trench igbt

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CONTENT
STORY
Enhanced Trench IGBTs and
Field Charge Controlled Diode
The Next Leap in IGBT and Diode Performance
Future generations of IGBT modules will employ Enhanced Trench ET-IGBTs and Field Charge
Extraction FCE diodes capable of providing higher level of electrical performance in terms of
low losses, good controllability, high robustness and soft diode reverse recovery.
By Liutauras Storasta, Chiara Corvasce, Maxi Andenna, Sven Matthias,
Raffael Schnell and Munaf Rahimo, ABB semiconductors
demonstrated that soft recovery performance under extreme switching conditions combined with low losses could be achieved while
having no drawbacks on other electrical parameters.
IC=75A, VDC=1800V, Lσ=2400nH, Tj=150 C
200
190
Turn-off losses (mJ)
Despite the fact that the Insulated Gate Bipolar Transistor (IGBT)
and antiparallel diode have experienced over the past two decades
important breakthroughs with respect to the device process and
design concepts which resulted in clear leaps in device overall performance, further development work is underway to achieve the next
level in terms of higher power densities, improved controllability and
robustness. In this article, we will first briefly discuss the current IGBT
and diode development trends while focusing on the next generation technologies; namely the Enhanced Trench IGBT (ET-IGBT) and
Field Charge Extraction (FCE) diode. Then, the new device concepts
and their electrical performance will be demonstrated for the 3.3 kV
voltage class.
180
170
160
150
For the fast diode part, the losses and reverse recovery softness
remain as a critical performance target for matching the performance
of the new ET-IGBTs. The Field Charge Extraction (FCE) concept
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gate
gate
IGBT and diode future development trends
ET-IGBT
140
The main three IGBT development trends today are targeting higher
EP-IGBT
130
power densities with (a) Enhanced Trench ET-IGBTs, (b) higher operating temperatures above the traditional 125°C mark and (c) IGBT/
120
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
Diode integration solutions referred to as Reverse Conducting RCIGBT or Bi-mode Insulated Gate Transistor (BIGT). In the BIGT case,
On-state voltage drop (V)
the single chip approach provides improved performance especially
Figure 1: 3.3kV IGBT trade-off curve between on-state voltage drop
with respect to the limitations due to the restriction in available diode Fig. 1. 3.3kV IGBT trade-off curve between on-state voltage drop and turn-off losses.
and turn-off losses. Comparison between the enhanced trench (ET)
area depending on the given application requirements. Nevertheless, Comparison between the enhanced trench (ET) and enhanced planar (EP) structures.
and enhanced planar (EP) structures
the traditional IGBT/Diode two chip approach remains as an important
development path for many mainstream applications. Today, state-ofThe ET-IGBT concept
the-art high voltage devices with a similar loss performance employ
The main approach followed for the realization of the ET-IGBT conEnhanced Planar IGBT (EP-IGBT) or Trench IGBT MOS cell concepts
cept with the targeted enhanced carrier concentration near the trench
on Soft Punch Through (SPT) structures. However, for lower voltage
emitter for lower losses is based on the introduction of a striped active
devices rated below 2 kV, in addition to trench IGBTs, advanced
Trench MOS Cell with an n-enhancement layer. In order to reduce the
ET-IGBTs are already an established technology. Furthermore, the
effective input capacitance for improved switching controllability, the
ET-IGBT concept is also capable of providing the next step in loss
focus is on the optimization of the regions between the active cells,
reduction for high voltage IGBTs. Figure 1 demonstrates the on-state
which contribute strongly to the device effective input capacitance
Vce(sat) loss reduction of a 3300 V IGBT for the same turn-off losses
value during switching. By eliminating gate regions between the
active cells as shown in the cross section in figure 2, we allow for a
Eoff achieved with the new ET-IGBT MOS cell on the same bulk SPT
low effective gate emitter input capacitance compared to state-of-theplatform. However, it is important to point out that the trench based
IGBTs, especially for higher voltage ratings, exhibit an inherently high
N-source
effective gate input capacitance when compared to planar based
devices which results in less controllability for optimum switching
P
performance during IGBT turn-on. Overcoming this negative aspect
n-enhancement
layer
combined with the lower losses of the ET-IGBT will provide an ideal
solution for the next generation high voltage IGBTs.
