266 research outputs found
Capacitance-Voltage Study on the Effects of Low Energy Electron Radiation on Al\u3ci\u3e\u3csub\u3e0.27\u3c/i\u3e\u3c/sub\u3eGa\u3ci\u3e\u3csub\u3e0.73\u3c/i\u3e\u3c/sub\u3eN/GaN High Electron Mobility Transistor
The effects of radiation on semiconductors are extremely important to the Department of Defense since the majority of the defense informational, navigational and communications systems are now satellite-based. Due to the high radiation tolerance of gallium nitride and a plethora of high temperature, high power and high frequency applications, the prospect that gallium nitride based devices will become key components in a multitude of military satellite-based systems is highly probable. AlGaN/GaN HEMTs were irradiated at low temperature (~80 K) by 0.45 – 0.8 MeV electrons up to fluences of 1×1015 e-/cm2. Following irradiation, low temperature capacitance-voltage measurements were recorded providing fluence-dependent measurements; additionally low-temperature post-irradiation capacitance-voltage measurements were recorded at twenty-four hour intervals up to 72 hours in order to investigate the room temperature annealing process. Using previously irradiated devices, the effects of a 9 month and 12 month room temperature anneal were also considered. Capacitance-voltage measurements indicate that low energy electron radiation results in an increase in the transistor channel drain current. These increases occur both at low and room temperature. The mechanism, clearly shown through capacitance-voltage measurements, causing the increase in drain current is an increase in the carrier concentration in the 2DEG. This result is due to donor electrons from a nitrogen vacancy in the gallium nitride. The devices begin to anneal immediately and show almost complete recovery after 72 hours
Combined Bulk and Surface Radiation Damage Effects at Very High Fluences in Silicon Detectors: Measurements and TCAD Simulations
In this work we propose a new combined TCAD radiation damage modelling
scheme, featuring both bulk and surface radiation damage effects, for the
analysis of silicon detectors aimed at the High Luminosity LHC. In particular,
a surface damage model has been developed by introducing the relevant
parameters (NOX, NIT) extracted from experimental measurements carried out on
p-type substrate test structures after gamma irradiations at doses in the range
10-500 Mrad(Si). An extended bulk model, by considering impact ionization and
deep-level cross-sections variation, was included as well. The model has been
validated through the comparison of the simulation findings with experimental
measurements carried out at very high fluences (2 10^16 1 MeV equivalent
n/cm^2) thus fostering the application of this TCAD approach for the design and
optimization of the new generation of silicon detectors to be used in future
HEP experiments.Comment: 8 pages, 14 figures. arXiv admin note: text overlap with
arXiv:1611.1013
DLTS and in situ C–V analysis of trap parameters in swift 50 MeV Li3+ ion-irradiated Ni/SiO2/Si MOS capacitors
Ni/SiO2/Si MOS structures were fabricated on n-type Si wafers and were irradiated with 50 MeV Li3+ ions with fluences ranging from 1×1010 to 1×1012 ions/cm2. High frequency C–V characteristics are studied in situ to estimate the build-up of fixed and oxide charges. The nature of the charge build-up with ion fluence is analyzed. Defect levels in bulk Si and its properties such as activation energy, capture cross-section, trap concentration and carrier lifetimes are studied using deep-level transient spectroscopy. Electron traps with energies ranging from 0.069 to 0.523 eV are observed in Li ion-irradiated devices. The dependence of series resistance, substrate doping and accumulation capacitance on Li ion fluence are clearly explained. The study of dielectric properties (tan δ and quality factor) confirms the degradation of the oxide layer to a greater extent due to ion irradiation
Measurement of the effect of Non Ionising Energy Losses on the leakage current of Silicon Drift Detector prototypes for the LOFT satellite
The silicon drift detectors are at the basis of the instrumentation aboard
the Large Observatory For x-ray Timing (LOFT) satellite mission, which
underwent a three year assessment phase within the "Cosmic Vision 2015 - 2025"
long-term science plan of the European Space Agency. Silicon detectors are
especially sensitive to the displacement damage, produced by the non ionising
energy losses of charged and neutral particles, leading to an increase of the
device leakage current and thus worsening the spectral resolution.
