Micromachined bistable valves for implantable drug delivery systems

For an implantable infusion pump, bistable silicon microvalves are developed. The paper reports on a novel bistable and bidirectional electrostatic actuator with pneumatic coupling. Two buckled Si/SiO₂ membranes span over connected air filled cavities with enclosed driving electrodes. The membranes operate in counteraction. If one electrode is pulled down electrostatically, the other is pushed up pneumatically, and vice versa. No voltage is applied across the fluid. The actuator module is designed to achieve with 60 V a deflection of ±10 μm. With first completed actuator modules the electrostatic/pneumatic driving principle could be demonstrated. Grey-tone lithography has been developed to fabricate curved driving electrodes on the cavity bottom. It is calculated that compared to flat electrodes the driving voltage then can be reduced up to a factor of five