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[IEEE 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Seoul, Korea (South) (2019.1.27-2019.1.31)] 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Ultra-thin Parylene-C Deposition on PDMS

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Ultra-thin Parylene-C Deposition on PDMS
Yaoping Liu1, #, Xiao Dong1, #, Xinyue Deng1, 2, Thuan Beng Saw3, 4, Chwee Teck Lim3, 4, 5, Jingquan
Liu6, 7 and Wei Wang1, 6, *
Institute of Microelectronics, Peking University, 100871, Beijing, CHINA; 2School of Basic Medical
Science, Peking University Health Science Center, 100191, Beijing, CHINA; 3Department of
Biomedical Engineering, National University of Singapore, 117583, SINGAPORE; 4Mechanobiology
Institute (MBI), National University of Singapore, 117411, SINGAPORE; 5Biomedical Institute for
Global Health, Research and Technology (BIGHEART), National University of Singapore,
117599, SINGAPORE; 6National Key Laboratory of Science and Technology on Micro/Nano
Fabrication, 100871, Beijing, CHINA; 7Institute of Micro/Nano Science and Technology,
Department of Micro/Nano-electronics, Shanghai Jiao Tong University, 200240, Shanghai, CHINA.
The two authors contributed to this work equally. *Email: w.wang@pku.edu.cn.
of the channel. Additionally, the coating thickness along

the channel varies, which cause the channel size to vary
along the channel and further make the hydraulic
characteristics of the device complicated. To solve the
above problems, Lei et al. [9, 10] developed a complete
process for pcPDMS-based microfluidic applications by
introducing a buffered hydrofluoric acid (BHF) bath to
remove the silica-like bonding barrier. However, this
process still depends on a long-time plasma etching and
hazardous BHF treatment. Kang et al. [11] developed a
thermal chemical vapor deposition (tCVD) process to
deposit Parylene-C into PDMS with substrate temperature
at temperatures up to 80oC to improve the penetration of
Parylene molecules into the PDMS via lowering the
Parylene-C deposition rate at the elevated temperature.
However, a continuous Parylene-C layer still formed on the
PDMS surface and prevented the oxygen plasma mediated
bonding. Liu et al. [12, 13] increased the PDMS substrate
temperature of tCVD to 135oC and achieved a successful
caulking ; of networks in PDMS matrix while avoiding
forming a continuous layer on the surface, i.e. retaining the
original surface property of pristine PDMS. Therefore, a
bonding-friendly pcPDMS was obtained for a surface
functionalized hybrid material. The tCVD process required
an embedded heating system and temperature calibration.
Wang et al. [14, 15] developed a controllable and reliable
ultra-thin Parylene (down to 1 nm thickness) deposition
based on a principle combining both molecular effusion
and diffusion. A thin-Parylene deposition chamber was
established via embedding a small chamber with a small
orifice on the top into the regular machine chamber of the
Parylene coating system. The ultra-thin CVD of ParyleneC was used to in this study to precisely modulate the
surface functionalization of PDMS, i.e. preparing a
controllable pcPDMS hybrid material. Depositions on
PDMS substrates with different prepolymer ratios (mass of
base to curing agent, @ 10:1, 30:1 and 50:1) were covered.

This study reports the ultra-thin Parylene-C
deposition on PDMS substrate for a controllable and
reliable process of Parylene-C caulked PDMS (pcPDMS).
This work covers the depositions on PDMS substrates with
different prepolymer ratios (mass of base to curing agent,
@ 10:1, 30:1 and 50:1). Stiffness could be modulated in a
wide range via the proposed pcPDMS process. The
prepared pcPDMS would find applications in biomedical
studies, such as mechanobiology.


Parylene-C, deposition, PDMS


Polydimethylsiloxane (PDMS) is the star polymer in
microfluidics because of its good characteristics such as
low cost, good optical transparency, high biocompatibility,
and easy microfabrication. However, PDMS suffers
problems such as small molecule diffusion, water
evaporation, due to a loose molecular network in its bulk
matrix. [1, 2] Therefore, it is very important to establish the
surface functionalization of PDMS to fulfill highperformance devices. In recent years, various
investigations have been done to functionalize the PDMS
surface. [3] Among which, caulking PDMS networks via
Parylene C, which is a biocompatible and microfabrication
processable polymer, is a widely used process. [4−13] The
deposition of Parylene C on PDMS can be categorized into
pre-bonding deposition [4−7] and post-bonding deposition
[8−10, 12, 13]. Sawano et al. [8] first developed a MEMS
compatible process for a low-permeability PDMS via
deposting Parylene-C onto the PDMS to prepare the
Parylene-C caulked PDMS (pcPDMS), The unavoidable
Parylene-C layer formed on the PDMS surface in the
regular deposition was removed via oxygen plasma etching,
while the Parylene-C monomers penetrated into the bulk
PDMS matrix was still caulked in the network. Therefore,
the flexibility of PDMS was stored. However, this process
failed to prepare a microfluidic device because the oxygen
plasma etching generated a silica-like layer, which is a
barrier in the oxygen plasma mediated PDMS bonding. To
address this bonding issue, some researchers [4−7] tried the
pre-bonding deposition, but a good coating and sealing can
only be achieved in large channels because the penetration
length is proportional to the effective cross-sectional area

978-1-7281-1610-5/19/$31.00 ©2019 IEEE


The pcPDMS process via ultra-thin CVD of Parylene-C is
schematically illustrated in Fig. 1. After the preparation of
PDMS substrate with a certain ratio of base to curing agent
(Fig. 1a), an ultra-thin Parylene-C deposition was
performed on the PDMS substrate to obtain the pcPDMS
(Fig. 1b). Different ratios of 10:1, 30:1 and 50:1 were tried
for parallel comparisons.


