Untersuchung des elektronischen Transports an 28nm MOSFETs und an Schottky-Barrieren FETs aus Silizium-Nanodrähten

As modern microelectronics advances, enormous challenges have to be overcome in order to further increase device performance, enabling highspeed and ultra-low-power applications. With progressive scaling of Silicon MOSFETs, charge carrier mobility has dropped significantly and became a critical device parameter over the last decade. Present technology nodes make use of strain engineering to partially recover this mobility loss. Even though carrier mobility is a crucial parameter for present technology nodes, it cannot be determined accurately by methods typically available in industrial environments. A major objective of this work is to study the magnetoresistance mobility μMR of strained VLSI devices based on a 28 nm ground rule. This technique allows for a more direct access to charge carrier mobility, compared to conventional current/ voltage and capacitance/ voltage mobility derivation methods like the effective mobility μeff, in which series resistance, inversion charge density and effective channel length are necessary to extract the mobility values of the short channel devices. Aside from providing an anchor for accurate μeff measurements in linear operation conditions, μMR opens the possibility to investigate the saturation region of the device, which cannot be accessed by μeff. Electron and hole mobility of nFET and pFET devices with various gate lengths are studied from linear to saturation region. In addition, the interplay between mobility enhancement due to strain improvement, and mobility degradation due to short channel effects with decreasing channel length is analyzed. As a concept device for future nanoelectronic building blocks, silicon nanowire Schottky field-effect transistors are investigated in the second part of this work. These devices exhibit an ambipolar behaviour, which gives the opportunity to measure both electron and hole transport on a single device. The temperature dependence of the source/drain current for specific gate and drain voltages is analyzed within the framework of voltage dependent effective barrier heights.:1. Einleitung 2. Theoretische Grundlagen 3. Charakterisierungsmethoden 4. Messaufbau 5. Ergebnisse der Untersuchungen an MOSFETs 6. Ergebnisse der Untersuchungen an SiNW Transistoren 7. Zusammenfassung Anhang Danksagunge

Development of nanowire devices with quantum functionalities

Silicon has dominated the microelectronics industry for the last 50 years. With its zero nuclear spin isotope (28Si) and low spin orbit coupling, it is believed that silicon can become an excellent host material for an entirely new generation of devices that operate under the laws of quantum mechanics [1}. Semiconductor nanowires however, offer huge potential as the next building blocks of nano-devices due to their one-dimensional structure and properties [2]. We describe a fabrication process to prepare doped vapor-liquid-solid (VLS) grown silicon nanowire samples in a 2- and 4-terminal measurement setup for electrical characterisation.Comment: 2 pages Optoelectronic and Microelectronic Materials & Devices (COMMAD), 2014 Conferenc

Iterative reconstruction from few-view projections

[EN] In the medical imaging field, iterative methods have become a hot topic of research due to their capacity to resolve the reconstruction problem from a limited number of projections. This gives a good possibility to reduce radiation exposure on patients during the data acquisition. However, due to the complexity of the data, the reconstruction process is still time consuming, especially for 3D cases, even though implemented on modern computer architecture. Time of the reconstruction and high radiation dose imposed on patients are two major drawbacks in computed tomography. With the aim to resolve them effectively, we adapted Least Square QR method with soft threshold filtering technique for few-view image reconstruction and present its numerical validation. The method is implemented using CUDA programming mode and compared to standard SART algorithm. The numerical simulations and qualitative analysis of the reconstructed images show the reliability of the presented method.This work has been supported by Universitat Politècnica de València and partially funded by ANITRAN PROMETEOII/2014/008 of the Generalitat Valenciana of Spain.Flores, LA.; Vidal, V.; Verdú Martín, GJ. (2015). Iterative reconstruction from few-view projections. Procedia Computer Science. 51:703-712. https://doi.org/10.1016/j.procs.2015.05.188S7037125

Expectation maximization (EM) algorithms using polar symmetriesfor computed tomography(CT) image reconstruction

We suggest a symmetric-polar pixellation scheme which makes possible a reduction of the computational cost for expectation maximization (EM) iterative algorithms. The proposed symmetric-polar pixellation allows us to deal with 3D images as a whole problem without dividing the 3D problem into 2D slices approach. Performance evaluation of each approach in terms of stability and image quality is presented. Exhaustive comparisons between all approaches were conducted in a 2D based image reconstruction model. From these 2D approaches, that showing the best performances were finally implemented and evaluated in a 3D based image reconstruction model. Comparison to 3D images reconstructed with FBP is also presented. Although the algorithm is presented in the context of computed tomography (CT) image reconstruction, it can be applied to any other tomographic technique as well, due to the fact that the only requirement is a scanning geometry involving measurements of an object under different projection angles. Real data have been acquired with a small animal (CT) scanner to verify the proposed mathematical description of the CT system.This work was supported by the Spanish Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica (I+D+I) under Grant, FIS2010-21216-CO2-01, Valencian Local Government under Grant Nos. PROMETEO 2008/114 and APOSTD/2010/012. The authors would like to thank Brennan Holt for checking and correcting the text.Rodríguez Álvarez, MJ.; Soriano Asensi, A.; Iborra Carreres, A.; Sánchez Martínez, F.; González Martínez, AJ.; Conde, P.; Hernández Hernández, L.... (2013). Expectation maximization (EM) algorithms using polar symmetriesfor computed tomography(CT) image reconstruction. Computers in Biology and Medicine. 43(8):1053-1061. https://doi.org/10.1016/j.compbiomed.2013.04.015S1053106143

Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy.

From Europe PMC via Jisc Publications RouterHistory: ppub 2020-10-01, epub 2020-10-07Publication status: PublishedLarge single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L2,3-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine FeI dopant ions to be linearly coordinated, occupying a D 6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe-N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner-Teller vibronic coupling and pseudo Jahn-Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L2,3-edge XAS from which the energy reduction of 3d z 2 due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L3-edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm-1), that corresponds with Orbach relaxation via the first excited, M J = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects