Masaru Izumisawa

Semisuperjunction MOSFETs: new design concept for lower on-resistance and softer reverse-recovery body diode

A new superjunction (SJ) structure offering remarkable advantages compared with the conventional SJ structure is proposed and demonstrated for a power-switching device. In the proposed structure (semi-SJ structure), an n-doped layer is connected to the bottom of the SJ structure. According to the results of experiment and simulation, the semi-SJ structure has both lower on-resistance and softer recovery of body diode than conventional SJ MOSFETs. The fabricated semi-SJ MOSFETs with breakdown voltage of 690 V realize on-resistance 28% lower than that of the conventional SJ MOSFET with same aspect ratio. The softness factor of the body diode is also improved by a factor of five. The proposed MOSFET is very attractive for H bridge topology applications, such as switching mode power supplies and small inverter systems, thanks to the low on-resistance and the soft recovery body diode.

A 15.5mΩcm 2 -680V Superjunction MOSFET Reduced On-Resistance by Lateral Pitch Narrowing

Si-MOSFETs with the breakdown voltage of 680 V and the specific on-resistance of 15.5 mOmegacm2 were demonstrated by the superjunction (SJ) structure. The lateral pitch for the SJ structure was narrowed to 12 mum for the on-resistance reduction. The demonstrated on-resistance is the lowest one among previously reported 600 V-class SJ-MOSFETs. The fabricated MOSFET also realized low RonQgd of 1.8 OmeganC and high avalanche current of 175 A/cm2

High breakdown voltage (>1000 V) semi-superjunction MOSFETs using 600-V class superjunction MOSFET process

Si-MOSFETs with the breakdown voltage of over 1000 V were demonstrated, for the first time, realizing low on-resistance below the theoretical Si limit. The fabricated MOSFETs have a semi-superjunction (SemiSJ) structure, which is the combination of a superjunction (SJ) structure and an n-bottom assisted layer. The SemiSJ MOSFETs realize both the high breakdown voltage of 1110 and 1400 V and the low on-resistance of 54 and 163 m/spl Omega/cm/sup 2/, respectively. The fabrication process for the high-voltage SemiSJ-MOSFET was completely equivalent to a 600-V class SJ-MOSFET process, which implies that a single optimized process for forming SJ structure for 600 V-class MOSFET can be used for a wide voltage range extending up to 1200 V MOSFET. Additionally the fabricated MOSFETs realized low R/sub on/Q/sub gd/ of 4.6 /spl Omega/nC for a 1110-V device and 13.1 /spl Omega/nC for a 1400-V device, and recovery characteristics of the body diode were softer than those for the SJ MOSFET. These results show the possibility of new Si power-MOSFET with a higher application voltage range.

Over 1000V semi-superjunction MOSFET with ultra-low on-resistance below the Si-limit

Si-MOSFETs with the breakdown voltage of over 1000 V were demonstrated, for the first time, realizing low on-resistance below the theoretical Si-limit. The fabricated MOSFETs have semi-superjunction (SemiSJ) structure, which is the combination of superjunction (SJ) structure and n-bottom assisted layer (BAL). The SemiSJ MOSFETs realize both the high breakdown voltage of 1100 and 1400 V and the low on-resistance of 54 and 163 m/spl Omega/cm/sup 2/, respectively. The fabrication process for the high voltage SemiSJ-MOSFET was completely equivalent to a 600-V class SJ-MOSFET process, which implies that a single optimized process for forming SJ structure for 600 V-class MOSFET can be used for a wide voltage range extending up to 1200 V MOSFET. These results show the possibility of new Si power-MOSFET with higher application voltage range.

600V semi-superconjunction MOSFET

New superconjunction (SJ) structure is proposed and demonstrated for the power-switching device with remarkable advantage over conventional SJ structure. An n-doped layer is connected to the bottom of the SJ structure for the proposed structure. It is found with experiment and simulation that the proposed structure shows both the lower on-resistance and the softer recovery of body diode than conventional SJ MOSFET. The fabricated Semi-SJ MOSFETs realize Ron as low as 54 m/spl Omega/cm/sup 2/ (48 m/spl Omega/cm/sup 2/ in calculation) at 690 V breakdown voltage with only half depth of the p-column than the conventional SJ MOSFET. The softness factor of body diode is also improved in the factor of 4.5. The proposed MOSFET is very attractive for H-bridge topology applications such as UPSs and small inverter systems thanks to the low on-resistance and the soft recovery body diode.

Improvement of switching trade-off characteristics between noise and loss in high voltage MOSFETs

A new MOS-gate structure was proposed and demonstrated to improve the switching trade-off characteristics between noise and loss in high-voltage MOSFETs. The lightly p-doped dummy base layer under the gate electrode modulates Cgd-Vds curve due to the depletion under high applied voltage and the turn-off dV/dt can be suppressed even with high-speed switching. The fabricated device showed the surge voltage suppression of 50 V or the turn-off loss reduction of 20% in the turn-off switching test with an inductive load. In the flyback converter operation, it was also shown that the trade-off characteristics between the radiation noise and total power loss were improved by the proposed dummy base structure.

The optimal profile design for SJ-MOSFET fabricated by double-ion-implantation and multi-epitaxial method

We investigated the profile dependency of specific on-resistance (RonA) under high- temperature and high-current-density conditions for 600 V-class semi-superjunction MOSFETs fabricated by the double-ion-implantation and multi-epitaxial method, for the first time. The column doping profile is an important design parameter for the RonA characteristics because the profile affects the electron mobility (mue) in the drift region. The n-column profile was modulated by the column diffusion time (tdiff) in this experiment. The optimal tdiff achieved minimal RonA under the high-temperature and high-current-density conditions.