Tesi sul tema "HEMT AlN/GaN"

During the last decade, AlGaN High Electron Mobility Transistors (HEMTs) have been intensively studied because their fundamental electrical properties make them attractive for highpower microwave device applications. Despite much progress, AlGaN HEMTs are far from fully understood and judged by the number of published papers the understanding of advanced structures is even poorer. This work is an exploration of the electrical and structural properties of advanced HEMT structure containing AlN exclusionlayer and double heterojunctions. These small modifications had great impact on the electrical properties.

In this work, AlGaN HEMT structures grown on SiC substrates by a hot-wall MOCVD have been characterized for their properties using optical microscopy, scanning electron microscopy, transmission electron microscopy, capacitance/voltage, eddy-current resistivity, and by homebuilt epi-thickness mapping equipment.

A high electron mobility of 1700 [cm2/Vs] was achieved in an AlN exclusion-layer HEMT. A similar electron mobility of 1650 [cm2/Vs] was achieved in a combination of a double heterojunction and exclusion-layer structure. The samples had approximately the same electron mobility but with a great difference: the exclusion-layer version gave a sheet carrier density of 1.58*1013 [electrons/cm2] while the combination of double heterojunction and exclusion-layer gave 1.07*1013 [electrons/cm2]. A second 2DEG was observed in most structures, but not all, but was not stable with time.

The structures we grew during this work were also simulated using a one-dimensional Poisson-Schrödinger solver and the simulated electron densities were in fairly good agreement with the experimentally obtained. III-nitride materials, the CVD concept, and the onedimensional solver are shortly explained.

La filière GaN est stratégique pour l'Union Européenne car elle permet d'améliorer la puissance et le rendement des systèmes radar et de télécommunication, notamment dans les bandes S à Ka (jusqu'à 30 GHz). Pour répondre aux besoins des futures applications, telles que la 5G et les systèmes militaires, le développement des technologies GaN vise à augmenter les fréquences jusqu'aux ondes millimétriques. Cela nécessite d'optimiser l'épitaxie et la réduction de la longueur de grille à moins de 150 nm, ainsi que l'utilisation de barrières ultrafines (<10 nm) pour éviter les effets de canaux courts. La substitution de la barrière AlGaN par du AlN représente une solution pour maintenir de bonnes performances tout en miniaturisant les composants. Dans ces travaux de thèse, plusieurs variantes technologiques à barrière AlN ultrafine (3 nm) sur des canaux GaN non-dopés de différentes épaisseurs, développées par le laboratoire IEMN sont étudiés. L'évaluation des performances et de la robustesse de ces technologies, cruciale pour leur qualification et utilisation dans des missions à long-terme, sont ainsi menées en mode DC et RF afin de définir les zones de sécurité de fonctionnement (SOA) et d’identifier les mécanismes de dégradation.La campagne de caractérisation DC et pulsée a révélé une faible dispersion des composants après leur stabilisation électrique, reflétant une bonne maîtrise technologique : ceci permet par ailleurs des études statistiques et des analyses génériques plus pertinentes sur l’ensemble des lots de composants étudiés. L'analyse de la sensibilité des dispositifs à des températures allant jusqu'à 200°C a prouvé la forte stabilité thermique des performances en mode diode et transistor, en suivant les indicateurs paramétriques représentatifs des modèles électriques des composants (courants de saturation et courants de fuite, tension de seuil, taux de retard aux commandes entrée sortie, …). L’ajout d’une barrière arrière AlGaN sur une couche tampon moyennement dopée C a réglé le compromis entre confinement des électrons et densités de pièges. Les tests de vieillissement accéléré en mode DC à différents points de polarisation et en mode RF par paliers de puissance d’entrée ont montré que la barrière arrière AlGaN confère une meilleure stabilité des courants de fuite et des courbes I(V) statiques, une réduction des effets de piégeage et d'auto-échauffement, ainsi qu'une extension de la SOA-DC opérationnelle. Les tests de vieillissement accéléré en mode dynamique à 10 GHz sur des HEMTs avec différents espacements grille-drain ont montré que la SOA-RF ne dépend pas de cet espacement, mais plutôt de la capacité de la grille à supporter des signaux RF élevés, avant dégradation brutale de cette dernière. En utilisant une méthode de modélisation non linéaire originale, prenant en compte le phénomène d'auto-polarisation, les dispositifs avec barrière AlGaN se sont révélés plus robustes également en RF. Cela se traduit par leur compression plus tardive de gain, allant jusqu’à +10dB et sans dégradation électrique ainsi que structurelle apparente (observée par photoluminescence). Indépendamment de la variante AlN/GaN, le mécanisme de dégradation en stress RF correspond au claquage abrupt de la grille Schottky conduisant à sa défaillance. Ces résultats prouvent que les composants sont plus sensibles aux conditions de polarisation DC qu’au niveau de signal RF injecté [...]
The GaN industry is strategic for the European Union because it enhances the power and efficiency of radar and telecommunication systems, especially in the S to Ka bands (up to 30 GHz). To meet the needs of future applications such as 5G and military systems, GaN technology development aims to increase frequencies to the millimeter-wave range. This requires optimizing epitaxy and reducing the gate length to less than 150 nm, as well as using ultrathin barriers (<10 nm) to avoid short-channel effects. Replacing the AlGaN barrier with AlN is a solution to maintain good performance while miniaturizing devices. In this thesis, several technological variants with an ultrathin AlN barrier (3 nm) on undoped GaN channels of various thicknesses, developed by the IEMN laboratory, are studied. The evaluation of the performance and robustness of these technologies, crucial for their qualification and use in long-term profil missions, is conducted in both DC and RF modes to define the safe operating areas (SOA) and identify degradation mechanisms.The DC and pulsed characterization campaign revealed low component dispersion after electrical stabilization, reflecting good technological control. This also allows for more relevant statistical studies and generic analyses across all component batches studied. The sensitivity analysis of the devices at temperatures up to 200°C demonstrated strong thermal stability in diode and transistor modes, following parametric indicators representative of the electrical models of the components (saturation currents and leakage currents, threshold voltage, gate and drain lags rates, ...). The addition of a AlGaN back-barrier on a moderately C-doped buffer layer resolved the trade-off between electron confinement and trap densities. Accelerated aging tests in DC mode at various biasing conditions and in RF mode by input power steps showed that the AlGaN back-barrier provides better stability in leakage currents and static I(V) curves, reduces trapping and self-heating effects, and extends the operational DC-SOA.Dynamic accelerated aging tests at 10 GHz on HEMTs with different gate-drain spacings showed that the RF-SOA does not depend on this spacing but rather on the gate's ability to withstand high RF signals before abrupt degradation occurs. Using an original nonlinear modeling method that considers the self-biasing phenomenon, devices with the AlGaN back-barrier proved to be more robust in RF as well. This is reflected in their later gain compression, up to +10 dB, without apparent electrical or structural degradation (as observed by photoluminescence). Regardless of the AlN/GaN variant, the RF stress degradation mechanism corresponds to the abrupt breakdown of the Schottky gate, leading to its failure. These results indicate that the components are more sensitive to DC bias conditions than to the level of injected RF signals [...]

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xxii, 182 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Leonard J. Brillson, Dept. of Electrical Engineering. Includes bibliographical references (p. 173-182).

