Download Next step towards higher power density with new IGBT and di

PCIM Europe 2013, 14 – 16 May 2013, Nuremberg
Next step towards higher power density with new IGBT and diode generation and influence on inverter design
Ciliox, Alexander, Infineon Technologies, Max Planck Str. 5, 59581 Warstein
Vogel, Klaus, Infineon Technologies, Max Planck Str. 5, 59581 Warstein
Dr. Niedernostheide, Franz-Josef, Infineon Technologies, Am Campeon 1-12, 85579 Neubiberg
Dr. Haertl, Andreas, Infineon Technologies, Am Campeon 1-12, 85579 Neubiberg
Abstract
Power density has become an important performance indicator for inverters. From this trend,
two requirements arise for power modules containing IGBTs and diodes: First, the power
modules must have a sufficient long lifetime even under higher thermal stress. One solution
to fulfill this requirement is the implementation of the .XT technology [1]. Second, the IGBTs
and diodes have to provide better performance in terms of static and dynamic losses. This
paper presents for the first time the common figures of merit of the new 1200V IGBT and diode generation of Infineon Technologies.
Looking at the whole system, the other inverter components have to be suitable to cope with
the demands of an increased power density as well. In the second part of this study, measurements with different inverter designs are performed to evaluate their thermal management. Based on these results design rules for high power density inverters can be extracted.
1.
The new 1200V IGBT and Diode generation
1.1.
Expanding the power range
The PrimePACKΠpower module housing (Fig. 1) has set a standard for power module
housing in the power range up to 700kW. Because of its success it is self-evident that the
launch of the new 1200V IGBT and diode generation will also take place in the
PrimePACKŒ2 housing.
Currently, the maximum available current rating in the PrimePACKŒ2 housing in half-bride
configuration is 900A. By using the new 5th IGBT and diode generation the current rating can
be pushed up to 1200A nominal current.
Fig. 1. (left): State of the art PrimePACKΠequipped with IGBT5. (right): Application of IGBT variants
in the PrimePACKŒ2
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1.2.
th
1200V 5 IGBT generation
The trend to increase the power density in power modules is directly supported by the increase of the operation temperature of the semiconductor devices.
Infineon has presented the concept of the trench-field stop IGBT for 1200V devices in 2000
for the first time. This so called 3rd IGBT generation was qualified for an operation temperath
ture of 125°C [2]. The next step towards higher power density was the introduction of the 4
th
IGBT generation. This generation is suitable for a junction temperature of 150°C [3]. The 5
generation of 1200V IGBTs and diodes is designed for an operating temperature of Tjop
=175°C. The IGBT5 is based on the successful trench field-stop concept as well.
Electrical performance
Furthermore, the IGBTs designers work constantly to improve the device performance by
reducing both the switching losses, and the stationary on-state losses. All this optimization is
done under the “constraint” that the well-established short-circuit withstand time of 10 µs at
operating temperature has to be guaranteed. The new approach to overcome this challenge
is depicted in Fig. 2.
Fig. 2. Comparison of IGBT4 (left) and IGBT5 (right). The IGBT5 has a reduced die thickness and a
new cell design which, however, is still based on the successful trench field-stop technology.
Moreover, copper is used as front-side metal instead of aluminum. The front-side copper thickness is significantly increased compared with the front-side aluminum thickness of the IGBT4.
The used approach in the IGBT development can be understood by investigating the event
of short circuit: In the short circuit condition the device temperature is increasing rapidly due
to the massive power dissipation, since power is equal voltage times current. The device
temperature itself is then given by the short-circuit energy divided by the thermal capacity of
the IGBT. This thermal capacity is defined by the silicon volume itself and by the metal top
layers. The increased thermal capacity of the new front-side metallization of the IGBT5 enables the successful short-circuit turn off by preventing the thermal runaway. It is worth mentioning that a high precision in the alignment of the copper layer and the IGBT trenches is
needed to assure that functionality, namely that every single IGBT cell needs to be well connected to its additional thermal capacity.
One measure to increase the performance was the reduction of the device thickness to
110µm. The trade-off relationship between the turn-off losses and the on-state saturation
voltage is shifted to lower values (see Fig. 3). Normally the on-state losses increase with increasing operation temperature. However, due to the better performance of the IGBT5 the
on-state voltage drop at 175°C is the same as for the IGBT4 at 150°C.
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Fig. 3. Turn-off losses vs. saturation voltage for different IGBT generations at Tj=150°C.
