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Proceedings of the 12th IEEE International
Conference on Nano/Micro Engineered and Molecular Systems
April 9-12, 2017, Los Angeles, USA
A novel packaging technology for disposable FETbased biosensors with microfluidic channels
Chen-Pin Hsu, Pei-Chi Chen, and Yu-Lin Wang
Institute of Nanoengineering and Microsystems,
National Tsing Hua University,
Hsinchu, 300, Taiwan, R.O.C.
on a large height difference chip, and it requires a threedimensional space. For microfluidic system, wire-bonding
may be influenced by the liquid in the channel. If the wirebinding is outside the chip, the chip size may be extremely
extended making the cost increase. Therefore, wire-bonding is
not the most appropriate way to package in biosensor chip.
Abstract—FET devices are extensively used for sensors,
including gas sensors and biosensors. In contrast to traditional
resistive devices, FET has transconductance gain, which can
significantly improve the S/N ratio. Recently, more applications
in biosensors combine microfluidic channels and FET system. In
FET-based biosensors, the wafer manufacturing process always
requires a lot of cost, and it is used for metal lines as
interconnects. Miniaturized chip plays a key role in reducing the
manufacturing cost. However, simultaneously integrating the
sensor and microfluidic channels on one chip is challenging. In
this study, a novel and robust packaging method has been
developed, to effectively reduce the size of the sensor chip and
thereby the cost. 1 mm × 1mm FET sensor chip has been
fabricated and embedded in epoxy. Photolithography and metal
deposition were done followed by lift-off process for metal
interconnect. The FET-embedded chip was passivated and
covered by the microfluidic channel made of PMMA.
Keywords—FET, biosensors, microfluidic channel, packaging
There are a lot of sensors being developed in recent years,
including pH sensors, pressure sensors, gas sensors, and
biosensors. With more and more widespread use of sensors,
industrial manufacturing and cost reduction is the future trend.
The development of biomedical sensors has become more and
more diverse like the point of care, home care, etc., making it
the market's attention recently. For most bio-marker, we
developed the disposable biosensor chip due to the baseline
shifting after measurement and the minimized chip size. The
advantage for disposable chip is the simple process, mass
production and cheap cost. To achieve the goal of low cost,
the most challenging and important part is the packaging
method. For the bio-sensor, there are many ways to package.
Include wire-bonding [1-9], flip-chip [10-13] and 3D package
[14]. The microfluidic channel packaging including: chip,
packaging subtract and microfluidic channel [15-21].
Wire-bonding is a common technique in commercial
packaging technology. It is can be automated production by
the setting machine. The material of wire-bond commonly
used gold or aluminum, in recent years, copper-bonding
technology was developed. Wire-bond technique can be used
978-1-5090-3059-0/17/$31.00 © 2017 IEEE
Field-effect transistor (FET) [22-30] based sensors such
as gas sensors and biosensors have gained popularity because
FET has transconductance gain. In recent years, a number of
microfluidic chips are used in the development of biosensor
systems. With FET sensors and microfluidic chips being the
future trend, it always requires a larger area FET chip and
wire-bonding technology. Wire-bond free packaging
technology is more important to be developed in order to save
space thereby reducing manufacturing cost. For example:
Edwin T. Carlen group fabricate a Silicon nanowire (Si-NW)
FET biosensors [3]. They have established a complicated
microfluidic system upon the chip using wire-bond to
transport signal from the chip to the PCB board. The chip has
an extremely large size of 10 mm x 20 mm because the
process needs more area for wire-bond. The drawback for a
large size chip is that the cost control of each chip is difficult
and the portable system is hard to be achieved. The design of
Antoni. Baldi Group used a PCB board with hole-drilled and
put the chip inside the designed hole [5]. Then, they placed the
microfluidic system made by polydimethylsiloxane (PDMS)
[35-41] on top of the chip. The chip size for this method is
approximately 3 mm × 3 mm and the connection between
PCB board and the chip is also wire-bond which limits the
capability for chip size minimization and increase the chip
There is another method called flip chip, which apply a
special substrate covered with the chip and remove the
substrate after the packaging process. This method doesn’t
need any wire-bond technique making the size of the chip can
be minimized and planarized easily. Yue Huang group has
made a 12.5 mm × 12.5 mm sensor chip with the flip chip
method [12]. The substrate of the flip chip is glasses. They
remove the substrate after the carrier is finished and make the
microfluidic channel on it. The microfluidic channel bonding
and liquid leakage issue can be controlled more easily because
of the surface planarization. Elisabeth Smela group has used
petri dish coated with PDMS substrate to make a sensor chip
[10]. However, the 3 mm × 3 mm chip size mounted on the
50mm diameter circle epoxy substrate caused a large amount
of cost increasing.
state and put in vacuum chamber for 10 minutes. After stirring
for 5 minutes to uniform, put the mixed PDMS into the
vacuum chamber for 10 minutes to degas. Used the vacuum
pump to remove the air bubble from PDMS, and pour in the
PMMA mold. After baking at 65 degree for 1 hour and
remove the PMMA mold, the PDMS mold was completed.
