Academic literature on the topic 'High workfunction oxides'

Introduction: A new analytical model is designed for Workfunction Modulated Rectangular Recessed Channel-Silicon On Insulator (WMRRC-SOI) MOSFET that considers the concept of groove gate and implements an idea of workfunction engineering. Methods: The impact of Negative Junction Depth (NJD) and oxide thickness (tox) are analyzed on device performances such as Sub-threshold Slope (SS), Drain Induced Barrier Lowering (DIBL) and threshold voltage. Results: The results of the proposed work are evaluated with the Rectangular Recessed Channel-Silicon On Insulator (RRC-SOI) MOSFET keeping the metal workfunction constant throughout the gate region. Furthermore, an analytical model is developed using 2D Poisson’s equation and threshold voltage is estimated in terms of minimum surface potential. Conclusion: In this work, the impact of Negative Junction Depth (NJD) on minimum surface potential and the drain current are also evaluated. It is observed from the analysis that the analog switching performance of WMRRC-SOI MOSFET surpasses RRC-SOI MOSFET in terms of better driving capability, high Ion/Ioff ratio, minimized Short Channel Effects (SCEs) and hot carrier immunity. Results are simulated using 2D Sentaurus TCAD simulator for validation of the proposed structure.

AbstractIn this paper we report high voltage MOS and Schottky Diode CV techniques for silicon and SiC power devices. 4H Silicon carbide is a wide bandgap semiconductor suitable for high voltage power electronics and RF applications due to high avalanche breakdown critical electric field, and thermal conductivity. The performance of various power devices, which may include MOSFET and Static Induction Transistor (SIT), can be affected by the deep level traps in the substrate and the oxide interfacial defects. We have characterized deep level trap (High Voltage Schottky Diode HF CV) and oxide interface trap densities (High Voltage HF MOS CV), measured the device channel doping profile for both 4H SiC and silicon, gate metal workfunction, and simulated the effects on DC/AC performance.

Abstract In this paper, the impact of workfunction engineering and lightly doped region near drain has been studied on lateral β-Ga2O3 metal oxide semiconductor field effect transistor (MOSFET) by employing exhaustive technology computer aided design simulations. The theoretically predicted value of breakdown voltage and power figure of merit (PFoM) for Ga2O3 based devices has not been achieved yet, and hence in order to improve these parameters, variable channel doping and work function engineering have been implemented on lateral β-Ga2O3 MOSFET for the first time in the present work. A thorough comparative assessment has been drawn by comparing the characteristics of the proposed device which incorporates work function engineering along with a variable doping in channel such that higher doping is near the source side and a lower doping region is near the drain end with conventional, doping engineered and work function engineered β-Ga2O3 devices and it is demonstrated that the proposed device offers significant improvement in breakdown voltage and PFoM. Furthermore, the performance of all devices under consideration has been evaluated at high temperatures as well and it is demonstrated that the proposed device offers superior performance in comparison to other devices, and hence is a suitable contender for high voltage and high temperature applications.

The relationship among the on-to-off current ratio, threshold voltage, and the gate metal work-function is investigated for a junctionless (JL) Gate-All-Around (GAA) MOSFET with a gate oxide film in which SiO2 and a high-k dielectric material are stacked. The JL structure works in the accumulation state, and the threshold voltage is defined as the gate voltage when the minimum potential in the channel becomes Fermi potential. The on-to-off current ratio Ion/Ioff is obtained by obtaining on-current Ion at the threshold voltage and off-current Ioff at the gate voltage of 0 V. As a result, if the channel doping concentration and silicon radius are increased to reduce the channel resistance, the on-to-off current ratio decreases along with the threshold voltage, but this problem can be solved through the increasing of the gate metal workfunction. In addition, even when the relative permittivity of the high-k dielectric is increased from 3.9 to 20, the gate metal work-function to maintain any on-to-off current ratio and threshold voltage is very slightly changed. Therefore it will be possible to improve the controllability of the gate by increasing the permittivity of the high-k dielectric without change in the work-function. The reduction of the channel resistance of the JL GAA MOSFET is possible with the stacked gate oxide while maintaining a reasonable on-to-off current ratio and threshold voltage by adjusting the gate metal work-function

AbstractAs the MOSFET gate lengths are scaled down to 50 nm or below, the expected increase in gate leakage will be countered by the use of a high dielectric constant (high K) material. The series capacitance from polysilicon gate electrode depletion significantly reduces the gate capacitance as the dielectric thickness is scaled down to 10 Å equivalent oxide thickness (EOT) or below. Metal gates promise to solve this problem and address other problems like boron penetration and enhanced gate resistance that will have increased focus as the polysilicon gate thickness is reduced. Extensive simulations have shown that the optimal gate work-functions for the sub-50 nm channel lengths should be 0.2 eV below (above) the conduction (valence) band edge of silicon for n-MOSFETs (p-MOSFETs). This study summarizes the evaluations of TiN, TaSiN, WN, TaN, TaSi, Ir and IrO2 as candidate metals for dual-metal gate CMOS using HfO2 as the gate dielectric. The gate work-function was determined by fabricating MOS capacitors with varying dielectric thicknesses and different post-gate anneals. The metal-dielectric compatibility and thermal stability was studied by annealing the stacks at different temperatures. The gate stacks were characterized using TEM, SIMS and X-ray diffraction. Based on workfunctions and thermal stability, TaSiN and TaN show most promise as metal electrodes for HfO2 n-MOSFETs.

