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Sensors and Actuators A 130–131 (2006) 419–429
The mechanical properties of atomic layer deposited alumina for use inmicro- and nano-electromechanical systems
Marie K. Tripp a,b,∗, Christoph Stampfer a, David C. Miller b, Thomas Helbling a, Cari F.Herrmann b,c, Christofer Hierold a, Ken Gall e, Steven M. George c,d, Victor M. Bright b
a Micro and Nanosystems, ETH Zurich, CH-8092 Zurich, Switzerland b Department of Mechanical Engineering, University of Co lorado, Boulder, CO 80309, USA
c Department of Chemistry, University of Colorado, Boulder, CO 80309, USAd Department of Chemical Engineering, University of Co lorado, Boulder, CO 80309, USA
e School of Materials Science and Engineering and George Woodruff School of Mechanical Engineering,
Georgia Institute of Technology, Atlanta, GA 30332, USA
Received 7 June 2005; received in revised form 22 December 2005; accepted 13 January 2006Available online 28 February 2006
Abstract
Mechanical characterization of atomic layer deposited (ALD) alumina (Al2O3) for use in micro- and nano-electromechanical systems has been
performed usingseveral measurementtechniques including: instrumented nanoindentation, bulgetesting,pointer rotation, and nanobeamdeflection.
Using these measurement techniques, we determine Young’s modulus, Berkovitch hardness, universal hardness and the intrinsic in-plane stress
for ALD Al2O3. Specifically, measurements for ALD Al2O3 films deposited at 177 ◦C with thicknesses between 50 and 300 nm are reported. The
measured Young’s modulus is in the range of 168–182 GPa, Berkovitch hardness is 12.3 GPa, universal hardness is 8 GPa, and the intrinsic in-plane
stress is in the range of 383–474 MPa. Multiple measurements of the same material property from different measurement techniques are presented
and compared. ALD Al2O3 is an advantageous material to use over various forms of silicon nitride, for micro- and nano-electromechanical systems
due in part to the low deposition temperature that allows for integration with CMOS processing. Also, Al 2O3, unlike silicon nitride, has a high
chemical resistance to dry-chemistry Si etchants. Although ALD Al2O3 has recently been used as both a coating and a structural layer for micro-and nano-electromechanical systems, its mechanical properties were not previously described.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Alumina; Nano-electromechanical systems; Micro-electromechanical systems; Young’s modulus; Berkovitch hardness; Intrinsic stress
1. Introduction
The performance and reliability of micro- and nano-
electromechanical systems depends strongly on the mechanical
properties of the constituent materials. For example, elastic
modulus dictates the mechanical resonance of a vibrating micro-
cantilever while hardness controls the resistance to wear on the
contact surface of a sliding device. Other mechanical proper-
ties such as strength and residual stress distribution play central
roles in the prediction of device reliability under various load-
ing conditions. Low-dimension materials such as nanofilms and
∗ Corresponding author at: Intel Corporation, Portland Technology Develop-
ment, RA3-301, 2501 NW 229th Avenue, Hillsboro, OR 97124, USA.
Tel.: +1 971 214 0635; fax: +1 971 214 7811.
E-mail address: [email protected] (M.K. Tripp).
nanowires typically have mechanical properties different from
their bulkcounterparts, driven primarily by their inherentlylarge
surface area to volume ratio and their different material struc-
tures created by unique processing methods. It is thus impor-
tant to characterize the mechanical properties of low-dimension
materials processed by emerging technologically relevant meth-
ods.
In this work, we utilized a variety of measurement tech-
niques to study the mechanical properties of atomic layer
deposited (ALD) alumina (Al2O3) for use in micro- and nano-
electromechanical systems. Instrumented nanoindentation is
used to measure Young’s modulus, Berkovitch hardness and the
universal hardness of ALD Al2O3 grown on a silicon substrate.
Membrane bulge testing is used to measure Young’s modulus
and the intrinsic in-plane stress of monolithic ALD Al2O3 cir-
cular membranes. Passive pointer test structures areused to mea-
0924-4247/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.sna.2006.01.029
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420 M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429
sure the intrinsic in-plane stress of ALD Al2O3. Finally, atomic
force microscope (AFM)-based nanobeam deflection is used to
measure Young’s modulus on suspended ALD Al2O3 cantilever
beams. The multiple measurement techniques resulted in redun-
dantmeasurements of both modulus and intrinsic in-plane stress,
which are compared to verify accuracy.
Knowledge of the material property values of ALD Al2O3
films is important for the design of micro- and nano-
electromechanical systems, which can use ALD films as either
surface coatings or as structural layers. ALD is a deposition
process new to the field of micro- and nano-electromechanical
systems and may be utilized for various applications. Recently
ALD films have been applied to polysilicon microstructures as
protective coatings [1], creep suppression coatings [2], coatings
preventing diffusional-transport [3], wear resistant coatings [4],
and hydrophobic coatings [5]. ALD films have also been used
to fabricate membranes with lateral dimensions ranging from
hundreds to thousands of microns [6,7].
Since ALD Al2O3 was originally developed as a dielectric
gate oxide for microelectronics, the growth [8–12] and elec-tronic properties [13,14] of Al2O3 have beenstudied extensively.
However, the mechanical properties of ALD Al2O3 have not yet
been studied in detail. Understanding the mechanical properties
makes it possible to correctly design ALD Al2O3 micro- and
nano-electromechanical systems. A new Al2O3 NEMS fabrica-
tion process and preliminary material property value measure-
ments have been previously presented [15]. In this work, we
present new measurements from two additional measurement
techniques, as well as finalized results from those presented in
[15].
2. Methods
2.1. ALD Al2O3 growth
All of the measurements presented were performed on ALD
Al2O3 films grown using a viscous flow reactor described
in prior work [16]. The growth chemistry that occurs inside
the reactor relies on sequential, self-limiting surface reactions
between gas-phase precursor molecules and a solid surface,
to obtain atomic layer control of deposition [8,17], as shown
schematically in Fig.1. For Al2O3, filmgrowth proceeds accord-
Fig. 1. Schematic of atomic layer deposition (ALD) process flow [8].
ing to the two half reactions [8–11,17]
Al–OH∗+Al(CH3)3→ Al–O–Al(CH3)2∗+CH4 (A)
Al–CH3∗+H2O → Al–OH∗+CH4 (B)
where the asterisks designate the surface species. The reactants
trimethyl aluminum (Al(CH3)3) and water (H2O) are alternately
injected into the nitrogen carrier gas using computer-controlledpneumatic valves. The surface is first exposed to reactant A,
which reacts with all of the initial surface sites. Then, after
purging away the by-products from reaction (A), the surface
is exposed to reactant B. This reaction regenerates the initial
functional groups and prepares the surface for the next expo-
sure to reactant A. The film is grown to the desired thickness by
repeating this AB sequence. The reactant doses are pulsed into a
1 Torr ultrahigh purity nitrogen flow with a purge time between
each exposure. The dose time is 1 s and the purge time is 5 s.
