Research On Breakdown Characteristics Of GaN HEMT In Dynamic Process

GaN-based high electron mobility transistors feature the characteristics of high breakdown voltage,high operating temperature,high power density and high operating frequency which is promising candidate for power application.Since the emerge of GaN HEMTs,after nearly 30 years of development,the commercial products have appeared and been used in the field of consumer electronics.Schottky P-GaN Gate HEMTs are one of the solutions for today's industry enhancement-mode.However,due to its complicated P-GaN / AlGaN / GaN multilayer gate structure,its dynamic threshold voltage,dynamic on-resistance,short-circuit robustness and other dynamic reliability have become the focus of scholars' research in recent years.In addition,the manufacturing and dynamic characteristics of enhancement-mode GaN MOS-HEMTs with high gate voltage swing is also one of the hot spots in the industryBased on the complicated gate structure of P-GaN Gate HEMTs and the static breakdown characteristics of GaN devices different which are from Si devices.During the switching of power devices,their breakdown characteristics affect system reliability and turn-off losses.This thesis focuses on the dynamic breakdown characteristics of GaN HEMTs power devices.Based on the gate carrier transport model of P-GaN Gate HEMTs proposed in our previous group work,the hole injection induced channel barrier lowering effect was proposed,which revealed the reason for the dynamic soft breakdown of P-GaN Gate HEMTs.Based on the development of UTB-GaN MOS-HEMTs,the breakdown characteristics under dynamic drain bias were characterized and preliminary explanations were made.The main contents of this article are as follows:(1)This thesis designs a reverse blocking current sampling test circuit,which has been verificated and fabricated.Based on the exisiting Schottky P-GaN Gate HEMTs gate hole injection model at high gate voltage,combined with the hole trapping effect of the donor defect level in the buffer layer,on-state the gate current flow is found Sub-transport will affect the height of the electron barrier in the channel during turn-off,revealing the cause of premature soft breakdown of the device.With the extension of the turn-on time of P-GaN HEMTs,it was found that the reverse blocking current of P-GaN HEMTs will rise firstly and then decrease,proving the correctness of the hole injection induced channel barrier lowering effect,while the decrease in current indicates that the gate carrier transport mechanism is affected by temperature,and a new equilibrium state is reached.(2)Based on the depleted interface 2DEG by the ultra-thin barrier layer,UTB-GaN MOS-HEMTs were fabricated and their basic characteristics were characterized.Via the experiment dynamic drain bias breakdown,it is found that its reverse blocking current increases with the increase of dynamic drain bias.Based on a controled experiment with different channel lengths and passive metal field plate devices,it was found that the electric field distribution in the channel was the cause of the increase in reverse blocking current under dynamic drain bias.Based on the dynamic bias time experiment,it is found that the mechanism that affects the dynamic breakdown characteristics of the device occurs within 5 ms.