Also linked to the thickness of the IGBT is the softness of the device. Softness is guaranteed
by a sufficient amount of tail current. Looking again at the current IGBT4 variants a
PrimePACKΠmodule with 1200A has to be equipped with the softer, so called High Power
variant. The new IGBT5 Medium Power variant has a better softness than the IGBT4 Medium Power variant. This optimization allows the designer to use the IGBT5 MePo variant with
a 1200A PrimePACKŒ2 module. Thus, he is also able to take advantage of reduced switching losses compared to the IGBT4 High Power variant. Fig. 4 shows the switching curves of
an IGBT5 which was turned-off by the nominal current (Inom=1200A) at 175°C and by double nominal current (2400A) at 25°C with an external gate resistor of zero ohms.
Fig. 4. (left):Turn-off curves at 2xInom= 2400A, 25°C without an external gate resistor and without
any external clamping and (right) turn-off curves of nominal current at 175°C. (Green: Vge,
black: Vce, red: Ic)
The controllability of the IGBT’s turn off is also of interest. The simplest approach to control
the switching speed of an IGBT is to adjust the gate resistor connecting a gate source voltage and the gate terminal of the IGBT. In Fig. 5, the dU/dt controllability of the IGBT4 MePo
variant and the IGBT5 MePo variant are compared by plotting the 10%-90%-dU/dt value as a
function of the total gate resistor. The 10%-90% dU/dt value was calculated from the measured collector-emitter voltages at 10% and 90% of the maximum collector-emitter voltage
during the turn-off period and the corresponding time difference. The total gate resistor is the
sum of the internal and external gate resistor. For the IGBT5, we found a distinct monotonic
decrease of the dU/dt on a large resistor range. In contrast to the IGBT4, this distinct monotonically decreasing dependence of the dU/dt value with the total resistor is valid even for
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very small resistors. Consequently, the range of controllability of the IGBT5 is enhanced
compared to the IGBT4.
IGBT4
MePo
IGBT5
MePo
IGBT5
MePo
150
150
175
Esw/A [%]
100%
96%
110%
Vcesat [V]
2,1
2
2,1
Tsc [μsec]
10
>10
10
I nom PP2 [A]
900
1200
1200
Tjop
Fig. 5. (left): 10%-90%-dU/dt value as function of the total gate resistor for the IGBT4 and IGBT5 at
maximum operating temperature and (right) table summarizes the most relevant electrical characteristics of the IGBT4 and IGBT5.
1.3.
1200V emitter controlled diode 5th generation
In power modules for inductive switching applications, the IGBT and diode are operated as
one unity. Consequently, the diode has to be designed in such a way that its electrical behavior matches the IGBT behavior. The new emitter controlled diode (EC5 diode) is also designed to support a maximum operating temperature of Tj=175°C.
The further optimization of the device in terms of thickness reduction and field stop design
enables an improved electrical performance of the EC5 diode, as depicted in Fig.6: it obtains
a better Vf- Erec tradeoff, while on the other hand maintaining a switching softness as least
as good as the previous diode generation EC4.
Fig. 6. (left): Dependence of the reverse-recovery energy on the forward voltage of the 1200V EC5
diode at 150°C. (right): Turn-off characteristics of the same diode at 1/10 nominal current at
room temperature illustrating the superior softness of the new diode generation.
The most critical operation mode for the free-wheeling diode is the surge-current condition.
The surge-current capability is typically reduced by ~5% for an increase of the operating
temperature by 25K. Our measurements of the EC5 have shown that we achieve at least the
same I²t-value at Tj=175°C as the EC4-diode features at Tj=150°C.This remarkable improvement is again based on the increase of the thickness of the front side metal stack,
providing the necessary additional thermal capacity.
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2.
Module performance
2.1.
Power cycling and thermal performance
Power cycling
th
The new 5 generation 1200V devices from Infineon are based on the .XT assembly techth
nology. Therefore, the excellent .XT power cycling performance is also obtained by the 5
generation. Fig. 7 shows the target power cycling curve [4].
Fig. 7. (left): Power cycling target curve of the .XT technology. (right): Comparison of the thermal performance of .XT assembly technology with the IGBT4 solder technique. In the time range larger than 0.2 sec, the Rth junction-case of .XT is about 15% better.
Rth decrease based on .XT
Thermal simulations were performed in order to compare the thermal resistance (Rth) of the
current solder standard technique in comparison with .XT. This simulation was done for a fully equipped PrimePACKŒ2 module. First we simulated the FF900R12IP4D powered by the
IGBT4, and for the second case we simulated the FF1200R12IE5D; Fig. 7 shows the
achieved results. An Rth junction-case improvement of about 15% for the same silicon size
was calculated, and this value was also confirmed by measurements.