The growth temperature is 177 ◦C for all experiments.
2.2. Instrumented indentation
Instrumented nanoindentation [18] was used to characterize
Young’s modulus, the Berkovitch hardness and the universal
hardness of ALD Al2O3. Nanoindentation is performed using a
Berkovitch tip on a DCM machine (MTS Systems Corporation).
Material properties are evaluated according to the Oliver–Pharr
method [18], which is used in conjunction with the continu-
ous stiffness method [19] to characterize specimens throughout
their thickness. Based on knowledge of the methods as well as
the standard deviation of the specimens, the nanoindentation
technique is accurate to within about 5–10% of the measured
values, being best when the results of multiple indentations are
averaged.
Specific details of the specimens and characterization are as
follows: Approximately 300 nm of Al2O3 is deposited onto a
0 0 1 silicon wafer at 177 ◦C. Immediately prior to indenta-
tion, the machine is calibrated using fused silica with the area
coefficients for the tip determined according to the procedure
described in [18]. The sink-in parameter, ε, is assumed to be
0.75 and the geometry factor, β, is assumed to be 1.05, based on
recent investigations [20]. Indents are made up to the depth of
100 nm at the constant (loading) strain rate of 0.05 s−1. A set of
20 indents are performed in a two-dimensional array ( x - and y-
spacing of 100m) across the specimen. Because of the effects
of substrate compliance, common to thin film specimens, thematerial property values areaveraged between 30 and50 nm into
the specimen, i.e.∼10% of the film thickness. A typical loading
profile (see Fig. 2) demonstrates the characteristic indentation
profile for the material, including a 30 s “creep hold” at the max-
imum load as well as a 30 s “thermal drift hold” at 10% of the
maximum load.
2.3. Membrane bulge testing
Bulge testing is another widelyused technique for the charac-
terization of thin film mechanical properties [21,22]. Measure-
ments of the load-deflection behavior of a thin film membrane
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Fig. 2. Example of indentation profile and measured modulus for ALD Al2O3.
The indentation consists of loading, creep hold, unloading, and thermal drift
segments. Using the continuous stiffness method, modulus can be determined
at any depth during loading.
enable extractions of the mechanical material propertiesYoung’smodulus, E , and the intrinsic in-plane stress, σ . In the experi-
mental setup, a differential pressure is applied to ALD Al2O3
membranes and the deflection is measured using a white light
interferometer (ZYGO New View 5020). Since the measured
deflection w0 of the membrane is small compared to the diame-
ter d 0, (w0 d 0), and the thickness t smaller than the deflection
w0, (t < w0), the membrane deforms in the large deflection
regime [23]. Curve fitting of the pressure-deflection measure-
ments is performed using the model for large deflection of a
circular membrane by Small and Nix [22] given by
p(w0
) =(7− ν)Et
3(1− ν)r4w3
0+
4tσ 0
r2 w
0 (1)
where ν is the Poisson’s ratio, E the Young’s modulus, t the
thickness and r is the radius of the Al2O3 membrane. The equa-
tion assumes that the initial intrinsic stress is equibiaxial, and
that no significant intrinsic through-thickness strain gradient
exists. Previous work has demonstrated that indeed no signif-
icant through-thickness strain exists, so long as specimens are
fabricated properly [26]. Rectangular membranes with various
aspect ratios would be superior to circular membranes for an
additional extraction of the Poisson’s ratio [24]. The extraction
of the Poisson’s ratio was not intended in this work.
For this experiment, bulk micromachining was used to fabri-
cate 100 nm thick circular Al2O3 membranes that are clampedalong the edge. The fabrication process is shown in Fig. 3, and
a detailed description is given in [25]. First the 100 nm thick
Al2O3 membrane layer is grown on a 1 0 0 Si substrate using
ALD (see Fig. 3(a)). Because of the conformal nature of ALD
coating, the Al2O3 thickness is the same on all surfaces of the
substrate. Openings are patterned in the ALD Al2O3 layer on the
backside of the sample, using standard ultraviolet photolithog-
raphy, to create an Al2O3 hard mask. The hard mask, located on
the backside of the sample, is patterned by inductively coupled
plasma dry etching (see Fig. 3(b)). The subsequent formation
of the cavities is performed by an anisotropic dry etching step
using the BOSCH process (see Fig. 3(c)). The BOSCH process
Fig. 3. Process flow to fabricate the Al2O3 membrane: (a) 100 nm of ALDAl2O3 are grown on a Si substrate, (b) the membrane openings are patterned
using standard photolithography, (c) substrate removal using anisotropic dry
etched from the backside, (d) the membrane is mechanically released, and (e) a
schematic of a final thin-film membrane.
is stopped when a few microns of bulk Si remain. The circular
membranes are released with an isotropic reactive ion dry etch
process that is optimized to avoid damaging the ultrathin Al2O3
membrane (see Fig. 3(d)). In Fig. 3(e) a schematic cross section
of the Al2O3 membrane is shown. For the bulge test measure-
ments, the membranes are placed in a pressure setup that enables
concurrent in situ white light interferometer measurements and
differential pressure measurements.
