INSTITUTE OF PHYSICS PUBLISHING

JOURNAL OF MICROMECHANICS AND MICROENGINEERING

J. Micromech. Microeng. 15 (2005) 237–243

doi:10.1088/0960-1317/15/1/033

Ultracompliant thermal probe array forscanning non-planar surfaces without
force feedback
Shamus McNamara, Amar S Basu, JooHyung Lee
and Yogesh B Gianchandani
Department of Electrical Engineering and Computer Science, University of Michigan,
Ann Arbor, MI 48109-2122, USA
E-mail: yogesh@umich.edu

Received 28 June 2004, in final form 11 October 2004
Published 29 October 2004
Online at stacks.iop.org/JMM/15/237
Abstract
This paper describes an array of micromachined thermal probes for scanningthermal microscopy for which the structural design and choice of materials
virtually eliminate the need for z-axis mechanical feedback in contact modescans. The high mechanical compliance accommodates significant
topographical variation in the sample surface and prevents damage to soft
samples. Thin film metal bolometers are molded into tips at the end of eachcantilever in the array, and are sandwiched between two layers of polyimide
that serves as the structural material. The probes overhang a Si substrate on
which they are fabricated. Since integrated actuators and accompanying
circuitry are no longer required, the prospect of scaling from the present
eight-probe version to large numbers of probes for high speed, highresolution thermal mapping of large areas with simple detection circuitry isenhanced. The scalability and performance of the eight-probe prototype are
evaluated, addressing issues of speed versus resolution, and thermal andmechanical decoupling. The results demonstrate that contact mode scans
can provide better than 2 µm spatial resolution at speeds greater than
200 µm s−1 and show a 6.5 bit topographical resolution over a 7 µm
dynamic range. Line scans obtained with a single-shank probe suggest that
there are good prospects of obtaining images showing a lateral spatial
resolution of less than 50 nm.

1. Introduction
First introduced in 1986 [1], scanning thermal microscopy(SThM) has found a unique place among the various
techniques for high resolution scanning microscopy. It permits
mapping of topography, temperature, thermal conductivity,
thermal capacitance and performing micro-calorimetry with
sub-50 nm spatial resolution [2, 3]. These functions cannot
typically be performed by optical imaging methods, which
are additionally limited by infrared wavelength to spatial
resolution of 10–12 µm. A number of applications can beenvisioned for tools with spatial resolution in the 0.05–5 µm
range, such as biomedical diagnostics or cellular mapping,semiconductor process monitoring for sub-surface defects, andsemiconductor device diagnostics such as failure analysis by
0960-1317/05/010237+07$30.00

hot-spot detection. The scanning probe has a thermal sensor(typically a bolometer or thermocouple) in the vicinity of a
sharp tip located at the end of a cantilever. Scanning isbest performed with the probe in contact with the sample
to eliminate the high thermal resistance of an air gap, but
this conventionally requires a mechanical feedback loop to
prevent the probe from scratching the sample. Similar to an
atomic force microscope (AFM), the contact force is sensed bymeasuring probe deflection with a reflected laser. The contactpressure of the probe is adjusted using a positioner that iscontrolled by the error signal from the laser detector. Thissignal also provides a measure of the topographical variationsin the sample independently of the variations in temperatureor thermal properties.

© 2005 IOP Publishing Ltd Printed in the UK

237

S McNamara et al

1

Portions of this paper have appeared in conference abstract form in [10].

