Electrostatic charge and field sensors based on micromechanical resonators
Riehl, P.S.
Scott, K.L.
Muller, R.S.
Howe, R.T.
Yasaitis, J.A.
Analog Devices, Cambridge, MA;
This paper appears in: Microelectromechanical Systems, Journal of
Publication Date: Oct. 2003
Volume: 12,
Issue: 5
On page(s): 577- 589
ISSN: 1057-7157
INSPEC Accession Number: 7779789
Digital Object Identifier: 10.1109/JMEMS.2003.818066
Current Version Published: 2003-10-27
Abstract
We have developed highly sensitive electrometers and electrostatic fieldmeters (EFMs) that make use of micromechanical variable capacitors. Modulation of the input capacitance, a technique used in macroscale instruments such as the vibrating-reed electrometer and the field-mill electrostatic voltmeter (ESV), moves the detection bandwidth away from the 1/f-noise-limited regime, thus improving the signal-to-noise ratio (SNR). The variable capacitors are implemented by electrostatically driven resonators with differential actuation and sensing to reduce drive-signal feedthrough. The resonators in the electrometer utilize a balanced comb structure to implement harmonic sensing. Two fabrication methods were employed - a hybrid technology utilizing fluidically self-assembled JFETs and SOI microstructures, and an integrated process from Analog Devices combining 0.8-μm CMOS and 6-μm-thick polysilicon microstructures. All devices operate in ambient air at room temperature. Measured data from one electrometer with an input capacitance of 0.7 pF indicates a charge resolution of 4.5 aC rms (28 electrons) in a 0.3 Hz bandwidth. The resolution of this electrometer is unequaled by any known ambient-air-operated instrument over a wide range of source capacitances. The EFM has a resolution of 630 V/m, the best reported figure for a MEMS device.
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