TRANSVERSAL TYPE PIEZOELECTRIC RESONATOR USING ZnO THIN FILM ON MICRO-FABRICATED ELINVER (Fe-Ni-Cr-Ti) ALLOY

摘要

A transversal type 3.58MHz piezoelectric resonator has been fabricated using piezoelectric ZnO thin film on ELINVER (Fe-Ni-Cr-Ti ) alloy. The ZnO/ELINVER structure piezoelectric resonator has been designed to have 2 ppm temperature coefficient of frequency (TCF) per degree from -20 degrees to 80 degrees centigrade. The temperature coefficient of ELINVER alloy can be controlled to cancel the TCF of ZnO thin film by heat annealing. The ZnO thin film on ELINVER alloy shows c-axis orientation. The c-axis orientation of the ZnO thin film is strongly influenced by the surface roughness of the ELINVER alloy. The wet etching process has been adopted to shape the resonator made from ELINVER alloy substrate. The cross section of the resonator is a structure tapered about 10 degrees, created using different sized photo masks on each side of the ELINVER surface. The tapered cross section of the transversal type resonator greatly improves the frequency characteristics of the resonator. The electrical characteristics of the resonator after the improvement include a resonance frequency of 3.58MHz trimmed by a YAG laser, and resonance resistance of about 200 Ω. The temperature coefficient of frequency is about 1.5 ppm per degree at a temperature range of -20 degrees to 80 degrees centigrade.