Investigation of two-level split finger transducers

Unidirectional characteristics of two-level split finger transducers are calculated as functions of the structure parameters, for several electrode materials (Al, Cu, Au etc.) on ST-X quartz, by using a method based on boundary integral equations for the grating structure. The calculation results show that the two-level structures have sufficiently large reflectivity by choosing the electrode materials and modifying the structure parameters. Moreover, 190 MHz range two-level structure filters are fabricated by using high accurate mask alignment techniques with a position error of 50nm. The experiments show a good agreement with the calculations. It is found that the two-level split finger transducers have a larger transduction coefficient and a high reflectivity, compared with other SPUDTs such as a distributed acoustic reflection transducer (DART) or an electrode width control (EWC) SPUDT. It is therefore possible to reduce an insertion loss of the SPUDT filters.