Electrostatically Driven Touch-Mode Poly-SiC Microspeaker

This paper presents an electrostatically driven microspeaker utilizing a SiC membrane operating in the touch-mode configuration. The device is formed using conventional wafer bonding to hermetically seal a low-stress, heavily-doped polycrystalline 3C-SiC (poly-SiC) membrane to a bulk micromachined silicon back-plate containing a thin oxide insulating layer. The bonding process is done in high vacuum, causing the poly-SiC membrane to flex down into contact with the back-plate when exposed to atmospheric pressure. Sound Pressure Level (SPL) measurements were recorded for a device with a poly-SiC membrane thickness of 1 mum, a diameter of 800 mum, and a diaphragm/back-plate spacing of 8 mum. At a distance of 10 mm, a maximum SPL of 73 dB was found at a frequency of 16.59 kHz.