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 letter, we show numerically and experimentally that a positional disorder of a collection of absorbing electromagnetic wave resonators operating in the long wavelength regime dramatically enhances the absorption bandwidth. The demonstration is performed by using single-size ring-shaped thin metal pieces periodically or randomly positioned onto a back-grounded dielectric layer. For periodic array, an optimum in the periodicity is pointed out with a narrow bandwidth, while the increasing influence of coupling effects for resonators in close vicinity explains a three-fold bandwidth enhancement in the case of positional disorder.
In this paper, we propose to optimize Al 0.29 Ga 0.71 N/GaN heterostructures on silicon substrate to obtain high electron mobility transistors featuring highpower/frequency performances. The polarization electric fields are engineered by varying the layer thicknesses of the cap and the barrier, and by changing the type of buffer (GaN or AlGaN). The aim of this paper is to find the best tradeoff between the active layer thickness reduction and the achievement of a reasonable drain current to satisfy the requirements for high performances. The optimum heterostructure device presents an output power density of 1.5 W/mm at 40 GHz, among the best reported on silicon substrate.Index Terms-AlGaN/GaN, high electron mobility transistor (HEMT), Ka-band, millimeter-wave transistor, power density.
We demonstrate the use of femtosecond laser micromachining for ablating macro-sized cavities in crystalline silicon. The method employed is laser milling in which the focused laser beam is raster scanned over the area to be removed. We report the achievement of very high volume ablation rates for the cavity of up to 8.48x10 6 µm 3 s -1 . To achieve such high rates, we make use of a high average power fiber laser source of 1030 nm wavelength and variable per pulse energy of up to 100 µJ. By carefully controlling the process variables such as pulse energy, repetition rate and scanner speed, the tradeoffs between micromachining quality and ablation rate are quantified. The developed process is applied on Siliconon-Insulator (SOI) wafers for improving performance of RF devices. By making use of laser removal and an additional step of selective silicon etch using XeF2, handler silicon is removed completely under RF circuits such as SP9T switch. The local removal of silicon under such circuits completely eliminates the losses and non-linearities caused by the coupling of RF signals to the semi-conducting substrate. Small-signal and large-signal RF measurements are performed before and after substrate removal to quantify the performance gain. The obtained performance after substrate removal is better than specialized RF-SOI substrates such as trap-rich SOI. This is of practical significance for next generation wireless technologies like 5G which operate at higher frequencies with stringent specifications. The proposed method is also potentially useful for fabricating membrane based devices in SOI technology such as pressure sensors.
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