Fabrication, characterization, and analysis of a DRIE CMOS-MEMS gyroscope

A gyroscope with a measured noise floor of 0.02°/s/Hz¹2/ at 5 Hz is fabricated by post-CMOS micromachining that uses interconnect metal layers to mask the structural etch steps. The 1 × 1 mm lateral-axis angular rate sensor employs in-plane vibration and out-of-plane Coriolis acceleration detection with on-chip CMOS circuitry. The resultant device incorporates a combination of 1.8-μm-thick thin-film structures for springs with out-of-plane compliance and 60-μm-thick bulk silicon structures defined by deep reactive-ion etching for the proof mass and springs with out-of-plane stiffness. The microstructure is flat and avoids excessive curling, which exists in prior thin-film CMOS-microelectromechanical systems gyroscopes. Complete etch removal of selective silicon regions provides electrical isolation of bulk silicon to obtain individually controllable comb fingers. Direct motion coupling is observed and analyzed.