.algan / Gan Hemt Breakdown Characteristics Of Research And Field Plate Structure Optimization Design

In recent year,AlGaN/GaN HEMTs are excellent candidates for high power microwave applications and the experiments show that the breakdown voltage can be improved remarkably by employing the technology of field plate(FP).In this work,we investigated the breakdown character and the design of AlGaN/GaN HEMT with field plate.Firstly,the basic breakdown character of device was studied.The breakdown of device occurs at the gate edge because there is one electric field peak at that place in the ideal AlGaN/GaN HEMT.If considering the effects of trap on the breakdown character,it is shown that the electric field peak rises at the drain edge while it falls at the gate edge.When the breakdown voltage goes beyond a certain voltage,the breakdown will occur in the neighborhood of the drain edge.This conclusion modifies the conventional viewpoint that the breakdown always occurs at the gate edge of HEMT.Secondly,we have finished designing mental field plate of AlGaN/GaN HEMT based on two optimized rules.According to the rule of electric field peak in channel equals breakdown field,we got three best geometrical variables when X_Al=0.25 and the thickness of AlGaN lay is 30nm,the breakdown voltage enhanced more than five times. However we often use another rule in practical project due to the unstable process of HEMT based on GaN.The rule is that the electric field peak achieve the lowest electric field along the channel for a given drain voltage V_d and material parameter,if chose appropriate geometrical variables.Through simulations,we obtain two different formulas for designing the optimum insulator thickness and the least length of field plate.Finally,AlGaN/GaN HEMT with high-k field plate(FP)was investigated.It was proved that the electric field was suppressed effectively and breakdown voltage was improved markedly in this structure.The numerical results show that the application of high-κFP makes the electric field peak at surface and channel reduced 69.6%and 73.1 %while V_d=100V and V_g=-6V,for the device with typical structural parameters.The numerical simulations suggest that the electric field peak in channel trends to saturation with the gate-drain separation,and complies with the exponential function with the permittivity and thickness of high-κmaterial,respectively.