होम [IEEE 2015 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS) - Estoril,...

[IEEE 2015 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS) - Estoril, Portugal (2015.1.18-2015.1.22)] 2015 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS) - Bonding-friendly pcPDMS: Depositing Parylene C into PDMS matrix at an elevated temperature

, , ,
यह पुस्तक आपको कितनी अच्छी लगी?
फ़ाइल की गुणवत्ता क्या है?
पुस्तक की गुणवत्ता का मूल्यांकन करने के लिए यह पुस्तक डाउनलोड करें
डाउनलोड की गई फ़ाइलों की गुणवत्ता क्या है?
साल:
2015
भाषा:
english
DOI:
10.1109/MEMSYS.2015.7050992
फ़ाइल:
PDF, 1.15 MB
0 comments
 

To post a review, please sign in or sign up
आप पुस्तक समीक्षा लिख सकते हैं और अपना अनुभव साझा कर सकते हैं. पढ़ूी हुई पुस्तकों के बारे में आपकी राय जानने में अन्य पाठकों को दिलचस्पी होगी. भले ही आपको किताब पसंद हो या न हो, अगर आप इसके बारे में ईमानदारी से और विस्तार से बताएँगे, तो लोग अपने लिए नई रुचिकर पुस्तकें खोज पाएँगे.
1

Books Received

साल:
1993
भाषा:
english
फ़ाइल:
PDF, 39 KB
2

Current Medical Literature

साल:
1930
भाषा:
english
फ़ाइल:
PDF, 1.81 MB
BONDING-FRIENDLY PCPDMS: DEPOSITING PARYLENE C INTO PDMS
MATRIX AT AN ELEVATED TEMPERATURE
Yaoping Liu1, Lingqian Zhang1, Wei Wang1, 2, 3* and Wengang Wu1, 2, 3
1
Institute of Microelectronics, Peking University, Beijing, 100871, CHINA
2
National Key Laboratory of Science and Technology on Micro/Nano Fabrication, 100871, CHINA
3
Innovation Center for Micro-Nano-electronics and Integrated System, Beijing, 100871, CHINA
[2, 3, 4]

The so-called pcPDMS achieved a good suppression
of small molecule diffusivity by effectively sealing the
permeable sites in PDMS matrix. However, their process
suffers a long time plasma etching to remove the
over-deposited Parylene C layer and a hazardous BHF
treatment to reactivate the surface for the posterior
bonding. Moreover, it is very tricky to control the etching
time length to only remove the Parylene C layer on the top
surface of PDMS but not influence Parylene C in the
PDMS matrix.
Here we developed an easy and performant one-step
process to prepare a bonding-friendly pcPDMS via
depositing Parylene C into PDMS matrix at temperature
higher than 135°C. The plasma boding strength was tested
via manual breaking from the bonding interface of
pcPDMS. To prove the suppression effect of small
molecules for the so-prepared bonding-friendly pcPDMS,
the diffusion of Rhodamine B was also characterized in the
pristine PDMS and the fabricated pcPDMS microfluidic
chips.

ABSTRACT
This paper reported a simple and effective process of
bonding-friendly Parylene C-caulked PDMS (pcPDMS)
for low-permeability required microfluidics. Parylene C
was deposited into PDMS matrix at an elevated
temperature (higher than 135°C) to caulk the permeable
sites. The so-prepared pcPDMS can be directly bonded
with oxygen plasma treatment just as pristine PDMS. SEM
EDAX and Laser scanning confocal microscopy (LSCM)
were introduced to characterize the Parylene C caulked
status in the PDMS matrix based on the specific Cl element
component and the firstly-found temperature-sensitive
autofluorescence of Parylen; e C. The preliminary results
indicated that the present bonding-friendly pcPDMS can
successfully suppress the diffusion of small molecules into
the PDMS matrix.

