Room-temperature bonding of lithium niobate and silicon wafers by argon-beam surface activation

The residual stress originating form the thermal expansion mismatch has been a serious problem in the bonding of piezoelectric crystals onto silicon wafers. The room-temperature bonding method using argon-beam surface activation is applied to the bonding of lithium niobate and silicon. In this method, the surfaces of the specimens are etched by fast argon atom beam and bonded to each other in vacuum. Bonding strength equivalent to that of the bulk material is achieved without any heat treatment. Transmission electron microscope observations show intimate contact at the interface. This method is quite suitable for bonding dissimilar materials with thermal expansion mismatch, because the bonding is performed at room temperature throughout the whole process and no thermal stress is generated.