L’émergence d’une grande variété de structures photoniques, au cours des dernières décennies, a permis le développement de composants intégrés sur puce réalisant des fonctions optiques en espace libre de plus en plus complexes. Parmi elles, les structures diélectriques membranaires ont permis d’implémenter une large panoplie de composants optiques planaires, allant du filtrage spectral résonant à la mise en forme de faisceau avec de faibles pertes. Toutefois, si ces structures permettent d’obtenir un contrôle quasi-total du champ électromagnétique rayonné, ce contrôle est généralement statique et déterminé par la fabrication. Un nombre croissant d’applications – telles que les télécommunications en espace libre, les capteurs pour systèmes autonomes ou encore l’imagerie – nécessitent pourtant des composants photoniques agiles, motivant ainsi la recherche de moyens de contrôle actifs de la réponse optique à implémenter au sein des structures diélectriques. À cette fin, différentes propriétés du graphène s’avèrent prometteuses. En particulier, la possibilité de moduler dynamiquement son absorption ouvre de nombreuses perspectives pour le contrôle électrique et optique des structures photoniques intégrant du graphène. Des modulateurs électro-optiques et tout-optique ont ainsi pu être réalisés, s’appuyant sur le développement récent de procédés de transfert des matériaux 2D qui permettent aujourd’hui d’obtenir des structures hybrides graphène/diélectrique de grande qualité. Dans ce contexte, les travaux présentés dans cette thèse cherchent à exploiter l’absorption modulable du graphène pour obtenir une accordabilité dynamique de la réponse optique des composants adressables par la surface, dans le cas particulier de structures photoniques diélectriques travaillant dans le proche infrarouge. Un modèle générique de composant hybride diélectrique/ graphène est tout d’abord développé en théorie des modes couplés afin d’identifier les paramètres d’intérêt pour maximiser le contrôle permis par l’absorption du graphène. Dans le cas à une résonance, le comportement du système est principalement déterminé par la condition de couplage critique classiquement définie pour l’étude de l’absorption du graphène. Dans le cas à deux résonances en revanche, un nouveau paramètre de contrôle – associé à la différence d’absorption induite sur les résonances – permet d’obtenir un levier d’accordabilité supplémentaire. Différentes stratégies de maximisation de ce paramètre sont proposées et les procédés technologiques nécessaires à leur implémentation sont étudiés expérimentalement afin d’évaluer – par le biais de la spectroscopie Raman et de la spectroscopie de photoélectrons – leur effet sur la qualité structurelle et chimique du graphène, intégré dans de telles structures. La modulation spatiale de l’absorption du graphène – proposée pour différencier l’absorption induite sur différents modes optiques – est ensuite étudiée expérimentalement à l’aide de structures exploitant le transfert de charges entre le graphène et un oxyde à grand travail de sortie, à savoir l’oxyde de tungstène. Les dispositifs réalisés permettent d’obtenir une modulation du potentiel chimique du graphène de 0.1eV – caractérisée par nano-XPS (ligne ANTARES du synchrotron SOLEIL) et spectroscopie Raman – pouvant aboutir à une modulation de l’absorption supérieure à 70% pour certaines longueurs d’onde. Finalement, une architecture de composant hybride actif permettant d’obtenir un contrôle dynamique de l’émission laser est proposée. Cette architecture repose sur l’utilisation d’une membrane à brisure de symétrie verticale et permet, en principe, d’obtenir une commutation entre deux angles d’émission par la modulation de l’absorption du graphène. L’intérêt de ces structures pour parvenir à une accordabilité continue de l’angle d’émission est également exposé
The emergence of a wide variety of photonic structures over the past decades has enabled the realization of on-chip devices performing increasingly complex free-space optical functions. Among them, dielectric membrane structures have made it possible to implement a wide range of planar optical devices, ranging from resonant spectral filtering to beam shaping, with negligible losses. While these structures provide almost a full control of the radiated electromagnetic field, this control is usually static and determined by manufacturing. An increasing number of applications - such as free-space telecommunications, sensors for autonomous systems or imaging - require agile photonic devices, thus motivating the search for means of active control of the optical response to be implemented within the dielectric structures. To this purpose, various properties of graphene are proving promising. In particular, the capability to modulate its absorption opens up numerous prospects for the electrical and optical control of photonic structures that integrate graphene. This has led to the demonstration of various electro-optic and all-optical modulators, by leveraging the recently developed 2D material transfer processes, which have made it possible to obtain high-quality hybrid graphene/dielectric structures. In this context, the work presented in this thesis seeks to exploit graphene’s tunable absorption to achieve dynamic control of surface-addressable device’s optical response, in the special case of dielectric photonic structures operating in the near infrared. A generic coupled mode theory model is first developed and adapted to hybrid dielectric/ graphene structures in order to identify the key parameters for maximising the control allowed by graphene absorption. In the single resonance case, the system’s response is mainly determined by the critical coupling condition classically defined for the study of graphene’s absorption. In the two-resonance case however, a new control parameter – associated with the absorption difference between the resonances – provides an additional tunability factor. Different strategies for maximising this parameter are therefore proposed and the technological processes underlying their implementation are studied experimentally in order to assess - by means of Raman spectroscopy and photoelectron spectroscopy - their effect on the structural and chemical quality of graphene. The spatial modulation of graphene’s absorption – here proposed to differentiate the absorption induced on different optical modes – is then studied experimentally using structures exploiting the charge transfer effect at the interface between graphene and an oxide with high workfunction, namely tungsten oxide. The devices developed here allow to obtain a graphene’s chemical potential modulation of 0.1eV - characterized by nano-XPS (ANTARES beamline of the SOLEIL synchrotron) and Raman spectroscopy - which can lead to an absorption modulation higher than 70% for certain wavelengths. Ultimately, an active hybrid device architecture enabling dynamic control of the laser emission is proposed. This architecture is based on a vertical symmetry breaking membrane and allows us, in principle, to switch between two emission angles by modulating graphene’s absorption. The interest of these structures in achieving continuous tunability of the emission angle is also presented

