A MEMS microvalve with PDMS diaphragm and two-chamber configuration of thermo-pneumatic actuator for integrated blood test system on silicon

In this paper, a thermo-pneumatic in-channel microvalve applicable to integrated blood test system is presented. Thermo-pneumatic actuator separated in drive chamber part and thermal expansion chamber part (two-chamber configuration) is newly proposed for the purpose to reduce direct heat transfer from microheater to flow channel. Polydimethylsiloxane (PDMS) is employed as the diaphragm material for a long stroke actuation in microvalve operation and high sealing performance of liquid. It is also used as adhesive layer between glass and silicon in the structure. The microvalve with the proposed structure was fabricated. Both static and dynamic flow control characteristics were evaluated with a liquid sample (DI water) and a gas sample (N2), respectively. A high ON/OFF ratio of liquid sample was obtained thanks to the soft PDMS diaphragm. Liquid sealing performance in the closed state was high enough for our application (<1 μL/min at 300 hPa). As a disadvantage of PDMS diaphragm, sticking problem which causes hysteresis and instability of sample flow-rate was observed. Also, the microvalve requires some improvements in its dynamic response. Some problems in actual use are remained in the present device. However, causes and countermeasures are discussed in this paper, and its high liquid sealing performance and heat shielding effect of the two-chamber configuration are very attractive for various applications including the blood test system that we have been developing.