Sub-50 nm Terahertz In0.8Ga0.2As Quantum-Well High-Electron-Mobility Transistors for 6G Applications

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Abstract
We present a systematic study on the gate length ( ${L}_{{g}}\text {)}$ scaling behavior and the impact of the side-recess spacing ( ${L}_{\text {side}}\text {)}$ on dc and high-frequency characteristics of In0.8Ga0.2As quantum-well (QW) high-electron-mobility transistors (HEMTs) with ${L}_{{g}}$ from 10 $\mu $ m to 20 nm, for the purpose of understanding the scaling limit of maximum oscillation frequency ( ${f}_{\text {max}}\text {)}$ and thereby demonstrating terahertz devices. The fabricated In0.8Ga0.2As QW HEMTs with ${L}_{{g}} =20$ nm and ${L}_{\text {side}} =150$ nm exhibited values of drain-induced-barrier-lowering (DIBL) of 60 mV/V, current-gain cutoff frequency ( ${f}_{{T}}\text {)}$ of 0.75 THz, and ${f}_{\text {max}}$ of 1.1 THz, while the device with ${L}_{\text {side}} =50$ nm showed DIBL of 110 mV/V and ${f}_{{T}}$ / ${f}_{\text {max}}$ of 0.72/0.53 THz. It was central to strictly control short-channel effects (SCEs) from the perspective of DIBL to maximize the improvement of ${f}_{\text {max}}$ , as ${L}_{{g}}$ was scaled down deeply. In an effort to understand the ${L}_{{g}}$ scaling behavior of ${f}_{\text {max}}$ , we carried out the small-signal modeling for both types of devices and found that the increase of the intrinsic output conductance ( ${g}_{\text {oi}}\text {)}$ played a critical role in determining ${f}_{\text {max}}$ in short- ${L}_{{g}}$ HEMTs. On the contrary, the fabricated devices with ${L}_{\text {side}} =150$ nm exhibited a tight control of SCEs at ${L}_{{g}}$ of 20 nm. As a result, ${f}_{\text {max}}$ in those devices was boosted to 1.1 THz, and more importantly this high ${f}_{\text {max}}$ was maintained even as ${L}_{{g}}$ was scaled down to 20 nm. The results in this work represent the best balance of ${f}_{{T}}$ and ${f}_{\text {max}}$ in any transistor technology on any material system, displaying both ${f}_{{T}}$ and ${f}_{\text {max}}$ in excess of 700 GHz simultaneously.
Funding Information
  • Samsung Research Funding and Incubation Center of Samsung Electronics (SRFC-IT2201-07)
  • National Research and Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2022M3I8A1078437)

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