If SAW filters without love wave's spurious consisting of ZnO film and specific cut angle quartz substrate

Abstract

The substrate with large electromechanical coupling factor and excellent temperature coefficient of frequency (TCF) is required to realize surface acoustic wave filters for the first intermediate frequency stage (1st IF). One of the authors (M. Kadota) realized a Rayleigh wave substrate with an excellent TCF and a large electromechanical coupling factor by a combination of a specific quartz substrate (ST-cut 35/spl deg/X propagation: ST- 35/spl deg/X) having a positive TCF with a ZnO film having a negative TCF. But, it has been clarified that the SAW filter having of a single electrode (strip) or single-phase unidirectional transducer (SPUDT) on the ZnO/ST-35/spl deg/X-quartz substrates, often had a large spurious response due to the Love wave which was a higher-order-mode of the Rayleigh wave. The new cutting angle and the propagating direction (26-27/spl deg/Y-X) on quartz has been developed in order to suppress the spurious response. The IF SAW filters for the wide-band and the narrow-band code division multiple access (W-CDMA: 380 MHz and N-CDMA: 183.6 MHz) have been developed by combining this 26-27/spl deg/YX quartz with the ZnO film. The IF filters which have a small-size, an excellent TCF, a low insertion loss, a cost advantage in their applications, and no spurious responses due to the Love wave have been realized. Their frequency shift per 1/spl deg/C from -20/spl deg/C to 80/spl deg/C was less than 0.37 ppm//spl deg/C, which was better than a Rayleigh SAW on an ST-cut X propagation quartz.