Resonant Acoustic MEMS Wake-Up Switch

We have designed a novel microelectromechanical systems (MEMS) resonant acoustic wake-up switch which is actuated by ambient sound waves, using zero power while waiting for a signal at its resonant frequency and less than 10 nW when the signal is detected. The system uses a battery to charge a capacitor through MEMS switches activated only by the target signals. The sensor is of rotational design allowing it to be insensitive to linear vibration and static gravity forces. Analysis and experimental results maximizing the Q of these resonators in air are presented. A simple, novel fabrication process is presented which uses silicon-on-insulator bonded wafers and still provides metal-metal electrical contacts. These devices have successfully detected 80-Hz sound as low as 0.005 Pa rms (48-dB SPL // 20 μ Pa) from a generator.