A Research Team Led by Prof. Kevin J. CHEN Inducted CMOS Circuits into the Family of Gallium Nitride (GaN) Electronics

Prof. Kevin J. CHEN and his research group have successfully fabricated a full family of gallium nitride (GaN)-based complementary (a more popular term is ‘CMOS’) logic circuits and realized multistage monolithic integration (i.e., with all circuits fabricated in a single semiconductor chip). Consequently, such an indispensable circuit architecture, which dominates the silicon-based modern integrated circuit industry, has been formally inducted into the realm of the ever-developing GaN electronics. Their research paper has been published in Nature Electronics. 

Zheng, Z., Zhang, L., Song, W., Feng, S., Xu, H., Sun, J., Yang, S., Chen, T., Wei, J. & Chen, K. J. Gallium nitride-based complementary logic integrated circuits. Nat. Electron. (2021). https://doi.org/10.1038/s41928-021-00611-y

GaN-based electronic devices have been recently commercialized and adopted in 5G wireless base stations, ultra-compact fast chargers for mobile devices, and LiDAR systems.  GaN-based power converters/supplies with unprecedented efficiency and power density are expected to see near-term adoptions in many emerging applications such as data centers, autonomous driving, electric vehicles, drones, robots, etc. All these applications are power-hungry and yet demand ultra-compactness in power supplies.

Monolithically integrating GaN power devices with other peripheral functional blocks would leads to much powerful and versatile GaN-based power conversion systems. Complementary circuits are the best choice for constructing ubiquitous logic circuits in the peripherals. However, due to the difficulties in implementing high-performance enhancement-mode p-channel GaN transistors and integrating the two complementary (i.e., n-channel and p-channel) GaN devices, there have only been intermittent demonstrations on preliminary inverters with less satisfactory performances. Complementary logic circuitry is indispensable yet one of the last few missing pieces of the GaN electron device family.

With a plasma treatment technique to fabricate high-quality p-channel transistors on a commercial GaN-on-Si platform on which n-channel devices have been well developed, Prof. Chen’s team successfully fabricated a family of GaN-based monolithic complementary logic circuits in the Nanosystem Fabrication Facility (NFF) of HKUST. The fabricated inverters, the most representative and elementary logic gate, exhibit all desired ‘CMOS-like’ behaviors, most of which have never been obtained before. Along with the inverter, other elementary complementary logic gates (NOR gate, NAND gate, and transmission gate) and multistage complementary logic circuits (latch and ring oscillator) are presented. The multi-stage circuit demonstration indicates that we can now start to build GaN-based MCU’s (Microcontroller Units) for some mission-critical applications such as planetary and deep space exploration.

“It is exciting to see GaN-based complementary logic circuits proven feasible. The horizon of GaN electronics has been substantially extended,” says Zheyang ZHENG, a postdoc fellow in Prof. CHEN’s group. As an immediate benefit, circuit designers can now start to design more powerful GaN ICs with more sophisticated functions. In the near-medium future, it becomes feasible to build GaN-based computing chips for critical missions such as planetary and deep space explorations. 

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