| To meet the growing demand for GaN monolithically integrated circuits,it is important to have a device model that accurately and completely characterizes the electrical properties of GaN HEMTs in their actual operating state.The model is a tool to characterize the electrical parameters of the device,a link between the device,the actual circuit and the circuit design engineer,and a guarantee for the effectiveness of the circuit design.The current models for GaN HEMT devices are mainly empirical models based on test data,which do not contain real device physics and cannot accurately characterize and predict the non-ideal effects of the device in actual operation.Some models are based on device physics,which can characterize most of the non-ideal effects of GaN devices and have excellent prediction ability,but they still cannot characterize the threshold voltage shift and on-state resistance degradation caused by the widespread substrate bias effect in GaN monolithically integrated circuits,which cannot meet the circuit design requirements.Therefore,based on the real physical mechanism of GaN HEMT devices on silicon in the substrate bias effect,this thesis investigates the modeling technology route that can accurately predict the threshold voltage shift and on-resistance degradation of GaN HEMT devices on silicon under different substrate bias stresses based on the real physical mechanism of GaN HEMT devices on silicon in the substrate bias effect,and establishes a compact GaN HEMT model based on device physics.physical model to provide support for monolithically integrated GaN system simulation.The main research contents of this thesis are as follows:(1)Study of the physical mechanism of the substrate bias effect in GaN-on-Si HEMT devices.The direct effect of substrate bias with different polarities on the twodimensional electron gas(2-DEG)concentration at the device Al GaN/GaN interface and the indirect effect of the trap-trapping effect on the 2-DEG concentration induced by the occurring GaN Buffer layer are first analyzed based on device physics.The field effect and trap effect due to substrate bias are identified as the main mechanisms leading to the device threshold voltage shift,on-state resistance degradation and current capability degradation,providing a theoretical basis for the subsequent modeling of the substrate bias effect.Next,four common connections of the common substrate of GaN-on-Si HEMT devices in monolithically integrated half-bridge circuits are combined with practical applications to analyze the change in substrate potential of the upper and lower tubes under each connection method,and to determine the test scheme for the substrate bias effect.(2)Modeling techniques for substrate bias effect of GaN-on-Si HEMT devices.Based on the above-mentioned research on the physical mechanism of the substrate bias effect of GaN-on-Si HEMT devices,the substrate bias effect model of GaN-on-Si HEMT devices under different switching states and different substrate bias polarities is established by combining the field effect of capacitive coupling and SRH statistical theory,including the prediction calculation of the device threshold voltage,effective mobility and final drain current.Secondly,the I-V characteristics of GaN HEMT devices on silicon are tested under different switching states and different substrate bias polarities based on the above proposed test scheme,and the model parameters are extracted.The average Rsquered value is not less than 0.98. |
