An integrated floating-electrode electric microgenerator

Microfabricated electric generators, scavenging ambient mechanical energy, are potential power sources for autonomous systems. Described presently are the design, modeling, and implementation of a single-wafer floating-electrode electric microgenerator, integrating a micromechanical resonator and a number of electronic devices. Forming a plate of a variable capacitor, the resonator is responsible for converting mechanical vibration to electricity. A sense transistor and a diode bridge are integrated, respectively, for monitoring the "charging"of the floating electrode and for rectification. A lumped electromechanical model of the generator is developed and expressed in terms of a set of nonlinear coupled state equations that are numerically solved. For small-amplitude excitation, a circuit based on a set of linearized equations is developed. The generator is realized using a compatible combination of standard complementary metal-oxide-semiconductor (CMOS) "floating gate"process and a post-CMOS photoresist molded electroplating process. Adequate agreement between model predictions and measurement results was obtained.