Estudio de la estabilidad térmica del a-SiNx:H producido mediante la técnica de plasma ECR-CVD

[SPA] La técnica de deposición química en fase de vapor activada por resonancia ciclotrónica de electrones (ECR-CVD) ha sido empleada para crecer láminas delgadas de nitruro de silicio hidrogenado (SiNx:H) de varias composiciones. Este dieléctrico de elevada permitividad tiene numerosas aplicaciones en microelectrónica, y reúne algunas características adecuadas para sustituir o complementar al óxido de silicio como aislante de puerta de transistores de efecto campo de estructura MOS en aquellos casos en que la continua reducción de las dimensiones laterales de los dispositivos conduce a alcanzar el mínimo espesor de óxido tolerable. Con posterioridad al crecimiento las muestras fueron sometidas a tratamientos térmicos rápidos (RTA) a temperaturas comprendidas entre 300 ºC y 1050 ºC con el objetivo de estudiar la evolución de las propiedades del SiNx:H en función de la temperatura de estos procesos. Un amplio número de técnicas analíticas y espectroscópicas han sido utilizadas para analizar el comportamiento del SiNx:H frente a la temperatura. La composición ha sido estudiada mediante técnicas de análisis de haces de iones: RBS y ERDA. La primera de ellas ha sido utilizada para determinar la proporción nitrógeno a silicio en las láminas, mientras que la segunda permite conocer el contenido de hidrógeno (que no puede ser detectado por RBS). La estructura de enlaces del material ha sido analizada mediante espectroscopia infrarroja, mientras que las imperfecciones o defectos presentes en la red (enlaces de silicio no saturados) fueron estudiados por resonancia de espín electrónico (ESR). Las propiedades de absorción óptica (índice de refracción y coeficiente de absorción) también han sido consideradas, estudiándose el borde de absorción de Urbach mediante espectroscopia en el ultravioleta-visible. Por último se realizaron estructuras metal-nitruro-silicio para investigar las características eléctricas y la densidad de centros de captura de carga en la intercara mediante medidas I-V y C-V. Las conclusiones del trabajo han permitido poner de manifiesto el papel determinante que desempeña el hidrógeno en las propiedades del SiNx:H. El hidrógeno se puede encontrar enlazado tanto a silicio como a nitrógeno, así como atrapado en las microcavidades de la red sin formar enlaces. Para temperaturas elevadas de RTA se producen reacciones de deshidrogenación que deterioran las características eléctricas y el orden estructural de la red de enlaces. El tipo de reacción y la temperatura a la que se produce dependen de las concentraciones relativas de enlaces Si-H y N-H. A temperaturas intermedias y bajas de RTA tienen lugar reacciones de incorporación y transferencia de hidrógeno, así como procesos de relajación estructural de las constricciones impuestas por los ángulos de enlace, todo lo cual se refleja tanto en el borde de absorción óptica como en las características de la intercara con el silicio.[ENG] Silicon nitride thin films with various compositions and hydrogen content (SiNx:H) have been grown by the electron cyclotron resonance chemical vapour deposition technique (ECR-CVD). This material is investigated due to its higher dielectric constant compared to silicon oxide, which allows increasing the gate dielectric thickness in MOS transistors and hence reduces gate leakage currents. After deposition, the films were subjected to rapid thermal annealing (RTA) treatments at temperatures between 300 ºC and 1050 ºC, with the objective of studying the evolution of the SiNx:H properties as a function of temperature. Composition was measured by RBS (Rutherford Back-Scattering spectroscopy) and heavy-ion ERDA (elastic recoil detection analysis), which allow the determination of the nitrogen to silicon ratio (stoichiometry) and hydrogen content of the samples. The bonding structure of the material has been analyzed by infrared spectroscopy, while the number of defects (silicon dangling bonds) was determined by electron spin resonance (ESR). The optical properties (refraction index and absorption coefficient) were measured by ultraviolet-visible-near infrared spectroscopy in order to explore the Urbach absorption edge and bandgap states. Finally, metal-SiNx:H-silicon structures were made to investigate the electrical characteristics and the density of interface states by I-V and C-V measurements. The results from this set of measurements have shown that the content and bonding of hydrogen has a key role in determining the properties of SiNx:H. Hydrogen can be bonded to silicon and nitrogen, as well as trapped in micro-cavities of the structure in the form of non-bonded hydrogen. At high annealing temperatures, dehydrogenation reactions take place that deteriorate the electrical characteristics and the structural order of the bond network. Depending on the relative concentrations of Si-H and N-H, the type of reaction and its threshold temperature are different. Below this threshold, at low and moderate annealing temperatures, bond reactions produce the incorporation of non-bonded hydrogen and the transfer of hydrogen from N-H to Si-H bonds. This is accompanied by a structural relaxation of the bond network, which is noticeable both in the optical absorption edge and in the electrical characteristics of the interface. Interestingly, the same effect of hydrogen transfer from N-H to Si-H bonds has been found when the source of energy is the ion beam used in the ERDA measurements.Universidad Complutense de Madri

Sistema y método para caracterización electromagnética de materiales.

