Stamp-and-Stick Room-Temperature Bonding Technique for

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JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 14, NO. 2, APRIL 2005
Stamp-and-Stick Room-Temperature Bonding
Technique for Microdevices
Srinath Satyanarayana, Rohit N. Karnik, and Arunava Majumdar, Fellow, ASME
Abstract—Multilayer MEMS and microfluidic designs using
diverse materials demand separate fabrication of device components followed by assembly to make the final device. Structural
and moving components, labile bio-molecules, fluids and temperature-sensitive materials place special restrictions on the bonding
processes that can be used for assembly of MEMS devices. We
describe a room temperature “stamp and stick (SAS)” transfer
bonding technique for silicon, glass and nitride surfaces using
a UV curable adhesive. Alternatively, poly(dimethylsiloxane)
(PDMS) can also be used as the adhesive; this is particularly
useful for bonding PDMS devices. A thin layer of adhesive is
first spun on a flat wafer. This adhesive layer is then selectively
transferred to the device chip from the wafer using a stamping
process. The device chip can then be aligned and bonded to other
chips/wafers. This bonding process is conformal and works even
on surfaces with uneven topography. This aspect is especially
relevant to microfluidics, where good sealing can be difficult to
obtain with channels on uneven surfaces. Burst pressure tests
suggest that wafer bonds using the UV curable adhesive could
withstand pressures of 700 kPa (7 atmospheres); those with PDMS
could withstand 200 to 700 kPa (2–7 atmospheres) depending on
the geometry and configuration of the device.
[1267]
Index Terms—Poly(dimethylsiloxane) (PDMS), room temperature, microelectromechanical systems (MEMS), microfluidics,
transfer bonding, ultraviolet (UV) curable adhesive.
I. INTRODUCTION
W
AFER and chip bonding techniques are critical steps in
fabrication and assembly of MEMS devices. Bonding
techniques can be briefly classified into two major categories—direct bonding and bonding with an intermediate layer.
A. Direct Bonding
Anodic bonding, fusion bonding, and activated surface
bonding [1], [2] fall in this category. For anodic bonding,
the wafers are cleaned extensively, aligned, and brought into
kV) and high temperature
pressure contact. High voltage (
(
C) cause an irreversible bond to form between the
substrates. Anodic bonding works well for bonding glass or
glass coated substrates with silicon and nitride substrates.
Manuscript received February 10, 2004; revised July 17, 2004. This work was
supported by the SIMBIOSYS program of DARPA, the Innovative Molecular
Analysis Techniques (IMAT) program of the National Cancer Institute (NIH),
the Department of Energy and the NSF. Subject Editor G. B. Hocker.
S. Satyanarayana and R. N. Karnik are with the Department of Mechanical
Engineering, University of California, Berkeley, CA 94720-1740 USA.
A. Majumdar is with the Department of Mechanical Engineering, University
of California, Berkeley, CA 94720-1740 USA and also with the Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
USA (e-mail: [email protected]).
Digital Object Identifier 10.1109/JMEMS.2004.839334
Fusion bonding relies on the attractive forces that exist between extremely clean flat surfaces in contact to form a strong
bond between them. This bonding process requires extensive
precleaning procedures and the alignment and bonding process
is usually performed under vacuum with external pressures
to help form good contact. The bonding process is followed
by a thermal cycling process to strengthen the bond. Fusion
bonding works very well for bonding silicon wafers. In the case
of surface activation bonding, the substrates are pre-treated
with oxygen plasma, hydration processes or other chemicals
to increase the reactivity, and then brought into contact with
or without external pressure and high temperature to form an
irreversible bond. The effect of surface treatment processes
lasts only for a small time interval and the bonding processes
including alignment need to be completed within this time
window. Activation with oxygen plasma [3] has been used
extensively for bonding PDMS devices to PDMS or glass,
which are commonly used materials in prototyping microfluidic devices. Liu et al. [4] have bonded PDMS to PDMS and
glass by incubating the device with the two surfaces to be
bonded in contact at 80 C. Lin et al. [5], [6], and Cheng et al.
