In recent years, new power electronic devices have played an important role in many innovative fields. For example, in China's new infrastructure proposed by the state in 2020, the development of 5G base stations, UHV, intercity high-speed rail and rail transit, charging piles for new energy vehicles, big data centers, artificial intelligence and industrial Internet can not be separated from the support of new power electronic device technologies.
Although new power electronic devices play an important role in new energy construction, the United States and Europe are still in the leading position in the international market competition. People in the industry agree that the introduction of new power electronic devices will bring a new revolution in power electronic technology, and will affect the world energy reform, which will play an important role in creating an energy-saving and environment-friendly society. Therefore, the research direction of new power electronic device technology is of great significance to the economic and social development and environmental protection in China and even in the world. Na Ren, an associate researcher at Zhejiang University, is focusing on new power electronic equipment based on silicon carbide semiconductor materials.
For the choice of major, Na Ren has his own unique vision. In 2006, she entered the School of Electrical Engineering of Wuhan University to study power system and its automation, which was the "iron rice bowl" major of State Grid at that time. On 20 10, she graduated with excellent results and was sent to the School of Electrical Engineering of Zhejiang University, and transferred to the major of power electronics.
Why do you want to change majors? Na Ren said there was a reason.
When Na Ren came to Zhejiang University, she happened to meet the great professor who returned to teach at Zhejiang University from the United States in 2009. After obtaining tenure at New Jersey State University, Professor Sheng gave up the generous treatment abroad and resolutely devoted himself to the impoverished power electronic devices and power semiconductors industry in China. As a scientist who has been engaged in the research of silicon-based and silicon carbide power electronic devices, packaging and applications for a long time, Professor Sheng is well aware of the gap between China and the leading teams in the world at that time, but he still devoted himself to it because he knows that many core technologies, once developed, can quickly subvert a product or even an era.
Professor Sheng's description of the research status of new power electronic devices and his imagination of future development are inspiring. At that time, silicon carbide power electronic devices have become a hot research topic in the world, while domestic research in this field has just started. I believe that under the leadership of Professor Sheng, domestic power electronic devices and power semiconductor industries can be developed. As the saying goes, a low starting point is not terrible, but a low realm is terrible. After understanding the important but backward background of the industry, he resolutely chose the research direction of silicon carbide power electronic devices, entered the power electronic device laboratory of Zhejiang University founded by Professor Sheng, and became a member of the earlier research and development team of silicon carbide power electronic devices in China.
Facts have also proved that Na Ren's choice is very forward-looking. Today, with the development of new energy, the importance of power electronic device technology is self-evident. Just ten years ago, her choice was still very courageous and enterprising.
After arriving in the United States, Na Ren never stopped studying. She found that many enterprises in the United States wanted to enter the power electronic device industry at that time, but because of the high technical threshold, they needed to seek cooperation from universities to jointly develop silicon carbide power electronic device products and technologies. This gave Na Ren a chance to exercise his ability. During her postdoctoral period, she led two large-scale school-enterprise cooperation projects. "These projects let me know how to apply the scientific research results of the laboratory to enterprise products and realize industrialization, and also let me know how to bridge the gap between scientific research and industrialization, which laid the foundation for my continued research on silicon carbide power electronic device technology after returning to China."
From unknown to mature, Na Ren has been devoted to the research of silicon carbide (SiC) power electronic devices, including the physical mechanism, structural design, process technology, chip development, device testing and failure analysis, performance and reliability optimization of SiC diodes and metal oxide semiconductor field effect transistors (MOSFET), and has achieved a series of research results. For example, he published 40 papers in internationally renowned journals and conferences in the field of devices, including 23 SCI papers, won 3 US patents and won the 20 17 International Power Electronics Conference Excellent Report Award.
Along the way, Na Ren has been taking every step steadily. During his Ph.D., Professor Sheng, the tutor, as the only "Changjiang Scholar" in the field of power electronic devices in China and the winner of the National Natural Science Foundation's Outstanding Youth Science Fund, was strict in requirements and carefully trained. Therefore, Na Ren inherited his tutor's rigorous academic style and clear logical thinking. During the postdoctoral period, in the study room of power electronic devices, Na Ren constantly improved his technical level, deepened international exchanges and cooperation, and accumulated contacts in the same industry. Whether at home or abroad, Na Ren has unconsciously stood at the forefront of the academic field over the years.
