Siddarth Sundaresan 1 , Ranbir Singh 1 , R. Wayne Johnson 2 1 GeneSiC Semiconductor Inc.

1. SiC “Super” Junction Transistors Operating at 500 oC Siddarth Sundaresan1, Ranbir Singh1, R. Wayne Johnson2 1GeneSiC Semiconductor Inc. 2Auburn University A significantportion of this research was performed under a Phase I SBIR grant from U.S. NASA (Award #NNX11CE28P)

2. Presentation Outline • SiC “Super” Junction Transistor (SJT) Device Structure • On-state characteristics up to 500 °C • Blocking voltage characteristics up to 500 °C • High temperature switching characteristics • Comparison with state-of-the-art Si IGBTs • Short-circuited safe-operation area (SCSOA) • Avalanche ruggedness • Overload current and voltage turn-off

3. Overview of SiC “Super” Junction Transistors (SJTs) • SJTs are high current gain SiC NPN BJTs developed by GeneSiC in 1200 V – 10 kV ratings. • Unlike Si BJTs, SiC SJTs are majority carrier devices • Fast switching speeds • Square RBSOA • Positive temperature co-efficient of VF • Free from SiC MOS reliability issues, which are especially severe at high operating temperatures. • High current gain (β>70) results in low Gate current drive requirements. Source Gate N+ Source P Base N- Drift N+ Substrate Drain

4. Off-eutectic Au-Sn die attach method • Ni-Au metallization on the SiC die • Sandwich Eutectic 80-20 AuSn pre-forms with TM = 280 °C between SiC die and Au plated substrate • Shift TM to 450 °C by decreasing Sn to 10 wt%. • Bonding conditions: 450 C/60 min in a vacuum furnace, bonding force = 500 grams Au-20wt%Sn Au-10wt%Sn

5. SJT Output Characteristics up to 500 °C • Up to 300 °C, output characteristics indicate purely unipolar operation • Above 300 °C, distinct quasi-saturation regions are observed implying minority carrier injection into n- layer • Increased voltage drop across n- layer and higher carrier lifetime at higher temperatures

6. Variation of Current Gain with temperature • Current gain (β) shows a negative temperature co-efficient up to 300 °C due to increasing ionization of Al acceptors in p-Base layer. • At > 300 °C, positive temperature co-efficient of β is due to increasing carrier lifetime in p-Base layer.

7. SJT Blocking Characteristics up to 500 °C • SJT blocking up to 500 °C demonstrated • The sharp increase in leakage current above 350 °C correlates well with the increase of intrinsic carrier concentration in 4H-SiC • First ever demonstration of blocking voltage characteristics of a high-voltage SiC transistor at 500 °C

8. High-temperature switching characterization setup • Inductively clamped chopper circuit and standard double-pulse gate drive scheme used for SJT switching measurements. • A 100 nF dynamic capacitor is used to speed up switching transients by providing high dynamic Gate currents.

9. High-Temperature SJT Switching transients • VDS = 800 V, ID = 7 A • Ultra-fast < 15 ns Drain current rise and fall times measured at 250 °C • Temperature independent switching characteristics obtained due to unipolar SJT operation, even at 250 °C

10. Eon and Eoff comparison with state-of-the-art Si IGBTs • Temperature independent Eon and Eoff for the all SiC, SJT+JBS free-wheeling diode pair up to 250 °C. • SiC SJT enables higher temperature operation and lowest overall switching energy losses, compared to all-Si or hybrid Si-SiC power modules.

11. Switching performance comparison with state-of-the-art Si IGBT technologies • The SiC SJT + Schottky Diode combination offers a 64% reduction in total power losses as compared to state-of-the-art Si IGBT/Rectifier co-packs. • Test frequency = 100 kHz, D=0.7

12. RBSOA Investigations – Overload Current, Voltage turn-off Over-current (22A) turn-off Over-voltage(1250 V) turn-off Successfully turned-off 7 A toa Drain Voltageof 1250 V in 115 ns • Successfully turned-off 22 A (740 A/cm2) toa Drain Voltageof 800 V in 110 ns

13. Avalanche Robustness • 1200 V SJT driven to avalanche by unclamped inductive switching (without free-wheeling diode). • Single-pulse avalanche energy of 20.4 mJ and tAV=5 µs obtained for turning-off 7 A at 1500 V. • Slight improvement in breakdown voltage observed after the 934 hour UIS testing with EAV=2.3 mJ pulses at a 30% duty cycle and 14.3 kHz switching frequency.

14. Operation under (hard) short-circuited fault conditions • 1200 V/3 mm2 SJT directly turned-on to a short-circuited load at VDS=800 V with IG = 200 mA • A short-circuit withstand time (tSC) = 22 µs and ISC = 10-12 A were recorded • Device destruction occurred at 24 µs • Low ISC at VDS = 800 V due to lack of short-channel effects in output characteristics.

15. Summary of Results • 500 °C operation of 1200 V-rated SiC SJTs demonstrated • First-ever demonstration of blocking-mode operation of a power transistor at 500 °C. • Output characteristics indicate unipolar operation at temperatures < 300 °C; distinct quasi-saturation regions form at 400-500 °C. • Temperature co-efficient of SJT current gain changes from negative to positive at > 300 °C. • Temperature independent, low switching losses obtained up to 250 °C. • 1200 V/5 A-rated SJT turned-off ID = 22 A (740 A/cm2) at 800 V; and 7 A at VDS = 1200 V, indicating square RBSOA. • SJT demonstrated good avalanche robustness • EAS = 20.4 mJ • No deterioration in device performance after a 934 hour repetitive avalanche stress. • Obtained reasonbly high tsc = 22 µs under short-circuit load conditions at VDS = 800 V • enabled by a low ISC =12 A at 800 V.

16. 250 °C capable 650 V and 1200 V SiC Schottky rectifiers • GeneSiC’s 650 V/1,5,20 A and 1200 V/1,5,20 A SiC Schottky rectifiers with TJ = 250 °C capability are now available as bare die! • Please contact Micross components or GeneSiC Semiconductor for product information and pricing. 650 V/20 A SiC SBD 1200 V/20 A SiC SBD IR = 55 µA at 1200 V IR = 32 µA at 650 V