During the LOFT assessment phase, we irradiated two silicon drift detectors
with a proton beam at the Proton Irradiation Facility in the accelerator of the
Paul Scherrer Institute and we measured the increase in leakage current. In
this paper we report the results of the irradiation and we discuss the impact
of the radiation damage on the LOFT scientific performance.Comment: 21 pages, 7 figures, 2 tables. Accepted for publication by Journal of
Instrumentation (JINST
Voyager electronic parts radiation program, volume 1
The Voyager spacecraft is subject to radiation from external natural space, from radioisotope thermoelectric generators and heater units, and from the internal environment where penetrating electrons generate surface ionization effects in semiconductor devices. Methods for radiation hardening and tests for radiation sensitivity are described. Results of characterization testing and sample screening of over 200 semiconductor devices in a radiation environment are summarized
Proton Damage Effects on Carbon Nanotube Field-Effect Transistors
This research investigated the effects of proton damage on single-walled carbon nanotube (SWCNT) transistors. The transistors were irradiated by 1.8 MeV protons to determine the damage induced in the SWCNTs and the device substrate using Raman spectroscopy, and to observe the effect on transistor functionality by measuring current-voltage characteristics. Irradiation of the SWCNT transistors to a fluence of 1x1013 protons/cm2 resulted in 67% increase in the Raman D/G peak intensity ratio, while at a fluence of 2x1013 protons/cm2 the increase in the D/G ratio was only 18%, likely due to radiation annealing. Current-voltage measurements indicated an increasingly negative threshold voltage shift in SWCNT transistors as a function of proton fluence: -1.3 V after a fluence of 1x1012 protons/cm2 and -1.9 V after a fluence of 2x1013 protons/cm2. The drain current decreased 33% after a fluence of 1x1012 protons/cm2 and 58% after a fluence of 2x1013 protons/cm2. Charge pumping of the SWCNT transistors revealed a significant error attributed to the combination of the non-uniform distribution of SWCNTs across the gate region, adsorbates on the exposed SWCNT and gate oxide surfaces, and inconsistency in transistor performance. The transistor hysteresis also increased as a function of the proton fluence due to interface and bulk charge trapping. This research provided insight into the effect on SWCNT transistors due to proton irradiations up to a fluence of 2x1013 protons/cm2 demonstrating both interface and bulk damage effects
A setup for soft proton irradiation of X-ray detectors for future astronomical space missions
Protons that are trapped in the Earth's magnetic field are one of the main
threats to astronomical X-ray observatories. Soft protons, in the range from
tens of keV up to a few MeV, impinging on silicon X-ray detectors can lead to a
significant degradation of the detector performance. Especially in low earth
orbits an enhancement of the soft proton flux has been found. A setup to
irradiate detectors with soft protons has been constructed at the Van-de-Graaff
accelerator of the Physikalisches Institut of the University of T\"ubingen. Key
advantages are a high flux uniformity over a large area, to enable irradiations
of large detectors, and a monitoring system for the applied fluence, the beam
uniformity, and the spectrum, that allows testing of detector prototypes in
early development phases, when readout electronics are not yet available. Two
irradiation campaigns have been performed so far with this setup. The
irradiated detectors are silicon drift detectors, designated for the use
on-board the LOFT space mission. This paper gives a description of the
experimental setup and the associated monitoring system.Comment: 20 pages, 10 figures, 4 table
Irradiation impact on optimized 4H-SiC MOSFETs
Silicon (Si) power device’ technologies have reached a high maturity level, but current
limitations on mechanic, temperature operation and electric performances require to investigate other semiconductor materials that can potentially compete with and overcome those border issues. This is the case of Silicon Carbide (SiC) and Gallium Nitride (GaN) which are becoming serious competitors to the Si due to their superior physical properties. Concerning SiC, the 4Hpolytype seems to be the best suitable candidate for high power MOSFETs according to its band gap, electric field strength, electron bulk mobility, and attainable threshold voltage, among others. But still, technological processes must be optimized in order to SiC MOSFETS can compete with their Si counterparts. This is the case of the gate oxidation process. A reduction of interface charge density is required for threshold voltage stability, and further improvements of the interface quality are also needed for high inversion mobility values. Once solved these problems, a path toward new perspectives of high power applications will be opened.
