A facile approach to fabricate ZnO thin film based micro-cantilevers

Abstract

In this study we report on the design, micro-fabrication and characterization of piezoelectric micro-cantilevers based on zinc oxide (ZnO) thin films. Array of micro-cantilevers are realized using silicon wet bulk micromachining process. ZnO films are very sensitive to nearly all chemicals, acids, base and even water. New unit process is developed to protect ZnO films, which utilizes wafer protection jigs. This jig allows tetra-methyl-ammonium hydroxide (TMAH) wet etching on single side of wafer, while protecting active devices on the other side. Highly c-axis oriented and room temperature deposited ZnO films are utilized for micro-cantilever fabrication. ZnO films used in this study have good crystalline quality with full width half maxima (FWHM) ~0.39°, grain size ~80nm and have minimal stress of ~41MPa. The micro-cantilever consists of Si/SiO2/Si3N4/Al/ZnO/Al multilayer stack for self-actuation of devices. Dynamic study is done using laser Doppler vibrometer. A customized relationship has been derived between resonance frequency and cantilever length considering multilayer structure. This inexpensive novel fabrication method provides flexibility to realize variety of other micro-electro-mechanical systems (MEMS) piezoelectric devices. The developed method is cost effective, easy, hassle free and may be preferred over deep reactive ion etching (DRIE) process.