Development of New Generation 3.3kV IGBT module

Transcription

1 Development of New Generation 3.3kV IGBT module

2 Mitsubishi_2_8 Seiten_neu.qxd :43 Uhr Seite 2 CONTENT Development of New Generation 3.3kV IGBT module Introduction Chip Technology Static Characteristics Dynamic Characteristics SOA Performance Inverter Output Performance Conclusion References

3 Mitsubishi_2_8 Seiten_neu.qxd :43 Uhr Seite 3 Development of New Generation 3.3kV IGBT module S. Iura 1), A. Narazaki 1), M. Inoue 1), S. Fujita 1), E. Thal 2) 1) Mitsubishi Electric Corp. Power Device Works, Imajukuhigashi, Nishi-ku, Fukuoka, Japan, Tel Iura.Shinichi@aj.mitsubishielectric.co.jp 2) B.V., Gothaer Str. 8, Ratingen, Germany Abstract: A High Voltage IGBT (HVIGBT) module with high performance such as low power loss and high reliability is required for high power applications. However, these performances often are in a reciprocal relationship to each other. Thus, in order to achieve a balancing performance, a newly developed chip-set adopts "Fine Planar MOSgate Light Punch Through HVIGBT (FP-LPT-HVIGBT)" and "Soft reverse Recovery HV-Diode with high robustness (SR-HVDi)" structure as advanced design. The new generation 3.3kV HVIGBT modules will be able to reduce the power loss and increase the rated current by utilizing this improved the new chip-set performances. Introduction HVIGBT modules have been in a widespread use in high power applications; such as railway propulsion and large industrial drives. In these high power applications a better performance of HVIGBT modules is desired, especially reduced losses, increased rated current and wider operation junction temperature. In addition, easy to use in parallel connection and good switching controllability for low EMI level is required. In order to achieve these objectives, we have been developing a new generation 3.3kV IGBT modules. Improvement of IGBT chip performance strongly depends on MOS-gate structure such as planar and trench, and vertical structure such called as LPT, FS and SPT. [1] [2] [3] Generally IGBT has a few correlative parameters: on-state loss, off-state loss, robustness and leakage current. [4] Therefore, the IGBT chip has to be designed, taking into account above parameters as well as low power loss design. It is important to make a design having a good balance among these parameters. Besides the IGBT chip also a better performance of free-wheel-diode chip and a high reliability package are needed. In this paper we will explain the main evaluation results of electrical characteristics of the new IGBT and diode. trench-gate IGBT can be reduced more than that of a planar-gate IGBT because of non-jfet region. But this VCE(sat)-reduction effect due to trench-gate structure is smaller for high voltage IGBT compared to low voltage IGBT, because of the thicker wafer. On the other hand the planar-gate structure is offering more suitable output- and transfer characteristics for parallel operation and a better switching controllability by gate driving conditions compared with the trench-gate. Therefore we adopted for our new 3,3kV IGBT-chip an advanced planar-gate design having a fine pattern MOS-structure. The cross-section of the new IGBT backside doping profile image is shown in Fig.1 compared with conventional IGBT. The red and blue lines in Fig.1 indicate the doping profiles of the new IGBT and conventional IGBT, respectively. The new IGBT s backside structure is optimizing the carrier concentration and is determined by shallow p-collector layer and deep n-buffer layer with no-lifetime control (i.e. so called LPT). Due to this structure, the new IGBT has obtained output characteristics with strong PTC and made a large contribution to low leakage current. Moreover, due to the adoption of the fine MOS gate pattern and the dense n-layer to the JFET region, the V CE(SAT) of the new IGBT was reduced remarkably compared with conventional IGBT. Chip Technology Our design concept of the new IGBT-diode chip set can be described as follows. IGBT: lower losses, di/dt and dv/dt controllability. Diode: reverse recovery current (Irr) reduction. Common: higher SOA robustness, Positive Temperature Coefficient (PTC) for easy paralleling. The gate structures of planar and trench IGBTs are well known. The on-state voltage (VCE(sat)) of a Fig. 1: IGBT backside structure comparison 3