2.2.
Inverter output current calculation
The IPOSIM tool from Infineon is used to calculate the maximum inverter output current
based on the presented values in this paper. In Fig. 8 the achieved result is depicted.
Fig. 8. Calculated inverter output current for IGBT5 &4 at max. junction temperature. Conditions: A
forced air cooler Rth h-a of 0.098 per arm, cosine phi=0.8 modulation factor= 0.8, DC link voltage 600V, same silicon placement
Looking at a typical switching frequency of 4 kHz the inverter output current based on the
IGBT5 MePo can be increased by ~23% as compared to the IGBT4 MePo, and by 33% as
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compared to the IGBT4 HiPo variant. The IGBT5 operated by 150°C leads to a power density increase by ~14% compared to the IGBT4 HiPo.
3.
Consideration on different inverter designs
Besides the development of the IGBT module technology to fulfill the requirements of high
power density and lifetime, the inverter thermal management will become more important to
obtain the best performance for such type of semiconductor device [5, 6]. The increase of
the operation temperature of the switching silicon leads to a higher heat sink temperature at
given cooling conditions. Considering this, it is very likely that compact air cooled systems
will suffer from an elevated temperature of the components neighboring the power electronic
module. To find out more about the influence of different thermal designs, two commercially
available 4kW inverters from drives applications are examined. The focus is the temperature
behavior of temperature sensitive components of the control electronics and DC-Link at
higher IGBT operation temperature up to 175°C. Figure 9 shows the different inverter concepts schematically. While one concept has a dedicated air flow implemented to cool the
electronic components, the other inverter has its PCBs cooled by convection. At the same
time, the latter is thermally coupled to the heat sink through the power electronic terminals.
Design 1: 4kW Inverter with 2,1kW/l
Design 2: 4kW Inverter with 1,6kW/l
Fig. 9. Different inverter design and different power density for drives application.
Design 1 has the heat sink completely inside the housing, while in design 2 is the heat sink a
part of the housing and larger in volume by circa 70%.
Two benefits of the 25K higher maximum operation temperature compared to IGBT 4 are
examined in two tests: one with an increase of the output current by 20% and the other with
a decrease of the cooling efforts by 25%. The temperature of various electronic components
is monitored with thermocouples and the results are shown in figure 10. Both inverters are
tested under load and overload conditions up to Tvj of 175°C.
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Design 1
Design 2
125
135
145
155
165
175
Temperature of the electronic components
Temperature of the electronic components
Temperature behavior of the electronic components at increased inverter output power up to IGBT Tvj = 175°C
150
140
130
120
110
100
90
80
70
60
50
40
150
140
130
120
110
100
90
80
70
60
50
40
125
135
145
IGBT operation junction temperature
DC-Link-Cap.
Filter
PCB
Trans. Core
Tran. Wind.
155
165
175
IGBT operation junction temperature
Transitor
IGBT Driver
DC-Link-Cap.
Elko (PCB)
PCB
Trans. Core
Tran. Wind.
PCB 2
IGBT Driver
150
140
130
120
110
100
90
80
70
60
50
40
105
115
125
135
145
155
165
175
Temperature of the electronic components
Temperature of the electronic components
Temperature behavior of the electronic components at reduced cooling efforts up to IGBT Tvj = 175°C resp. 140°C
150
140
130
120
110
100
90
80
70
60
50
40
105
IGBT operation junction temperature
DC-Link-Cap.
Filter
PCB
Trans. Core
Tran. Wind.
Transitor
115
125
135
145
155
165
175
IGBT operation junction temperature
IGBT Driver
DC-Link-Cap.
Elko (PCB)
PCB
Trans. Core
Tran. Wind.
PCB 2
IGBT Driver
Fig. 10. Temperature behavior of the electronic components by increasing the IGBT operation temperature up to 175°C in two different inverter designs. Dotted lines represent the maximum allowed
temperature for the respective components.
As can be recognized easily, the measured temperatures inside of the inverter 1 are lower in
all operation points in comparison to inverter 2. Due to the fact that Inverter 1 has the higher
power density, this is a good indication for a better thermal design compared to 2. The temperature spread over the different measurement points is larger for design 1 in comparison
to design 2. Especially at Tvj_op = 175°C the captured points of all measured components
are distributed in the whole Inverter 2 within 12K. For this operation point, the temperature
spread in Inverter 1 is 49K. Due to the inverter design with a small heatsink close to the air
output side, Design 1 has “cold” areas inside the housing and the IGBT junction temperature
does not influence all areas of the inverter evenly. In design 2 the large heatsink is heated up
and through convection and conduction along the module terminals, the above situated electronic components are heated up and stressed uniformly. Using Design 1 the development
engineer has the possibility to place the thermal sensitive components in the “cold” areas of
the inverter, while this is not possible with design 2.
