SAW unidirectional interdigital transducer with ultra-low insertion loss and wide band in 10MHZ-10GHZ range

Abstract

Surface acoustic wave (SAW) filters employing unidirectional interdigital transducers (UDT) show low loss properties. We proposed a single phase unidirectional transducer (UDT) with about /spl lambda//4 electrode width of the best transducer efficiency. The UDTs are obtained by IDT on the very thin dielectric grating with /spl lambda//8 shifts. The electromechanical couplings (k/sup 2/) of electrodes on SiO/sub 2/ films decrease rapidly for film thickness. Therefore the good properties of UDT are obtained for the very thin thickness of SiO/sub 2/ grating (about 0.03/spl mu/m at 2GHz with electrode thickness of Al of 0.07/spl mu/m). In this paper we describe the experimental results of wide band and very low loss filters with below 1dB insertion loss at 500MHz and 2GHz-range.