Low-loss unidirectional SAW filters using integrated microinductors

The design and testing of a low-loss integrated SAW filter using group-type unidirectional transducers (GUDTs) for excitation and detection are reported. The phase-shifting and matching network design comprises a 1-mm-sq, 176-micron-pitched 6-nH thin-film square-spiral inductor printed on an SiO2 film magnetron-sputtered on 128-deg-rotated Y-X LiNbO3 substrate, and a 400 sq-micron 1000-A-thick 56-pF SiO2-film capacitance, for operation at 260 MHz and IRF = 0.1. A prototype device using a 3000-A-thick SiO2 film and a smaller coil, and operating with IRF = 0.4 was found to have a minimum insertion loss of about 1.6 dB. This type of filter requires no external discrete component, can be manufactured using present LSI fabrication techniques, and has applications in signal processing for the higher VHF and UHF ranges.