【Expert Interview】Prof. Luo Xiaorong, Academic Leader of Gallium Oxide: The integration of Industry/Science and Education to Promote Gallium Oxide Industry Development

      In 2023, the Asian Gallium Oxide Alliance (hereinafter referred to as "AGOA") has expanded a new channel - Expert Interview. Council units, member units and expert committees within the Alliance contribute to explain their different views on the field of Gallium Oxide. Lead us to know Gallium Oxide, understand Gallium Oxide, in-depth Gallium Oxide.

      This time we have the honor to interview the Alliance technical expert Committee experts - University of Electronic Science and Technology of China, Chengdu University of Information Technology Professor Luo Xiaorong, to share her unique views on Gallium Oxide.

Guest Introduction

      Professor Luo Xiaorong, PhD supervisor, National Talent Program candidate, has been engaged in power semiconductor device and integration technology research for a long time, and won the second prize of National Science and Technology Progress, the first prize of Sichuan Province Science and Technology Progress, the second prize of Natural Science of the Ministry of Education, the second prize of Sichuan Province Technology Invention and the second prize of National Defense Technology invention. She has presided over more than 30 key projects of the Military Science and Technology Commission (Chief Technology), the National Talent Youth Science Fund, and the National Natural Science Regional Joint Innovation Fund. She has published more than 140 SCI papers, published more than 40 papers as the first or corresponding author in authoritative international journals IEEE TPE, IEEE EDL, IEEE TED, etc. As the first inventor, she has been authorized 6 U.S. patents and more than 90 Chinese invention patents. She has published 4 monographs and textbooks; She is a TPC member of ISPSD, the top international academic conference in the field of Power semiconductors, and a member of IEEE EDS Power Devices and ICs Technical Committee.

AGOA: Please introduce your team, research direction, research progress and results

      Professor Luo Xiaorong leads the research group of "New Power Semiconductor Devices and Integrated Circuits". The research group consists of 29 members, including 2 doctoral supervisors, 3 postdoctors, 8 doctoral students and 16 master students. The team has strong academic ability, high cohesion and harmonious and warm research atmosphere. The research group is determined to contribute to the cause of power semiconductor in China, contributing wisdom and strength.

Research direction: New power semiconductor devices and integrated circuits

Research progress and Achievements:

① Gallium Oxide Power Devices: In view of the technical difficulties that the breakdown voltage of Gallium Oxide power devices is far below the theoretical limit and it is difficult to achieve enhanced devices, the project team proposed a new structure of a series of devices, one is to improve the withstand voltage of the rectifier device and reduce the opening voltage, the other is to increase the threshold voltage of the field effect transistor and reduce the reverse pilot voltage drop. A Gallium Oxide Schottky Barrier Diode with a composite structure of air bridge plate and thermal oxidation terminal and a NiO/ Gallium Oxide heterojunction Barrier Schottky Diode were developed. Based on the design concept of Fin-type Gallium Oxide power devices, low power consumption Gallium Oxide junction free diodes and inverse conduction FINFETs with both low inverse conduction voltage and high threshold voltage are proposed to enhance their application potential in high power and low loss power conversion systems.

② Gallium Oxide MOSFET Reliability: Gallium Oxide power devices are expected to work under high power and high temperature scenarios, so it is important to study their defect response mechanism under multiple physical fields such as electric and thermal fields, and propose reliability reinforcement technology to promote their engineering applications. The team systematically analyzed the instability of Gallium Oxide MOSFET under electro-thermal stress, revealed the mechanism and physical model of device performance degradation under electric and thermal fields, and proposed an ionization trap model to explain the non-uniform mechanism under positive/negative bias stress. The degradation mechanism of heterojunction gate FETs under different stress voltages and stress times is found to provide theoretical guidance for the development of reliability strengthening technology for Gallium Oxide heterojunction devices.

      Since 2021, Professor Luo Xiaorong's research group has led and participated in two key projects of a national science and technology plan in terms of Gallium Oxide power devices and integration technology, one of which is the University of Electronic Science and Technology of China as the lead unit and Luo Xiaorong as the chief technology officer. With the efforts of all participating units, the project has made a series of important progress.

AGOA: The team studied the difficulties encountered at present

      Gallium Oxide has an ultra-wide band gap and high critical electric field strength, enabling smaller sizes and lower losses at the same breakdown voltage, making it suitable for high power and low loss applications. Recent challenges:

① For the problem that the withstand voltage of Gallium Oxide devices is much lower than the theoretical value, and the lack of P-type Gallium Oxide makes it difficult to improve the withstand voltage by conventional junction terminal technology, a Gallium Oxide Schottky Barrier Diode (SBD) with ultra-fast reverse recovery and increased withstand voltage is proposed. The developed device has improved withstand voltage by 176%, achieved ultra-low reverse recovery time of 7.5 ns and charge of 1.0 nC, and has good rectification characteristics and temperature stability.

