La evolución de los dispositivos MOS ha conllevado una reducción de tamaño de los mismos con el fin de mejorar sus prestaciones. Sin embargo, este continuo escalado se ha topado con un límite físico: la delgada capa aislante de SiO2 (entre otros), que fuerza la búsqueda de nuevas alternativas que permitan abastecer al exigente mercado tecnológico. En las dimensiones en las que actualmente se trabaja, del orden de nanómetros, los fenómenos cuánticos adquieren gran importancia siendo, entre otros, las corrientes de fuga uno de los principales escollos con los que se ha de lidiar. Estas corrientes provocan un aumento del consumo de potencia y disminución de la fiabilidad del dispositivo. Entre las alternativas que se perfilan como posibles opciones para reducir estas corrientes de fuga, la sustitución del hasta ahora principal aislante de la electrónica, el SiO2, por un material con una mayor constante dieléctrica, high-k (HK), ocupa una posición aventajada. Estos nuevos materiales HK permitirían mantener la misma capacidad del óxido que se obtendría usando un determinado grosor de SiO2 pero, utilizando un grosor físico mayor, reduciendo de esta manera las corrientes de fuga a través de la puerta del MOSFET. Aunque es una idea ampliamente aceptada no por ello es una tarea sencilla, ya que la introducción de estos nuevos materiales no está exenta de problemas que puedan influir en la fiabilidad del dispositivo. Por ejemplo, la morfología de los high-k y su impacto en las propiedades eléctricas del stack son factores importantes que deben ser considerados ya que pueden influir en el correcto funcionamiento del dispositivo. Los materiales bajo estudio son varios y diversos, pero gran parte de la comunidad científica apunta hacia el HfO2, o aleaciones relacionadas, y el Al2O3, como sustitutos del SiO2. Esta tesis, enmarcada en el campo de la microelectrónica, y concretamente en el estudio de la fiabilidad y caracterización eléctrica de los dispositivos MOS (Metal Óxido Semiconductor) de última generación, basados en HfO2, se centra principalmente en la evaluación, a escala nanométrica, de las propiedades morfológicas y eléctricas de dispositivos MOS fabricados con dieléctricos high-k (en concreto el HfO2). Particularmente, se analiza la influencia de la cristalización de la capa de HfO2, característica que adquiere tras haber sido sometida a un proceso de annealing durante el proceso de fabricación, en las propiedades eléctricas de la misma. Dicha cristalización puede alterar las propiedades morfológicas del material, lo que a su vez, puede repercutir en su homogeneidad eléctrica y su fiabilidad. También se ha llevado a cabo el estudio a escala nanométrica del fenómeno Resistive Switching, principal principio de operación de las memorias resistivas de acceso aleatorio (ReRAM). La evaluación del impacto de la cristalización, a escala nanométrica, se ha llevado a cabo mediante el uso de técnicas y herramientas de caracterización con resoluciones nanométricas como el AFM (Atomic Force Microscope) y técnicas relacionadas como el C-AFM (Conductive Atomic Force Microscope) o el Kelvin Probe Force Microscope (KPFM). / The evolution of MOS devices has involved an important shrinking in the transistor size with the aim of improve their benefits. However, this continuous miniaturization has found its physical limits in the thin SiO2 dielectric layer with current sizes at nanometric scale. Due to the continuous SiO2 layer thickness shrinking in a MOS transistor, tunnelling current increased more and more becoming the dominant source of device leakage. The main consequences of this leakage current enlargement are, on one hand, the consumption increase and, on the other hand, the impoverishment of the reliability of the device, which can be understood as an increment of the probability that the device failure happens for shorter times than usually. As a possible alternative to reduce the tunnelling current and also to avoid reliability issues, materials with higher dielectric constant were proposed to replace the SiO2 layer. These materials, known as high-k dielectrics, allow to obtain the equivalent performance for the capacitance with a larger physical thickness reducing, therefore, the leakage current. However, this substitution, although it sounds simple it is really a complicate issue since the introduction of new materials has associated new challenges and difficulties that must be solved. For example, the morphology of the high-k material and its impact on the electrical properties of the stack are important factors to be considered. Different materials are under study but HfO2, and related alloys, and Al2O3 are highlighted materials. This thesis, enshrined in the field of microelectronics and, specifically, in the reliability and electrical characterization of MOS devices based on high-k dielectrics, has been devoted to the analysis of nanoscale morphological and electrical properties of thin HfO2 layers with the aim to gain more insight in these new materials and related problems. Concretly, the influence of their polycrystallization on the electrical properties and breakdown (BD) of a HfO2 based gate stack has been evaluated. The study of the Resistive Random Access Memory (ReRAM) operating principle, Resistive Switching (RS), has been also investigated on MIM structures with HfO2 as dielectric. Since many of the problems associated to these materials (like, for example, their polycrystallization) and the failure mechanisms that affect the gate oxide are phenomena that have been found to have a nanometric origin, these analyses have been performed with AFM and related techniques as CAFM (Conductive Atomic Force Microscopy) or KPFM (Kelvin Probe Force Microscopy).

