A Study of Effect of Stress on the AlGaN/GaN High Electron Mobility Transistor PDF Download
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Author: 徐啓桓
Publisher:
ISBN:
Category :
Languages : en
Pages : 70
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Book Description
Author: 徐啓桓
Publisher:
ISBN:
Category :
Languages : en
Pages : 70
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Author: Sameer Jayanta Joglekar
Publisher:
ISBN:
Category :
Languages : en
Pages : 161
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Book Description
Gallium Nitride (GaN) belongs to a class of materials called wide band-gap semiconductors. In recent years, the versatile nature of this material has been exploited for a wide range of applications from solid state lighting to RF and microwave communication, as well as high power switching. The first part of this thesis discusses planar AlGaN/GaN transistors. GaN is a piezoelectric material, and changes in mechanical stress result in a change in the charge density which in turn affects the maximum current in AlGaN/GaN transistors. Finite element modelling techniques were applied to quantify the mechanical stress distribution in planar AlGaN/GaN RF transistors resulting from device fabrication, and operation in the on- and off-state. Thereafter, two important surface and interface effects were studied in this thesis. In the first one, the impact of surface cleanings, surface treatments and plasma-based dry etch conditions on two different types of ohmic contact technologies was investigated. Contact resistance measurements were correlated with surface characterization results. The second was that of interface positive charges at the Al2O3-GaN interface and the increase in electron density in the device resulting from them. In both these problems, a combination of device electrical measurements and material characterization techniques was used to establish direct correlations between device behavior and material properties. The second part of the thesis deals exclusively with nano-ribbon (NR) or fin-like AlGaN/GaN transistors. Fundamental transport properties of charge density and mobility in NR devices were studied in order to understand the difference in behavior of these devices from planar devices. The influence of passivation films on the charge density in these structures was investigated, using Al2O3 passivation as a specific example. Electron mobility degradation due to sidewall-scattering in NR devices was quantified using different mobility extraction methods based on device measurements. The thesis concludes with a potential application of NR AlGaN/GaN transistors for high linearity power amplification. A new kind of transistor with varying threshold voltages along the gate width is proposed to improve the DC and RF linearity of GaN-based devices.
Author:
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ISBN:
Category :
Languages : en
Pages : 4
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Current collapse is observed to be induced in AlGaN/GaN high-electron-mobility transistors as a result of short-term bias stress. This effect was seen in devices grown by both metalorganic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). The induced collapse appears to be permanent and can be reversed by SiN passivation. The traps responsible for the collapse have been studied by photoionization spectroscopy. For the MOCVD-grown devices, the same traps cause the collapse in both unstressed and stressed devices. These effects are thought to result from hot-carrier damage during stress.
Author: D. Nirmal
Publisher: CRC Press
ISBN: 0429862520
Category : Science
Languages : en
Pages : 434
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Book Description
This book focusses on III-V high electron mobility transistors (HEMTs) including basic physics, material used, fabrications details, modeling, simulation, and other important aspects. It initiates by describing principle of operation, material systems and material technologies followed by description of the structure, I-V characteristics, modeling of DC and RF parameters of AlGaN/GaN HEMTs. The book also provides information about source/drain engineering, gate engineering and channel engineering techniques used to improve the DC-RF and breakdown performance of HEMTs. Finally, the book also highlights the importance of metal oxide semiconductor high electron mobility transistors (MOS-HEMT). Key Features Combines III-As/P/N HEMTs with reliability and current status in single volume Includes AC/DC modelling and (sub)millimeter wave devices with reliability analysis Covers all theoretical and experimental aspects of HEMTs Discusses AlGaN/GaN transistors Presents DC, RF and breakdown characteristics of HEMTs on various material systems using graphs and plots
Author: Amit Gupta
Publisher:
ISBN:
Category :
Languages : en
Pages : 143
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Book Description
AlGaN/GaN HEMT technology is promising for RF and high power applications. However commercial usability of this technology is currently hindered because of its limited electrical reliability which still remains a major concern. AlGaN/GaN HEMTs have been shown to degrade irreversibly under typical device operation and there is widespread disagreement on the underlying fundamental physics for the observed device degradation. Electrical degradation in AlGaN/GaN HEMTs due to DC stressing is studied typically by performing electrical step stress tests and a critical voltage is determined. Device degradation is characterized by changes measured in electrical parameters, such as increase in Rs and RD, decrease in IDsat, decrease in gm, Vt shift and sub-threshold change. The widely accepted theory attributes such degradation to the inverse piezoelectric effect. Electric field due to applied bias generates biaxial tensile stress which together with intrinsic stress from lattice mismatch increases the elastic energy of AlGaN layer.
