High-Speed 600V NPT-IGBT with Unclamped
Inductive Switching (UIS) Capability
Masakazu Yamaguchi, Ichiro Omura, Satoshi Urano and Tsuneo Ogura
中秋节时间
Discrete Semiconductor Division, Semiconductor Company, Toshiba Corporation
1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8583, Japan
Tel : +81-44-549-2603, Fax : +81-44-549-2883, E-mail : masakazu.jp
Abstract — In this paper, a new design concept is propod for 600V IGBTs to achieve both fast switching and unclamped inductive switching (UIS) capability. The concept is bad on optimizing p-emitter efficiency (γ) for each condition of on-state and sustaining mode. Here the γ is reduced in on-state to lower the turn-off loss, but kept enough in sustaining mode to suppress the electric field. In particular, it is shown that the γ of more than 0.4 in sustaining mode prevents the short-time UIS failure. The concept was successfully applied to NPT-IGBT, and the fabricated device has demonstrated fast switching adaptable to a frequency of 150kHz and UIS capability of 28mJ/mm 2 at a high current density (J C ) of 200A/cm 2 (about 6 times the J C of MOSFETs).
Index Terms - IGBT, p-emitter efficiency, unclamped inductive switching, turn-off loss
I. INTRODUCTION
IGBTs have the significant advantage of high-current handling capability over power MOSFETs. Therefore, if IGBTs replace MOSFETs in switch mode power supplies (SMPS), the size and cost of SMPS will be effectively reduced. For this replacement, IGBTs are required to be fast for frequencies over 100kHz and to be rugged under the sustaining mode operation in unclamped inductive switching (UIS).
Recent studies on the UIS characteristics of IGBTs have shown some UIS failure mechanisms and improved UIS capability [1-3]. However, to realize the high-speed IGBT with UIS capability, the correlation between turn-off speed and UIS capability must be taken into account, which has not been well discusd yet.
The purpo of this work is to propo a design concept for realizing 600V IGBT with fast switching and UIS capability under high current density. We report this work as the following two steps. First, the characteristics of punch through (PT) IGBT are examined to show its problem of UIS failure. A key parameter for UIS capability is revealed as p-emitter efficiency (γ), which also affects turn-off speed mainly owing to on-state carrier profile. Second, the concept is applied to non-punch through (NPT) IGBT.
The esnce of concept is optimizing the γ value for each condition of on-state and sustaining mode. Here γ can be controlled to different values for each condition, depending on the device design. The fabricated NPT-IGBT has achieved fast switching and high UIS energy.
intentionally distributed.
Fig.5 Two dimensional carrier distribution at the initial voltage drop of 1.5µc in Fig.4, reprenting the current crowding in the right-hand cells.送外甥
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II. IGBT STRUCTURES FOR HIGH-SPEED写人的作文450字
APPLICATIONS
Cross ctional views of the fabricated high-speed 600V PT- and NPT-IGBT are shown in Fig.1. fabricated on float zone wafers, utilizing 100µm thin wafer process and low temperature annealing for p-emitter activation. An implantation do of p-emitter dopant was controlled so as to optimize the γ value for each condition of on-state and sustaining mode. On the other hand, PT-IGBTs with low carrier lifetime were fabricated on epitaxial wafers with lifetime-killer diffud at various temperatures to evaluate the correlation between UIS capability and turn-off speed.
III. PROBLEM OF UIS FAILURE IN PT-IGBT
In this ction, experimental results indicate that the UIS capability is not compatible with the fast turn-off in PT-IGBTs. To explain the results, the UIS failure model is prented, in which current crowding leads to an increa in electric field at the collector side, depending on the γ value.
A. Experimental Results
The UIS energy was measured as a function of saturation voltage (V CE(sat)) for the fabricated PT-I
GBTs to evaluate the correlation between UIS capability and turn-off speed, where V CE(sat) is related directly to turn-off loss (E OFF ), and the IGBTs of higher V CE(sat) have lower E OFF . As shown in Fig.2, the UIS energy changes dramatically across V CE(sat) of 2.7V . The devices of V CE(sat)>2.7V are fast but have almost no UIS capability, which means that the UIS capability is not compatible with the fast switching in PT-IGBTs. From now on, PT-IGBTs of V CE(sat)≤2.7V are named Type-A and ones of V CE(sat)>2.7V are named Type-B.
The experimental UIS waveforms for Type-A device are shown in Fig.3. The sustaining voltage (V SUS ) indicates an initial drop, whereas V SUS is normally suppod to increa steadily in IGBTs [4]. In particular, Type-B devices destroyed just at this initial voltage drop for a very short time. Regarding the failure time, it has been reported that the UIS failure can be classified into two cas [3]. One is long-time failure (>a few µc) [1-3] and the other is short-time failure (<1µc). The failure of Type-B devices corresponds to the short-time ca, for which the detailed mechanism has not been analyzed yet.
B. Simulation Results and UIS Failure Modeling
The UIS characteristics have been numerically analyzed to examine the short-time UIS failure mech
anism. The UIS waveforms and carrier dynamics are calculated using 2-D device simulator ISE-DESSIS [5] on the planar gate structure of IGBT for simplicity and convergence of calculation.
Fig.4 shows the simulated sustaining waveforms for the multicell PT-IGBT, in which gate oxide thickness is intentionally distributed with thinner oxide in the right-hand cells. The waveforms of Fig.4 reproduce the feature of the experimental waveforms of Fig.3 very well. As illustrated in Fig.5, the current crowding up to 2000A/cm 2 occurs in the right-hand cells at the initial voltage drop of Fig.4, when Type-B devices destroyed in UIS measurement. This indicates that the short-time UIS
is remarkable that Type-A devices didn’t destroy but Type-B ones destroyed at that initial voltage drop.
