Silicon Carbide Power Device Technology; Fabrication issues and state of the art devices Prof. Mikael Östling
Outline Introduction and motivation Summary of fabrication issues Device review Schottky, JFET, MOSFET, BJT Application examples High temperature and drive electronics Summary
Width of the drift region (cm) On-Resistance, R ON (mωcm 2 ) 10-1 10-2 10-3 10-4 10-5 10 2 4H-SiC Unipolar Limit 10 1 10 0 For 1 kv Si : 100 μm SiC : ~10 μm 10 1 10 2 10 3 10 4 Breakdown Voltage(V) Breakdown Voltage (V) Si unipolar limit Si Unipolar Limit Si GaAs 6H-SiC 4H-SiC SiC unipolar limit p + E Ec Anode R on sp High Electric Field x 10 0 W n - Drift region = W qμ N WE V = B 2 n D n + Cathode = 4V εµ 2 B 3 nec SiC on-resistance > 100 times lower than that of Si! x C 10 1 10 2 10 3 10 4 Breakdown Voltage, V BD (V)
Issues with process technology Bulk material growth Epitaxial growth Ion implantation SiC etching Dielectrics Metals
Brief History of SiC 1824 Jöns Jacob Berzelius synthesized SiC (Also credited with identifying the chemical elements silicon, selenium, thorium, and cerium) 1885 Eugene and Alfred Cowles invented the electric smelting furnace, adopted 1892 by Acheson for making of SiC ( Carborundum ) and other abrasives
Brief History of SiC CREE wafer sizes etc 1991 first commercial wafer (6H 30 mm) 1993 4H polytype commercial 1997 2 inch (50 mm) commercial 2001 3 inch (75 mm) commercial 2005 100 mm commercial (demo 1999, Semi-insulating 2003, 2007 zero micropipe) 2012 150 mm commercial (demo 2010) 30 mm 50 mm 75 mm 100 mm
Epitaxial Growth CVD main method Concerns: Purity Material quality Wafer diameter Growth rate, thickness uniformity Doping uniformity
Etching Wet etching Dry etching Etching machines RIE ICP ECR Concerns: Anisotropy Mask material and selectivity Etch rate Damage
Oxidation Uses for oxides/dielectrics in SiC technology Thermal oxidation Sacrificial oxidation Deposited oxides High-K dielectrics Testing of oxide quality
150 mm wafers available
SiC Schottky Diodes Power factor correction Solar inverters Industrial motor drivers Output rectification Cree CID150660 Insulated Gate Bipolar Transistor with Silicon Carbide Schottky Diode
1700 V Schottky Diodes Forward I-V characteristics of a 1700 V, 25 A SiC Schottky diode. CREE, available since 2010.
No reverse recovery in SBD
System solution
High Switching Speeds Enable Greater Power Density Low Frequency Silicon vs. High Frequency Silicon Carbide Comparisons PCB Area Volume Weight Density 80kHz 200kHz Delta 23.9 in 2 14.8 in 2 154.1 cm 2 95.5 cm 2-38% 47.8 in 3 29.6 in 3 782.8 cm 3 485.1 cm 3-38% 18.4 oz. 10.4 oz 521.6 gm 294.8 gm -44% 10.5 W/ in 3 3 16.9 W/ in 0.64 W/ cm 3 1.03 W/cm 3 +61%
High Switching Speeds Enable Greater Power Density Low Frequency Silicon vs. High Frequency Silicon Carbide 90VAC Input Efficiency Measurements 100,0% 97,0% 94,0% 91,0% 80kHz Si 200kHz SiC 88,0% 50W 150W 250W 350W 450W 85,0% Performance Improvements can be used to Increase Switching Frequency and keep the Efficiency High
10 kv PiN diode on on-axis 4H SiC A. Salemi et al. Materials Science Forum Vols. 778-780 (2014) pp 836-840 A. Salemi et al, MRS Spring Meeting 2014
Conductivity Modulated On-axis 4H-SiC 10+ kv PiN Diodes Before and after lifetime enhancement Low V F of 3.3 V at 100 A/cm 2
Bipolar and temperature stability No bipolar degradation Lifetime is decreased (from 3 to 1.15 µs) during processing specially in the ion implantation followed by high temperature annealing step.
