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Optical triggering of 4H-SiC thyristors (18 kV class) to high currents in purely

inductive load circuit

Article  in  Semiconductor Science and Technology · August 2014

DOI: 10.1088/0268-1242/29/11/115003

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Optical triggering of 4H-SiC thyristors (18 kV class) to high currents in purely inductive load

circuit

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2014 Semicond. Sci. Technol. 29 115003

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Optical triggering of 4H-SiC thyristors (18kVclass) to high currents in purely inductiveload circuit

S L Rumyantsev1,2,5, M E Levinshtein1, T Saxena2, M S Shur2, L Cheng3,J W Palmour3 and A Agarwal4

1 Ioffe Institute, 26 Politekhnicheskaya, 194021 St. Petersburg, Russia2Department of Electrical, Computer, and Systems Engineering and Physics, Applied Physics, andAstronomy, CII 6017, Rensselaer Polytechnic Institute, Troy NY 12180-3590, USA3Cree Inc., 4600 Silicon Dr, Durham NC 27703, USA4EERE, US Department of Energy, 1000 Independence Ave. SW, Washington DC, USA

E-mail: roumis2@rpi.edu

Received 3 March 2014, revised 7 July 2014Accepted for publication 21 July 2014Published 20 August 2014

AbstractOptical switch-on of a very high voltage (18 kV class) 4H-SiC thyristor with an amplificationstep (pilot thyristor) to the current Imax = 1225 A is demonstrated using a purely inductive loadand a calibrated air transformer. Increasing the inductance of the transformer primary windingslows down the turn on process. However, the inductance has little effect during the initial stageof the switch-on process when the voltage drop on the thyristor and its internal resistance is high.The results show that a further switch-on current increase can be only achieved by introducingadditional amplification steps in the pilot thyristor.

Keywords: silicon carbide, power devices, thyristors, optical triggering

(Some figures may appear in colour only in the online journal)

1. Introduction

Si-based photoconductive switching devices are widely usedin many power applications including exсimer lasers drivers,electrical insulation of high power rectifiers, protection ofpower klystrons, reactive power compensators, and powerpulse generators (see, e.g. [1–5]). The study of power SiCphotoconductive switching devices began more than decadeago [6]. These devices include high voltage/high powerswitchers based on semi-insulating SiC [6, 7], SiC transistors[8], and thyristors [9, 10].

In just a few recent years SiC thyristors have progressedfrom relatively low voltage and low current devices to devicescapable of blocking up to 18 kV and switching more than1 kA (for 12 kV thyristors) [11–13]. The thyristors turn-onusing UV LEDs was reported in [14, 15].

The first results on optically triggered 4H-SiC thyristorof 18 kV class (160 μm thick blocking base) were presented

in [13]. In a purely resistive load circuit, the switch-on torelatively low currents I⩽ 12 A is different from that in12 kV 4H-SiC thyristors with 90 μm blocking base [12, 16].In particular, the 18 kV thyristors demonstrate two-stageswitching, even at the maximum light pulse energyP∼ 50 μJ and a rather high anode bias V0∼ 800 V. Duringthe first stage, the initial current increase with the char-acteristic time, τ∼ 15–20 ns is followed by the current drop.This drop is followed by the second (final) stage of thecurrent rise. The maximum and minimum current valuesduring the first stage are determined by the anode voltage,V0 and the load resistance RL. The one- dimensional modelof this unusual mechanism of the turn-on process wasdescribed in [17].

The two-stage switching process might present a seriousproblem in high current circuits because the thyristor residualvoltage remains high for a longer time. Such a combination ofhigh voltage and high current for a long time leads to unac-ceptable power dissipation.

Semiconductor Science and Technology

Semicond. Sci. Technol. 29 (2014) 115003 (5pp) doi:10.1088/0268-1242/29/11/115003

5 Author to whom any correspondence should be addressed.

0268-1242/14/115003+05$33.00 © 2014 IOP Publishing Ltd Printed in the UK1

In this paper, we report on the switch-on process in18 kV class 4H-SiC thyristors at currents up to 1200 A andcomment on the power dissipation problem.

