High temperature stable GHz-range low-loss wide band transducers and filter using SiO/sub 2//LiNbO/sub 3/, LiTaO/sub 3/

GHz-range low-loss transducers and filters are required for communication systems, especially mobile telephone communication systems. Many types of low insertion-loss transducers and filters utilizing the high electromechanical coupling coefficient (K/sup 2/) materials such as LiNbO/sub 3/ and LiTaO/sub 3/ have been developed. Unfortunately, these materials have large temperature coefficients of the frequency (TCF). In this paper, SAW substrates with high coupling coefficients and low propagation attenuations and small temperature coefficient of frequency in the GHz-range are theoretically and experimentally investigated. The experimental results show very low propagation loss of 0.02 dB//spl lambda//sub 0/ and larger K/sup 2/ than those of the substrates of LiNbO/sub 3/ and LiTaO/sub 3/ at the TCF of below -5 ppm//spl deg/C at 1/spl sim/2 GHz-range. The low-loss filter results using internal reflection types of IDT show the insertion loss of about 2.9 dB at 1 GHz and 4.9 dB at 2 GHz under the TCF's of 0 and +20 ppm//spl deg/C. These materials are applicable for devices at GHz-range because SiO/sub 2/ thickness is very thin such as below 1 /spl mu/m and the center frequency shift of the filter versus SiO/sub 2/ thickness is very small.<
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