0 cut has the advantage

of high wave velocity, high coupling coefficient, and low wave attenuation.

Its sensitivity to metal loading can also be an advantage since it provides a means for frequency trimming. The -50.5° cut, on the 'other hand, has

the advantage of better temperature stability. The overall property of

the +35.5 0 cut made it a more attractive substrate. For Phase I, +35.50

cut substrates were exclusively employed.

2.2. 1 GHz Delay lines ana Oscillators

The basic structure of a SBAW delay line is quite similar to 

a SAW delay line. As shown in Figure 2-4, interdigital transducers

are used to launch and detect a SBAW. Design techniques commonly used

for SAW transducers are therefore expected to work for SBAW devices.

During the Phase I investigation, four different designs were implemented for

the 1 GHz SBAW delay line. These include fundamental thinned electrode,

? third harmonic, dnergy trapping and segmented transducer designs. The

various device configurations are shown in Fi 9 Figure 2,5, The conclusion 9

from this study is that while only the segmented transducer design failed

to work satisfactorily, the 3rd harmonic design has the unique

potential for higher frequency operation.

t i

INPUT OUTPUT

TRANSDUCER TRANSDUCER

ENERGY DISTRIBUTION

Figure 2-4. Basic SBAW Device Configuration

The third harmonic transducer thus forms the baseline approach

for the 1 GHz SBAW delay line.

As shown in Figure 2-6, a typical 3rd harmonic device has an unmatched

insertion loss of 26 dB, a 3 dB bandwidth of 2.28 MHz, and an oscillator Q

of 1220. The minimum linewidth for the transducer finger is 1.78 um.

Five 1.072 GHz SBAW oscillators were developed under Phase I

of the program. The schematic diagram of these oscillators is shown

in Figure 2.7.

2-q 
ORIGINAL PACK-,' &

OF POOR QUAL11Y

Figure 2-5(a). Thinned Electrode Transducer Configuration

N N

Figure 2-5(b)• Third Harmonic Transducers

^IIIIIIIIIIII illlll 111111 1111111 ^IIIIII

Figure 2-5(c). Delay Line Employing Energy

Trappings Gratings

4*

Figure 2-5(d). Segmented Transducer Design

Figure 2-5. Various Transducer Configurations

2-5
20

30

m

A

z

0 40

H

xw

2

60

tin 

1060 1064 1068 1072 1076 1080 1086

FREQUENCY (PAHz)

Figure 2-6. Frequency Response of SBAW Delay Line with Third

Harmonic Transducers

12, 31

32

---41.072 CHZ OUTPUT 

SBAW AMP HYBRID PHASE ADJUST COAXIAL LINE

15 1

LEVEL SET ATTENUATOR

15 SBAW DELAY LIME d'-

HYBRID S

Figure 2-7. 1.072 GHz Hybrid Packaged SBAW Oscillator Schematic

The SBAW oscillator's circuitry was divided into two functional

sections which were packaged separately. One hybrid package contained

the SBAW delay line. The second containedthe 1 GHz amplifier circuitry.

A phase set coaxial line and 'level set attentu.,.tor which were used

to control the oscillator's feedback characteristics are mounted external

to the hybrid packages. The two hybrid packages with a minimum of

external circuitry form a complete 1.072 GHz SBAW oscillator. The

complete 1.072 GHZ SBAW oscillator assembly is mounted on a 3.4 x

2.7 x 0.25 inch brass plate.

2-6
The key performance parameters of the four 1.072 GHz SBAW hybrid

packaged oscillators are summarized in Table 2-2. The temperature

stability of the four 1.072 Gliz SBAW oscillators varied from X0.0025 to

x• 0.0047% over a -20 to +500 C temperature range.

Table 2-2. 1.072 GHz Hybrid Packged SBAW Oscillator Data Summary

Parameter SN35290 SN35288 SN35296 SN35289

Power Output +6.6 dBm +5.5 dBm +5.5 dBm +6.1 d8m

Frequency 1.07145 GHz 1.07172 GHz 1.07206 GHz 1.07166 GHz

Frequency Settability + 0.83 MHz + 1.065 MHz + 1.035 MHz + 0.8 MHz

Temperature Stability + 0.0033 % + 0.0025 % + 0.0047 % + 0.0042 %

-20 to 50°C

Prase Noise dBc,Hz

1 kHz -R6 -84 -84 =84

10 kHz -106 -105 -105 -105

100 kHz -126 -126 -125 -125

1 MHz -145 -144 -142 -140

Aging measurementswere also performed on 4 of the 5 oscillators.

By the end of Phase I, approximately three months of aging data were

collected.

2.3 Other Developments

The remaining tasks of the Phase I effort included the investigation of

SBAW in AW U2 0 3 , the 2.144 GHz SBAW delay line study, and the frequency

selectability and settability study.

