Interdigitated Comb Fins for Capacitive Sensing in a MEMS Directional Microphone

W. Cui
State University of New York at Binghamton, US

Keywords: MEMS microphone, interdigitated fins, miniature diaphragm, stress, comb sense

Summary:

Presented here is an innovative capacitive sensing MEMS directional microphone with interdigitated fins that successfully overcomes the difficulties of low capacitance and fabrication-induced stresses. The biologically-inspired miniature microphone diaphragm is composed of a stiffened plate supported on a pair of carefully designed hinges [1-5]. The structure is fabricated on a silicon chip that supports the hinges. The diaphragm is separated from the surrounding substrate by etching a slit around the perimeter while leaving the connection at the hinges intact. The diaphragm is intended to rotate like a rigid body without bending so that its motion is dominated by rotation about its central axis. The interdigitated fins accomplish three goals that are critical to the success of micro-scale capacitive devices: 1) they provide a means of achieving a substantial amount of capacitance between the moving and stationary elements, 2) they strengthen the planar microstructure and protect it from stresses during the fabrication process, and 3) they introduce minimal viscous damping due to interactions between the structure and the surrounding air. This method has wide range applications in micro-scale devices that utilize planar diaphragms including micro-mirrors and micro-actuators.