Development of High Frequency Surface Acoustic Wave Devices Using MOCVD ZnOPiezoelectric Thin Films on Sapphire Substrates

摘要

The primary purpose of this program was to develop high quality piezoelectricthin films deposited by Metalorganic Chemical Vapor Deposition (MOCVD) process over 3 Sapphire substrates and to fabricate high frequency surface acoustic wave (SAW) devices has been accomplished. Fabricated films have been characterized for thickness, thickness uniformity, orientation of the film and surface morphology. Annealing displayed a good thermal stability and improved surface morphology and crystallinity. A test photomask was designed-and used for evaluating the stability of the MOCVD ZnO film as well as photolithography process for SAW device applications. The test mask also includes test structures for measurements of the basic SAW design parameters. The ZnO film resistivity was identified as a major issue. The development of a simple but reliable Li-diffusion process significantly alleviates this problem. Although the ZnO film resistivity remains to be an important issue for practical device applications, very good Rayleigh wave properties have been demonstrated. These include moderately high SAW velocity, strong electo-mechanical coupling as well as high electrode reflectivity, which are essential for high frequency low-loss SAW devices. As a result of this study areas of further improvement to realize practical high-frequency SAW devices are identified.