ruggedness of 1200v sic mps diodes - laas-cnrs

Microelectronics Reliability xxx (2015) xxx–xxx

MR-11639; No of Pages 5

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Microelectronics Reliability

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Ruggedness of 1200 V SiC MPS diodes

S. Fichtner a,⁎, S. Frankeser a, J. Lutz a, R. Rupp b, T. Basler b, R. Gerlach b

a Technische Universität Chemnitz, Reichenhainer Straße 70, 09126 Chemnitz, Germanyb Infineon Technologies AG, Am Campeon 1-12, 85579 Neubiberg, Germany

⁎ Corresponding author.E-mail address: [email protected]

http://dx.doi.org/10.1016/j.microrel.2015.06.0880026-2714/© 2015 Elsevier Ltd. All rights reserved.

Please cite this article as: S. Fichtner, et al., Ruj.microrel.2015.06.088

a b s t r a c t
a r t i c l e i n f o
Article history:Received 25 May 2015Received in revised form 18 June 2015Accepted 18 June 2015Available online xxxx

Keywords:RuggednessMPS diodeSchottky diodeSurge currentReverse recoveryOvercurrentSiCSilicon carbide

SiC merged-pin-Schottky (MPS) diodes possess fast switching ability combined with low losses. Compared toconventional Schottky diodes they also provide a high surge current capability making them rugged againstsurge current pulses ofmore than seventeen times the rated current for a 10ms half-sine pulse. In this paper fur-ther aspects of device ruggedness are presented such as the surge current capability of two diodes in parallel andthe turn-off behavior at application condition and at overcurrent. Itwas found that the turn-off characteristics arealmost independent from the applied voltage. Further, the diode could withstand turn-off from fifteen times therated current.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Diodes of silicon carbide (SiC) are characterized by faster switchingand lower turn-off losses than their silicon counterparts [1]. With thedevelopment of a 600 V merged-pin-Schottky (MPS) diode these prop-erties were complemented by a high surge current capability [2,3].Meanwhile the product scope was expanded by a novel 1200 V MPSdiode from Infineon. Its surge current behavior has already been inves-tigated both in experiment and simulation. It was found that theseMPSdiodes are able to withstand up to 17 times of their rated current for ahalf-sine pulse of 10 ms [4].

This paper will present further characteristics of this novel 1200 VSiC MPS diode. Due to its remarkable properties especially at highercurrents the surge current ruggedness of two diodes in parallelwas of special interest. The turn-off behavior at nominal current con-ditions was also investigated as well as the turn-off behavior atovercurrent.

2. Function principle of an MPS diode

An MPS diode is a combination of a Schottky and a pin-diode.Integrated into the Schottky area an MPS diode contains additional

(S. Fichtner).

ggedness of 1200 V SiC MPS

p-doped regions on the anode side. In normal operation mode, i.e. atrated current, the whole current is carried by the Schottky regions.The diode is unipolar and behaves like a conventional Schottky diode.At higher currents the p-doped regions become active and the diodeturns bipolar. The overall current is made up of the Schottky and thepin current. A simplified structural model of anMPS diode and the func-tion mechanism are illustrated in Fig. 1.

The activation of the p-doped regions depends on their sizes. Largerp-regions become active at lower currents, smaller p-regions are acti-vated later at higher currents [5]. To obtain the surge current rugged-ness the diode contains p-regions of various sizes that are successivelyactivated with rising current. However, the more p-areas are placedthe less Schottky area is available. This directly leads to an increase ofthe forward resistance Ron. Normally, the diode is operated in Schottkymode. Therefore a trade-off between Schottky and pin area must befound.

3. Samples and characterization

For device testing several discrete 1200 V SiC MPS diodes fromInfineon with a rated current of 10 A were used. A sample overview ispresented in Table 1. The diodes of type A in a TO-220 package containone MPS diode chip with a rated current of 10 A. Type B diodes containtwo diode chips in a TO-247 package. Each diode chip has a rated cur-rent of 5 A. The two outer legs of the package access the anode of thediode chips. The middle leg accesses the joint cathode.

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Fig. 1. Schematic illustration of the function principle of an MPS diode. At normal opera-tion the current is carried only by the Schottky regions. In surge current mode thep-doped regions become active. From [2].

Fig. 2. Forward characterization of one diode chip of a 1200 V SiCMPS diode (type B) fromInfineon. Measured at room temperature with a curve tracer Tektronix 371B.