For the sake of being disposable, industrial production
and low cost mass production are all needed. The size of our
FET sensor has been extremely minimized and the substrate is
replaced by the plastic. Comparing to FET, the plastic
substrate cost is low relatively and can be applied in mass
production rapidly. On the other hand, the process time and
the final cost of the product can be largely lessoned with
simplifying the process step and instrument. In our previous
studies [6], the 9.0 mm × 2.5 mm FET chip was used in
microfluidic channel system. Miniaturization of the FET chip
can save more cost in semiconductor process. The chip size
has been reduced from 22.5 mm2 to 1 mm2, which means the
amount of the chip may increase to the order of 22.5. In the
present work, a novel and highly efficient packaging
technology has been developed using 1mm × 1mm FET sensor
chip integrated with microfluidic channel. Planarization
technology was used on FET chip and epoxy. The design
enables ease of fabrication by changing the shape and
depositing metal on the surface, and uses a micro-SD card
reader to read signals.
Figure 2 shows the process of the packaging technique.
First, embed the 1mm × 1mm FET chip on the PDMS mold[1824]
and inject epoxy over the chip. There are three different
proportions of the filler. The filler was composed by SiO2. The
liquidity of epoxy was affected by the composition of filler. In
previous experiments, the epoxy with 50% filler has good
liquidity before curing. However, the epoxy has poor hardness
after baking. It is easily scratched and deformed by external
force. Another epoxy with 80% filler is the opposite case. This
kind of epoxy had poor liquidity before curing but good
hardness after baking. In this case, the epoxy with 65% filler
was used. The glass transition of this epoxy is large than 140
degree, and the coefficient of thermal expansion is smaller
than 25 ppm per degree. The water absorption (100 degree/ 5
hours) is less than 0.5 %. The epoxy is heated 90 minutes at
125 degrees and 90 minutes at 160 degrees for thermal curing.
After thermal curing, epoxy will become structurally very
strong. Metal lines with 200Å Ti and 1000Å Au were
deposited on the chip side to provide interconnects. Platinum
or nickel can be added to increase the hardness. In this case,
500 Å Pt was added in the metal layer. Photo-resist of 1.8 μm
(Shipley S1818) was coated to encapsulate interconnects on
the surface, and photo lithography process was used to open
the sensing area. The microfluidic channel was made from
PMMA by Laser engraving or injection molding. 1 mm width
channel was used in this case. Finally, the combination of the
microfluidic channel and the FET chip which embedded
epoxy. Used the UV ozone for surface modification, and
washed by 1 M dilute hydrochloric acid.
Figure 1 shows the schematic of the package sample;
package sample with a FET device, epoxy, metal wires and a
microfluidic channel. This FET is in the same surface as
epoxy. The FET chip size is 1mm × 1mm, and the final
package size is 20 mm × 9 mm. The compact size of the
package is highly convenient for end user, measuring the same
size as a micro-SD card. On top of epoxy is PMMA with two
openings in order to allow liquid to enter the microfluidic
Figure 1. Schematic of the package sample. include FET chip(1mm ×
1mm) , epoxy, metal wires and a microfluidic channel.
Figure 2. The process of the package, the FET device embedded with
epoxy, deposited the metal line and coated the photo resist on the epoxy.
Finally, combined with microfluidic channel.
In this case, the PMMA with 2 mm thickness was used to
carve the mode by the LASER engraving. Design a layout for
the LASER engraving with the scanned rate at 400 mm/s, than
the PMMA mode was carved by the LASER. The PDMS is
184 model purchased by SYLGARD, mix the reagent A and
reagent B by the weight ratio of 10 to 1. Stirred for 5 minutes
Figure 3 shows the real packaged sample under different
steps of processing. First, the FET chip is embedded in epoxy
as shown in figure 3(a). This epoxy has a smooth surface, and
the metal lines are deposited on device for interconnects as
shown in figure 3(b). These wires connect the FET chip and
the adapter, and signal is transmitted to the measuring
instruments from the FET device. Finally, the device and
microfluidic channel are then combined as shown in figure
3(c). The Multi-sensor chip was designed to show in figure
sample has high hardness and low moisture absorption, and it
was easily separated by using PDMS. The process used direct
vapor deposition metal lines on the epoxy surface to skip wirebond step. The microfluidic channel is very important for
biosensors, and the planarized surface keeps good combine
ability to microfluidic channel. Finally, it provides an easy
method of reading electrical signals, because the friendly
mode of operation make more people can use.
Acknowledgment (Heading 5)
This work was partially supported by research grants from
Ministry of Science & Technology (MOST 104-2221-E-007142-MY3), National Health Research Institutes (NHRIEX104-10428EI) and National Tsing Hua University
(104N2047E1). We thank the technical support from National
Nano Device Laboratories (NDL) in Hsinchu and the Center
for Nanotechnology, Materials science, and Microsystems
(CNMM) at National Tsing Hua University.
Figure 3. (a)The device with FET chip embedded in epoxy, (b)metal line
was deposited on device, (c)the FET biosensor chip combined with
microfluidic channel and (d) Multi-sensor chip.
The Figure 4(a) shows the package sample use the adapter
to read the signals. A micro-SD shaped packages can easily be
read, because there are commercial adapter can be used.
Figure 4(b) shoes the handheld device for multi-sensor. Such a
package using a simple interface, so that more people can use
Figure 4. (a) The package sample using the micro-SD card adapter to read
the signals. (b) The handheld device for multi-sensor.
In summary, a planarized packaging technology has been
developed, that enables semiconductor devices integrated with
microfluidic channel to be robust and more convenient. It
reduces the cost of semiconductor manufacturing process
considerably because the minimization equals less cost. The
Epoxy in this case used high proportion filler so that the
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