Electronic devices such as high power devices, microprocessors and memories in integrated circuit are primarily composed of metal-oxide-semiconductor field effect transistors (MOSFETs), due to the advantages of low cost, low power consumption and easy to scale down. However, the aggressively scaled conventional MOS devices have suffered remarkable short channel effects such as drain induced barrier lowering, punch-through, and direct-tunneling gate leakage. These problems not only lower the gate controllability but also increase the standby power consumption. Because the SiO2 dielectric and poly-gate are improper for CMOS application below 45 nm technology node due to the critical gate leakage current. Therefore, we investigate the electrical characteristics and physical mechanisms of MOSFETs with HfO2/TixN1-x gate stacks by using split C-V, pulsed Id-Vg, and charge-pumping techniques. The experimental results indicate that dynamic stress is more serious than static stress, and hot-carrier effect corresponding to different gate stress biases demonstrate distinct dominant degradation behaviors and the charge-trapping phenomenon. Furthermore, different concentration of titanium in TiN metal gate significantly affect device characteristics associated with the amount of nitrogen diffusion from the metal gate to high-k bulk and the SiO2/Si interface layer.

In this study, high-pressure oxygen (O2 and O3) technologies were employed originally to effectively improve the properties of low-temperature-deposited metal oxide dielectric films. In this work, 5 nm ultra-thin HfO2 and ZrO2 films were deposited by sputtering method at room temperature. Then, the low temperature high-pressure oxygen treatments at 150 ¢XC were used to replace the conventional high temperature annealing for HfO2 and ZrO2 improvement. From the experimental results, O3 produced by UV light illumination in O2 ambient has the superior passivation ability than O2, and it can further suppress leakage current density and improve capacitance characteristics. According to the XPS analyses, the absorption peaks of Hf-O and Zr-O bonding energies apparently raise and the quantity of oxygen in HfO2 and ZrO2 film also increases from XPS measurement. In addition, both the leakage current density of 5nm HfO2 and ZrO2 film can be improved to 10-8 A/cm2 at |Vg| = 3 V, and the conduction mechanisms were transferred from trap-assisted tunneling to thermal emission because of the significantly reduction of defects. All the experiment processes in this study, the temperatures were controlled below 150 ¢XC. The proposed low-temperature and high pressure O2 or O3 treatment for improving high-k dielectric films is novel and applicable for the future flexible electronics.

