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3
Adhesive Bonding
W. B
rockm
ann, P. L. G
eiß
, J. Klin
gen, B
. Sch
röder,
Ad
hesiv
e B
on
din
g, M
ate
rials
, Ap
plic
atio
ns a
nd
Te
ch
nolo
gy
, 20
09
.
4
SU-8 Epoxy-based negative photoresist Thickness <1um to >300um Formulated in gamma butyrolactone (GBL) solvent (or in
cyclopentanone) High chemical and thermal stability Can be used for building rigid mechanical structures HAR 40:1 Relatively cheap, easy to process The strongest adhesion to Ti and TiO2
J. Micromech. Microeng. 17 (2007) R81–R95
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Drawbacks of SU-8
Difficult removal after curing High coefficient of thermal expansion
(52 ppm/◦C, for silicon and glass ~ 3 ppm/◦C)
High level of tensile stress Poor adhesion to Ni substrates
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General bonding procedure Clean silicon and Pyrex wafers in piranha solutions then
dehydrate the wafers at 200◦C for at least 40 min Deposit, pre-bake, expose, post-bake and develop the first
SU-8 layer on the silicon wafer Spin-coat and pre-bake the second SU-8 layer on the Pyrex
wafer Join the two wafers at different bonding temperatures then
apply pressure to eliminate trapped air bubbles with a pair of tweezers After the bonded stack cools to room temperature, blanket
expose the second SU-8 layer through the Pyrex wafer Post-bake the stack with temperature ramping while applying
pressure Low cooling to reduce thermal mismatch stresses in the layers
J. Micromech. Microeng. 13 (2003) 732–738
Sensors and Actuators A 120 (2005) 408–415
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MicronozzelsThermal oxidation
Litho from unpolished back side
Etching of SiO2 in BHF
DRIE
Patterning of 10 µm SU-8
Etching of SiO2 membranes
Spinning and backing SU-8 on Pyrex
Contact of Si and Pyrex substrates
Exposure through the Pyrex wafer and post bake
J. Micromech. Microeng. 13 (2003) 732–738
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Capacitive pressure sensor
Sensors and Actuators A 147 (2008) 672–676
Bonding with a pressure of 60N by pumping 1 h with a surrounding pressure of 10−4 Pa, then heating in ramp for 1 h to 70 ◦C and 100 ◦C, and finally cooling down to room temperature
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Calorimetric flow sensorBy applying an electrical signal to the heater element, the surrounding liquid is heated up. Then, temperature distribution is measured by means of resistance change at the downstream and upstream sensors
20 µm SU-8, exposurePMMA substrate
Ti/Pt, lift-off
Ox treatment for cleaning
5 µm SU-8 to prevent contact Me/liquid
20 µm SU-8 to define microchannel
125 µm KaptonPMMA substrate
60 µm SU-8 to define inlet and outlet connections
Bonding Removal
from 0 ul/min to 25ul/min
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