Improved dispersion control and gate stability in scaled RF GaN HEMTs using ALD TiN gate

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In this work, atomic layer deposition (ALD) TiN is investigated as the Schottky T-gate electrode for scaled Ga-polar AlGaN/GaN high-electron-mobility transistors (HEMTs), and its performance is compared with Ni/Au-gate devices fabricated under identical process conditions to elucidate the benefits of TiN gates for electrical, thermal, and reliability performance in RF applications. The TiN-gate devices achieve an on-state drain current density of 1.25 A/mm and a peak transconductance of 0.28 S/mm at Vgs = −4 V. Pulsed IV measurements at Vgsq = −6 V and Vdsq = 20 V show only 4.3% current collapse, markedly lower than the 22.6% observed for Ni/Au-gate devices, indicating superior large-signal stability. A breakdown voltage of ∼50 V (∼1 MV/cm) is achieved under pinch-off, with post-measurement recovery confirming a soft-breakdown mechanism without permanent degradation. With a 120 nm gate length, an ft/fmax of 66/87 GHz is achieved at room temperature and 37/60 GHz at 150 °C. Small-signal analysis reveals that high-temperature degradation is dominated by phonon-limited carrier transport, while TiN gate capacitances remain stable. Under prolonged stress (Vds = 18 V, Vgs = −4 V, 1800 s), TiN devices show only ∼1.8% drain current variation, significantly lower than Ni/Au-gate counterparts. Statistical analysis of ten devices confirms reproducibility with an average variation of 2.5% (σ = 1.4%). These results demonstrate the promise of ALD TiN Schottky gates for reliable scaled RF GaN HEMTs.