Novel Fabrication of Comb Actuator Using Reactive Ion Etching of Polysilicon and (110) Si Anisotropic Bulk Etching in KOH

A bulk-micromachined interdigitated comb actuator suspended by surface-micromachined polysilicon springs is proposed and fabricated for excitation of resonating motion. The excitation force electrically generated by the interdigitated (110) Si comb pair of 420 µm height is more effective than that obtained using a comb pair with 3–5 µm height fabricated by polysilicon micromachining. The interdigitated comb finger array, whose geometry is 420 µm high, 20 µm wide and 5 µm from the neighboring interdigitated comb finger, is fabricated by anisotropic bulk etching of 420-µm-thick (110) Si in KOH. A 5-µm-thick phosphorous-doped low pressure chemical vapor deposition (LPCVD) polysilicon film is used for the fabrication of flexures of the actuator, using reactive ion etching. The double-sided aligned fabrication technique accomplishes not only polysilicon flexure formation on both sides of the actuator but also the removal of two slant (111) planes in concave corners of the (110) Si structure, which have limited the interdigitated comb actuator design on (110) Si.