[7] have demonstrated localized fusion bonding process either
using patterned micro heaters or using a focused laser. Localized heating eliminates the thermal cycling of the entire wafer
during the bonding process. However, this bonding technique
requires additional lithography steps.
B. Bonding With Intermediate Layer
Adhesive bonding, eutectic bonding, solder bonding, and
thermocompression bonding fall in this category. Adhesive
bonding [1], [2] does not require high temperatures or voltages,
but requires a thin adhesive layer on the device, which is
usually obtained by spin coating. However, spin coating is a big
problem when the wafers to be bonded have nonuniform topography. Some typical adhesives used are epoxy, spin-on-glass
and UV curable glue. Eutectic bonding [8] uses a thin gold
layer as an adhesive to bond silicon wafers. The wafers to be
bonded are brought into contact and the temperature is raised
to gold-silicon eutectic point to form an irreversible bond. Lin
and others [5]–[7] improved this process to bond locally using
patterned gold lines and in situ electrical heating. Localized
bonding overcomes the high temperature problem but requires
the deposition and patterning of one or more additional bonding
layers (gold, silicon). This may not be compatible with some
device materials like plastics and polymers or with some
fabrication processes. Solder bonding and thermocompression
bonding again involve the deposition and patterning of additional layers like solder or other soft metals and use either heat
1057-7157/$20.00 © 2005 IEEE
SATYANARAYANA et al.: STAMP-AND-STICK ROOM-TEMPERATURE BONDING TECHNIQUE FOR MICRODEVICES
Fig. 2.
Fig. 1. Adhesive transfer process. (a) Uniform adhesive layer on a wafer
obtained by spinning, (b) the cover wafer with patterns brought into contact
with the adhesive, (c) selective transfer of the adhesive to the cover wafer,
and (d) the cover wafer aligned with a device wafer, brought into contact and
bonded.
and/or pressure to form bonds between substrates. Detailed
analysis of these bonding processes and additional references
can be found in the review paper by Schmidt [1]. Recently,
Noh et al. [9] have demonstrated a conformal bonding process
where intermediate parylene layers, deposited on the wafers to
be bonded, were selectively heated using variable frequency
microwave to form a bond. Parylene deposition is conformal
and it is also a biocompatible polymer, but additional lithography steps are required to limit the bonding to selective regions
on the chip.
Due to the stringent requirements of the above-mentioned processes, they are unsuitable for devices with labile
biomolecules, nonuniform topography and high temperature
sensitive components. In this paper we describe an innovative
bonding technique, which we call “Stamp-and-Stick (SAS)”.
SAS is compatible with devices with the above-mentioned
constraints. The bonding process uses an intermediate adhesive
layer like ultraviolet (UV) curable polymer or uncured PDMS.
The problem of obtaining a uniform adhesive layer on the
bonding areas is solved by an adhesive transfer process as
shown in Fig. 1.
Once the adhesive layer is transferred to the cover wafer, it
is aligned and brought into contact with a device wafer. The
bonding process is completed by curing the intermediate layer
by exposure to UV radiation1 at room temperature or by baking
at 90 C. The salient features of this bonding technique are: i)
room temperature process; ii) variable adhesive layer thickness
(can be optimized based on the requirements); and no need for
iii) extensive cleaning procedures or ultra clean surfaces; or (iv)
external pressure. Furthermore, reversible bonding can be obtained in certain cases (when using PDMS adhesive for bonding
PDMS devices to glass). The first part of this paper discusses the
UV adhesive bonding process while the second part discusses
PDMS adhesive bonding. Very recently, Schlautmann et al. described a similar stamping process using a UV curable adhesive
[10]. Though their process shares some common features with
the present work, it is important to note that our process is suited
for bonding different types of substrates, which include, glass,
1Both
the UV curable adhesive and PDMS are transparent to visible light.
393
Pressure testing setup for the device under test (DUT).
silicon and PDMS. Secondly, our process does not suffer from a
limited time window for bonding and alignment. The chemical
inertness of the adhesives used in our process also makes it well
suited for biosensors, which usually operate in liquid/saline environments.
