Study On Field Plate For High Breakdown Voltage GaN-based Power Devices

Gallium nitride(GaN),due to its wide band gap,large critical electric field,high electron mobility and good thermal conductivity,has met the requirements of the next generation of electronic equipment for more power,higher frequency,smaller size and more severe high-pressure and high-temperature operation of power devices.Especially in the intelligent quick charging field,GaN power device quick charger has the advantage of larger power,smaller volume and faster charging speed.The breakdown voltage is an important parameter to enhance the power processing and conversion capability of GaN power devices.As one of the most mature and effective technologies to improve the breakdown voltage process,field-plate structure still has many problems: for example,the average breakdown electric field of field-plate structure devices is far lower than the critical breakdown field of GaN materials,and the optimization period of complex field-plate structure device is too long.Therefore,the optimization of complex field-plate structure and the design and optimization of high breakdown field-plate structure are of great significance to improve the voltage resistance characteristics of field-plate structure devices.Based on GaN power device,the composite field-plate structure and related parameters are studied and optimized.Firstly,on the simulation platform,the parameters such as field-plate length,thickness and passivation layer thickness of the gate field-plate,source field-plate and drain field-plate structure devices are optimized respectively.Then,according to the simulation results,some parameters of the composite field-plate structure devices are determined,and length of the source field-plate and the passivation layer thickness under the source field-plate are further optimized.Finally,combined with regulation of simulation,the parameters of the actual composite field-plate structure device are optimized,and the composite field-plate structure device with up to 1820 V breakdown voltage is fabricated,which is 12% higher than the structure device without field-plate.In this paper,GaN power devices with slant gate field-plate structure and discrete field-plate structure are studied,and the relevant parameters are optimized.Firstly,on the simulation platform,the slant gate field-plate structure is simplified into the corresponding stepped field-plate structure.After optimizing the parameters such as the number of steps,the thickness of steps and the thickness of passivation layer under the gate field-plate,the breakdown voltage of 502 V of this device is obtained.On this basis,a multi-discrete field-plate structure is proposed.By comparing the influence of the two structures on the electric field distribution in the channel of the device under the same voltage,it can be found that the multi-discrete field-plate structure can also improve the breakdown voltage of the device effectively.Furthermore,the parameters such as the field-plate length,the field-plate spacing and the thickness of the passivation layer under the field-plate are optimized for single discrete field-plate and double discrete field-plate structure devices.Finally,combined with the regulation of simulation,the parameters of GaN power devices with actual single discrete field-plate structure and double discrete field-plate structure are optimized,and the double discrete field-plate structure device with a breakdown voltage of 1350 V is fabricated,which is about 108% higher than that structure device without field-plate.