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| Fig. 1: On-resistance versus breakdown voltage for Si and other wide-bandgap materials. (Image Source: J. Kim,, following Pearton et al. [5] |
As the demand for efficient energy conversion continues to rise, the transition from traditional silicon (Si)-based semiconductors to wide-bandgap materials like Gallium Nitride (GaN) and Silicon Carbide (SiC) is becoming increasingly significant. [1] Si has long been the dominant material in power electronics due to its established manufacturing processes and reliability. However, its limitations in handling higher voltages, temperatures, and frequencies are becoming more apparent as modern applications require enhanced performance, high efficiency, and low conversion losses. In contrast, GaN and SiC offer remarkable advantages, including higher breakdown voltages, faster switching capabilities, and improved thermal performance, which collectively lead to reduced power conversion losses. [2] This essay will investigate conduction loss and switching loss that determine total conversion losses, enabling a comprehensive energy-loss comparison between traditional Si and wide-bandgap materials.
On-resistance is a critical parameter in power semiconductor devices, determining the conduction loss of power converters. It represents the resistance encountered by current when the device is in the "on" state; thus, lower on-resistance leads to reduced conduction losses. The Baliga Figure of Merit (BFOM) provides a valuable framework for evaluating and comparing the performance of different semiconductor materials in this context. [3] Specifically, the BFOM is defined as the square of the breakdown voltage divided by on-resistance. This indicates the trade- off relationship between the breakdown voltage of transistors and on-resistance, as higher breakdown voltage is typically achieved in larger devices with longer resistive paths. However, wide-bandgap semiconductors have higher critical electric fields, allowing them to achieve higher breakdown voltages without increasing transistor size. As shown in the BFOM, wide-bandgap materials like GaN and SiC demonstrate significantly lower on-resistance compared to traditional Si at the same breakdown voltage (Fig. 1). Theoretically, on-resistance can be reduced by approximately three orders of magnitude when using GaN or SiC-based transistors instead of Si-based ones.
Switching losses in power semiconductor devices occur during the transition between the "on" and "off" states and are influenced by several factors, including capacitance and carrier mobility. As noted in the BFOM, GaN and SiC exhibit critical electric fields approximately 10 times higher than that of Si. This allows GaN or SiC devices to be designed with approximately 10 times smaller in size. Consequently, their output capacitance (Coss) is reduced by approximately 10 times, significantly lowering the energy loss associated with charging and discharging the output capacitance during switching periods (Eloss = 1/2CossV2). Furthermore, because GaN devices are fabricated on undoped substrates, their output capacitance can be further reduced beyond this theoretical advantage. [4] Additionally, GaN devices demonstrate switching speeds that are more than three times faster (i.e., with a transition time (tr) that is three times shorter) compared to state-of-the-art Si- based devices. [4] This improvement is attributed to the shorter drift region as well as approximately two times higher carrier mobility (2000 cm/V/s), compared to that of Si (about 1000 cm/V/s). [2] As a result of these advantages, GaN-based devices can achieve more than three times lower overlap loss (Eoverlap = 1/2VItr) during the transition periods between the "on" and "off" states.
In conclusion, the transition from Si to wide-bandgap materials such as GaN and SiC represents a significant advancement in power device technologies. This essay has assessed the power conversion losses associated with wide-bandgap materials, highlighting their advantages in terms of conduction and switching losses.
© Jeongkyu Kim. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] A. Das et al., "Review on Wide Band Gap Semiconductor," IEEE 10032898 Int. Conf. of Electron Devices Society Kolkata Chapter (EDKCON), 26 Nov 22.
[2] K. Boutros, R. Chu and B. Hughes, "Recent Advances in GaN Power Electronics," IEEE 6658400, Proc. IEEE Custom Integrated Circuits Conference, 22 Sep 13.
[3] B. J. Baliga, Fundamentals of Power Semiconductor Devices, 2nd Ed. (Springer, 2018).
[4] K. J. Chen et al., "GaN-on-Si Power Technology: Devices and Applications," IEEE 7862945, IEEE Trans. Electron Dev. 64, 779 (2017).
[5] S. J. Pearton et al., "A Review of Ga2O3 Materials, Processing, and Devices," Appl. Phys. Rev. 5, 011301 (2018).