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1、1 Silicon Carbide Power Electronics: Challenges and Opportuni:es James A. Cooper Professor of Electrical and Computer Engineering Birck Nanotechnology Center Purdue University West Lafayee, IN 47907 USA 2 One of the hardest materials known Breakdown electric field 7x higher than silicon Power device
2、 figure-of-merit 300x higher than silicon Proper:es of Silicon Carbide 3 Silicon Silicon EG = 1.12 eV Carbon Diamond EG = 5.47 eV SiC Crystal Structure Silicon Carbide Silicon Carbon EG = 3.25 eV 4 SiC Surprises Because the bandgap is 3x wider than silicon. ni is 18 orders-of-magnitude smaller than
3、in silicon. (7x10-9 cm-3 at 300 K) Thermal genera:on rate (dark current) is 1018 :mes lower than in silicon. Intrinsic temperature is hundreds of degrees higher than silicon. MOS capacitors do not go into inVersion at room temperature. MOS interface states haVe Very long response :mes at room temper
4、ature. Total number of MOS interface states is 3x larger than in silicon. pn junc:on forward Voltage drop is 3x higher than in silicon. 5 SiC Surprises (Con:nued.) Because the crystal structure is hexagonal and polar. One surface is composed only of silicon atoms, and the other surface is composed o
5、nly of carbon atoms (polar crystal). Electrical proper:es (mobility, ioniZa:on coefficients) are anisotropic. Oxida:on rates depend upon which crystal face is being oxidiZed. MOS interface proper:es (QF, DIT, N) depend on crystal face. 6 SiC Surprises (Con:nued.) Because the crystal bonds are strong
6、. Many processing temperatures are aboVe the mel:ng point of silicon. Diffusion of dopants is negligible. Doping is by ion implanta:on only. No known chemical etchants. Etching is by reac:Ve ion etching. Crystal growth by CZochralski method is difficult. Bulk growth is by Vapor phase transport (subl
7、ima:on). Wafers are smaller and more expensiVe. SiC is physically and mechanically stable to Very high temperatures. Property Silicon 4H-SiC GaN EG (eV) 1.12 3.26 3.4 2 N (cm/Vs) 1400 1000 1200 EC (MV/cm) 0.4 2.8 3.0 Thermal Cond. (W/cm K) 1.3 3.3 1.3 FOM (rela:Ve to Si) 1.0 300 400 7 Basic Material
8、 Proper:es Micropipe Density (cm-2) 8 3” SiC Wafer SiZe and Quality Micropipe density does not limit yield! 6” 5” 4” 150 mm Wafers 10 2” 1.0 1” 0.1 9 SiC Power DeVices 10 Thyristor Gate n+ Anode p+ n Anode p+ p- Epilayer n+ Substrate 400 m Cathode IGBT Emitter Gate p+ n Emitter p+ n p- Epilayer n+ S
9、ubstrate 400 m Collector Bipolar Transistor Base Base Emitter n+ p n- Epilayer n+ Substrate 400 m Collector MOSFET n- Epilayer n+ Substrate 400 m Gate Source n+ p Source n+ p Drain Drain JFET n- Epilayer n+ Substrate 400 m Gate p+ Source n+ p+ Source n+ p+ n- Epilayer Schottky Barrier Diode Anode n+
10、 Substrate 400 m Cathode n- Epilayer PiN Diode Anode p+ Anode n+ Substrate 400 m Cathode n- Epilayer JBS Diode Anode n+ Substrate 400 m Cathode SiC Power DeVices Diode Rec:fiers Unipolar Switches Bipolar Switches 11 Thyristor Gate n+ Anode p+ n Anode p+ p- Epilayer n+ Substrate 400 m Cathode IGBT Em
11、itter Gate p+ n Emitter p+ n p- Epilayer n+ Substrate 400 m Collector Bipolar Transistor Base Base Emitter n+ p n- Epilayer n+ Substrate 400 m Collector MOSFET n- Epilayer n+ Substrate 400 m Gate Source n+ p Source n+ p Drain Drain JFET n- Epilayer n+ Substrate 400 m Gate p+ Source n+ p+ Source n+ p
12、+ n- Epilayer Schottky Barrier Diode Anode n+ Substrate 400 m Cathode n- Epilayer PiN Diode Anode p+ Anode n+ Substrate 400 m Cathode n- Epilayer JBS Diode Anode n+ Substrate 400 m Cathode SiC Power DeVices Diode Rec:fiers Unipolar Switches Bipolar Switches 12 Op:mum Design of the Drim Region - - +
13、+ + - - + + + + p+ - - - + n- + - - + + - - - - + + - 13 EM |E(x)| x 0 V ., 19, 487-489 (1998). Oxide-Protected UMOSFET Source 36 Components of UMOSFET On-Resistance At 1200 V, Ron,sp 0.9 m cm2. RDRIFT is the largest component, followed by RCHAN and RSUB. 37 VB = 1200 V T = 23 C RSUB Cell Pitch = 3
14、m Substrate = 400 m RSOURCE RCHAN RJFET RDRIFT RCHAN RCHAN RDRIFT RSUB 2.5 m 100 m RDRIFT RSUB 2.5 m 100 m Current State-of-the-Art SiC MOSFETs 38 How does this compare to silicon? Specific On-Resistance ( cm2) 39 Blocking Voltage (V) 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 10 100 1,000 10,000 SiC D
15、rim Region Limit Channel + RCHANNEL Substrate RSUBSTRATE Silicon, SiC, and GaN Power FETs Silicon Drim Region Limit 1.0E-01 Silicon LDMOSFETs Silicon SJ MOSFETs Si IGBTs (EffecJve) SiC DMOSFETs SiC UMOSFETs GaN HEMTs H. Ohashi, Intl. Symp.Power Semi. Devices (ISPSD), 2012. 40 Current Issues and Limita:ons 41 RCH,SP = LCHS CHCOX(VG VT ) MOSFET
