Surface acoustic wave filter in high frequency with narrow bandwidth and excellent temperature characteristic

A radio frequency (RF) filter in high frequency such as MediaFLO™ and Tenestrial Mobile Multimedia Broadcasting (T-MMB) in China handy phone TV system requires a narrow bandwidth, and also very excellent temperature coefficient of frequency (TCF). Among substrate having excellent TCF of less than 5ppm/°C such as an Al-electrode/ST-X quartz, a ZnO/quartz, and a langasite, a flattened SiO2/high density metal electrode/36°–48°YX-LiTaO3 structure has been applied to these applications because it has suitable coupling factor, reflection coefficient, excellent TCF, and permitivity to realize desired frequency characteristics and the impedance of 50Ω in input or/and output terminal of the filter. By optimizing the thickness of SiO2 and metal electrode, the RF filter having very excellent TCF of −1.01ppm/°C, a good insertion loss, and large outband rejections has been realized.