UMOSFET structures

However, after the first years of great expectations supported by early impressive results reported by Palmour et al. in 1994 [5], it became clear that initial predictions of a revolutionary improvement in power switching by employing vertical SiC MOSFETs are difficult to accomplish due to multiple reasons. In particular, a critical analysis of performance advantages and limitations of 4H-SiC power UMOSFET structure has been made by Agarwal et al. in 1996 [6]. The main issues raised in this work were ... 

Agarwal, A. K., et ah, A Critical Look at the Performance Advantages and Limitations of 4H-SiC Power UMOSFET Structures, Proc. of 8th Inti. Symposium on Power Semiconductor Devices and ICs, May 23, 1996, pp.119-122. 

Figure 8 The power UMOSFET structure and the electric field profile in the blocking state.

So far there has been no published data on inversion channel mobility in metal-HfO -SiC structures. However, even assuming extremely poor channel mobility of 0.1 cmV(V s), HfO -SiC UMOSFET can offer total specific on-resistance equal to... 

Figure 5.4 Comparison of Ron sp classical structure 4H-SIC UMOSFET with different gate dielectrics and channel mobilities.

As previously discussed, silicon dioxide appeared to be a nonideal gate dielectric to be used with silicon carbide in UMOS configuration. Different design solutions used to protect SiO gate dielectric from a high electric field in SiC UMOSFETs resulted in dramatically complicated transistor structure. Because of the problems with SiC UMOSFET, the classical vertical double-diffused MOSEET (VDMOS)... 

Because of the problems with SiC UMOSFETs pointed out in the previous section, it becomes important to consider alternative device embodiments. Two device structures described in this section make it possible to circumvent these issues. 

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