② In view of the current situation that there are few researches on large-size and high-power Gallium Oxide devices and their thermal stability, our research group proposed high withstand voltage design technology for high-power Gallium Oxide devices, and developed Gallium Oxide junction Barrier Schottky Diode and SBD with surface charge regulation capability, which can achieve high withstand voltage and high current while low reverse leakage current. The long-term stress test results show excellent thermal stability, which indicates the great potential of Gallium Oxide power diodes working at high temperatures.

③ The traditional finned longitudinal diode/transistor may increase the on-voltage/threshold voltage and on-loss at the same time as the withstand voltage is increased. Therefore, this research group proposes a new design concept of low-power finned Gallium Oxide power device, which realizes the normally off mode by clamping the channel through depletion action, and adopts no-junction ohmic contact instead of Schottky contact to achieve extremely low on-voltage of no-junction diode. Therefore, an enhanced low-power inverse-conduction FinFET is proposed, which has both low inverse conduction voltage and high threshold voltage.

AGOA: What are the development potentials of Gallium Oxide？

      In theory, Gallium Oxide semiconductor devices have higher withstand voltage, higher power, lower power loss, smaller size and stronger radiation resistance, which is conducive to improving the power density and conversion efficiency of the application system to meet the market demand of high voltage and low power consumption, and meet the development needs of high efficiency, integration and miniaturization of the new generation of power electronic systems.

      Schottky Barrier Diode due to its high-speed characteristics and the absence of P-type doping, Gallium Oxide Schottky Barrier Diode is used as an advanced core component in the new generation of power electronic systems such as smart grid, automotive electronics and photovoltaic inverter.

AGOA: The direction of campus talent training, how to better train high-quality talents?

      Facing the major strategic needs of the national development of (Ultra) wide band gap semiconductor and integrated circuit industry, the domestic Gallium Oxide industry is still in the early stage of development, lacking high-level technical talents with core competitiveness. The talents trained by colleges and universities need to meet the needs of industrial development and enterprise development. Therefore, the cultivation of top innovative talents requires the integration of industry and education, and the integration of science and education. That is the integration of production, university and research. On the one hand, based on scientific projects, students' innovative thinking should be cultivated in scientific research. On the other hand, it is necessary to take the needs of industrial development as the guidance, the deep integration of industry, university and research, and cultivate students' skills in solving practical problems, as well as the ability of organization and coordination and the sense of social responsibility in engineering application, so as to master professional skills in industrial development in advance, meet the needs of enterprise and social development, and drive the high-quality development of industry with high-quality development of talents.

AGOA: How do you view the role of university-enterprise cooperation and the combination of industry, university and research in the industrialization of Gallium Oxide？

① School-Enterprise Cooperation: Theoretical innovation of universities and technological progress of enterprises rely on each other and promote each other, thus promoting the innovation and development of Gallium Oxide industry. The engineering practice platform provided by enterprises is conducive to cultivating high-quality top-notch innovative talents, and the demand of enterprises for top-notch innovative talents can be timely and accurately fed back to colleges and universities, so as to cultivate comprehensive talents to meet the development needs of enterprises; Relying on the production and practice platform of the enterprise, the scientific research team of the university and the enterprise jointly tackle the key problems, but also for the enterprise to solve some key core technical problems, promote the innovation and development of the enterprise, and promote industrial upgrading.

② Combination of Industry, University and Research: Promoting deep cooperation between industry, university and research can solve the key technical bottlenecks of Gallium Oxide and achieve industrial development, which is related to the further development of China's power electronics field and the fundamental way to realize the autonomy and control of key areas/key links. On the one hand, the combination of production, university and research is conducive to cultivating high-quality and top innovative talents with innovative thinking and practical skills; on the other hand, it can promote the transformation of scientific and technological achievements, accelerate industrial transformation and upgrading, thus enhancing the international core competitiveness, further energizing universities for innovation, and promoting the orderly flow and efficient allocation of Gallium Oxide technical elements. Deep cooperation between industry, university and research will help to promote the double acceleration and deep integration of Gallium Oxide semiconductor innovation and industrialization iteration.

AGOA: What kind of support would you like the alliance to provide?

      On the one hand, the alliance will lead or assist in organizing academic exchange conferences, promote academic technology progress, and promote the transformation of scientific research results into enterprises. On the other hand, it establishes close relations with ministries and commissions and local governments, recommends scientific research projects of member units to ministries and commissions and local governments, and promotes the establishment or incubation of enterprises where scientific research results are supported by local governments.