Made available in DSpace on 2018-08-01T22:29:42Z (GMT). No. of bitstreams: 1 tese_8916_Dissertação Moacir Cézar.pdf: 11454685 bytes, checksum: d1e7703b13b2f4b4e041b4d6cd4ef056 (MD5) Previous issue date: 2015-04-30 / Neste trabalho foram utilizados cálculos de primeiros princípios baseado na Teoria do Funcional Densidade (DFT) para investigar a formação de interfaces de monocamada de grafeno (G) e bicamada de grafeno (BLG) com óxido de háfnio amorfo (a-HfO2). Defeitos de vacâncias de Carbono (VC) e defeito de vacância de Oxigênio (VO) também foram considerados nas folhas de grafeno e na superfície do a-HfO2, respectivamente. Mais especificamente, foram explorados diferentes interfaces, a citar: (i) G(VC)/a-HfO2, (ii) G(VC)/a-HfO2(VO) e (iii) BLG(VC)/a-HfO2. Do ponto de vista de estabilidade energética, os resultados obtidos mostraram que a formação das interfaces são um processo exotérmico, nos casos (i) e (iii) regidos pela interação de van derWaals. Entretanto, para a interface (ii) verificou-se uma energia de interação duas vezes maior que as anteriores, além do surgimento de ligações químicas entre Hf-C na região da interface. Do ponto de vista estrutural, após a formação das interfaces surge uma corrugação nas folhas grafênicas e a distância média de equilíbrio entre a folha de grafeno interfacial e o substrato foi de 3,0 Å em ambos os casos. Além disso, determinou-se que o estado fundamental do sistema é magnético para as interfaces (i) e (iii) e não magnético para a interface (ii). Assim, os resultados indicam que as propriedades estruturais, eletrônicas e magnéticas das folhas de grafeno são sensíveis a presença do substrato de a-HfO2.

No description available.

No presente trabalho é apresentado o estudo sistemático das interações hiperfinas, em compostos de óxido de háfnio (HfO2) dopados com silício (Si), ferro (Fe), ítrio (Y) e lantânio (La) em porcentagens de 5% e 10%. A técnica aplicada para esse estudo foi o de correlação angular gama-gama perturbada (CAP) utilizando o núcleo de prova 181Hf(181Ta). Além disso, o estudo também foi estendido para o háfnio (Hf) na estrutura de ortosilicatos (HfSiO4) dopado com 20% Fe e na forma de filmes finos de HfO2. As amostras foram produzidas pelo método sol gel e para os filmes finos foi utilizado a técnica de spin coating. A caracterização estrutural destas amostras foi pela técnica de difração de raios-X e para morfologia foi utilizada as microscopias eletrônicas de varredura e transmissão. O núcleo de prova 181Hf(181Ta) presente na rede cristalina de todos os compostos forneceu os resultados da frequências de quadrupolo elétrico para o sitio monoclínico do óxido de háfnio (m- HfO2) bem caracterizado e um segundo sítio relacionado as vacâncias de oxigênio e defeitos na rede cristalina do HfO2. Além disso, as medições CAP que foram realizadas para as amostras de HfO2 dopadas, apresentam a formação de um terceiro sítio que está relacionado com o tamanho da partícula e a dopagem. Para o composto de HfSiO4 os resultados CAP indicam a temperatura de difusão do silício (Si), por volta de 700 °C e para o Fe- HfSiO4 mostra a influência do ferro na nucleação do composto que é superior em 30% em relação ao HfSiO4. Para as amostras de filmes finos os resultados CAP evidenciam os efeitos de superfície observado pelo surgimento de um terceiro sítio, ao longo do tratamento térmico 200 - 900 °C durante a medida. Este sítio também foi observado em temperaturas ambiente. / In this study, the development of a methodology for the synthesis of powder samples of Si-, Fe-, Y-, and La-doped hafnium oxide (HfO2) with concentrations of 5% and 10% is presented as well as the synthesis of orthosilicates (HfSiO4) samples doped with 20% of Fe. In addition, a procedure to produce HfO2 thin films using the spin coating method was also developed. All samples were characterized by usual techniques, such as X-ray diffraction, for structural verification and transmission and scattering electron microscopy, to study the size and morphology. Also a non-usual technique, perturbed angular correlation (PAC) was used to perform a systematic investigation of the hyperfine interactions in the doped samples, and at the Hf positions in the HfSiO4:Fe and HfO2 thin film samples. For PAC measurements 181Hf(181Ta) probe nuclei were used. The benefit in using 181Hf(181Ta) probe nuclei in these measurements is that the 180Hf isotope is naturally present in these samples, thus allowing the acquisition of 181Hf acquisition by the activation of the 180Hf in the IEA-R1 nuclear reactor. This method guarantees that probe nuclei are at Hf sites in the samples. The presence of 181Hf in the crystalline structure in all the compounds provided the hyperfine interaction results, such as electric quadrupole frequency, asymmetry parameter and delta, for the monoclinic site of the hafnium oxide (m-HfO2), and a second site related to the oxygen vacancies and defects in samples crystalline structure. Moreover, PAC measurements performed with the doped HfO2 samples revealed that probe nuclei occupy a third site related to the presence of the dopant. PAC measurements for HfSiO4 samples indicate the temperature of the silicon diffusion around 700 °C, and for the iron doped sample show the influence of iron atoms in the compound nucleation, which is 30 % higher when comparing to pure HfSiO4. For the thin film samples PAC results indicate the presence of surface defects, confirmed by the occurrence of a third site during a 200 - 900 °C annealing made during the measurement. This site has also been noted after a room temperature measurement after annealing.

No presente trabalho é apresentado o estudo sistemático das interações hiperfinas, em compostos de óxido de háfnio (HfO2) dopados com silício (Si), ferro (Fe), ítrio (Y) e lantânio (La) em porcentagens de 5% e 10%. A técnica aplicada para esse estudo foi o de correlação angular gama-gama perturbada (CAP) utilizando o núcleo de prova 181Hf(181Ta). Além disso, o estudo também foi estendido para o háfnio (Hf) na estrutura de ortosilicatos (HfSiO4) dopado com 20% Fe e na forma de filmes finos de HfO2. As amostras foram produzidas pelo método sol gel e para os filmes finos foi utilizado a técnica de spin coating. A caracterização estrutural destas amostras foi pela técnica de difração de raios-X e para morfologia foi utilizada as microscopias eletrônicas de varredura e transmissão. O núcleo de prova 181Hf(181Ta) presente na rede cristalina de todos os compostos forneceu os resultados da frequências de quadrupolo elétrico para o sitio monoclínico do óxido de háfnio (m- HfO2) bem caracterizado e um segundo sítio relacionado as vacâncias de oxigênio e defeitos na rede cristalina do HfO2. Além disso, as medições CAP que foram realizadas para as amostras de HfO2 dopadas, apresentam a formação de um terceiro sítio que está relacionado com o tamanho da partícula e a dopagem. Para o composto de HfSiO4 os resultados CAP indicam a temperatura de difusão do silício (Si), por volta de 700 °C e para o Fe- HfSiO4 mostra a influência do ferro na nucleação do composto que é superior em 30% em relação ao HfSiO4. Para as amostras de filmes finos os resultados CAP evidenciam os efeitos de superfície observado pelo surgimento de um terceiro sítio, ao longo do tratamento térmico 200 - 900 °C durante a medida. Este sítio também foi observado em temperaturas ambiente. / In this study, the development of a methodology for the synthesis of powder samples of Si-, Fe-, Y-, and La-doped hafnium oxide (HfO2) with concentrations of 5% and 10% is presented as well as the synthesis of orthosilicates (HfSiO4) samples doped with 20% of Fe. In addition, a procedure to produce HfO2 thin films using the spin coating method was also developed. All samples were characterized by usual techniques, such as X-ray diffraction, for structural verification and transmission and scattering electron microscopy, to study the size and morphology. Also a non-usual technique, perturbed angular correlation (PAC) was used to perform a systematic investigation of the hyperfine interactions in the doped samples, and at the Hf positions in the HfSiO4:Fe and HfO2 thin film samples. For PAC measurements 181Hf(181Ta) probe nuclei were used. The benefit in using 181Hf(181Ta) probe nuclei in these measurements is that the 180Hf isotope is naturally present in these samples, thus allowing the acquisition of 181Hf acquisition by the activation of the 180Hf in the IEA-R1 nuclear reactor. This method guarantees that probe nuclei are at Hf sites in the samples. The presence of 181Hf in the crystalline structure in all the compounds provided the hyperfine interaction results, such as electric quadrupole frequency, asymmetry parameter and delta, for the monoclinic site of the hafnium oxide (m-HfO2), and a second site related to the oxygen vacancies and defects in samples crystalline structure. Moreover, PAC measurements performed with the doped HfO2 samples revealed that probe nuclei occupy a third site related to the presence of the dopant. PAC measurements for HfSiO4 samples indicate the temperature of the silicon diffusion around 700 °C, and for the iron doped sample show the influence of iron atoms in the compound nucleation, which is 30 % higher when comparing to pure HfSiO4. For the thin film samples PAC results indicate the presence of surface defects, confirmed by the occurrence of a third site during a 200 - 900 °C annealing made during the measurement. This site has also been noted after a room temperature measurement after annealing.