Author: Michael Hosch
Publisher: Cuvillier Verlag
ISBN: 3736938446
Category : Technology & Engineering
Languages : en
Pages : 129
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Book Description
This thesis deals with the analysis and optimization of some of the most prominent non-ideal effects in AlGaN/GaN high electron mobility transistors used in microwave applications as well as the optimization of the RF gain. The effect of current collapse, the root cause of leakage currents as well as field-dependent self-heating effects have been investigated by eletrical characterization using well established techniques and have been analyzed using 2-dimensional physical device simulations. It will be shown that the origin of all effects is strongly related to the device surface and some are even competing effects making device optimization a challenge. However, a detailed localization of the regions affecting device performance will be given leading to a better understanding for fabrication process optimization. Finally, I simulation study is conducted giving suggestions for RF gain improvement based on very simple device layout variations.
Author: Eldad Bahat-Treidel
Publisher: Cuvillier Verlag
ISBN: 3736940947
Category : Science
Languages : en
Pages : 220
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Book Description
Gallium nitride (GaN)-based High Electron Mobility Transistors (HEMTs) for high voltage, high power switching and regulating for space applications are studied in this work. Efficient power switching is associated with operation in high OFF-state blocking voltage while keeping the ON-state resistance, the dynamic dispersion and leakage currents as low as possible. The potential of such devices to operate at high voltages is limited by a chain of factors such as subthreshold leakages and the device geometry. Blocking voltage enhancement is a complicated problem that requires parallel methods for solution; epitaxial layers design, device structural and geometry design, and suitable semiconductor manufacturing technique. In this work physical-based device simulation as an engineering tool was developed. An overview on GaN-based HEMTs physical based device simulation using Silvaco-“ATLAS” is given. The simulation is utilized to analyze, give insight to the modes of operation of the device and for design and evaluation of innovative concepts. Physical-based models that describe the properties of the semiconductor material are introduced. A detailed description of the specific AlGaN/GaN HEMT structure definition and geometries are given along with the complex fine meshing requirements. Nitride-semiconductor specific material properties and their physical models are reviewed focusing on the energetic band structure, epitaxial strain tensor calculation in wurtzite materials and build-in polarization models. Special attention for thermal conductivity, carriers’ mobility and Schottky-gate-reverse-bias-tunneling is paid. Empirical parameters matching and adjustment of models parameters to match the experimental device measured results are discussed. An enhancement of breakdown voltage in AlxGa1-xN/GaN HEMT devices by increasing the electron confinement in the transistor channel using a low Al content AlyGa1-yN back-barrier layer structure is systematically studied. It is shown that the reduced sub-threshold drain-leakage current through the buffer layer postpones the punch-through and therefore shifts the breakdown of the device to higher voltages. It is also shown that the punch-through voltage (VPT) scales up with the device dimensions (gate to drain separation). An optimized electron confinement results both, in a scaling of breakdown voltage with device geometry and a significantly reduced sub-threshold drain and gate leakage currents. These beneficial properties are pronounced even further if gate recess technology is applied for device fabrication. For the systematic study a large variations of back-barrier epitaxial structures were grown on sapphire, n-type 4H-SiC and semi-insulating 4H-SiC substrates. The devices with 5 μm gate-drain separation grown on n-SiC owning Al0.05Ga0.95N and Al0.10Ga0.90N back-barrier exhibit 304 V and 0.43 m × cm2 and 342 V and 0.41 m × cm2 respectively. To investigate the impact of AlyGa1-yN back-barrier on the device properties the devices were characterized in DC along with microwave mode and robustness DC-step-stress test. Physical-based device simulations give insight in the respective electronic mechanisms and to the punch-through process that leads to device breakdown. Systematic study of GaN-based HEMT devices with insulating carbon-doped GaN back-barrier for high voltage operation is also presented. Suppression of the OFF-state sub-threshold drain leakage-currents enables breakdown voltage enhancement over 1000 V with low ON-state resistance. The devices with 5 μm gate-drain separation on SI-SiC and 7 μm gate-drain separation on n-SiC exhibit 938 V and 0.39 