238

BridgeLNA

LPF DAQ

Pr
ob
e

PSPD

er
Las

In the case of the bolometer (or thermistor) probe thethermal bias between the probe and the sample is provided by
the resistor that also serves as a sensor. Heat flows from thisresistor at the probe tip through the sample to the supporting
substrate, which is nominally at a fixed temperature. As
the probe is rastered across the sample surface, variationsin temperature, thermal properties or physical properties that
affect thermal conductance of the sample can be sensed
by the resistor. These variations are mapped in one of
two ways: applying constant power to the resistor andmonitoring the changes in its resistance (which is indicativeof its temperature), or using a servo-controlled circuit tomaintain the resistor at a constant temperature and monitoring
the variations in power required to do this. For a passive
sample that is at constant temperature, this image can contain
information related to variations in both topography andthermal properties. For some applications this information
does not need to be separated, particularly if the either oneof the two variables is not changing significantly. In casesthat require the thermal information to be separated, this canbe done by subtracting the topographic image, obtained as
described previously, from the composite image.
The desire to increase throughput in scanning probe
microscopy (both SThM and AFM) has prompted the designof arrays in which multiple probe tips scan in parallel [4–9].
The mechanical feedback loop in a conventional SThM canbe either at the chip level, causing the entire array to beraised and lowered, or at the probe level. For data storage
applications, in which the topographical variation is only a
few tens of nanometers, chip level feedback may be sufficient,as was shown by the first large scale (32 × 32) thermal probearray, IBM’s Millipede [4]. However, for general purpose
scientific applications, the local topographical variations canbe in excess of 1 µm, and each thermal probe must be able
to deflect independent of the other probes in order to follow
the surface. This is best performed by individual feedback
for each tip. As the array size is increased, however, this
rapidly becomes a difficult issue because parallel scanningrequires each cantilever to have its own addressable feedback
loop. Individual actuation of cantilevers has been exploredusing piezoelectric films [5, 6], electrostatic actuators [7] andelectrothermal bimorphs [8, 9], for example. While theseapproaches are effective for limited variations in topography,
they do not easily accommodate samples with micrometerscale topographical variation, such as integrated circuits or
biological cells. Furthermore, all methods of integrating
actuators on the thermal probe require additional fabrication
steps, control circuitry and electrical interconnect, which
greatly increase the manufacturing and calibration complexity.
In this work1 we present an ultracompliant probe array foruse in thermal imaging that can be scanned across a sample
with minimal contact force and without mechanical feedback.
The use of polyimide as the cantilever structural material,
previously reported by our group, offers not only a highthermal isolation, but a very high compliance [3], resulting
in a 10–100× reduction in contact force over conventionalscanning probes. The contact force for each cantilever in thearray remains low over a wide range of deflections, eliminating
the need for probe level feedback that is typically required to

XY Micromanipulator

XY ScanController

ComputerInterface
Z Axis Actuation Not Needed

Figure 1. Z-axis feedback and integrated actuators are not requiredin the ultracompliant thermal probe array presented here. A simple
open loop interface circuit is sufficient to both bias the probe tip
temperature and read the tip temperature via changes in probe
resistance.

Figure 2. SEM of the thermal probe array after assembly with an
inset showing the metal probe tip. Individual cantilevers protrude
from a common beam segment. The entire array is flipped over andheld in place in one step.

prevent damage to the sample and the tip. In addition, thestructure (figure 1) can be designed in a manner such that thecantilevers are decoupled both thermally and mechanically,
enabling high-speed parallel thermal mapping of samples
with large topographical variation using simple detection
circuitry and no integrated actuators. A dynamic range of>5 µm is targeted to permit use in several target applications
including thermal analysis of integrated circuits, profiling of
surface micromachined MEMS and thermal characterizationof irregular polymer samples.