The ever increasing demand for higher power devices at higher frequencies has prompted much research recently into the aluminium nitride/gallium nitride high electron mobility transistors (AlN/GaN HEMTs) in response to theoretical predictions of higher performance devices. Despite having superior material properties such as higher two-dimensional electron gas (2DEG) densities and larger breakdown field as compared to the conventional aluminium gallium nitride (AlGaN)/GaN HEMTs, the AlN/GaN devices suffer from surface sensitivity, high leakage currents and high Ohmic contact resistances. Having very thin AlN barrier layer of ∼ 3 nm makes the epilayers very sensitive to liquids coming in contact with the surface. Exposure to any chemical solutions during device processing degrades the surface properties, resulting in poor device performance. To overcome the problems, a protective layer is employed during fabrication of AlN/GaN-based devices. However, in the presence of the protective/passivation layers, formation of low Ohmic resistance source and drain contact becomes even more difficult. In this work, thermally grown aluminium oxide (Al2O3) was used as a gate di- electric and surface passivation for AlN/GaN metal-oxide-semiconductor (MOS)-HEMTs. Most importantly, the Al2O3 acts as a protection layer during device processing. The developed technique allows for a simple and effective wet etching optimisation using 16H3PO4:HNO3:2H2O solution to remove Al from the Ohmic contact regions prior to the formation of Al2O3 and Ohmic metallisation. Low Ohmic contact resistance (0.76Ω.mm) as well as low sheet resistance (318Ω/square) were obtained after optimisation. Significant reduction in the gate leakage currents was observed when employing an additional layer of thermally grown Al2O3 on the mesa sidewalls, particularly in the region where the gate metallisation overlaps with the exposed channel edge. A high peak current ∼1.5 A/mm at VGS=+3 V and a current-gain cutoff frequency, fT , and maximum oscillation frequency, fMAX , of 50 GHz and 40 GHz, respectively, were obtained for a device with 0.2 μm gate length and 100 μm gate width. The measured breakdown voltage, VBR, of a two-finger MOS-HEMT with 0.5μm gate length and 100 μm gate width was 58 V. Additionally, an approach based on an accurate estimate of all the small-signal equivalent circuit elements followed by optimisation of these to get the actual element values was also developed for AlN/GaN MOS-HEMTs. The extracted element values provide feedback for further device process optimisation. The achieved results indicate the suitability of thermally grown Al2O3 for AlN/GaN-based MOS-HEMT technology for future high frequency power applications.

AlN/GaN high-electron mobility transistors (HEMT) are subject to internal structural and electrostatic fields originating mainly from: (i) the fundamental crystal atomicity and the interface discontinuity between dissimilar materials, (ii) atomistic strain, (iii) piezoelectricity, and (iv) spontaneous polarization (pyroelectricity). In this thesis, through numerical simulations, we have studied the origin and effects of these competing internal fields on the electrostatics and the I-V characteristic of scaled nitride HEMT structures. It is shown that strain in these devices is asymmetric and long-ranged (demanding simulations using millions of atoms). The resulting piezoelectric polarization is arge and atomistic in nature. However, the pyroelectric potential is significantly larger than the piezoelectric counterpart and opposes the latter at the InN/GaN interface as opposed to AlGas which only produces a piezoelectric potential. The polarization induced charge density is computed using a three-dimensional Poisson solver and shown to be strongly dependent on the thickness of the AlN barrier layer. This finding has been validated using available experimental data. We have also demonstrated that the olarization fields alone can induce channel carriers at zero external bias and lead to a significant increase in the ON current.