m × cm2 and 942 V and 0.39 m × cm2 respectively. Power device figure of merit of ~2.3 × 109 V2/-cm2 was calculated for these devices. The impacts of variations of carbon doping concentration, GaN channel thickness and substrates are evaluated. Trade-off considerations in ON-state resistance and of current collapse are addressed. A novel GaN-based HEMTs with innovative planar Multiple-Grating-Field-Plates (MGFPs) for high voltage operation are described. A synergy effect with additional electron channel confinement by using a heterojunction AlGaN back-barrier is demonstrated. Suppression of the OFF-state sub-threshold gate and drain leakage-currents enables breakdown voltage enhancement over 700 V and low ON-state resistance of 0.68 m × cm2. Such devices have a minor trade-off in ON-state resistance, lag factor, maximum oscillation frequency and cut-off frequency. Systematic study of the MGFP design and the effect of Al composition in the back-barrier are described. Physics-based device simulation results give insight into electric field distribution and charge carrier concentration depending on field-plate design. The GaN superior material breakdown strength properties are not always a guarantee for high voltage devices. In addition to superior epitaxial growth design and optimization for high voltage operation the device geometrical layout design and the device manufacturing process design and parameters optimization are important criteria for breakdown voltage enhancement. Smart layout prevent immature breakdown due to lateral proximity of highly biased interconnects. Optimization of inter device isolation designed for high voltage prevents substantial subthreshold leakage. An example for high voltage test device layout design and an example for critical inter-device insulation manufacturing process optimization are presented. While major efforts are being made to improve the forward blocking performance, devices with reverse blocking capability are also desired in a number of applications. A novel GaN-based HEMT with reverse blocking capability for Class-S switch-mode amplifiers is introduced. The high voltage protection is achieved by introducing an integrated recessed Schottky contact as a drain electrode. Results from our Schottky-drain HEMT demonstrate an excellent reverse blocking with minor trade-off in the ON-state resistance for the complete device. The excellent quality of the forward diode characteristics indicates high robustness of the recess process. The reverse blocking capability of the diode is better than –110 V. Physical-based device simulations give insight in the respective electronic mechanisms. Zusammenfassung In dieser Arbeit wurden Galliumnitrid (GaN)-basierte Hochspannungs-HEMTs (High Electron Mobility Transistor) für Hochleistungsschalt- und Regelanwendungen in der Raumfahrt untersucht. Effizientes Leistungsschalten erfordert einen Betrieb bei hohen Sperrspannungen gepaart mit niedrigem Einschaltwiderstand, geringer dynamischer Dispersion und minimalen Leckströmen. Dabei wird das aus dem Halbleitermaterial herrührende Potential für extrem spannungsfeste Transistoren aufgrund mehrerer Faktoren aus dem lateralen und dem vertikalen Bauelementedesign oft nicht erreicht. Physikalisch-basierte Simulationswerkzeuge für die Bauelemente wurden daher entwickelt. Die damit durchgeführte Analyse der unterschiedlichen Transistorbetriebszustände ermöglichte das Entwickeln innovativer Bauelementdesignkonzepte. Das Erhöhen der Bauelementsperrspannung erfordert parallele und ineinandergreifende Lösungsansätze für die Epitaxieschichten, das strukturelle und das geometrische Design und für die Prozessierungstechnologie. Neuartige Bauelementstrukturen mit einer rückseitigen Kanalbarriere (back-barrier) aus AlGaN oder Kohlenstoff-dotierem GaN in Kombination mit neuartigen geometrischen Strukturen wie den Mehrfachgitterfeldplatten (MGFP, Multiple-Grating-Field-Plate) wurden untersucht. Die elektrische Gleichspannungscharakterisierung zeigte dabei eine signifikante Verringerung der Leckströme im gesperrten Zustand. Dies resultierte bei nach wie vor sehr kleinem Einschaltwiderstand in einer Durchbruchspannungserhöhung um das etwa Zehnfache auf über 1000 V. Vorzeitige Spannungsüberschläge aufgrund von Feldstärkenspitzen an Verbindungsmetallisierungen werden durch ein geschickt gestaltetes Bauelementlayout verhindert. Eine Optimierung der Halbleiterisolierung zwischen den aktiven Strukturen führte auch im kV-Bereich zu vernachlässigbaren Leckströme. Während das Hauptaugenmerk der Arbeit auf der Erhöhung der Spannungsfestigkeit im Vorwärtsbetrieb des Transistors lag, ist für einige Anwendung auch ein rückwärtiges Sperren erwünscht. Für Schaltverstärker im S-Klassenbetrieb wurde ein neuartiger GaN-HEMT entwickelt, dessen rückwärtiges Sperrverhalten durch einen tiefgelegten Schottkykontakt als Drainelektrode hervorgerufen wird. Eine derartige Struktur ergab eine rückwärtige Spannungsfestigkeit von über 110 V.
