Bonded substrate and a manufacturing method thereof, and a surface acoustic wave device using the said bonded substrate

Abstract

An object of the present invention is to provide a bonded substrate which is excellent in temperature characteristics and suppresses unnecessary response due to reflection of an elastic wave at a bonding interface. [Means to Solve the Problems] The present invention is unique in that a bonded substrate is constructed by bonding a LiTaOsubstrate and a base plate wherein a Li concentration at a base plate-bonding face of the LiTaOsubstrate is higher than that at a LiTaOsubstrate-side end face of the bonded substrate, that the difference between the Li concentration at the base plate-bonding face of the LiTaOsubstrate and the Li concentration at the LiTaOsubstrate-side end face of the bonded substrate is 0.1 mol % or greater, that the Li concentration at the base plate-bonding face of the LiTaOsubstrate satisfies an equation Li/(Li+Ta)×100=(50+α) mol %, where α is in the range of −1.2<α<0.5, that the Li concentration at the LiTaOsubstrate-side end face of the bonded substrate satisfies an equation Li/(Li+Ta)×100=(48.5+β) mol %, where β is in the range of −0.5<β<0.5, and that the thickness measured from the base plate-bonding face of the LiTaOsubstrate to the LiTaOsubstrate-side end face of the finished bonded substrate becomes greater than 5 times but less than 20 times the wavelength of the surface acoustic wave or that of the leaky surface acoustic wave.