II. PROCESS CHARACTERIZATION AND EXPERIMENT DESIGN
Several methods like burst pressure test, tensile/shear test,
knife-edge or double cantilever technique [1], [2] can be used to
measure the efficacy of the bonding process. Burst pressure tests
do not yield much information about the nature and strength of
the bond because of the complicated loading at the interface,
but they give results that have engineering significance. In addition, the tests are also easier to perform. Hence, burst pressure
was chosen as the criterion for evaluating the bond strength. The
burst pressure depends on several factors, which include device
geometry, area under bond, stress concentration, type of substrate and curing methods. For the pressure tests, standard microfluidic devices like channels and chambers were fabricated
in silicon, PDMS and glass and the test devices were made by
bonding them together using two types of adhesives—UV curable adhesive and liquid PDMS. The schematic of the pressure
testing setup, which was built in-house, is shown in Fig. 2. A
syringe pump (SP 200i, World Precision Instruments) was used
to pressurize the devices by filling them with water and the pressure was monitored using a micro pressure gauge (Honeywell,
model # 24PCFFA6G). The flow rate in the syringe pump was
set to ramp the pressure at a rate of 3 kPa/s and the pressure drop
in the tubing was calculated to be negligible at this flow rate.
Additionally razor-blade tests as described by Maszara et al.
[11] were also performed to measure the adhesive fracture energies and to compare these values with the fracture energies of
typical adhesives. In this test, a razor blade of known thickness
is inserted between the bonded samples and the length of the resulting crack is measured. From the material properties and the
geometry of the test sample, the adhesive fracture energy
can be evaluated using (1)
(1)
where is the elastic modulus of the bonded sample, is the
is the blade thickness, is
thickness of the bonded sample,
Poisson’s ratio, and is the crack length.
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JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 14, NO. 2, APRIL 2005
Fig. 4. Test device assembly. Details of a microfluidic device (inset) showing
dark, bonded regions and light, non-bonded regions.
Fig. 3. Silicon-glass test device (Type I). (a) Silicon wafer—the white areas
are etched 375 m deep. (b) Glass wafer—the white areas are etched to a depth
of 30 m. (c) Silicon and glass dies bonded together and a tube connected from
the side for fluid I/O.
TABLE I
DESIGN PARAMETERS FOR THE SILICON-GLASS TEST DEVICE (TYPE I)
Fig. 5. Silicon-glass test device (Type II). (a) The glass component of the
device; the white areas are etched to a depth of 30 m. (b) Silicon and glass dies
bonded together and a tube connected from the side for fluid I/O. The silicon
part of the device is same as that of the Type I device.
A. UV Adhesive Bonding Process
Two types of test devices were fabricated to test the bonding.
The type I device was designed to test the bond strength and
the type II device was designed to test process reliability. Both
the devices consist of silicon and glass chips that were bonded
together. A schematic of the type I test device and its components is shown in Fig. 3. The different values for the test device
dimensions that were varied are listed in Table I. The fluidic
channels as shown in Fig. 3 were formed using a deep-reactive
ion etch (DRIE) process (Surface Technology Systems (STS)
Advanced Silicon Etch (ASE) system) and standard photoresist
masking on a one-side polished silicon wafer. After the etching
process the wafer was diced to 10 mm by 15 mm chips. The
glass wafers were etched 30 m deep with concentrated HF acid
(49%) using an amorphous silicon mask to form the microchannels and chambers (see Fig. 3). The glass wafers were diced
to 15 mm by 20 mm chips. The glass and silicon chips were
bonded together using the UV adhesive, as described earlier in
this paper. The UV curable adhesive (NEA 121) was obtained
from Norland Products, NJ. This particular adhesive can also be
cured thermally, which is useful when bonding substrates that
are opaque to UV radiation. The adhesive was spun at 6000 rpm
for 2 minutes to obtain a thin layer ( – m) on the transfer
wafer. Once the adhesive was transferred to the glass chip, it was
aligned with the silicon chip and brought into contact. Special
care was taken during this step to prevent any shear between the
device chip and the transfer wafer as shear causes filling of features on the device chip. The adhesive was cured by exposure
to UV radiation for 10 minutes. The UV lamp used for curing
was obtained from Spectronics (Model no. SB-100P,
mW/cm ).
