Applications of micromachining and MEMS technology in microfluidics

The dissertation research is to use micromachining and Micro-Electro-Mechanical Systems (MEMS) technology in microfluidic applications. Two core microfluidic devices, a piezoelectrically actuated check valve diaphragm micropump to precisely delivery small volume liquid or gases and a real time continuous flow through polymerase chain reaction (PCR) chip for DNA amplifications, have been developed.; The piezoelectrically actuated micropump is made from two Silicon-on-Insulator (SOI) wafers and one general silicon wafer with only four photomasks. The core components of the micropump, the two one-way microvalves, the diaphragm, and the chamber, mainly are formed from technique of SOI/SOI bonding and etching back followed by a second bonding. The piezoelectrically actuated diaphragm is optimized using finite element analysis (FEA) software ANSYS. Driven by Vpp 320V (peak-to-peak voltage), the fabricated micropump (14.5mmx9mmx1.1mm) is able to self prime. The pumping rate of the micropump linearly increases when its driven frequency increases from 0 to 125Hz with the same amplitude voltage. Its maximum pumping pressure is about 11psi when it is driven by Vpp 240V square waves in the linear frequency range. The power consumption of the device is less than 1.2mW when driven by square waves at 100Hz with 50% duty cycle and Vpp 240V. The tested stroke volume and the maximum pumping pressure of the micropump both agree to predictions by FEA.; A continuous flow through PCR chip is made from two Pyrex 7740 wafers and one silicon wafer. The serpentine microchannels are made in the middle Pyrex wafer and sealed by the bottom Pyrex wafer with flow inlet and outlet ports. Three silicon pieces integrated with platinum heaters and temperature sensors are bonded to the top of the middle Pyrex wafer. The application of the PCR is that when the DNA sample passes through three heated zones along the serpentine microchannels, the targeted strand of DNA is doubled. In our design, the three silicon pieces are not directly connected. Electrical-thermal coupled-field simulation tool ANSYS is used in optimization. The PCR chip offers two optical transparent windows which provide the possibility of using fluorescent real time detection method. We also have developed a simple and energy saving packaging method: metal wires are soldered to the electrical pads which can directly be plugged into a breadboard or a printed circuit board (PCB). Both infrared (IR) image and simulation show that the chip has desired temperature profiles. The power consumption is confirmed close to our simulation. The adapted PCR chip successfully amplified DNA.