Novel Fabrication Of Comb Drive Actuator Using RIE Of Polysilicon And [110] Si Anisotropic Bulk Etching In KOH

A bulk-micromachined interdigitated comb actuator supported by surface-micromachined polysilicon springs is proposed and fabricated for excitation of resonating momentum. The excitation force electrically generated by the interdigitated comb pair with a 420 height of (110) wafer is more effective than that obtained using a comb pair with a few height fabricated by a surface micromachining technique. The geometry of the interdigitated comb finger pair is 420 high, 20 wide, 5 apart from the neighboring interdigitated comb finger, respectively. A (110) oriented 420-thick Si wafer is used to fabricate the interdigitated comb electrode array using the technique of anisotropic bulk etching in KOH aqueous solution. A 5-thick phosphorous-doped LPCVD polysilicon film is used for fabrication of the flexures of the comb actuator using the technique of reactive ion etching. Repetition of the LPCVD Si3N4 film deposition and reactive ion etching process builds a Si3N4 structure, which envelopes and protects the released polysilicon structure from KOH aqueous etchant without an additional mask for passivation patterning. Using a double-sided aligned fabrication technique realizes not only polysilicon flexures formation on both sides of the actuator but also removal of two slant (111) planes in concave corners of the interdigitated comb finger array, which appear during (110) Si orientation-dependent etching and limit the interdigitated comb actuator design.