GaN HEMT Dynamic ON state Resistance characterisation and

Gan Hemt Dynamic On State Resistance Characterisation And-Free PDF

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when device switches in a power converter Conclusions are Voltage bias circuit. given at last,II G A N HEMT DYNAMIC ON STATE RESISTANCE D2. MEASUREMENT Vcom1,ID measurement,560 F Voltage Clamping. A Measurement circuit Lpara Rload D circuit, GaN device RDS on values can be obtained by measuring D1 gm. device ON state voltage VDS on across it and current ID Lpara. through it in an electrical circuit As the measured bias Vcom. S VDS measurement, voltage when device is OFF VDS off could achieve more than. several hundred times higher than device VDS on a voltage a Measurement configuration. clamping circuit is necessary to reduce the measured VDS off. in order to increase measurement accuracy For this reason the Vcom1 Vcom1. measurement circuit shown in Fig 2 is constituted by a bias. circuit to control device trapping time when it is OFF and. a voltage clamping circuit to measure device VDS on value. when it is ON t, In the bias circuit a transistor T1 is used to control DUT.
trapping time A resistive load Rload is used to set the current. level when DUT is in ON state Because of the parasitic. inductance Lpara of the Rload two diodes D1 D2 offer a 0 t. free wheeling path of the current when either T1 or DUT is 0 t1 t2 t t1 t2 t3 t4. b Control signal to measure steady c Control signal to measure dy. switched from ON to OFF state RDS on namic RDS on, The voltage clamping circuit is constituted by a depletion Fig 2 GaN HEMT dynamic ON state resistance measurement. mode D mode Si MOSFET and a zener diode DUT mea circuit and control signals. surement voltage VDS m is measured across the zener diode. The principle of the voltage clamping circuit is that when. DUT is ON D mode Si MOSFET is in ON state Vgm sm is Load Voltage clamping circuit. superior to MOSFET threshold voltage Vth so points sm. and dm are almost in the same potential and DUT VDS on. can thus be measured directly VDS m VDS on When, DUT is OFF zener diode junction capacitance is charged at. first so VDS m increases to the zener diode clamping voltage. Vclamp and then Vgm sm is inferior to Vth Afterwards D mode. MOSFET is pinched OFF and its inter electrode capacitance. Cdm sm is charged to withstands almost the whole bias VDS. voltage VDS VDS m It is to be noted that as there D1 DUT. is a leakage current balance between D mode MOSFET and T1. Zener diode VDS m is inferior to Vclamp in steady state. Instead of measuring voltage range between VDS on and VDS. a much smaller voltage range between VDS on and Vclamp. Fig 3 Realization of the measurement circuit, is measured thus the measurement sensitivity is increased. Compared to the similar type voltage clamping circuits that are. analyzed by authors in 6 less components and no external. all the bias voltage is across DUT Afterwards at t3 DUT. power supply are used in this clamping circuit, is switched ON again so current ID flows through the DUT. Device steady state RDS on could be measured by applying Finally at t4 T1 is switched OFF Thus DUT trapping time. the control signal shown in Fig 2b where DUT is kept always is controlled by t2 t3 while detrapping time is controlled by. in ON state and T1 is controlled by a single pulse t3 t4 so RDS on values of different trapping and detrapping. time could be measured, Device dynamic RDS on could be measured by applying.
the control signal shown in Fig 2c where DUT is initially The realization of the measurement circuit is shown in. kept in ON state and T1 blocks all the bias voltage Then at Fig 3 In the measurement Rload 100 T1 is a commercial. t1 DUT is switched OFF and at t2 T1 is switched ON thus GaN HEMT EPC2012C 200V 5A while D1 and D2 are the. Dynamic RDS on 120V,Dynamic RDS on 80V,Steady state RDS on. 0 5 10 15 20 25 30 35 40 45 50,0 5 10 15 20 25 30 35 40 45 50. 0 5 10 15 20 25 30 35 40 45 50 102 100,t Time s 10 2. Fig 4 Measured waveforms when device is bias at 80V for Fig 5 Comparison of steady state RDS on and dynamic. 10 s RDS on at 25 C,same Schottky diode MBRS4201T3G 200V 4A Dynamic. RDS on values of a DUT which is the same as T1 is measured. by the above circuit of which the results are presented in the. next section,B Measurement results, Several major parameters of the measurement equipments A.
