High-Temperature Switching Characteristics of 6H-SiC Thyristor
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NTRODUCTION SiC is a highly promising semiconductor for high-temperature and high-power electronics applications due to its wide bandgap, high breakdown field and high thermal conductivity [1,2]. These superior properties would result in a high power density (100 times higher than Si counterpart) and low thermal budget for SiC based power systems. It is suggested, under the ideal conditions, that the SiC based MOSFETs are the choice of future power devices because of its many ideal properties, such as low forward drop, high blocking voltage and high frequency operation [3]. However, in reality, many problems are hindering the development of SiC based MOSFETs. The quality of thermal oxide on p-type SiC is still far from acceptable for n-channel MOSFETs applications. The channel mobility of SiC UMOSFETs is around 20 cm 2V.s, orders magnitude less than that of the Si counterpart [4]. The reliability of Si0 2 at high temperature under high field has proven to be a serious problem even in Si technology [5]. The maximum oxide field is limited to less than 2MV/cm when operating temperature is increased to 350 0C. However, in order to utilized the high breakdown field of SiC, the electric field on the oxide film on SiC will be around 5 MV/cm due to the low dielectric constant of the oxide. It is obvious that such high fields will pose serious problem if the SiC based MOSFETs are to be operated at high temperature. In Si power technology, thyristor structures have been used for high-voltage and high-current applications due to their low forward drop and high current handling capability [6]. Advanced MOS-controlled Si thyristors (MCT) offers additional advantage of voltage gate control. It is expected that SiC thyristors will operate reliably under high-voltage, high-current and high temperature conditions by avoiding the problems associated with oxide based devices. Furthermore, because of the lack of high fields on the oxide, a SiC based thyristor with MOS controlled turn-off could be more easily developed. Thus, of the various SiC power devices demonstrated, the SiC based thyristor is the most promising power device for ultra high-voltage and high-current applications, including high power motor drives for electric vehicle, aircraft engine controls and utilities. In our earlier work, we have reported a high-current and high-temperature SiC thyristor with a blocking voltage of 100 V [7]. In this work we report the switching characteristics of a 280 V 6H-SiC thyristor operated at temperature up to 400 'C.
EXPERIMENT The 6H-SiC pnpn thyristor structure used in this work is illustrated in the Figure 1. The structure consists of a 0.8 gm p-type base layer grown on an n+ 6H-SiC substrate, a 7.5 tm undoped ntype blocking layer and a 0.5 gm Al doped p+ layer. The doping level in the n- type blocking layer was designed to be 8x 1015/cm3 for a blocking voltage of 400 V. The gate contact was placed on the n-type base layer. The gate recess and device isolation etching were accomplished by 93 Mat. Res. Soc. Symp. Proc. Vol. 423 0 1996
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