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In order to further improve the electrical characteristics of AlGaN-buffer devices, we propose a new in situ SiN/AlGaN-sandwich-barrier (SWB)/GaN/Al0.05GaN high-electron mobility transistors (HEMTs). The dc, channel temperature, and RF temperature of the proposed AlGaN-buffer devices have been systematically studied and analyzed. The SWB structure can effectively reduce the peak value of the electric field, thus effectively reducing the self-heating effect and improving the breakdown characteristics. Through the channel temperature extraction method of pulsed IV and TCAD thermal simulation, the channel temperature of devices with different barrier structures is compared and analyzed, which proves that SWB structure can effectively reduce the channel temperature of devices. Due to the more obvious potential modulation effect between gate and drain, the ƒmax of device can improve more effectively with the increase of drain voltage. In addition, load-pull measurement at 10 GHz revealed that a saturated power density increased from 7.3 to 8.4 W/mm and an associated PAE increased from 24.9% to 29.4%. [ABSTRACT FROM AUTHOR]

A hybrid Schottky–ohmic drain technology for millimeter-wave (mmW) AlGaN/GaN high-electron-mobility transistors (HEMTs) is proposed. The Schottky metal extension in the ohmic region of drain reduces the actual source–drain spacing, resulting in a smaller ON-resistance and a higher maximum current. Extended Schottky metal in the drain region modulates the electric-field distribution, thereby leading to an improved breakdown voltage, suppressed current collapse, and high reliability. Compared with the ohmic drain, the current gain cutoff frequency (${f}_{T}$) was improved from 64 to 76 GHz, and the maximum oscillation frequency (${f}_{\text {max}}$) was improved from 125 to 157 GHz, resulting from the decreased parasitic drain resistance (${R}_{d}$). Moreover, large-signal measurements in continuous wave (CW) at 30 GHz demonstrated a peak power-added efficiency (PAE) of 45.5% and a saturated output power density (${P}_{\text {sat}}$) of 8.5 W/mm at ${V}_{\text {ds}}= {30}$ V. In addition, the direct current (DC) and radio frequency (RF) characteristics showed a negligible degradation after large-signal measurements at 30 GHz. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Si-rich SiN/Si3N4 bilayer passivation were studied in this article. The use of a Si-rich SiN interlayer leads to improved channel transport property, current collapse, power performance, and temperature-dependent stability. Devices without Si-rich SiN interlayer passivation exhibit an increase in the gate leakage current by over three orders of magnitudes with temperature increasing from 300 to 420 K, leading to an increase in a current collapse from 9.7% to 24.7%, while the devices with Si-rich SiN passivation exhibit a weak temperature dependence of leakage current and a constant current collapse about 5%. Small signal characterization shows that Si-rich SiN passivation results in a remarkable decrease in the effective gate length by ~15% with temperature up to 420 K. At 17 GHz, devices with Si-rich SiN interlayer passivation exhibit an output power density of 7 W/mm and a peak power-added efficiency (PAE) of 56%. The improved power performance of devices using Si-rich SiN interlayer passivation is attributed to the suppressed current collapse and superior device stability under high channel temperature. [ABSTRACT FROM AUTHOR]

The submicrometer gate HEMT is fabricated with an ultrathin-barrier (UTB) AlGaN/gallium nitride (GaN) combined with in situ SiN passivation. The sheet resistance of the UTB Al0.2Ga0.8N (4 nm)/GaN heterostructure is effectively reduced by the SiNx passivation layer grown by metal organic chemical vapor deposition (MOCVD), from 6500 to $312~ \Omega $ /⬜. With the 20-nm stress-engineered in situ SiN, the device not only provides a large output current of 1.05 A/mm but also demonstrates promising potential on the RF applications, which gives AlGaN material two records high cutoff frequency ${f} _{\text {T}}/{f} _{\text {max}}$ of 157 GHz/334 GHz for 100-nm gated device and 211 GHz/379 GHz for 70-nm gated device. During the continuous wave (CW) power measurement at 30 GHz, the 70-nm devices exhibit a large output power of 4.6 W/mm associated with a peak power-added efficiency (PAE) of 48.1% and a gain of 11.6 dB (${V} _{\text {ds}} =20$ V), and a high PAE of 53.8% with an output power density of 1.9 W/mm and a gain of 10.8 dB (${V} _{\text {ds}} =10$ V), respectively. The huge potential of the UTB-AlGaN/GaN is demonstrated for high-frequency and large-output power applications when it is combined with the in situ SiN, which is necessary for future communication systems. [ABSTRACT FROM AUTHOR]

In this letter, we explore the impact of configuration parameters for Fin-like high-electron-mobility transistors (HEMTs) formed by partially etching barrier under the gate on improving transconductance (Gm) and cutoff frequency (ƒT) linearity. It is found that the Gm profile for Fin-like HEMTs can be optimized by choosing appropriate device parameters, including the etching depth (HR) and width (WR) of recess region, as well as the duty ratio (α) of the planar elements in a periodic unit along the gate width. In general, not only does WR affect the gate voltage swing (GVS) but also HR and α have an important role in Gm profile flatness. In addition, the fabricated Fin-like HEMTs shows a GVS of the transconductance plateau larger than 5.6 V and a constant ƒT/ƒmax of 45 GHz/65 GHz over a wide gate voltage range. Furthermore, the proposed architecture also features an exceptional linearity performance at 8 GHz with an output third-order intercept point (OIP3) of 38.5 dBm, whereas that of the planar HEMT is 31 dBm. The device demonstrated in this article has great potential to be a new paradigm for future wireless communication systems where high linearity is essential. [ABSTRACT FROM AUTHOR]