2. Device structure and operation
A fabricated thermal probe array is shown in figure 2. Eightindividual cantilevers extend off a common beam segment
overhanging from the edge of the die. At the end of eachcantilever is a pyramid-shaped thermal probe tip extendingout from the cantilever comprising a thin film metal resistor.
The cantilevers and shank are made of polyimide, providing
excellent thermal isolation and high mechanical compliance.
Electrical interconnect from the substrate to the thermalprobes is embedded within the polyimide. The cantilevers
are 180 µm long by 60 µm wide, the common beam segment
is 560 µm long by 650 µm wide and the probe tips are spaced
85 µm apart.
To scan a sample, the thermal probe array is inverted andmounted on a motorized XYZ scanning stage (figure 1). The
z-axis actuation is used to lower the thermal probe array onto
the sample and pre-deflect the thermal probes. The amount of
pre-deflection together with the surface forces between the tip
and sample determines the deepest valley that may be scanned

without losing contact. The x- and y-axis actuations are thenused to raster the probe array across the sample. The thin film
metal resistor on each probe tip is used both to heat the tip
and to detect temperature variations that occur during the scandue to the thermal coupling between the thermal probe andsubstrate. Each probe in the array is connected to a separate
Wheatstone bridge that provides the bias current and senses
the changes in resistance. A separate low noise amplifier andlow pass filter on each probe channel are used to minimize
noise. A computer interface is used for data acquisition and tocontrol the position of the xy scanning stage. It is notable thatthe simplicity of this apparatus is afforded in large part by themechanical compliance of the probes, which permits them tobe operated without force feedback.
There are a number of advantages that arise from thechoice of flexible polyimide as the structural material for theprobe. First, the Young’s modulus of polyimide is about 50×
lower than that of silicon nitride, the conventional materialof choice for force microscopy probes. For example, thespring constant of a 3 µm thick probe in the array of thedimensions described at the beginning of this section canbe estimated as 0.15 N m−1, which is an order of magnitude
smaller than what is typical of probes for AFM. Thus, withthe polyimide probes, a topographical variation of 0.2 µm
scanned without mechanical feedback causes a variation of
30 nN in the contact force, which is acceptable for a number
of applications. (In addition, the tip diameter for thermalprobes is larger than for AFM probes, so the contact pressure
is lower for the same applied force.) For samples that are
more sensitive to contact pressure, longer probe shanks canprovide even smaller variations in contact force. Second, thecompliant nature of polyimide is also advantageous in termsof its reliability and dynamic range. Using a first order beam
analysis, the maximum deflection that causes beam fractureis [11]
σT S
2L2
∝
3EH
E
where E is the Young’s modulus, σT S is the tensile strengthof the material and L is the length of the beam. Ignoring
cantilever dimensions, a figure of merit for the dynamic range
of a structural material is σT S /E. Silicon nitride has a Young’s
modulus of about 270 GPa and will fracture at about 500 MPa
tensile stress. Polyimide deforms at a yield stress of 350 MPa,but has a Young’s modulus of only 8.5 GPa. The dynamic
range of the polyimide probe, therefore, is over an order ofmagnitude better than a nitride probe of the same dimensions,allowing for larger topographies to be scanned without damage
to the cantilever. This also tends to reduce the overall fragilityof the polyimide probes compared to silicon nitride probes.
The choice of flexible polyimide is also very helpful in the
fabrication and assembly of the probes, as will be discussed in
the section on fabrication.
The mechanical operation of the array is depicted infigure 3(a). Prior to the scan, the probe array is brought into
contact with the sample and the cantilevers are pre-deflectedby an amount that is application-specific and user-definable.
Ideally, each probe deflects without affecting the otherprobes. Some degree of coupling is inevitable because, during
fabrication, all the probes are simultaneously flipped using a
wMAX = σT S

(Co
mm Probeon
Be Shan
am k
Se
gm
ent
)

Ultracompliant thermal probe array for scanning non-planar surfaces without force feedback

Ks

Probe nProbe n+1

K2 ...

