This thesis investigates the response to ionising radiation, of p-type Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) (REM Oxford (UK)) and a reader system developed by the Centre for Medical Radiation Physics, The University of Wollongong, to determine their feasibility for measurements of dose during radiotherapy treatment (in vivo dosimetry (IVD)). Two types of MOSFET probes were used -"single sensitivity", for measuring low doses, and "dual sensitivity", to measure both high and lose doses. Sensitivity, linearity of response with dose, and response changes with accumulated dose and direction of incident radiation (angular dependence) were investigated. The average sensitivity reduction over the lifetime of the probes was 22.37% with a standard deviation of 0.63%. This reduction in sensitivity can be corrected for by the use of "drift equations". MOSFETs have a limited "lifetime" due to saturation effects with increasing accumulated dose. Saturation occurred at an average of 40 Gray (Gy) accumulated dose, for the high sensitivity probes investigated. The high sensitivity probes were linear within 1.6% for doses between 5 and 140 cGy, and 3.8% for the high sensitivity probes for doses between 50 and 500 cGy. Drift (changes in readings with time since irradiation due to electronic processes) over the long-term (from hours to weeks following irradiation) has been previously well characterised in the literature. This work focuses on shortterm drift, within the first few seconds or minutes following irradiation, being the most clinically relevant for in vivo measurements. Drift is investigated for various reading methods, such as reading frequency, and delays between irradiation and readings. It is shown that sensitivity, and consequently dose determination, is significantly influenced by the reading methodology. During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). When two post-irradiation readings were taken following an irradiation, the difference between them generally increased as the time interval between the two readings increased, by up to 8.8%. Delays in taking pre-and post-irradiation readings resulted in drift of up to 5.7% or 9.3% respectively, compared with readings without a delay. These results emphasise the necessity for consistent methodologies between calibration and measurement in the clinical situation. Greater sensitivity was measured with the epoxy bubble, rather than the substrate side, facing the beam. The greatest variation, for orientations other than the bubble side facing directly towards the beam, was 10%, or 5% uncertainty in dose. The variations with angle were found to be reproducible, so that appropriate correction factors could be applied to correct measurements at angles other than with the sensitive area of the probes facing directly towards the radiation beam. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1368262 / Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, 2009

Th. doct.-ing.--Electronique et communications--Paris--ENST, 1993. / Résumé en français et en anglais. Notes bibliogr.

High-frequency noise modeling and characterization of nanoscale MOSFETs are essential driving forces for highly scaled CMOS technology to be used in radio-frequency applications. Continuous downscaling increases the operating frequency of the MOSFETs, reduces the power supply voltage but does not scale noise accordingly. This makes the noise issue of future low-power technology more prominent and therefore accurate noise modeling more important. In this thesis, several important issues regarding noise modeling and characterization for nanoscale MOSFETs are studied. First, a new noise factor deembedding algorithm is proposed for on-wafer noise measurements. It solves the problem of noise factor deembedding in which the active two-port device is surrounded by a four-port parasitic network. Based on it, a new deembedding-first and optimization-last noise parameter deembedding approach is proposed and its performance is evaluated using experimental data. Second, the noise performance of modern sub-100-nm MOSFETs are evaluated using the noise sheet resistance as a figure of merit. It shows that future technologies generally have degraded noise performance. In addition, two accuracy issues regarding the calibration of noise receiver for high-frequency noise measurements are investigated and methods to mitigate these issues are discussed. Third, a novel Z-parameter based approach to extract the gate resistance is proposed for MOSFET characterization. It is evaluated against other published methods using experimental data. In addition, the extraction of the resistance of the lightly-doped-drain region and the gate contact is also performed and discussed. Finally, a new perspective to interpret the MSOFET channel noise as suppressed shot noise is presented. An easy-to-use analytical expression for the suppression factor is derived and it only relies on two process parameters – threshold voltage and effective oxide thickness – to predict the level of suppression for the channel noise of MOSFETs. It is evaluated using published experimental data on various CMOS technology nodes. / Thesis / Doctor of Philosophy (PhD)