2 S. Fichtner et al. / Microelectronics Reliability xxx (2015) xxx–xxx

Initially the diodes were characterized both in forward and reversedirection. The forward characteristics of both diode types are picturedin Fig. 2. For these characteristics the type B diode was measuredusing one outer leg and the middle leg. Thus, only one diode chip witha rated current of 5 A was investigated. Up to a forward current ofapproximately 50 A, i.e. ten times the rated current, the type Bdiode (blue) is unipolar, behaving like a conventional Schottkydiode. Then the p-regions are activated and diode turns bipolar.The shape of the forward characteristics of a pin-diode can clearlybe seen in this current regime. Despite of a further rising currentthere is hardly any voltage increase between 50 A and 100 A, i.e. be-tween ten times and 20 times the rated current. At currents beyondthat regime the forward voltage increases again. The measurementswere performed with a curve tracer Tektronix 371B with a pulsewidth of 300 μs at room temperature.

4. Surge current characterization

The surge currentmeasurements were performedwith a purposely-builtmeasuring system [6]. The circuit diagram is displayed in Fig. 3. Thesystem is based on an LC resonator. With ω = (L·C)−1/2 the frequencyof the resonator is calculated. The system has a fixed, non-adjustable,capacitor. Several air-core coils as inductors are used to vary the pulsewidth according to tFS= π·(L·C)1/2. The surge current event is triggeredby the thyristor. The maximum current value during the sine shapedsurge current can be approximatedby IFSM=VC·(C/L)1/2with the capac-itor voltage VC. For the followingmeasurements a half-sine pulse with awidth of 10 ms was used.

4.1. Surge current behavior of a single diode

Fig. 4 shows the surge current behavior of a type AMPS diodewith arated current of 10 A during a half-sine surge current pulse with a max-imum current of 113 A. The black line marks the ascending and the redline the descending current path, respectively. After approximately 80Athe diode turns bipolar. Since the diode contains p-doped regions of var-ious sizes they are activated successively starting with the largest areas.This goes alongwith a voltage decrease until the peak current of 113 A isreached. Then, the voltage decreases with the current. In the current

Table 1Diode samples.

Name Rated current Package Number of chips

Type A 10 A TO-220 1Type B 10 A TO-247 2

Please cite this article as: S. Fichtner, et al., Ruggedness of 1200 V SiC MPSj.microrel.2015.06.088

regime between 80 A and 113 A of the ascending branch there is a neg-ative differential resistance (NDR). This may be a problem in parallelarrangement when the major part of the current is taken over by thediode with the earlier onset of NDR. Thus, this issue was investigatedsubsequently.

4.2. Surge current behavior of two parallel diodes

The surge current behavior of two parallel MPS diodes was investi-gated. The measurements were performed with two diodes of type A(DUT 1 & DUT 6) with a rated current of 10 A each. The measurementswere performed on the surge current measuring system described pre-viously. The parallel connected diodes were imposed half-sine surgecurrent pulses with a pulse width of 10ms. The total current was variedup to 180 A.

The result is displayed in Fig. 5 showing the time development ofboth diode currents (top) and voltages (bottom). At a total current of68 A the current is distributed equally, every diode is carrying 34 A.As seen in Fig. 4 at 34 A the diode is still unipolar without a negativedifferential resistance in the current–voltage-characteristics. Anasymmetric current sharing is occurring at a current of 133 A startingat approximately 3ms. DUT 6 (red) carries more than 70 Awhile DUT1 (black) carries only 60 A. The reason is in Fig. 6 which shows thecurrent–voltage-characteristics of both DUTs for this measurement.Until approx. 2.5 ms (pt. 1) both characteristics are almost equal.At 4 ms (pt. 3) both diodes have a voltage drop of approx. 5.9 V.DUT 6 enters the NDR regime. Due to its I–V-characteristics it cancarry a higher current than DUT 1. After. 7.8 ms (pt. 4) both diodesagain behave equally. Similarly, at 180 A the current difference be-tween both DUTs is considerable. While a current of 100 A is flowingthrough DUT 6, DUT 1 carries merely 80 A. However, this is alreadyten times, respectively eight times, the rated current of the device.The surge current ruggedness does not degrade in parallelarrangement.

