Humidity-Induced Voltage Shift on MEMS Pressure Sensors

The pressure sensor is one of the major applications of microelectromechanical systems (MEMS). An absolute pressure sensor utilizes anodic bonding to create a vacuum cavity between the silicon diaphragm and glass substrate. The manifold absolute pressure (MAP) sensing elements from a new supplier have exhibited negative voltage shifts after exposure to humidity. A hypothesis has been established that poor anodic bonding causes an angstrom-level gap between the silicon substrate and glass. Once moisture enters the gap in a vapor form and condenses as water droplets, surface tension can induce a piezoresistive stress effect that causes an unacceptable voltage shift. Finite element analyses were performed to simulate the phenomenon and the results correlated well with experimental observations.