Teflon tubing (OD 250 m) was connected to the test device
from the sides with super glue as the adhesive (see Fig. 4). More
details about the tubing connections can be found in [12]. 25 G
needles (Becton Dickinson) with standard Luer ends were then
connected to the Teflon tubing for external interfacing.
The glass chip in the type II device had channels etched in it as
opposed to chambers in the type I device (see Fig. 5). The width
and the spacing between the channels were varied and the different values are listed in Table II. Devices with small patterns,
70- m-wide channels with 10 m spacing, were bonded using
this technique without any clogging.
The samples for razor-blade test were prepared as follows.
The adhesive was spun on a clean glass slide at 4500 rpm for
two minutes. This adhesive was then transferred to a new glass
slide by the stamping process described above and bonded flush
to another slide and cured under the UV lamp (see Fig. 6). After
curing, a clean razor blade was inserted slowly in between the
two slides and the formed crack was allowed to stabilize for a
day.
1) Pressure Test Results: All the silicon-glass test devices
survived a pressure of 700 kPa (7 atmospheres) without failure
(we could not test for higher pressures as the micro-pressure
sensor’s range was limited). During the test the pressure in the
SATYANARAYANA et al.: STAMP-AND-STICK ROOM-TEMPERATURE BONDING TECHNIQUE FOR MICRODEVICES
395
TABLE II
DESIGN PARAMETERS FOR THE SILICON-GLASS TEST DEVICE (TYPE II).
Fig. 7. Microfluidic cells formed by bonding glass covers to silicon device
chips.
Fig. 6. (a) Razor-blade test sample before blade insertion, and (b) after blade
insertion showing the crack front.
devices was maintained at 700 kPa for 30 min. Testing the devices at higher pressures (test-to-failure) would involve using a
different pressure sensor and a different test setup. We decided
not to pursue this any further, because 7 atm is a reasonably high
pressure in the context of microfluidic devices and this would
by itself justify the usefulness of this bonding process to the microfluidic community.
2) Razor-Blade Test Results: The average length of the measured cracks in the test specimens was 2.69 cm (four test specimens, std. deviation of 0.06 cm, see Fig. 6). This crack length
corresponds to adhesive fracture energy of
J/m
calculated using (1). Typical values of adhesive fracture energies for nontoughened adhesives are of the order of 10–100 J/m
[13] (the adhesive layer thicknesses in these tests are of the order
of 1 mm). The surface energy of directly bonded wafers using
methods like diffusion bonding is of the order of 0.1 J/m [14].
The adhesive fracture energy is usually much higher than the
surface energy values because of the additional component as a
result of energy expended in plastic deformation of the adhesive
layer during crack formation. The energy expended in plastic
deformation reduces when the adhesive layer thickness is decreased and this may be one of the reasons for the lower value
obtained in our test when compared to the values from [13].
The material properties and the dimensions of the glass slide
used in the above calculation are as follows: Elasticity modGPa, Poissons ratio
, slide thickness
ulus
mm and razor blade thickness
m.
3) Transfer Characteristics: To characterize the stamping
process the adhesive was spun on a glass slide and several
stamping processes using small silicon chips were performed
within a short period of time. The glass slide was then cured
under the UV lamp. The amount of adhesive transferred during
the stamping process is given by the adhesive height difference
between the stamped and unstamped areas. The adhesive layer
thickness was measured using a surface profiler (Alpha-Step IQ
Surface Profiler, KLA-Tencor). The thickness of the adhesive
film on the transfer slide was 3.3 m. The average height difference between the stamped and unstamped regions was 1.61 m
Fig. 8. Schematic of the PDMS test devices showing the top view and cross
section. The outer bonded areas were 1 cm 1 cm for device A and 1 cm 2.7
cm for device B. Height of poured PDMS was 3–5 mm and channel or chamber
height (H) for both devices was 40 m.
2
2
(six readings, std.
m) and this corresponds
% adhesive transfer during the stamping process.
to
An array of microfluidic cells formed by bonding a patterned
glass cover to a silicon device wafer using the above-mentioned
bonding process is shown in Fig. 7. The bonding in the chip is
very uniform and there are no voids or defects seen.