Le marché des télécommunications tire profit des nouvelles technologies Nitrures qui sont en véritable rupture de performances par rapport aux technologies traditionnellement utilisées. Les recherches actuelles ouvrent de nombreuses pistes et solutions alternatives afin de couvrir des contraintes parfois antagonistes de coût, de performances et/ou de fiabilité. La plupart des HEMTs AlGaN / GaN est fabriquée sur un substrat de silicium hautement résistif à faible coût ou sur substrat SiC beaucoup plus onéreux et sensible du point de vue approvisionnement. Les contraintes de performances électriques requises lors de l'intégration de ces technologies dans les systèmes radars, les satellites et en télécommunication rendent les HEMTs très dépendants au paramètre de température de fonctionnement, essentiellement liée à la forte puissance dissipée lors du transfert d'énergie statique/dynamique. En effet, ces composants sont capables de générer des densités de puissance élevées dans le domaine des hyperfréquences. Aussi, l'augmentation de la fréquence de fonctionnement s'accompagne d'une augmentation de la puissance dissipée engendrant le phénomène d'auto-échauffement qui influe sur les performances des composants (ID,max,ft,fmax...). Dans ce contexte, plusieurs solutions ont déjà été proposées dans la littérature (utilisations des substrats composites, passivation des composants, etc...). De plus, la technologie de transfert des HEMTs d'un substrat de croissance initial vers un substrat hôte de bonne conductivité thermique (tel que le substrat de diamant) est une solution prometteuse, encore peu détaillée à ce jour. L'objectif de ce travail de thèse est d'améliorer la dissipation thermique et donc les performances et la fiabilité des transistors HEMT hautes fréquences en utilisant la technologie de transfert de couche. Les hétérostructures AlGaN/GaN sont développées sur substrat de silicium par MOCVD au CHREA. Après la fabrication des HEMTs sur substrat de silicium au sein du laboratoire IEMN, les composants (pour lesquels le substrat silicium a été retiré) sont transférés sur un substrat de diamant. Ce transfert est obtenu grâce à un collage par thermocompression de couche d'AlN pulvérisées sur chaque surface à assembler (face arrière des transistors et substrat diamant). Le procédé de transfert développé n'a pas endommagé la fonctionnalité des transistors HEMTs AlGaN/GaN à faible longueur de grille (Lg = 80 nm). Les transistors de développement 2x35 µm transférés sur diamant présentent un courant ID,max = 710 mA.mm-1, une fréquence de coupure ft de 85GHz et une fréquence d'oscillation fmax de 144GHz. Toutefois, la technique de transfert mérite des phases d'optimisations (notamment pour diminuer l'épaisseur et améliorer la qualité cristalline et la conductivité thermique des couches d'AlN) afin de mieux satisfaire aux contraintes de réduction de résistance thermique de cette couche d'assemblage et ainsi limiter le phénomène d'auto-échauffement relevé à l'issue de ces travaux de thèse
Wireless telecommunication market largely benefits from new nitride technologies, which reach outstanding performance compared with traditional technologies. Current research is opening up many new strategies and alternative solutions to address simultaneously antagonist considerations such as cost, performances and/or reliability. Most AlGaN / GaN HEMTs are fabricated on a low cost, highly resistive silicon substrate or on a much more expensive and supply sensitive SiC substrate. However, the electrical performance constraints required when these technologies are integrating into radar systems, satellites and in telecommunications systems make them dependent to the operating temperature parameter, mainly linked to the high power dissipation during static/dynamic energy transfer. Indeed, these components are capable of generating high power densities in the microwave range. However, the operating frequency increase leads an increase of the power dissipation, generating the self-heating phenomenon which influences the devices performance (ID,max,ft,fmax...). In this context, several solutions were already proposed in the literature (use of composite substrates, passivation of devices, etc.). Furthermore, the layer transfer technology to report HEMTs from growth substrate onto a host substrate with a good thermal conductivity (such as diamond substrate) is a promising solution, still poorly detailed to date. The objective of this thesis work is to improve the heat dissipation and thus the performance and reliability of high-frequency HEMT transistors by using a layer transfer technology. AlGaN / GaN heterostructures are grown on a silicon substrate by MOCVD at CHREA. After the fabrication of HEMTs on a silicon substrate, AlGaN / GaN devices (for which the silicon substrate has been removed) are transferred onto a CVD diamond substrate. This transfer is obtained by thermocompression bonding of sputtered AlN layers on each surface to be assembled (backside of the transistors and diamond substrate). This transfer process has not damaged the functionality of the transistors with short gate length (Lg = 80 nm). The AlGaN/GaN HEMTs with a 2x35 µm development transferred onto diamond of feature a current ID,max = 710 mA.mm-1, a cutoff frequency ft of 85GHz and an oscillation frequency fmax of 144GHz. However, this transfer technique requires optimization phases (especially to reduce thickness and improve the crystalline quality and thermal conductivity of AlN layers) in order to reduce the thermal resistance of this adhesion layer and to limit the self-heating phenomenon noted at the end of this thesis work