Aujourd'hui, le marché des mémoires non-volatile est dominé par la technologie Flash. Cependant, cette technologie est en passe d'atteindre ses limites de miniaturisation. Ainsi, dans le but de poursuivre la réduction des dimensions, de nouveaux concepts mémoires sont explorés. Parmi les technologies émergentes, la mémoire résistive OxRRAM basée sur la commutation de résistance d’une structure Métal/Isolant/Métal, cette technologie présente des performances prometteuses, supporte une réduction de ses dimensions critiques et offre une bonne compatibilité avec les filières CMOS. Toutefois, cette technologie mémoire n'en est qu'au stade du développement et se heurte à une compréhension que partielle des mécanismes de commutation de résistance.Ce travail de thèse s'intègre dans ce contexte et vise à apporter une contribution supplémentaire au développement de cette technologie. La première partie est consacrée à la sélection du meilleur couple électrodes/matériau actif. A l’aide d’une analyse des caractéristiques électriques de commutation, l’empilement TiNHfO2Ti est retenu pour être intégré dans une structure 1T1R. Une seconde partie présente la caractérisation électrique avancée de l’architecture mémoire 1T1R. L'influence des différents paramètres de programmation est analysée et les performances électriques sont évaluées. La dernière partie apporte des éléments d'analyse et de compréhension sur les mécanismes de commutation de résistance. La mesure, en fonction de la température, des caractéristiques électriques de commutation a permis d'analyser l'influence de la température et du champ électrique sur les mécanismes physiques à l'origine du changement de résistance. / Today, non-volatile memory market is dominated by charge storage based technologies. However, this technology reaches his scaling limits and solutions to continue miniaturization meet important technological blocks. Thus, to continue scaling for advanced nodes, new non-volatile solutions are developed. Among them, oxide based resistive memories (OxRRAM) are intensively studied. Based on resistance switching of Metal/Isolator/Metal stack, this technology shows promising performances and scaling perspective but isn’t mature and still suffer from a lake of switching mechanism physical understanding.Results presented in this thesis aim to contribute to the development of OxRRAM technology. In a first part, an analysis of different materials constituting RRAM allow us to compare unipolar and bipolar switching modes and select the bipolar one that benefit from lower programming voltage and better performances. Then identified memory stack TiNHfO2Ti have been integrated in 1T1R structure in order to evaluate performances and limitation of this structure. Operating of 1T1R structure have been carefully studied and good endurance and retention performances are demonstrated. Finally, in the last part, thermal activation of switching characteristics have been studied in order to provide some understanding of the underling physical mechanisms. Reset operation is found to be triggered by local temperature while retention performances are dependent of Set temperature.