Theoretical calculation of wave properties in AQN/Az 2 0 3 shows

that no coupling exists for a horizontal shear wave bulk mode on basal

plane sapphire. As a consequence,it is unlikely to find useful SBAW's

2.-7
in that materi^- 1 . The ;,':144 SBAW delay line design study pointed to

the use of 3rd and 5th harmonic transducers. The investigation of

frequency selectability and settability suggests that up to 1-21%

change in operating frequency can be achieved with one photomask

using substrates of different crystal orientations.

2-8
r

3. AGING STUDY OF 1 GHz SBAW OSCILLATORS

The first task of the Phase II program is a continuation of the

aging measurement of the 1,072 GHz SBAW oscillators. Four oscillators

were aged under continuously operating conditions, The oscillator-s were

mounted on a common baseplate to minimize temperature differentials

between units. Before initiation of the aging test,the oscillators were

temperature cycled between 100 and 1500 F to minimize any frequency

hysteresis caused by thermally induced mechanical stress and movement

in the oscillator comr Ant. The measurementsof oscillator frequency,

output power and baseplate temperature were performed daily. Temperature

of the baseplate is normally 28 i10C.

The aging measurement was interrupted several times during the course

of the aging study. Each interruption caused a'discontihOity in frequency,

as shown in Figure 3-1, To properly analyze the data, these discontinuities

were removed. Figures 3-2 through 3-5 show the results of the aging measurement. Thore are 5 ppm of medium term fluctuations over a time period of

weeks.;»,, d term baseline drift, on the other hand, is quite small.

`iable 3.1 summarizes the measured aging rates. These rates are a result

of fitting the data to a straight line. Extremely small long term aging

rates (< 1 ppm/year) were observed for two of the four oscillators.

Table 3,1 Measured Aging Rates

OSCILLATOR NO, RATE (PPM/YEAR)

35288 -0.47

35289 -4.6

35290 +2.9

35292 -0.1

3-1

• ... 

..... _..

A--.,.« -+.x:.1w1-.:'Ih"o--°w.."-.t=^:T: rte.. ., /

DURATION (MONTH)

18

16

18

18
1071.7:

1071.71

1071.71

1071,69

1071.67

^^ T. /PP.R . 1 wMY xr1 ULI My KG am TES PM WR MT JURL JOLT

1181 1962

D' 'E

Figure 3.2. Data of SBAW Oscillator Number 35288

with Discontinuities Removed

C^^^IGINA^L Pi^,l.l^

OF POOR U

f` J v -v

MOVED SBAW

OSCILLATOR i POWER SUPPLY

POWER SUPPLY RESTORED 70

VOLTAGE

INCREASED 15V

ACCIDENTALLY

30

4 20

10

;r

0

10

NOV

1981 1982

DATE

Figure 3.1. Original Data of SBAW Oscillator Number 35288

MOVEDiSSAD

1 

ER SUPPLY

OSCILLATOR VOLT SUPPLV VOLTAGE VOLT AOE RESTOREO TO

SMCREASED •

1SV

ACC100TLL0
aD

20

w

S

N

10

0

-10

a

,^ z

=1

•1

J

0RIGIiVAL P.,!, ,M EJ

OF POOR QUAl 177

"tot SUPPLY

VOLTAGE

0

INCRIAS

ACCITALLY DENE0

o

MOVED $RAN

( OSCILLATOR POWEP Su ►PLY

VOLTAGE

RESTORED TO

0 DTI'

MAT JOIE JOLT AUM SEPT OCT NOY DEC JAR FE{ MTl APO MT JUTE JOLT Alit

1961 1962

DATE

Figure 3,3. Data of SBAW Oscillator Number 35289 with

with Discontinuities Removed

MAR AK MT AN AIXT AUG SEPY OCT NOY DEC JAR FEE MR AN MAT JUNE JULY AUG

1161 1982

DATE

Figure 3.4. Data of SBAW Oscillator Number 35290

with Discontinuities Removed

MOVED SDAW J

OSCILLATOR

POWEP SLIMY f

VOLTAGE POYER sUPPLr

INCREASED i:rnTACE

ACCIDENTALLY RESTORED TO

ISV

1 1 1 f ! 1 1-- ^i 1 1 1 1 1 1 ! 1--ti

WA AM: MT JI/[ JULY AUG SEPT OCT RtlY Off. JN CCII Itlt ADR Wr .11rc .RY r lPK

1961 1962

DATE

Figure 3,5. Data of SBAW Oscillator Number 35292

with Discontinuities Removed

3-3

i

20

x

N

G tD

0W

` 0

-]0
4. 2 GHz SBAW DELAY LINE DEVELOPMENT

The deve l opment of the 2 GHz SBAW delay line is based on the analysis

and experimental results of the Phase I effort which established the harmonic operating transducers as the baseline approach. Since there are two

temperature stable cuts found in the singly rotated Y-cut quartz family,

both were investigated to determine which one is more suitable for delay

line oscillator application.

