Breakthrough High Temperature Electrical Performance of SiC

Breakthrough High Temperature
Electrical Performance of SiC
“Super” Junction Transistors
SiC are being explored for power electronic conversion applications
The SiC based 1200 V/220 mÙ Super Junction Transistors (SJTs) feature high temperature (> 300 °C) operation capability, faster switching transitions (< 20 ns), extremely
low losses and superior avalanche ruggedness performance (36 mJ). Integration of SiC
SJTs with GeneSiC’s freewheeling SiC JBS rectifiers will result in a power loss reduction
by about 64% than its comparable Si counterpart.
By Deepak Veereddy, Device Engineer, Siddarth Sundaresan, Director-Device Design &
Fabrication, Stoyan Jeliazkov, Process Engineer, Michael Digangi, Chief Business
Development Officer and Ranbir Singh, President, GeneSiC Semiconductor, Inc.
With Silicon almost reaching its theoretical limit, alternate semiconductor materials like SiC are being explored for power electronic conversion applications [1]. SiC transistors are identified as an attractive
alternate solution to the existing Si counterparts in the high voltage
regime (1.2 kV-10 kV), particularly for medium and high frequency
applications [2]. Though SiC based Schottky diodes were readily
available since 2001[3], commercial SiC transistors came into limelight only in the last two to three years [4-5].
GeneSiC is developing the innovative SiC power switch, “Super”
Junction Transistor (SJT) in 1.2 kV to 10 kV voltage ratings for high
efficiency power conversion in Switched-Mode Power Supply
(SMPS), Uninterruptible Power Supply (UPS), aerospace, defense,
down-hole oil drilling, geothermal, Hybrid Electric Vehicle (HEV) and
inverter applications. The Gate-oxide free, normally-off, current driven, quasi-majority device, SJT is a “Super-High” current gain SiC
based BJT that features a square reverse biased safe operating area
(RBSOA), high temperature (> 300 °C) operation capability, low
VDS(on) and faster switching capability (10’s of MHz) than any other
competitor SiC switch. The MOS interface reliability related issues
and high channel resistance of SiC MOSFETs have limited their temperature capability to 150 °C where as the Gate-oxide and channel
free SiC SJTs deliver high temperature performance (> 300 °C).
Unlike SiC SJT, SiC MOSFET requires a custom made Gate driver
design due to its poor transconductance characteristics. On the other
hand, the commercially available SiC normally-off JFET displays a
very high positive temperature coefficient of VDS(on) and lower temperature capability as compared to the SiC SJT. GeneSiC’s 1200
V/220 mΩ SiC SJTs are packaged in standard TO-220 and high temperature TO-257 packages (see Figure 1). The following three bestin-class Si IGBT co-packs with internally integrated anti-parallel Si
FREDs were chosen for comparing their electrical performance with
that of 1200 V/220 mΩ SiC SJT:
NPT1: 125 °C/1200 V rated Si Non Punch Through IGBT
NPT2: 150 °C/1200 V rated Si Non Punch Through IGBT
TFS: 175 °C/1200 V rated Si Trench Field Stop IGBT
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On-state and Blocking Performance
An almost temperature independent blocking performance of a 1200
V/220 mΩ SJT till 225 °C operating temperature is depicted in Figure
1. The leakage current in a SJT while blocking 1200 V do not change
by a large extent up to temperatures as high as 225 °C. Leakage currents of < 100 μA were measured even at 325 °C on a 1200 V/220
mΩ SJT. Figure 2 shows the comparison of the temperature dependent leakage currents of the three Si IGBT co-packs and SiC SJT.
Unlike Si IGBTs, the leakage current in SJTs do not show a strong
dependence of temperature. Moreover, the operation temperature
capability (< 325 °C) of SJTs is solely limited by the power package
Figure 1:
Temperature variant blocking performance of a 1200 V/220 mΩ SJT
The on state characteristics of a 1200 V/220 mΩ SJT were generated
using a curve tracer for operating temperatures up to 250 °C (see
Figure 3). The distinct lack of quasi-saturation region and merging of
the on state curves for various Gate currents in the saturation region
of a SJT indicate the absence of the minority carrier injection and
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clearly distinguishes it from a Si “BJT”. Appropriate metallization
schemes and an optimized device design yield low Drain Source saturation voltages. The On-state voltage values of SJT are relatively
smaller than the existing same current/voltage rated Si IGBTs with
VDS(on) values of 1.5 V at 25 °C and 2.6 V at 125 °C at 7 A of drain
current. SJTs display a positive temperature coefficient of VDS(on)
that make their paralleling easy for high current configurations. A
highest Common Source current gain value of 88 was measured on
this batch of SJTs.
Figure 2: Leakage current comparison of Si IGBTs and 1200 V/220
mΩ SJT as a function of temperature
switching performance. A Drain current rise time of about 12 ns and a
fall time of 14 ns were obtained for 7 A, 800 V SJT switching at a
temperature of 250 °C, resulting in extremely low switching energies
when compared to the Si IGBT co-packs.
