BAW resonator design considerations - An overview

Bulk-Acoustic-Wave (BAW) filters are on their way to replace conventional RF-filters in major wireless communication standards such as PCS, WCDMA, WiFi, or WiMAX. The main advantage is a performance which is unmatched by SAW filters or ceramic filters, while maintaining low manufacturing costs. In order to achieve excellent device characteristics, regardless if this device is a simple band pass filter or a oscillator circuit, it is necessary to have high performance resonators available. The fundamental requirements for such a high performance resonator are an accurate frequency position, high quality factor, sufficient piezoelectric coupling (high bandwidth), small TCF (temperature coefficient of frequency), and spurious mode free operation. In this paper, the necessary optimization process for each of these characteristics will be reviewed.