Researchers demonstrated a strategy to implement gallium nitride (GaN) based complementary logic integrated circuits.
Most integrated circuits developed today are based on silicon complementary metal-oxide-semiconductor (CMOS) technology. However, silicon has a narrower bandgap which limits its usage in high frequency, energy efficient circuits. Therefore, researchers are trying to implement ICs using other materials with a wider bandgap, such as gallium nitride (GaN).
GaN based transistors have significant advantages over silicon-based transistors like high switching speed, current handling capability, and lower switching losses. Therefore, they are preferred for the development of power electronics, radiofrequency power amplifiers and devices designed to operate in harsh environments. But implementing GaN based elements on ICs is challenging due to low mobility of holes in the material and the lack of a suitable strategy for integrating n-channel and p-channel field-effect transistors (n-FETs and p-FETs) on a single substrate.
Researchers at the Hong Kong University of Science and Technology (HKUST) have developed a series of GaN-based complementary logic ICs. They realized a power converter IC with GaN HEMTs (high-electron-mobility transistors). To be efficient and completely integrated, a power converter requires active switching devices such as transistors and rectifiers, and peripheral circuits that enable their driving, sensing, protective and control functionalities. Therefore, to unlock the full potential of GaN HEMTs, it is preferred to embed the active switches and peripherals onto a single chip.
“Current GaN HEMTs are all n-FETs with electrons as the carriers, thus all the peripheral circuits are also based on n-FETs,” Dr. Zheyang Zheng, one of the researchers who carried out the study, explained. “However, logic gates (which are a major constituent in the peripheral circuits) solely based on n-FETs, are much less energy-efficient than the well-known CMOS (complementary MOS) logic architecture that features complementary n-FETs and p-FETs.”
“We demonstrate a suitable strategy to monolithically integrate GaN n-FETs and p-FETs and manifests the feasibility of constructing GaN-based complementary logic integrated circuits,” Zheng said. “Logic gates based on complementary n-FETs and p-FETs (i.e., the complementary logic gates) are the most energy efficient architectures for implementing digital logic circuits, as the use of complementary n-FETs and p-FETs results in substantially suppressed static power dissipation at both logic states (i.e., logic “1” and “0”), rail-to-rail input and output capability, well-placed logic transition threshold, and large noise margins.”
Researchers have realized a full family of logic circuits based on their fabrication strategy, including NOT (inverter), NAND, NOR and transmission gates. They also demonstrated multi-stage digital ICs, such as a latch cell and ring oscillators, that can operate both at room temperature and at higher temperatures.
“Our study unambiguously manifests the feasibility of implementing GaN-based complementary logic circuits by demonstrating both a complete set of elementary logic gates and two multistage circuits,” Chen said. “Our findings imply that all GaN-based complementary logic circuits are technically within reach. Firstly, all building blocks are available. Secondly, they can be integrated together for more complex entities.”
“We are going to work on down-scaling the devices, especially the p-channel transistors, for higher operating speed and lower power consumption,” Zheng added. “As these circuits are made on a commercial GaN-on-Si platform for manufacturing GaN power HEMTs, we would seek collaboration with the industry to deploy GaN complementary logic circuits in the peripheral circuits and integrate with the power HEMT for constructing more energy-efficient power conversion systems.”
The research appeared in the journal Nature Electronics.