Posted on 01 July 2019

6500V SPT+ HiPak Modules

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Higher power and higher SOA performance

The next generation 6500V HiPak IGBT modules employing the newly developed SPT+ IGBT and diode chips is presented. The SPT+ IGBT range achieves significantly lower overall losses while exhibiting higher safe-operating area (SOA) and the same desirable electrical characteristics as the successful SPT generation.

By A. Kopta, M. Rahimo, U. Schlapbach, A. Baschnagel, ABB Switzerland Ltd, Semiconductor


Development trends in power electronic systems continue to demand power devices with continuously improved characteristics in terms of reduced losses, increased ruggedness and improved controllability. Following the introduction of the new generation of 1700V, 3300V and 4500V SPT+ IGBT HiPak range, the next generation 6500V HVHiPak IGBT modules employing SPT+ IGBTs and diodes will be presented in this article. The SPT+ IGBT platform has been designed to substantially reduce the total semiconductor losses while increasing the turn-off ruggedness above that of the current SPT technology. The SPT+ platform exploits an enhanced carrier profile through optimization of ABB’s planar cell structure. The new cell technology significantly increases the plasma concentration at the emitter, which reduces the on-state voltage drop without affecting the turn-off losses. Due to the combination of the enhanced cell design and the softpunch- through (SPT) buffer concept, the SPT+ IGBT design platform enables ABB to establish a new technology benchmark for the 6.5kV voltage class.

The on-state losses of the new 6.5kV IGBT exhibits approximately a 30% reduction as compared to the standard SPT device. This in combination with the increased ruggedness of the SPT+ IGBT has enabled the current rating to be increased from 600A for the standard 6.5kV HiPak up to 750A for the new SPT+ version. The new SPT+ modules will provide high voltage system designers with enhanced current ratings and simplified cooling while further enhancing the recently acquired robustness of the SPT IGBTs.

6.5kV SPT+ chip-set technology

The SPT+ IGBT platform was developed with the goal to substantially reduce the on-state losses while maintaining the low switching losses, smooth switching behavior and high turn-off ruggedness of the standard SPT (Soft-Punch-Through) IGBTs. This was achieved by combining an improved planar cell design with the already well-optimized vertical structure utilized in the SPT technology.

In Fig. 1, a cross-section of the SPT+ IGBT can be seen. The planar SPT+ technology employs an N-enhancement layer surrounding the P-well in the IGBT cell. The N-layer improves the carrier concentration on the cathode side of the IGBT, thus lowering the on-state voltage drop (VCE,on) without significantly increasing the turn-off losses. A further reduction of VCE,on was achieved by reducing the channel resistance by shortening the lateral length of the MOS-channel. By optimizing the shape of the N-enhancement layer, the turn-off ruggedness (RBSOA) of the SPT+ cell could be increased even beyond the level of the already very rugged standard SPT cell. In this way, the SPT+ technology not only offers significantly lower losses but also an increased SOA capability as compared to the standard technology.

SPT+ IGBT (left) and Diode (right) technology

Fig. 1 shows also a cross-section of the SPT+ diode. The SPT+ diode technology utilizes a double local lifetime-control technique to optimize the shape of the stored electron-hole plasma. Due to the improved plasma distribution, the overall losses could be reduced while maintaining the soft recovery characteristics of the standard SPT diodes. On the anode side, the SPT+ diode employs the same design as used in the standard SPT technology, utilizing a highdoped P+-emitter. The anode emitter efficiency is adjusted using a first He++ peak placed inside the P+-diffusion. In order to control the plasma concentration in the N-base region and on the cathode side of the diode, a second He++ peak, implanted deeply into the N-base from the cathode side is used. In this way, a double local lifetime profile as shown in Fig. 1 is achieved. With this approach, no additional homogenous lifetime control in the N-base is necessary. Due to the improved shape of the stored electron-hole plasma, a better trade-off between total diode losses and recovery softness was achieved.

6.5kV/750A HV-HiPak electrical performance

The 6.5kV HV-HiPak module is an industry-standard housing with the popular 190 x 140 mm footprint. It uses Aluminium Silicon Carbide (AlSiC) base-plate material for excellent thermal cycling capability as required in traction applications and Aluminium Nitride (AlN) isolation for low thermal resistance. The HV-HiPak version utilized for the 6.5kV voltage class is designed with an isolation capability of 10.2kVRMS. To verify the performance of the 6.5kV SPT+ chips and the HV-HiPak module, extensive measurements were carried out. The results of this characterization will be presented in this section. The nominal rated current of the 6.5kV HV-HiPak module is 750A, which corresponds to a current density of 34.3A/cm2 for the IGBT and 77.5A/cm2 for the diode. For dynamic measurements, the nominal DC-link voltage was 3600V, while SOA and softness measurements were carried out at 4500V.

In Fig. 2-a, the on-state curves of the 6.5kV SPT+ IGBT can be seen. The typical on-state voltage drop (VCE,on) at nominal current and Tj=125°C is 4.0V. The SPT+ IGBT shows a positive temperature coefficient of VCE,on, starting already at low currents, which enables a good current sharing capability between the individual chips in the module. In Fig. 2-b, the on-state characteristics of the 6.5kV SPT+ diode are shown. Due to the advanced plasma shaping utilizing a double He++ irradiation scheme, the diode has a strong positive temperature coefficient of VF already well below the nominal current. At rated current and 125°C, the diode has a typical on-state voltage drop of 3.5V.