A Aproximação de Massa Efetiva para a função evnvelope multi-componente, na presença de uma interface, desenvolvida por Marques e Sham, será utilizada aqui, para materiais de gap estreito do grupo II-VI, da seguinte maneira: A) A forte interação entre bandas de condução e valência, nestes materiais, é justificada em um Hamiltoniano de Kane (6x6) modificado, contendo todas as ondas de Bloch propagantes e evanescentes. Na presença de uma interface, a função de onda eletrônica, &#936, é composta de uma onda de Bloch incidente, uma refletida e duas evanescentes, com a mesma energia E e momento paralelo k. Já que a estrutura da maioria dos isolantes utilizados são desconhecidos, a interface semicondutor-isolante por ser considerada como uma barreira infinita, de modo que, &#936, se anule na interface. Existe uma fina região de espessura &#945 na interface, onde o decaimento das ondas evanescentes é indispensável. Distante desta região, as ondas evanescentes possuem um papel insignificante e eventualmente anulam-se. O limite de &#945 &#8594 0 determina as condições de contorno para cada componente da função de onda envelope na interface. B) As condições de contorno são usadas para computar a estrutura de subbandas e o potencial auto-consistente para o Hg1-xCdxTe. A mais interessante característica é o afastamento dos estados de spin duplamente degenerados. Estes resultados serão utilizados para encontrarmos a dependência da energia das subbandas com um campo magnético perpendicular à interface. C) A magneto-condutividade longitudinal é calculada como função do campo magnético B &#8869. Efeitos das interações elétron-elétron e elétrons-impureza são levadas em conta nas aproximações de Hartee-Foch e auto-consistente de Born, respectivamente. Para uma interação elétron-impureza finita, encontram-se fatores de preenchimentos críticos dos níveis de Landau, onde transições de fase são observadas. Estes resultados explicam as descontinuidades presentes, em medidas experimentais, na magneto-resistividade longitudinal e transversal (Hall), em MISFET de Hg (Cd)Te. / The Effective Mass Approximation for multi-component envelope wave function in the presence of an interface in the MOSFET system, developed by Marques and Sham, will be used here, for II-VI narrow-gap semiconductors, in the following way: A) The strong interaction between conduction and valence bands, in these materials, is justified. The (6x6) Kane type modified Hamiltonian is used and the total wave function contains every propagating and evanescent waves. For an interface, the total function, &#936, is composed of one incident and one reflected and two evanescent Bloch waves, with energy E and parallel wave-vector k. Since the band structure of the most used insulators is usually not well known, the insulator-semiconductor interface can be assumed as an infinite barrier; therefore, the total wave-function there can set to zero. The semiconductor evanescent Bloch waves are indispensable in a thin layer, of thickness &#945, close to this region. Far away from the interface their role are insignificant and can be neglected. In the limit &#945 &#8594 0, the boundary condition for each the limit the total Bloch wave function, are derived. B) These boundary conditions are used to calculate the self-consistent electric subband and potential for MISFET of Hg1-xCdxTe. The subbands present a very important spin splitting, due to the internal electric field. C) The effect of a perpendicular magnetic field is also studied and the longitudinal magneto-conductivity are calculated. The effect of electron-electron and electron-impurity interactions are respectively accounted for in the Hartee-Fock and self-consistent Born approximations. For critical electron-impurity interaction, the Landau level filling shows a phase transition at a given fractional occupation (or magnetic field). These results are experimentally observed in both longitudinal and transverse (Hall) magneto-resistance for Hg(Cd)Te.

Thèse de doctorat : SCIENCES ET TECHNIQUES : Metz : 1999. / 1999METZ034S. 49 ref.

In the current study, we present measurements of peripheral dose that is absorbed by specific radio-sensitive organs outside the radiation field for five clinical cases, and compare them with the corresponding values that are given by ISIS 3D Treatment Planning System, as well as with the values given by a software that can calculate peripheral doses called ‘Peridose’. The measurements were made with MOSFET dosimeters in anthropomorphic phantom. / Στην παρούσα εργασία, παρουσιάζουμε μετρήσεις της περιφερειακής δόσης που απορροφάται από συγκεκριμένα ακτινευαίσθητα όργανα εκτός του πεδίου ακτινοβόλησης για πέντε κλινικές περιπτώσεις, και τις συγκρίνουμε με τις αντίστοιχες τιμές που δίνονται από το ISIS 3D Treatment Planning System καθώς και από τις τιμές που δίνει ένα πρόγραμμα το οποίο μπορεί να υπολογίσει περιφερειακές δόσεις που λέγεται ‘Peridose’. Οι μετρήσεις έγιναν με δοσίμετρα MOSFET σε ανθρωπόμορφο ομοίωμα.

