High gain 110-GHz low noise amplifier MMICs using 120-nm metamorphic HEMTs and coplanar waveguides

This paper presents the design and performance of 110-GHz low noise amplifier MMICs, based on coplanar technology, and utilizing 120-nm gate-length Metamorphic HEMTs. Thanks to a cascode device, a single-stage amplifier achieves 8-dB small signal gain, with less than 4-dB noise figure at 105 GHz, within a chip size of only 0.725 mm2. The 2- and 3-stage LNAs exhibit small signal gains of more than 15- and 22-dB, respectively over the 100-115 GHz frequency range, with associated measured noise figures of 4.5 dB at 105 GHz; the chip area for these circuits are less than 2- and 3 mm2. To the author’s knowledge, these results are amongst the lowest noise figures reported to date for uniplanar amplifier MMICs operating at these frequencies

Failure signatures on 0.25 mu m GaN HEMTs for high-power RF applications

GaN HEMTs for high-frequency operation are now exhibiting outstanding results in both RF performances and long-term stability, but at the moment there is not a unique indication of which failure mechanism affects the device performances in long-time scale, nor a proved technique which allows to identify the best failure accelerating factor useful for a consistent life-time extraction. In this topic, the paper tries to point-out the efficacy of short-term tests on the investigation of failure modes on two generations of AlGaN/GaN 0.25 mu m gate-length HEMT transistors, highlighting the failure signatures corresponding to the early appearance of the failure modes typical of this technology: (i) a first mode correlated with a limited performance degradation marked by a left threshold voltage shift, and (ii) a second much more degrading failure mode, associated with a right threshold voltage shift. As a result, this simple preliminary investigation gives a consistent evaluation of the really improved reliability behaviour of the new HEMT technology, which shows excellent robustness from high-field to extremely high-power bias conditions, pushing out the more damaging failure mechanism from the typical operating conditions. (C) 2014 Elsevier Ltd. All rights reserved

Proton induced trapping effect on space compatible GaN HEMTs

In order to assess the space compatibility of GaN-HEMT technology, radiation hardness tests are an essential requirement. In this field, Gallium Nitride exhibits excellent robustness with respect to radiation and GaN-based devices are providing very promising results for most of the typical space configurations. Nevertheless, in presence of very high fluence levels, displacement damage takes place reducing the device performances from the static to the dynamic point of view. This paper shows how the combination of radiation hardness tests and the improvement of deep level analysis allows us to quantify the DC and pulsed performance decrease induced by proton irradiation on a technology designed for space applications, highlighting some signatures useful for an early detection of the displacement damage. Results provide a consistent demonstration of (i) threshold voltage positive shift and (ii) trapping effect enhancement correlated with the proton irradiation fluences. (C) 2014 Elsevier Ltd. All rights reserved