Insulated gate bipolar transistor

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Insulated gate bipolar transistor

  1. 1. Insulated Gate Bipolar Transistors (IGBTs) MANGAL DAS M.TECH VST SHIV NADAR UNIVERSITYCopyright © by John Wiley & Sons 2003 1
  2. 2. Outline • Why we need IGBT? • Physical operation • Construction and I-V characteristics • SPICE simulation modelsCopyright © by John Wiley & Sons 2003 2
  3. 3. *Turn Off timeBJT *Lower conduction losses *Larger blocking voltage *Turn on time small MOSFET IGBT Copyright © by John Wiley & Sons 2003 3
  4. 4. Multi-cell Structure of IGBT• IGBT = insulated gate bipolar transistor. contact to source emitter diffusion conductor field oxide gate oxide gate width N+ N+ N+ N+ P P N- buffer layer N+ (not essential) P+ collector metallization gate conductor Copyright © by John Wiley & Sons 2003 4
  5. 5. Cross-section Of IGBT • Cell structure similar to power MOSFET cell. • P-region at collector end unique feature of IGBT compared to MOSFET. • Punch-through (PT) IGBT - N+ buffer layer present. • Non-punch-through (NPT) IGBT - N+ buffer layer absent.Copyright © by John Wiley & Sons 2003 5
  6. 6. Blocking (Off) State Operation of IGBT gate emitter SiO 2 + + J N N 3 P Ls J 2 N- Drift layer + N Buffer layer P+ J - Unique feature of IGBT collector Buffer layer 1 (not essential) Parasitic thyristor• •Blocking :state operation - Vcreated GE(th) Vgs<Vth No inversion layer GE < V • Wit h N+ buffer lay er, junct ion J1 has -• •Junction Jlayer is created along J2 ,which expands as Vgs increases. Depletion 2 extends principally in to n drift small breakdownv olt age and t hus IGBT •In ‘NONsince the THROUGH’ region is purposely has litlargerev erse voltage Region, PUNCH p-type body no buffer layer is present so t le reverse blocking capabilit y - Doped much more heavily than drift region. ant i-sy mmet ric IGBT• blocking capacity. Drift region is large enough to The thickness of Accommodate the depletion layer. •In ‘PUNCH THROUGH ’ buffer layer is present shorter drift region, speeds up dev ice t urn-off which lower This type of IGBT is called as symmetrical IGBT. • Buffer lay er on-state losses but reverse voltage blocking capacity will be low. Copyright © by John Wiley & Sons 2003 6
  7. 7. IGBT On-state Operation gate emitter + + N N P lateral (spreading) - N resistance + N + + + + P+ + + + + collector•Vgs>Vth , Channel is shorting Body-Drain-Drift regions.•P+ inject holes in to N+ region•Holes moves towards body region along a random path .•Many holes will attracted by emitter metallization.•Some holes recombines with electrons.Copyright © by John Wiley & Sons 2003 7
  8. 8. Approximate Equivalent Circuits for IGBTs Conduction path resulting collector drift region resistance in thyristor turn-on (IGBT V latchup) if current in this J1 V path is too large driftgate I R gate C channel Principal (desired) Body region path of spreading resistance• Approximate equivalent circuit for collector IGBT valid for normal operating current emitter conditions. • IGBT equivalent circuit showing• V CE( on) = V J1 + V drif t + I C Rchannel transistors comprising the parasitic thyristor. Copyright © by John Wiley & Sons 2003 8
  9. 9. IGBT I-V Characteristics and Circuit Symbols increasing V i GE i C C v GE4• No Buffer Layer v GE3 VRM - BV CES v v V GE• With Buffer Layer GE2 GE(th) v GE1 V -0 RM • Transfer curve v CE V BV RM • Output characteristics Vth CES drain collector gate gate • N-channel IGBT circuit symbols source emitter Copyright © by John Wiley & Sons 2003 9
  10. 10. Development of Spice IGBT Model• Nonlinear capacitors Cdsj and Ccer due to N-P junction depletion layer. • Reference - "An Experimentally Verified• Nonlinear capacitor Cebj + Cebd due to P+N+ junction IGBT Model Implemented in the• MOSFET and PNP BJT are intrinsic (no parasitics) devices SABER Circuit Simulator", Allen R.• Nonlinear resistor Rb due to conductivity modulation of N - drain drift region of Hefner, Jr. and Daniel MOSFET portion. M. Diebolt, IEEE Trans. on Power Electronics,• Nonlinear capacitor Cgdj due to depletion region of drain-body junction (N -P junction). Vol. 9, No. 5, pp. 532- 542, (Sept., 1994)• Circuit model assumes that latchup does not occur and parasitic thyristor does not turn. Copyright © by John Wiley & Sons 2003 10
  11. 11. Parameter Estimation for Spice IGBT Model • Built-in IGBT model requires nine parameter values. • Parameters described in Help files of Parts utility program. • Parts utility program guides users through parameter estimation process. • IGBT specification sheets provided by manufacturer provide sufficient informaiton for general purpose simulations. • Detailed accurate simulations, for example device dissipation studies, may require the user to carefully characterize the selected IGBTs. Drain Cebj + Cgdj Cebd • Built-in model does not model Ccer ultrafast IGBTs with buffer layers Coxd Rb (punch-through IGBTs) or reverseGate Cdsj free-wheeling diodes. Cm + Coxs Source Copyright © by John Wiley & Sons 2003 11
  12. 12. Application• Current rating of single IGBT can be up to 1200 volts,400Amps.• Frequency of operation:20Khz.• It is useful for medium power applications • Ac and DC motor drives. • Solid state relays • High frequency signal choppers.(not preferred) Copyright © by John Wiley & Sons 2003 12
  13. 13. THANK YOUCopyright © by John Wiley & Sons 2003 13

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