Número de publicación: 2 611 553 Número de solicitud: 201630964El sistema tiene: un primer sensor (S1) aplicado a un material desconocido (M); un equipo de medidas (EM); una primera guía de transmisión (G1) conectando el primer sensor (S1) con el equipo de medidas (EM); una primera transición (T1) para realizar una conexión entre el primer sensor (S1) y la primera guía de transmisión (G1); una segunda transición (T2) para realizar una conexión entre la primera guía de transmisión (G1) y el equipo de medidas (EM). El método incluye acondicionar el material desconocido (M). El acondicionamiento puede incluir: el material desconocido (M); el material desconocido (M) depositado sobre un material conocido (Mc); el material desconocido (M) depositado sobre un material conductor (Mcond); el material desconocido (M) depositado sobre dos capas que tienen un material conocido (Mc) y un material conductor (Mcond); un material conocido (Mc) depositado sobre dos capas que tienen el material desconocido (M) y un material conductor (Mcond).Universidad Politécnica de Cartagen

Crecimiento y caracterización de láminas delgadas de dieléctricos de alta permitividad para su aplicación en la estructura de puerta de transistores de efecto campo

La industria microelectrónica necesita desarrollar nuevos materiales dieléctricos que puedan sustituir al óxido de silicio en la estructura de puerta de los transistores de efecto campo CMOS, especialmente conforme nos acercamos a niveles de integración con dimensiones de tan solo 45 nm para la longitud del canal. Con este fin serán necesarios dieléctricos de mayor permitividad que el óxido de silicio, denominados genéricamente dieléctricos de alta k. La mayor constante dieléctrica de estos materiales permite incrementar el espesor del dieléctrico respecto al valor que debería tener una lámina de óxido de silicio equivalente, resolviendo así los problemas de corrientes de túnel que presenta el óxido de silicio de espesor ultra-delgado. En este artículo realizamos un resumen de algunas de las técnicas experimentales que empleamos en este área.Escuela Técnica Superior de Ingeniería de Telecomunicació

Optimization of chirped and tapered microstrip koch fractal electromagnetic band gap (KFEBG) structures for improved low-pass filter design

This study presents electromagnetic bandgap (EBG) structures in microstrip technology based on onedimensional Koch fractal patterns (Koch fractal EBG (KFEBG)). This fractal geometry allows to adjust the radius r and distance a between patterns so that a low-pass filter response is obtained when the ratio r/a is higher than 0.5. However, in such case undesired strong ripples appear in the low bandpass region. We demonstrate that the performance in the passband of this filter can be improved by applying a tapering function to the Koch fractal dimensions and to the width of the microstrip line, while simultaneously chirping (modulating) the Koch fractal periodic pattern distance (a) so as to maintain a constant r/a ratio. Several tapering functions scaled by a factor K are presented, and the results of their application to the KFEBG microstrip structure are compared by means of relevant characteristic parameters. Optimal performance has been obtained for the Kaiser and Cauchy distributions applied to the Koch fractal pattern, combined with a rectangular and Cauchy distribution applied to the microstrip width, respectively.This work was supported by the Ministerio de Economía y Competitividad of Spain and the European Regional Development Funds (TEC2013-47037-C5-5-R)

Teaching-learning model for the science of electronics

We present a method for the teaching of Electronics, defined as the scientific discipline that studies the movement and behavior of electrons in semiconductor materials and in vacuum. Electronics can be considered as a science with a solid physical foundation. Within the field of Electronics there are different disciplines, some of them can be considered as pure science, while some others are more oriented to applications. Our methodology has been applied to the wide range of courses that develop the different approaches to Electronics, from the physics of semiconductors or the physics of microelectronic devices, generally taught at physics faculties, to microelectronic fabrication technology or microelectronic design, subjects that typically have a more application-oriented character. To ensure an effective learning of these subjects, a teaching-learning model has been established. This model involves the criteria for developing the programs and defining objectives according to the curricular competences, as well as the development of a series of activities in which the methods, techniques, forms of presentation and didactic resources most useful to achieve the proposed objectives will be used. An evaluation system that assesses the effectiveness of the educational process and detects its anomalies is also included. The impact of this method on the effectiveness of the teaching-learning process was evaluated by a comparative analysis of the results of the surveys distributed by the university to the students for the assessment of quality, together with surveys to the lecturers of the subjects of ElectronicsPeer Reviewe

Substrate integrated waveguide (SIW) with koch fractal electromagnetic bandgap structures (KFEBG) for bandpass filter design

High-performance bandpass filters (BPFs) based on substrate integrated waveguide (SIW) and half mode SIW (HMSIW) with Koch fractal electromagnetic bandgap (KFEBG) patterns etched on the waveguide surface are proposed. These BPFs are designed using a new methodology. The BPF responses are improved by applying a chirped and tapered technique to the KFEBG patterns, which exhibit a radius-to-period ratio r / a ≥ 0.5. Simulation results and experimental verification are presented. Low insertion loss and high rejection are achieved.This work was supported by the Spanish Ministerio de Economía y Competitividad (TEC2013-47037-C05-5-R) and European regional funds (FEDER)