AlGaN/GaN high electron mobility transistors (HEMTs) have appeared as attractive candidates for high power, high frequency, and high temperature operation at microwave frequencies. In particular, these devices are being considered for use in the area of high RF power for microwave and millimeter wave communications transmitter applications at frequencies greater than 100 GHz and at temperatures greater than about 150 °C. However, there are concerns regarding the reliability of AlGaN/GaN HEMTs. First of all, thermal reliability is the chief concern since high channel temperatures significantly affect the lifetime of the devices. Therefore, it is necessary to find the solutions to decrease the temperature of AlGaN/GaN HEMTs. In this study, we explored the methods to reduce the channel temperature via high thermal conductivity diamond as substrates of GaN. Experimental verification of AlGaN/GaN HEMTs on diamond substrates was performed using micro-Raman spectroscopy, and investigation of the design space for devices was conducted using finite element analysis as well. In addition to the thermal impact on reliability, environmental effects can also play a role in device degradation. Using high density and pinhole free films deposited using atomic layer deposition, we also explore the use of ultra-thin barrier films for the protection of AlGaN/GaN HEMTs in high humidity and high temperature environments. The results show that it is possible to protect the devices from the effects of moisture under high negative gate bias stress testing, whereas devices, which were unprotected, failed under the same bias stress conditions. Thus, the use of the atomic layer deposition (ALD) coatings may provide added benefits in the protection and packaging of AlGaN/GaN HEMTs.

En électronique de puissance, le GaN est devenu un matériau de choix : il répond à des enjeux de haute performance énergétique, tout en favorisant une compacité et une légèreté des composants. Lors de la fabrication de dispositifs de puissance basés sur une hétérostructure AlGaN/GaN, la gravure plasma induit des dégradations dans le matériau et réduit les propriétés électroniques des composants notamment les diodes et les HEMT (High Electron Mobility Transistors). Ces travaux de thèses se sont focalisés sur l’étude de ces dégradations et proposent des procédés de gravure industrialisables qui diminuent l’impact de ces plasmas. Nous nous sommes concentrés dans un premier temps sur les mécanismes de dégradation intervenant pendant la gravure du SiN avec arrêt sur AlGaN, en fonction de différents paramètres plasma. Les caractérisations électriques et physico-chimiques (notamment l’XPS) ont permis de mettre en avant différents mécanismes de dégradations et d’en proposer un modèle synthétique. Nous avons identifié deux facteurs principaux de dégradation électrique : d’une part, le bombardement ionique énergétique qui modifie les stœchiométries de surface, favorise l’implantation de contaminants, perturbe la qualité cristalline de la maille et provoque la pulvérisation de l’AlGaN. Un seuil en énergie, sous lequel les dégradations restent limitées, a cependant été démontré et éprouvé. Le second facteur identifié est l’épaisseur modifiée. Plus l’épaisseur modifiée est importante, plus elle a une influence sur le canal électronique et ses propriétés. Cette épaisseur peut être augmentée par une haute énergie de bombardement ou par l’utilisation d’éléments légers qui s’implantent en profondeur dans l’AlGaN. Dans un second temps, ces résultats ont servi de cadre pour le développement de procédés innovants afin de limiter l’endommagement lors de la gravure GaN. Nous avons étudié trois procédés cycliques de type ALE : O2-BCl3, Cl2-Ar et Cl2-He. Leurs études ont permis de mettre en évidence leurs différentes caractéristiques d’autolimitations et de sélectivités ainsi que de proposer des modèles de mécanismes de gravure. La caractérisation et la comparaison avec les procédés standards ont soulignés leurs performances et notamment leurs capacités à diminuer les dégradations électriques induites pendant la gravure
In power electronics, GaN has become a material of choice: it meets the challenges of high energy performance, while promoting compactness and lightness of the components. When manufacturing power devices based on an AlGaN / GaN heterostructure, plasma etching induces degradations in the material and reduces the electronic properties of the components, in particular diodes and HEMT (High Electron Mobility Transistors). These thesis works focused on the study of these degradations and proposes industrializable etching processes which reduce these plasma impacts. We first focused on the degradation mechanisms involved during the etching of SiN with stop on AlGaN, according to different plasma parameters. The electrical and physicochemical characterizations (in particular the XPS) made it possible to highlight various degradation mechanisms and to propose a synthetic model. We have identified two main factors of electrical degradation: the first one is the energy ion bombardment which modifies the surface stoichiometries, favors the implantation of contaminants, disturbs the crystal quality of the lattice and causes the sputtering of AlGaN. An energy threshold, below which degradations remain limited, has however been demonstrated and tested. The second factor identified is the modified thickness. The greater the modified thickness, the more it has an influence on the electronic channel and its properties. This thickness can be increased by high bombardment energy or by the use of light elements which are deeply implanted in AlGaN. These results then served as a framework for the development of innovative processes in order to limit the damage during GaN etching. We studied three cyclic processes of the ALE type: O2-BCl3, Cl2-Ar and Cl2-He. These studies made it possible to highlight their different self-limiting and selectivity characteristics as well as to propose etching mechanisms models. Characterization and comparison with standard processes have highlighted their performance and in particular their ability to reduce the electrical degradation induced during etching