To examine the physical difference between Type-A and B devices under current crowding, the electric field and carrier concentration profiles were simulated at two different values of the collector current density (J C) in sustaining mode with single cell structure, as shown in Fig.6. The J C of 200A/cm2 and 3000A/cm2 correspond to the steady current and the crowding current, respectively. In Type-A device, as J C increas from 200 to 3000A/cm2, the electric field decreas owing to the stored carriers, especially at the collector side of n-ba region. Contrastingly, in Type-B device, the electric field increas at the collector side with increasing J C, resulting from less hole concentration than electron concentration. This condition occurs when the γ obtained from I h/(I e+I h) at the edge of depletion region is less than 0.4. This value of 0.4 equals µp/(µn+µp) under high electric field, where µn and µp are the electron and hole mobility. The analys indicate that the increa of electric field at the collector side under current crowding results in the short-time failure, and reveal a key parameter for UIS capability to be the γ value. In other words, it is suggested that the γ of more than 0.4 in sustaining the carrier storage at the collector side.
The γ values in each condition of on-state and sustaining mode were calculated as a function of V C
E(sat) to examine the correlation between turn-off speed and UIS capability, where the γ was obtained from I h/(I e+I h) at the edge of n-ba region for on-state and at the edge of depletion region for sustaining mode. As is shown in Fig.7, the γ values fall below 0.4 when V CE(sat)>2.6V, especially in sustaining mode, which demonstrates the experimental results of Fig.2 substantially. This indicates the validity of design limit (γ≥0.4) for UIS capability and the esntial reason why the UIS capability is not compatible with the fast switching in PT-IGBTs.
IV. HIGH-SPEED NPT-IGBT WITH UIS
CAPABILITY
In this ction, the numerical and experimental results are prented for the NPT-IGBT with a new concept of optimizing the γ value for each condition of on-state and sustaining mode. The γ is reduced in on-state to lower the turn-off loss, but kept enough in sustaining mode to realize the UIS capability.
A. Simulation Results
Fig.8 shows the simulated electric field and carrier concentration profiles at two different values of J
C in sustaining mode. In contrast to Type-A device of PT-IGBT in Fig.6(a), NPT-IGBT has the stored carriers at the collector side in sustaining mode, therefore the electric field remain zero at that side even in a J C of 3000A/cm2.
Fig.9 shows the relation between the γ and the V CE(sat) in each condition of on-state and sustaining mode. In marked contrast to PT-IGBT shown in Fig.7, the γ value has been successfully reduced below about 0.3 in on-state as well as kept over 0.4 in sustaining mode for any V CE(sat), which corresponds to the design concept of optimizing the γ. According to
the above-mentioned model for UIS capability, the short-time UIS failure should be prevented owing to the γ of more than 0.4. On the other hand, the reduced γ in on-state will offer a lower E OFF.
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酷英文B. Experimental Verification
Relationship between UIS energy and total power dissipation for the fabricated PT- and NPT-IGBTs is prented in Fig.10. The total power dissipation was derived from the experimental values of V CE(sat), turn-on loss and turn-off loss at 125°C, assuming a 150kHz square wave operation. The propod NPT-IGBT with the optimized γ has realized low power dissipation adaptable to a frequency of 150kHz and UIS capability of 28mJ/mm2 at a high J C of 200A/cm2. The power dissipation of 10.2W/mm2 for NPT-IGBT is 20% smaller than that for Type-A device of PT-IGBT with UIS capability. At the same time, the UIS capability of 28mJ/mm2 for NPT-IGBT is 60% higher than that for Type-A device of PT-IGBT. Besides, this J C of 200A/cm2 is about 6 times the J C of MOSFETs.
V. CONCLUSION
In this paper, a high-speed 600V NPT-IGBT with UIS capability has been reported. The propod NPT-IGBT has been designed bad on a new concept of optimizing p-emitter efficiency (γ) for each 生菜怎么炒
condition of on-state and sustaining mode, in which the γ value is controlled less than about 0.3 in on-state and more than 0.4 in sustaining mode. The design concept has been verified by measurements on the fabricated devices, and it has been confirmed that the propod NPT-IGBT is preferable to fulfill fast switching and UIS capability with high current density, compared to PT-IGBTs.
ACKNOWLEDGEMENT
The authors would like to thank Senior Manager Yasuo Ashizawa for his support and encouragement for this work.
REFERENCES
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[2] C. -C. Shen, A. R. Hefner, D. W. Berning and J. B. Bernstein, “Failure Dynamics of the IGBT During Turn-Off for Unclamped Inductive Loading Conditions”, IEEE Trans. Industry Application, V ol.36, pp.614-624, 2000
[3] J. Yedinak B. Wood, P. Shenoy, G. Dolny, D. Lange and T. Morthorst, “Optimizing 600V Punchthro
ugh IGBT’s for Unclamped Inductive Switching (UIS)”, Proceedings of ISPSD’00, pp.363-366, 2000.
[4] K. Matsushita, I. Omura, A. Nakagawa and H. Ohashi, “Theoretical investigations on IGBT snubberless, lf-clamped drain voltage switching-off operation under a large inductive load”, Proceedings of ISPSD’93, pp.46-51, 1993.
[5] ISE TCAD Manuals, ISE Integrated Systems Engineering AG, Zurich, 1999.
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