K1

Kn

Probe n+2(a )Sample

(b )

F1

F2

Fn

Figure 3. (a) Schematic showing the conceptual operation of theprobe array over a sample with large topographic variation. (b) First
order mechanical model of the array structure. For effective
mechanical decoupling, the spring constant of the shank KS should
be large compared to the cantilever spring constants K1 , K2 , etc.

common segment of the beam for easier handling. Intuitively,
the system can be thought of as the simple mechanical network
shown in figure 3(b), with an array of springs representing
individual cantilevers coupled to a single spring representing
the common beam segment. The precise value of mechanicalcross-talk between beams depends on a number of factors,
including the length and width of the individual beams andthe common segment (and other dimensions), the amountof pre-deflection of the beams when in contact with thesample, and the magnitude of attractive surface forces thatexist between each tip and the sample. This attractive force isdependent upon scan conditions, but is typically in the rangeof 10–100 nN [12].
For proper operation, all the thermal probes in the arraymust stay in contact with the sample during the scan. However,since the probes are all connected by a common segment,
excessive deflection in one probe can cause other probes in
the array to lift off the sample. It is worthwhile to know the
maximum topographical variation that a single probe can scanover without adjusting adjacent probes off the sample. This isdefined as the maximum dynamic range.
Predicting the maximum dynamic range is somewhat
challenging because the movement of individual probes causes
both bending and twisting of the common beam segment.
Since it depends upon the amount of pre-deflection and tipsample adhesion forces, the maximum dynamic range of asingle probe is influenced by the instantaneous deflection of
every other probe in the array. To illustrate some common
situations encountered, finite element analysis (FEA) was
performed using ANSYS to determine the dynamic range forscan conditions that will provide a large dynamic range as wellas conditions for a small dynamic range. A constant 100 nN
force is used to model the attractive forces between the tip andthe sample. The dynamic range for varying amounts of predeflection is found by raising probe A and determining whenprobe B lifts off the sample. Figure 4(b) shows the results ofthe simulation for adjacent probes at the center of the array(middle line), for probes at the two ends of the array (topline) and for the case where all probes except one are raised(bottom line). From the viewpoint of the designer, it is best to
increase the lengths of the separated segments and minimize
the length of the common segment. Eventually, the dynamic
range becomes limited not by coupling, but by the range ofdeflection of the cantilever itself.
239

S McNamara et al
Probe A

Probe B

FelA

FelB

SiO2 tip sharpen silicon nitride

Probe A

Probe BFelA

Dynamic Range (µm)(a )Dynamic
Range

notch for tip

FelB
Fadhesion(d )upper polyimide

sacr. material

(b )

(e )
lower polyimide

Au

Au

30
(c )

25
20
15
10
5
0

(f )

(g )

0
(b )

5

10
15
20
25
Pre-deflection (µm)

30Figure 4. (a) Pre-deflection of the probe array results in elastic
forces on adjacent probes A and B (FelA and FelB ). As probe A
moves over a bump, coupling through the common beam segment
causes the elastic force exerted on B to reverse direction, and if thereversed force is larger than opposing forces, probe B will lift off thesample, thus limiting the dynamic range. (b) FEA modeling resultsof the maximum dynamic range as a function of pre-deflection. For
all cases, the adhesion force is 100 nN.

The thermal coupling ratio between adjacent probes
can be defined as tP1 /tP2 , i.e. the temperature shift
in a probe caused by a temperature shift in the adjacentprobe. Finite element analysis was performed in ANSYS,
ignoring convection and assuming that the array is held
15 µm above a thermally conductive substrate.
The
primary path of heat exchange between adjacent probe
tips was found to be lateral conduction through the airgap, and the thermal coupling ratio was found to be−24 dB. The thermal coupling ratio improves by 10× if
the distance between probe tips is doubled to 170 µm.
When the probe tips are in contact with the sample, thecross-talk may increase or decrease depending on the thermal
conduction between points of contact and how that compareswith conductance through the thickness of the sample.

