Reliability of GaN High-Electron-Mobility Transistors: State of the Art and Perspectives
TL;DR: In this article, failure modes and mechanisms of AlGaN/GaN high-electron-mobility transistors are reviewed, and data from three de-accelerated tests are presented, which demonstrate a close correlation between failure mode and bias point.
Abstract: 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.
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TL;DR: This paper reviews the experimental evidence behind a new failure mechanism recently identified in GaN high-electron mobility transistors subject to electrical stress and suggests several paths to enhance the electrical reliability of GaN HEMTs.
441 citations
TL;DR: The principles, applications, future opportunities, and challenges of piezoelectric biomaterials for medical uses are reviewed thoroughly and can spark a new age in the field of medicine.
Abstract: Recent advances in materials, manufacturing, biotechnology, and microelectromechanical systems (MEMS) have fostered many exciting biosensors and bioactuators that are based on biocompatible piezoelectric materials. These biodevices can be safely integrated with biological systems for applications such as sensing biological forces, stimulating tissue growth and healing, as well as diagnosing medical problems. Herein, the principles, applications, future opportunities, and challenges of piezoelectric biomaterials for medical uses are reviewed thoroughly. Modern piezoelectric biosensors/bioactuators are developed with new materials and advanced methods in microfabrication/encapsulation to avoid the toxicity of conventional lead-based piezoelectric materials. Intriguingly, some piezoelectric materials are biodegradable in nature, which eliminates the need for invasive implant extraction. Together, these advancements in the field of piezoelectric materials and microsystems can spark a new age in the field of medicine.
388 citations
TL;DR: In this paper, the authors present a methodology to study trapping characteristics in GaN HEMTs that is based on current-transient measurements and identify several traps inside the AlGaN barrier layer or at the surface close to the gate edge and in the GaN buffer.
Abstract: Trapping is one of the most deleterious effects that limit performance and reliability in GaN HEMTs. In this paper, we present a methodology to study trapping characteristics in GaN HEMTs that is based on current-transient measurements. Its uniqueness is that it is amenable to integration with electrical stress experiments in long-term reliability studies. We present the details of the measurement and analysis procedures. With this method, we have investigated the trapping and detrapping dynamics of GaN HEMTs. In particular, we examined layer location, energy level, and trapping/detrapping time constants of dominant traps. We have identified several traps inside the AlGaN barrier layer or at the surface close to the gate edge and in the GaN buffer.
370 citations
TL;DR: In this article, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance.
Abstract: GaN and AlGaN have shown great potential in next-generation high-power electronic devices; however, they are plagued by a high density of interface states that affect device reliability and performance, resulting in large leakage current and current collapse. In this review, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance. With this in mind, they present the current research on surface states on GaN and AlGaN and interface states on GaN and AlGaN-based heterostructures. Since GaN and AlGaN are polar materials, both are characterized by a large bound polarization charge on the order of 1013 charges/cm2 that requires compensation. The key is therefore to control the compensation charge such that the electronic states do not serve as electron traps or affect device performance and reliability. Band alignment modeling and measurement can help to determi...
179 citations
TL;DR: In this paper, the surface morphology of electrically stressed AlGaN/GaN high electron mobility transistors was investigated using atomic force microscopy and scanning electron microscopy after removing the gate metallization by chemical etching.
Abstract: We have investigated the surface morphology of electrically stressed AlGaN/GaN high electron mobility transistors using atomic force microscopy and scanning electron microscopy after removing the gate metallization by chemical etching. Changes in surface morphology were correlated with degradation in electrical characteristics. Linear grooves formed along the gate edges in the GaN cap layer for all electrically stressed devices. Beyond a critical voltage that corresponds to a sharp increase in the gate leakage current, pits formed on the surface at the gate edges. The density and size of the pits increase with stress voltage and time and correlate with degradation in the drain current and current collapse. We believe that high mechanical stress in the AlGaN layer due to high-voltage stressing is relieved by the formation of these defects which act as paths for gate leakage current and result in electron trapping and degradation in the transport properties of the channel underneath.
161 citations
References
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16 Jan 2008
TL;DR: The latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, are reviewed to achieve the state-of-the-art microwave and millimeter-wave performance.
Abstract: 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
1,503 citations
"Reliability of GaN High-Electron-Mo..." refers background in this paper
...can represent a major challenge due to the peculiarities of the physics of gallium nitride devices, to material imperfection, to the stability of fabrication processes [29]....
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TL;DR: In this article, the surface potential changes are caused by electrons which tunnel from the gate under high bias stress and get trapped at the surface states near the gate, which correlates with a large improvement in microwave power performance in these devices after passivation.