A Aproximação de Massa Efetiva para a função evnvelope multi-componente, na presença de uma interface, desenvolvida por Marques e Sham, será utilizada aqui, para materiais de gap estreito do grupo II-VI, da seguinte maneira: A) A forte interação entre bandas de condução e valência, nestes materiais, é justificada em um Hamiltoniano de Kane (6x6) modificado, contendo todas as ondas de Bloch propagantes e evanescentes. Na presença de uma interface, a função de onda eletrônica, &#936, é composta de uma onda de Bloch incidente, uma refletida e duas evanescentes, com a mesma energia E e momento paralelo k. Já que a estrutura da maioria dos isolantes utilizados são desconhecidos, a interface semicondutor-isolante por ser considerada como uma barreira infinita, de modo que, &#936, se anule na interface. Existe uma fina região de espessura &#945 na interface, onde o decaimento das ondas evanescentes é indispensável. Distante desta região, as ondas evanescentes possuem um papel insignificante e eventualmente anulam-se. O limite de &#945 &#8594 0 determina as condições de contorno para cada componente da função de onda envelope na interface. B) As condições de contorno são usadas para computar a estrutura de subbandas e o potencial auto-consistente para o Hg1-xCdxTe. A mais interessante característica é o afastamento dos estados de spin duplamente degenerados. Estes resultados serão utilizados para encontrarmos a dependência da energia das subbandas com um campo magnético perpendicular à interface. C) A magneto-condutividade longitudinal é calculada como função do campo magnético B &#8869. Efeitos das interações elétron-elétron e elétrons-impureza são levadas em conta nas aproximações de Hartee-Foch e auto-consistente de Born, respectivamente. Para uma interação elétron-impureza finita, encontram-se fatores de preenchimentos críticos dos níveis de Landau, onde transições de fase são observadas. Estes resultados explicam as descontinuidades presentes, em medidas experimentais, na magneto-resistividade longitudinal e transversal (Hall), em MISFET de Hg (Cd)Te. / The Effective Mass Approximation for multi-component envelope wave function in the presence of an interface in the MOSFET system, developed by Marques and Sham, will be used here, for II-VI narrow-gap semiconductors, in the following way: A) The strong interaction between conduction and valence bands, in these materials, is justified. The (6x6) Kane type modified Hamiltonian is used and the total wave function contains every propagating and evanescent waves. For an interface, the total function, &#936, is composed of one incident and one reflected and two evanescent Bloch waves, with energy E and parallel wave-vector k. Since the band structure of the most used insulators is usually not well known, the insulator-semiconductor interface can be assumed as an infinite barrier; therefore, the total wave-function there can set to zero. The semiconductor evanescent Bloch waves are indispensable in a thin layer, of thickness &#945, close to this region. Far away from the interface their role are insignificant and can be neglected. In the limit &#945 &#8594 0, the boundary condition for each the limit the total Bloch wave function, are derived. B) These boundary conditions are used to calculate the self-consistent electric subband and potential for MISFET of Hg1-xCdxTe. The subbands present a very important spin splitting, due to the internal electric field. C) The effect of a perpendicular magnetic field is also studied and the longitudinal magneto-conductivity are calculated. The effect of electron-electron and electron-impurity interactions are respectively accounted for in the Hartee-Fock and self-consistent Born approximations. For critical electron-impurity interaction, the Landau level filling shows a phase transition at a given fractional occupation (or magnetic field). These results are experimentally observed in both longitudinal and transverse (Hall) magneto-resistance for Hg(Cd)Te.

<p>Increasing demand for higher power density in many applications such as Hybrid Electric Vehicles (HEVs) and renewable power generation has led to great technological advances in power electronics. To meet this increasing demand, a power semiconductor device needs to have low on resistance, increased switching speeds and reduced total system cost. Silicon (Si) power devices have been used for several decades but they are fundamentally limited by material properties. Silicon carbide (SiC) as a power semiconductor material offers superior electrical and thermal properties compared to silicon, which it can replace in a large spectrum of applications. Because of a lower critical electric field, drift regions in Si power transistors need to be much thicker and more lightly doped, which in turn increases the specific onresistance Ron,sp. To combat the drift resistance component for higher blocking voltages, superjunction MOSFETs for medium voltages and Si IGBTs for high voltages are used. Since IGBTs are bipolar transistors, they exhibit much higher switching energy losses than MOSFETs. The SiC MOSFET is an excellent candidate in the medium to high voltage range, which mainly targets the HEV market.</p><p><br></p><p>Due to their low channel mobility, SiC MOSFETs have not reached the theoretical limit below 1200 V where channel resistance is dominant. Planar DMOSFETs dominate the</p><p>commercial SiC market today because of higher yield and relatively simpler fabrication process, but trench MOSFETs can be made with a smaller cell area and thus lower Ron,sp. Due to lower cell-pitch and high integration density of trench-gate devices, they offer an opportunity to reduce the size and weight of HEV power control units by replacing IGBTs with MOSFETs. The single-trench UMOSFET was first reported in 1994 by CREE and the first oxide protected trench MOSFET in 1998 by Purdue. This structure inserts a grounded p-type region below the gate trench to protect the oxide in the blocking state. In 2012, Rohm Semiconductor reported a novel double-trench UMOSFET with separate gate and</p><p>field-protection trenches. In 2017, Infineon published their new trench UMOSFET, known as Cool-SiC, with high gate oxide reliability. In this work a deeply-scaled, fully-self-aligned trench MOSFET is fabricated and characterized. The innovative process described enables a record cell-pitch of 0.5 μm per channel, equivalent to a channel density 6Å~ higher than currently available commercial UMOSFETs.</p>