B. PDMS Bonding Process
The microfluidic devices for testing the PDMS bonding
process consisted of two components: a glass slide and a PDMS
component containing the channels and test features. The
PDMS component was fabricated first and the final devices
were obtained by bonding the PDMS component to a glass
slide.
To fabricate the PDMS component, a microchannel mold was
made by patterning a silicon wafer with photoresist masking
and etching the silicon approximately 40 m deep in a DRIE
system (Surface Technology Systems (STS) Advanced Silicon
Etch (ASE) system) to leave a positive relief of the channels.
The silicon mold was then placed in a desiccator with a few
drops of tridecafluoro-1, 1, 2, 2-tetrahydrooctyl-1-trichlorosilane (United Chemical Technologies, Bristol, PA) to create a
monolayer on the surface of the silicon. This monolayer has
been found to aid in the future removal of the PDMS [3]. PDMS
was mixed in a 10:1 ratio of monomer and curing agent as
per manufacturer instructions (Sylgard 184, Dow Corning, Midland, MI) and poured over the mold. The PDMS was degassed
and cured at 70 C–80 C for 20–25 min and then removed
from the mold. The inlet holes were formed by drilling the
molded PDMS with a 300 m diameter drill bit (Drill Bit City,
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JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 14, NO. 2, APRIL 2005
Fig. 9. Variation of burst pressure with square size (S) for device A. Each bar represents one device.
# 05M030). The PDMS was further hard-cured at 120 C for 20
min. This step was found to minimize device shrinkage during
the curing step of the bonding process.
The PDMS was then bonded to a glass slide using the transfer
bonding technique with uncured PDMS as the adhesive. 1–2 ml
of freshly mixed PDMS was poured on a glass slide, which was
then spun at 8000 rpm for 8–9 min. This resulted in a thin layer
of uncured PDMS of thickness 1–1.5 m. The previously fabricated PDMS component was cleaned with isopropyl alcohol
(IPA) using a swab. It was then placed on the glass slide (about
15 min after spinning) and lifted off, leaving a layer of uncured
PDMS on it. Another glass slide was prepared for bonding by
cleaning with IPA. The PDMS component with the thin layer
of uncured PDMS was then placed on the glass slide and cured
at 90 C for 15 min to obtain the final device (PDMS can also
be cured at room temperature, which takes about a day). The
inlet connections were made by inserting 0.006” ID, 0.016” OD
PTFE tubing (Cole Parmer Instrument Company, Vernon Hills,
IL) into the drilled holes. This tubing was inserted into 0.012”
ID 0.030” OD PTFE tubing (Cole Parmer Instrument Company,
Vernon Hills, IL) that was connected to a syringe via a 27G
needle.
The samples for the razor-blade test were prepared as follows:
The PDMS was spun on a clean glass slide at 8000 rpm for two
minutes. This PDMS was then transferred to a new glass slide
by the stamping process described above and bonded flush to
another slide and cured. After curing, a clean razor blade was
inserted slowly in between the two slides and the formed crack
was allowed to stabilize for a day.
1) Pressure Test Results: The two test devices used for the
PDMS bonding process test are shown in Fig. 8. For device A,
the burst pressure was tested for different sizes of the square
chamber. For device B, the channel width was varied. The
pressure test was carried out as described for the UV bonding
process. The results are presented in Figs. 9 and 10. The devices
could withstand pressures of 200 to 700 kPa (2–7 atmospheres)
depending on device geometry. All type A devices could withstand at least 400 kPa before bursting, while those of type B
could withstand 200 kPa. There is no clear correlation between
burst pressure and either square size or channel width, but the
difference in burst pressure between the two types of devices is
evident. In addition to the pressure test, pieces of PDMS were
bonded together and peeled apart. Often, the PDMS tears (see
Fig. 11) instead of separating at the interface, which suggests
that the bond strength is close to that of bulk PDMS.
