Scaled Self-Aligned N-Polar GaN/AlGaN MIS-HEMTs With $f_{T}$ of 275 GHz

Abstract

In this letter, we demonstrate state-of-the-art performance from N-polar GaN/AlGaN metal-insulator-semiconductor high-electron-mobility transistors. Self-aligned gate-first process was used for the fabrication of transistors. Graded InGaN and InN contact layers were used to achieve low ohmic contact resistance. The GaN channel thickness was scaled to 7 nm from previous generation of N-polar GaN devices to improve the aspect ratio and hence achieve better small-signal performance. The devices reported f T of 210 GHz for L G = 30 nm. To further improve the device performance, SiN sidewall spacers were etched and replaced with air gaps resulting in further boost in f T to a state-of-the-art value of 275 GHz.

Fabrication and Characterization of Gate-Last Self-Aligned AlN/GaN MISHEMTs With <italic>In Situ</italic> SiN_{<italic>x</italic>} Gate Dielectric

“…Even when L G scales down to 30 nm for an optimized gate geometry, the extra gate fringing capacitance induced by the dielectrics surrounding the gate is still not the major factor impacting the device performance. It has been reported that the f T for the devices with a relatively high-κ SiN x or SiON layer surrounding the gate was only ∼23% lower than that of the devices with the gate surrounding dielectrics removed [5], [8]. One can expect that carefully optimizing the gate geometry and using low-κ dielectrics under the gate head can further reduce the parasitic gate fringing capacitance.…”

“…ohmic contact regrowth [2]- [9], [12], [13], advanced T -gate fabrication process [2]- [6], [9], or a gate-first self-aligned approach [4], [8]. f T and f max of GaN HEMTs can be primarily improved through the downscaling of device geometry, whereas the aspect ratio (gate length and gate-to-channel distance) has to be maintained for the mitigation of short-channel effects.…”

“…The devices also feature precisely defined gate-to-regrown-S/D distances (L GS /L GD ) by the SiN x sidewall spacers. Compared with the gate-first self-aligned process [4], [8], the T -shaped gate formed in this gate-last approach enables high f T and f max simultaneously. In addition, the demonstrated gate-last self-aligned process is 0018-9383 © 2015 IEEE.…”

Very high channel conductivity in ultra-thin channel N-polar GaN/(AlN, InAlN, AlGaN) high electron mobility hetero-junctions grown by metalorganic chemical vapor deposition

“…With the development of epitaxial growth and processing techniques, both excellent highfrequency and RF power performance have been achieved in N-polar GaN/AlGaN HEMTs. [4][5][6] Specifically, the gate length (L g ) of GaN HEMTs has been aggressively scaled down to improve the high frequency performance of transistors. However, various non-idealities including short-channel effects have restricted the performance of ultra-scaled GaN HEMTs.…”

Converse piezoelectric effect induced misfit dislocation scattering in metal/AlGaN/GaN heterostructures

“…[http://dx.doi.org/10.1063/1.4799286] AlGaN/GaN heterostructure-based high electron mobility transistors have attracted considerable attention for their excellent performance in high-frequency and high-power applications. [1][2][3][4] However, heteroepitaxial AlGaN layers grown on GaN substrates are subjected to significant mechanical stresses because of the large lattice mismatch between AlN and GaN. The existence of biaxial stress results in the appearance of in-plane strain.…”