MOSFETs
1700 V MOSFETs (B.A. Hull et al, Cree)
Commercial MOSFETs
JFETs
SiC power devices @ Infineon SBD technology after 10 years at the market now in 3 rd gen., technology based on surge current optimized structure with highest power densities and reliability enabled by new assembly technologies 40 35 30 25 IF (A) Combined Schottky diode characteristics forward characteristic surge current 20 15 Bipolar pn diode forward characteristic 10 5 0 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 V F (V) Device spectrum from discrete 2A die up to module solutions (> 100 Amps, up to 1700V), target markets PFC and Solar or high end drives Transistor technology based on normally-on JFET technology complemented by silicon power transistors and driver for ease of use and highest reliability Key customers in solar and comparable applications with emphasize on efficiency, general purpose will follow For all components, discrete and module based solutions will be offered to the customer Gate Source Source n+ p n+ p+ p+ n- Drift region 4H n+ Substrat SiC technology is a key enabler for Infineon s strategy towards efficiency and energy saving Drain 1ED Ready Reset 1ED S id
1200V CoolSiC
1200V CoolSiC
BJTs
SiC power bipolar junction transistors by TranSiC Emitter contact N D + SiO 2 surface passivation Base contact P JTE implant N Base implant N + substrate Collector contact Emitter Base Vertical epitaxial NPN structure Dry etching to form base-emitter and base-collector junctions Al implantation for low-resistive base contact and junction termination (JTE) Surface passivation by SiO 2, reduced surface recombination Large area BJT has many narrow emitter fingers Deposited isolation oxide, via holes and Al metal pads Active areas between 4.3mm 2 and 15 mm 2
Switching waveforms at 150 C Turn-on to I C =6 A (140 A/cm 2 ), V CE fall-time of 15 ns Turn-off to 800 V with V CE rise-time of 12 ns, and negligible tail current Fast switching using 22 nf external base cap for dynamically increased I B
Recent Performance of SiC BJTs Collector current (A) 40 35 30 25 20 15 10 5 T=25 C 4.3 mm 2 BJT I =400 ma B I =300 ma B I =200 ma B h =117 FE I =100 ma B Collector current (A) 5 10-7 4 10-7 3 10-7 2 10-7 1 10-7 Ic I C (V CEO =1200 V)=160 na 0 0 1 2 3 4 5 Collector emitter voltage V CE (v) 0 0 500 1000 1500 Collector voltage V C (v) Current gain at T=25 C : h FE =117 at I C =22 A V CESAT =0.95 V at I C =15 A (J C =350 A/cm 2 ), ρ ON =2.7 mωcm 2 Low leakage current at V CEO =1200 V, Open-base breakdown 1800 V
5.8 kv BJT with optimized JTE Hossein Elahipanah et al, KTH IEEE ELECTRON DEVICE LETTERS, VOL. 36, NO. 2, FEBRUARY 2015
5.8 kv BJT with optimized JTE Hossein Elahipanah et al, KTH IEEE ELECTRON DEVICE LETTERS, VOL. 36, NO. 2, FEBRUARY 2015
5.8 kv BJT with optimized JTE Hossein Elahipanah et al, KTH IEEE ELECTRON DEVICE LETTERS, VOL. 36, NO. 2, FEBRUARY 2015
15 kv-class BJTs and PiN Diodes Zone JTE1 JTE2 JTE3 JTE4 Mesa Etching depth 260 nm 80 nm 80 nm 120 nm 1.5 µm Lengh 350 µm 263 µm 175 µm 87 mm 80 µm % of total length 33 25 17 8 7 Epi from Ascatron
I-V characteristics of the BJTs A current gain record of 139 for 15 kv-class BJTs
Current gain wafermap
21 kv BJT (T. Kimoto Kyoto University) MIYAKE et al. IEEE ELECTRON DEVICE LETTERS, VOL. 33, NO. 11, NOVEMBER, 2012, p.1598
21 kv BJT (T. Kimoto Kyoto University) Active area small 0.0035 mm 2 MIYAKE et al. IEEE ELECTRON DEVICE LETTERS, VOL. 33, NO. 11, NOVEMBER, 2012, p.1598
High Injection Level
Application Examples
Power Modules CREE: 1200V/100 A module 5 (25A) SiC MOSFETs+3 (50A) SiC JBS CREE: 1200V/880 A module 11 (80A) SiC MOSFETs+11 (50A) SiC JBS J. Richmond, et. al., Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE, pp.106-111, 20-24 Sept. 2009
40 kva SiC Inverter with an efficiency of 99.47 % Prof H-P Nee, KTH 2012
LARGE SCALE FIELD TESTS IN JAPAN Tokyo's Ginza subway line is part of a trial to test what improvements silicon carbide circuits can make to transportation systems.
