3C-1 Review of Wave Propagation in BAW Thin Film Devices - Progress and Prospects

During the last few years the bulk acoustic wave (BAW) filters have emerged as a viable alternative to surface acoustic wave (SAW) devices. They offer superior performance regarding filtering characteristics, power handling, ESD robustness and size. The first enabling ingredient has been the rapid development in deposition techniques for the thin film piezoelectric layer. Today multiple equipment manufacturers are offering systems for depositing high quality layers with excellent piezoelectric properties. Along with the development in manufacturing issues there has also been important development in understanding the basic device physics of BAW resonators. Like any reactance elements for constructing filters there are three major concerns when designing BAW resonators: sufficient effective coupling coefficient, high Q-values and operation free of spurious modes. These properties enable the fabrication of filters with sufficient band width, low insertion loss, steep transition bands and ripple free characteristics. In this paper developments leading to state-of-the-art BAW resonators are reviewed.