4 Mitsubishi_2_8 Seiten_neu.qxd :43 Uhr Seite 4 One of the aims of the new diode is Irr reduction. In consequence, the peak power during reverse recovery and the turn-on switching energy of IGBT can be reduced. Furthermore, the new diode has been designed maintaining a high robustness regarding di/dt and peak power so that turn-on IGBT performance is not spoiled by limitation of diode robustness. The doping profile and lifetime image of the new diode is shown in Fig.2 compared with conventional diode. The red and blue lines in Fig.2 indicate a doping profile and lifetime of the new IGBT and conventional IGBT, respectively. The new diode has balanced design between high performance and high robustness due to optimized n-buffer layer structure at cathode side and lifetime control. Fig. 3: IGBT output characteristics at 25 C and 125 C Fig. 2: Diode cross-section structure comparison Carrier concentration and carrier lifetime in n-drift region Static Characteristics The output characteristics of 1200A modules with new IGBT and diode are given in Fig.3 and Fig.4 respectively. The current density of the new IGBT chip in Fig.3 is 94% compared with conventional IGBT, and that of the new diode chip in Fig.4 is the same as conventional diode. The VCE(sat) of the new IGBT is 30% less than conventional IGBT at rated current and 125 C conditions. The new IGBT is having a strong PTC as shown in Fig.3. The forward voltage (V EC ) of the new diode is 7.5% less than conventional diode under the same conditions as IGBT and having a cross-point from NTC towards PTC at half rated current. Fig. 4: Diode forward characteristics at 25 C and 125 C Fig.5 shows the collector-emitter leakage current characteristics as function of the forward blocking voltage up to 3300V and temperature up to Tj=175 C. The leakage current at Tj=150 C of the new IGBT is reduced by a factor of 4 compared to conventional IGBT when a voltage of 3300V is applied. Besides, thermal run-away has not occurred under Tj=175 C condition. 4

5 Mitsubishi_2_8 Seiten_neu.qxd :43 Uhr Seite 5 Fig. 5: Leakage current characteristics of IGBT chips Between Collector-Emitter, AC60Hz half-sine wave Fig. 6: Turn-on switching waveforms at 125 C V CC =1800V, I C =1200A, V GE =15V, di/dt=3800a/µs, L S =150nH Dynamic Characteristics The evaluation results of dynamic characteristics of 1200A modules with new IGBT and diode are presented below. The tests carried out the turn-on and turn-off switching under the half-bridge circuit with inductive load at 125 C, DC-link voltage of 1800V and collector current of 1200A. Fig.6 shows the turn-on switching waveform in case of different diode with identical new IGBT at same di/dt conditions. The blue line in Fig.6 indicates the combination of the new IGBT and new diode, while the red line indicates the combination of the new IGBT and conventional diode. The peak collector current (i.e. Irr of diode) of blue line waveform was 20% less than red line waveform. In consequence the IGBT turn-on switching energy (Eon) is reduced by 10%: 1.54J/pulse with the new FWDi and 1.73J/pulse with conventional FWDi. In addition, the new diode has a softer behavior during reverse recovery, as the waveforms in Fig.6 are indicating. The Eon and di/dt values during turn-on switching of the new IGBT are plotted in Fig.7 as a function of gate resistor. This result is indicating that the di/dt can be controlled in a wide range by selecting the turn-on gate resistor value. Fig. 7: Turn-on di/dt and Eon vs. Rg characteristics V CC =1800V, I C =1200A, V GE =15V, L S =150nH Fig.8 shows the turn-off switching waveform of the new IGBT compared with conventional IGBT at same dv/dt conditions. The blue line indicates the new IGBT and red line indicates the conventional IGBT. The two waveforms are very similar resulting in about the same turn-off switching energy (Eoff) level. The relationship between VCE(sat) and Eoff trade-off is given in Fig. 9. It can be seen that the trade-off characteristic of the new IGBT was improved by about 25% compared with conventional IGBT. The Eoff and dv/dt values during turn-off switching of the new IGBT are plotted as a function of gate resistor as shown in Fig. 10. From this result it becomes clear that selecting the turn-off gate resistor value can control the dv/dt. 5

