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Fabrication of a Thermopneumatic Micropump with Aluminum Flap Valves

With the development of silicon micromachining technologies, various micropumps have been investigated by many researchers. The diaphragm-type micropump consists of a pressure chamber having a flexible diaphragm driven by an actuator and two passive check valves. The check valves and the actuator determine the performance, such as the flow rate and the output pressure. The output pressure of the micropump is directly determined by the force available from the actuator, and the flow rate is determined by the dynamic characteristics of the actuator diaphragm. In the case of the check valve, a large resistance ratio of the backward flow to the forward flow is required to maximize the pump efficiency. There are several actuation technologies for mechanical micropumps: piezoelectric [1], thermopneumatic [2], electrostatic [3], electromagnetic [4] etc. Although the thermopneumatic micropump generates heat in the pump chamber, it can provide a large deflection for a low input voltage. In general, the thermopneumatic actuator consists of a flexible membrane and a cavity filled with a material whose volume is changed by heating and cooling. Jeong and Yang [5] investigated the mechanical behavior of a thermopneumatic actuator with a p silicon diaphragm. That paper shows that because of the stress release effects of the corrugation, the flexibility of a corrugated diaphragm is about three times that of a flat one, and a corrugated p diaphragm is preferable for thermopneumatic micropumps. Prior to the present work, a thermopneumatic micropump with a nozzle and a diffuser was fabricated to pump fluid with small par-