【Member Papers】First Demonstration of Ga₂O₃ Reverse Blocking Transistors with BV²/Rₒₙ,ₛₚ Figure-of-Merit Over 1 GW/cm² and Dual Blocking of 8 kV by Double Super-Junction Design

日期：2026-08-20阅读：23

Researchers from the Xidian University have published a paper titled First Demonstration of Ga₂O₃ Reverse Blocking Transistors with BV²/Ron,sp Figure-of-Merit Over 1 GW/cm² and Dual Blocking of 8 kV by Double Super-Junction Design in VLSI Technology and Circuits.

Background

Reverse blocking transistors are core power electronic components that can replace the traditional series topology of transistors and diodes, simplifying circuit structures such as AC-AC matrix converters. Commercial reverse blocking devices based on Si IGBTs have been developed, yet silicon suffers from a low critical breakdown electric field, limiting its application in high-voltage and high-power systems. The ultra-wide bandgap (UWBG) semiconductor Ga₂O₃ possesses a bandgap of 4.8 eV and a theoretical critical electric field of 8 MV/cm, making it a promising candidate for next-generation high-voltage power devices. Heterojunctions formed by p-NiO and n-Ga₂O₃ have been adopted to fabricate bipolar devices with breakdown voltages exceeding 10 kV. Nevertheless, power devices inherently face a trade-off between specific on-resistance Rₒₙ,ₛₚ and breakdown voltage (BV). Super-junction (SJ) technology is recognized as an effective strategy to mitigate this limitation. Integrating SJ structures into reverse blocking transistors reduces turn-on voltage Vₒₙ and conduction loss via the junction barrier Schottky (JBS) structure at the drain region. However, state-of-the-art reverse blocking transistors based on Si, SiC, GaN and Ga₂O₃ all fail to achieve a reverse blocking voltage over 5 kV, and fundamental physical and manufacturing engineering challenges of SJ technology in Ga₂O₃ transistors remain unresolved. To address these bottlenecks, this work proposes and fabricates p-NiO/n-Ga₂O₃ double super-junction MOS junction-FETs (DSJ-MOSJFETs) for the first time, with comprehensive device fabrication, electrical characterization and simulation analysis performed.

Abstract

This work reports the first demonstration of reverse blocking n-Ga₂O₃ transistor by constructing p-NiO/n-Ga₂O₃ double super-junction (DSJ) MOS junction-FETs (DSJ-MOSJFETs). The DSJ-MOSJFET is beneficial for boosting on-state performance, leading to a large gate swing of 9.5 V and low specific on-resistance (Rₒₙ,ₛₚ) of 5.67 mΩ·cm². Meanwhile, DSJ technique also enhanced the breakdown voltage (BV) under the charge balance condition, resulting in a BV of 2.4 kV at gate-to-p-NiO spacing (L_GP) of 4 μm. Thus, the average electric field (E_AV) is pushed to be 6.1 MV/cm and the BV²/Rₒₙ,ₛₚ power-figure of merit (P-FOM) is yielded to be over 1 GW/cm². The repeated measurement and stress tests with both shift in V_TH less than 0.1 V illustrate the strong stability for this work. Combined with the both forward and reverse BV delivered to be >8 kV, this work shows the great promise for future high-power and high-voltage power conversion applications.

Highlights

①First-ever fabrication of reverse blocking p-NiO/n-Ga₂O₃ DSJ-MOSJFET, breaking the limitation that reverse blocking voltage of existing Ga₂O₃ transistors is below 5 kV;

②Fin-shaped p-NiO drain-side super-junction alleviates channel depletion effect, reduces turn-on voltage Vₒₙ and specific on-resistance Rₒₙ,ₛₚ, and achieves a wide gate swing of 9.5 V with greatly improved on-state performance;

③Charge-balanced double super-junction realizes 3D uniform electric field modulation. At L_GP=4 μm, forward/reverse BV reaches 2.4 kV with average electric field E_AV=6.1 MV/cm, delivering a record power FOM over 1 GW/cm² (twice the critical electric field of GaN and SiC); bidirectional blocking voltage exceeds 8 kV with enlarged gate-drain spacing;

④Outstanding device stability verified by cycling and gate stress tests: V_TH shift is only 0.03 V after 150 transfer cycles, and V_TH drift is less than 0.1 V after 1000 s positive gate stress, proving high-quality gate oxide SiO₂ and p-NiO/n-Ga₂O₃ heterojunction interface.