碩士
國立交通大學
電子物理系所
106
GaN, Al1-xGaxN, and AlN epilayers were grown by molecular beam epitaxy system (MBE). The in situ reflection high-energy electron diffraction (RHEED) measurements were used to find the best growth conditions of substrate temperature and element flux ratio. The optical properties and surface morphology were analyzed by photoluminescence (PL), cathodoluminescence (CL), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the electrical properties of two dimensional electron gas (2DEG) of AlN/GaN heterostructure were investigated by the Hall measurements. By the control of substrate temperature and Ga/N ratio, the luminescence signal from Ga vacancy could be suppressed and a better surface roughness about 0.4 nm for GaN was achieved. In the case of Al1-xGaxN growth, the substrate temperature was fixed at 740 oC for high Al composition samples. By using the migration enhanced epitaxy (MEE) for the interface expitaxy of AlN/GaN heterostructure, the decomposition of GaN channel layer can be significantly suppressed. The raising substrate temperature to 740 oC enhances migration of the AlN to fill the surface pits. It improves the electron mobility up to 988 (cm2/V•s) in 2DEG.

碩士
長庚大學
光電工程研究所
101
This paper is research AlGaN / GaN HEMT structures, with the barrier layer (AlGaN) and the buffer layer (GaN) is inserted between the interlayer of AlN, to increase the electron mobility. In the experiment, the growth of different thicknesses of the interlayer of AlN, found that when inserted into the AlN, the electron mobility is indeed a significant improvement. But when the interlayer of AlN than the critical thickness (about 3.55 nm), the mobility but will decreased.Theoretically, when the epitaxial growth of AlGaN aluminum gallium compositions and uneven distribution of components will be deposited, and produce alloy scattering, fixed aluminum components by inserting the AlN, the channel can be isolated or lower alloy scattering probability, thereby enabling increased electron mobility. The AlN is too thick may cause stress problems and deterioration of the crystal quality and defect formation, decreased the interfacial flatness, thus reducing the electron mobility in the channel. Finally, Experimental results obtained by the AlN growth time of 15 s (thickness of about 1.121 nm), the electron mobility can reach 1490 cm2/v-s, and the corresponding carrier concentration of 1.369×1013 cm-2. Therefore AlGaN / AlN (thickness of 3.55 nm or less) / GaN high electron mobility transistor structure, can effectively improve the devices of the electron mobility.

碩士
逢甲大學
電子工程學系
106
The thesis investigates field-plate-Al2O3-TiO2-dielectric InAlN/AlN/GaN metal-oxide-semiconductor heterostructure Field-effect transistors(MOS-HEMTs) with planar structure by using the ultrasonic spray pyrolysis deposition (USPD) and sputter technique to deposit oxide layer. Due to the enhanced gate control, the DC characteristic of device has been effectively improved. Depositing the high-k aluminum dioxide and titanium dioxide as a gate-dielectric layer, the gate leakage reduced by gate insulation and surface passivation. Providing the comparison of the characteristics, In this thesis, schottky -HEMT, Al2O3-MOS-HEMT, TiO2-MOS-HEMT, FP-Al2O3-TiO2-MOS- HEMT, and FP-TiO2-Al2O3-MOS-HEMT MOS Fin-HEMT have been achieved, including maximum drain-source saturation current density (IDS, max) of 544.2 mA/mm, 810.4 mA/mm, 815.7 mA/mm, 858.2 mA/mm, and 868.3 mA/mm, drain-source current density at VGS = 0 V (IDSS0) of 291.1 mA/mm, 331.3 mA/mm, 256.3 mA/mm, 650.3 mA/mm, and 670.4 mA/mm, maximum extrinsic transconductance (gm, max) of 212.2 mS/mm, 180.4 mS/mm, 194.7 mS/mm, 209 mS/mm and 210.1 mS/mm, gate leakage current (Ig) at VGS = -10 V of sample A to sample E were 1.4×10-2 mA/mm, 1.1×10-6 mA/mm, 4.1×10-3 mA/mm, 4×10-8 mA/mm, and 5.1×10-9 mA/mm, two-terminal off-state gate-drain breakdown voltage (BVGD) of -126 V, -185.5 V, -143.5 V, -232.2 V, and -311.1 V, respectively, at 300 K. From the experiment results, the superior performance of FP-TiO2-Al2O3 metal-oxide-semiconductor HEMTs (MOS-HEMT) can be effectively improve DC characteristics by sputter and USPD technique, and the field plate structure not only decrease leakage current but increase breakdown voltage of device.