2.4. Pointers
Passive pointer structures may be used to measure intrinsic
in-plane stress, since they will mechanically deform (rotate) in
proportion to this stress. The fabrication process used to make
pointer structures is shown schematically in Fig. 4(a–g) and is
discussed in detail in [26]. First, 1 0 0 silicon substrates are
diced and cleaned in preparation for ALD Al2O3 coating. The
final cleaning step is 15 min in 5% hydrofluoric (HF) acid to
remove the native oxide immediately before ALD. The Al2O3
structural layer is grown on a silicon substrate using ALD (seeFig. 4(a)). Next approximately 440 nm of nitrogen rich silicon
nitride (SiN x ) is grown using plasma enhanced chemical vapor
deposition (see Fig. 4(b)). SiN x is to become the mask for pat-
terning the Al2O3 layer. Polymethyl methacrylate (PMMA), an
electron beam sensitive polymer, is spin coated, patterned using
electron beam lithography and developed. The PMMA layer is
now ready to serve as a mask for etching the SiN x layer (see
Fig. 4(c)). Reactive ion etching is used to pattern the SiN x layer
using the PMMA mask (see Fig. 4(d)). After reactive ion etch-
ing, the PMMA mask is removed using acetone at 50 ◦C in an
ultrasonic bath and the SiN x mask is ready for patterning the
Al2O3 layer (see Fig. 4(e)). Inductively coupled plasma reactive
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422 M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429
Fig. 4. Fabrication process flow for atomic layer deposited (ALD) alumina
(Al2O3) NEMS (not drawn to scale): (a) Si wafer (t =500 m) coated with
ALD Al2O3 (t = 100 nm), (b) PECVD deposited SiN x , (c) spin, PMMA, pattern
with e-beam lithography and develop, (d) CHF3 /O2 etch to pattern SiN x , (e)
remove PMMA, (f) Cl2 etch to pattern Al2O3, and (g) SF6 etch to remove SiN x
and under-etch Al2O3.
ion etching is used to pattern the Al2O3 with the SiN x mask (see
Fig. 4(f )). The final step removes the SiN x mask and undercuts
the Si below the Al2O3 structures (see Fig. 4(g)) using sulfur
hexafluoride-based isotropic reactive ion etching. With this pro-
cess, Al2O3 structures ranging in thickness from 50 to 100 nm
with lateral features ranging from 100 nm to 100m in size have
been fabricated.A variety of pointer test structures were fabricated to char-
acterize deformation generated by the intrinsic in-plane stress.
Fig. 5(a) is a drawing of a pointer structure, which may be used
to relate displacement to intrinsic in-plane stress as [27]
σ =EOy
(1 − ν)(LA +LB)(LC + 0.5O)
1
Cf (2)
where O, LA, LB, and LC are given in Table 1, E = 180 GPa
is the Young’s modulus of alumina from the nanoindentation
measurements discussed previously, ν = 0.24 [28] the assumed
Poisson’s ratio, σ the stress, y the displacement of the pointer
and C F is the a correction factor. Eq. (2) assumes that the strain
Fig. 5. (a) A schematic of a pointer test structure [27], (b) close up micrograph
of a displaced pointer tip.
distribution through the thickness of the material is uniform, the
strain is equibiaxial for the in-plane directions, and that the other
material properties are known.
Fig. 6 shows a scanning electron microscope (SEM) (Zeiss
Gemini 1530 FEG) image of a suspended ALD Al2O3 pointer
structure. The dimensions of this pointer are; t =100nm,
bp = 1m, LC = 13.5m, LA = LB = 10m, and O = 1m. Four
different geometries of pointers were fabricated and examined.
Table 1 summarizes the measured geometries of the four dif-
ferent pointers. A hinge is created by thinning the beam with
where the two anchored specimen arms connect to the indica-
tor beam (see Fig. 6). The correction factors, which take into
account the non-idealities of the hinges and the undercut at the
ends of the specimen arms, are calculated using finite element
Table 1
A summaryof the measureddimensions for the fourdifferent pointer geometries
Pointer A Pointer B Pointer C Pointer D
LA (m) 9.9 10 9.9 10
LB (m) 9.9 10 9.9 10
LC (m) 13.5 13.5 13.5 12.5
bp (m) 0.8 1 0.8 1
O (m) 0.8 1 1 2
C f 0.64 0.66 0.74 0.93
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M.K. Tripp et al. / Sensors and Actuators A 130–131 (20 06) 419–42 9 423
Fig. 6. An SEM image of a pointer structure with dimensions t = 100 nm,
bp = 1m, LC = 13.5m, LA = LB = 10m, and O = 1m. The arrows highlight
the hinges upon which the structure will rotate.
models (ANSYS) and are found to be the same for both thick-
nesses (50 and 100 nm) of Al2O3. This is as expected, since the
hinge width to thickness ratios are roughly the same for both
thicknesses. The deflection of the pointer tip y was measured by
examining SEM images, such as the one shown in Fig. 5(b), andcombined with Eq. (2) yielding the intrinsic in-plane stress.
2.5. Nanobeam deflection
Using the same fabrication process as for the pointers, a set
of cantilever beams were created for nanobeam deflection mea-
surements. For the nanobeam tests, an atomic force microscope
(AFM) in tapping mode was used to image the suspended Al2O3
cantilever structures (see e.g. Fig. 7(b)), and the AFM in force
mode was used to measure the force versus deflection profile
[29]. The nanobeam bending experiments consist of a series of
force versus deflection measurements (e.g. Fig. 7(c)) performed
as a function of the contact point x , which is defined as the point
where the AFM deflects the cantilever (see insert in Fig. 7(a)).
In this study, the contact point was made to vary along the length
of the beams. By evaluating the force versus deflection measure-
ments, the deflection of the Al2O3 cantilever at a constant force
is extracted. The total spring constant k tot = kk AFM /(k + k AFM) is
a function of the givenAFM cantilever spring constant k AFM and
the spring constant k ( x ) of the Al2O3 cantilever. Also, the force
versus deflection measurement is restricted to the small deflec-
tion regime in order to apply Euler–Bernoulli beam theory [30]to extract the Young’s modulus of the investigated material. In
Fig. 7. AFM-based nanobeam deflection measurements. (a) Deflection ( z) vs. contact point x (i.e. force vs. displacement measurements) performed on Al2O3
cantilevers (l = 5m and w = 1m) with two different geometries (thickness t = 50 nm [triangles] and t = 100nm [circles]). The solid lines plot the result of the
elastic beam theory (see Eq. (3) in text), (b) shows an SEM image (top view) of the 100 nm thick Al2O3 cantilever, which has been measured, and (c) shows a
characteristic force vs. deflection measurement.
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424 M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429
the framework of elastic beam theory, a point load F acting on
the contact point x leads to the following deflection z:
z(x) =12
3
Fx3
Ewt 3 (3)
where E is the Young’s modulus, w the width, t the thickness
of the cantilever and x is the contact point. The inverse of Eq.
(3) can be used to extract Young’s modulus from the measured
data.