Conclusion

In conclusion, we have innovatively integrated DSJ design in the reverse blocking Ga₂O₃ transistors with the achievement of record P-FOM over 1 GW/cm² and dual blocking of over 8 kV. These results indicate the huge potential for future high-power and high-voltage power conversion applications.

Project Support

This work was supported by the National Natural Science Foundation of China (Grant No. 62421005, 62525402), Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (No. JYB2025XDXM105), and National Key Research and Development Program of China under Grant 2024YFE0205300.

Fig. 1: Three-dimension schematic view and major fabrication steps for the p-NiO/n-Ga₂O₃ double super-junction (DSJ) MOSJFET with L_P1D and L_GP2 set to be the same in each device to achieve the similar BV in the bidirectional characteristics. The SJD with drain metal of Ni/Au stack builds the foundation for the reverse blocking capability. DSJ-MOSJFET is beneficial for the decrease in Rₒₙ and Vₒₙ due to the reduced depletion effect by finshape P-NiO. Meanwhile the forward and reverse BV is also boosted by the DSJ-MOSJFET since the E distribution is modulated smoothly in three-dimension directions.

Fig. 2: (a) Top-view SEM image at the drain edge region with n-Ga₂O₃ width (W_D) and P-NiO width (W_A) of 700 nm and 1400 nm. (b) Cross-sectional view of gate region with the insulating ALD SiO₂ layer between the p-NiO and the gate Ni/Au metal and the p-NiO thickness (T_A) of 70 nm. (c) The HRTEM image of the interface between the p-NiO and n-Ga₂O₃. (d) The list of the main structure and the values for the devices. The Ga₂O₃ donor concentration (N_D)/n-Ga₂O₃ thickness (T_D)/T_A is 3×10¹⁷ cm⁻³/450 nm/70 nm for all devices. The acceptor concentration (N_A) for p-NiO is 1.2×10¹⁸ cm⁻³ and 2×10¹⁸ cm⁻³ for the D-mode and E-mode DSJ-MOSJFETs, respectively. N_D・T_D・W_D and N_A・T_A・W_A is set almost the same to pursuing the charge balance condition for achieving SJ technique.

Fig. 3: Well-behaved linear-scale output characteristics for the D-mode and E-mode p-NiO/n-Ga₂O₃ DSJ-MOSJFET. The Rₒₙ for E-mode device is exacted to be 170 Ω・mm and 1570 Ω・mm at L_SD of 9 μm and 108 μm, respectively. Due to the decreased depletion effect for the smaller N_A of p-NiO, the Rₒₙ is reduced to be 63 Ω・mm and 563 Ω・mm for D-mode device, respectively. The Vₒₙ for both DSJ-MOSJFETs are exacted to be 0.7 V by the linear extrapolation of I_D.

Fig. 4: (a) linear-scale I_D-g_m-V_gs and (b) semi-log-scale I_D-I_g-V_Gs transfer characteristics for the E-mode p-NiO/n-Ga₂O₃ DSJ-MOSJFET. The I_D on/off ratio is demonstrated to be ~10⁹ and the V_TH is determined to be 0.5 V for both devices. The SS is extracted to be 70 mV/dec and 86 mV/dec with L_sd of 10 um and 100 um at the same I_D ranging from 10^-7 mA/mm to 10⁴ mA/mm. The high-quality ALD SiO₂ between p-NiO and gate metal serve as an effective carrier blocking layer, so that the I_g can be suppressed over 4 magnitudes lower than I_D and the gate swing can be enlarged to 9.5 V.

