Integrated Circuits and Materials

Figure 1236a shows two primary types of SiC MOSFETs based on their gate and drift structures: planar and trench MOSFETs. Planar MOSFETs, also known as DMOSFETs, have a lateral gate structure that allows for high-voltage operation. Trench MOSFETs, or UMOSFETs, incorporate a vertical gate structure within a U-shaped trench, which enhances the channel mobility by minimizing JFET resistance and reducing on-resistance.

(a)	(b)

Figure 1236b shows the structure and its circuit equivalent diagram of a planar gate SiC MOSFET.

(a)	(b)

Figure 1236c shows an N-channel MOSFET. The structure involves an n-epi layer and an n+ substrate. The cross-section of SiC MOSFET in Figure 1236c (a) shows if the JFET (Junction Field-Effect Transistor) width becomes narrow, it can become a bottleneck and the ON-state resistance will increase. However, by optimizing the JFET doping, the ON-state resistance in the planar MOSFETs can be significantly reduced. Figure 1236c (b) shows the electron flow in an N-channel MOSFET.

(a)	(b)	(c)

The device's performance of planar gate SiC MOSFET is limited by low channel mobility, primarily due to scattering at the 4H-SiC/insulator interface, which significantly reduces interface mobility compared to the bulk. Additionally, parasitic junction FET resistance contributes to higher conduction losses under forward operation. [5] A 4H-SiC planar MOSFET with a blocking voltage of 2.3 kV has been proposed, [6] featuring a gate oxide thickness of 27 nm, which provides an adequate gate oxide electric field. This device, fabricated using a commercial foundry, shows an improvement in specific on-resistance (R_on,sp) and a high-frequency figure of merit (FOM) by 1.3 times with a 15 V gate bias. Despite these benefits, the device experiences gate voltage overshoot failure due to the thin gate oxide. Another 4H-SiC planar MOSFET, designed with multiple floating guard-rings for edge termination, achieves a blocking voltage of 2.4 kV and a specific on-resistance of approximately 42 mΩ·cm². [7] This device demonstrates a channel mobility of 22 cm²/V·s and a threshold voltage of around 8.5 V.

[1] Jifan Yao, Working principle and characteristic analysis of SiC MOSFET, Journal of Physics, 2435, 012022, 2023.
[2] https://eepower.com/technical-articles/the-next-generation-of-sic-power-modules/#.
[3] Rainer Kraus, Alberto Castellazzi, A Physics-Based Compact Model of SiC Power MOSFETs, EEE Transactions on Power Electronics, 31(8), pp. 5863 - 5870, 2016.
[4] Shan Yin, Yitao Liu, Yong Liu, Comparison of SiC Voltage Source Inverters Using Synchronous Rectification and Freewheeling Diode, IEEE Transactions on Industrial Electronics, DOI: 10.1109/TIE.2017.2733483, 2017.
[5] Minamisawa, R.; Bartolf, H. Simulations and Fabrication of Novel 4H-SiC Nano Trench MOSFET Devices. Project A9.7, 2021.
[6] Agarwal, A.; Baliga, B.J. Performance Enhancement of 2.3 kV 4H-SiC Planar-Gate MOSFETs Using Reduced Gate Oxide Thickness. IEEE Trans. Electron Devices 2021, 68, 5029–5033.
[7] Ryu, S.H.; Agarwal, A.; Richmond, J.; Das, M.; Lipkin, L.; Palmour, J.; Saks, N.; Williams, J. Large-area (3.3 mm  3.3 mm) power MOSFETs in 4H-SiC. In Materials Science Forum; Trans Tech Publications Ltd.: Zurich-Uetikon, Switzerland, 2002; pp. 1195–1198.
[8] Catherine Langpoklakpam, An-Chen Liu, Kuo-Hsiung Chu, Lung-Hsing Hsu, Wen-Chung Lee, Shih-Chen Chen, Chia-Wei Sun, Min-Hsiung Shih, Kung-Yen Lee and Hao-Chung Kuo, Crystals, 12, 245, 2022.