Kazuyuki Sawada

40mΩ / 1700V DioMOS (Diode in SiC MOSFET) for High Power Switching Applications

Device technologies of SiC MOSFETs have nearly matured to the level of mass production and one of the remaining tasks is to serve better solutions in view of both costs and performances for practical systems. Elimination of external reverse diodes in inverter circuits is one of the solutions, by which total area of the SiC chips is greatly reduced leading to lower material cost. A DioMOS (Diode in SiC MOSFET) successfully integrates the reverse diode without any increase of the chip size from the original MOS transistor by utilizing an n-type epitaxial channel under the MOS gate for the reverse conduction path of the diode. The basic concept of the DioMOS has been proposed [1]; meanwhile, further reduction of the on-state resistance together with confirmation of high-speed switching is necessary for its application in power switching systems. In this paper, low on-state resistance (Ron) of 40mΩ and blocking voltage (BVds) of 1700V as well as improved switching performances of DioMOS are demonstrated. The measured results suggest DioMOS to be satisfactory for practical use.

A 800 V Hybrid IGBT Having a High-Speed Internal Diode for Power-Supply Applications

A new lateral 800 V hybrid IGBT with a high-speed internal diode is proposed for switch-mode power supply (SMPS) applications. The hybrid IGBT operates as a MOS only when the collector/drain current is small. Then, the device shifts to IGBT operation with an RonA of 72 mOmegacm2 when the collector voltage is 6 V. The switching speed of the device is made fast enough to turn off in around 100 nsec, achieved through several methods such as a shorted anode structure, a lightly- doped collector, and electron irradiation. Besides that, the hybrid IGBT has a high-speed internal diode which achieves around 100 nsec of reverse recovery time (trr). The device can be fabricated easily without any expensive or complicated processes like epitaxial growth or trench etching. A 70 W flyback SMPS application using the hybrid IGBT is experimentally demonstrated.

Sense Device Structure in Hybrid IGBT with Constant Current Sense Ratio for Entire Collector Current Range

A new sense device structure is proposed for hybrid IGBTs in which current sensing ratio (CSR) is constant for a wide range of collector currents (ICE)- Hybrid IGBTs are a new type of switching device, with 2 operation modes: MOS operation mode at low ICE and IGBT operation mode at high ICE. Although the current flow mechanism is different between the two modes, it is preferable that CSR in both MOS IGBT operation modes be the same. It is also important to reduce the difference in CSR when the hybrid IGBT changes from MOS to IGBT operation mode. The new sense structure allows maintaining a constant CSR for the entire range of ICE. Moreover, CSR has low temperature dependence when the new sense device is adopted. As a result, ICE can be controlled more stably over a wide temperature range (-50degC - 125degC) even for hybrid IGBTs

(CD-5) TDDB breakdown of th-SiO 2 on 4H-SiC: 3D SEM failure analysis

We analyzed SiO2 void volumes formed on samples which failed during TDDB tests by constructing three-dimensional (3D) images in FIB-SEM system. We succeeded in visualizing the breakdown spots within SiO2 on 4H-SiC substrates and provided clear evidence of the influence of SiO2 void volume on 4H-SiC TDDB failure (ex. Tbd or Rbd). The small SiO2 voids play a very important role in the degradation of TDDB reliability. The present 3D SEM technique applied to th-SiO2 on 4H-SiC can be very useful in the investigation of TDDB failure mechanism.