MEMS 2019, Seoul, KOREA, 27-31 January 2019



modulus results are shown in Fig. 3. There presented an
increase in Young’s modulus of hybrid material (pcPDMS)
compared to that of the pristine PDMS, which proved the
successful caulking of Parylene-C with a high Young’s
modulus (GPa) into the PDMS matrix with a low Young’s
modulus (kPa). Furthermore, ultra-thin Parylene-C
depositions with different diameters of orifices were
performed on the PDMS (50:1) substrates to investigate the
controllability of different surface property modulations.
The corresponding Young’s modulus results are shown in
Fig. 4. The Young’s modulus of pcPDMS samples
increases with the diameter of orifices used in the ultra-thin
Parylene-C deposition, which could be attributed to the
more Parylene-C molecules diffusion into the deposition
chamber and more caulking inside PDMS network at an
elevated orifice diameter.

Parylene-C island
on PDMS surface
Parylene-C caulked
in PDMS networks

PDMS matrix
with networks

Figure 1. The schematic of ultra-thin Parylene-C
deposition on the PDMS substrate for pcPDMS
The deposition system for ultra-thin Parylene-C deposition
is based on a previously reported work [15]. A home-made
deposition chamber was put inside and connected with the
regular machine chamber through a microfabricated orifice
with feature size smaller than 1 mm (Fig.2a) to realize the
ultra-thin deposition with the pressure inside the deposition
chamber predictably and controllably reduced, according to
the free molecular flow theory. The PDMS samples were
placed on a homedesigned platform (a PMMA holder)
inside the deposition chamber (Fig.2b). Different orifice
sizes were applied for different caulking statuses of
Parylene-C inside the PDMS matrix.

Young’s Modulus (kPa)




393 μm






Ratio of base to curing agent
Figure 3.
The Young’s modulus results of
pcPDMS samples with different prepolymer ratios
(10:1, 30:1 and 50:1) after ultra-thin Parylene-C
deposition with orifice diameter of 1250 μm.


Deposition chamber
Deposition chamber

Figure 2. (a) The system for ultra-thin ParyleneC deposition, (b) the homedesigned deposition
chamber and sample holder.
The characterizations of prepared pcPDMS samples were
performed under an atomic force microscope (AFM) to
measure the stiffness (i.e. Young’s modulus). Before
measurement, the pcPDMS samples were immersed with 1%
bovine serum albumin (BSA, w/v) in a 35 mm petri dish.
This treatment was for avoiding the non-specific adhesion
of AFM tip and soft surface of pcPDMS during force
loading to obtain the force-displacement curve collection
and extract the Young’s modulus.


pcPDMS samples prepared with different PDMS
prepolymer ratios (10:1, 30:1 and 50:1) were successfully
functionalized via ultra-thin Parylene-C deposition with
orifice diameter of 1250 μm. The corresponding Young’s

Young’s Modulus (kPa)

Source of ParyleneC monomers




Sample platform











Diameter of the orifice (μm)
Figure 4.
The Young’s modulus results of
pcPDMS (50:1) samples with different diameters of
orifice during ultra-thin Parylene-C deposition.


In conclusion, we have established a precise surface
property modulation and functionalization on PDMS


substrates based on a reliable and controllable ultra-thin
Parylene-C deposition process. The mechanical property
(stiffness), a hot topic in mechanobiology, of the prepared
pcPDMS samples were investigated via AFM. The results
show a wide range (<100 kPa − ~ 1 MPa) could be achieved,
which could match stiffness of different tissues, and will be
potential for ex in-vivo mimic studies. We consider the
prepared pcPDMS would find wide applications in
biomedical studies, especially mechanobiology, to uncover
the pathogenesis mechanism and guide the personized
therapy in the coming Precision Medicine.





This work was financially supported by the Major State
Basic Research Development Program (973 Program)
(Grant No. 2015CB352100), the National Natural Science
Foundation of China (Grant No. U1613215), the Beijing
Natural Science Foundation (Grant No. L172005), the
Advanced Research Program of the Ministry of Education
(Grant No. 6141A02033604), the Postdoctoral Science
Foundation of China (Grant No. 2018M631261), and the
Seeding Grant for Medicine and Information Sciences
(2018-MI-03) awarded by Peking University. The authors
thank the MBI microscopy core for support.




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Wei Wang, w.wang@pku.edu.cn.