The University of Science and Technology of China has made important progress in the field of gallium oxide power electronic devices

Recently, two papers from the research group of Professor Long Shibing of the School of Microelectronics of the University of Science and Technology of China were selected for the 34th International Conference on Power Semiconductor Devices and Integrated Circuits (ISPSD, full name: IEEE International Symposium on Power Semiconductor Devices and ICs). ISPSD is the world’s top academic conference in the field of power semiconductor devices and integrated circuits.

The rapid development of energy, information, national defense, rail transit, electric vehicles and other fields has put forward higher requirements for the performance of power semiconductor devices, and high-withstand voltage, low loss, and high-power devices have become the trend of future development. As a new generation of power semiconductor materials, gallium oxide is expected to play an extremely important role in the field of power devices in the future with large bands and strong resistance to extreme environments. However, there are still many problems in the industrialization of gallium oxide power semiconductor devices, including difficulty in suppressing the edge peak electric field and difficulty in achieving enhanced transistors. The research group has done the following work on these two pain points:

1. High pressure gallium oxide diode

At present, due to the challenges of gamella P-type doping, gatum homogeneous PN junction as an extremely important basic device is temporarily difficult to achieve, resulting in the lack of homogeneous PN junction to suppress the peak electric field of the anode edge (such as field ring, junction terminal expansion, etc.) in gallium diode devices. For this reason, the use of other suitable P-type oxide materials to form heterojunctions with gallium oxide is a viable solution. P-type semiconductor NiO is currently a better choice due to its large bandgap width and controllable doping.

Based on the niO growth process and the preliminary research basis of heterogeneous PN (Weibing Hao, et.al., Applied Physics Letters, 118, 043501, 2021), the group designed the Junction Termination Extension (JTE), optimized the annealing process, and successfully prepared a gallium oxide heterojunction diode that is resistant to high pressure and high temperature. The JTE design used in this study can effectively alleviate the electric field aggregation effect of niO/Ga2O3 junction edge and increase the breakdown voltage of the device. The annealing process can greatly reduce the reverse leakage current of the heterojunction and increase the current switching ratio. The final test results show that the device has a low on-resistance of 2.5 mΩ·cm2 and a high breakdown voltage of 2.66 kV at room temperature, and its power-to-quality factor is as high as 2.83 GW/cm2. In addition, the device maintains a breakdown voltage of 1.77 kV at 250 °C, exhibiting excellent high temperature blocking characteristics, which is the first high temperature breakdown characteristic reported in the field. The research results were published in ISPSD 2022 under the title “2.6 kV NiO/Ga2O3Heterojunction Diode with Superior High-Temperature Voltage Blocking Capability”. The first author is Hao Weibing, a doctoral student in the School of Microelectronics of our university, and Professor Long Shibing of the School of Microelectronics and Xu Guangwei, a special associate researcher, as the co-corresponding authors of the paper.

Figure 1: Junction terminal extension NiO/β-Ga2O3 heterojunction diode (a) cross-sectional diagram and key manufacturing details of the device, (b) compared with the reported performance of gallium Schottky diodes and heterojunction diodes.

2. Enhanced gallium oxide field effect transistor

Enhanced transistors are self-protecting by false turn-on and require only a single supply, so enhanced devices are often used in power applications. However, due to the lack of gallium oxide P-type doping technology, field-effect transistors are generally depletion-type devices, and enhanced structures are difficult to design and implement. Common enhanced designs tend to significantly increase the open-state resistance of the device, resulting in excessively high on-ramp losses.

In view of the above problems, based on the original enhanced transistor design (Xuanze Zhou, et.al., IEEE Transactions on Electron Devices, 68, 1501-1506, 2021), the group introduced P-type NiO, which is also a wide bandgap semiconductor material, and combined with the groove structure, successfully designed and prepared gallium oxide enhanced heterojunction field effect transistors. The device achieves a threshold voltage of 0.9 V, a low sub-threshold swing (73 mV/dec), a high device transconductance (14.8 mS/mm), and near-zero device backlash, which indicate good gate control capability. In addition, the on-resistance of the device is well maintained at 151.5 Ω·mm and the breakdown voltage reaches 980 V.

The research results were published in ISPSD 2022 under the title “Normally-offβ-Ga2O3Power Heterojunction Field-Effect-Transistor Realized by p-NiO and Recessed-Gate” The first author is Zhou Xuanxuan, a doctoral student in the School of Microelectronics of our university, and Professor Long Shibing and Xu Guangwei, a special associate researcher of the School of Microelectronics, are the co-corresponding authors of the paper.

Fig. 2. Based on heterogeneous PN Gallium Oxide junction type field effect transistor (a) structure diagram and process flow diagram, (b) transfer characteristics of different drain bias voltages, (c) output characteristic curves, and (d) breakdown characteristic curves.

The two studies were funded by the National Natural Science Foundation of China, the Strategic Pilot Research Program of the Chinese Academy of Sciences, the Key Research Program of Frontier Science of the Chinese Academy of Sciences, the Science and Technology Commission of Guangdong Province, the Key Research and Development Program of Guangdong Province, and the Key Laboratory of Microelectronic Devices and Integrated Technology of the Institute of Microelectronics of the Chinese Academy of Sciences. Supported by the Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nanotechnology and Nanobionics, Chinese Academy of Sciences.

ISPSD2022 Conference Official Website:https://ispsd2022.com/

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