【Domestic Papers】β-Ga₂O₃ diodes with ultra-high surge current enabled by Ag/AMB-AlN flip-chip packaging

      Researchers from the Beijing Microelectronics Technology Institute and Tsinghua University have published a dissertation titled "β-Ga₂O₃ diodes with ultra-high surge current enabled by Ag/AMB-AlN flip-chip packaging " in Journal of Electronic Science and Technology.

Background

      The ultra-wide bandgap semiconductor, gallium oxide (Ga₂O₃), with its wide bandgap (4.5–4.9 eV), high critical electric field (6–8 MV/cm), high Baliga’s figure of merit (3000–4000) and low intrinsic carrier concentration is recognized as one of the most promising materials for the fourth-generation high-voltage power devices. However, its low thermal conductivity (approximately 1/6 that of silicon (Si)) leads to significant self-heating during operation, which severely limits the device performance.

Recent advancements in packaging, such as nano-silver paste, direct bond copper (DBC) substrates (achieving ∼2.8 K/W junction-to-case thermal resistance (R_th(J-C)) for Ga₂O₃ devices), and flip-chip structures, have improved thermal management. However, nano-silver paste faces electromigration failure under a high current density despite offering high thermal conductivity (>200 W/mK), and DBC substrates risk interfacial delamination at extreme temperatures (>250 °C). Moreover, solders (temperature-limited <220 °C) and copper substrates (coefficient of thermal expansion (CTE)-mismatch-induced stress) are used in traditional flip-chip solutions, which results in compromised reliability. Therefore, more innovative methods contributing to a further decrease in the thermal resistance while ensuring high reliability is still challenging. In this study, we demonstrate a low-R_th(J-C) solution via nano-silver thin-film hot-pressing on aluminum nitride active metal brazing (AMB-AlN) substrates with a flip-chip structure. Comprehensive reliability performance of different β-Ga₂O₃ devices, such as  mesa-terminated Schottky barrier diodes (SBDs) and hetero-junction diodes (HJDs) with such advanced Ag/AMB-AlN flip-chip packaging, is evaluated including the high-temperature storage, reverse recovery, and surge current tests. The results provide key insights for Ga₂O₃ power device packaging.

Abstract

      Owing to superior breakdown voltage and exceptional robustness, the β-Ga₂O₃ power device has emerged as a pivotal research frontier in power electronics. Although advanced packaging strategies, including nano-silver paste sintering, alumina direct bond copper (DBC) substrates, and flip-chip structures, have been adopted to mitigate β-Ga₂O₃’s intrinsic low thermal conductivity. However, a further reduction in the thermal resistance while maintaining high reliability remains a challenge. This study introduces a novel packaging methodology that synergistically integrates nano-silver films with aluminum nitride active metal brazing (AMB-AlN) substrates, achieving an ultra-low junction-to-case thermal resistance. Comprehensive reliability assessments were conducted on β-Ga₂O₃ Schottky barrier diodes (SBDs) and p-NiO/β-Ga₂O₃ hetero-junction diodes (HJDs), encompassing high-temperature storage test, reverse recovery analysis, and surge current characterization. The SBDs and HJDs exhibit surge current densities of ∼0.88 kA/cm² and ∼0.78 kA/cm², respectively, ranking among the highest reported levels for β-Ga₂O₃ power devices, which represents a significant advancement in device performance benchmarks. These advancements provide critical insights into packaging design for high-reliability ultra-wide bandgap semiconductor systems.

Conclusions

      In this study, we packaged the β-Ga₂O₃ SBDs and HJDs with dimensions of . By utilizing a high-thermal-conductivity AMB substrate and a nano-scale silver sintering process to achieve low junction-to-case thermal resistance, the device reliability was evaluated. The results demonstrate that the β-Ga₂O₃ SBDs have excellent switching performance, featuring a reverse recovery time of 13.8 ns and a reverse recovery charge of 11.3 nC, highlighting their fast switching speed. Benefiting from their low turn-on voltage and optimized anode thermal design, the SBDs achieved a peak surge current density of ∼0.88 kA/cm² under a 10 ms pulse width. In contrast, the β-Ga₂O₃ HJDs exhibited a superior breakdown voltage, lower reverse leakage current, and exceptional high-temperature stability, with negligible performance degradation during HTST at 250 °C. This work underscores the excellent robustness of β-Ga₂O₃ diodes and provides theoretical guidance for selecting devices tailored to different operational environments.