Vibration of micromachined circular piezoelectric diaphragms

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 53; no. 4; pp. 697 - 706
• Main Authors: Eunki Hong, Trolier-McKinstry, S., Smith, R., Krishnaswamy, S.V., Freidhoff, C.B.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2006; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Biomembranes; Capacitive sensors; Diaphragms; Electrodes; Excitation; Lead zirconate titanates; Membranes; Nonlinearity; Piezoelectric films; Piezoelectricity; Q factor; Resonance; Resonant frequency; Semiconductor films; Silicon; Vibration; Vibrations
• ISSN: 0885-3010; 1525-8955; 0885-3010
• DOI: 10.1109/TUFFC.2006.1621496

The electrically and mechanically excited resonances in micromachined circular piezoelectric diaphragms have been investigated. The diaphragm structures were piezoelectric unimorphs consisting of Pb(Zr/sub 0.52/,Ti/sub 0.48/)O/sub 3/ (PZT) films and thermally grown silicon oxide (SiO/sub 2/) layers. For electrical excitation, ring-shaped interdigitated (IDT) electrodes formed on the top of the PZT layer were used to induce strain in the diaphragms. The diaphragm structures behaved much like circular membranes in which the membrane tension was /spl sim/206 N/m, at the fundamental modes. For higher modes, the resonance frequencies deviated from the theoretical values due to the finite stiffness of the diaphragms. Under mechanical drive, both symmetric and asymmetric modes were excited. However, for electrical excitation, the symmetric modes were dominant due to the symmetry of the driving IDT electrodes. At a pressure of 727 Torr, the quality factor was /spl sim/250, and this rose to 2000 at pressures below 1 Torr. When a forward bias was applied to the diaphragm, the membrane tension decreased, but under reverse biases the tension increased. However, because of repoling under reverse biases greater than the coercive field of the PZT film, the achievable increase in the membrane tension was limited. In the diaphragm structure, the nonlinear vibration was governed by geometric nonlinearity rather than material nonlinearity. In addition, evidence of non-180/spl deg/ domain wall motion of the PZT layer in released diaphragms was observed.