We report on a 3 nm AlN/GaN HEMT technology for millimeter-wave applications. Electrical characteristics for a 110 nm gate length show a maximum drain current density of 1.2 A/mm, an excellent electron confinement with a low leakage current below 10 μA/mm, a high breakdown voltage and a F T /F max of 63/300 GHz at a drain voltage of 20V. Despite residual trapping effects, state of the art large signal characteristics at 40 GHz and 94 GHz are achieved. For instance, an outstanding power added efficiency of 65% has been reached at V DS = 10V in pulsed mode at 40 GHz. Also, an output power density of 8.3 W/mm at V DS = 40V is obtained associated to a power added efficiency of 50%. At 94 GHz, a record CW output power density for Ga-polar GaN transistors has been reached with 4 W/mm. Additionally, room temperature preliminary robustness assessment at 40 GHz has been performed at V DS = 20V. 24 hours RF monitoring showed no degradation during and after the test.

In this paper, we report on an enhancement of mm-wave power performances with a vertically scaled AlN/GaN heterostructure. An AlGaN back barrier is introduced underneath a non-intentionally doped GaN channel layer, enabling the prevention of punch-through effects and related drain leakage current under a high electric field while using a moderate carbon concentration into the buffer. By carefully tuning the Al concentration into the back barrier layer, the optimized heterostructure offers a unique combination of electron confinement and low trapping effects up to high drain bias for a gate length as short as 100 nm. Consequently, pulsed (CW) Load-Pull measurements at 40 GHz revealed outstanding performances with a record power-added efficiency of 70% (66%) under high output power density at VDS = 20 V. These results demonstrate the interest of this approach for future millimeter-wave applications.

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We report on a vertically scaled AlN/GaN HEMT technology design optimization for millimeter-wave applications. The undoped GaN channel thickness and carbon concentration into the buffer are extensively varied and systematically characterized. It is found that a thin GaN channel, typically below 150 nm improves the electron confinement, but increases the trapping effects, especially when using shorter gate lengths. Moreover, high carbon concentration into the buffer enables not only high electron confinement but also low leakage current under a high electric field at the expense of trapping effects. As a result, the optimum epi-design enabled state-of-the-art RF performances at 40 GHz.