Research On Electrothermal Model For Millimeter-Wave GaN Power Devices

Gallium Nitride?GaN?high electron-mobility transistors?HEMTs?are becoming the important power amplifier device for radar,electronic warfare and the fifth-generation mobile communication?5G?system in millimeter-wave band due to their high frequency,high-power,and high-efficiency characteristics.Since the influence of ambient temperature and self-heating are main constraints on electrical property and reliability of GaN HEMT,the related research on ambient temperature-dependent electrothermal large-signal model is of great significance for the design and optimization of GaN HEMT circuit,improving the design success rate and reducing the design cycle and cost.However,up to now,the large-signal modeling of millimeter-wave GaN HEMTs,especially the modeling of electrothermal effect of these devices under high/low ambient temperatures is still not mature enough.With the further application of domestic GaN devices in millimeter-wave high-power and high/low temperature environments,it is urgent to study the large-signal characteristics and mechanism of GaN HEMT in millimeter-wave band and to develop the electrothermal large-signal model which can accurately describe the effect of ambient temperature and self-heating to achieve efficient design of millimeter-wave GaN monolithic circuits and improve circuit performance.Therefore,based on the electrothermal effect mechanism of the device,the electrothermal large-signal modeling technology of millimeter-wave GaN HEMT fabricated by domestic process line has been systematically studied by using equivalent circuit modeling approach with the support of national major projects.The main research content and innovation are as follows:1.Due to the poor accuracy of infrared thermal measurement and finite element simulation in thermal resistance extraction,a new nonlinear thermal resistance extraction method combining infrared thermal measurement and finite element analysis?FEA?is proposed for millimeter-wave GaN HEMT according to the heat conduction theory of semiconductor device.The thermal conductivity of FEA is calibrated by infrared measurement to make the calculated channel average temperature close to the infrared measurement,so as the peak temperature and the corresponding thermal resistance of the device can be extracted accurately and efficiently.Measured results show that the thermal resistance can be over-estimated of about 28%by using only FEA,while the thermal resistance is under-estimated of about 35%by using only infrared thermal measurement.Finally,based on this method,the nonlinear thermal resistance of a GaN HEMT with 0.15?m gate-length under different bias conditions and ambient temperatures is extracted,and the scaling law of GaN HEMTs with different gate width and gate fingers is also deduced,provides a theoretical basis for the establishment of electrothermal model.2.Aiming at the difficulty of direct extraction of small-signal parasitic parameters in millimeter-wave GaN HEMT,a new inter-electrode coupling capacitance extraction method is proposed according to the mechanism of intrinsic capacitance of device depletion region.The method uses high drain voltage to suppress the intrinsic capacitance value in the pinch-off state to directly extract the coupling capacitance between the gate and the drain,and avoids negative capacitance extraction value of the gate-drain intrinsic capacitance caused by the multi-valued problem of the conventional optimization extraction method.In addition,the scan dimension of parasitic capacitance parameters required for model parameter extraction is reduced from two-dimensional of conventional method to one-dimensional,which can improve the extraction efficiency of small-signal parameters.Based on this method,the small-signal model parameters of GaN HEMT with0.15?m gate-length are extracted.The results show that the average S-parameter calculation error of the small-signal model extracted by this method is less than 5.5%over the entire bias domain.3.Aiming at the shortcoming of the conventional method in electrothermal effect modeling of the millimeter-wave GaN HEMTs under high/low ambient temperature,the influence of temperature-dependent access resistances on large-signal modeling of millimeter-wave GaN HEMTs under high/low ambient temperature has been deeply studied.According to the physical composition of access resistance and their temperature dependence,a new separate extraction method of temperature-dependent drain and source access resistance is proposed.The combination of small-signal and pulsed I-V measurements are carried out to solve the difficulties in separate extraction of these two temperature-dependent access resistances,and improve the extraction efficiency.Besides,the influence of temperature-dependent access resistances on the extraction of small-signal intrinsic parameters of a 0.15?m GaN HEMT is analyzed.Based on the improvement of the conventional Angelov model,a Ka-band electrothermal large-signal model considering the temperature dependent access resistances is established.Measured and simulated large-signal results at different ambient temperatures?-55°C to 85°C?show that:by considering the temperature-dependent access resistances,the saturated output power(P_sat)and power added efficiency?PAE?simulation accuracy of the electrothermal model can be improved by about 0.55 dB and 10%,respectively,at-55°C?corresponding to a junction temperature of 21°C?and by about 0.35 dB and 13.6%,respectively,at 85°C?corresponding to a junction temperature of 199°C?,and the temperature fitting parameters required by the model is reduced.Moreover,for GaN HEMTs with unequal gate-to-drain and gate-to-source spacing,the simulation accuracy of the output power and PAE can be improved by using the temperature coefficients of the drain and the source aceess resistance independently in the Angelov GaN model.The Psat and the corresponding PAE simulation accuracy of the Ka-band electrothermal model at-55°C,25°C and 85°C is above 90%,and the established electrothermal model can accurately describe the effects of ambient temperature and self-heating on the millimeter-wave large-signal characteristics of the device.Finally,a Ka-band electrothermal scalable model is established based on the investigation of parameter scaling law of multi-finger millimeter-wave GaN HEMT devices.On-Wafer measurement results show that the Ka-band electrothermal scalable model can accurately predict the large-signal performances of GaN HEMTs with different gate-finger and different gate-width.Based on the scalable model,a 5 W Ka-band GaN monolithic power amplifier is designed and verified.The measured results show that the simulation accuracy for both P_sat and PAE of the Ka-band model are over 90%in the frequency range from 33 GHz to 39 GHz.4.Aiming at the serious parameter dispersion effect of conventional small-signal model in W-band,a new W-band small-signal model is proposed.By introducing the bus-bar parasitic capacitance into the conventional model topology,the dispersion of parameter extraction is improved,and the S-parameter calculation error of the small-signal model at the application bias point is reduced from 26.1%of the conventional model to 8.2%for the new model.In addition,aiming at the more obvious short-channel effect of the 0.1?m GaN HEMT devices,an improved Angelov current source model is proposed.By modifying the polynomial coefficients of current source,the accuracy of the model for describing the threshold voltage shift of the millimeter-wave GaN HEMTs is improved.Finally,a W-band electrothermal scalable model is established by considering the scaling law of the bus-bar capacitances,and a 1 W W-band GaN MMIC is designed using the scalable model and to verify the model accuracy.The measured data show that considering the effect of bus-bar capacitance,the simulation accuracy for P_satat and PAE of the W-band model are improved by 5.9%and 7.8%respectively,reaching82.5%and 81.6%respectively.The accuracy of W-band GaN HEMT electrothermal model is validated.