Fig. 5: (a) linear-scale I_D-gₘ-V_GS and (b) semi-log-scale I_D-I_G-V_GS transfer characteristics for the D-mode p-NiO/n-Ga₂O₃ DSJ-MOSJFET. I_D on/off ratio of ~10⁹ and V_TH of -4 V are delivered for both devices. The DIBL is decreased from 30 mV/V to 0.6 mV/V by enlarging the L_SD from 10 μm to 100 μm. SS is calculated to be 72 mV/dec and 76 mV/dec at I_D range of 10⁻⁷ ~ 10⁻⁴ mA/mm. The carefully designed hybrid MOS-JFET structure at the gate region is beneficial for the maintained decent gate control ability even with the additional SiO₂ layer.

Fig. 6: Well-behaved (a) linear-scale I_D-gₘ-V_GS and (b) semi-logscale I_D-I_G-V_GS transfer characteristics for the E-mode p-NiO/n-Ga₂O₃ DSJ-MOSJFET with L_SD 100 μm at a repeated test of 150 cycles. There is no obvious difference for each parameter. The maximum I_D is only decreased by 0.5 mA/mm and the peak gₘ is reduced by 0.6 mS/mm in the repeated 150 cycles. The off-state I_D still holds the noisy floor of 10⁻⁸ mA/mm and the V_TH shift is exacted to be only -0.03 V within the repeated 150 cycles.

Fig. 7: The comparison of (a) output characteristics and (b) reverse blocking breakdown characteristics for the p-NiO/n-Ga₂O₃ DSJ-MOSJFET and p-NiO/n-Ga₂O₃ MOSJFET with PN structure drain. The Vₒₙ in I_D-V_DS curve is decreased from 1.9 V to 0.7 V by just shaping the drain structure to fin-shaped p-NiO. The reverse blocking voltage is increased from -400 V to -1500 V by embedding the SJ terminal technique to suppress the peak E at the drain side effectively.

Fig. 8: The stress-time dependent (a) linear-scale and (b) semi-logscale transfer characteristics for the p-NiO/n-Ga₂O₃ DSJ-MOSJFET. The gate stress voltage is biased to be 5 V with the stress time changes from 0 to 1000 s. Under the positive gate bias, the electron is attracted at the interface, leading to an extension of depletion depth and the positive shift for V_TH. The off-state I_D and I_G display negligible change and V_TH remains at a small increase of 0.1 V after a stress time of 1000 s, illustrating the high quality of the interface under the gate region.

Fig. 9: The top-view schematic of three-dimensional simulated E distribution at V_GS of 2 V and V_DS of -400 V for the p-NiO/n-Ga₂O₃ DSJ-MOSJFET with N_A of (a) 5×10¹⁷ cm⁻³, (b) 1×10¹⁸ cm⁻³ and (c) 1.5×10¹⁸ cm⁻³, respectively. The peak E crowds at the drain edge for the N_A of 5×10¹⁷ cm⁻³ since β-Ga₂O₃ channel is just partly depleted. While the peak E located at p-NiO corner for the N_A=1.5×10¹⁸ cm⁻³ due to the not fully depleted surface p-NiO serving as the conducting layer. The E in the channel layer is flattened by meeting the charge balance condition at the N_A of 1×10¹⁸ cm⁻³, so that the device holds the ability to sustain a higher BV.

Fig. 10: (a) The forward and reverse blocking characteristics for the D-mode p-NiO/n-Ga₂O₃ DSJ-MOSJFET with L_GP2 of 4/20/60 μm. The BV yields to be 8 kV at L_GP2=60 μm. Due to ALD SiO₂ constructed underneath the gate electrode, the forward BV is slightly higher than the reverse direction. (b) The calculated E_AVand P-FOM for the p-NiO/n-Ga₂O₃ DSJ-MOSJFET. The forward and reverse BV is 2.44 and -2.40 kV at a L_P1D of 4 μm, so that the E_AVis yielded to over 6 MV/cm. Combined with the Rₒₙ,ₛₚ 5.67 mΩ・cm², the P-FOM = BV²/Rₒₙ,ₛₚ can be reaching over 1 GW/cm² for the DSJ-MOSJFET under the charge balance condition.

DOI :

10.1109/VLSITechnologyandCir65830.2026.11577432