4.1 Devices on 36.250 Rotated Y Cut Quartz

The 1.072 GHz device developed in Phase I uses 36.25 0 rotated

Y cut quartz as the substrate. The SBAW in this substrate is somewhat

less temperature stable than the SAW in ST quartz. A comparison of

temperature stabilities of two stable SBAW cuts and the SAW in ST quartz

is shown in Figure 4.1. The advantages of the 36.25° rotated Y-cut quartz

SBAW over the -50.25 0 rotated Y cut SBAW are that it has a faster wave velocity, and a higher degree of coupling, resulting in a lower insertion loss. 

A design baso d on the 3rd harmonic transducer approach was implemented using

this substrate and was found to yield good device performance. The design

parameters of the delay line are listed in Table 4.1, and its performance

parameters in Table 4.2. The frequency response of this device is shown

in Figure 4.2. 

Table 4.1. Design of the Third Harmonic SBAW Delay Line

FINGER WIDTH (u M) 0.8916 

TRANSDUCER LENGTH (a 0 ) 451

OSCILLATOR Q 1496

3 dB BANDWIDTH (MHz) 2.95

SUBSTRATE 36.250 ROTATED Y-CUT QUARTZ

Table 4.2. Performance of the Third Harmonic SBAW Delay Line

CENTER FREQUENCY 2141.7 ± 1.0

3 dB BANDWIDTH (MHz) 3.4 ± 0.3

UNMATCHED INSERTION LOSS (dB) 2.7

OSCILLATOR Q 1441

4-1
ORIGINAL. PAG' 6

OF POOR QUALITY

so

/ Iwo

CIO \J

.L

^G

a

0

-So

-100

PPM

-150

-200

9

N

pN

7

z

O

H

i

W

2

TEMPERATURE °C

Figure 4.1. Comparison of Temperature Stability Between

SAW and SBAW Devices

E

I SERTION LOSS

FREQUENCY (MHz)

Figure 4.2, Frequency Response of SBAW Device with Third

Harmonic Transducers

4-2

r
Prior to the design and fabrication of the device of Figure 4.2, a

series of experiments were performed to determine the tradeoff between

insertion loss and phase slope (oscillator Q) of the delay line on 36.25°

rotated Y-cut quartz. Oscillator Q for the device is defined as wt/2, where

w is the oscillator frequency in units of radians, and t is the delay time.

The short term stability of the oscillatory controlled by the SBAW delay line,is

such that for maximum stability the SBAW device must have minimum insertion

loss and highest Q,or rapidly changing phase slope as a function of frequency.

In actual devices, however, high Q means a 'larger separation between transducers

and therefore higher propagation loss.

A device was designed to have a transducer whose length is 750 wavelengths

long at the operating frequency. The insertion loss of thrd device fabricated

with 400 A of aluminum embedded in 350 A grooves was typically 40 dB. The

length of the transducer was then reduced systematically by laser trimming.

In this laser trimming experiment, the fingers at the outer edges of the

SBAW transducer- were disconnected by evaporating the finger metallization

with a laser pulse. The length of the transducer was effectively shortened.

At each stage of the experiment, the insertion loss of the device was measured.

The results of this study showed that for 36.25° rotated Y-cut devices, 450 a

represents an optimum transducer length.

4.2 Devices on -50.5 0 Rotated Y Cut Quartz

The wave velocity of the SBAW in -50.5 0 rotated Y cut quartz

is much slower than that of the 36.25 0 cut substrate. To achieve

2.143 GHz using the third harmonic design requires finger widths

of 0.58 um. Such line widths border at the limit of photolithographic

techniques. To relieve such stringent fabrication tolerance,; a

fifth harmonic design was adopted. The fifth harmonic design employs a

6 finger per period, in a 3-up, 3-down configuration, as shown in Figure

4.3. The design details of this device are listed in Table 4.3.

4-3
9 ORIGINAL

OF POOR QU AD fY

Figure 4.3. Fifth Harmonic 2.144 GHz Delay Line

i

Table 4.3. Design of the Fifth Harmonic SBAW Delay Line

• FINGER WIDTH = 0.65 pm

• TRANSDUCER LENGTH = 750a0

• OSCILLATOR Q = 2479

t

• 3 dB BANDWIDTH = 1.9 MHz

• -50.5 0

 ROTATED Y CUT QUARTZ

Performance of the device on -50.50 rotated Y cut quartz varied from

device to device. Their unmatched insertion loss is at the order of

35-45 dB. One of the lowest loss devices shown in Figure 4.4 was matched

to show only 24 dB of insertion loss. The temperature stability of the device

was measured by incorporating the delay line into an oscillator loop.