2. Experimental details

4H-SiC 18 kV class optically triggered thyristors designedand fabricated by Cree Inc., have a single amplification step(pilot thyristor), which is located at the centre of the structureand has the area of∼ 0.0311 cm2. The total chip size of thethyristor is 1 cm2 with an active conducting area of∼ 0.5 cm2.Figure 1 (from [13]) shows the detailed cross-section of thedevice.

The blocking p-base layer doped to 2 × 1014 cm−3 was160 μm thick. The 2.5 μm thick n-base was doped to1 × 1017 cm−3. Carrier lifetimes τ in the layers of the structureswere estimated based on the detailed simulations [17]. In thep++-emitter doped to 2 × 1019 cm−3, τ= 8 × 10−4 μs. Lifetimesin n- and p-bases were 0.7 and 2 μs, respectively.

Thyristors were turned on by a UV pulse laser with thewavelength of 266 nm, pulse duration of about 30 ps, totalpulse energy P≈ 40 μJ, and repetition rate of 1 Hz or smaller.We used unfocused laser beam with diameter∼ 5 mm. Arelaxation generator with the storage capacitor Сch (see theinset in figure 2) was used for switching to relatively lowcurrents. The resistor RL connected in series with the thyristorserved as a load. Switching to the higher currents was per-formed using the mixed resistor—inductive or purely induc-tive load of L= 1.8 μH (see figure 2). The current wasmeasured using an air transformer calibrated at low andintermediate currents using the resistor RL0 in series with theprimary winding of the transformer. The resistor RL0 wasremoved for the high current measurements.

3. Results and discussion

As shown in [13], the turn-on process of 18 kV thyristorsunder investigation is realized in two stages, at least forI⩽ 12 A. Figure 3(a) shows the turn-on process in purely

Figure 1. (a) Schematic cross-section and (b) a photograph of top view of the 18 kV class SiC optically triggered thyristor under study(from [13]).

Figure 2. Schematic of measuring circuit. Purely inductive loadallows measuring maximum achievable current. Inset in the upperright corner shows the circuit for measuring small currents (purelyresistive load).

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Semicond. Sci. Technol. 29 (2014) 115003 S L Rumyantsev et al

resistive circuit at different anode voltages with the loadresistor RL = 53.6Ω [13]. As seen, the two-stage process isbecoming less pronounced with the current increase; how-ever, it still can be distinguished at the ‘on’ current Ion∼ 12 Aand the anode voltage V0 = 800 V. With the mixed inducti-ve–resistive load (L= 1.8 μH. RL0 = 6.26Ω) the two-stageprocess is observed up to approximately the same current Ionand V0 = 100 V. At higher anode voltages (and/or ‘on’ cur-rents) the two stage turn-on process vanishes, i.e. the currentincreases monotonically.

Figure 3(c) shows the signals from the secondary wind-ing of the transformer. These dependences allowed us tocalibrate the transformer at the intermediate currents. Thesecondary winding of the transformer has its own character-istic relaxation time. Therefore, shape of the pulse from thesecondary winding is slightly different from the current shape

in the primary circuit (figure 3(b)), i.e. transformation coef-ficient slightly depends on time.

Figure 4 illustrates turn-on process at higher currentswith the mixed load L= 1.8 μH and RL0 = 0.2Ω.

As expected, due to the increase in L/RL0 time constantthe current rise time significantly increases in comparisonwith the process shown in figure 3(b). However, at thebeginning of the turn-on process (inset in figure 4(a)), the rateof the current rise, dI/dt∼ 3.5 × 108 A s−1, is rather high. Aswas shown in [12], this effect is due to the high resistance ofthe thyristor itself, Rth, at the initial stage of the turn-onprocess.

Figure 4(b) shows the shape of the signal obtained fromsecondary winding of the transformer and used to calibratethe transformer. Figure 5 shows the calibration line plotted fort= 9 μs, i.e. at the instant time corresponding to the currentmaximum.