Forward characteristics of the 6.5kV SPT+ IGBT

Forward characteristics of the 6.5kV SPT+ Diode

Fig. 3-a shows the turn-off waveforms of the 6.5kV HiPak module measured under nominal conditions i.e. at 750A and 3600V. Under these conditions, the fully integrated turn-off losses of the module amount to 5.2J. The module was switched-off using an external gate resistor (Rg,off) of 15Ω, which results in a voltage rise of 2000V/µs. The optimized N-base region combined with the Soft-Punch-Through (SPT) buffer allows the collector current to decay smoothly, ensuring a soft turn-off behavior without any disturbing voltage peaks or oscillations even at high DC-link voltages and stray inductances.

6.5kV SPT+ IGBT turn-off under nominal conditions measured

Fig. 3-b shows the turn-on waveforms under nominal conditions. The low input capacitance of the planar SPT+ cell allows a fast drop of the IGBT voltage during the turn-on transient. This, combined with the low-loss SPT+ diode, brings the turn-on switching losses down to a typical value of 6.4J. By carefully designing the diode cathode-sided He++ peak, a short, but still smoothly decaying current tail was achieved. Under nominal conditions, the diode recovery losses are 2.8J. Thanks to the high ruggedness and soft recovery behavior, the diode can be switched with a high diF/dt, which significantly reduces the IGBT turn-on losses.

6.5kV SPT+ IGBT turn-on under nominal conditions measured

In Fig. 4 the trade-off curve between the IGBT on-state voltage drop and the turn-off losses for the SPT+ as well as the standard SPT IGBT measured at chip level can be seen. The different points on the technology curves correspond to IGBTs with different anode emitter efficiencies. The devices were measured at a collector current of 25A, which is the nominal current of the SPT IGBTs. The new SPT+ IGBT exhibits an approximately 30% lower on-state voltage drop (VCE,on) for the same turn-off losses as compared to the standard SPT chip. The final point on the technology curve for the SPT+ IGBTs was carefully selected based on the trade-off between reverse leakage current and turn-off softness while maintaining a good balance between switching and conduction losses.

6.5kV SPT+ IGBT technology curve measured at chip level

In order to evaluate the performance of the 6.5kV SPT+ module under real application conditions a thermal simulation of the output current as function of the switching frequency was made. The results can be seen in Fig. 5. The 6.5kV SPT+ IGBTs have been optimized to operate in an application environment with high stray inductances utilizing low switching frequencies.

6.5kV SPT+ HiPak module output current as function of the switching frequency

One of the main advantages of the new 6.5kV SPT+ IGBT is its extremely high turn-off ruggedness, setting a new benchmark for this voltage class. Fig. 6-a shows a turn-off waveform at module level, where a current of 2400A, which corresponds to more than three times the nominal current, was switched-off against a DC-link voltage of 4500V at a junction temperature of 125°C. The test was conducted with an external gate resistance of 1.0Ω, without using any clamps or snubbers. The stray inductance in this test was 750nH, which is more than double of that expected in the targeted application environment even under worst case conditions. Thanks to the ruggedness of the SPT+ cell, the IGBTs are capable of sustaining a long period of strong dynamic avalanche during the turn-off transient showing an excellent SOA capability. In this test the turn-off peak power reached a value of 11.7MW. In the standard production-level testing all modules are subjected to a turn-off SOA test with three times nominal current (2250A) where the modules are driven into dynamic avalanche. This very harsh test has been implemented in order to ensure high quality and reliability of all shipped 6.5kV HV-HiPak modules.

6.5kV SPT+ IGBT turn-off under SOA conditions measured at module level. Ppoff =11.7MW

Fig. 6-b shows a diode reverse recovery SOA test at module level measured with a forward current of 750A (nominal current) and a DClink voltage of 4500V. Due to the IGBT turn-on characteristics the diode peak power reaches its maximum value close to the nominal current and starts decreasing again for higher forward currents. The diode was switched using an external gate resistor (Rg,on) of 1.2Ω reaching a switching speed of 7000A/us and a peak power of 9.0MW.

6.5kV SPT+ diode reverse recovery under SOA conditions measured at module level.

The short circuit waveforms of the 6.5kV SPT+ module can be seen in Fig. 7. The IGBT was carefully designed to withstand a short circuit at VGE=15.0V for all DC-link voltages up to 4500V and junction temperatures between –40°C and 125°C. The desired short-circuit ruggedness was achieved by optimizations of the SPT-buffer and the anode emitter efficiency.

6.5kV SPT+ IGBT short-circuit characteristics measured at module level

Finally, to verify the surge current capability of the 6.5kV SPT+ diode, the HiPak module was subjected to 100 surge pulse with a magnitude of 9.9kA and pulse duration of 10ms (I2t = 523kA2s) as shown in Fig. 8. After the 100th pulse, the module was electrically retested to ensure that no degradation had taken place. In the subsequent destruction test the single pulse surge current capability was determined. The diodes reached a peak current of 12.3kA, corresponding to an I2t value of 705kA2s before failing. This excellent surge current capability was achieved thanks to a combination of the strongly doped P+-emitter and a low on-state voltage drop facilitated by the optimum plasma distribution shaped by the double He++ irradiation scheme.

6.5kV SPT+ diode surge current waveforms at module level



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