INTRODUCTION
PDMS is a commonly-used material in microfluidics
due to its good characteristics: cheap, transparent,
biocompatible and easy to fabricate. However, there come
some issues when it is applied in biomedical researches.
Among which the diffusion of small molecules caused by
porosities in PDMS is the most serious and still being
problem. Many researchers have attempted to solve this
problem through different approaches. The developed
methods are mainly two types, one is to change of curing
time and base/curing agent ratios, and the other is surface
coating. The straightforward variations of curing time and
base/curing agent ratios really work to change porosity in
PDMS bulk, but the performance is very limited. The
surface coating relied on various surface modification and
heavy manual operation. Besides, the shape and size of
microchips could be altered after coating. These methods
are time-consuming and also exits a questionable
long-time reliability because there is a risk that coating
layer would partially lift off from the surface during
high-temperature reaction or under other extreme
condition.
Parylene C, a well-known biocompatible polymer, is
often deposited as passivation coating to achieve low
adhesion and good barrier properties to moisture, inorganic
and organic molecules. Young et al., proposed
PDMS-based micro PCR chip with Parylene C coating and
identified the possibility of preventing adsorption of Taq
DNA polymerase and DNA. But the size and shape of this
chip were limited because Parylene C deposition onto the
inner surface of chips was carried out after PDMS bonding
due to the bonding problem caused by Parylene C coating
on PDMS surface. [1] Sawano and our previous work
demonstrated a method for low-permeable PDMS
fabrication by depositing Parylene C onto PDMS substrate.

978-1-4799-7955-4/15/$31.00 ©2015 IEEE

EXPERIMENTAL RESULTS AND
DISCUSSIONS
Device Fabrication
Fig.1 schematically shows the fabrication process.
First, 10:1 PDMS was used to make the flat PDMS and
PDMS microchannel with the standard soft lithography.
Second, the prepared PDMS substrate was heated to an
elevated temperature (higher than 135°C) with a
homemade heating system installed in the Parylene C
deposition chamber (PDS 2010, SCS, USA.) to prepare the
so-called pcPDMS. Third, the pcPDMS microfluidic chip
could be prepared after 5 s oxygen plasma treatment
(oxygen flow rate 1500 sccm, chamber pressure 35 Pa, and
etching power 100 W) induced irreversible bonding. The

main structure of the chip is the multi tortuous
microchannel and the dimension of the single
microchannel is 60 μm × 50 μm.
(a)

PDMS

(b)

Reflected
Parylene C

Parylene
C Source
Heater: Th >135°C
(d)

467

pcPDMS Chip

(c)

MEMS 2015, Estoril, PORTUGAL, 18 - 22 January, 2015

Figure 1: Schematic illustration of fabrication process, (a)
preparation of flat PDMS and PDMS microchannel with
the standard soft lithography, (b) Parylene C deposition
into PDMS at 135oC with a home-made heating system, (c)
pcPDMS bonding by oxygen plasma treatment for 5s.

percentage of Cl/Si indicates the diffusion depth of
Parylene C into the PDMS matrix, as shown in Fig. 3(a).
(a)

1

C

O

Cl

0
0

1
2
Energy (KeV)

OK

O
C
1
2
Energy (KeV)

Interface

Si K

3

Cl K
pcPDMS

PDMS
Si
CO
Energy (KeV)

(b) 40

Interface

Figure 2: Transparency of the pristine PDMS and the
present pcPDMS (a), manual peeling test of bonded
pcPDMS microfluidic chip (b) and cross-sectional SEM
view of the bonded pcPDMS.

pcPDMS-270℃
Annealed
pcPDMS-None
annealed
PDMS

35
30
25
20

50

PDMS

pcPDMS
PDMS

40
30
20
10
0

None
250℃
270℃
annealed Annealed Annealed

Air

15

PDMS matrix
Interface
Interface

10

As the sticking coefficient of Parylene C deposition
decreases dramatically with the temperature increment, the
deposition rate on the PDMS surface with temperature
above 135°C was small enough to avoid forming an intact
film. [5] This enables Parylene C monomers migrate deeper
into the PDMS matrix and caulk the nano-scale sites there.
Therefore the so-prepared pcPDMS could be bonded
directly through oxygen plasma treatment with no
continuous Parylene C film forming on top of surface.

