Electrical isolation process for molded, high-aspect-ratio polysilicon microstructures

A new process for fabricating molded, thin-film microstructures with electrical and mechanical interconnects is presented. A two step molding process is used to create a composite structure of undoped polysilicon, silicon nitride, and doped polysilicon. The doped poly is used to create regions of conductivity within a nonconducting structure. Thus it is possible to create high-aspect-ratio, monolithic electromechanical microstructures which are transferable from a reusable mold. These microstructures are more resistant to thermal changes and misalignment errors compared to microstructures transferred in segments. A suspended electrostatic microactuator was successfully fabricated using this process. High-aspect-ratio structures, 100 μm and 75 μm tall, were fabricated with 7 μm wide capacitive gaps. Experimental verification of the isolation showed an acceptable 10 nA current leakage at ±25 V and 150 nA leakage at ±50 V