High Performance and Highly Robust AlN/GaN HEMTs for Millimeter-Wave Operation

Abstract

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.

First RF Power Operation of AlN/GaN/AlN HEMTs With >3 A/mm and 3 W/mm at 10 GHz

“…By significantly enhancing device breakdown, field plates also increase output power, but due to the complexity of properly implementing field plates in highly-scaled RF devices [6], it can be valuable, for the purpose of evaluating the potential for a new heterostructure, to compare devices without field-shaping. Without field plates, the AlGaN/GaN and other heterostructures have been assessed, with AlGaN/GaN HEMTs showing 10.5 W/mm at 40 GHz [7], AlN/GaN HEMTs demonstrating 4 W/mm at 94 GHz [8], and InAlGaN barrier HEMTs showing 3 W/mm at 96 GHz [9]. Most notably, N-polar GaN HEMTs have demonstrated over 8 W/mm at the range of 10 to 94 GHz [10]- [12].…”

Short Term Reliability and Robustness of ultra-thin barrier, 110 nrn-gate AlN/GaN HEMTs

“…A 10 nm in-situ SiN layer was grown to protect the surface and reduce surface trapping. Further experimental details can be found in [5]. The devices under test are two-fingers devices with gate length (LG) of 0.11 µm, gate width (WG) of 2 × 50 µm; gate-drain distances (LGD) are designed to be 0.5 µm, 1.5 µm and 2.5 µm.…”

“…Cut off frequency (FT) and maximum oscillation frequency (Fmax) are respectively 63 GHz and 300 GHz, and can be achieved at VDS = 20V. A thorough DC and RF characterization is discussed in [5].…”

“…Therefore, it is necessary to optimize the epilayer design and the device layout, and reduce the gate to channel distance [3]. Recently, AlN/GaN heterostructures have been proven to be able to reach a maximum current of 2.3 A/mm and peak transconductance of 480 mS/mm [4], and state-of-the-art PAE over > 65% at 40 GHz [5], by adopting an ultra-thin (3-4 nm) AlN barrier. Good stability and robustness have been achieved by AlN/GaN/AlGaN HEMTs for Ka band operation during constant voltage stress tests [6].…”

On the performance of GaN‐on‐Silicon, Silicon‐Carbide, and Diamond substrates

“…In addition to that, the acceptor traps are responsible for the anomalous kink effect in the drain current of GaN‐HEMT . The traps could also exist in the surface, which causes the gate‐lag that limits the maximum drain current and reduces the on‐resistance . The carrier‐scattering reduces the electron velocity/mobility in the channel and thereby reduces the drain current and cut‐off frequency.…”