Author: Erica Ann Douglas
Publisher:
ISBN:
Category :
Languages : en
Pages :
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High reverse bias of the gate has been shown to induce the inverse piezoelectric effect, resulting in a sharp increase in gate leakage current due to crack formation. The introduction of elevated temperatures during high reverse gate bias indicated that device failure is due to the breakdown of an unintentional gate oxide. RF stress of AlGaN/GaN HEMTs showed comparable critical voltage breakdown regime as that of similar devices stressed under dc conditions. Though RF device characteristics showed stability up to a drain bias of 20 V, Schottky diode characteristics degraded substantially at all voltages investigated. Results from both dc and RF stress conditions, under several bias regimes, confirm that the primary root for stress induced degradation was due to the Schottky contact.
Author: Yufei Wu (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 129
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Book Description
AlGaN/GaN High Electron Mobility Transistors (HEMTs) have enjoyed tremendous market growth in RF power amplifiers over the past decades. In the quest for enhancing the operating frequency of GaN HEMTs, there has been a great effort to scale down the gate length. Maintaining acceptable short-channel effects requires shrinking the barrier thickness at the same time. However, a limitation exists since there is a minimum barrier thickness that is needed to obtain a sufficiently high two-dimensional electron gas density. One possible solution to this problem is the use of a new barrier material, i.e., InAlN. Due to its high spontaneous polarization, if InAlN is used as a barrier material in GaN HEMTs, a much smaller layer thickness is required compared with conventional HEMTs. This enables further barrier thickness scaling and therefore gate length scaling and a higher frequency response. However, as a relatively new structure, reliability studies of InAlN/GaN HEMTs are still lacking. Solid reliability is essential before the wide commercial deployment of this new technology. This thesis investigates the most relevant degradation mechanisms under important stress regimes, aiming at building a comprehensive understanding of InAIN/GaN HEMT reliability. Through investigating various voltage, current, and temperature stress levels, we have identified one recoverable degradation mechanism as well as three permanent degradation mechanisms. Under high drain voltage, hot-electron trapping results in temporary drain current decrease and drain resistance increase. In addition, under high drain voltage but relatively low drain current level, permanent negative threshold voltage shift and drain current increase have been observed. We attribute the phenomena to dehydrogenation of pre-existing defects in GaN channel by hot electrons. Under high positive gate bias, defect generation in the AIN interlayer due to high electric field across AIN has proven to be responsible for the observed gate leakage current increase. Also, under high-power stress conditions, positive threshold voltage shift and maximum drain current decrease have been consistently observed. We verified through both thermal stress experiments and Transmission Electron Microscopy (TEM) analysis that Schottky gate sinking is the cause. This work provides fundamental understanding of potential reliability concerns in InAlN/GaN HEMTs and is essential in accelerating the future commercialization of this promising technology.
Author: Matteo Meneghini
Publisher: Springer
ISBN: 3319431994
Category : Technology & Engineering
Languages : en
Pages : 383
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Book Description
This book presents the first comprehensive overview of the properties and fabrication methods of GaN-based power transistors, with contributions from the most active research groups in the field. It describes how gallium nitride has emerged as an excellent material for the fabrication of power transistors; thanks to the high energy gap, high breakdown field, and saturation velocity of GaN, these devices can reach breakdown voltages beyond the kV range, and very high switching frequencies, thus being suitable for application in power conversion systems. Based on GaN, switching-mode power converters with efficiency in excess of 99 % have been already demonstrated, thus clearing the way for massive adoption of GaN transistors in the power conversion market. This is expected to have important advantages at both the environmental and economic level, since power conversion losses account for 10 % of global electricity consumption. The first part of the book describes the properties and advantages of gallium nitride compared to conventional semiconductor materials. The second part of the book describes the techniques used for device fabrication, and the methods for GaN-on-Silicon mass production. Specific attention is paid to the three most advanced device structures: lateral transistors, vertical power devices, and nanowire-based HEMTs. Other relevant topics covered by the book are the strategies for normally-off operation, and the problems related to device reliability. The last chapter reviews the switching characteristics of GaN HEMTs based on a systems level approach. This book is a unique reference for people working in the materials, device and power electronics fields; it provides interdisciplinary information on material growth, device fabrication, reliability issues and circuit-level switching investigation.
