Gan Based Hemt Pressure Structure Of The Research And Design

The peak of gate electronic field determinates the breakdown voltage of normal GaN HEMTs, so it is important to reduce the peak of gate electronic field and thus enhance the breakdown voltage.Bases on the device physics, the electric field distribution model, which is along the surface and the channel, is established in this paper. It can be used in the devices with and without field plates both. This model fixes well to the simulation results and shows that, with the gate field plate, the peak of gate electronic field is saturated with the improving drain voltage. The saturation value of gate electronic field is reduced exponentially by thinning the gate dielectric and increased exponentially by extending the field plate. However, the peak of field plate electronic field will increase with the drain voltage until device is breakdown. Based on the model, we optimize the thickness of gate dielectrics, and obtain the quantitative relationship between the optimized thickness and drain voltage..Furthermore, we also discuss the influence of field plate structure to other device characteristics. Due to the field plate structure, the conductive resistance of the device increase and the fT decreases. The quantitative relationship between the two factors and field plate parameters is established.At last, the influence of impurities and surface states to the breakdown voltage is discussed. Because the impurities extend the channel depletion layer, breakdown voltage decreases. Although the surface states lower the peak of field plate electronic filed, they increase the peak of gate electronic field. When surface states vary between 1012 cm-2 and 1013cm-2, the breakdown voltage is nearly the same as the one with no surface states.