SiC power modules save 40 percent Power in Mitsubishi Traction Inverter Mitsubishi Electric has announced that an all-sic traction inverter installed in a 1000 series urban train operated by Odakyu Electric Railway in Japan, have been verified to achieve an approximate 40-percent savings in power consumption compared to a train using conventional circuitry. The traction inverter, which is rated for 1,500V DC catenaries, was tested over a four-month period. The verification compared a car retrofitted with an all-sic traction inverter and another car fitted with a conventional gate turn-off thyristor traction inverter, both of which were put into actual commercial service. The test measured power consumption and electric power regeneration ratio of the two cars' main circuits, which comprise traction inverters, high-efficiency main motors and filter reactors. The following results are average values measured between January 17 and May 8, 2015: 17 percent power savings during powered operation; an increase from 34.1 percent to 52.1 percent in power regeneration ratio, calculated as power from regenerative brakes to catenaries divided by total electric power to drive the rail car; and 40 percent power savings overall.
Full SiC converter are getting on-board Specifications of Main Circuit Mitsubishi Electric Corporation announced in July 2015 that it has completed the installation of, and begun testing, railcar traction converter/inverter systems with all-silicon carbide (SiC) power modules on N700 Shinkansen bullet trains for Central Japan Railway Company (JR-Central). These are the first 3.3kV, 1500A traction systems to be installed on a high-speed train line, according to the company s own research. Mitsubishi Electric has been working to downsize its traction system for Shinkansen bullet trains. The use of SiC power modules reduces the size and weight of its new converter/inverter system by approximately 55% and 35%, respectively, compared to existing systems. The weight of the traction motor, including this system, is reduced by approximately 15%. The power modules were developed with support from the New Energy and Industrial Technology Development Organization of Japan. Input voltage: Main circuit system: Control system: Cooling system: 2,500V AC Large-capacity all- SiC power modules Three-level PWM inverter with regenerative brakes Four traction motors with 305kW, parallel control Self-cooling
Toyota to Trial New SiC Power Semiconductor Technology
Price Scenario SiC Source: Dr Anant Agarwal, US Department of Energy
Applications for HT & harsh environments Application Type Temperature Radiation Oil and gas drilling P, S 600 C No Industrial motor drives P 300 C No Automotive P, S 300-600 C No Aviation P, S 300-600 C (Yes) Space exploration S 600 C Yes Nuclear energy (P) S 300-600 C Yes P = Power switching applications S = Sensor signal processing
From Power to IC
First 600 o C of SiC BJT logic gates PhD thesis 2014, Luigia Lanni, KTH
11-stage Ring Oscillator PhD thesis 2014, Luigia Lanni, KTH
11-stage Ring Oscillator
A new high temperature SiC electronics project WOV Working on Venus $ 3,3M Project funding 2014 2018
WOV Working on Venus
Summary SiC power switches using SBD, JFET, MOSFETs and BJTs are already commercially available Long term stability has been dramatically improved and the bipolar degradation effect is practically eliminated Power modules are already available Cost is still the main issue. Volume production must yield switch devices at a price level of 10-20 cents/amp @ 1200 V rating High temperature operation and radiation hard devices yet to be fully explored. With integrated driver circuits in SiC, the system advantages will be considerable
Acknowledgments The KTH research team The Swedish Energy Agency The Swedish Research Council VINNOVA research and innovation for sustainable growth Swedish Foundation for Strategic Research KAW Foundation