Control of electric field in 4H-SiC UMOSFET: Physical investigation

• 4H-SiC UMOSFET is presented to improve the electrical characteristics.
• The key idea is increasing the uniformity of the electric field distribution.
• A region with a graded doping density is inserted in the drift region.
• Breakdown voltage and specific on-resistance of the new structure are improved.

In this paper, we show how breakdown voltage (VBR) and the specific on-resistance (Ron) can be improved simply by controlling of the electric field in a power 4H-SiC UMOSFET. The key idea in this work is increasing the uniformity of the electric field profile by inserting a region with a graded doping density (GD region) in the drift region. The doping density of inserted region is decreased gradually from top to bottom, called Graded Doping Region UMOSFET (GDR-UMOSFET). The GD region results in a more uniform electric field profile in comparison with a conventional UMOSFET (C-UMOSFET) and a UMOSFET with an accumulation layer (AL-UMOSFET). This in turn improves breakdown voltage. Using two-dimensional two-carrier simulation, we demonstrate that the GDR-UMOSFET shows higher breakdown voltage and lower specific on-resistance. Our results show the maximum breakdown voltage of 1340 V is obtained for the GDR-UMOSFET with 10 µm drift region length, while at the same drift region length and approximated doping density, the maximum breakdown voltages of the C-UMOSFET and the AL-UMOSFET structures are 534 V and 703 V, respectively.

We propose a novel power 4H-SiC UMOSFET using control of the electric field in order to improve the breakdown voltage (VBR) and the specific on-resistance (Ron).Figure optionsDownload as PowerPoint slide