and clamping circuit devices are summarized in TABLE I. In the measurement the maximal measured VDS voltage is 2 2 5 3 3 5 4 4 5 5. 3 3V which could achieve a measurement accuracy of at least. 28 0 013V by using a 8 bit resolution oscilloscope GaN. 3 3 Fig 6 RDS on values of different VGS voltages at 25 C. HEMT dynamic RDS on values are measured when it is biased. at 80V and 120V,III G A N HEMT DYNAMIC ON STATE RESISTANCE. When GaN HEMT is biased at 80V and trapping time is MODELLING. 10 s the measured voltage VDS m current ID and voltage. VGS are shown in Fig 4 Because of the voltage clamping A Behavioural model. circuit VDS m is about 1 7V when DUT is OFF which is. much smaller than the bias voltage 80V It is to be noted When in steady state the measured device RDS on values. that maximal VDS m almost does not change when the bias of different VGS voltages at 25 C is shown in Fig 6 which. voltage increases to 120V thus the measurement accuracy is presents that RDS on values increase when VGS voltage de. improved in comparison to a direct measurement creases. DUT dynamic RDS on values are calculated after instant According to this RDS on VGS relation the obtained dy. t in Fig 4 which is 1 s after OFF ON transition when namic RDS on values could be represented by static RDS on. each electrical parameter stabilizes The obtained RDS on values at the equivalent gate voltage shown in Fig 6 where. values based on the above waveforms is shown in Fig 5 in point A corresponds to the RDS on value when it is obtained at. which RDS on values are compared between steady state and steady state and point B corresponds to the RDS on value af. dynamic state when device is biased at 80V and 120V at 25 C ter certain trapping time The VGS voltage difference between. point A and point B which is defined as Vcomp could be. As shown in the results RDS on values increase with the. applied to represent RDS on change during the trapping and. trapping time and it decreases with detrapping time and it. detrapping process After adding Vcomp in gate circuit which. increases more with a higher bias voltage For this device. is shown in Fig 7 device VGS voltage VGS VG Vcomp, it is observed that when device biased by a certain trapping. after trapping time could be adjusted thus a dynamic RDS on. time it needs a longer detrapping time to reduce its dynamic. value could be obtained, RDS on values to the steady state values which shows that. effective RDS on values are likely to be higher than theoretical It is shown that Vcomp increases with the trapping time and. values in application A behavioural model is proposed based decreases with the detrapping time in which the phenomena. on the measurement results which will be presented in the could be modelled in the form of an RC circuit which is. next section presented in Fig 7 In each RC unit Vcompn increases when. Vcomp D Measurement,Trapping time 100ms Model,1 s 10 s 100 s. 10 6 10 5 10 4 10 3 10 2 10 1, C1 Cn Fig 8 Comparison between the measurement and model on.
V1 k1 VDS Vcomp1 Vn kn VDS Vcompn dynamic RDS on values as a function of detrapping time for. different trapping times when VDS 80V,Vcomp Vcomp1 Vcompn. Fig 7 Dynamic RDS on values representation by behavioural 0 45. model Measurement,Trapping time 100ms Model, capacitor Cn is charged by a controlled voltage source Vn. through resistor Rnt and it decreases when Cn is discharged 10 s. through resistor Rnd Thus GaN HEMT trapping and detrap 0 15 1 s. ping effect could be represented by a series of the RC units. and Vcomp value is the sum of the voltage of the capacitor in. each unit Based on the measurement results shown in Fig 5 10 6 10 5 10 4 10 3 10 2 10 1. when bias voltage is 80V seven RC units are used to represent Time s. device dynamic RDS on values in which parameters V1 V7 Fig 9 Comparison between the measurement and model on. C1 C7 R1d R7d and R1t R7t are obtained by fitting methods dynamic RDS on values when VDS 120V. The values of the above parameters are given in TABLE II. The comparison between the model and the measurement is. shown in Fig 8 where the model represents generally well B Model extension for different bias voltage. dynamic RDS on values of different trapping and detrapping. time Following by that the same model is used to represent the. measurement results when the device is biased at VDS 120V. After obtaining the above parameters the model illustrated. In order to represent device dynamic RDS on values of. in Fig 7 could be easily implemented in a circuit simulator. different bias voltages by the model and easily implement it. In this paper the model is implemented in PSPICE where. only V1 V7 are fitted again when VDS 120V while the. Vcomp and V1 V7 are represented by voltage controlled. other parameters are the same as obtained when VDS 80V. voltage source and coefficients k1 k7 could be calculated. once V1 V7 are known In such a case bigger Vcomp values might be obtained so. TABLE I Major parameters of the measurement equipments and clamping circuit devices. Oscilloscope Current probe Voltage probe D mode MOSFET Zener diode. DPO4104B 1GHz 8 bit TCP312 100MHz 30A TPP1000 1GHz 300V BSP149 200V Vth 1 4V BZT52C3V3 3 3V. TABLE II Parameters using to represent GaN HEMT trapping effect when device is bias at 80V. V1 V2 V3 V4 V5 V6 V7,0 51V 0 6V 0 28V 0 25V 0 66V 0 1V 0 97V. R1d R2d R3d R4d R5d R6d R7d, 2 5 109 8 5 105 2 7 103 1 1012 1 1012 1 1014 1 1010. R1t R2t R3t R4t R5t R6t R7t,85 6 5 6 31 5 2 106 1 6 104 2 9 107 0 05.
