Novel Structures Of GaN-based Power Devices With 3D-RESURF

High energy efficiency,small size and high power density have becoming the demand for power system,required by the modern development of digitization,intelligence and greenness.Gallium nitride(GaN)material with its advantages of large band gap,high critical field strength,and high electron saturation speed is going to be more demand-satisfied than conventional silicon material in power electronics field.Although GaN-based high electron mobility transistor(HEMT)power devices have achieved preliminary commercialization after more than two decades of development,due to conventional HEMTs structural limitations,they still have the problems of un-uniform internal electric field distribution and weak blocking ability.In view of the above-mentioned problems existing in the current GaN HEMT,this thesisproposes a new high-performance GaN HEMT structure,which realizes a new electric field modulation method that is different from the conventionalfield plate technology in GaN lateral devices.The main research contents of this thesis are as follows:(1)A 3D-RESURF GaN HEMT(3-Dimensional Reduced-Surface-Field GaN High Electron Mobility Transistor)structure with P-type GaN insertion layeris proposed.Its characteristics are as follows:1.The P-type GaN insertion layer is introduced to achieve electric field modulation.A p-n junction composed of P-GaN—2DEG is formed at the drift region,while in blocking-state the depletion and expansion of the space charge region of the p-n junction introduces a new electric field components in the parallel direction with the gate width,which changes the original electric field direction and makes the electric field distribution more uniform in the drift region.Meanwhile,the p-n junction is capable of assisting the depletion of the 2DEG,which effectively reduces the leakage current and improves the voltage block capability of the device for a given drift region length.By simulation analysis,the introduction of the new structure reduces the electric field spike at the drain side gate edge by more than 20%,and the breakdown voltage of the device increases from 340V to 733V,improved by 115%.While achieving the same breakdown voltage and on-resistance as the conventional device,the new device can achieve a 41.9%area saving.2.The P-type GaN insertion fingers extend to the source side and connect to the source of the device to provide the source of holes,protecting P-type region quickly recover during turn-on state.(2)The relationship between the key parameters(such as L_p,N_p,T_p and W_p)of the device and the device characteristics is discussed,and an optimization strategy of device structural parameters is proposed.In order to quantify the area-advantage brought by the new structure,the area-gain-factor parameter and its calculation method is proposed.(3)The processing flow of the new structure device is discussed and designed to demonstrate the feasibility of the new structure device.