Figure 2: ET-IGBT MOS Cell concept
Fig. 2: ET-IGBT MOS Cell concept.
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STORY
3.3 kV ET-IGBT module prototypes
3.3 kV ET-IGBT and FCE-diode chips were manufactured with an active area of approximately 1 cm2 per chip with a defined rating of 75 A
for the IGBT and 150 A for the diode. The chips were employed in a
standard high voltage insulated module (140 x 70) mm2 having a dual
configuration as shown in the inset of figure 4. Each IGBT/diode part
in the dual package consists of a single substrate containing 4 x ETIGBTs and 2 x FCE-diodes. The resulting current rating of the module
is 300 A compared to today’s 250 A for an equivalent EP-IGBT.
art trench IGBT designs while providing optimum reverse blocking
capability. The lower on-state losses of the 3.3 kV ET-IGBT provides
potentially a 20% increase in the rated current capability compared to
the EP-IGBT generation.
Nominal
T = 25°C
T = 150°C
ET-IGBT
Current (A)
200
EP-IGBT
100
0
0
1
2
3
4
Voltage (V)
Figure 4: 300A/3.3kV ET-IGBT module output I-V characteristics at
25°C and 150°C.
Fig. 4: 300A/3.3kV ET-IGBT module output I-V characteristics at 25 C and 150 C.
The modules were tested electrically under static and dynamic conditions. Figure 4 shows the on-state characteristics for the ET-IGBT at
Figure 3: The combination of FCE and FSA concepts (a) and (b)
25°C and 150°C and compared to the EP-IGBT. The ET-IGBT module
cross sections, (c) doping profile
exhibits much lower static losses compared to the EP-IGBT together
combination of FCE and FSA concepts (a) and (b) cross sections,
doping
profile.
with(c)
strong
positive
temperature coefficient for safe paralleling of
chips. At the rated current of 300 A, the ET-IGBT design has a Vce(sat)
The FCE diode concept
For the new diode, a combination of the Field Charge Extraction
of 2.75 V compared to 3.55 V for the EP-IGBT at 150°C.
(FCE) concept and the well-established Field Shielded Anode (FSA)
design is utilized as shown in figure 3 when compared to a convenFigure 5 show the nominal turn-off and turn-on switching waveforms
tional design. The thickness of the n-base plays a key-role for the
for both ET-IGBT and the reference EP-IGBT, respectively. The test
overall loss generation where low-loss diodes require a thin n-base
conditions were kept the same to better evaluate the device perfordesign. However, further reductions of the thickness of the n-base
mance. The devices were switched against an applied DC-link voltage
region have been typically restricted by the snappy reverse recovery
of 1800 V and a rated current of 300 A at 150°C with a gate emitter
behavior of the resulting diodes. By introducing small p-doped areas
capacitance of 47 nF. The stray inductance was 600 nH and the turnat the cathode side of the diodes as shown in figure 3, a field-induced
off gate resistance was 9Ω while the turn-on gate resistance varied
carrier injection process is enabled during the recovery phase, which
per design as indicated. The turn-off losses Eoff of the ET-IGBT were
generates inherently soft diodes. Therefore, the n-base of a 3.3 kV
at around 650mJ compared to 600 mJ for the EP-IGBT. However,
rated diode can be thinned by 10% while the blocking capability is
larger variations were obtained for the turn-on losses Eon where the
maintained by increasing the
3000
600
3000
resistivity without compromis75
75
EP-IGBT (R =10)
EP-IGBT
Current
ET-IGBT
ET-IGBT (R =18)
ing soft reverse recovery. The
300
2500
2500
500
60
60
benefit of this approach is
2000
Voltage
45
45
a 20% improvement on the
2000
400
Voltage
Current
technology curve. Moreover,
30
30
200
1500
1500
300
the robustness of these inherGate
Gate
15
15
ently soft diodes has been
1000
1000
200
improved due to the absence
0
0
100
500
of large overshoot voltages
500
100
-15
-15
during reverse recovery.
