Wide bandwidth silicon nitride membrane microphones

Brian T. Cunningham, Jonathan J. Bernstein

Research output: Contribution to journalConference articlepeer-review

Abstract

Small, low cost microphones with high sensitivity at frequencies greater than 20 KHz are desired for applications such as ultrasonic imaging and communication links. To minimize stray capacitance between the microphone and its amplifier circuit, process compatibility between the microphone and onchip circuitry is also desired to facilitate integration. In this work, we have demonstrated micromachined microphones packaged with hybrid JFET amplifier circuitry with frequency response extending to 100 KHz, and voltage sensitivity of ∼2.0 mV/Pa from 100Hz to 10 KHz, and 16.5 mV/Pa at 30 KHz with a bias voltage of 8.0 V. The microphones are fabricated with membranes and fixed backplates made of low temperature plasma-enhanced chemical vapor deposited (PECVD) silicon nitride. Because the maximum temperature of the fabrication process is 300 °C, microphones may be built on silicon wafers from any commercial CMOS foundry without affecting transistor characteristics, allowing integration with sophisticated amplifier circuitry. Low stress silicon nitride deposition was used to produce membranes up to 2.0 mm diameter and 0.5 μm thickness with +/- 0.10 μm flatness. The excellent planarity of both the diaphragm and the backplate, combined with a narrow sense gap (∼2 μm) results in high output capacitance (up to 6.0 pF). The high output capacitance results in noise spectral density which is approximately 3x lower than silicon diaphragm microphones previously fabricated by the authors. Diaphragms with corrugations were fabricated to relieve tensile stress, to increase deflection per unit pressure, and to increase deflection linearity with pressure.

Original languageEnglish (US)
Pages (from-to)56-63
Number of pages8
JournalProceedings of SPIE - The International Society for Optical Engineering
Volume3223
DOIs
StatePublished - Dec 1 1997
Externally publishedYes
EventMicromachining and Microfabrication Process Technology III - Austin, TX, United States
Duration: Sep 29 1997Sep 29 1997

Keywords

  • Corrugated membrane
  • Micromachined microphone
  • Silicon nitride membrane

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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