Figure 6 shows the current pulse while switching thethyristor to the pure inductive load. The pulse is taken from

Figure 3. Transient switch-on processes in 4H-SiC thyristor of 18 kVclass at different anode biases V0. (a) Purely resistive circuit;RL = 53.6Ω [13]. (b) Mixed resistor–inductive circuit; L = 1.8 μH,RL0 = 6.26Ω. Output signals proportional to the current are takenfrom series resistor RL0. (Note the different current scales in Figures.(a) and (b)). (c) Mixed resistor–inductive circuit; L = 1.8 μH,RL0 = 6.26Ω; time dependences of the output signals on thesecondary winding of the transformer (see figure 2).

Figure 4. Switch-on processes in 4H-SiC thyristor of 18 kV 4H-SiCat different values of anode bias V0. Mixed resistor–inductive circuit;L = 1.8 μH and RL = 0.2Ω. (a) Output signals proportional to thecurrent are measured across the resistor RL0 = 0.2Ω. (b) Timedependences of the output signals on the secondary winding of theair transformer at the same values of V0. The inset magnifies theinitial stage of the process for V0 = 400 V.

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Semicond. Sci. Technol. 29 (2014) 115003 S L Rumyantsev et al

the secondary transformer winding. The data are plotted usingthe calibration line shown in figure 5.

As seen, the maximum achieved current is 1225 A. Thedevice survived a few pulses before it was destroyed. Thismaximum current is only slightly smaller than the maximumcurrent of 1300 A achieved in [12] for the 12 kV class 4H-SiCthyristor with the blocking base of 90 μm. It is noteworthythat the voltage drop and power dissipated in 18 kV structurewith 160 μm blocking base width should be much higher.

As shown in [13, 18], the 12 kV thyristors contain so-called ‘weak points’, which are characterized by a sub-stantially smaller critical charge [19–21] than that within theremaining part of the optical window [16, 20–22]. Theseweak points are caused by technological non-homogeneities,and current density in the narrow current filaments around the

weak points is extremely high [12]. According to [18], the18 kV thyristors apparently do not have these kinds of ‘weakpoints’. The ability of 18 kV class thyristors to switch almostthe same currents as 12 kV thyristors is one more argumentsupporting this hypothesis.

An inductive circuit slows down the turn-on process. Asa result, turn-on state spreads to a larger area reducing themaximum current density during the turn-on process. How-ever, inductance has little effect during the initial stage of theprocess when the voltage drop on the thyristor and its resis-tance are still high. Therefore, a further current increase isonly possible to achieve by introducing additional amplifi-cation steps in the pilot thyristor [23].

4. Conclusion

An optical switch-on of a very high-voltage (18 kV class) 4H-SiC thyristor to the current Imax = 1225 A has been demon-strated. Pure resistive and mixed resistive-inductive loadswere used to calibrate the air transformer. The maximumcurrent was obtained with a purely inductive load, L = 1.8 μH.Although the voltage drop and power dissipated in 18 kVstructure with blocking base width, Wp = 160 μm should bemuch higher than those in 12 kV thyristor with Wp = 90 μm,the maximum achieved currents are virtually equal for bothstructures. This can be explained by the absence of ‘weakpoints’ in the 18 kV structures. A further switch-on currentincrease will require introducing additional amplificationsteps in the pilot thyristor.

Acknowledgment

At Cree Inc., this work was supported by Mr Charles Scozzieof Army Research Laboratory, Adelphi, Maryland. At theIoffe Institute this work was partly supported by the RussianFoundation for Basic Research. The work at RensselaerPolytechnic Institute was supported by the Army ResearchLaboratory under ARL MSME Alliance (Project Monitor DrMeredith Read).