3. Measurements
3.1. Indentation
From indentation, the elastic modulus, corrected
(Berkovitch) hardness and universal hardness are found
to be 180.0± 8.2 GPa, 12.3± 1.0 GPa and 8.0± 0.5 GPa,
respectively. Universal hardness is defined as the instantaneous
ratio of the applied load over the area of the indentation, and
does not account for the geometric sinking-in of the indentationsite or recoverable elastic deformation. The retained energy
ratio, which compares the deformed shape of the indent to total
indentation profile, is 58.2±0.7%, suggesting that a significant
portion (∼40%) of the work occurring during indentation is
elastic. The sink-in ratio, defined as the ratio of the depth of
indentation upon exiting the sample to the maximum indenta-
tion depth, is 59.1±2.4%. The sink-in ratio is less than 70%,
suggesting the absence of pile-up around the indenter, which is
known to cause error in measurement [18]. Fig. 2 demonstrates
the measured modulus throughout the loading profile. In this
case, the modulus converges to a relatively stable value at
about 30 nm into the specimen. The parameters of hardness,P / S 2 [31], and K [32] also remained well converged beyond
the depth of 30 nm, lending validity to the measurements and
suggesting that the modulus of the substrate is reasonably
well-matched to the Al2O3 film. Note that the parameter P / S 2,
here 3.18× 10−4±1.14× 10−5 GPa−1, may be used to relate
the material’s modulus and hardness, irrespective of the area
(calibration) of the indentor tip [31]. The parameter K , here
364.1± 23.4 GPa, may be used to estimate the amount of
elastic or inelastic deformation occurring during the indentation
loading curve [32]. The parameter K is related to an idealized
power-law fit of the P / h loading profile and is not related to the
stiffness of the specimen, machine compliance, etc. Lastly, no
excursions are seen in the load/displacement curve that wouldindicate fracture or other aberrant activity.
3.2. Membrane bulge testing
A set of load-deflection measurements, from a circular Al2O3
membrane, are shown in Fig. 8. Data was obtained in both load-
ing and unloading, i.e. trace–retrace. One set of measurement
data is shown for the deflection w0 of a circular membrane
versus the applied differential pressure p. For simplicity, only
the trace (loading) measurement data is shown. The extracted
Young’s modulus and the intrinsic in-plane stress are found
as E =181± 20 GPa and σ = 383±27 MPa. These results are
Fig. 8. Measurements of the deflection w0 vs. an applied differential pressure p.
The measured data points (circles) are fitted with a model for large deflection of
circular membranes. Fromthat fitting, the material parametersYoung’s modulus
E and intrinsic stress is σ are extracted.
derived assuming a Poisson’s ratio value of ν = 0.24 [28]. The
diameter of the membrane is measured as d 0 = 202.3m, the
deposited thickness of the ALD Al2O3 layer is t = 100 nm, as
measured during deposition with a quartz crystal microbalance.
The error calculation for the extraction of the Young’s modu-
lus and the intrinsic in-plane stress accounts for three sources of
errors: instrumental errors, geometric errors and measurement
errors. The high precision pressure sensor (Burster 8263-100)
and the white light interferometer have inherent instrumenta-
tion error. The pressure sensor has a maximal absolute error
of 450 Pa, i.e. 0.065% of the maxim loading pressure value of
100 psi. The white light interferometer has a lateral (in-plane)
error of 0.69 m and a vertical (through-thickness) error of 0.4 nm. Geometric errors are found in the thickness t of the
membrane. The thickness is measured for various membranes
using spectroscopic ellipsometry (SENTECH SE850) with an
estimated error of 4 nm. Measurement errors are given as the
standard deviation of the measured pressure-deflection points
and the curve fitting to these points. The material parameters are
quantified using standard error propagation analysis.
3.3. Pointers
Thepointersexaminedare from two differentfabricationruns
on five different silicon substrates, with between 1 and 3 point-ers measured in different areas on a single substrate. Pointers
oriented in orthogonal directions, but fabricated on the same
substrate were measured. A total of 33 pointers were imaged
using an SEM so that their displacements could be measured
resulting in σ = 474± 70 MPa and σ = 427±34 MPa for 50 and
100 nm thick films, respectively. Measurement of the pointer tip
displacement is done manually using a ruler to measure the dis-
placedstructure on a printed image.The SEMimages were better
resolved for the 100 nm thick Al2O3 than for the 50 nm thick
Al2O3. The accuracy of the measured displacement is given for
each of the four different pointer designs in Table 2. The result-
ing average error due to measurements is±34 and±70 MPa for
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M.K. Tripp et al. / Sensors and Actuators A 130–131 (20 06) 419–42 9 425
Table 2
A summary of the measurement error and corresponding error in stress for the four different pointer structures
Error Pointer A Pointer B Pointer C Pointer D Average
y (100nm) (m) ±0.025 ±0.025 ±0.025 ±0.025 ±0.025
σ (100 nm) (MPa) ±27 ±32 ±29 ±47 ±34
y (50nm) (m) ±0.05 ±0.05 ±0.05 ±0.05 ±0.05
σ (50 nm) (MPa) ±54 ±64 ±57 ±95 ±67
100 and 50nm thick Al2O3, respectively. The standard deviation
of measurements matches closely the calculated measurement
error.
Variation of stress between different specimens is thought to
depend most upon error in measurements, i.e. imaging and data
extraction. Variation in stress across the film and across different
depositions is smaller than the resolution of our measurements,
i.e. ±70 MPa. Measurement resolution could be improved by
incorporating a vernier gauge on the end of the pointer as a
reference for more accurate readings.
3.4. Nanobeam deflection
Fig. 7(a) shows the experimental data of the deflection z of
a 50 and 100 nm thick Al2O3 cantilever (w = 1 m, l = 5m;
see Fig. 7(b)) as a function of the contact point x at a constant
loading force, F = 30 nN. The maximum measured deflection z
of the 100 nm (50 nm) thick cantilever is in the range of 85 nm
(100 nm), which is still in the small deflection regime (radius of
curvature R z)since Rmax = 156m 85nmforthe100nm
thickcantilever and 41m 100 nmfor the 50 nmversion. This
corresponds to a maximum bending angle of 1.9◦ and3.4◦ for the
100 and 50 nm cantilevers, respectively. In both cases, assuming
that the Euler–Bernoulli linear-elastic beam theory [30] applies,
the error is estimated to be less than 1% [30]. Prior to testing, the
AFM cantilever spring constant was calibrated using a thermal
noise method [33], where AFM cantilever displacement mea-
surements of the thermal fluctuations are performed near the
resonant frequency of the cantilever. The spring constant of the
AFM cantilever is found to be k AFM = 8.85 nN/nm. In order to
avoid large non-linear deflections of the cantilevers, the mea-
surementswere restricted (i.e. triggered) using a maximum force
F max of 100 nN. Finally, the regression fit to the measured data
(see Fig.7(a)) leads to a Young’s modulus of E =168± 8GPafor
the 100 nm thick cantilever and E =182±32 GPa for the 50 nm
thick cantilever. The measurements were performed on four dif-
ferent structures. Moreover, Fig. 7(a) confirms the elastic beam
model (solid lines) for the two measured geometries, which are
compared with the experimental data.
