Capacitive Absolute Pressure Sensor with Vacuum Cavity Formed by Bonding Silicon to Soiwafer for Upper Air Observations

We present a capacitive absolute pressure sensor with a large deflected diaphragm that was fabricated with a sealed vacuum cavity formed by removing handling silicon wafer and oxide layers from a SOI wafer after eutectic bonding of a silicon wafer to the SOI wafer. The deflected displacements of the diaphragm formed by the vacuum cavity in the fabricated sensor were similar to simulation results. This result was estimated because of the dense interface produced between cavity-formed Si and the top Si layer of the SOI wafer by the Si-Au eutectic bonding process. Initial capacitance values were about 2.18pF and 3.65pF under normal atmosphere, where the thicknesses of the diaphragm used to fabricate the vacuum cavity were 20 μm and 30 μm, respectively. Also, it was confirmed that the differences of capacitance value from 1000hPa to 5hPa were about 2.57pF and 5.35pF, respectively.