Sven Matthias, Arnost Kopta, Munaf Rahimo, Lydia Feller, Silvan Geissmann, Raffael Schnell, Sven Klaka

Transcription

1 33V HiPak modules for high-temperature applications Sven Matthias, Arnost Kopta, Munaf Rahimo, Lydia Feller, Silvan Geissmann, Raffael Schnell, Sven Klaka ABB Switzerland Ltd, Semiconductors, Fabrikstrasse 3, CH-56 Lenzburg, Switzerland Tel.: +41 / () , sven.matthias@ch.abb.com URL: Abstract The market for IGBT modules in high power applications is continuously seeking lower overall losses and higher safety margins at elevated operating temperatures. In this paper we will present the newly developed 3.3kV high-temperature module generation rated at 15A, which combines the superior dynamic properties of the previous SPT+ version with the 15 C operation capability. 1. Introduction High voltage IGBT modules are widely used in high power applications, such as traction and large drives. These applications demand high reliability modules and power devices with improved electrical characteristics in terms of reduced losses, increased ruggedness and good controllability for an increased temperature range. The previous SPT+ 3.3kV module rated at 15A offered superior static and dynamic electrical properties [1]; however it was designed for 125 C operation. In this paper we present the newly developed IGBT and diode chip-set and the HiPak package for extending the operating temperature range towards 15 C. This step has been achieved by improving the design of IGBT and the free-wheeling diode on the power semiconductor device side. The package has been upgraded with low-resistance, high-current terminals [2]. Fig. 1 below shows the new module and the associated losses at 125 C for reference. I CES,max 3 ma sat 3.1 V V F 2.25 V E on 2.24 J E off 2.83 J E rec 1.97 J Fig. 1. The 3.3kV HiPak module using the new high-temperature chipset and module design (standard footprint of 14mm x 19mm). ABB SPT+ high temperature module (nominal conditions: T j =125 C, V DC =1.8kV, I C =15A, R Gon = 1.5 Ω, C GE = 33 nf, R Goff = 1. Ω, = ±15 V, L σ = 1 nh).

2 2. Design elements for high-temperature operation 2.1. IGBT Today`s IGBTs apply soft-punch through (SPT) or field-stop designs to optimize for low conduction losses as is schematically shown in Fig. 2 [3]. The choice of the SPT-buffer and the anode strength was proven to have a major influence on device safe operating area (SOA) during switching, shortcircuit operation, on-state losses, turn-off losses, recovery softness and leakage current. This is usually described with the term bipolar transistor gain. During the blocking state, there is a certain number of electrons drifting through the n-base. This electron current forward biases the anode np-junction. As a result holes are injected into the buffer region (see Fig. 2). A fraction of these holes recombines while some reach the emitter front-side and contribute to the leakage current. Raising the doping levels of the buffer and anode in a way that the injection efficiency remains constant maintains the key electrical parameters. On the other hand it reduces the bipolar gain and hence the rate of hole generation which leads to lower leakage current levels. However, this optimization is limited by the reverse blocking capability of the IGBT which is important during diode turn-on. Fig. 2. Soft-punch through or field-stop IGBT in cross-sections Diode In addition to the IGBT, also the diode is contributing to the module leakage current and has been limiting the operating temperature so far. A conventional diode shown in Fig. 3 is based on applying local lifetime control for achieving the desired plasma distribution in the device during conduction. However, in case of reverse blocking, the evolving space charge region at the pn-junction overlaps with the radiation defects generated by local lifetime control and thus resulting in a high leakage current. Conventional FSA concept Anode p+ Deep levels E-field n+ Cathode Anode p+ n+ Cathode n- n- Fig. 3. Diode schematic drawings of the doping profile, electrical filed and lifetime control.. a) Conventional diode. b) Field-Shielded Anode (FSA) diode.