3. Fabrication
The ultracompliant thermal probe array is fabricated witha low temperature 7-mask process suitable for post CMOS
fabrication. As shown in figure 5, the process consists
primarily of a sequence of surface micromachining steps
followed by a flip-over and a thermocompression bonding step
to point the tip of the probe away from the substrate.
A pyramidal mold for the tip structure is first created byanisotropic etching of a (100) silicon wafer, masked by a thinlayer of silicon nitride (figure 5(a)). To obtain a sharper tip,
the silicon is optionally thermally oxidized at 950 ◦ C [13]. A
layer of sacrificial titanium is deposited below the cantileverstructures and inside the mold to facilitate the release of thecantilevers (figure 5(b)). The cantilever itself is formed of
two polyimide layers (HD Microsystems P2610) with two
metal layers embedded within. The first layer of polyimide isetched from the mold region (figure 5(c)). A thin metal layer240

Si substrate(a )Resistive materials

Au thermo-compression
bond

Figure 5. Process flow for fabricating the polyimide-based thermalprobe array, suitable for post-IC processing. A tip notch is created,followed by a sacrificial layer, a resistor sandwiched between twolayers of polyimide and a gold layer for thermo-compression
bonding. After etching the sacrificial layer, the probe is flipped,
resulting in a probe overhanging the edge of the die.

consisting of Cr/Au (100 Å/1200 Å) is then deposited in themold to form both the metal tip and the resistor. A second,
thicker metal layer consisting of Cr/Au/Cr (100 Å/2500 Å/
100 Å) forms low-resistance electrical interconnects from thebonding pads to the probe tip (figure 5(d)). The top layer ofpolyimide is used to insulate the metal and provide strength tothe probe tip (figure 5(e)). Thick gold patterns are deposited
on top of the second polyimide layer for thermo-compression
bonding (figure 5(f )). The cantilevers are released by etching
the sacrificial titanium layer in dilute HF. Finally, the probeshank is manually flipped over (for which the mechanicalflexibility of the probe shank is essential), and a thermocompression bond is formed at a temperature of 200 ◦ C(figure 5(g)), resulting in a probe shank overhanging the edgeof the wafer die with the probe tip pointed away from thesubstrate (figure 2). The pre-released device is shown infigure 6.
The final shape of the probe tip, as determined by the(111) planes in a (100) cut Si wafer, is a pyramid of squarecross section and 54.7◦ sidewalls. The height of the pyramid isapproximately 7 µm. The tip diameter of the probe, which may
be rounded somewhat due to processing non-idealities such as
deposition characteristics of the sacrificial layer, is typically<100 nm. As indicated previously, sidewall oxidation of
the pyramidal mold reduces this below 50 nm. The entire
pyramidal tip is covered with the Cr/Au metal layer, whichforms the sensing resistor. A thicker layer of the same metals
runs back along each probe shank in two parallel lines to large
pads. (Adjacent probes may optionally share a pad for the
ground line.)

4. Experimental results and discussion
The thermal isolation of a single probe in the array wasmeasured while suspended in air (emulating a sample with
low thermal conductance) and while in contact with a silicon
substrate (emulating a sample with high thermal conductance).

Ultracompliant thermal probe array for scanning non-planar surfaces without force feedback

(a )

(b )

(c )

Resistance (Ohms)

170

120

In Air

169
168
167

100
80

166
165
164
163

60
40

On Sample
0

10

20

30

20

Tip Temperature (oC)

Figure 6. Photograph of the thermal probe array before the flip-overstep. The interconnect is a thick metal line to reduce the series
resistance to the thin-film bolometer. The two gold regions matewhen performing the thermo-compression bond.

Figure 8. Reconstruction of a thermal image by combining
overlapping scan regions. Shown here is a 750 µm × 200 µm area
on a commercial IC containing 60 µm × 85 µm bonding pads with
120 µm pitch. (a) Thermal images obtained from four probes
spaced 170 µm apart scanning at 25 µm s−1. (b) Optical image.
(c) Horizontal line scan taken with a surface profilometer showing
2 µm topographical features between bond pads. In this scan, thethermal image conveys primarily topographical information, withsensitivity of 12 mV µm−1, dynamic range greater than 2 µm and anoise limited minimum detectable topography of 80 nm.

