Piezoelectric properties and residual stress of sputtered AlN thin films for MEMS applications

• Published in: Sensors and actuators. A. Physical. Vol. 115; no. 2; pp. 501 - 507
• Main Authors: Iborra, E., Olivares, J., Clement, M., Vergara, L., Sanz-Hervás, A., Sangrador, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 21-09-2004
• Subjects: AlN; MEMS; Piezoelectric; Sputtering; Stress; AlN; MEMS; Sputtering; Piezoelectric; Stress
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2004.03.053

In this work we investigate the suitability of piezoelectric aluminium nitride (AlN) films deposited by RF sputtering as the actuating element in microelectromechanical system (MEMS) devices. We have studied the influence of some sputtering parameters (substrate bias voltage and pressure) on the preferred orientation, grain size, residual stress and piezoelectric response of the films. X-ray diffractometry (XRD) has been used to obtain the preferred orientation and grain size. The residual stress was deduced from measurements of wafer curvature. The piezoelectric response was evaluated from the frequency response of surface acoustic wave (SAW) filters. A careful control of the energy supplied to the substrates enabled us to grow films with pure
c-axis orientation and good piezoelectric response. The sputtering pressure had to be adjusted to reduce the amount of residual stress. As a result, we have determined the relationship between the sputtering parameters and the film characteristics. We present preliminary results of the fabrication of micromachined suspended bridge structures formed by AlN/polysilicon bimorphs.