A GaAs acoustic sensor with frequency output based on resonant tunneling diodes

This paper reports a novel acoustic sensor with a frequency output based on AlAs/InxGa1−xAs/GaAs resonant tunneling diode (RTD). The RTD is incorporated in a 1 μm thick membrane and the fabrication technology of the membrane is based upon the selective etch of GaAs with AlAs as an etch stop layer. A relaxation oscillator is obtained with the RTD biased in the negative differential resistance (NDR) region. Acoustic pressure applied to the RTD changes the frequency of oscillation due to the shift in current–voltage characteristics. The main feature of this sensor type is the direct frequency output, which is linearly dependent on pressure, and the linear sensitivity can be up to 21 kHz/kPa.