4. Discussion
As seen in Table 3, the results are found to be compara-
ble with those previously published for other amorphous Al 2O3
deposition techniques. Although indentation has the least sig-
nificant error, all of our measurements of Young’s modulus
are the same, within the range of error, and in agreement with
previously reported values. Our measurements apply to Al2O3
fabricated using ALD, a technique which has not previously
been subject to mechanical characterization. Additionally, uni-
form material property values were measured for indentation
depths between 50 and 100 nm, such that Young’s modulus can
be considered constant throughout this range. The Berkovitch
hardness is slightly higher than those reported by Moody et al.
[34] f or similar ALD films. One possible explanation for this dif-
ference is that the previous work was performed using an older
Table 3
A summary of Al2O3 properties presented in literature as well as those measured in this work
Deposition process Measurement techniques T (◦C) t (nm) E (GPa) σ (MPa) BH (GPa) UH (GPa) Reference
ALD NI 177 300 180.0± 8.2 12.3± 1.0 8.0± 0.5 TW
ALD BT 177 100 181± 20 383± 27 TW
ALD PR 177 100 427± 34 TW
ALD PR 177 50 474± 70 TWALD NBD 177 100 168± 8 TW
ALD NBD 177 50 182± 32 TW
ALD NI 100 300 150–155 8 [37]
ALD NI 177 169± 19 8.8± 1.7 [34]
Evaporation WC 170 0–700 564 [35]
Evaporation WC 200 0–700 272± 25 331 [35]
AO TM 100 100 195–380 [38]
PVD NI 150 9.5 [39]
ECR plasma NI 170 177 9.6 [40]
Evaporation NI 160–180 [41]
AO NI 160 [41]
The symbols used in the table stand for anodic oxidation (AO), Berkovitch hardness (BH), bulge testing (BT), Young’s modulus ( E ), electron–cyclotron resonance
(ECR), thickness (t ), nanobeam deflection (NBD), nanoindentation (NI), pointer rotation (PR), physical vapor deposition (PVD), stress ( σ ), temperature (T ),
tensilometer (TM), this work (TW), universal hardness (UH), and wafer curvature (WC).
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426 M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429
Table 4
A comparison of Al2O3 stress with silicon nitride (Si x N y) for MEMS applications
Deposition techniques Material Measurement techniques t (nm) T (◦C) σ (MPa) Reference.
ALD Al2O3 PR 100 177 427± 34 (T) TW
ALD Al2O3 PR 50 177 474± 70 (T) TW
LPCVD Si x N y BT 500 PolyMUMPs 114–130 (T) [42]
LPCVD Si x N y PR 150–500 850 125–967 (T) [43]
LPCVD Si x N y BT 2000 800 98 (T) [44]
LPCVD Si x N y WC 4–20 780–840 1000 (T) [45]
LPCVD Si x N y BT 100–300 790 1000 (T) [46]
LPCVD Si x N y BT ∼290 785 120–150 (T) [24]
LPCVD Si x N y MBT ∼760 840 291 (T) [47]
PECVD Si x N y WC 320–380 180 (C) [45]
PECVD Si x N y BT 500 300 110 (C) [46]
PECVD Si x N y WC, XRD ∼1000 400 150–1610 (C) [48]
BT: bulge testing; C: compressive; LPCVD: low-pressure chemical vapor deposition; MBT: microbridge test; PECVD: plasma enhanced chemical vapor deposition;
PR: pointer rotation; t : thickness, T : temperature; T: tensile; TW: this work; WC: wafer curvature; XRD: X-ray diffraction.
MTS Systems Corporation Nano II indentation machine, which
is not as accurate at the small indentation depths required forALD specimens.
The values for the intrinsic in-plane stress presented here are
slightly higher than those presented earlier in [15]. This increase
is because we used a more accurate value for Young’s modulus
( E = 180 GPa) in calculations of Eq. (2). Proost and Saepen [35]
show the average stress for film thicknesses ranging from 0 to
700nm is constant fora given temperature for evaporated Al2O3.
Our results, based on three fabrication runs and two different
film thicknesses, also suggest the intrinsic stress is relatively
unaffected by the thickness of the ALD fabricated material. Fol-
lowing the work of Proost and Saepen [35], it may be possible to
reduce the magnitude of intrinsic in-plane stress by increasing
the deposition temperature. In this case, stress due to thermal
mismatch will be higher for a higher deposition temperature
upon cooling to ambient temperature. Adatom mobility, how-
ever, will also be greater at elevated deposition temperature,
which can have a more significant effect on the overall in-plane
stress than thermal mismatch. A more detailed study of how the
intrinsic in-plane stress varies for different deposition parame-
ters, including changes in temperature and flow rates, of Al 2O3
is neededto improve the growth process for usein various micro-
and nano-electromechanical systems applications.
Table 4 compares ALD Al2O3 with various types of silicon
nitride (Si x N y). Since very little work has been done using ALD
Al2O3 as a structural material, Si x N y is presented as a referencematerial because of its similar material properties. Even with-
out performing any optimization to the deposition process, the
intrinsic stress for ALD Al2O3 is comparable to that of Si x N y
deposited at conditions optimized for stress reduction.
ALD Al2O3 has similar electrical properties to various com-
positions of PECVD or LPCVD Si x N y, and can be used for
many of the same micro- and nano-electromechanical systems
applications. Yet, ALD Al2O3 offers the advantage of its low
deposition temperature [36], which readily allows for integration
with CMOS processing. It also has a high chemical resistance
to gas-phase Si etchants. Instead of KOH, which is commonly
used to selectively etch Si relative to Si x N y, SF6 or CHF3, dry
chemistries can be used to mechanically release ALD Al2O3
structures. Dry etching is advantageous over liquid etching forthe release of long thin structures, where surface forces asso-
ciated with the hydrophilic interaction between the structures
and the liquid meniscus can cause surface driven adhesion, i.e.
“stiction”. Such forces can also prevent the liquid from entering
small features, inhibiting their mechanical release, and there-
fore limiting the minimum feature size. ALD Al2O3 surfaces are
typically less hydrophobic than bare silicon surfaces. Lastly the
hardness of Al2O3 (∼12 GPa) is not as large as typical Si x N y
films (∼30 GPa), however it is observed to be comparable to
that of silicon itself (∼12 GPa). High hardness is of advan-
tage in tribological applications, where the rate of wear may be
reduced.
