Yasukazu Seki

A study on the short-circuit capability of field-stop IGBTs

The short-circuit failure mechanism of 1200 V trench gate field-stop insulated gate bipolar transistor (IGBT) has been investigated in this paper. Experimental testing shows that most of the devices failed during the blocking state after a few hundred microseconds of the short-circuit turn-off condition. This unusual failure mode was analyzed both with experimental and numerical investigation. It has been determined that due to significantly large leakage current, thermal run-away can occur causing device failure after short circuit turn-off. Due to the smaller heat capacity of the FS-IGBT structure, the device temperature after the turn-off becomes so high that the local heating produced by the high temperature leakage current results in the thermal run-away.

The guard-ring termination for the high-voltage SiC Schottky barrier diodes

In this report, we propose the guard-ring structure as the edge termination for the high-voltage SiC Schottky barrier diodes. The local oxidation process is used to form the mesa of a p-n junction as the guard-ring. The comparison between the Al/Ti Schottky barrier diodes with and without the guard-ring indicates the effectiveness of the guard-ring to relax the electric field, from the results that the breakdown voltage is about two times larger with high yield.<<ETX>>

A new IGBT with a monolithic over-current protection circuit

A new IGBT structure with a monolithic overcurrent sensing and protection circuit has been developed. The feature of this device is a novel integration of a sensing and protection circuit which consists of a sensing IGBT, lateral n-MOSFET, polycrystalline silicon diode and resistor with an IGBT structure. The conventional IGBT fabrication process is available to this device with only one more photomask. Comparison of not only a short circuit safe operating area but both a trade-off characteristics between an on-state voltage drop and a turn-off loss and reverse biased safe operating area with a conventional IGBT has been investigated. Since exhibiting a large short circuit safe operating area without deterioration of any other device characteristics, this device can be applied to not only a soft switching application like voltage resonant circuit but a hard switching application like snubberless inductive load circuit.

Analysis on the low current turn-on behavior of IGBT module

This paper presents the noise emission mechanism from IGBT module, which is strongly required to be improved because of EMC regulations. The various 600 V/100 A IGBT module structures were experimentally and numerically tested to improve the current ringing during low current turn-on. As a result, it has been found that the parasitic inductance in the module should be as small as possible to suppress RLC resonant, which consists of parasitic components in the module and the capacitance in the power devices. It is also confirmed that the extra capacitance attached between gate-emitter of IGBT effectively improves the noise emission without increase the switching loss.

A new vertical IGBT structure with a monolithic over-current, over-voltage, and over-temperature sensing and protecting circuit

A new 600 V vertical Insulated Gate Bipolar Transistor (IGBT) structure with monolithically integrated over-current, over-voltage, and over-temperature sensing and protecting functions has been developed to exploit an extremely excellent trade-off characteristic between an on-state voltage drop and turn-off time for the first time. This device can be easily made by the conventional IGBT fabrication process. An accurate and a real-time device temperature detection, as well as a high withstand capability against over-current and over-voltage conditions (short circuit immunity of 30 /spl mu/sec, clamped collector voltage of 640 V), have been achieved. Furthermore, an excellent trade-off characteristic of 1.40 V as an on-state voltage drop and of 0.18 /spl mu/sec as a fall time is also obtained.<<ETX>>

The IGBT with monolithic overvoltage protection circuit

A novel IGBT (insulated-gate bipolar transistor) with a monolithic overvoltage protection circuit has been developed to obtain high resistance to overvoltage stress. This device is characterized by novel integration of an avalanche diode with an IGBT structure. The conventional IGBT process can be used to fabricate this device without any additional photomasks. Since it exhibits a large safe operating area, this device can be applied not only to a soft switching application like a voltage resonant circuit but also to a hard switching application like a snubberless inductive load circuit.<<ETX>>

Investigation on the short-circuit capability of 1200 V trench gate field-stop IGBTs

The short circuit failure mechanism of newly developed 1200 V/150 A trench gate field-stop IGBT has been investigated. The devices mainly fail after a few hundred microseconds of the short-circuit turn-off. It has been found that the leakage current due to extreme temperature rise in the backside layers results in thermal runaway during off-state. The device with improved backside layer achieved more than 15 /spl mu/s of short circuit capability while keeping the low on-state voltage drop of 1.55 V.

Ultra high-power 2.5 kV-1800 A power pack IGBT

The Power Pack IGBT has been tested in detail under several practical inverter systems and has obtained much useful data. Using this data and advanced technology, we have improved some items and finally developed an ultra high-power 2.5 kV-1800 A Power Pack IGBT (flat-packaged Reverse Conducting IGBT). One of the important improvements is the contact technology for the IGBT chip, and another is the electric discharge capability of the IGBT and diode chips. In addition to these important improvements, using our original 27.5/spl times/27.5mm/sup 2/ large IGBT and diode chips, and square flat package structure, we have achieved a compact and powerful device. The saturation voltage is 4.5 V at the collector current of 1800A and Tj=125/spl deg/C. The on-state voltage of the diode part is 3.5 V at the anode current of 1800 A and Tj=125/spl deg/C. The turn-off capability is over 4000A at the peak collector voltage of 2400 V. In this paper, the device structure, the chip technology, the parallel connection technology inside the package, the high blocking voltage capability, and other important experimental results are described.

Enhanced oxidation of ion-implanted Si-face of 6H-SiC

The Si-face of 6H-SiC is slowly oxidized even at temperatures as high as 1200° C in steam. We found that the oxidation rate of the implanted Si-face is several times faster than that of the non-implanted face. This oxidation rate strongly depends on the mass number of the implanted ion, and on the acceleration energy. Based on the study of the oxidation rate, dosage and acceleration energy dependence, this phenomenon is concluded to be induced by the amorphous layer of the implanted region. We demonstrated the selective oxidation technique utilizing this phenomenon in its application to various devices.

Low-Frequency Photocurrent Oscillations in CdIn2S4 Single Crystals

Low-frequency photocurrent oscillations in CdIn2S4 single crystals when a high electric field is applied at low temperature have been studied through simultaneous observations of the photocurrent and the photoluminescence. Several parameters necessary for analysis of the oscillations have been determined from additional experiments. We found that the pulse-type oscillations disappeared when light of photon energies between 1.97 and 2.54 eV was superposed. The distribution of the electric field in the sample was measured and it was found tbat the region of high electric field, the so-called domain, does not move in space but that the electric field varies periodically, leading to the current oscillation. The mechanism of the pulse-type photocurrent oscillations in CdIn2S4 single crystals is well-explained by the three-center model considering the thermal quenching process.