5. Turn-off measurements

At normal operation MPS diodes behave like conventional Schottkydiodes. So the typical fast switching that is only limited by the chargeof the junction capacitance is expected at rated current and atovercurrent below the bipolar regime [1]. When switching off fromhigher currents – with the p-doped regions already active – thereverse-recovery behavior of a pin-diode with higher reverse recov-ery charge QRR and higher maximum reverse recovery current IRRM isexpected providing that the diode remains undamaged. This behav-ior occurs at approx. eight to ten times the rated current. A post-




Fig. 3. Circuit diagram of the surge current measuring system. From [6].

3S. Fichtner et al. / Microelectronics Reliability xxx (2015) xxx–xxx

characterization shall determine if the diode kept its blocking abilityand the forward characteristics after the overcurrent measurements.

For the turn-off measurements a low inductive new double pulsemeasurement system has been built up for the purpose of characteriz-ing both fast diodes and switches up to 1200 V. Circuit boards withslots for TO-packages allow fast changing of DUTs. The circuit diagramis displayed in Fig. 7. The currentmeasurementswere donewith shuntsof type SDN-414-05 [7]. The IGBT G7PH50UPbF from International Rec-tifier was used as the switching device [8]. All measurements were per-formed at room temperature.

5.1. Turn-off measurements at rated current

For the measurements a diode of type B accessing both chips wasused so that the rated current is 10 A. The turn-off measurements atrated current were performed for various DC-link voltages between400 V and 1000 V. The gate resistor of the IGBT was set to Rg = 20 Ω.As shown in Fig. 8 the current waveform and characteristic valuessuch as the maximum reverse current or the current slope di/dt are

Fig. 4. Surge current behavior of a 1200V SiCMPSdiode from Infineonwith a rated currentof 10 A (type A). The surge current pulse was a half-sine with a duration of 10 ms and apeak current of 113A. Theblack line shows the ascending path, the red line thedescendingpath. (For interpretation of the references to color in this figure legend, the reader is re-ferred to the web version of this article.)


almost independent of the applied voltage. As expected, the switchingbehavior is characterized by short switching times and low losses thatare typical for a Schottky diode.

5.2. Turn-off measurements at overcurrent

Further turn-off measurements testing the diodes ruggednesswere performed again using a diode of type B. This time only onediode chip was used. The rated current was 5 A. The gate resistorwas kept at Rg = 20 Ω. After imposing a forward current between5 A and 75 A, i.e. one to fifteen times the rated current, the diodewas switched off. The measurements are displayed in Fig. 9. Up to acurrent of 25 A the diode shows the typical fast switching character-istics of a Schottky diode as in the previous measurements. At 50 A,however, the tendency to a bipolar reverse-recovery behavior canbe presumed. At this forward current the first p-doped regions are al-ready active and the diode is slightly bipolar. When imposing a for-ward current of 75 A before the turn-off the diode becomes bipolar.This is reflected in the switching behavior which is similar to the oneof a pin-diode. This goes along with a clearly increased reverse-recovery time and higher losses.

Fig. 5. Surge current behavior of two parallel MPS diodes of type A. While at 68 A thecurrent is distributed equally there is an asymmetric current sharing at 133 A.




Fig. 6. Current–voltage-characteristics of both diodes in Fig. 5 at a surge current of 133 A.

Fig. 8. Turn-off behavior of anMPS diode at 10 A rated current (type B). The current wave-form is almost independent of the applied battery voltage.

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With increasing forward current the maximum reverse current andthe current slope di/dt increase considerably from approximately 1.5 Ato 10 A and from 370 A/μs to 1100 A/μs.

5.3. Turn-off with higher di/dt and du/dt

For these measurements Rg was reduced to 1 Ω. As a consequencethe IGBT performs faster turn-on. The switching measurements wereperformed with a diode of type B. Both legs were accessed, i.e. therated current of the diode is 10 A. The forward current through thediode was varied between 10 A and 150 A before switching off. The re-sults are displayed in Fig. 10. At rated current the maximum voltageslope du/dt is close to 120 V/ns. It decreases gradually to 50 V/ns for aforward current of 150 A. Similarly, the maximum current slopes de-crease from more than 3000 A/μs for 10 A to approximately 1200 A/μsfor 150 A. The reason for the higher slopes at lower currents is theIGBT specification which has a shorter risetime tR at lower currents[8]. At 150 A when the diode is already operating in the bipolar modea snap-off with high overvoltages occurs that is often seen for pin-diodes ([9] and references therein).

