Performance Evaluation and Fabrication of Gallium Nitride (GaN) MEMS Devices

GaN and related group III nitrides were heavily investigated in the applications of lighting, solar cell and other optical devices. Many research have focused on improving crystal structure purity, light generating efficiency, power efficiency and band-gap manipulating. One of the exciting applications of GaN based devices is micro electrical mechanical system (MEMS). In this report, several mechanical properties, including Young's modulus, hardness, Poisson's ratio, thermal expansion, thermal conductivity and piezoelectricity, were discussed. By using finite element analysis (FEA) software further confirmed that GaN has better performance in both thermal and piezoelectric properties comparing to conventionally used silicon (Si). The simulation results showed that GaN performed much better than Si in the simulations of a sensor due to its high Young's modulus. Another simulation, a thermo-controlled actuator, showed that even though GaN and Si had similar thermal conductivity in high temperatures, the sensor of GaN performed better due to its higher thermal expansion coefficient in high temperature. Moreover, GaN is stable at high temperatures so that it is a more desirable than Si at high temperatures. In the end of this thesis, a special etching technique, PEC wet etching, was demonstrated by machining an InGaN/GaN epitaxial multilayer. The result showed that PEC technique was able to selectively etch InGaN thin films. However, the dislocations appeared to be an obstacle to obtain a smooth surface. Therefore, the assistance of dry etching might as well be needed. Although the quality of GaN thin film is still far from perfect, the superior properties of GaN and the effective fabrication method of GaN has been proved promising in this report.