The data from the temperature measurement is shown in Figure 4.5.

The SBAW devices on -50.5 0 rotated Y cut quartz exhibit 'two features

which are not obvious from theoretical predictions. The insertion loss

of the device was found to be affected very little by embedding the

transducer fingers as long as the metallization waskept thin. The

device reported in Figure 4-4,for example, was fabricated without

4-4
OF POOR QUALM-7

i

i

f

t ^ PHASE

I

(

i

i AMPLITUDE

i

s

I

1

I t

t

2160 7165 7170

FREQUENCY (MHO

Figure 4.4. Amplitude and Phase Response of a Matched Fifth

Harmonic Device on -50.5 Rotated Y-Cut Quartz

0

1 -10

H

LL

s

v1 -20

Y

U

Z

w

M

w -30

0:

U.

-40

-50 

0

TEMPERATURE (°C

Figure 4.5. Temperature Stability of 2.144 GHz SRAW Delay

Line on -50.5° Rotated Y-Cut Quartz

4-5

to

N

p 40

r

W

Z

50

60

70

-90

uW

O

N

C

-Q

5

z

-90
OF POOR QUALii1(

embedded transducers by using 350 A of aluminum. A five dB difference in

insertion loss would normally be expected from a third harmonic 35,50

rotated Y cut device if the fingers were not embedded. The second

feature of the 50.50 rotated Y cut SBAW device is that the optimum

length of the transducer is much longer than that of the 35.5° device.

Laser trimming experiments performed on the device with a transducer

length of 750 x indicate that the optimum length is 'larger than 750 X.

It therefore seems that while the wave velocity and coupling coefficient

are lower than the 35.5° device, the -50.5* rotated Y-cut substrate exhibited

the combined properties of high Q (> 3000) and good temperature stability

at the frequency range near 2 GHz.

4.3 Fabrication and Packaging Techniques

Two fabrication techniques were employed for the device fabrication,

depending on whether the transducer fingers were embedded. For the

unembedded transducer, the etching technique was used. As shown

in Figure 4.6, a thin metal film is deposited on the quartz substrate 

HO TO RESIST

METAL

LM

, i

^ * 

\ 

SUBSTRATE

rrk

• 

Y \

NEENINSW\

Figure 4-6. Schematic Illustration of Etching Technique

followed by spin coating of Shipley 1350) positive photoresist. The

resist is then exposed with a highly uniform monochromatic UV light

source through a light field photomask. After exposure, the resist is

developed, forming a transducer pattern over the metal film. The

metallic pattern is defined by ion beam etching through the developed 

photoresist pattern. Ion beam etching was found to produce lines with

better definition and reproducibility than the conventional chemical

etching.

4-6
OF BOOR QUALV

The fabrication process for the embedded transducer is shown

schematically in Figure 4.7. After the photoresist pattern is developed,

the substrate is ion-milled to create the desired groove depth.

Aluminum metallization is then evaporated to fill up the grooves and

the resist removed using acetone as the final step. The metal

thickness must be within 100 H 'of the groove' depth'..'this can be

be verified by a surface profile measurement using a Dek.tak machine.

A titanium layer of 30-40 A can also be placed between the substrate

and the aluminum to improve film adhesion.

PHOTORESIST

;

SUBSTRATE

^^

ION AEAM, ETCHING

DEPOSITED

METAL FILM

Figure 4-7. SBAW Delay Line Fabrication

(Embedded Transducer)

The SBAW delay line was packaged in a 20-pin Tekform flatpack.

The procedures for device packaging areAescribed* below.

The SBAW delay line was mounted in the flatpack with a 71-1

Ablestik adhesive. Only a small drop of Ablestik was applied to the

back of the delay line so that most of the SBAW substrate is free from

any stress that may arise from mounting. The Ablestik was cured in

an oven with a continuous hydrogen flow for one hour at 300°C.

Ablestik was selected because of its low outgassing rate, thereby

increasing the possibility of having low aging rates.

4-7

4
4.4 Electromagnetic Feedthrough

The electrical performancesof the SBAW devices described in

Sections 4.1 and 4.2 were measured using a test fixture with greater

than 60 dB feedthrough suppression designed specifically for the

testing of unpackaged devices. After the device 'is packaged in the

20 pin flatpack,the device performance deteriorates due to electromagnetic feedthrough. The main effect of the feedthrough is reduced

sidelobe level. When the feedthrough level is comparable to the

signal, distortion in passband: shape can also result. Since the

feedthrough level of the flatpack is at the order of -40 dB at

2 GHz, the performance of the -50.50 rotated Y cut device is degraded

to the extent that it is not usable in the oscillator circuit.

Due to time and equipment constraints,further research into different

packages;was not feasible. Only the devices fabricated on 36.250

rotates; Y cut quartz were used for oscillator application.