Fluorescent Intensity

100μm

Channel

Fluorescent Intensity

(c)

Broken point

1

0

10μm

(b)

Si

0

3

K Count

pcPDMS

2

Si

K Count

K Count

Fig.2 (a) shows the same transparency of pcPDMS
with the pristine PDMS. The broken points from the bulk
pcPDMS in the manual peeling test reveals that the
bonding strength of pcPDMS is also compatible to that of
PDMS, shown in Fig. 2 (b). And the cross-sectional SEM
pictures of the so-prepared pcPDMS microfluidic chip was
shown in Fig.2 (c).

(a)

2

5
0

0

10

20

30

40

50

60

70

80

90 100

Scanning Distance (μm)

Figure 3: The SEM EDAX results (a): there is a
characteristic spectra peak of Cl element in Parylene C
spot analysis, while no for PDMS, and LSCM results (b):
the distribution in the depth direction of the Parylene C
blue autofluorescence, the inserted one shows the
differences for different annealing treatments.

Characterizations
The SEM EDAX line scan and the LSCM slice scan
were used to characterize the Parylene C caulking status in
this paper.

The LSCM characterization is based on the
autofluorescence of Parylene C. The autofluorescence of
Parylene has been reported by Kochi et al., [6] and Lu et al.,
[7]
found that blue autofluorescence intensity of Parylene C
was much higher than green or red fluorescence and
accordingly the blue autofluorescence was selected to
identify Parylene C from PDMS. Moreover, we firstly
found that annealing in vacuum at 270°C or above can
considerably increase the autofluorescence contrast
between Parylene-C and PDMS, as shown in the inserted
pictures of Fig.3 (b), which provide an alternative way to
characterize the caulking status. In our LSCM
characterization, the pcPDMS samples were thermally
treated by annealing in vacuum at 270oC and then scanned
layer by layer at a specified step size (0.5 μm) with the
340-380 nm excitations and 435–485 nm emissions (Gate

For the SEM EDAX, there is no Cl element in PDMS
molecule while no Si element in Parylene C molecule, so
the ratio of Cl/Si could suggest the depth of Parylene C in
the PDMS matrix, as indicated in Fig.3 (a). For the sample
preparation of SEM EDAX, a silicone rubber (704 RTV
Silicone Rubber, Nanda, China) was manually coated to
the pcPDMS surface, forming a 704-pcPDMS-PDMS
sandwich structure, and deposited at room temperature
overnight. A longitudinal cut was placed from the top of
the so-called sandwich to get a thin sliced SEM EDAX
sample. Under the SEM EDAX system, a spot detection
was firstly swept near the interface of 704 and PDMS to
define the range of line scan of Cl and Si element. The

468

(b)

1.2

)

Both the SEM EDAX and LSCM results indicated the
caulking depth of Parylene C in PDMS is more than 5μm.

Fluorescent Intensity
Diffusion Width (μm)

(a)

10 20 30 40 50 60

0.6
1

Exp
Cal

PDMS

0 10 20 30 40 50
Diffusion Width (μm)
0

4

8

12

16

20

24

Diffusion Width (μm, W)
Figure 4: Diffusion of Rhodamine B and its fluorescent
intensity distribution in pcPDMS and pristine PDMS
microchannels (a) and the fitted diffusivities of Rhodamine
B (b).

ACKNOWLEDGEMENTS
This work was financially supported by the National
Natural Science Foundation of China (Grant No. 81471750
and 91023045), the Major State Basic Research
Development Program (973 Program) (Grant Nos.
2009CB320300 and 2011CB309502).

