The rapid development of the RF power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance GaN-based RF power devices have made substantial progresses in the last decade This paper attempts to review the latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, to achieve the state-of-the-art microwave and millimeter-wave performance The reliability and manufacturing challenges are also discussed

GaN-Based RF Power Devices and Amplifiers

Failure modes and mechanisms of AlGaN/GaN high-electron-mobility transistors are reviewed. Data from three de-accelerated tests are presented, which demonstrate a close correlation between failure modes and bias point. Maximum degradation was found in "semi-on" conditions, close to the maximum of hot-electron generation which was detected with the aid of electroluminescence (EL) measurements. This suggests a contribution of hot-electron effects to device degradation, at least at moderate drain bias (VDS 30-50 V), new failure mechanisms are triggered, which induce an increase of gate leakage current. The latter is possibly related with the inverse piezoelectric effect leading to defect generation due to strain relaxation, and/or to localized permanent breakdown of the AlGaN barrier layer. Results are compared with literature data throughout the text.

Reliability of GaN High-Electron-Mobility Transistors: State of the Art and Perspectives

GaN HEMT reliability

Long-term ON-state and OFF-state high-electric-field stress results are presented for unpassivated GaN/AlGaN/GaN high-electron-mobility transistors on SiC substrates. Because of the thin GaN cap layer, devices show minimal current-collapse effects prior to high-electric-field stress, despite the fact that they are not passivated. This comes at the price of a relatively high gate-leakage current. Under the assumption that donor-like electron traps are present within the GaN cap, two-dimensional numerical device simulations provide an explanation for the influence of the GaN cap layer on current collapse and for the correlation between the latter and the gate-leakage current. Both ON-state and OFF-state stresses produce simultaneous current-collapse increase and gate-leakage-current decrease, which can be interpreted to be the result of gate-drain surface degradation and reduced gate electron injection. This study shows that although the thin GaN cap layer is effective in suppressing surface-related dispersion effects in virgin devices, it does not, per se, protect the device from high-electric-field degradation, and it should, to this aim, be adopted in conjunction with other technological solutions like surface passivation, prepassivation surface treatments, and/or field-plate gate

Current Collapse and High-Electric-Field Reliability of Unpassivated GaN/AlGaN/GaN HEMTs

High-electric-field degradation phenomena are investigated in GaN-capped AlGaN/GaN HEMTs by comparing experimental data with numerical device simulations. Under power- and OFF-state conditions, 150-h DC stresses were carried out. Degradation effects characterizing both stress experiments were as follows: a drop in the dc drain current, the amplification of gate-lag effects, and a decrease in the reverse gate leakage current. Numerical simulations indicate that the simultaneous generation of surface (and/or barrier) and buffer traps can account for all of the aforementioned degradation modes. Experiments also showed that the power-state stress induced a drop in the transconductance at high gate-source voltages only, whereas the OFF-state stress led to a uniform transconductance drop over the entire gate-source-voltage range. This behavior can be reproduced by simulations provided that, under the power-state stress, traps are assumed to accumulate over a wide region extending laterally from the gate edge toward the drain contact, whereas, under the OFF-state stress, trap generation is supposed to take place in a narrower portion of the drain-access region close to the gate edge and to be accompanied by a significant degradation of the channel transport parameters.

Investigation of High-Electric-Field Degradation Effects in AlGaN/GaN HEMTs

Reliability of large periphery GaN-on-Si HFETs

The degradation of 36mm AlGaN/GaN HFETs-on-Si under DC stress conditions has been studied on a large number of nominally identical devices that were chosen randomly across a production process. A common and primary degradation phenomenon was observed in the devices. A combination of electrical and physical analysis was used to identify a possible failure mechanism related to the Ni/Au Schottky gate diode that appears to explain the degradation of the FET. Based on the analysis, a gate anneal step was added into the fabrication process of AlGaN/GaN HFETs-on-Si. Nominal devices processed using a gate anneal showed (a) a modified gate metal-semiconductor interface (b) forward diode characteristics that are unchanged upon stress and (c) improvement in overall reliability relative to control devices.

GaN-ON-Si Failure Mechanisms and Reliability Improvements

GaN-on-Si transistors are put through an extensive suite of reliability tests in order to accurately assess the drift characteristics of the technology. Data is presented on DC-HTOL, RF-HTOL, and 3-temperature DC tests. In all cases results are compared with the previous generation of technology and reveal improved results. Highlights include an increase in the activation energy from 1.7eV to 2.0eV and a 50% reduction in the 20-year drift rate as predicted by DC-HTOL testing

GaN-On-Si Reliability: A Comparative Study Between Process Platforms

In this paper, the qualification of a production GaN process platform is discussed. Details of the process repeatability, reliability and qualification methodologies are covered in detail. Additionally, concurrent product development efforts are also described. Reliability results include three-temperature DC testing that resulted in an activation energy of 2.0eV and DCHTOL testing demonstrating 20-yr drift rates of less than 3% when operated at 150°C.

Qualification and Reliability of a GaN Process Platform

AlGaN/GaN HFET devices demonstrate remarkable performance. For commercial acceptance of this technology, long-term device stability must meet stringent industry standards. We review the current status of GaN reliability and contrast it with the requirement for commercial viability. Results analyzing degradation pertaining to buffer leakage and gate diode forward failure will be presented.

Device Degradation Phenomena in GaN HFET Technology: Status, Mechanisms, and Opportunities

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