4-8
5-1 

OF NUuR QUALITY

5. 2 GHz SBAW OSCILLATOR DEVELOPMENT

5.1 Detail Design

The 2 GHz SBAW oscillator is mounted on a 3" x 3 112" brass

baseplate as shown in Figure 5-1.

Figure 5.1. 2 GHz SBAII Oscillator

The schematic diagram is shown in Figure 5 and the drawing

is shown in Figure 5-3.

+15 VDC

LIN(

E^

Figure 5-2. 2.144 GHz Oscillator Block Diagram
ORIGINAL PAGE 19,

OF POOR QUALrii Y

Top View

t

3

Side View

Figure 5-3. Drawings of the 2 GHz SBAW Oscillator

The components used in the oscillator circuit and their gain/

loss analysis are listed in Table 5.1.

A

aTable 5.1. Component/Gain of Oscillator Loop.

COMPONENT GAIN/LOSS (dB)

1 (a) NARDA N-62335-211 Amplifier +33.00

F

1 (b) NARADA N-62335-209 Amplifier +44.00

2 Anaren 10230-3 Quadrature Hybrid - 3.25

3 Resistive Pad TBD P

4 SBAW Device -26.00

5 Variable Length Line - 0.10

r

Excess Loop Gain 4.0-6.0

5-2
.•

The quadrature hybrid power splitter and the SRAW device were assembled

on a 25 mil thick Duroid circuit board which was mounted on the base

plate. The loop amplifier, on the other hand, was mounted directly

to the baseplate. Out of the 5 amplifiers there were three that had

33 dB gain and two that had 44 dB gain. The resistive pad was used to

adjust the excess loop gain to within 4 to 6 dB. Semi-rigid coaxial

cables were used to connect the amplifier to the circuit board.

Frequency adjustment was accomplished by varying the length of these

cables.

5.2 Spurious Output and Phase Noise Characteristics

Five oscillators were constructed, one of which has the SRAW

delay line mounted in a flatpack without its cover for display purposes.

Performance data was taken on the remaining four oscillators and is

summarized in Table 5-2.

A typical spectrum analyzer measured output of a SRAW oscillator

is shown in Figure 5.4. No spurious noise is observed at frequencies

close to the desired output frequency. The output power is +18.3 dBm for

this oscillator. When a much wider frequency range is searched, harmonics

of the fundamental frequency are observed up to 15 GHz (Figure 5.5).

These harmonics are due to the nonlinear characteristics of the loop

amplifier when it is driven into saturation and is typical of this type

of oscillator.

5-3
5-4

OF POOR

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Figure 5-4. Spectrum Analyzer Measurement of Oscillator Output

N A SA SS!WC SN 2143-3-15 5!4.'83 tet4tR 2. 14 GHz

REF 20.0 d9m ATTEN 30 d8 -13. 80 d8

10 CiO"

START 2.0 GHz STOP 22..0 CH=

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Figure 5.5. Harmonic Frequencies of the Oscillator
4"

ORIGIN►:. PAQQ .4 L$

OF POOR QUALI'T'Y

Table 5-2. 2.14 GHz SBAW Oscillator Data Summary

PARAMETER 2143-3-07 2143-3-08 2143-3-11 2143-3-15

OUTPUT FREQUENCY GHz 2.143282 2.143590 2.143862 2.140749

OUTPUT POWER, dam +14.5 +13.1 +15.5 +18,0

TEMPERATURE STABILITY,ppm +42 t30 ±48 ±22

(-20 to +50°C)

SSB PHASE NOISE, dRc/Hz

at

1 KHz -70 -70 -68 -64

10 KHz -100 -•103 -98 -94

100 KHz -132 -133 -126 -126

1 MHz -158 -158 -156 -155

The phase noise characteristics of the oscillators are shown in

Figures 5-6 through 5-9. They were measured in the TRW Metrology Department

using computer controlled phase noise measurement equipment. This

fully automated system is based on the HP3585A, 8566A, and 

analog type automatic spectrum analyzers and the HP5429A digital signal

analyzer (dual-channel fast Fourier transform type). The controller

is the HP9845T desktop computer, The system provides the basic

capability of measuring phase noise from microhertz to the 1500 MHz 

Fourier frequency range of the carrier. 

A plot of the theoretical calculation of the phase noise characteristics based on amplifier noise figure, device insertion loss, loop power

and device delay time is shown as the dotted line in Figure 5-6, The

agreement between theory and experiment is good. The 1/f3 dependence of

the phase noise indicated that the dominant noise process in the oscillator

is flicker FM.