C1 C2 C3 C4 C5 C6 C7, 1 9 10 9 F 1 3 107 F 1 10 9 F 8 6 10 10 F 2 8 10 11 F 2 2 10 9 F 9 4 10 11 F. Vcom1 Vcom,Simulation,Measurement,0 t1 0 t1 0 15, Fig 10 Control signal when device switches continuously in. a power converter,Steady state RDS on, bigger dynamic RDS on values would be represented when 0 05. device is biased at the same trapping time as VDS 80V It 10 10 10. corresponds to the measurement results shown in Fig 5 that a Duty cycle is 50. bigger dynamic RDS on values are obtained when device is. bias at 120V than at 80V 0 25,Simulation, Obviously all the above 28 parameters could be fitted again Measurement. to represent the measurement results when VDS 120V 0 2. However it might be difficult to find the trend of each. parameter with the bias voltage especially that of Rnd Rnt. and Cn In contrary the trend of Vn with the bias voltage is. easier to be found and implemented in the model, The obtained parameters of V1 V7 in this situation are.
Steady state RDS on, given in TABLE III The comparison between the model and. the measurement when device biased at 120V is shown in 0 05. 10 10 10 10 10, Fig 9 where it is shown that the model could represent the Time s. measurement in a reasonable way b Duty cycle is 90. As GaN HEMT suffered from trapping effect its RDS on Fig 11 Comparison between the measurement and simulation. values might increase when it switches continuously in a on RDS on values when device switches at 80V. power converter For this reason RDS on values estimated. by the above model is compared with the measurement and. the results will be presented in the next section, IV M ODEL VALIDATION varies from 50 s to 90 s According the measurement results. shown in Fig 8 dynamic RDS on values are not influenced. A Switching voltage at 80V by detrapping time obviously in this detrapping time range. which might explain that a change of duty cycle does not. The same electrical circuit shown in Fig 2a with the control change device RDS on values obviously The trapping effects. signal shown in Fig 10 is used to measure device dynamic can increase RDS on values very quickly when trapping time. RDS on values when it switches continuously In order to inferior to 10 s thus it might still increase device RDS on. avoid device self heating it switches at 10kHz with different values when device using in high frequency converter more. duty cycles and a duration of 0 1s than 100kHz However if device switches in high frequency. the switching loss might increase device junction temperature. When switching voltage is 80V and duty cycle D is 50. Tj which would also increase device RDS on values, and 90 the comparison of the RDS on values is shown in. Fig 11a and in Fig 11b separately As explained previously It is also shown in Fig 11 that the trend of the RDS on. device detrapping time to reach its steady state RDS on value values increase in the measurement is represented generally. is longer than trapping time to increase its dynamic RDS on well by the simulation where the difference between the mea. values which explains that the measured RDS on values surement and the simulation in both situations is within 17. increase to a factor of two higher than its steady state value The difference between the simulation and the measurement. after 0 1s in the measurement The trapping time in the above might be due to the difference between the model and the. measurements varies from 50 s to 10 s and detrapping time measurement shown in Fig 8 on dynamic RDS on values. TABLE III Parameters using to represent GaN HEMT trapping effect when device is bias at 120V. GaN HEMT Dynamic ON state Resistance characterisation and Modelling Ke Li Paul Evans Mark Johnson Power Electronics Machine and Control group University of Nottingham UK Email ke li nottingham ac uk paul evans nottingham ac uk mark johnson nottingham ac uk Abstract GaN HEMTs suffer from trapping effects which might increase device ON state resistance R DS on values Thus dynamic R

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