On September 20 19, Na Ren returned to China to teach at the School of Electrical Engineering of Zhejiang University. In March 2020, he was employed by the Advanced Semiconductor Research Institute of Hangzhou International Science and Technology Center of Zhejiang University. Her research work mainly includes reliability research and device optimization design of SiC diodes and MOSFET devices, new trench SiC MOSFET device technology, and ultra-high voltage SiC gate turn-off thyristor device technology.
In the recently selected Outstanding Young Talents Program of Science and Technology Innovation Center of Zhejiang University, Na Ren plans to challenge two major difficulties: one is the silicon carbide trench gate MOSFET technology that breaks through the performance of existing devices, and the other is the development of ultra-high voltage silicon carbide gate turn-off thyristor devices.
In the SiC power electronic device industry, MOSFET device is the most promising type of switch tube in the medium and low voltage application field, but the existing planar gate MOSFET technology route faces the problems of large specific on-resistance and limited on-current capacity per unit area. How to break through this performance limit and further improve the performance of power devices is a huge challenge in the field of silicon carbide MOSFET devices.
In this project, Na Ren will explore the influence mechanism of trench gate structure and advanced trench gate oxidation technology on channel mobility, study the regulation mechanism and method of electric field distribution inside the chip, develop key processes such as silicon carbide trench etching, gate oxide layer growth, trench filling and injection, form an electric field shielding structure, realize high-performance and high-reliability silicon carbide trench MOSFET devices, greatly improve the on-current density of silicon carbide chips, and break through the performance level of existing devices.
Although the challenge is very difficult, years of industry penetration and knowledge accumulation have made Na Ren full of fighting spirit. She said: "After years of scientific research, we often encounter difficulties such as non-convergence of simulation, failure of process technology development, and failure of device performance. However, encountering problems is the starting point for solving problems. It's not terrible to encounter problems. The terrible thing is that we don't insist on using the right method to constantly try to overcome it. I believe that every effort is a step closer to success. "
In addition to breaking through the existing device technology, Na Ren will also challenge the development of ultra-high voltage silicon carbide gate turn-off thyristor. She explained that today, power electronic devices have developed to the third generation, that is, device technology represented by new wide band gap semiconductor materials SiC and GaN, but at present, high-voltage and high-power applications such as power systems still use traditional silicon-based high-power devices or modules, which limits the improvement of system efficiency and the realization of miniaturization and lightweight goals. The application of silicon carbide gate turn-off thyristor in high voltage and high power system can reduce the number of devices, power loss, system efficiency, cooling equipment and system volume. Therefore, the development of ultra-high voltage silicon carbide gate turn-off thyristor devices is of great significance to the development of the country in the energy field.
However, the development of ultra-high voltage silicon carbide gate turn-off thyristor is also facing many technical challenges: the influence mechanism and containment technology of silicon carbide material defects on carrier lifetime in devices have not been verified, silicon carbide material defects will lead to the performance degradation of bipolar devices and affect the reliability of devices, the physical theory and device model of silicon carbide gate turn-off thyristor are not mature, and the manufacturing process of silicon carbide devices is very complicated, which is very different from traditional silicon devices. It is necessary to independently develop relevant technology and platform. Silicon carbide gate can turn off the combination of thyristor devices and system applications, and special gate drive and circuit topology need to be designed.
However, Na Ren knows in his heart that the future development of power electronic devices will definitely be smaller, lighter, faster, more efficient and more reliable. Therefore, she will go all out to achieve breakthrough research results in the field of silicon carbide power electronic devices.
In addition to the Young Talents Program, in the near future, the Youth Fund of the National Natural Science Foundation of Na Ren and the Delta Power Electronics Science and Education Development Fund will also be launched simultaneously. Although the business is very busy, she said, "People can't do anything without asking for more happiness."
In the future, Na Ren hopes to develop world-class silicon carbide power electronic device technology and make due contributions to the country's major strategic development in the energy field with its own strength. "I hope that in the future, human society can benefit more from today's large number of scientific research results, which is also the ultimate goal of our scientific research activities." For the direction of scientific research, Na Ren said: