A Piezo-Avalanche Accelerometer

We are reporting on the first use of the piezo-avalanche effect in a micromachined sensor for the measurement of inertial forces. The device integrates a pn junction at the base of a beam that is used as the spring for the microstructure. Movements of a proof-mass at the opposite end of the beam produce stress at the location of the junction. To measure this stress, the junction is forced into its reverse breakdown region while monitoring its current-voltage relationship. The mechanical stress modifies the bandgap of the material, eventually leading to a change in its breakdown voltage. It is shown that this simple structure provides a high sensitivity of ~3 nA/g when the device is biased with a fixed voltage in its breakdown region. The device operation is modeled analytically, and results are found to be in good agreement with the experiments. The piezo-avalanche effect scales favorably and can be utilized for stress measurements at arbitrary locations on a structure as well as at nanoscales. [2019-0247]