Afin de poursuivre la réduction d'échelle des transistors MOS, l'industrie des semiconducteurs a su anticiper les limitations de la miniaturisation par l'introduction de nouveaux matériaux ou de nouvelles architectures. L'avènement des structures à triples grilles (FinFET) a permis de maitriser les effets canaux courts et poursuivre les efforts de miniaturisation (nœud technologique 14 nm en 2014). Le cas ultime pour le contrôle électrostatique de la grille sur le canal est donné par une grille entourant totalement le canal du dispositif. A cet effet, un transistor à nanofil à grille entourante est considéré comme la structure la plus adaptée pour les nœuds technologiques en dessous de 7 nm. Au cours de cette thèse, un procédé de réalisation large échelle de transistors MOSFET miniaturisés à base de nanofils verticaux en silicium a été développé. Tout d'abord, les nanofils verticaux ont été réalisés par une approche descendante via le transfert par gravure d'un masque de résine en Hydrogène Silsesquioxane (HSQ), réalisé par lithographie électronique à basse tension d'accélération. Une stratégie de dessin inédite dite "en étoile " a été développée pour définir des nanofils parfaitement circulaires. Les nanofils en Si sont obtenus par gravure plasma puis amincis par oxydation humide sacrificielle. Ce procédé permet d'obtenir des nanofils verticaux en Si avec des parois parfaitement anisotropes, une parfaite reproductibilité et un rendement maximal. L'implémentation des MOSFETs sur les réseaux nanofils a été effectuée par l'ingénierie successive de couches minces nanométriques (conductrices et diélectriques). Dans ce cadre, un procédé innovant de réalisation de couches d'isolations en HSQ par gravure chimique contrôlée a démontré une excellente planéité associée à une rugosité de surface inférieure à 2 nm. Enfin, un procédé utilisant la photolithographie UV conventionnelle a été développé pour réaliser le transistor de longueur de grille nanométrique. Ces dispositifs ont démontré d'excellentes performances électriques avec des courants de conduction supérieurs à 600 µA/µm et une excellente maîtrise des effets de canaux courts (pente sous le seuil de 95 mV/dec et DIBL à 25 mV/V) malgré l'extrême miniaturisation de la longueur de grille (15 nm). Enfin, nous présentons une première preuve de concept d'un inverseur CMOS à base de cette technologie à nanofils verticaux. / In order to further downscaling of the MOS transistors, the semiconductor industry has anticipated the limitations of miniaturization by the introduction of new materials and new architectures. The advent of triple gate structures (FinFET) allowed mastering the short channel effects and further miniaturization efforts (14 nm technology node in 2014). The ultimate case to the electrostatic control of the gate on the channel is given by a gate completely surrounding the device channel. For this purpose, Gate All Around (GAA) nanowire transistor is considered as the most suitable structure for technology nodes below 7 nm. In this thesis, a large scale process for the realization of miniaturized MOSFETs based on vertical silicon nanowires has been developed. Firstly, the vertical nanowires were made by a top down approach by the transfer by etching of hard mask made of Hydrogen silsesquioxane (HSQ) resist created at low voltage electron beam lithography. An original design strategy called "star" was developed to define perfectly circular nanowires. Si nanowires are obtained by plasma etching then thinned by sacrificial wet oxidation. This method allows obtaining vertical Si nanowires with perfectly anisotropic walls, a perfect reproducibility and a maximum yield. The implementation of the MOSFETs on the nanowire network was done by successive engineering of nanoscale thin films (conductive and dielectric). In this context, an innovative process for producing insulation layers in HSQ by controlled chemical etching showed excellent flatness associated with surface roughness of less than 2 nm. Finally, a method using conventional UV photolithography has been developed to achieve the nanometer gate length transistor. These devices have demonstrated excellent electrical performances with conduction currents superior than 600 µA/µm and excellent control of short channel effects (subthreshold slope of 95 mV/dec and DIBL of 25 mV/V) despite extreme miniaturization of the gate length (15 nm). Finally, we present a first proof of concept of a CMOS inverter based on vertical nanowires technology.

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