ALD Al2O3 has many other properties that make it attractive
as a new material for micro- and nano-electromechanical sys-
tems. It is amorphous and has been shown to consistently be a
pinhole-free, uniform layer with a precise known thickness and
a roughness equal to or lower than the surface of the substrate
[8]. Additionally, ALD allows for excellent conformal growth
on all exposed surfaces. Investigations have been performed to
demonstrate the ability of ALD to coat uniformly high aspect
ratio trench structures [9]. Although Al2O3 is not conductive, it
can be doped with varying amounts of zinc oxide (ZnO) [14,37],
to produce a conductive surface coating. This method allows the
possibility of tuning the electrical and/or mechanical properties
of the material.These initial results improve theunderstanding of ALDmate-
rials for use in micro- and nano-electromechanical systems. The
material properties presented here are for films that have been
optimized for maximum growth rate on silicon. Yet, many Si x N y
films exhibiting comparable properties, such as residual stress,
have been previously optimized for mechanical properties. Opti-
mizing the growth process for lower values of in-plane stress is
one step that must be taken. Additionally, further mechanical
characterization of ALD Al2O3 /ZnO composites would allow
tunable electrical and mechanical properties to be accounted
for in device design. This will expand the possible applica-
tions beyond those already envisioned which use ALD as either
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M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429 427
a coating or as structural layer, including the fields of ultra-
sonic transducers, pressure sensors, RF MEMS, and optical
MEMS.
5. Conclusion
We used indentation, bulge testing, pointer rotation, andnanobeam deflection to measure the mechanical properties of
ALD Al2O3. Measured mechanical properties include Young’s
modulus, Berkovitch hardness, universal hardness and intrin-
sic in-plane stress. Our measurements are in agreement with
one another as well as with previously published results for
amorphous Al2O3 from other growth methods. With knowl-
edge of the material properties, intelligent design of micro- and
nano-electromechanical systems that use ALD Al2O3 as either
a coating or as a structural layer is possible. Further work is nec-
essary to optimize the ALD Al2O3 growth process for improved
mechanical properties. Finally, further mechanical characteri-
zation of Al2O3 /ZnO composites may allow both mechanical
tuning and electrical tuning of the materials, in turn expanding
the range of applications for ALD materials.
Acknowledgments
The authors wish to thank Alain Jungen and Debajyoti
Sarangi, Frank DelRio, Katrin Sidler, Otte Homan, Robert
Wueest, and Patric Strasser. The CAMPmode Industrial Advi-
sory Board, NSF, IGERT: 1530112, DARPA/MTO Grant no:
NBCH1040003, DGE-9870665 and the Air Force Office of
Scientific Research are gratefully acknowledged for their finan-
cial support. Support by the ETH FIRST Lab and finan-
cial support by the ETH Zurich (TH-18/03-1) are gratefullyacknowledged.
References
[1] N.D. Hoivik, J.W. Elam, R.J. Linderman, V.M. Bright, S.M. George,
Y.C. Lee, Atomic layer deposited protective coatings for micro-
electromechanical systems, Sens. Actuators A 103 (2003) 100–108.
[2] Y. Zhang, M.L. Dunn, K. Gall, J.W. Elam, S.M. George, Deforma-
tion of nanocoated thin film microstructures, J. Appl. Phys. 95 (2004)
8216–8225.
[3] D.C. Miller, C.F. Herrmann, H.J. Maier, S.M. George, C.R. Stoldt,
K. Gall, Intrinsic stress development and microstructure evolution of
Au/Cr/Si multilayer thin films subject to annealing, Scripta Mat. 52(2005) 873–879.
[4] T.M. Mayer, J.W. Elam, S.M. George, P.G. Kotula, Atomic layer deposi-
tion of wear-resistant coatings for micromechanical devices, Appl. Phys.
Lett. 82 (2003) 2883–2885.
[5] C.F. Herrmann, F.W. DelRio, V.M. Bright, S.M. George, Conformal
hydrophobic coatings prepared using atomic layer deposition seed layers
and non-chlorinated hydrophobic precursors, J. Micromech. Microeng.
15 (2005) 984–992.
[6] M.K. Tripp, C.F. Herrmann, S.M. George, V.M. Bright, Ultra-thin mul-
tilayer nanomembranes for short wavelength deformable optics, in: Pro-
ceedings of the 17th IEEE Conference on Micro Electro Mechanical
Systems (MEMS 2004), Maastricht, The Netherlands, January 25–29,
2004, pp. 77–80.
[7] L.L. Liu, O.M. Mukdadi, M.K. Tripp, C.F. Herrmann, J.R. Hertzberg,
S.M. George, V.M. Bright, R. Shandas, Atomic layer deposition for
fabricating capacitive micromachined ultrasonic transducers: initial char-
acterization, in press.
[8] S.M. George, A.W. Ott, J.W. Klaus, Surface chemistry for atomic layer
growth, J. Phys. Chem. 100 (1996) 13121–13131.
[9] M. Ritala, M. Leskela, J. Dekker, C. Mutsaers, P. Soinonen, J. Sharp,
Perfectly conformal TiN and Al2O3 films deposited by atomic layer
deposition, Chem. Vapor. Depos. 5 (1999) 7–9.
[10] A.C. Dillon, A.W. Ott, J.D. Way, S.M. George, Surface chemistry
of Al2O3 deposition using Al(CH3)3 and H2O in a binary reactionsequence, Surf. Sci. 322 (1995) 230–242.
[11] A.W. Ott, J.W. Klaus, J.M. Johnson, S.M. George, Al2O3 thin film
growth on Si (1 0 0) using binary reaction sequence chemistry, Thin
Solid Films 292 (1997) 135–144.
[12] J.W. Elam, S.M. George, Growth of ZnO/Al2O3 alloy films using atomic
layer deposition techniques, Chem. Mater. 15 (2003) 1020–1028.
[13] M.D. Groner, J.W. Elam, F.H. Fabreguette, S.M. George, Electrical
characterization of thin Al2O3 films grown by atomic layer deposition
on silicon and various metal substrates, Thin Solid Films 413 (2002)
186–197.
[14] J.W. Elam, D. Routkevitch, S.M. George, Properties of ZnO/Al2O3 alloy
films grown using atomic layer deposition techniques, J. Electrochem.
Soc. 150 (2003) G339–G347.
