【Member Papers】Internal Field Optimization Using a Localized Bottom SiO₂ in Vertical β-Ga₂O₃ FinFETs

Background

      The booming development of electric vehicles, renewable energy conversion and data center power supplies puts forward higher requirements for power transistors with high breakdown voltage, low conduction loss and stable operation under high electric field. Ultra-wide bandgap semiconductors have superior performance owing to their large bandgap and high critical breakdown electric field. As a representative material, β-Ga₂O₃ has a bandgap of 4.8–4.9 eV and a theoretical critical electric field of 8 MV/cm, and large-size single crystal substrates can be fabricated, making it highly suitable for high-voltage power switching devices.

      Vertical β-Ga₂O₃ Schottky barrier diodes have been well developed, while the lack of feasible p-type doping hinders the application of conventional enhancement-mode MOSFETs based on p-n junctions. Vertical FinFETs can realize normally-off operation without p-type doping. However, severe electric field crowding at the trench corners of fin channels causes premature breakdown, which limits the reverse blocking capability and device reliability. A localized dielectric internal field optimization structure is proposed in this work to regulate the internal electric field distribution.

Abstract

      Vertical β-Ga₂O₃ FinFETs are promising candidates for high-voltage power switching because they enable normally-off operation through geometric depletion while leveraging the ultra-wide bandgap for high electric-field blocking. However, premature breakdown can still be triggered by severe electric-field crowding at the trench bottom corners. In this work, we demonstrate a vertical β-Ga₂O₃ FinFET with enhanced reverse blocking enabled by an internal field-optimization (IFO) structure, realized by introducing an 100nm SiO₂ dielectric liner locally at the fin bottom/corner regions. Owing to the dielectric field management, the device achieves a breakdown voltage of 1440 V, representing a substantial improvement over the control device without IFO. The FinFET exhibits enhancement-mode characteristics with VTH=1.31 V, a subthreshold swing of 98.8 mV/dec, an on/off current ratio of 10⁹, and a strongly suppressed transfer hysteresis of 15 mV. A maximum drain current density of 519.4 A/cm², with a differential specific on-resistance (Ron, sp) 12 mΩ·cm². These results highlight dielectric-assisted corner field shaping as a practical route toward simultaneously improving breakdown robustness and maintaining low conduction loss in vertical β-Ga₂O₃ FinFET power transistors.

Highlights

      A novel internal field optimization structure with localized 100 nm SiO₂dielectric at fin bottom and corners is proposed to relieve electric field crowding, which is fully compatible with existing fabrication processes.

      The breakdown voltage is increased from 965 V to 1440 V with low leakage current before breakdown, and the reverse blocking capability is greatly improved.

      The device retains excellent enhancement-mode performance, including proper threshold voltage, low subthreshold swing and tiny transfer hysteresis.

      The device achieves low specific on-resistance and high drain current density, with a Baliga figure of merit of 137 MW/cm², showing excellent trade-off between conduction loss and blocking voltage.

      The breakdown position transfers to the edge of active region, which verifies the effective electric field regulation of the proposed structure.

Conclusion

      In conclusion, we show that localized corner-dielectric field shaping is an effective and process-compatible approach to improve the blocking robustness of vertical β-Ga₂O₃ FinFETs. By introducing an 100nm SiO₂ IFO at the fin bottom/corner regions, the breakdown voltage increases from 965 V to 1440 V while maintaining low pre-breakdown leakage. Post-breakdown SEM indicates that the failure shifts to the perimeter corner of the square active region, consistent with suppressed internal trench-bottom field crowding. The device preserves enhancement-mode operation and strong forward conduction, suggesting that further improvements are achievable by co-optimizing external edge termination with the internal dielectric liner.

Project Support

      This work was supported in part by the National Natural Science Foundation of China (Nos. 62074053), in part the Key Scientific Research Project in Colleges and Universities of Henan Province (Grant No. 26B140020), the Natural Science Foundation of Henan (Grant No. 252300423347), in part by the Funded by Basic Research Program of Jiangsu (Grant No. BK20253003), in part by the Suzhou Critical Core Technology Research Project (Grant No. SYG2024003). The authors would like to thank Nano Fabrication Facility and Vacuum Interconnected Nanotech Workstation (NANO-X) of Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences for their technical support.