1D Koch fractal electromagnetic bandgap microstrip structures with r/a ratios higher than 0.5

A 1-D Koch fractal electromagnetic bandgap (KFEBG) microstrip structure is proposed. It is conceived by replacing the conventional holes etched in the ground plane of a microstrip line by level-1 Koch fractal cell geometries, which have been obtained from a hexagonal shape. In the case of the conventional 1-D EBG microstrip structure with periodic hole pattern, the design is limited to r / a ratios lower than 0.45, while the proposed pattern allows achieving r / a ratios higher than 0.5. It is shown the conventional EBG and KFEBG microstrip structures behave as a stopband filter as r / a ≤ 0.45 . However, for r/ a = 0.55, the measurements have confirmed that the 1-D KFEBG microstrip structure presents a ultrawide stopband and, therefore, the proposed structure with r / a > 0.5 can be useful for the design of low-pass filters

Novel compact wide-band EBG structure based on tapered 1-D koch fractal patterns

This letter presents a novel electromagnetic bandgap (EBG) structure in microstrip technology based on nonuniform one-dimensional (1-D) Koch fractal patterns whose dimensions and period are modulated by a tapering function that significantly improves the width of the bandgap. This wide bandgap is achieved by maintaining the r/a (radius to period) ratio of the Koch fractal patterns larger than 0.5 in the whole structure. In the pass-band region, an improved flat response is obtained by tapering the dimensions of the Koch fractal patterns etched in the ground plane, together with the width of the microstrip line, with a Kaiser distribution which also modulates the periodicity of the fractals. A major consequence of this modulation of the periodicity of the pattern is that this structure is much more compact than a uniform conventional one.This work was supported by Ministerio de Educación y Ciencia of Spain (TEC2010-21520-C04-04/TCM)

Optical properties and structure of HfO2 thin films grown by high pressure reactive sputtering

Thin films of hafnium oxide have been grown by high pressure reactive sputtering on transparent quartz substrates (UV-grade silica) and silicon wafers. Deposition conditions were adjusted to obtain as well as amorphous films. Optical properties of the films deposited on the silica substrates were investigated by transmittance and reflectance spectroscopy in the ultraviolet, visible and near infrared range (UV-VIS-NIR). A numerical analysis method that takes into account the different surface roughness of the polycrystalline and amorphous films was applied to calculate the optical constants (refractive index and absorption coefficient). Amorphous films were found to have a higher refractive index and a lower transparency than polycrystalline films. This is attributed to a higher density of the amorphous samples, which was confirmed by atomic density measurements performed by heavy-ion elastic recoil detection analysis (ERDA). The absorption coefficient gave an excellent fit to the Tauc law (indirect gap), which allowed to obtain a band gap value of 5.54 eV. The structure of the films (amorphous or polycrystalline) was found to have no significant influence on the nature of the band gap. The Tauc plots also give information about the structure of the films, because the slope of the plot (the Tauc parameter) is related to the degree of order in the bond network. The amorphous samples had a larger value of the Tauc parameter, i.e., more order than the polycrystalline samples. This is indicative of a uniform bond network with percolation of the bond chains, in contrast to the randomly oriented polycrystalline grains separated by grain boundaries

Dielectric constant tunability at microwave frequencies and pyroelectric behavior of lead-free submicron-structured (Bi0.5Na0.5)1-xBaxTiO3 ferroelectric ceramics

In this article we show that the dielectric constant of lead-free ferroelectric ceramics based on the solid solution (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3, with compositions at or near the morphotropic phase boundary (MPB), can be tuned by a local applied electric field. Two compositions have been studied, one at the MPB, with x=0.06 (BNBT6), and another one towards the BNT side of the phase diagram, with x=0.04 (BNBT4). The tunability of the dielectric constant is measured at microwave frequencies between 100 MHz and 3 GHz by a non-resonant method and simultaneously applying a DC electric field. As expected, the tunability is higher for the composition at the MPB (BNBT6), reaching a maximum value of 60 % for an electric field of 900 V/cm, compared with the composition below this boundary (BNBT4), which saturates at 40 % for an electric field of 640 V/cm. The high tunability in both cases is attributed to the fine grain and high density of the samples, which have a submicron homogeneous grain structure with grain size of the order of a few hundred nanometers. Such properties make these ceramics attractive for microwave tunable devices. Finally, we have tested these ceramics for their application as infrared pyroelectric detectors and we have found that the pyroelectric figure of merit is comparable to traditional lead containing pyroelectrics.This work was supported by Ministerio de Ciencia e Innovación of Spain (TIN2009-14372-C03-02), Fundación Séneca (15303/PI/10), and CSIC (PIE 201060E069)