Influence of bulk wave excitation on performance of impedance elements SAW filters realised on 36/spl deg/ and 42/spl deg/-LiTaO/sub 3/ substrates

This paper presents new results of the influence of bulk wave excitation on the performance of impedance elements (IE) SAW filters in the 200-950 MHz frequency range realized on 36° and 42°-LiTaO₃ substrates. It was found experimentally, for devices using metal film thickness to wavelength ratio h/λ in the range of 5%-8%, that bulk wave activity on 42°-LiTaO₃ substrate is essentially less than that for the 36°-LiTaO₃ substrate. Another result of this paper is that the amplitude ripple, rejection and the insertion loss in the bandwidth of IE filters realized on 36° and 42°-LiTaO₃ substrates depend on the roughness of the wafer backside, type of glue and thickness of metal film. Three different filters are presented: a low loss filter in the 900 MHz range with 4% relative bandwidth and a measured insertion loss of less than 0.5 dB, a filter at about 450 MHz with 2% relative bandwidth and more than 50 dB level of rejection and finally a filter in the 200 MHz range with a relative bandwidth of about 4% and an insertion loss of 0.7 dB.