Study On AlGaN/GaN HEMT Intrinsic Capacitance And Fringing Capacitance Model

AlGaN/GaN high electron mobility transistor(HEMT)is an important device in modern microwave circuits.The AlGaN/GaN HEMT capacitance model has important research significance for accurately predicting analog/digital chips in microwave and millimeter waves.At present,many modeling methods of AlGaN/GaN HEMT capacitance models have been proposed,but the physical factors affecting the intrinsic capacitance can be further discussed.When the device works at a large gate bias,the influence of parasitic channel carriers in the barrier layer on the intrinsic capacitance needs to be further studied.The gate capacitance is composed of intrinsic capacitance and fringe capacitance.If the influence of the fringing capacitance is ignored,there will be a large error in the final result.A total gate capacitance model including fringe capacitance needs to be established.In order to study the effect of AlGaN barrier layer carriers(n _B)on the intrinsic capacitance,this paper considers the barrier layer carriers in the V_g-n_s model,and establishes an intrinsic capacitance based on the Ward-Dutton charge distribution principle.Based on this capacitance model,the relationship between V_g-n_s and V_g-n _B is analyzed,and the effect of n _B on intrinsic capacitance under different bias conditions is studied.In this paper,the conformal mapping method is used to model the outer fringing capacitance.At the same time,considering the channel length modulation effect,the bias voltage variable and the process parameter variable are introduced into the outer fringing capacitance model of the drain,and a characteristic of bias voltage and C_ofd physical model of process parameters.Based on this model,the relationship between bias voltage and process parameters and C_ofd is analyzed.In order to obtain a complete gate capacitance model,this paper uses conformal mapping method and add transition functions to establish the inner fringe capacitance(C_ifs/d)model,and combines the intrinsic capacitance and the outer fringe capacitance model to obtain the source/drain total gate capacitance model.Based on this model,the relationship between the bias condition and the fringe capacitance is analyzed.We compare the difference of the effect of external bias on gate capacitance when the fringe capacitance is considered and when the fringe capacitance is not considered,and the error rate of the gate capacitance in the on state is calculated without considering the fringe capacitance.