MOSFET-mode ultra-thin wafer PTIGBTs for soft switching application $theory and experiments

Abstract

We have proposed and analyzed MOSFET-mode operation of ultra-thin wafer PTlGBTs in ISPSD02[1]. The present paper, for the first time, presents analytical theory of MOSFET-mode operation, and shows that the SOA is determined by a mechanism similar to the second breakdown of npn bipolar transistors.demonstrates, for the first time, that the MOSFETmode IGBTs are strongly effective for sofl switching application. The developed MOSFET-mode 9OOV 60A thin wafer Trench Gate PTlGBTs have reduced turn-off loss by 55% at 125OC, compared with the conventional (4" generation) sofl switching PTIGBTs. MOSFET-mode OperationMOSFET-mode operation is defined in such a way that the anode efficiency y is less than yuos, which represents pd(pn +h). The anode efficiency y is defined as the ratio of the hole current over the total current at the n-base n-bufferjunction, being identical to the product of pemitter injection efficiency Y~~ and transport factor in the n-buffer ar. (Please note that y in the present paper is different from the conventional injection efficiency of the p-emitter.)The ywosvalue dynamically changes as the electric field changes inside the device because the mobility p is a function of the electric field. Figure I shows yMos as a function of electric field. IGBTs may change its operation mode as the forward voltage increases and the electric field inside the device increases.The present paper also experimentally 0.5 I 1 g0.4 E f o . 4 1 M;FET-Mode., 1 '1E2 1E3 1E4 1E6.Fig.1 Area for MOSFET-mode operation.In the MOSFET-mode operation, several unique characteristic features are distinguished. The features are very similar to the operation of pure MOSFETs. Elwtcic Field (V/cmcm)

Key criteria for the short-circuit capability of IGBTs

“…TCAD simulations show that the relocation of the electric-field peak from the chip front side towards the field-stop layer [6]- [7], and the occurrence of a lowfield/quasi-plasma region beneath the MOS cells [8], are necessary for the filament formation. The short-circuit current/gate-emitter voltage at which these two conditions are fulfilled increases with the collector-emitter voltage (Fig.…”

Progress in IGBT development

“…If it is too low, the negative space charge caused by the electrons flowing from the cathode to the anode may cause a strong increase of the electric-field strength near the n − -n junction formed by the n − -base region and the n-FS region. Extensive investigations [29][30][31][32][33] have shown that the uniform current-density distribution under such conditions can be destabilised by the appearance of single or multiple current filaments. Furthermore, recent device simulations [33] have shown that destabilisation of the uniform current-density distribution may be triggered even in the absence of impact ionisation in the anodeside high-field region.…”

1200V IGBTs operating at 200°C? An investigation on the potentials and the design constraints

“…To further investigate the ruggedness of the 1200V IGBT, unclamped inductive tests were carried out to evaluate the device avalanche capability at high temperatures. The dynamic tests forces the IGBTs into self-clamp mode during turn-off and measures the device ruggedness and such conditions [4]. Figure (7) shows the voltage and current waveforms obtained from avalanche testing at 200°C.…”