Figure 3 : Temperature variant output characteristics of a 1200 V/220
Dynamic Electrical Performance
The dynamic test setup for comparing the switching performance of
SiC SJT and Si IGBTs comprises of an inductively loaded chopper
circuit configuration. A GeneSiC 1200 V/ 7A SiC Schottky diode [6]
and Si IGBT co-packs were used as Free Wheeling Diodes (FWDs)
in the switching test circuit. The Gate Source terminals of Si IGBT copack (FWD) are tied together (VGS = 0 V) to avoid the IGBT conduction during the dynamic testing. A 1 μF charging capacitor, a 150 μH
inductor, 22 Ω Gate resistor and a supply voltage of 800 V were used
in the testing process. A commercially available IGBT Gate driver
with an output voltage swing from -8 V to 15 V is used for driving all
the devices. A 100 nF dynamic capacitor connected in parallel with
the Gate resistor generated an initial large dynamic Gate currents of
4 A and -1 A (Figure 4 and Figure 5) during turn-on and turn-off
switching respectively, while maintaining a constant Gate current of
0.52 A during its turn-on pulse. The initial dynamic Gate currents
charge/discharge the device capacitance rapidly, yielding a superior
Figure 4:Turn-Off switching transients of a 1200 V/220 mΩ SJT
A comparison of the overall power losses measured on the SJT and
Si IGBT co-packs is shown in Figure 6 for a switching frequency of
100 kHz and 0.7 Duty Cycle. Si TFS + SiC FWD represents Si TFS
IGBT as the DUT and SiC Schottky diode as FWD respectively
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where as Si TFS + Si TFS represents Si TFS IGBT as DUT and Si
TFS IGBT co-pack as FWD respectively. The calculated gate drive,
conduction and switching losses of SJT are 5.25 W, 26.65 W and
20 W respectively at 250 °C operating temperature. Though the gate
driver losses of SJT are higher than Si IGBTs, their contribution to the
overall losses is insignificant. The relatively high conduction losses of
SJT when compared to the Si IGBT co-packs can be attributed to its
high temperature operation (250 °C). An all-SiC solution reduces the
overall losses by about 64% when compared to an all-Si solution.
Figure 7 : Unclamped Inductive Switching waveforms of a 1200
V/220 mΩ SJT
GeneSiC highly rugged SJTs offer significant benefits over the Si
IGBTs and SiC competitor transistors by reducing the power losses
tremendously and delivering high temperature performance respectively. These benefits result in improving the system efficiencies, and
reducing its cost and size. As SiC SJTs are direct replacement to the
Si IGBTs, they can be driven using the standard IGBT/MOSFET gate
Figure 5: Turn-On switching transients of a 1200 V/220 mΩ SJT
Figure 6 : Power loss comparison of SiC SJT and Si IGBT co-packs
at their maximum operating temperature
Avalanche Ruggedness Performance
A single pulse Unclamped Inductive Switching (UIS) [7] setup was
used to obtain the nonrepetitive avalanche energy rating on the SiC
1200 V/220 mΩ SJTs. Using a supply voltage of 60 V and 210 μH
inductor for the single pulse UIS test, resulted in non-repetitive avalanche energy and current ratings of 36 mJ and 20 A respectively
(see Figure 7). The measured avalanche voltage (1650 V) is about
37% larger than the rated blocking voltage (1200 V).
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[1] B.J. Baliga, “Trends in power semiconductor devices”,
IEEE Trans. Electron Devices, vol 43, pp. 1717-31, 1996.
[2] A. Hefner et al, “Recent Advances in High-Voltage,
High-Frequency Silicon-Carbide Power Devices,” in IEEE 2006
Industry Applications Conference, 2006, pp. 330-337.
[3] I. Zverev, M. Treu, H. Kapels, O. Hellmund, R. Rupp,
“SiC Schottky Rectifiers: Performance, Reliability and Key Applications”, Proceedings of EPE 2001 Conference, August 2001.
[4] I. Sankin, D.C. Sheridan, W. Draper, V. Bondarenko, R. Kelley,
M.S. Mazzola, J.B. Casady, “Normally-off SiC VJFETs for 800 V
and 1200 V Power Switching Applications”, in ISPSD 2008 International Symposium on Power Semiconductor Devices and IC’s,
2008, pp. 260-262.
[5] B.A. Hull, J. Henning, C. Jonas, R. Callanan, A. Olmeda, R.
Sousa, J.M. Solovey, “1700V 4H-SiC MOSFETs and Schottky
diodes for next generation power conversion applications” in
IEEE 2011 Applied Power Electronics Conference and Exposition, 2011, pp. 1042-1048.
[6] GeneSiC Semiconductor, Inc. Available:
[7] Microsemi Application note,
October 2011