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 technology. I. INTRODUCTION (HEADING 1) 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 . 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 375 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 . 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 . 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 cost. 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 . 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 . 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 , 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 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. II. EXPERIMENTAL 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 channel. 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 III. RESULT AND DISCUSSION 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 376 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 3(d) 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. References 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 it. . . . . . . . . . . . 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. 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