Cette thèse concerne l’étude des procédés de fabrication des grilles HKMG des technologies FDSOI 14 et 28 nm sur les performances électriques des transistors MOS. Elle a porté spécifiquement sur l'aspect fiabilité et la maîtrise du travail de sortie effectif (WFeff), au travers de la diffusion des additifs comme le lanthane (La) et l’aluminium (Al). Ce travail combine des techniques de caractérisation électriques et physico-chimiques et leur développement. L'effet de l'incorporation de ces additifs sur la fiabilité et la durée de vie du dispositif a été étudié. Le lanthane dégrade les performances de claquage TDDB et de dérives suite aux tests aux tensions négatives. L’introduction d’aluminium améliore le claquage TDDB, mais dégrade les dérives aux tensions positives. Ces comportements ont été reliés à des mécanismes physiques. Par ailleurs, la diffusion de ces additifs dans l’empilement de grille a été étudiée pour différents matériaux high-k en fonction de la température et de la durée de recuit de diffusion. Les doses d’additifs ont pu être ainsi mesurées, comparées et corrélées au décalage de travail de sortie effectif de grille. On a également étudié, les influences des paramètres du procédé de dépôt de grille TiN sur leur microstructure et les propriétés électriques du dispositif, identifiant certaines conditions à même de réduire la taille de grain ou la dispersion d’orientation cristalline. Toutefois, les modulations obtenues sur le travail de sortie effectif de grille dépendent plus du ratio Ti/N, suggérant un changement du dipôle à l'interface SiO2 / high-k. Enfin, une technique éprouvée de mesure de spectroscopie à rayon X sous tension a pu être mise en place grâce des dispositifs spécifiques et une méthodologie adaptée. Elle permet de mesurer les positions relatives des bandes d’énergie à l'intérieur de l’empilement de grille. Cette technique a démontré que le décalage du travail de sortie effectif induits par des additifs (La or Al) ou par des variations d'épaisseur de grille métallique TiN provient de modifications du dipôle à l'interface SiO2/ high-k
This Ph.D. thesis is focused on the impact of the 14 and 28 nm FDSOI technologies HKMG stack processes on the electrical performance of MOS transistors. It concerns specifically the reliability aspect and the engineering of effective workfunction (WFeff ), through diffusion of lanthanum (La) and aluminum (Al) additives. This work combines electrical and physicochemical characterization techniques, and their development. The impact of La and Al incorporation, in the MOS gate stack, on reliability and device lifetime has been studied. La addition has a significant negative impact on device lifetime related to both NBTI and TDDB degradations. Addition of Al has a significant negative impact on lifetime related to PBTI, but on the contrary improves the lifetime for TDDB degradation. These impacts on device lifetime have been well correlated to the material changes inside the gate oxides. Moreover, diffusion of these additives into the HKMG stack with annealing temperature and time has been studied on different high-k materials. The diffused dose has been compared with the resulting shift in effective workfunction (WFeff), evidencing clear correlation. In addition, impact of TiN metal gate RF-PVD parameters on its crystal size and orientation, and device electrical properties has been studied. XRD technique has been used to obtain the crystal size and orientation information. These properties are significantly modulated by TiN process, with a low grain size and a unique crystal orientation obtained in some conditions. However, the WFeff modulations are rather correlated to the Ti/N ratio change, suggesting a change in the dipole at SiO2/high-k interface. Lastly, using specific test structures and a new test methodology, a robust and accurate XPS under bias technique has been developed to determine the relative band energy positions inside the HKMG stack of MOS devices. Using this technique, we demonstrated that WFeff shift induced by La and Al or by variations in gate thickness originates due to modifications of the dipole at SiO2/high-k interface