Abstract
A novel temperature compensated SAW substrate was developed by using direct bonding techniques. This method has merits to keep the same coupling factor and propagation loss as the original piezoelectric substrate and need not strict control of substrate thickness. Temperature compensating method using direct bonding techniques requires support substrate with small thermal expansion coefficient and large elastic coefficients. Sapphire is one of the ideal materials for the support substrate. Thickness of the piezoelectric substrate has large influence on the temperature characteristics and spurious responses caused by reflection of bulk acoustic wave at the bonding interface. We found appropriate thickness of LiTaO3 with good temperature characteristics and no spurious responses. Using bonded LiTaO3/sapphire SAW substrate, US-PCS SAW duplexer with small temperature coefficient of frequency and good frequency characteristics was developed. Power durability of the duplexer using bonded LiTaO3/sapphire SAW substrate was excellent because of high thermal conductivity of sapphire.
