Localized Si-Au eutectic bonding around sunken pad for fabrication of a capacitive absolute pressure sensor

In this paper, we present a method that using localized Si-Au eutectic bonding around the pads sunk in the bonding interface to enhance the vacuum package of the capacitive pressure sensor in the process of anodic bonding. Generally, the connection wires can cause the gas leakage of the sensor with a vacuum cavity. For preventing the leakage from the wires, a new structure with sunken pad is developed that the wire bonding pads are sunk under the silicon wafer. It has the characteristic that opened window in silicon wafer is with a smaller size than the bonding pad and eutectic bonding occurs around the pad. The experiment results illustrate that good vacuum hermetic sealing can be obtained with a strength of 10.65 MPa and a leak rate of less than 2.4 × 10−4 Pa cm3/s under the conditions of bonding temperature of 375 °C and chromium/gold step height less than 50 nm.