In addition to the above devices, the PDMS bonding process
was successfully used to bond channels running over steps 1 m
in height without any leakage along the step. This bonding technique was found to work on silicon and silicon nitride surfaces
as well. The bonding process was applied to make microchannels running over an array of Ag electrodes 0.5 m in height on
silicon oxide [15] (see Fig. 12). Selective electrochemical reaction on the Ag (bright) electrodes to form AgCl (dark) was carried out in the channels; absence of reaction outside the channel
area is an indication of a good conformal seal. Tests using fluorescent dyes also confirmed a good seal.
2) Razor-Blade Test Results: The average length of the measured cracks was 1.91 cm (four readings, std. deviation of 0.063
cm). This crack length corresponds to adhesive fracture energy
J/m calculated using (1).
of
3) Transfer Characteristics: The PDMS was spun on a glass
slide as described previously. Several stamping processes were
performed using small pieces of previously poured and cured
PDMS to transfer the adhesive. Thickness of the transferred
layer was measured as with the UV adhesive and the results are
presented in Table III. The PDMS layer transfers well when
stamping is performed within half an hour of spinning, after
which transfer becomes unreliable. Since the thickness of the
SATYANARAYANA et al.: STAMP-AND-STICK ROOM-TEMPERATURE BONDING TECHNIQUE FOR MICRODEVICES
397
Fig. 10. Variation of burst pressure with channel width (W) for device B. Each bar represents one device. The square size (S) was 1 mm and the channel length
(L) was 20 mm.
Fig. 11. Two pieces of PDMS peeled after bonding. Note the piece of PDMS
torn from one of the bonded components and stuck to the other, indicating that
the bond strength is comparable to that of bulk PDMS.
spun layer of PDMS is about 1–1.5 m, we see that 50% or
more of the spun layer is transferred. Further, the permeability
of PDMS helps to release trapped air, making uniform bonding
over large areas feasible (Fig. 13). For uneven topography, a
thicker layer of transferred PDMS is desirable. This can be
easily achieved by spinning the PDMS at lower speeds and
shorter durations or by spinning after a few hours of curing at
room temperature.
Fig. 12. Microchannel formed by bonding molded PDMS to a silicon
wafer with patterned silver electrodes using PDMS as the adhesive. Selective
electrochemical reaction at the electrodes (black surface, due to formation of
AgCl) is an indication of a good conformal seal. Microchannel cross section is
40 40 m and the electrode height is 0.5 m.
2
III. DISCUSSION
The devices bonded using UV adhesive did not fail at 700 kPa
(maximum range of the pressure gauge). Hence, test to failure
could not be conducted on these devices.
For the devices bonded using PDMS it was observed that the
burst pressure of the devices is a function of geometry. The corners of the fluidic chamber in case of the type A devices are
convex, while those in type B devices are concave. This difference in geometry may explain why type B devices failed at a
lower pressure. Smaller features will in general result in lower
stress concentrations, though this is not evident in the current
burst pressure tests. The inlet/outlet connections often place a
limitation on the minimum feature size and may consequently
limit the pressure the device can withstand. Failure of the bond
was observed to occur through a delaminating process. Delamination was also found to depend on the quality of transfer of uncured PDMS. Transfer of a thin (
nm) layer often resulted
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play a very important role in determining the quality of bonding.
The bonding process described here provides an easy and versatile process for bonding PDMS, glass, silicon and silicon nitride
surfaces.
ACKNOWLEDGMENT
Fig. 13. A PDMS device bonded to glass. The lighter region is the square
chamber and microchannel. Note the uniform bonding area around the
microchannel indicated by the darker region. The drilled hole appears as a dark
line below the square chamber.
The authors would like to thank V. Milanovic, K. Dunphy, M.
Yue, and S. Zimmerman for help with microfabrication and/or
helpful discussions, and the Microfabrication Laboratory, University of California, Berkeley, for providing the fabrication facilities.
REFERENCES
TABLE III
TRANSFER CHARACTERISTICS OF PDMS
in a rough edge and consequently lower burst pressure. However, a good design can ensure that the device can withstand a
pressure of several atmospheres. The PDMS transfer bonding
process was found to be reversible for PDMS-glass, PDMS-silicon and PDMS-nitride bonding. However, PDMS-PDMS bond
could not often be peeled without tearing the PDMS.