[15] M.K. Tripp, C. Stampfer, C.F. Herrmann, S.M. George, C. Hierold, V.M.
Bright, Low stress atomic layer deposited alumina for nano electrome-
chanical systems, in: Proceedings of the 13th International Conference
on Solid-State Sensors, Actuators and Microsystems (Transduers 2005),
Seoul, Korea, June 5–9, 2005, pp. 851–854.
[16] J.W. Elam, M.D. Groner, S.M. George, Viscous flow reactor with quartz
crystal microbalance for thin film growth by atomic layer deposition,
Rev. Sci. Instrum. 73 (2002) 2981–2987.
[17] M. Ritala, M. Leskela, Atomic layer deposition chemistry: recent devel-
opments and future challenges, Angew. Chem. Int. Ed. 42 (2003)
5538–5554.
[18] W.C. Oliver, G.M. Pharr, Measurement of hardness and elastic modulus
by instrumented indentation: advances in understanding and refinements
to methodology, J. Mater. Res. 19 (2004) 3–20.
[19] D.L. Joslin, W.C. Oliver, A new method for analyzing data from con-
tinuous depth-sensing microindentation tests, J. Mater. Res. 5 (1990)
123–126.
[20] J.H. Strader, S. Shim, H. Bei, W.C. Oliver, G.M. Pharr, An experimental
evaluation of the constant relating the contact stiffness to the con-
tact area in nanoindentation, Proc. Mater. Res. Soc. Symp. 841 (2005)
R1.4.1–R1.4.6.
[21] J.S. Mitchell, C. Zorman, T. Kicher, S. Roy, M. Mehregany, Examina-
tion of bulge test for determining residual stress, Young’s modulus and
Poisson’s ratio of 3c-SiC thin film, J. Aerospace Eng. 16 (2003) 46–54.
[22] M.K. Small, W.D. Nix, Analysis of the accuracy of the bulge test in
determining the mechanical properties of thin films, J. Mater. Res. 7
(1992) 1553–1563.
[23] S.P. Timoshenko, S. Woinowsky-Krieger, Theory of Plates and Shells,
2nd ed., McGraw Hill, New York, 1959.
[24] J.J. Vlassak, W.D. Nix, A new bulge test technique for determining
Young’s modulus and Poisson’s ratio of thin films, J. Mater. Res. 12
(1992) 3242–3249.
[25] T. Helbling, Fabrication of single walled carbon nanotube based pressure
sensor, Master Thesis, ETH Zurich, Zurich, Switzerland, 2005.
[26] M.K. Tripp, Atomic layer deposited thin films for micro- and nano-
electromechanical systems with applications in short-wavelength adap-
tive optics, PhD Dissertation, University of Colorado, Boulder, Colorado,
USA, 2005, Appendix D.
[27] B.P. van Drieenhuizen, J.F.L. Goosen, P.J. French, R.F. Wolffenbuttel,
Comparison of techniques for measuring both compressive and tensile
stress in films, Sens. Actuators A 37/38 (1993) 756–765.
[28] G. Simmons, H. Wang, Single Crystal Elastic Constants and Calculated
Aggregate Properties: A Handbook, 2nd ed., M.I.T. Press, Cambridge,
Massachusetts, 1971, p. 146.
[29] B. Bhushan, Handbook of Nanotechnology, Springer-Verlag, New York,
2004, p. 66.
7/21/2019 The Mechanical Properties of Atomic Layer Deposited Alumina for Use in Mems and NemsTripp2006
http://slidepdf.com/reader/full/the-mechanical-properties-of-atomic-layer-deposited-alumina-for-use-in-mems 10/11
428 M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429
[30] A.N. Cleland, Foundations of Nanomechanics, Springer-Verlag, New
York, 2003.
[31] T.F. Page, G.M. Pharr, J.C. Hay, W.C. Oliver, B.N. Lucas, E. Herbert,
L. Riester, Nanoindentation characterization of coated systems: P / S 2—a
new approach using the continuous stiffness technique, Proc. Mater. Res.
Soc. Symp. 522 (1998) 53–64.
[32] M.R. McGurk, T.F. Page, Using the P–δ2 analysis to deconvolute the
nanoindentation response of hard-coated systems, J. Mater. Res. 14
(1999) 2283–2295.[33] L.-O. Heim, M. Kappl, H.-J. Butt, Tilt of atomic force microscope can-
tilevers: effect on spring constant and adhesion measurements, Langmuir
20 (2004) 2760–2764.
[34] N.R. Moody, T.E. Buchheit, B.L. Boyce, S. Prasad, T.M. Mayer, S.M.
George, Thickness effects on the mechanical behavior of ALD film, in:
Presented at the MRS Spring Meeting, San Francisco, CA, USA, April
12–16, 2004.
[35] J. Proost, F. Spaepen, Evolution of the growth stress, stiffness, and
microstructure of alumina thin films during vapor deposition, J. Appl.
Phys. 91 (2002) 204–215.
[36] M.D. Groner, F.H. Fabreguette, J.W. Elam, S.M. George, Low-
temperature Al2O3 atomic layer deposition, Chem. Mater. 16 (2004)
639–645.
[37] C.F. Herrmann, F.W. DelRio, S.M. George, V.M. Bright, Properties of
atomic layer deposited Al2O3 /ZnO dielectric films grown at low temper-
atures for RF MEMS, in: Proceedings of the SPIE on Micromachining
and Microfabrication Process Technology X, vol. 5715, January, 2005,
pp. 159–166.
[38] R.W. Hoffman, Nanomechanics of thin films: emphasis: tensile proper-
ties, MRS Symp. 130 (1989) 295–305.
[39] T.C. Chou, T.G. Neih, S.D. McAdams, G.M. Pharr, Microstructures and
mechanical properties of thin films of aluminum oxide, Scripta Mater.
25 (1991) 2203–2208.
[40] J.C. Barbour, J.A. Knapp, D.M. Follsteadt, T.M. Mayer, K.G. Minor,
D.L. Linam, The mechanical properties of alumina films formed by
plasma deposition and by ion irradiation of sapphire, Nucl. Instrum.
Methods Phys. Res. B 166/167 (2000) 140–147.
[41] N.G. Chechein, J. Bøttiger, J.P. Krog, Nanoindentation of amorphous
aluminum oxide films III. The influence of the substrate on the elastic
properties, Thin Solid Films 304 (1997) 70–77.
[42] R.L. Edwards, G. Coles, W.N. Sharpe Jr., Comparison of tensile and
bulge tests for tensile silicon nitride films, Exp. Mech. 44 (2004) 49–54.