5.4. Pre- and post-characterization

Prior to the switching measurements the diode samples were char-acterized both in forward and reverse direction with a curve tracerTektronix 371B at room temperature. The forward pre- and post-characterization of the measurements in Section 5.2 is shown inFig. 11. The rated current of the diode chip is 5 A. Starting froma forwardcurrent of 60A there is a small deviation of the voltage between the pre-and post-characterization that rises to a maximum of 0.2 V. This devia-tion is led back to different measuring conditions since the

Fig. 7. Circuit diagram of the double pulse measuring system.


measurementswere performedwith time lag. At higher currents the re-sistance of the legs has to be taken into account. A resistance of 1 mΩ at150 A already causes a deviation of 0.15 V. Assuming that the diode willprobably never be operating in that high current regime above 50 A thisdeviation is negligible. Nevertheless, up to a forward current of 50 A,that is ten times the rated current, the post-characterization does notdiffer from the characterization before the strain measurements. Since

Fig. 9. Turn-off behavior of anMPS diode of type B using one chip. The rated current is 5 A,Rg=20Ω. The forward currentwas varied between one to fifteen times the rated current.Whereas at rated current the diode shows a Schottky behavior, the turn-off characteristicat 75 A is that of a pin-diode.




Fig. 10. Turn-off behavior of an MPS diode of type B with a rated current of 10 A andRg = 1 Ω. The forward current was varied between one and fifteen times the ratedcurrent. Above 100 A the diode behaves like a pin-diode. At 150 A a snap-off with highovervoltage occurs.

Fig. 11. Forward pre- and post-characterization of a diode chipwith 5 A rated current thatwas switched off from fifteen times the rated current.

5S. Fichtner et al. / Microelectronics Reliability xxx (2015) xxx–xxx

turn-off from the bipolar mode was done only once per sample the bi-polar degradation as origin for the deviation can be excluded.

It is noted that the diode maintained its blocking ability after thestress measurements. The same results were obtained for the othersamples. However, the diode should normally not be operated in thebipolar mode except under pulse (surge) conditions.

6. Conclusion and summary

The performed measurements show the ruggedness of the novel1200 V SiC MPS diodes from Infineon also under extreme overloadconditions. Theywere able towithstand turn-off frommore than fifteentimes the rated current and high du/dt and di/dt. Above approximatelyeight to ten times the rated current their switching behavior is that of apin-diode. Parallel surge current measurements did not degrade thesurge current ruggedness.


Acknowledgments

This work is supported by the German Federal Ministry of Educationand Research (BMBF) (16N11509) and the public–private partnershipENIAC JU (ENIAC-2010-1_270722-2). Jens Kowalsky and ShanmuganathanPalanisamyare acknowledged for performing the surge current and charac-terization measurements.

References

[1] A. Hefner Jr., D. Berning, J.S. Lai, C. Liu, R. Singh, Silicon carbide merged PiN Schottkydiode switching characteristics and evaluation for power supply applications,Conference Records of the Industry Application Conference, 2000.

[2] R. Rupp, M. Treu, S. Voss, F. Björk, T. Reimann, ‘2nd generation’ SiC Schottky diodes: anew benchmark in SiC device ruggedness, Proc. ISPSD, 2006.

[3] B. Heinze, J. Lutz, M. Neumeister, R. Rupp, M. Holz, Surge current ruggedness of siliconcarbide Schottky- and merged PiN-Schottky diodes, Proc. ISPSD, 2008.

[4] S. Fichtner, J. Lutz, T. Basler, R. Rupp, R. Gerlach, Electro-thermal simulations andexperimental results on the surge current capability of 1200 V SiC MPS diodes,Proc. CIPS, 2014.

[5] R. Rupp, R. Gerlach, A. Kabakow, Current distribution in the various functional areasof a 600 V SiC MPS diode in forward operation, Mater. Sci. Forum 717–720 (2012)929–932.

[6] J. Kowalsky, Stoßstromverhalten von IGBTs(Master thesis) Technische UniversitätChemnitz, Germany, 2014.

[7] Datasheet Coaxial Shunts SDN-414-05.[8] Datasheet IGBT G7PH50UPbF from IR.[9] J. Lutz, H. Schlangenotto, U. Scheuermann, R. De Doncker, Semiconductor Power

Devices. Physics, Characteristic, Reliability, Springer, 2011.


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