Low Loss 1–2 GHz SAW Filters with Submicron Finger Period Electrodes

Low loss GHz SAW filters with submicron finger-period double electrodes have been developed. One was a 1 µm period 0.9 GHz filter with 5 dB insertion loss and the other a 0.5 µm period 1.9 GHz filter with 7 dB loss, both having three-transducer configurations on a 128° Y-X LiNbO3 substrate. These filters were realized by a new fabrication process, using direct wafer electron beam writing, two step mask transfer from electron resist PMMA to photoresist AZ-1350J and ion beam etching. The insertion loss was lowered mainly by optimizing ion beam etching conditions to decrease acoustic propagation losses due to electrode edge geometries, ion etched surface damages and electrode film absorption.