5-5
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Figure 5.6. Normalized Phase Boise Sideband Power Spectral

Density for Oscillator SN 2143-3-07

Y

u

9

/OURJU FREQUENCY 04)

Figure 5-7. Normalized Phase Noise Sideband Power Spectral

Density for Oscillator SN 2143-3-08.

a ._ r

Me-
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OF FOUR QUAIL a tl

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Figure 5-3. Normalized Phase Noise Sideband Power Spectral

Density for Oscillator SN 2143-3-11

L t

t• IM IK 19K INK 111 —r IMM

FOURIER FREQUENCY, (N:1

Figure 5-9. Normalized Phase Noise Sideband Power Spectral

Density for Oscillator SN 2143-3-15 .
0

5.3 Temperature Stability

The temperature stability of the SBAW oscillator was measured

using an experimental set-up which automatically cyclesthe temperature

of the environmental chamber and rerordsthe output frequency of

the oscillator. During each experiment one oscillator was placed

inside the chamber,and the temperature of the chamber was cycled

up and down in 10° C steps over the range between -'LO° C and 60°C. At

least 15 minutes was allowed at each temperature step before the frequency

measurement was taken so that the device had time to reach thermal

equil-lbrium within the chamber.

The resultsof the temperature stability measurements are shown in 

Figs. 5-10 through 5-13. The turnover temperature generally lies between

10° and 20°C. Absolute frequency excursion between -20°C to 50°C

varied from ± 22 ppm to ±48 ppm. The parabolic temperature dependence

is typical of devices fabricated on 36.250 rotated Y cut quartz.

s 5.4 Long Term Aging Characteristics 

The long term stability of the SBAW oscillator is determined by the 

long term stability o f -the SBAW delay line. The aging characteristics of 

the SBAW delay line .are thought to depend on many complex factors,

including crystal polish, metal film stress, device mounting stress, 

contamination and device packages. Since good aging was observed for 

k the 1 GHz SBAW delay lines, similar mounting and packaging techniques

were employed for the 2 GHz device. The SBAW delay lines were attached

to the 20-pin Tekform flatpack using 71-1 Ablestik adhesive. Only a small

drop of Ablestik was used at the center portion of the crystal, therefore 

allowing most of the substrate to be free from any stress. The Ablestik

was cured in an oven with continuous hydrogen flow for one hour at 300°C.

r The devices were then hermetically sealed with resistive welding in a

nitrogen atmosphere.

a

r Aging of three SBAW oscillators began on December 13, 1982. The

g' oscillators were mounted onto a common aluminum baseplate. A theretocouple was at= tached to the .iaseplate so that the temperature could be

monitored. Over the duratic:. of the aging experiment,rthe baseplate

temperature variation was ±1 0 C. Figures 5-14 through 5-16 show

the variatiorsin output frequency as a function of time. A discontinuity
0

a

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AMBIENT TEMPERATURE (CENTIGRADE)

Figure 5-10. Temperature Stability of Oscillator SN 2143-3-07

AMBIENT TEMPERATURE (CENTRIGRADE)

Figure 5-11. Temperature Stability of Oscillator SN 2143-3-08.

5-9
20

0

20

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O -40

U

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-80

QMNAL PAGE 19

Of POOR QUALITY

AMBIENT TEMPERATURE (CENTIGRADE)

Figure 5-12. Temperature Stability of Oscillator SN 2143-3-11.

1

-30 -20 -16 0 10 20 30 40 S0

TEMPERATURE (CENTIGRADE)

Figure 5-13. Temperature Stability of Oscillator SN 2143-3-15.

5-10
Wix

ORIGINAL PAGE W

OF POOR QUALITY

U

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DECEMBER JANUARY FEBRUARY I MARCH I APRIL MAY

TIME

Figure 5-14. Long Term Stability of Oscillator SN 2143-3-07.

....... . .

5-11

DECEMBER I

JANUARY I FEBRUARY I MARCH I APRIL I MAY

TIME

Figure 5-15. Long Term Stability of Oscillator SN 2143-3-08.
2.113170

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ORIGINAL PAGE 15

OF POOR QUALITY

NEW COUNTER

TEST SET MOVED

10 DAYS

DECEMDER I

JANUARY I FEBRUARY I MARCH APRIL I MAY

TIME

Figure 5-16. Long Term Stability of Oscillator SN 2143-3-11.

appears in one of the plots, this occurred on the day the test set was moved

to a new laboratory.

Table 5.3 summarizes the estimated aging rates of the oscillators as

determined by a least-squares straight line fit to the measured data. This

much higher aging rate compared to the 1 GHz SBAW oscillator's was disappointing. Therefore, it was decided that meaningful data could be obtained

by temperature cycling all three oscillators between -12 O C and 54 0 0 and

then continuing the aging measurement for an additional three months. A

fourth oscillo•ter (SN 2143-3-15) was also temperature cycled and added to

increase the data base. The results of the additional measurements are

summarized in Figure 5-.17. The oscillator SN 2143-3-11 showed random frequency fluctuations. The SN 2143-3-08 unit continued its upward frequency

drift, although i;.s rate was reduced to 37,5 ppm/year from 59,4 ppm/year.

l '!i

The SN 2143-3-07 unit showed less than 1 ppm/year aging rate, and SN 2143-3-15

had a -10.4 ppm/year rate.