Increasing of the output power leads to an increase of the inverter temperature. This is,
however, not alone due to the higher IGBT operation temperature, but also due to the higher
current through DC-Link capacitors and PCBs. The results show that, compared with Design
2, the PCB and the IGBT driver in Design 1 suffer from a higher temperature elevation when
increasing Tvjop from 150°C to 175°C by a current increase. This can be explained with a
stronger coupling of these components with the heatsink in the more compact design.
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Nevertheless, the margin to the maximum allowed component temperature in Design 1 is
higher than in Design 2.
Regarding the DC-Link capacitors, the temperature rise is similar in both designs. Design 2
requires 105°C capacitors against 85°C in Design 1, a clear disadvantage for design 2 due
to the passive cooling of this part of the inverter.
Design 2 comes in trouble with the reduction of the cooling efforts. This is equivalent to an
increase of the heatsink thermal resistance Rth_ha. Already at a temperature of Tvj = 115°C
most of the components are above the maximum permissible temperature. A worsening of
the heatsink leads to an increase of the heatsink temperature, the heat remains in the inverter housing and is dissipated towards the control part of the inverter trough convection
and conduction via the module terminals. Design 1 can manage this situation better. All
measured parts operated inside the allowed temperature up to a Tvj_op of 175°C of the
IGBT. The distance to the maximum allowed operation temperature of the electronic components during the operation of the IGBT at 175°C and the increase compared to operation
at Tvj = 150°C is shown in the next table.
PCB
'HVLJQ
Design 2
'HVLJQ
Design 2
IGBT Driver
DC-Link
Margin to
max
Delta to
IGBT
150°C
Margin to
max
Delta to
IGBT
150°C
Margin to
max
Delta to
IGBT
150°C
Ĺ,RXW Tvj_op 175°
13K
+10K
13K
+10K
25K
+5K
7K
+5K
8K
+7K
8K
+7K
Ĺ
Rth_ha =
Tvj_op 175°C
17K
+10K
3K
+15K
21K
+6K
x
x
x
x
x
x
* compared to an IGBT 4 solution
A core element when increasing the power density in inverters is the lifetime consideration of
the components. Using the same component technology at higher temperature automatically
leads to a decrease of the lifetime. A smart inverter design with “cold” areas and forced convection on electronic level will help to handle this challenge. It is shown that despite of the
dimensioning of DC-link capacitors, which has to be adjusted to higher power densities anyway, an inverter design implementing a designated PCB cooling may draw benefits from increased junction temperatures straight away. In contrast, considerable redesign efforts have
to be considered if the electronics part is thermally coupled to the main heat sink through
power terminals of the module.
Conclusion
This paper presents the achievable level of power density increase based on the new 1200V
IGBT and diode technology. The achievable inverter output current can be increased by 23%
th
compared to the current IGBT generation. The first available module with the 5 IGBT generation will be a FF1200R12IE5D in the PrimePACKŒ2 housing. Besides this, the importance of the inverter’s thermal design on the ability to provide the higher power density
with new module packages is presented and discussed. Care must be taken regarding the
temperature raise seen at other system components to guarantee that the frequency inverter`s lifetime remains constant. A smart inverter design is the best way to handle with an
IGBT Tvj = 175°C without the need of expensive components with new technologies for
higher temperature.
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4.
[1]
[2]
[3]
[4]
[5]
[6]
Literature
A. Ciliox et al: New Module generation for higher lifetime, PCIM , Nuremberg, Germany, 2010
M. Hornkamp: IGBT Modules, 2011 Infineon Technologies AG, Munich, Germany
M. Bäßler et al: 1200V IGBT4- High Power- a new Technology Generation with optimized Characteristics for High current Modules, PCIM, Nuremberg, Germany, 2006
K. Guth et al: New assembly and interconnects beyond sintering methods, PCIM, Nuremberg,
Germany, 2010
K. Vogel et al: IGBT with higher operation temperature - Power density, lifetime and impact on inverter design, PCIM 2011, Nuremberg, Germany
K. Vogel et al: IGBT inverter with increased power density by use of a high-temperature-capable
and low-inductance design, PCIM 2012, Nuremberg, Germany
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