Study Of GaAs-Based Resonant Tunneling Piezo-resistive Acoustic Sensor

This thesis reports a novel nano electronical mechanical system (NEMS) cantilever acoustic sensor. The cantilever acoustic sensor is based on the pizeo-resistive effect of GaAs/AlAs/InGaAs Resonant Tunneling Structure (RTS).The applied pressure on the cantilever induces stress in the layers of the RTS, which will induce change in the electrons effective mass and the generated piezoelectric fields inside the well and the barrier materials. Then the energy states will also change. These variations will change the peak current and voltage of the RTS. It is equivalent to the change of electrical resistance of RTS in a definite bias voltage. The mechanical-electrical conversion can be realized through the piezo-resistive effect.The thesis introduces detailedly the principle, structure design and process of the cantilever acoustic sensor based on the piezo-resistive effect of RTS. The design of RTS and cantilever structure are discussed respectively. To more further, the basic cantilever structure of the acoustic sensor is calculated and simulated through the acoustic analysis theory and Ansys finite element analysis software respectively. Finally, the structure dimensions of GaAs/AlAs/InGaAs RTS and the cantilever are confined.The process flow of the cantilever acoustic sensor based on the RTS is established combining the molecular beam epitaxy (MBE), the process of micro-electronics and NEMS. The double air-bridges technology is used to decrease the resonant tunneling current and parasitized capacitance, and control holes technology is used to fabricate the cantilever. Finally, the process integration of RTS and M/NEMS is realized.The encapsulation and tests of the GaAs-based cantilever acoustic sensor are accomplished primarily. The test results show that: the sensitivity of cantilever structure is 0.226uV/Pa (4.4KHz), the frequency response is 1.2KHz-10KHz; The sensitivity of swatter cantilever is 1.0uV/Pa (9KHz), the frequency response is 0.75KHz-20KHz.The main research fruits are as following:(1) Design a novel acoustic sensor based on the piezo-resistive effect of RTS(2) The double air-bridges technology is used to fabricate the RTS which could decrease the resonant tunneling current and parasitized capacitance;(3) The basic cantilever structure of the acoustic sensor is fabricated, and the acoustic sensor is encapsulated and tested. The test results show that the performance of the acoustic sensors is good.