Publication Type:Conference Paper
Source:2016 IEEE 29th International Conference on Micro Electro Mechanical Systems (MEMS), IEEE, Shanghai, China (2016)
We report the fabrication and broadband actuation of capacitive electrostatic MEMS microspeakers formed by the contact-transfer printing of suspended 125-nm-thick gold membranes over cavities in a 430-nm-thick silicon dioxide (SiO2) spacer layer on a conducting substrate. The membranes deflect repeatedly to produce sound upon electrostatic actuation with a time-varying signal. The microspeaker has a flat acoustic frequency response that is devoid of any resonance peaks. Its output sound pressure level (SPL) increases at 40 dB/decade with increasing frequency, in the 3 highest octaves of the human audio range, for constant excitation voltage autospectral density. The microspeaker consumes 24 W of real electric power under broadband actuation in free field. It outputs 35 dB (SPL/VoltRMS) of acoustic pressure at 20 kHz drive. The microspeaker operates at a 10Vdc bias, thus enabling the use of electrostatic sound sources in portable audio applications such as hearing aids and earphones. The diaphragm-forcing Vbias-Vrms product is reduced to 19 V2. The total thickness of the microspeakers is dominated by the silicon wafer substrate, with an active device thickness of less than 700 nm.