High-frequency enhancement-mode millimeterwave AlGaN/GaN HEMT with an f T/f max over 100 GHz/200 GHz* *Project supported by the National Key Research and Development Program of China (Grant No. 2020YFB1804902), the National Natural Science Foundation of China (Grant No. 61904135), the China Postdoctoral Science Foundation (Grant Nos. 2018M640957 and BX20200262), and the Natural Science Foundation of Shaanxi Province, China (Grant No.

Abstract

Ultra-thin barrier (UTB) 4-nm-AlGaN/GaN normally-off high electron mobility transistors (HEMTs) having a high current gain cut-off frequency (f T) are demonstrated by the stress-engineered compressive SiN trench technology. The compressive in-situ SiN guarantees the UTB-AlGaN/GaN heterostructure can operate a high electron density of 1.27 × 1013 cm−2, a high uniform sheet resistance of 312.8 Ω/□, but a negative threshold for the short-gate devices fabricated on it. With the lateral stress-engineering by full removing in-situ SiN in the 600-nm SiN trench, the short-gated (70 nm) devices obtain a threshold of 0.2 V, achieving the devices operating at enhancement-mode (E-mode). Meanwhile, the novel device also can operate a large current of 610 mA/mm and a high transconductance of 394 mS/mm for the E-mode devices. Most of all, a high f T/f max of 128 GHz/255 GHz is obtained, which is the highest value among the reported E-mode AlGaN/GaN HEMTs. Besides, being together with the 211 GHz/346 GHz of f T/f max for the D-mode HEMTs fabricated on the same materials, this design of E/D-mode with the realization of f max over 200 GHz in this work is the first one that can be used in Q-band mixed-signal application with further optimization. And the minimized processing difference between the E- and D-mode designs the addition of the SiN trench, will promise an enormous competitive advantage in the fabricating costs.