Optimal Design of Diamond Field Effect Transistors Towards a Key Milestone for Diamond Power Electronics

In power electronics, the active devices are at the core of power converters. The successful introduction of wide bandgap (WBG) materials such as GaN and SiC in power converters has allowed many benefits: the replacement of Silicon bipolar devices (e.g. IGBT, bipolar diodes) with WBG unipolar devices (e.g. SiC MOSFETs and SiC unipolar diodes) led to much smaller switching losses and comparable or lower conductions losses, together with smaller required chip area and lower gate charges for WBG Field Effect Transistors (FET). Consequently, the classical trade-off (efficiency vs. power density) of power converters can be pushed even more further with WBG devices, thanks to higher switching frequencies, smaller total losses and smaller cooling systems or moving from active to passive cooling.<br/>In this context, the next generation of power semiconductor devices will be based on ultra wide bandgap (UWBG) materials, such as monocrystalline diamond, thanks to its outstanding physical properties and continuous breakthroughs in the growth quality and specific device architectures [1-3]. The benefits of diamond power devices are well predicted, with a high impact on power converters [1,2], while new record diamond devices are being demonstrated within the research community [4-7].<br/>In this presentation, I will first introduce the performances of competitive power devices in Silicon, WBG materials, and benchmark those with diamond theoretical and experimental performances. Although the performances are already attractive with CVD diamond, with breakdown voltages above 1 kV, lateral and vertical structures and specific on state resistances in the range of mΩ●cm², the key milestone is now to reach a total current in on state above 1 A, with a total on state resistance below 1 Ω at high junction temperatures. The challenges and optimal design of diamond FET architectures with multiple paralleled fingers will be detailed, in a close relationship with technological constraints, diamond properties and fabrication parameters. The trade-off between elementary-cell, transistor performances and safety margins are discussed. The simulation and optimal design of a 1kV (off state) and 1A (on state) diamond FET are presented, for several diamond FET architectures. In collaboration with Néel Institute and DIAMFAB in the framework of the DCADE European Research project, the preliminary data will be shared, with an outlook of future developments and implementation in power converters.<br/>This project has received funding from the Clean Sky 2 Joint Undertaking (JU) under grant agreement No 101007868. The JU receives support from the European Union’s Horizon 2020 research and innovation program and the Clean Sky 2 JU members other than the Union.<br/>[1] H. Umezawa, "Diamond Semiconductor Devices, state-of-the-art of material growth and device processing," 2020 IEEE International Electron Devices Meeting (IEDM), 2020, pp. 5.6.1-5.6.4.<br/>[2] N Donato et al 2020 J. Phys. D: Appl. Phys. 53 093001<br/>[3] Cédric Masante et al 2021 J. Phys. D: Appl. Phys. 54 233002<br/>[4] N. C. Saha, S. -W. Kim, T. Oishi, Y. Kawamata, K. Koyama and M. Kasu, "345-MW/cm² 2608-V NO2 p-Type Doped Diamond MOSFETs With an Al2O3 Passivation Overlayer on Heteroepitaxial Diamond," in IEEE Electron Device Letters, vol. 42, no. 6, pp. 903-906, June 2021.<br/>[5] S. Imanishi et al., "Drain Current Density Over 1.1 A/mm in 2D Hole Gas Diamond MOSFETs With Regrown p++-Diamond Ohmic Contacts," in IEEE Electron Device Letters, vol. 42, no. 2, pp. 204-207, Feb. 2021.<br/>[6] J. Tsunoda et al., "Low ON-Resistance (2.5 mΩ●cm²) Vertical-Type 2-D Hole Gas Diamond MOSFETs With Trench Gate Structure," in IEEE Transactions on Electron Devices, vol. 68, no. 7, pp. 3490-3496, July 2021.<br/>[7] C. Masante, J. Pernot, J. Letellier, D. Eon and N. Rouger, "175V, &gt; 5.4 MV/cm, 50 mΩ●cm² at 250°C Diamond MOSFET and its reverse conduction," 2019 31st International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2019, pp. 151-154.