High performance and miniature surface acoustic wave devices with excellent temperature stability using high density metal electrodes

Currently, miniature surface acoustic wave (SAW) devices (filters and duplexers) with a good temperature stability are strongly required. In order to realize its requirement, various SAW substrates combining a high density metal electrode and a substrate were researched. Combination of SAW substrates using high density metal electrodes offers excellent properties such as large electrode reflection coefficient, large mechanical coupling factor, low velocity, and good temperature stability. This paper reviews following application of their structures for the realization of miniature SAW devices with low insertion loss and good temperature stability from various aspects: Intermediate frequency (IF) filters in mobile phones using an shear horizontal (SH) wave propagating on the high density metal electrode on ST-90 degrees X quartz substrate, SAW duplexers for personal communication service system in the United States (US-PCS) and wide band code division multiple access system (W-CDMA) using LSAW on a flattened SiO2 film on high density metal electrodes on LiTaO3 or LiNbO3 substrates, and radio frequency (RF) filters using SH type of elastic boundary wave (EBW) propagating on SiO2 film on high density metal electrode on LiNbO3.