Table 5.3 NASA 2 GHz SBAW Oscillator Aging Rates

AGING RATE (ppm/year) s SER. N0. TEST INTERVAL

+42.6 100

2143-3-08 +59.4 115

2143-3-11 +28.8 130
25

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OF POOR QUALITY

^ v - AULtUb I bhV 1 tMbhK

TIME

Figure 5-17. Results of Three-Month Aging Measurements of

4 2.144 GHz SBAW Oscillators

Since the aging rates are not consistent among oscillators, it is difficult to precisely identify the cause of aging. The only consistent trend of

the data is that much higher aging rates were observed for the 2 GHz SBAW

oscillator as compared to the 1 GHz SBAW oscillators. The probable cause of

this is overdriving of SBAW transducers. The 2 GHz SBAW transducers are more

susceptible to this effect because they contain fl ngers twice as narrow as

the 1 GHz transducer and have a much thinner metal thickness.

5-13
6. REFERENCE SOURCE EVALUATION

The objective of the reference source evaluation task was to

demonstrate the compatibility and improvement in performance of

the SBAW oscillators in the circuits presently utilizing the

surface acoustic wave (SAW) oscillator. Since the SBAW device is

constructed similar to the SAW device, a direct replacement of the SAW

device in a SAW oscillator, circuit by a SBAW device is possible. The

comparison of the 1 GHz SAW and SBAW devices was performed in this manner.

The comparison of the 2 GHz SAW and SBAW devices presented somewhat of a

problem because the 2 GHz SAW oscillator developed under NAS5-25095

was packaged in such a way that direct replacement of the SAW

device by the SBAW device was not feasible. In this case, the comparison

1. was made between SAW and SBAW oscillators constructed with different

circuit components.

6.1 Comparison Between 1 GHz SAW and SBAW Oscillators

After termination of the 1 GHz SBAW oscillator aging study,one

f; of the SBAW delay lines wa'sremoved from its oscillator circuit and

replaced by a SAW delay line. The SAW delay line has performance

parameters similar to that of the SBAW delay line it replaced. Its

insertion loss was 25 dB and the time delay was 0.35 usec., approximately

20% shorter than that of the SBAW delay line. The phase noise and

temperature stability comparison of the oscillators is shown in

Table 6.1. The phase noise characteristics of the two oscillators

are basically identical. The larger temperature shift in the SAW

oscillator is due primarily to the fact that the turnover temperature

of the device is -10°C.

Table 6.1 1.07 GHz Oscillator Comparison

PARAMETER SAWO SBAWO

TEMPERATURE STABILITY ±75 ppm

(-20 0 C to +50 0C)

PHASE NOISE, dBc/Hz

1 KHz OFFSET -74

1 MHz OFFSET -134

LONG-TERM STABILITY N/A

6-1

±47 ppm

-74

-136

1x10-7 pp day
6.2 Comparison Between 2 GHz SAW and SBAW Oscillator

The 2 GHz SAW oscillator developed udder a previous contract

NA S5-25095 used a SAW delay line fabricated on an AtN/Az 2 0 3 substrate

in its oscillator loop. The comparison between the two oscillators is

shown in Table 6.2. The SBAWO has much better temperature stability, and

the phase noise characteristics are better due to the lower insertion loss

of the SBAW device.

Table 6.2 2.14 GHz Oscillator Comparison

PARAMETER SAWO SBAWO

TEMPERATURE STABILITY,ppm ±1200 ±42

(-20 C to +50 C)

PHASE N[ISE, dBc/Hz 

1 KHz OFFSET -68 -70

1 MHz OFFSET -136 -158 

LONG TERM STABILIT`r 2.25x10`6 pp uay 1x10" 7 pp day

6.3 Trade-off'Between 1 GHz and 2 GHz Reference Sources

Both the 1 GHz and 2 GHz SBAW oscillators have demonstrated superior 

performance over their SAW counterparts. For an application, such as a

Ku band source, the 2 GHz SBAW oscillator has an advantage over the 1 GHz

version becasue less multiplication will be required. This will result in

lower circuit complexity and less power consumption. The phase noise of

the 1 and 2 GHz SBAW oscillators is basically a function of the noise figure

of the loop amplifier, and a comparison between Tables 6.1 and 6.2 shows

that the 2 GHz oscillator is already slightly superior in this aspect. It

should be noted that phase noise of the 1 GHz oscillator followed by . a multiplier circuit will be greater than that from the 2 GHz oscillator.

