A capacitive vibration-to-electricity energy converter with integrated mechanical switches

Due to recent advances in low-power VLSI design technology, it has become feasible to power portable or remote electronic devices by scavenging the ambient energy. The design, fabrication and measurement of a capacitive vibration-to-electricity energy converter are presented in this paper. With a device area constraint of 1 cm(2) and an auxiliary battery supply of 3.6 V, the device was designed to generate an output power of 31 mu W with an output saturation voltage of 40 V. An external mass of 4 g was needed to adjust the device resonance to match the input vibration of 2.25 m s(-2) at 120 Hz. Mechanical contact switches were integrated onto the device to provide accurate charge-discharge energy conversion timing. The device was fabricated in SOI (silicon-on-insulator) wafers by deep silicon etching technology. Parasitic capacitance was minimized by partial back side substrate removal. Resonant frequencies of the fabricated device with and without the external mass agreed with the expected values. Without the external mass, the measured ac output power was 1.2 mu W with a load of 5 M Omega at 1870 Hz. Detailed circuit modeling and ac output power measurement of the devices with the external mass attached are in progress.