7 µm
4 µm 10 µm

10 µm 4 µm

2 µm
Feature10 µm/sNormalized Voltage

The thermal isolation depends upon the thermal conductanceof the sample with which the probe is in contact. A known
current is passed through the thermal probe, the voltage
drop across the bolometer is measured and the resistance isplotted as a function of input power (figure 7). Temperature
is calculated from resistance using a TCR of 450 ppm(determined in a separate experiment), and the thermal
isolation is found to be 2400 K W−1 in air and 1700 K W−1
when the probe is in contact with a silicon substrate.
To validate the functionality of the probe array, a
750 µm × 200 µm area was scanned on a commercial IC
containing bond pads. Four of the eight probes in the array
were used, each generating a 200 µm × 200 µm image
consisting of 100 lines scanned at 25 µm s−1. The raw data
were subjected to standard signal processing to remove scan
artefacts such as linear trends, and to filter out high frequency
noise. The optical image of the scan region and the thermal
images obtained from the four probes are shown in figure 8.
The scan results illustrate how a thermal image may bereconstructed by merging overlapping scan regions. The scan,which includes surface variations of up to 2 µm (as verified
by a line scan taken with a surface profilometer and plotted

20 µm

DektakPower (mW)

Figure 7. Thermal isolation of a single thermal probe that issuspended in air and in contact with a silicon sample. Probetemperature and resistance increase linearly as input power isramped.

Gold
Polyimide
Silicon

20 µm/s
50 µm/s
50Hz
Resonance

100 µm/s
200 µm/s
500 µm/s
1000 µm/s

02550Distance (µm)

75

Figure 9. Speed scaling study. Two 7 µm pits coated withpolyimide and gold were scanned at increasing speeds. A 2 µm
feature (labeled) is observed at speeds up to 200 µm s−1.
Mechanical resonance at 50 Hz was observed at speeds above
100 µm s−1.

in figure 8(c)), is performed without force feedback. Thisis an example of where the thermal image conveys primarily
topographical information. Used in this manner, the probearray can perform parallel, high speed topographical imaging
of integrated circuits and surface micromachined MEMS,
allowing detection of mechanical defects. However, such an
application would probably also require quantitative models
that co-relate the images to variations in both topographical241

S McNamara et al
Probe 1 Start
Probe 2 Start
6 µm

Cu

(b )

Voltage (mV)

(a )

20

Voltage (mV)Cu

Probe 1

0
-20
20

(a )

0

200

400

600

Probe 2

0
-20

(c )

Polymer
Coating

0

200
X (µm)

400

600
(b )

Figure 11. (a) Lines scan obtained at 10 µm s−1 scan speed from asingle probe using mechanical feedback control as well as a
servo-controlled interface circuit that maintains constanttemperature. (b) A topography scan obtained simultaneously with(a), using a reflected laser. This demonstrates that by changing thesystem parameters and operating conditions, high resolution scans
can be obtained from polyimide probes.

(d )

(e )

Figure 10. Mechanical decoupling. (a) Optical image and (b) A–A
cross section of a via with 6 µm topography. (c) Line scans taken
simultaneously from two thermal probes spaced 85 µm apart.
(d), (e) Two-dimensional thermal images obtained from the twoprobes simultaneously.

and thermal properties, as well as standard samples to calibratethese models.
With throughput being the main motivation behindarrayed probes, it is interesting to gauge the scan speed atwhich features can be resolved. A sample consisting of two
7 µm deep anisotropically etched silicon trenches coated withpolyimide and gold were scanned at varying speeds. Linescans in figure 9 reveal that a 2 µm long feature can be resolved
at speeds up to 200 µm s−1 and that a 10 µm feature can be
resolved at a speed up to 2 mm s−1. The effective scan speed,which scales with the number of probe tips, is 1600 µm s−1
at 2 µm resolution for the eight-probe array. This suggeststhat a 1.5 mm × 1.5 mm IC with 2 µm minimum features
can be imaged in approximately 12 min. However, to put thisin perspective, it is also necessary to consider dynamic range,
242