3 The newly developed Field-Shielded Anode (FSA) design is characterized by a modified doping profile. While the depth of the anode is maintained, the net doping concentration is reduced resembling a low p-doped buffer for supporting the electrical field during the reverse blocking state. On the other hand, the shallow highly doped p-layer ensures good contact and strong anode injection in the high-current regime for good surge current capability. Therefore, the FSA design separates the radiation defects spatially from the space charge region resulting in a significantly reduced leakage current. Nevertheless, the challenge has been to maintain the high safe-operating area (SOA) of the previous diode generation and combine it with the desired high temperature operation. It is important to note that the presented doping profile is also present laterally and requires design modifications to ensure good switching behavior under harsh operating conditions. A junction extension region was introduced in between the active area and the guard-ring termination to enable high SOA as demonstrated in the dynamic results later in this article Package Apart from the improvements introduced for the chip-set, the HiPak module is also required to support the high junction-temperature operation. The package is primarily designed to chemically and mechanically protect the chips against the environment, to provide high isolation, to efficiently remove the heat generated during operation to a cooler and to electrically connect the chips to the bus bar. The module is normally assembled of matched components fulfilling the complex functions of high isolation and guaranteed long lifetime under strongly varying loads in traction and heavy drives applications. The major improvement here has been applied on the conductor leads from the outer contacts to the chips. These terminals contribute to the overall conduction losses and lead to heat dissipation to the bus bar and which then will require bus bar cooling. Fig. 4. The new high current, low resistance and low stray-inductance terminals used in the hightemperature module. With the newly developed terminals, the resistance is reduced by 17% with an equal spring constant. The heat dissipation caused by high currents is significantly reduced, while keeping the mechanical properties constant as was confirmed in thermal cycling and power cycling tests [2]. Furthermore, these terminals are optimized for a low stray inductance value within the module. This is beneficial in particular for hard switching events when the new terminals can help to reduce potential overshoot voltages.

4 3. Electrical performance of the 3.3kV HiPak module 3.1. Static characteristics Tj=25 C Tj=15 C 15 1 Tj=25 C Tj=15 C =15V [V] V F [V] Fig. 5. Forward characteristics of the 3.3kV high-temperature module. a) IGBT. b) Diode. Fig. 5 shows the static forward characteristic of the IGBT and diode at module level with minimized static losses. While the positive temperature coefficient for the IGBT is present already at low currents, the on-state curves for the diode cross at around half the nominal current Switching under nominal conditions 3 V DC =18V, =15V, T j =15 C, L σ =1nH 16 3 V DC =18V, =15V, T j =15 C, L σ =1nH 4 [V], [V]x I C [V], [V]x I C V DC =18V, I C =15A, T j =15 C, L σ =1nH 2 3 I C =5A, V DC =25V, T j =25 C, L σ =1nH I F V Diode [V] V R [V] V R Time [us] -3 c) d) Fig. 6. Waveforms of the 3.3kV SPT+ high temperature module under nominal conditions (see Fig. 1). a) IGBT turn-off waveforms E off =3.8J. b) IGBT turn-on waveforms E on =2.36J. c) Diode reverse recovery waveforms E rec =2.26J. d) Diode reverse recovery waveforms at room temperature and low forward current of I F =5A. -6

