Research On GaN HEMT Physically Based Scalable Model Method

Gallium nitride(GaN),as an outstanding representative of the third generation semiconductor materials,has excellent properties such as high thermal conductivity,high electron mobility,high breakdown field strength and high temperature resistance.Due to these excellent properties,high electron mobility transistor(HEMT)based on GaN is one of the best choices for power applications.A high-precision model of GaN HEMT can not only reduce the cost and development cycle,but also guide the circuit design of the devices.Therefore,it is of great significance to study the modeling of GaN HEMT.At present,GaN HEMT models mainly include empirical-based and physical-based models,which have been studied extensively by domestic and foreign researchers.Among them,the most parameters of physical-based model have physical significance,and physical-based model has good scalability,which also has a guiding effect on the optimization and improvement of devices,so it is a research hotspot.However,GaN HEMTs are difficult to test and have complex physical effects,which greatly increases the difficulty of physical modeling.Therefore,this thesis carried out an in-depth study on the modeling method of the physical-based scalable model of GaN HEMT.The main research contents and innovations of this thesis are as follows:(1)The basic theoretical knowledge of GaN materials and GaN HEMTs is introduced.This thesis introduces the ASM-HEMT model in detail,deduces the core formula of the model,and introduces the modeling method of physical effects.It provides theoretical support for the subsequent improvement of physical-based scalable model of GaN HEMT based on ASM model.(2)Considering the parasitic effect of field plate in GaN HEMT,a small signal model of GaN HEMT with field plate parasitic capacitances is proposed.The on-chip test technology and data embedding of GaN HEMT are introduced.Finally,the parameter extraction method of the small signal model is described in detail,and the proposed small signal model is verified.The verification results show that the model has good precision and high universality.(3)Based on the surface-potential-based ASM-HEMT model,the physical-based large signal model of GaN HEMT is improved.The improved model combines and simplifies the field-plate models,greatly improving the simulation speed and convergence of the model.The equation of gate current model is modified,and the drain current model and capacitance model are improved by adding the empirical equation,which improves the fitting accuracy of the model.The trapping effect is modeled dynamically by RC network with diodes,and the self-heating effect is studied by pulse measurement.(4)The parameter extraction process of the improved physical-based large signal model of GaN HEMT proposed in this thesis is introduced in detail,and the fitting results of the model are demonstrated by combining with the measured data of domestic GaN HEMTs with a gate length of 0.25 μm.The scaling equations of the proposed large signal model of GaN HEMT are established,and the scaling rules are introduced in detail to obtain a complete large signal model.At last,the large signal scalable model is verified through the measured data of GaN HEMTs of different sizes.The verification results show that the physical-based large signal scalable model proposed in this thesis has the advantages of high precision,strong scalability and good convergence.