[43] P.J. French, P.M. Sarro, R. Mallee, E.J.M. Fakkeldij, R.F. Wolffenbut-
tel, Optimization of a low-stress silicon nitride process for surface-
micromachining applications, Sens. Actuators A 58 (1997) 149–157.
[44] M. Sekimoto, H. Yoshihara, T. Ohkubo, Silicon nitride single-layer X-
ray mask, J. Vac. Sci. Technol. 24 (1982) 1017–1021.
[45] M. Stadtmueller, Mechanical stress of CVD-dielectrics, J. Electrochem.
Soc. 12 (1992) 3669–3674.
[46] O. Tabata, K. Kawahata, S. Sugiyamia, I. Igarashi, Mechanical property
measurements of thin films using load-deflection of composite rectan-
gular membranes, Sens. Actuators 20 (1989) 135–141.
[47] T.-Y. Zhang, Y.-J. Su, C.-F. Qian, M.-H. Zhao, L.-Q. Chen, Microbridge
testing of silicon nitride thin films deposited on silicon wafers, Acta
Mater. 48 (2000) 2843–2857.
[48] J.A. Taylor, The mechanical properties and microstructure of plasma
enhanced chemical vapor deposited silicon nitride films, J. Vac. Sci.
Technol. 9 (1991) 2464–2468.
Biographies
Marie K. Tripp earned a BSE in engineering physics at the University of
Michigan in 1999 and a MS in electrical engineering at the University of
Colorado in 2001. Most recently, she received her PhD in electrical engi-
neering from the University of Colorado in 2005 where she specialized in
optical micro- and nano-electromechanical systems. She spent a short time
as a postdoctoral research associate at ETH Zurich in Zurich, Switzerland.
Where her research interests included the study of thin film structures made
with atomic layer deposition (ALD) and the development of specialized fab-
rication processes to incorporate carbon nanotubes (CNT) as active elements,
along with these ALD structures, for the fabrication of novel devices. Marie
is currently a process engineer at Intel Corporation in Portland, Oregon, USA.
Christoph Stampfer has studied technical physics and electrical engineering
at the TU Vienna, Austria where he received his Dipl-Ing and completed his
BSc in applied physics with computing at the Napier University (Edinburgh,
GB). He is currently a PhD student at the chair of micro- and nano-systemsat the Swiss Federal Institute of Technology Zurich (ETH), Switzerland.
His current research interests include applications of carbon nanotube-based
NEMS, electromechanical properties of single walled carbon nanotubes and
ballistic electron transport in open quantum billiards.
David C. Miller in 1998 earned a BS degree in mechanical engineering
at the University of Minnesota. He earned a MS in mechanical engineering
at the University of Colorado in 2000. He has worked at Network Photon-
ics where he helped develop a MEMS-based wavelength switch for optical
telecommunications. He is currently pursuing a PhD in mechanical engineer-
ing. His current research interests include materials science, solid mechanics,
and applications for micro- and nano-thin films.
Thomas Helbling received in 2005 his MS degree in electrical engineering
at the Swiss Federal Institute of Technology (ETH) Zurich. His main focus
has been the design of integrated electronic circuits and the use of carbonnanotubes in MEMS applications, which is the focus of his current research.
Cari F. Herrmann received her BS in chemistry and mathematics from Muh-
lenberg College in Allentown, PA in 1996. In May of 2001, She received
a PhD in physical chemistry/materials science from the University of North
Carolina at Chapel Hill. She joined the University of Colorado as a postdoc-
toral research associate in June of 2002. Her research interests include using
atomic layer deposition to enhance the reliability of MEMS devices.
Christofer Hierold is professor for micro- and nano-systems at the Swiss
Federal Institute of Technology Zurich since April 2002. Before, he was
11 years with Siemens AG, Corporate Research, and Infineon Technologies
AG in Munich, Germany, working on CMOS compatible microsystems. His
major research at ETH Zurich is now focused on the field of nanotransducers,
evaluation of new materials for MEMS and advanced microsystems. He has
been serving in program committees of numerous scientific conferences and
he is member of the International Steering Committee of the European Con-
ference on Solid-State Transducers. He is subject editor of the IEEE/ASME
Journal of Micro Electromechanical Systems, JMEMS, and joint editor of
Wiley-VCH’s book series on “advanced micro- and nano-systems”.
Ken Gall received the BS, MS, and PhD degrees in mechanical engineer-
ing from the University of Illinois at Urbana-Champaign in 1995, 1996,
and 1998, respectively. He is currently an associate professor of materials
science and engineering and mechanical engineering at Georgia Institute of
Technology. Prior to this appointment he spent 6 years at the University of
Colorado in the department of mechanical engineering. His research interests
lie at the interface of mechanics and materials with emerging applications in
bioengineering, microsystems, and nanotechnology.
Steven M. George is a professor of chemistry and chemical engineeringat the University of Colorado in Boulder. Prior to joining the University
of Colorado in 1992, he was an assistant professor of chemistry at Stan-
ford University. His research interests are in the areas of surface chemistry,
thin film growth and nanostructure engineering. He is currently directing an
internationally recognized research effort focusing on atomic layer deposition
(ALD). He chaired the first Topical Conference on atomic layer deposition
(ALD 2001) sponsored by the American Vacuum Society. He is also co-
founder of ALD nanosolutions, a startup company working to commercialize
ALD. He is a Fellow of the American Physical Society (1997) and a Fellow
of the American Vacuum Society (2000). He has authored or co-authored
more than 200 refereed papers in a variety of areas.
Victor M. Bright is a professor of mechanical engineering at the University
of Colorado at Boulder. Prior to joining the University of Colorado, he was
a professor in the department of electrical and computer engineering, Air
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M.K. Tripp et al. / Sensors and Actuators A 130–131 (2006) 419–429 429
Force Institute of Technology, Wright-Patterson Air Force Base, Ohio (6/92-
12/97). From January through July 2004 he has served as a visiting professor
at the Swiss Federal Institute of Technology (ETH-Zurich), Switzerland. He
has served on the Executive Committee of the ASME MEMS Division, on
the Technical Program Committee of the IEEE MEMS 2000 through 2005
conferences, and as a General Co-Chair for the IEEE MEMS 2005. He
also served on the Technical Program Committee for the Transducers’03 and
IEEE/LEOS Optical MEMS 2003 through 2005. He has taught short courses
on MEMS Packaging at Transducers’03 and Transducers’05. He is an author
of over 70 archived journal articles in the field of MEMS and microsystems.
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