Wafer bonding of lead zirconate titanate to Si using an intermediate gold layer for microdevice application

A technique was developed for precisely bonding lead zirconate titanate, PZT, to a Si wafer using thin gold film as an intermediate layer. PZT is used in various types of sensors and actuators, and bonding of bulk ceramic PZT to a Si wafer is the key to fabricating microactuators that can generate a large force. A tight bonding of more than 20 MPa was attained at bonding temperatures of 450, 500, and 550 °C and a pressure of 0.8 MPa. The strength initially increased with the bonding time up to about 2–7 h, depending on the bonding temperature, and then decreased. An intermediate layer thickness of about 0.8 µm was needed to obtain a tight bonding. The bond strength also depended on the poling process. The fracture mechanism in a tensile test of bonded wafers was investigated. Testing of a cantilever- type actuator to which a bonded wafer had been applied demonstrated that this technique produces bonded wafers with sufficient strength for actuator application.