$beta$-Ga2O3 in Power Electronics Converters - Opportunities & Challenges

At a Glance

Metadata	Details
Publication Date	2024-01-01
Journal	IEEE Open Journal of Power Electronics
Authors	Saeed Jahdi, Akhil S. Kumar, Matthew Deakin, Phil Taylor, Martin Kuball
Institutions	University of Bristol, Newcastle University
Citations	26
Analysis	Full AI Review Included

Executive Summary

Core Value Proposition: β-Ga₂O₃ is identified as a highly competitive Ultra-Wide-Bandgap (UWBG) semiconductor due to its high theoretical Baliga’s Figure of Merit (BFOM, ~40 GW/cm²) and low manufacturing cost enabled by melt-grown substrates (similar to Si).
Performance Benchmark: The latest experimental NiO_x/β-Ga₂O₃ and β-Ga₂O₃/diamond devices significantly outperform incumbent SiC-FET and Si-IGBT modules in high-power converter applications.
Thermal Management Solution: The poor thermal conductivity of bulk β-Ga₂O₃ (0.2 W/cm·K) is effectively mitigated by heterogeneous integration with diamond substrates, reducing thermal resistance (R_th) by up to 100x compared to bulk devices.
Application Focus: Modular Multilevel Converters (MMC-VSC) for MVDC (6 kV) and HVDC (320 kV) transmission are the most promising topologies to exploit the high voltage and efficiency benefits of β-Ga₂O₃.
Efficiency Gains: In the 320 kV HVDC testbed, β-Ga₂O₃/diamond devices achieved module power losses up to one-third lower than incumbent Si-IGBT and SiC-FET modules.
Future Potential: Theoretical analysis of β-Ga₂O₃/diamond Superjunction (SJ) structures predicts even superior performance, including switching losses (E_sw) reduced to 0.02x that of SiC, enabling further simplification of converter topologies.

Technical Specifications

Parameter	Value	Unit	Context
β-Ga₂O₃ Theoretical BFOM	~40	GW/cm²	Assuming mobility 250-300 cm²/V·s
β-Ga₂O₃ Critical Electric Field (E_C)	8	MV/cm	Theoretical limit
Bulk β-Ga₂O₃ Thermal Conductivity	0.2	W/cm·K	8x smaller than GaN, 30x smaller than SiC
NiO_x/β-Ga₂O₃ Experimental V_BR	8.32	kV	Record high breakdown voltage
NiO_x/β-Ga₂O₃ Experimental R_ON	5.24	Ω·cm²	Record low on-resistance
NiO_x/β-Ga₂O₃ Experimental BFOM	13.2	GW/cm²	Latest experimental result
Early β-Ga₂O₃ (2017-19) R_ON (Relative)	5x	-	Relative to SiC baseline
Early β-Ga₂O₃ (2017-19) R_th (Relative)	10x	-	Relative to SiC baseline (bulk material)
NiO_x/β-Ga₂O₃ (2022) R_ON (Relative)	0.2x	-	Relative to SiC baseline
β-Ga₂O₃/Diamond SJ Theoretical E_sw (Relative)	0.02x	-	Relative to SiC baseline (Superjunction structure)
β-Ga₂O₃/Diamond R_th (Relative)	0.1*x	-	Epitaxially grown on diamond (100x lower than bulk)
HVDC Converter DC Voltage	320	kV	VSC-MMC testbed
HVDC Converter Power Rating	225	MW	VSC-MMC testbed
MVDC Converter DC Voltage	6	kV	VSC-MMC testbed
MVDC Converter Power Rating	0.65	MW	VSC-MMC testbed
HVDC Module Case Temp (Early β-Ga₂O₃ Inv.)	>350	°C	Worst-case inverter operation (due to high R_th)

Key Methodologies

The study employed a circuit and system-level simulation approach using the Modular Multilevel Converter (MMC-VSC) half-bridge topology as the principal architecture for evaluation.