5 The waveforms for nominal switching conditions at T j =15 C are shown in Fig. 6. The devices show soft switching behavior with minimized losses for IGBT turn-on and turn-off as well as diode turn-off. By applying our well-established Soft-Punch-Through (SPT) buffer structure, a good switching controllability and exceptionally soft turn-off waveforms without voltage peaks or oscillations is ensured. Even for very low forward currents (3% of the nominal current) the diode switches softly without generating overshoot voltages Maximum ratings ABB s high voltage HiPak modules have been a benchmark in terms of safe operating area. The 24x lgbts inside the module are able to controllably switch off current beyond 5 times nominal. This confirms that in addition to the reduced leakage current, the adapted buffer and anode doping is maintaining good current sharing characteristics with the associated excellent SOA-capability ( Fig. 7). In addition, this module is the first product utilizing the FSA-concept. The modification in the anode-side doping profile required certain design adaptations for ensuring high safe-operating margins and good surge current capability. Fig. 7b shows the high current commutation of more than 1kA/μs at an elevated temperature and harsh switching conditions. These waveforms confirm that the high SOAmargins could be kept with the new anode design. [V], [V]x I C =78A, V DC =25V, T j =15 C, Lσ=11nH I C >5x I nominal V R [V], Power [kw] I C =225A, V DC =25V, T j =15 C, Lσ=11nH Peak power 6.7MW di/dt = 1kA/µs Fig. 7. a) 3.3kV SPT+ high-temperature HiPak turn-off SOA waveforms. b) 3.3kV SPT+ hightemperature diode reverse recovery waveforms. Fig. 8a shows the short circuit safe operating area at room temperature under elevated conditions. The module survives a 1μs pulse with a current peak exceeding 8kA. Furthermore, due to the high doping concentration at the anode, the FSA-diode does not compromise the surge current capability. A sequence of 1 pulses exceeding 9x times the nominal current could be applied without degrading the devices. -4 [V], [V]x V DC =25V, =16.4V, T j =25 C, Lσ=11nH I C T=15 C 1st surge current pulse 1th surge current pulse 9x I nominal V [V] Fig. 8. a) 3.3kV SPT+ high-temperature HiPak short circuit characteristics. b) 3.3kV SPT+ hightemperature diode surge current (t p =1ms).

6 V DC =18V, m=1, cos(phi)=.85, R th(h-a) =9.5K/kW, T A =4 C 2 5SNA 15E3335 SPT+ 15 C 15 5SNA 15E3335 SPT+ 125 C 5SNA 15E333 SPT+ 125 C 2 15 V DC =18V, m=1, cos(phi)=.85, R th(h-a) =9.5K/kW, T A =4 C 5SNA 15E3335 SPT+ 15 C 5SNA 15E3335 SPT+ 125 C 5SNA 15E333 SPT+ 125 C I out,rms [A] 1 I out,rms [A] f sw [Hz] f sw [Hz] Fig. 9. Simulated output current as function of the switching frequency of the 33V / 15A hightemperature module. a) Rectifier mode (diode). b) Inverter mode (IGBT& diode). Finally, Fig. 9 shows the simulated maximum output current as function of switching frequency of the new high-temperature module (5SNA 15E3335) in comparison to the previous 125 C rated generation (5SNA 15E333). The figure shows that the module output current in rectifier mode (Fig. 9a) and inverter mode (Fig. 9b) almost matches at a junction temperature of T j =125 C the previous module generation. This confirms that the optimization for lower leakage current and a higher junction temperature did not compromise on the overall output performance. At a junction temperature of T j =15 C both modes are matched well and the output power has significantly improved. 4. Conclusions In summary, we have presented a new high temperature 33V / 15A HiPak module. The module was realized by an SPT+ IGBT with optimized buffer and anode designs, diode chips utilizing the FSAconcept and new low-resistance terminals. The module offers exceptionally low losses and high Safe Operating Area (SOA). Smooth switching characteristics and high dynamic ruggedness has been demonstrated under the new conditions. The new module will provide high power systems with enhanced current ratings and open possibilities for optimized system designs. 5. Acknowledgement The authors gratefully acknowledge the support by Rolf Schütz, who performed some of the shown measurements. 6. Literature [1] Kopta, A.; Rahimo, M.; & Schlapbach, U.: A Landmark in Electrical Performance of IGBT Modules Utilizing Next Generation Chip Technologies. Proc. ISPSD 26, pp 17-2, Italy, 26. [2] Hartmann, S.; Truessel, D.; Schneider, D. & Schnell, R.: Reduction of conductor lead resistance in high current power modules. Proc. PCIM 21, Germany, pp , 21. [3] Rahimo, M.; Kopta, A. & Linder, S.: Novel Enhanced-Planar IGBT Technology rated up to 6.5kV for Lower Losses and Higher SOA capability. Proc. ISPSD 26, pp 33-36, Italy, 26. [4] Schnell, R. & Schlapbach, U.: Realistic benchmarking of IGBT-modules with the help of a fast and easy to use simulation-tool. Proc. PCIM 24, Germany, 24.