Papers by Keyword: Buried Channel

Abstract: SiC lateral MOSFETs with multi-layers epi-channels were studied in this work. The epi-channel with a high concentration n-type epilayer sandwiched by two lightly doped p-type layers showed a maximum field effect mobility of 17 cm²/V.s, improved from 1.53 cm²/V.s of devices without epi-channels. These devices are normally-off with an average threshold voltage of 1.34V.

Abstract: Fabricated were 4H-SiC p-channel MOSFETs in two types of ion-implanted n-well regions and in the n-type substrate as a control. Effects of the n-well structure on the electrical properties were investigated. P-channel MOSFETs fabricated in the uniform doped n-well by using multiple ion-implantations showed inferior on-state characteristics to that of the control MOSFET, while those fabricated in the retrograde n-wells by using single-shot ion-implantation without additional implantation to form the surface p-type region indicated improved channel properties. The Vth values were controlled by the impurity concentration and depth of the surface p-type region, and the values of channel mobility were nearly equal to that of the control MOSFET. Good sub-threshold characteristics for the type II devices were demonstrated.

Abstract: The channel mobility in the SiC MOSFET degrades on the rough surface of the p-well formed by ion implantation. Recently, we have developed a double-epitaxial MOSFET (DEMOSFET), in which the p-well comprises two stacked epitaxially grown p-type layers and an n-type region between the p-wells is formed by ion implantation. This device exhibited a low on-resistance of 8.5 m
cm2 with a blocking voltage of 600 V. In this study, to further improve the performance, we newly developed a device structure named implantation and epitaxial MOSFET (IEMOSFET). In this device, the p-well is formed by selective high-concentration p+ implantation followed by low-concentration p- epitaxial growth. The fabricated IEMOSFET with a buried channel exhibited superior characteristics to the DEMOSFET. The extremely low specific on-resistance of 4.3 m
cm2 was achieved with a blocking voltage of 1100 V. This value is the lowest in the normally-off SiC MOSFETs.

Abstract: In our previous study, the on-resistance of the SiC-based vertical MOSFET had been reduced in double-epitaxial MOSFET (DEMOSFET). The device exhibited an on-resistance (Rons) of 8.5 mWcm2 with a blocking voltage (Vbr) of 600 V. This study analyzed the characteristics of the DEMOSFET using a numerical simulation. The results showed the trade-off relationship between the specific on-resistance and the blocking characteristics when the concentration of the nitrogen ions increases in the surface of the n-type region between the p-wells. Specially, the specific on-resistance was drastically improved by increasing the concentration of the nitrogen ions. The thick gate oxide on the n-type region between the p-wells had an advantage to suppress the electric field in the gate oxide.