Piezoelectric Pb(Zrx, Ti1-x)O3 thin film cantilever and bridge acoustic sensors for miniaturized photoacoustic gas detectors
Abstract
Novel, highly sensitive piezoelectric acoustic sensors based on partially unclamped Pb(Zrx, Ti1-x)O3 (PZT) coated cantilever and bridge have been fabricated by silicon micromachining. High sensitivity at low frequencies (5-100 Hz) has been achieved by patterning very narrow slits (3 to 5 µm) around the structures. A typical response of 100 mV Pa-1 and a noise equivalent pressure of 1.6 mPa Hz1/2 at 20 Hz have been measured using a 10 pF charge amplifier. Stress compensation, dry etching and integration of high performance piezoelectric thin films were the key issues. PZT/Pt/SiO2 stacks have been patterned by reactive ion etching and stress compensation has been achieved by compensating the PZT film's tensile stress by adjusting the thickness of a thermal SiO2 layer. The integration of sol-gel PZT films with a transverse piezoelectric coefficient e31,f of -12.8 C m-2 has been realized without any degradation of the properties. The microphones were successfully integrated into a miniature photoacoustic detector and tested for CO2 detection. Concentrations down to 330 ppm could be measured with significant signals.
- Publication:
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Journal of Micromechanics and Microengineering
- Pub Date:
- December 2004
- DOI:
- 10.1088/0960-1317/14/12/008
- Bibcode:
- 2004JMiMi..14.1650L
- Keywords:
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- acoustic sensor cantilever bridge piezoelectric PZT thin film photoacoustic