碩士
國立交通大學
國際半導體產業學院
107
In this thesis, a research of the application to the high power GaN metal-insulator-semiconductor HEMT (MIS-HEMT) was done. The result indicated that by using plasma enhanced ALD (PEALD) AlN as a stack layer deposition between oxide layer and semiconductor, the composite passivation structure could not only reach a higher current density, transconductance, and breakdown voltage, but also have the effect of suppressing leakage current and improving time-dependent dielectric breakdown (TDDB) reliability. We use ALD to deposit four kinds of passivation layer: Al2O3(12nm), HfO2(12nm), Al2O3+AlN(10+2nm), and HfO2+AlN(10+2nm), basing on the same AlGaN/GaN HEMTs epitaxial structure on Si, and we also discussed the difference between etching the passivation layer under the gate electrode or not. By comparing the DC characteristics, breakdown voltage, on-state and off-state leakage current ratio, CV measurement, and TDDB reliability between different passivation materials, we found that Al2O3 has the problem of insufficient effective dielectric constant, while HfO2 meets the difficulty in poor deposition quality. Both of the shortcomings could be traded-off by depositing a PEALD-AlN stack layer prior to the oxygen-related passivation, which is attributed to the quality improvement by nitrogen-related passivation effect and the high density positive fixed charges induced by PEALD-AlN.

碩士
國立交通大學
電子工程學系 電子研究所
102
Gallium nitride-based high-electron-mobility transistors (HEMTs) have demonstrated outstanding performance for high-power and high-frequency applications for defense and communication systems. However, there are many undesirable effects such as current collapse and increase in dynamic ON-resistance due to the surface donor states and the high polarization nature of the material. Nitride-based materials are more desirable for GaN passivation because the oxide-based materials have many oxygen contaminations on GaN. SiN has been proved as an effective passivation dielectric to reduce the surface states and can efficiently suppress current collapse in the GaN HEMTs. However, the bandgap of SiN (∼5 eV) is not high enough to suppress leakage current. AlN has a large bandgap (∼6.2 eV) can effectively reduce leakage current as passivation layer. In this work, we demonstrate GaN MIS-HEMT using AlN/SiN bilayer gate dielectric and passivation layer which combine the advantages of SiN and AlN. For comparing the performance of GaN MIS-HEMT with AlN/SiN bilayer gate dielectric, we also prepared reference devices with single layers dielectric. The wafer was divided into three samples after mesa and ohmic contact process. In conclusion, SiN was been proved that it has many good effects for GaN passivation such as decreasing of channel resistance, low surface state, low interface trapping density and low current collapse effect. AlN with high bandgap nature can suppress the leakage current. However, it would increase channel resistance, and cause severe current collapse effect. In this study, an effective AlN/SiN bilayer dielectric and passivation layer have been demonstrated for reducing current collapse effect and leakage current in GaN MIS-HEMT.

碩士
亞洲大學
資訊工程學系碩士班
100
In this study, the effect of AlN materials as passivation over AlGaN layer on AlGaN/GaN HEMTs performance was investigated using fully-coupled electro-thermo-mechanical analysis by TCAD simulations and analytic calculations. It found that AlN passivation layer on AlGaN/GaN HEMTs effectively spread the surface heat resulting in reduction of the maximum lattice temperature and enhances the electrical and mechanical properties. The drain current in the AlGaN/GaN device with AlN-passivation significantly increases about 30% higher than AlGaN/GaN unpassivated device which is in a good agreement with previous study. This study also demonstrates that the current collapse can be suppressed by dielectric AlN passivation.