System Definition: Two testbeds were defined: a 6 kV MVDC converter (650 kW) and a 320 kV HVDC converter (225 MW). System parameters (V_DC, V_AC, I_AC, P) and converter parameters (module voltage, number of modules, utilization, switching frequency) were established based on industry standards and literature.
Device Parameter Input: Performance metrics (R_ON, V_BR, E_sw, R_th) for various β-Ga₂O₃ generations (early bulk, NiO_x/β-Ga₂O₃, and β-Ga₂O₃/diamond, including theoretical SJ structures) were extracted from the best reported experimental and simulated data in the literature (Table 1).
Loss Calculation Modeling: Converter losses were calculated using a model based on datasheet information for Si and SiC devices, and extrapolated data for β-Ga₂O₃.
- Conduction Loss (P_cond): Calculated based on the instantaneous load current (I_N(t), I_P(t)), duty cycle (D), and ON-state voltage drop (V_DS/V_F), derived from look-up tables.
- Switching Loss (P_sw): Calculated as P_sw = f_sw (E_on + E_off + E_rec), where switching energy (E) is extrapolated for different current levels using a second-order polynomial fitting factor (K).
Thermal Modeling: Total combined losses (P_Total) were input into a thermal model derived from datasheet thermal impedance characteristics (R_th-j-a) to calculate the junction temperature rise (ΔT = T_j - T_a).
Iterative Analysis: The calculated junction temperature (T_j) was fed back into the loss equations (P_cond and P_sw) to determine temperature-dependent losses, ensuring a steady-state thermal condition was reached for accurate performance comparison.

Commercial Applications

The unique combination of high voltage capability, low R_ON, and potential for low-cost substrate manufacturing positions β-Ga₂O₃ for significant market penetration in high-power utility and industrial sectors.

HVDC Transmission Systems:
- VSC-HVDC (Voltage-Sourced Converter High Voltage Direct Current) links, particularly those using MMC topology.
- Enables higher voltage ratings per submodule, drastically reducing the required number of series-connected submodules per valve, simplifying the overall converter design.
MVDC Distribution Networks:
- Distribution-level energy networks (e.g., 6 kV systems) where high efficiency and low losses are critical due to the extensive infrastructure length.
Flexible AC Transmission Systems (FACTS):
- Devices like STATCOMs (Static Compensators) that require high-power, high-frequency switching for dynamic grid control and power quality improvement.
High-Performance MV Drives:
- Industrial AC drive applications (typically 2 kV to 15 kV) where WBG devices are used to achieve high power density and efficiency, currently dominated by SiC MOSFETs.
Offshore Platforms and Constrained Environments:
- Applications requiring high volumetric and gravimetric density, benefiting from the reduced heat generation and smaller cooling systems enabled by highly efficient β-Ga₂O₃ devices.

View Original Abstract

In this work, the possibility of using different generations of <inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3 as an ultra-wide-bandgap power semiconductor device for high power converter applications is explored. The competitiveness of <inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3 for power converters in still not well quantified, for which the major determining factors are the on-state resistance, <inline-formula><tex-math notation=“LaTeX”>$R_{\text{ON}}$</tex-math></inline-formula>, reverse blocking voltage, <inline-formula><tex-math notation=“LaTeX”>$V_{\text{BR}}$</tex-math></inline-formula>, and the thermal resistance, <inline-formula><tex-math notation=“LaTeX”>$R_{\text{th}}$</tex-math></inline-formula>. We have used the best reported device specifications from literature, both in terms of reports of experimental measurements and potential demonstrated by computer-aided designs, to study power converter performance for different device generations. Modular multilevel converter-based voltage source converters are identified as a topology with significant potential to exploit these device characteristics. The performance of MVDC & HVDC converters based on this topology have been analysed, focusing on system level power losses and case temperature rise at the device level. Comparisons of these <inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3 devices are made against contemporary SiC-FET and Si-IGBTs. The results have indicated that although the early <inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3 devices are not competitive to incumbent Si-IGBT and SiC-FET modules, the latest experimental measurements on NiO<inline-formula><tex-math notation=“LaTeX”>$_\mathrm{X}$</tex-math></inline-formula>/<inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3 and <inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3/diamond significantly surpass the performance of incumbent modules. Furthermore, parameters derived from semiconductor-level simulations indicate that the <inline-formula><tex-math notation=“LaTeX”>$\beta$</tex-math></inline-formula>-Ga2O3/diamond in superjunction structures delivers even superior performance in these power converters.

Tech Support

Original Source

DOI: https://doi.org/10.1109/ojpel.2024.3387076

References

2020 - 2.3 kVA new voltage class for Si IGBT and Si FWD
2023 - Analysis of performance and reliability of sub-kV SiC and GAN cascode power electronic devices