Abstract: Very slow drain current and surface potential transients have been observed in AlGaN/GaN heterostructure field effect transistors that are subjected to high bias stress. Simultaneous measurements of drain current and surface potential indicate that large change in surface potential after stress is responsible for the reduction in drain current in these devices. Measurements of surface potential profile from the gate edge toward the drain as a function of time indicate that surface potential changes occur mostly near the gate. It is proposed that the surface potential changes are caused by electrons which tunnel from the gate under high bias stress and get trapped at the surface states near the gate. Passivation of the surface with SiN/sub x/ reduces the transient magnitudes to a large extent. This correlates with a large improvement in microwave power performance in these devices after passivation. UV illumination of these devices totally eliminates the drain current and surface potential transients.
231 citations
"Reliability of GaN High-Electron-Mo..." refers background in this paper
...potential of the gate-drain region, with accumulation of negative charge [31]....
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...duced by hydrogen indiffusion, associated with PECVD SiN deposition [31], [32]; reliability is improved if a low-power NH3 plasma treatment is adopted before depositing the SiN passivation layer [33]....
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01 Dec 2006
TL;DR: In this paper, the authors carried out systematic experiments of the electrical reliability of state-of-the-art GaN HEMTs and found that degradation is mostly driven by electric field and that there is a critical electric field below which negligible degradation is observed.
Abstract: We have carried out systematic experiments of the electrical reliability of state-of-the-art GaN HEMTs. We have found that degradation is mostly driven by electric field and that there is a critical electric field below which negligible degradation is observed. Device degradation is associated with the appearance of prominent trapping behavior. Degradation is consistent with a model of defect formation in the AlGaN barrier as a result of the high electric field. We postulate that lattice defects are introduced by excessive stress associated with the inverse piezoelectric effect. Electron trapping at these defects reduces the extrinsic sheet carrier concentration and the maximum drain current.
205 citations
"Reliability of GaN High-Electron-Mo..." refers background in this paper
...[41] P. Saunier, C. Lee, A. Balistreri, D. Dumka, J. Jimenez, H. Q. Tserng, M. Y. Kao, P. C. Chao, A. Souzis, I. Eliashevich, S. Guo, J. del Alamo, J. Joh, and M. Shur, “Progress in GaN performance and reliability,” in Proc....
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...A specific hypothesis has been recently formulated by Joh and del Alamo [43], [44]; according to the proposed mechanism, the electric field in the gate-drain region would increase the strain in the AlGaN/GaN heterojunction (“inverse piezoelectric effect”) eventually resulting in strain relaxation and crystallographic defect formation....
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...[43] J. Joh and J. A. del Alamo, “Mechanisms for electrical degradation of GaN high electron mobility transistors,” in IEDM Tech....
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...[44] J. Joh and J. A. del Alamo, “Gate current degradation mechanisms of GaN high electron mobility transistors,” in IEDM Tech....
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...Joh and del Alamo [44] have found that there is a critical gate-drain voltage which triggers this effect, around VGD ≈ 20−30 V for the tested devices....
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01 Dec 2006
TL;DR: The performance of novel AlInN/GaN HEMTs for high power / high temperature applications is discussed in this paper, where the maximum output current density of more than 2 A/mm at room temperature and more than 3 A /mm at 77 K have been obtained even with sapphire substrates.
Abstract: The performance of novel AlInN/GaN HEMTs for high power / high temperature applications is discussed. With 0.25 mum gate length the highest maximum output current density of more than 2 A/mm at room temperature and more than 3 A/mm at 77 K have been obtained even with sapphire substrates. Cut-off frequencies were fT = 50 GHz and fMAX = 60 GHz for 0.15 mum gate length without T-gate. Pulsed measurements reveal a less unstable surface than in the case of AlGaN/GaN structures. Although limited by buffer layer leakage, with field plates a maximum drain bias of 100 V has been reached with these devices. The high chemical stability of this unstrained heterostructure and its surface has been demonstrated with successful operation at 1000 degC in vacuum
171 citations
"Reliability of GaN High-Electron-Mo..." refers background in this paper
...InAlN/GaN HEMTs have already demonstrated high breakdown voltage, low leakage current, and high-temperature operation [49]....
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TL;DR: In this paper, an analysis of ON-state and OFF-state high-electric-field stress results for unpassivated GaN/AlGaN/GaN high-electron-mobility transistors on SiC substrates is presented.
Abstract: 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
163 citations
"Reliability of GaN High-Electron-Mo..." refers background in this paper
...Two-dimensional numerical device simulations [14], [15], [30] indicated that gate-lag effects should be ascribed to...
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...Increase in Schottky barrier height consequent to high-temperature dc testing was also described in [14] and [15]....
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