6-2 
4

7. FREQUENCY SELECTABILITY AND SETTABILITY

The conclusion of the Phase I study of the frequency selectability

and settability was that up to i 21% change in device center frequency is

possible for a given mask design if the rotated Y cut angle of the

substrate is properly chosen, Accompanying these frequency changes were

variations in temperature coefficient of the device time delay,

For smaller changes in frequency on a given substrate, approximately

± 1% could be realized by adjusting the metal film thickness of the SBAII

transducer. A similar amount of frequency settability can be achieved by

adjusting the phase in the oscillator loop.

The Phase II program continued this Phase I effort by designing

a single mask and fabricating devices on five different cuts of singly

rotated Y cut quartz substrates. The five target frequencies were

2287.5, 2230.0, 2208.0, 2116.0 and 2106.4 MHz. The following sections

describe the approach and experimental results.

7.1 Analysis and Device Design

r. Based on design curves calculated during Phase I of the program

and reproduced in figure 7.1,it is evident that if the 2287.5 MHz device

was fabricated on +35.5 0 rotated Y cut quartz, the devices at the other

frequencies must be fabricated on substrates whose rotated Y-cut angle,

e, is somewhat larger than 40 0 . Table 7-1 summarizes the details of

the theoretical analysis to select the desired substrate angle. The

design of the mask for this study was based on the third harmonicdesign for the 2.144 GHz SBAW delay line described in Section 4.1.

The transducer portion was sim p ly scaled down by a factor which

reduced the finger width from 0.89 um to 0.836 um.

7-1
WAVE VELOCITY

IST ORDER TCD

^P r

-rte

-30 M

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8 U

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. 40 ti a

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ORIGINAL PAGE IS

OF POOR QUAL" Y

49

s

4500 1

35 40 45L150 55

SUBSTRATE ANGLE 0(DEC)

Figure 7-1. SBAW Velocity and First Order TCD as a

Function of 0 in Rotated Y-Cut Quartz,

Table 7-1. Theoretical Calculations

TARGET FREQUENCY WAVELENGTH CRYSTAL CUT CALCULATED WAVE

(MHz) (A) ANGLE 0 (DEG) VELOCITY (M/SEC)

2287.5 2.226 35.5 5092

2230.0 2.226 44.0 4964

2208.0 2.226 46.2 4915

2116.0 2.226 53.4 4710

2106.4 2.226 54.0 4689

7-2
ORIGINAL V3

OF POOR QUA',:i`1 f

0

7.2 Data Summary

V

Approximately 5 devices on each substrate were fabricated using

the mask whose designed finger width was 0.536 um. All devices were

fabricated with embedded fingers. The embedded groove depth was approximately 350 X and the aluminum metal thickness 400 A. The measured center

frequencies as summarized in Table 7.2 of these devices were generally

12-17 MHz lower than the target frequencies. A 0.5Z error in mask linewidth error was confirmed by laser interferometric measurements. There

were, however, additional errors which amount to 0.1 or 0.2%. Such

errors were attributed partly to fabrication errors such as finger/gap

ratio variance and metal/groove depth variance. Additional errors were

due to crystal angle uncertainties which could amount to 0.1Z in frequency

shift for a 15 minute angle error.

Table 7-2. Results of Frequency Settability Study

TARGET FREQUENCY MEASURER FREQUeNMv

CRYSTAL ANGLES (MHz) (MHz) % OFF

35.5 0 2257.5 2270.0 ± 2.9 0.77

44.0 0 2230.0 2217.2 + 1.5 0.58

46.2 0 2208.0 2197.4 + 2.5 0.48

53.4° 2116.0 2102.2 + 1.0 0.65

54.0 0 2106.4 2093.5 + 1.7 0.61

2

6

One effect of this method of oscillator frequency selection is that

the temperature stability of the oscillators deteriorates. To fully characterize this effect, the delay lines were place in an oscillator loop and

their temperature coefficient of delay measured. Table 7.3 summarizes

the results of this measurement. Another effect which is a consequence

7-3
M

of changing the substrate angle 0 is a change in delay line insertion

loss due to the change in the coupling constant. The typical unmatched

loss for the delay lines is also included in Table 7.3. The results are

in agreement with the theoretical predictions, except for the one insertion

loss anomaly at 0 = 53.4°; this could be attributed to device imperfection.

Table 7-3. Insertion Loss and First Order TCD of SBAW

Devices.

a

REFERENCE FREQUENCY o ITCD^ UNMATCHED IL

GHz DEGREES ppm/c (dB)

2.270 +35.5 -2.0 22

f<. 2.217 +44.0 31.3 21

2.197 +46.2 38.5 16

.4° 2,101 +53.4 54.5 24

2,093 +54.0 58.5 21

ORIGII< AL ^^R ,,"L",

orPOO'R Q

7-4