6 Mitsubishi_2_8 Seiten_neu.qxd :43 Uhr Seite 6 Fig. 8: Turn-off switching waveforms at 125 C V CC =1800V, I C =1200A, V GE =15V, di/dt=3500a/µs, L S =150nH SOA Performance The turn-off switching SOA test result of the new IGBT chip is demonstrated in Fig.11. The junction temperature test conditions were Tj=125 C and Tj=150 C. The test at Tj=125 C was carried out by gradually increasing the DC-link voltage up to 2800V at turn-off current of four times rated current (4x67A=270A). The obtained test result is shown in Fig.11(a). In addition, under the Tj=150 C condition, the test result at turn-off current of three times rated current and DC-link voltage of 2500V is shown in Fig.11(b). Fig.12 shows the traced voltage and current from test waveform in Fig.11(a) and (b). It can be seen that the specified SOA-curve at 2 x rated current can be fulfilled with a wide margin. Fig. 9: Measured trade-off between V CE(sat) and Eoff at 125 C V CC =1800V, I C =1200A, V GE =15V, di/dt=3500a/µs, L S =150nH Fig. 11: IGBT chip turn-off switching waveforms Rated I c = 67A, V GE =15V, R g =75W, L S =2.2µH Fig. 10: Turn-off dv/dt and Eoff vs. Rg characteristics V CC =1800V, I C =1200A, V GE =15V, L S =150nH 6

7 Mitsubishi_2_8 Seiten_neu.qxd :43 Uhr Seite 7 Fig. 12: RBSOA V-I curve Conclusion This paper is describing the superior performance of new generation 3.3kV HVIGBT module with FP- LPT-HVIGBT and SR-HVDi compared to conventional HVIGBT module. The advanced new IGBT is improving the trade-off characteristic between V CE(SAT) and Eoff by 25% without deteriorating the robustness. In addition, Eon improved by the advanced new diode with reduced Irr and soft reverse recovery behavior maintaining the robustness capability of conventional diode design. Thereby the new generation 3.3kV HVIGBT module will be able to reduce the power loss and increase the rated current by utilizing the improved new chip-set performance. The reverse recovery SOA test of the new diode chip (rated I F = 67A) was also carried out and the peak power (Prr) was monitored by gradually increasing the di/dt at Tj=125 C and DC-link voltage of 2600V. As result a Prr withstand capability per diode chip of kW at di/dt of 700A/µs was confirmed. When these chip-test values convert into module values, this is resulting in about 2.7 to 2.85 times larger Prr values than the currently specified Prr limit. Inverter Output Performance Fig.13 shows the calculated inverter output current Io as function of PWM switching frequency fc for the new HVIGBT module compared with conventional HVIGBT module. From this results, the RMS output current can be increased by approximately 200A assuming a maximum junction temperature of Tj=125 C at fc=400hz. Besides, if the maximum operating junction temperature will be Tj=150 C, the output current Io could be increased by another 550A. References [1] K. Nakamura, et al. Advanced wide cell pitch IGBT having Light Punch Through (LPT) structures ISPSD 2003 [2] J. Biermann, et al. New 3300V Trench IGBT Module for Highest Converter Efficiency PCIM 2004 [3] N. Tsukamoto, et al. World first 3,3kV/1,2kA IEGT in trench-gate technology PCIM 2004 [4] M. Rahimo, et al. SPT+, the Next Generation of Low-Loss HV-IGBTs PCIM 2005 Fig. 12: Inverter output current vs. PWM frequency by a thermal calculation 7

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