This work is the direct continuation of the Aurore Constant’s work. It is focused on 4HSiC
based devices, more specifically on the gate oxidation processes and their behaviour under
different harsh environments. Up to now, most of the works carried out were focused on the
improvement of the Silicon Dioxide-Silicon Carbide (SiO2/SiC) interface quality. Solving those
problems would allow designing high-speed and low-switching losses MOSFETs. In the past
work, the main strength was focused on a new surface pre-treatment and on a gate oxidation
process. Results showed improved electrical performances. However, we are convinced that
better values can be obtained by optimizing the post-oxidation annealing step, by performing
surface counter doping or by performing special irradiation treatments. All the efforts of this
work will oriented to the development of reliable SiC MOSFETs with improved electrical
parameters, which can operate under harsh environments (like high temperature or
proton/electron irradiated environment). Thus, the mains guidelines of this Ph. D. Thesis are in accordance with the following lines:
1. State of the art on various SiC related fields.
2. Electrical characterization processes.
3. Proton irradiation impact on 4H-SiC MOSFETs and charge build-up mechanisms theory at
the SiO2/SiC interface.
4. Electron irradiation impact on 4H-SiC MOSFETs.
5. Gate oxidation and implantation processes optimization.
6. Robustness limit of the improved processes under irradiation environments.Las tecnologías de dispositivos de potencia en silicio (Si) han alcanzado una gran madurez. Sin embargo, las limitaciones del Si debidas a sus restricciones mecánicas, térmicas y eléctricas hacen necesario otros materiales semiconductores que puedan competir con el Si y superar sus limitaciones. Este es el caso del Carburo de Silicio (SiC) y del Nitruro de Galio (GaN) que ya comienzan a ser serios competidores del Si debido a sus mejores propiedades físicas. En lo que respecta al SiC, el politipo 4H es el candidato más adecuado para la integración de MOSFETs de potencia debido, entre otros, a los valores del bandgap, campo eléctrico crítico, movilidad volumíca de los electrones y tensión umbral alcanzable. A pesar de estas ventajas teóricas del material, es necesario optimizar cada uno de los procesos tecnológicos involucrados en la fabricación de un MOSFET en SiC para que realmente pueda competir con su contrapartida en Si. Este es el caso del proceso de oxidación para la formación del dieléctrico de puerta. Concretamente, una buena estabilidad de la tensión umbral del componente requiere disminuir la densidad de cargas en la interfase óxido/semiconductor, y mejoras adicionales en la calidad de esta interfase son también necesarias para obtener altos valores de la movilidad de los portadores en el canal de inversión. La solución de los problemas tecnológicos anteriormente enunciados abrirá nuevas perspectivas a las aplicaciones de alta potencia. Este trabajo es una continuación directa del de Aurore Constant. Se centra en dispositivos basados en 4H-SiC, y más específicamente en los procesos de oxidación de puerta, y de sus comportamientos eléctricos en diferente ambientes de trabajo hostiles. Hasta la fecha, la mayor parte de la investigación se ha centrado en la mejora de la calidad de la interfase dióxido de silicio/carburo de silicio (SiO2/SiC). La solución de estos problemas debería permitir el diseño de MOSFETs muy rápidos y con pérdidas de conmutación muy bajas. El objetivo del trabajo previo de Aurore Constant fue encontrar un nuevo procedimiento de limpieza de la superficie antes de realizar la oxidación, y en definir un nuevo proceso de oxidación para la formación del dieléctrico de puerta. Los resultados obtenidos mostraron claras mejoras del comportamiento eléctrico de los componentes. Sin embargo, estamos convencidos que la mejora podría ser aún mayor optimizando la etapa del recocido post-oxidación, utilizando un proceso adicional de dopaje superficial, o realizando un adecuado proceso de irradiación. Todos los esfuerzos de este trabajo se han dirigido al desarrollo de MOSFETs en SiC fiables, con mejores características eléctricas, y capaces de trabajar en ambientes de alta temperatura y de irradiación protónica o electrónica. En resumen, las principales líneas de esta Tesis son las siguientes: 1. Estado del arte de los diferentes dominios de trabajo del SiC. 2. Procesos y técnicas de caracterización eléctrica. 3. Impacto de la irradiación de protones en MOSFETs fabricados en 4H-SiC, y descripción teórica de los mecanismos de creación de carga en la interfase SiO2/SiC. 4. Impacto de la irradiación electrónica en MOSFETs fabricados en 4H-SiC. 5. Optimización de los procesos de oxidación y de implantación. 6. Límite de robustez de los procesos tecnológicos optimizados en ámbitos irradiados.Postprint (published version
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