碩士
國立交通大學
國際半導體產業學院
107
Over the past few years, the high electron mobility transistors which were made of III-V compound semiconductors had been comprehensively applied in high-frequency and high-power area. Especially, gallium nitride (GaN) exhibits many outstanding material characteristics, for instance, high band gap, high saturated electron velocity, high electric breakdown voltage and so on, which make itself be the rising star in high-voltage and high-current electronic devices. The researches utilizing metal-organic chemical vapor deposition (MOCVD) to deposit the GaN-based epitaxy film on SiC and sapphire substrates have gradually mature. Moreover; considered the market demands and the cost, it inevitably used Si substrates for epitaxial growth. However; there is still parasitic RF loss issue, which needs to be resolved in order to enhance the RF performances of GaN-HEMT on Si substrate. In this research, we mainly investigate and discuss the mechanisms of RF loss at the interface between AlN nucleation and Si substrate for the GaN-based HEMT structure. We find that the RF losses are attributed to two mechanisms; the first parasitic conductive channel is the p-type conductive diffusion layer caused by the Al/Ga diffusing into Si substrate, and the second one is the n-type inversion channel resulted from the piezoelectric field which is generated by the residual stress in the tensile AlN layer grown on Si. The transmission line within coplanar waveguide (CPW) was measured to characterize the RF loss of the GaN-based HEMTs on Si and their buffer. The RF loss resulted from the atomic Al/Ga diffusion can be improved by simply reducing the amount of remaining by-product atom in the carrier of MOCVD. (For example: The diffusion effect can be minimized by baking the MOCVD chamber and the carrier at very high temperature in H2 ambient.) Therefore, the key of this study was development of the high-low-high temperature AlN nucleation (HLHT AlN) for the release of the residual stress and further minimized the impact of n-type inversion channel caused from piezoelectric field. However, the RF loss caused by the n-type inversion channel must be overcome by optimum design structure and epitaxial growth process to minimize the residual tensile stress in the AlN layer. In this work, the thinner AlN nucleation layer and a low-temperature AlN inserted in the middle of AlN nucleation layer are adopted to effectively reduce the residual tensile stress in the AlN layer and the consequent RF loss. As the results of using the thin HLH AlN nucleation, the RF loss of GaN-based HEMTs on Si can be reduced by 49%; breakdown voltage was enhanced by reducing the impact of inversion channel; Ft and Fmax were 57GHz and 90GHz without de-embedded and the minimum noise figure was 1.89dB at 38GHz application. Moreover, we found the optimized HLHT AlN nucleation significantly took effectiveness on RF loss of GaN-based HEMT grown on high-resistivity Si substrate. Based on this result, high-resistivity Si substrate would be upgraded the value of RF application.

碩士
國立交通大學
照明與能源光電研究所
103
AlGaN/GaN HEMTs have high electron mobility, high saturation velocity and high breakdown, comparing with other electron device. AlGaN/GaN HEMTs have been wide applications for high frequency and high power densities. However, their performance is limited by current collapse. The surface passivation layer has shown remarkable improvement in reducing the current collapse effect. Compared with those of SiNx, AlN thin film has a larger band-gap (6.2 eV), which can suppress traps to surface. DC and pulse IV measurement results are used to compare with AlGaN/GaN HEMTs with SiNx passivation layer .The results indicated that AlGaN/GaN HEMTs with AlN passivation layer, larger current-gain cutoff frequency (fT) and maximum oscillation frequency (fmax). Beside, small signal equivalent circuits are used to extract variation of intrinsic capacitance. AlGaN/GaN HEMTs with AlN passivation layer has small intrinsic capacitances. Complementary, the wet chemical treatments of AlGaN surface prior to deposition AlN passivation layer can reduce surface roughness and the presence of dangling bond (Ga-O). It can improve the device performance.