The process described above can be used to bond features
that are either more than 20 m in depth or width. Filling in of
features becomes a problem with decreasing feature size. Uncured PDMS from surrounding areas tends to flow into the features and permeability of PDMS to air favors this. In order to
reduce filling in of features, the PDMS needs to be pre-cured
to increase its viscosity. The time for optimal pre-cure at room
temperature has been found to vary from 15 minutes to about an
hour. However, longer pre-curing time is undesirable since the
transfer becomes unreliable. Alternatively, larger dummy features adjoining small features of interest can act as reservoirs
for inflowing PDMS, preventing filling in of the small features.
IV. CONCLUSION
A new adhesive bonding process for microfabrication has
been developed and tested. The process overcomes the disadvantages of the traditional MEMS wafer bonding processes that
have been borrowed from the IC industry. The salient features of
the new bonding technique include: (i) low/room temperature;
(ii) multi-material compatibility; (iii) reversibility; and (iv) biocompatibility (PDMS has been widely used to make devices for
biomolecular analysis [3], [4] and UV adhesive being inert to
most chemicals is likely to be biocompatible). The stampinglike transfer process ensures the formation of a uniform adhesive layer on patterned substrates. The thickness of the intermediate adhesive layer when chosen properly can accommodate
small variations in height such as the ones caused by electrical
interconnect lines. UV adhesive bonded devices could easily
withstand pressures up to 700 kPa (seven atmospheres) without
failure. In the case of the PDMS bonded devices the geometry
of the device, material of the surfaces and the transfer process
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Electrochem. Soc., vol. 147, no. 6, pp. 2343–2346, 2000.
[15] Spatially Controlled Microfluidics Using Low-Voltage Electrokinetics,
to be published.
Srinath Satyanarayana received the B.Tech. degree
in mechanical engineering from the Indian Institute
of Technology, Madras, in 1999 and the M.S. degree
also in mechanical engineering from the Georgia
Institute of Technology, Atlanta, in 2001. He is
currently working toward the Ph.D. degree in mechanical engineering at the University of California,
Berkeley.
He is a recipient of the Central Board of Secondary
Education Scholarship (awarded by the Government
of India, 1995). His current research interests include
design and fabrication of MEMS and nanoscale devices, microfluidics, biosensors and optical systems.
SATYANARAYANA et al.: STAMP-AND-STICK ROOM-TEMPERATURE BONDING TECHNIQUE FOR MICRODEVICES
Rohit N. Karnik received the B.Tech. degree in
mechanical engineering from the Indian Institute
of Technology, Bombay, in 2002. He is currently
working toward the Ph.D. degree in mechanical
engineering at the University of California, Berkeley.
He is a recipient of the Institute Silver Medal (Indian Institute of Technology, Bombay, 2002) and the
National Talent Search Scholarship (Government of
India, 1996). His current research interests include
nanofluidics and micro-mixing.
399
Arunava Majumdar received the Ph.D. degree in
mechanical engineering from the University of California, Berkeley, in 1989.
He holds the Almy and Agnes Maynard Chair
Professorship in Mechanical Engineering, University
of California, Berkeley, where he served as the vice
chair from 1999–2002. He served on the Mechanical
Engineering faculties at Arizona State University
(1989–1992) and University of California, Santa
Barbara (1992–1996).
Dr. Majumdar is a recipient of the NSF Young
Investigator Award, the ASME Melville Medal, ASME Heat Transfer Division
Best Paper Award, and 2001 ASME Gustus Larson Memorial Award. He is
currently serving as an Editor for the International Journal of Heat and Mass
Transfer, Editor-in-Chief of Microscale Thermophysical Engineering, and
member of the editorial board of Mechanics and Chemistry in Biosystems. He
also serves as Chair, Board of Advisors, ASME Nanotechnology Institute;
Member, Council on Materials Science and Engineering, US Department
of Energy; Member, Chancellor’s Advisory Council on Nanoscience and
Nanoengineering at University of California, Berkeley; and Member, Nanotechnology Technical Advisory Group to the President’s Council of Advisors
on Science and Technology (PCAST). He is a Fellow of both ASME and
AAAS and a Member of the National Academy of Engineering.