References

[1] Auston D H 1975 Appl. Phys. Lett. 26 101[2] Jensen J-P and Merz W 2003 Proc. of the Particle Accelerator

Conf. (Portland, OR, 12–16 May, 2003) pp 749–51[3] Hur J H, Hadizad R, Hummel S G, Dzurko K M, Dapkus P D,

Fetterman H R and Gundersen M A 1990 IEEE Trans.Electron Dev. ED-37 2520

[4] Korobovand V and Mitin V 1996 Journ. Appl. Phys. 79 1143[5] Baliga B J 2008 Fundamental of Power Semiconductor

Devices (Berlin: Springer)[6] Doǧan S, Teke A, Huang D, Morkoc H, Roberts C B, Parish J,

Ganguly B, Smith M, Myers R E and Saddow S E 2003Appl. Phys. Lett. 82 3107–9

[7] Kelkar K S, Islam N E, Fessler C M and Nunnally W C 2006J. Appl. Phys. 100 124905

Figure 5. The relationship between the thyristor’s current at theinstant of time t = 9 μs and voltage at the secondary transformerwinding (calibration curve).

Figure 6. Time dependences of the current in the circuit with pureinductive load L = 1.8 μH at different values of anode bias V0. Signalwas taken from the secondary winding of the transformer. The datarepresented on the vertical axis are plotted using the calibration lineshown in figure 5.

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[8] Feng Zhao and Mohammad M I 2010 IEEE Trans. ElectronDevices Lett. 31 1146–8

[9] Levinshtein M E, Ivanov P A, Agarwal A K and Palmour J W2002 Electron. Lett. 38 592

[10] Levinshtein M E, Ivanov P A, Agarwal A K and Palmour J W2003 Proc. of the 2002 European Conf. on Silicon Carbideand Related Materials ECSCRM2002 (Linkoping, Sweden)Mater. Sci. Forum 433-436 851–4

[11] Zhang Q J et al 2012 2011 ICSCRM (September 11–16, 2011,Cleveland, OH) Mater. Sci. Forum 717-720 1151–4

[12] Rumyantsev S L, Levinshtein M E, Shur M S, Cheng L,Agarwal A K and Palmour J W 2013 Semicond. Sci.Technol. 28 045016

[13] Rumyantsev S L, Levinshtein M E, Shur M S, Cheng L,Agarwal A K and Palmour J W 2013 Semicond. Sci.Technol. 28 125017

[14] Dheilly N, Paques G, Planson D and Scharnholz S 2011 Proc.of the 2010 European Conf. on Silicon Carbide and RelatedMaterials ECSCRM2010 (Oslo, Norway) Mater. Sci. Forum679-660 690–3

[15] Dheilly N, Paques G, Scharnholz S, Bevilacqua P, Raynaud C,Nguyen D, De Doncker R W and Planson D 2011 Electron.Lett. 47 459

[16] Rumyantsev S L, Levinshtein M E, Shur M S, Saxena T,Zhang Q J, Agarwal A K and Palmour J W 2012 Semicond.Sci. Technol. 27 015012

[17] Mnatsakanov T T, Yurkov S N, Levinshtein M E, Cheng L andPalmour J W 2014 Semicond. Sci. Technol. 29 055005

[18] Levinshtein M E, Rumyantsev S L, Shur M S,Mnatsakanov T T, Yurkov S N, Zhang Q J, Agarwal A K,Cheng L and Palmour J W 2013 Semicond. Sci. Technol. 28015008

[19] Uvarov A I 1971 Physics of Electron-Hole Junctions andSemiconductor Devices ed S M Ryvkin and Y V Shmartsevvol 170 (New York: Consultants Bureau) p 216

[20] Shockley W 1961 Sol. State Electron. 1 35[21] Gerlach W 1981 Thyristoren (Heidelberg: Springer)[22] Mnatsakanov T T, Yurkov S N, Levinshtein M E,

Tandoev A G, Agarwal A K and Palmour J W 2003 Solid-State Electron. 47 1581

[23] Martynenko V, Hapugin A, Grishanin A, Chibirkin V,Konyuhov A, Veselova I and Surma A 2009 SilovayaElectronika (Power Electronics) 8–14 www.power-e.ru/2009_5_8.phpIn Russian

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Semicond. Sci. Technol. 29 (2014) 115003 S L Rumyantsev et al

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