Micromachined Vibrating-Reed Electrometer in Silicon-on-Glass Technology

Abstract

Designing charge sensors for electrometry is deemed significant because of the sensitivity and resolution issues in the range of micro-scales. This chapter presents the design of microelectromechanical systems (MEMS) vibrating-reed (VR) electrometer developed based on micromechanical variable capacitors in silicon-on-glass (SOG) process. By using vibrating-reed technique, the resonator is driven at the frequency above the corner frequency of Flicker noise and the charge measurement is performed at the second harmonic of the resonator’s frequency. This chapter also describes the noise characterization and the referred-to-input (RTI) noise reduction methods for operational amplifier (opamp) based preamplifier. The design of an improved noninverting topology overcame the issues of leakage current and charge resetting during measurement. A comprehensive noise model has been proposed considering all electronic noise contributors including the preamp in conjunction with capacitive MEMS sensor in silicon-on glass (SOG) process and ancillary components. The research findings proved that the blocking capacitor and shunt resistor have significant impact on the RTI noise of the preamp and the charge resolution of the electrometer. The noise analysis and measurement results provide a practical guideline for low noise electrometer interface circuit design. Trade-offs among opamp selection, blocking capacitor value, shunt resistor value etc. have been discussed to provide an original and in-depth analysis for noise and resolution performance optimization in the design of MEMS electrometers.