because most high throughput thermal probe systems [4, 6]
are not intended for mapping samples with large topographic
variation.
Also demonstrated in figure 9 are dynamic range andtopographical resolution. Since this structure is coated witha thin gold layer of uniform thickness, it is expected that thethermal signal obtained will convey primarily topographicalcharacteristics. This is because the primary heat loss fromthe tip is conduction through the gold layer and across the
sample to its underside, which is in contact with a chuckthat is uniformly at room temperature [3, 13]. Using a
12 mA bias current, a 90 mV contrast is obtained overa 7 µm topographical variation, indicating a sensitivity of
12 mV µm−1. The observed noise voltage is 1 mV, translating
to a minimum detectable signal (MDS) of approximately
80 nm. The probe, therefore, permits scanning with 6.5-bit
resolution over a 7 µm dynamic range. This range is 10–100×
higher than typical thermal probe arrays aimed at data storage
applications.
Mechanical decoupling between adjacent probes wasverified by scanning a via on a printed circuit board that
contains a 6 µm depression, shown in figure 10. Two adjacentprobes were used simultaneously. Figure 10 shows that thethermal images from the two probes are independent of eachother. Although the thermal images are not identical (variationin tip resistance and tip wear can cause differences in theobtained signal), it is clear that the movement of probe 2
into the basin does not affect the signal of probe 1. Both theline scan and the two-dimensional thermal images support astrong degree of mechanical decoupling over a 12 µm
topography.
It is instructive to compare the results obtained from themulti-probe array operating without mechanical feedback toUltracompliant thermal probe array for scanning non-planar surfaces without force feedbackothers obtained from single-shank probes fabricated by thesame process. The performance of these single probes using
three different kinds of interface circuits: an open-loop circuit
using a buffer and a filter (similar to the circuit used for themulti-probe array), a servo-controlled circuit that maintains
the probe temperature at a constant user-defined value, anda circuit that dithers the probe temperature and demodulates
the output signal to reduce electronic noise are described in[3, 14, 15]. As a point of comparison, figure 11 presents
a line scan of a patterned photoresist sample showing submicron lateral resolution. It was obtained at a scan speed of
10 µm s−1, using both force feedback as well as electronic
temperature control. The compromise in resolution that mightoccur individually due to the elimination of force feedback, thechange in scan speed, the change to a multi-probe geometry,etc, are context dependent. However, comparing the resultsthat are available, there it is evident that probes polyimideshank probes fabricated by the method described are capableof both high speed scanning and high resolution scanning.

5. Conclusions
This effort has demonstrated that a mechanically decoupledeight-probe array can be used for parallel, high-resolution
thermal mapping of features with large topographical variation
without force feedback. Elimination of feedback is enabled
by using ultracompliant probes that minimize contact force,
preventing damage to both the tip and fragile samples. In
non-feedback mode, 2 µm lateral features were resolved
at scan speeds up to 200 µm s−1 per probe, and 10 µm
features can be resolved even at 2 mm s−1. (These tests were
performed not to test the resolution of the device but rather,
the scanning speeds.) Noise limited MDS for topographicalvariations was found to be 80 nm, and the dynamic range
is >7 µm. In comparison, single-shank probes fabricatedby the same process can provide lateral spatial resolution<50 nm when operated with mechanical servo-control at scan
speeds of 10 µm s−1 and interfaced with appropriate low-noise
circuitry. These results suggest that there are good prospectsof obtaining images with high spatial resolution with themulti-probe device.

Acknowledgments
These devices were fabricated and tested at the SolidState Electronics Laboratory at the University of Michigan.
The authors gratefully acknowledge facilities support by thelaboratory staff, as well as the assistance of Mr Milind Chinoy
in assembling readout circuits.

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