En raison de leur faible consommation d'énergie, les mémoires non volatiles (MNV) sont En raison de leur faible consommation d'énergie, les mémoires non-volatiles sont particulièrement intéressantes pour l'électronique portative (clé USB, téléphone, ordinateur portable …). Les mémoires Flash, qui dominent le marché, atteignent leurs limites physiques et doivent être remplacées. L'introduction de nouveaux matériaux et architectures mémoire est proposée. Les mémoires OxRRAM (Oxide Resistive Random Access Memory) sont des candidats potentiels. Il s'agit de structures M-O-M (Métal-Oxyde-Métal). Le stockage de l'information est basé sur la modulation de la résistance de l'oxyde à l'application d'un champ électrique ou d'un courant. Une meilleure compréhension du mécanisme de changement de résistance de ces dispositifs est nécessaire pour contrôler leurs performances. Nous nous intéressons au claquage diélectrique de l'oxyde, qui initie le mécanisme de changement de résistance. Les mesures physico-chimiques à l'échelle nanométrique sont indispensables à sa compréhension et font défaut dans la littérature. Dans cette thèse, nous proposons des mesures physico-chimiques, des mesures électriques et des méthodes de préparation d'échantillon adaptées. Les oxydes de nickel et d'hafnium sont investigués. En plus de la dégradation électrique (chute de résistance), les modifications de ces deux oxydes sont investiguées à trois niveaux : la composition chimique, la morphologie et la structure électronique. Mots-clés : mémoire résistive, mécanisme de changement de résistance, claquage diélectrique, NiO, HfO2, spectroscopie de photoélectrons, microscopie électronique en transmission, microscopie à forme atomique, lacunes d'oxygène. / With low energy consumption, non-volatile memories are interesting for portative applications (USB, mobile phone, laptop …). The Flash memory technology is reaching its physical boundaries and needs to be replaced. New materials and architectures are currently investigated. Oxide Resistive Random Access Memory (OxRRAM) is considered as a good candidate. It is based on a M-O-M (Metal-Oxide-Metal) stack. The information is stored using an electric field or a current that modulates the resistance of the oxide. A better understanding of the resistance switching mechanism is required in order to control the performances of the devices. We investigate the dielectric breakdown that activates the resistance switching properties. Physico-chemical characterization at the nanoscale is required. In this work, we propose proper physico-chemical and electrical measurements. Sample preparation is also considered. Nickel and hafnium oxide are investigated. Besides the evolution of the electrical properties, we analyze the oxide modification at three levels : the chemical composition, the morphology and the electronic structure. Keywords : resistive memory, resistance switching mechanism, dielectric breakdown, NiO, HfO2, photoelectron spectroscopy, electronic transmission microscopy, atomic force microscopy, oxygen vacancies.

Die überraschende Entdeckung von ferroelektrischem Hafniumoxid durch Böscke et al. im Jahre 2011 eröffnet zahlreich technologische Möglichkeiten wie zum Beispiel voll CMOS kompatible ferroelektrische RAM Speicherzellen. Als kristallographische Ursache für dieses Verhalten erwies sich die Raumgruppe Pca21. In theoretischen Untersuchungen mit Hilfe der Dichtefunktionaltheorie erwies sich diese Phase jedoch als thermodynamisch instabil. Ziel dieser Dissertation ist daher zu klären, wie diese Phase stabilisiert werden kann. Dazu werden Faktoren wie Stöchiometrie, Temperatur, Druck, Spannung, Grenzflächenenergie sowie Defekte und Dotierung mit Hilfe der Dichtefunktionaltheorie untersucht. Die errechneten Ergebnisse werden mit Hilfe von Modellen interpretiert, welche im laufe dieser Dissertation erarbeitet werden. Es zeigt sich, dass neben dem energetischen Zustand auch der Herstellungsprozess des Materials eine bedeutende Rolle in der Stabilisierung der ferroelektrischen Phase von Hafniumoxid spielt. Abschließend wird versucht Verbindung zum Experiment herzustellen, in dem experimentell zugängliche Stellschrauben aufgezeigt werden, welche die ferroelektrischen Eingenschaften von Hafniumoxid verbessern können und sich aus den erarbeiteten Ergebnissen ableiten. / The surprising discovery of ferroelectric hafnium oxide by Böscke et al. in 2011 enables various technological possibilities like CMOS compatible ferroelectric RAM devices. The space group Pca21 was identified as the crystallographic cause of this behavior. However, this phase was proved to be thermodynamically unstable by several theoretical studies using density functional theory. Therefore, the goal of this dissertation is to investigate physical effects contributing to the stabilization of the ferroelectric phase by means of density functional theory. These effects include stoichiometry, temperature, stress, strain, interface energy, as well as defects and dopants. The computational results will be interpreted with models, which will be developed within this dissertation. It will become apparent, that in addition to the energetic state, the production process of a sample plays an important role in the stabilization of the ferroelectric phase of hafnium oxide. In the conclusion, this work will attempt to find a connection to the experiment, by identifying experimentally accessible parameters within the computational results which can be used to optimize the ferroelectric properties of ferroelectric materials.