REFERENCES
[1] Y. Shin, K. Cho, S. Lim, S. Chung, S. Park, C. Chung,
D. Han and J. Chang, “PDMS-based micro PCR chip
with Parylene coating”, J. Microemech. Microeng.,
13 (5), pp. 768-774, 2003.
[2] S. Sawano, K. Naka, A. Werber, H. Zappe and S.
Konishi, “Sealing method of PDMS as elastic material
for MEMS”, IEEE MEMS 2008, Tucson, AZ, USA,
January13–17, 2008.
[3] Y. Lei, Y. Liu, W. Wang, W. Wu and Z. Li, “Studies
on Parylene C-caulked PDMS (pcPDMS) for low
permeability required microfluidic applications”, Lab.
Chip., 11 (7), pp. 1385-1388, 2011.
[4] Y. Lei, Y. Liu, W. Wang, W. Wu and Z. Li,
“Fabrication and characterization of Parylene
C-caulked PDMS for low-permeable microfluidics”,
IEEE MEMS 2011, Cancun, MX, USA, January
23–27, 2011.
[5] J. B. Fortin and T. M. Lu, “A model for the chemical
vapor deposition of Poly(para-xylylene) (Parylene)
thin films”, Chem. Mater., 14 (5), pp. 1945-1949,
2002.
[6] M. Kochi, K. Oguro and T. Mita, “Photoluminescence
of solid aromatic polymers-I. Poly (p-Xylylene)”, Eur.
Polym. J., 24 (10), pp. 917-927, 1988.
[7] B. Lu, S. Zheng, B. Q. Quach and Y. Tai, “A study of
the autofluorescence of parylene materials for μTAS
applications”, Lab Chip., 14 (11), pp. 1826-1834,
2010.

PDMS

80
70
60
50
40
30
20
10
0
30

0 10 20 30 40 50
Diffusion Width (μm)

0

10 20 30 40 50 60

20

pcPDMS
0

0

90

10

X pcPDMS

Exp
Cal

0.2

Diffusion Width (μm)

0

* PDMS

0.4

Fluorescent intensities and the dynamic diffusion
length of Rhodamine B in the so-prepared pcPDMS and
pristine PDMS microfluidic chips at 5 min, 10 min, 20 min,
30 min, and 40 min after the sample loading are shown in
Fig. 4 (a). Compared to the pristine PDMS, the diffusion of
Rhodamin-B was significantly suppressed in the pcPDMS
device, as shown in Fig.4 (a). The diffusivity of
Rhodamine B in the native PDMS and pcPDMS was fitted
based on the experimental measurements according to
Fick’s first law with the diffusion data at 5 min under a
constant-source diffusion assumption. The diffusivities of
Rhodamin-B in the pristine PDMS and the pcPDMS were
2.43±0.019×10-13 m2/s and 1.21±0.023×10-13 m2/s,
respectively, shown in Fig. 4(b).
5 min
10min
20min
30min
40min

1

Intensity

W/( 2

To identify the blocking effect of small molecules of
the so-prepared bonding-friendly pcPDMS, we introduced
Rhodamine B to characterize the diffusion coefficient in
the pcPDMS and PDMS microfluidic chips. 150μM
Rhodamine B (Sigma, S9012) in water was pumped
through PDMS and pcPDMS microfluidic channels and
where the fluorescent signals were recorded at different
time points after sample loading with a CCD camera under
a fluorescent microscope (Leica DMI 6000B, Germany).
The filled large reservoirs guaranteed the microfluidic
channels filled with enough Rhodamine B molecules
during the recording period, eliminating the influence of
evaporation. The fluorescent intensities in images were
analyzed by MATLAB to define the diffusion width of
Rhodamine B.

pcPDMS

1.0
0.8

Rhodamine B Diffusion Test

1.0
0.8
0.6
0.4
0.2
0

1.4
Intensity

voltage: 845.8 V, Smart offset: -1.2%, Pinhole: 60.63 μm).
The intensity change of scanned fluorescent photos was
analyzed with MATLAB processing to characterize the
distribution of Parylene C in the depth of PDMS matrix.

CONTACT

40

*Wei Wang, Tel: +86-010-62769183
E-mail: w.wang@pku.edu.cn

Time (min)

469