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1. Insulated Gate Bipolar Transistors (IGBTs)
MANGAL DAS
M.TECH
VST
SHIV NADAR UNIVERSITY
Copyright © by John Wiley & Sons 2003 1

2. Outline
• Why we need IGBT?
• Physical operation
• Construction and I-V characteristics
• SPICE simulation models
Copyright © by John Wiley & Sons 2003 2

3. *Turn Off time
BJT *Lower conduction losses
*Larger blocking voltage
*Turn on time
small
MOSFET
IGBT
Copyright © by John Wiley & Sons 2003 3

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. 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. 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. 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. 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
drift
gate
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. 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. 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. 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 reverse
Gate Cdsj free-wheeling diodes.
Cm +
Coxs
Source
Copyright © by John Wiley & Sons 2003 11

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. THANK YOU
Copyright © by John Wiley & Sons 2003 13