0
G
-30
-30
0
0
1
2
3
4
5
6
-500
Time (s)
Current (A)
Voltage (V)
Gate voltage (V)
Voltage (V)
Current (A)
Gate voltage (V)
G
0
0
0
2
4
6
8
Time (s)
Figure 5: 300A/3.3kV module Turn-off (left) and Turn-on (right) waveforms (1800V, 300A, 150°C).
Fig. 5: 300A/3.3kV module Turn-off (left) and Turn-on (right) waveforms (1800V, 300A, 150 C).
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ET-IGBT Turn-off and Short Circuit SOA Performance
The turn-off (RBSOA) behavior was tested for two paralleled chips
under high current and voltage conditions. For the RBSOA, the ETIGBT was tested against a high DC-link voltage of 2500 V and the
maximum achieved switchable current is approximately 5x and 4x the
nominal current at 25°C and 125°C, respectively as shown in figure 8.
The device enters and withstands both stress conditions known as dynamic avalanche and Switching Self Clamping Mode SSCM at 25°C.
At a temperature of 125°C, the device experiences stronger dynamic
avalanche as expected due to the higher levels of carrier concentrations which results in a lower but still sufficient turn-off capability.
ET-IGBT was at 860 mJ albeit with a different gate resistor compared
to 910 mJ for the EP-IGBT. The total switching losses for all tested
devices were approximately at the same level just below 1.5 J. The
FCE-diode reverse recovery performance can also be seen in the
IGBT turn-on waveforms. The controllability of the ET-IGBT is illustrated in figure 6 when plotting the turn-on parameters (Icmax, Eon and
di/dt) against the variation in the gate resistance.
550
500
1500
EP-IGBT
ET-IGBT
1200
1360
680
0
20
900
Current (A)
0
600
600
-20
-40
-60
-80
400
1.5
2.0
2.5
Time (s)
3.0
3.5
Figure 7: 300A/3.3kV module reverse recovery (1800V, 15A, 25°C).
200
5
10
15
20
25
Fig. 7: 300A/3.3kV
module
recovery
15A,
25carried
C). out at 1800 V
The
singlereverse
chip ET-IGBT
short(1800V,
circuit test
was
Gate resistor ()
and 25°C and the resulting waveforms are shown in figure 8. At a
short circuit current level of around 300 A, a smooth and stable beFigure 6: Effect of varying the gate resistance on the turn-on paramhavior
the
gate
resistance
on
the
turn-on
parameters
(1800V,
300A,
150was
C).obtained for pulse widths of at least 15 us.
eters (1800V, 300A, 150°C).
With the above SOA performance, it is encouraging that the improvements achieved for lowering the on-state losses of the ET-IGBT have
not compromised the device robustness, which is strongly required
especially when targeting higher power densities for the next generation HiPak and LinPak modules.
The FCE diode softness was also tested under the same circuit setup
but at the critical softness conditions with a lower current of 15 A and
a lower temperature of 25°C as shown in figure 7. The FCE diode
clearly shows very soft recovery performance under these extreme
conditions when compared to the standard diodes exhibiting a typical
current snap-off along with the associated high overshoot voltage.
3600
3000
600
2400
4×Inom
1800
300
1200
150
600
0
voltage
Voltage (V)
750
450
600
2400
Voltage (V)
Current (A)
900
750
3000
4200
25°C
150°C
www.abb.com/semiconductors
450
1800
300
current
1200
Current (A)
varying
Standard diode
FCE diode
2040
450
Voltage (V)
Average di/dt (A/s) Turn-on losses (mJ)
IC max (A)
600
150
600
0
0
0
1
2
3
4
5
Time (s)
6
0
0
2
4
6
8
10
12
14
16
18
-150
Time (s)
Figure 8: 3300V ET-IGBT Turn-off RBSOA (2500V, Rg=33Ω, Ls=2400nH, Vge=20V)
and short circuit
SOA
(1800V,
tsc=15us,
Rg=33Ω,
Ls=2400nH,
T=25°C)
waveforms
Fig. 8:
3300V
ET-IGBT
Turn-offVge=15V,
RBSOA (2500V,
Rg=33Ω,
Ls=2400nH,
Vge=20V)
and short circuit
28
SOA (1800V, tsc=15us, Vge=15V, Rg=33Ω, Ls=2400nH, T=25 C) waveforms
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