Bulk micromachined electrostatic RMS-to-DC converter

• Published in: IEEE transactions on instrumentation and measurement Vol. 50; no. 6; pp. 1508 - 1512
• Main Authors: de Graaf, G., Bartek, M., Xiao, Z., van Mullem, C.J., Wolffenbuttel, R.F.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2001; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidth; Beams (radiation); Biomembranes; Dynamic range; Electric potential; Electrostatics; Glass; Harmonics suppression; Low voltage; Membranes; Micromachining; Micromechanics; Silicon; Voltage; Wafer bonding
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/19.982936

Bulk micromachining in silicon and glass wafers and subsequent silicon-to-glass anodic bonding have been used for the realization of an electrostatic RMS-to-DC converter. A suspended membrane has been designed for: large dynamic operating range (detection limit by minimum mechanical-thermal noise and high value of the pull-in voltage), maximum bandwidth (low series resistance, high second harmonic suppression using squeeze film damping and suspension beam design), long-term stability, and a sufficient displacement-to-voltage sensitivity (membrane area and suspension arm length). Prototypes are typically composed of a 3 /spl times/ 3 mm/sup 2/ perforated membrane area suspended by four beams of 200 /spl mu/m length, 500 /spl mu/m width, and 4 /spl mu/m thickness micromachined out of silicon and aligned to a counter electrode on glass with 4-/spl mu/m spacing in between. Measurements on realized devices show a 4.5 pF nominal capacitance. Static measurements indicate a sensitivity of 5 fF/V/sup 2/ and a voltage shift of 0.2 V. The nominal square relation is achieved within a 0.5% nonconformity error.