Direct bonding of lithium tantalate to silicon at room temperature by using a self-sputtered bonding method

Abstract

The direct bonding of a piezoelectric substrate to a support substrate with a low coefficient of thermal expansion is a method used in fabricating temperature-compensating surface-acoustic-wave devices. We propose a novel technique for bonding a lithium tantalate (LiTaO3) wafer to a silicon (Si) wafer at room temperature. The surface of the Si wafer is etched and activated by Ar plasma, while a thin film of Si is deposited on the surface of the LiTaO3 wafer under a high vacuum. The two wafers are then immediately brought into contact. A crack-opening method and tensile testing confirmed that the bond between the wafers was stronger than that produced by a surface-activated bonding method. An amorphous intermediate layer, approximately 8 nm thick, was observed at the bonding interface by transmission electron microscopy. Our proposed technique is useful for room temperature direct bonding of dissimilar materials with a large mismatch in their thermal expansivities.