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

Charge sensors (also known as charge electrometers) have a broad range of applications, such as those involving the measurement of ionization radiation, detection of bio-analyte and aerosol particles, mass spectrometry, scanning tunneling microscopy, and quantum computation. Designing charge sensors for electrometry is deemed significant because of the sensitivity and resolution issues in the range of micro-scales. A microelectromechanical systems (MEMS) vibrating-reed electrometer has been developed based on micromechanical variable capacitors. An electrostatically actuated MEMS resonator is utilized as one of the terminals or electrodes of a variable or vibrating capacitor, whereas another electrode is used as a sense electrode. By using vibrating-reed technique, the resonator is driven above the flicker noise and charge measurement is performed in the second harmonic of the resonator's frequency in the white noise floor. This research aims to design and develop a high resolution micromachined charge sensor for room temperature applications. By doing so, designing a highly sensitive MEMS sensing devices and a low noise front-end circuit has been explored to improve the overall charge resolution performance of electrometry systems. A sensing device has been fabricated in silicon-on-glass (SOG)-MEMS process compared to silicon-on-insulator (SOI)-MEMS counterparts. Advantage of adopting this fabrication technology is to reduce the parasitic capacitance for high sensitivity. For readout circuits, a non-inverting operational amplifier-based preamplifier (preamp) has been constructed. To block DC leakage current and to reset the DC charge, an R-C network has been introduced in the preamplifier design. A charge sensor's sensitivity of 1.43x1011 V/C has been achieved at room temperature and atmospheric pressure. Finally, the best charge resolution of 1.03 e/√Hz@5.7 kHz has been attained by optimizing and calibrating both the MEMS sensing device and preamp circuit.