Effects of Si3N4 and DLC passivation layers on characteristics of SAW filters

Silicon nitride (Si3N4) and diamond-like carbon (DLC) passivation layers were deposited on Surface Acoustic Wave (SAW) filters with Al inter-digital electrodes formed on LiTaO3 substrates. The adhesion of the DLC film to LiTaO3 substrate has been enhanced by introducing SiO2 interlayer. Si3N4 passivation layer is found to be capable of minimizing the variations of both insertion loss and bandwidth of the SAW filters during power durability test (PDT), while DLC layers show little effect on these variations.