lpt type trench igbt - university of illinois at chicagoajohar/lpt type trench igbt.pdf · trench...
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LPT Type Trench IGBT: A Comparison with NPT Planar IGBT
Amanjyot Singh Johar
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IGBT
w Becoming very popular device of choice in 500V -1700 V applicationsw Positive temperature coefficient at high current
makes them easy to parallel and construct modulesw Forward voltage drop: diode in series with on-
resistance 2.4V typicalw Ease to drive similar to MOSFETs
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Competing IGBT Structures
w Punch Through IGBTs have traditionally had an advantage at voltage ratings lower than 1.2kV [*] whereas NPT devices were suitable for higher voltages
w Reassessment of above conclusions n Ultra-thin wafer processing technologyn Local lifetime control technology n Trench technology
all aim at reducing forward voltage drop
* S. Azzopardi, C. Jamet, J.M. Vinassa and C. Zardini, 'Switching performances comparison of 1200 V punchthrough and nonpunch-through IGBTs under hardswitching at high temperature', Proceedings of PESC'98, 1998, pp. 1201-1207
* V. Benda, J. Gowar and D.A. Grant, 'Power Semiconductor Devices - Theory and applications', 1999, John Wiley & Sons Ltd., Chichester
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Planar IGBT
w Improving the performance of existing IGBT technology has become increasingly difficult due to the constraints of the planar IGBT structure.n The "JFET" resistance (RJFET) in
a planar IGBT exists due to the constriction of current flow in the region between adjacent cells.
n Channel forms parallel to the chip surface
w Limitations of the planar IGBTn the resistance of the JFET region
between adjacent cells in the MOSFET portion of the device
n forward voltage VF of the diode structure in the bipolar portion of the device.
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Trench IGBT
w Gate oxide and conductive poly-silicon gate electrode are formed in a deep narrow trench below the chip surface
w The channel n forms along the vertical wall of the trench n perpendicular to the surface of the chipn less chip area leads to substantial increase in cell density n The consequent increase in channel width per unit area
results in a reduction in the R-channel portion of the IGBTs on-state voltage drop
w Eliminates JFET region. n Uniform current flow which, combined with greater cell density, increases the rated current density
compared to planar
w Punch through (PT) device, using local lifetime control processn Carrier lifetime is reduced in the n+ buffer layer only. n Turn-off losses can be reduced whilst maintaining a higher carrier lifetime in the n- drift region n This results in a greater carrier concentration in the drift region during conduction which reduces
the R N- component of VCE(sat)
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CSTBT
w Light Punch Through Vertical Structurew Single Crystal wafer eliminates need for
epitaxial base wafer materialw Addition of an n-type layer with a relatively
high impurity density between the p-type base layer and the n- layer in the trench IGBT
w Holes movement restricted to the P-base layer
w Low on state voltagew Improved short circuit ruggedness w Reduces drive powerw Wide cell pitch for short circuit ruggedness
Cross-section of a CSTBT
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Simulated CSTBT Device Structure
Vertical Device Length: 85u
Cell Pitch: 5u
Trench Depth: 1.1uBuried N layer between P body region and N drift region
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Static CharacteristicsSimulated Breakdown Curve
Negligible Leakage Current
P+ substrate and N- Drift region junction supports the reverse voltage
P-base and N- drift region junction supports the forward voltage
Collector Voltage (V)
Col
lect
or C
urre
nt (A
)
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Static CharacteristicsSimulated Forward Voltage Drop Characteristic
VG = 15 V
Forward Voltage Drop due to channel resistance
Wider the cell pitch, lesser the voltage drop
Minimum Forward Voltage drop is 0.5V
Voltage drop at 40A = 1.76 V
Collector-Emitter Voltage (V)
Col
lect
or C
urre
nt (A
)
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Current Flow in Trench IGBT
Contours showing the flow of current in the CSTBT
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Switching CharacteristicSimulated Hard Switching
Switching Conditions:
Vbus = 400 V
T = 25 C
IC = 50 A
Lgate = 1nH
R gate= 5Ω
Pulse width = 3µs
Excessive tail current seen in planar IGBT structure enhancing turn on and turn off losses
Time (us)
Col
lect
or C
urre
nt (A
)
Planar IGBTCSTBT
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Turn Off Energy Loss in CSTBT
Time (us)
Col
lect
or C
urre
nt (A
)
( )
+++= tail
tailifCtfvrCCoff Q
ItVttVIE
221
Eoff = 67 µJ at 400V, 50A(simulated value)
Eoff = 1.68 mJ at 600V, 150A for planar IGBT (datasheet value)
Col
lect
or V
olta
ge (V
)
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Turn On Energy Loss in CSTBT
Time (us)
Col
lect
or C
urre
nt (A
)
Col
lect
or V
olta
ge (V
) Eon = 140 µ J at 400V, 50A(simulated value)
Eon = 6.69 mJ at 600V, 150A for planar IGBT (datasheet value)
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Turn Off Energy Loss in Planar IGBT
Eon = 1.1 mJ at 400V, 50A(simulated value)
Eon = 1.68 mJ at 600V, 150A for planar IGBT (datasheet value)
Col
lect
or V
olta
ge (V
)
Time (us)
Col
lect
or C
urre
nt (A
)
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Turn On Energy Loss in Planar IGBT
Time (us)
Col
lect
or C
urre
nt (A
)
Eon = 3 mJ at 400V, 50A(simulated value)
Eon = 6.69 mJ at 600V, 150A for planar IGBT (datasheet value)
Col
lect
or V
olta
ge (V
)
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Device CharacteristicsSimulated Capacitance
Collector Voltage(V)
Cap
acita
nce
(F)
GCGEies CCC +=
Cies = 13200 pF(simulated value)
Cies(planar) = 15458 pF(datasheet value)
MHzf
VVOVV
CC
GE
1
30
=
==
Input Capacitance Cies
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Device CharacteristicsSimulated Capacitance
Collector Voltage(V)
Cap
acita
nce
(F) Reverse Transfer
Capacitance Cres
MHzf
VVOVV
CC
GE
1
30
=
==
Cres = 75 pF(simulated value)
Cres(planar) = 1056 pF(datasheet value)
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Device CharacteristicsSimulated Capacitance
Collector Voltage(V)
Cap
acita
nce
(F)
Output Capacitance Cies
GCCEoes CCC +=
MHzf
VVOVV
CC
GE
1
30
=
==
Coes = 550 pF(simulated value)
Coes(planar) = 487pF(datasheet value)
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Comparing CSTBT with Planar IGBT
w CSTBT 1200V/150A (based on Simulated results)n LPT type with a single crystal wafer n Forward Voltage Drop of 1.76 V at
40A
n Turn on Energy 140 µ J n Turn off Energy 67 µJ n Input Capacitance 13200 pFn Output Capacitance 550 pF
w IGBT as used in converters 1200V/150A (based on datasheet values)n NPT type with an epitaxial
layern Forward Voltage Drop of 2.1 –
2.6 V at 40An Turn on Energy 3 mJ n Turn off Energy 1.1 mJ n Input Capacitance 15458 pFn Output Capacitance 487pF
•CSTBT can be a good replacement for planar IGBT as accounted by its simulated hard switching performance
•A complete comparison can be made after analyzing the performance of the CSTBT in the converter