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Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: John G. Ekerdt. Vita. Includes bibliographical references. Also available from UMI.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Jack C. Lee. Vita. Includes bibliographical references.

Hafnium Dioxide(HfO₂) thin films were deposited on glass, metal, and silicon wafer substrates using magnetron RF reactive sputtering techniques. Structure and morphology of the thin films were investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Results revealed that the sputtered HfO₂ thin films were (111) preferred oriented with single crystalline or polycrystalline natures. The sputtering parameters, including gas flow ratios of Ar/O₂, substrate temperature, pressure, and RF power levels, were examined, and their effects on the thin film structure and properties are discussed. Transparent hafnium oxide thin films can be deposited only when the RF power is lower than a certain level, which is limited by the gas flow ratio of Ar/O₂. High substrate temperature is critical for high (111) orientation in thin films while a high gas flow ratio of Ar/O₂ is important for crystal structure and adhesion. Annealing in oxygen atmosphere following the deposition was also found to be effective in improving thin film adhesion and resistance of losing adhesion during thermal cycles. Refractive index, and electrical resistance measurements show that HfO₂ thin films deposited by RF reactive sputtering under optimized conditions have promising electrical and optical properties which deserve further study. / Master of Science

Studies of the radiative properties of thin films and near-field radiation transfer in layered structures are important for applications in energy, near-field imaging, coherent thermal emission, and aerospace thermal management. A comprehensive study is performed on the optical constants of dielectric tantalum pentoxide (Ta₂O₅) and hafnium oxide (HfO₂) thin films from visible to the far infrared using spectroscopic methods. These materials have broad applications in metallo-dielectric multilayers, anti-reflection coatings, and coherent emitters based on photonic crystal structures, especially at high temperatures since both materials have melting points above 2000 K. The dielectric functions of HfO₂ and Ta₂O₅ obtained from this work may facilitate future design of devices with these materials. A parametric study of near-field TPV performance using a backside reflecting mirror is also performed. Currently proposed near-field TPV devices have been shown to have increased power throughput compared to their far-field counterparts, but whose conversion efficiencies are lower than desired. This is due to their low quantum efficiency caused by recombination of minority carriers and the waste of sub-bandgap radiation. The efficiency may be improved by adding a gold mirror as well as by reducing the surface recombination velocity, as demonstrated in this thesis. The analysis of the near-field TPV and proposed methods may facilitate the development or high-efficiency energy harvesting devices. Many near-field devices may eventually utilize metallo-dielectric structures which exhibit unique properties such as negative refraction due to their hyperbolic isofrequency contour. These metamaterials are also called indefinite materials because of their ability to support propagating waves with large lateral wavevectors, which can result in enhanced near-field radiative heat transfer. The energy streamlines in such structures are studied for the first time. Energy streamlines illustrate the flow of energy through a structure when the fields are evanescent and energy propagation is not ray like. The energy streamlines through two semi-infinite uniaxially anisotropic effective medium structures, separated by a small vacuum gap, are modeled using the Green’s function. The lateral shift and penetration depth are calculated from the streamlines and shown to be relatively large compared to the vacuum gap dimension. The study of energy streamlines in hyperbolic metamaterials helps understand the near-field energy propagation on a fundamental level.

We have investigated the structure and interfacial structure of two types of high-k dielectric thin films on Si using combined experimental and theoretical approaches. In the Hf-based high- k dielectrics, the crystallinity of three films, pure HfO2, Y-incorporated HfO2 and Al-incorporated HfO2, is examined by transmission electron diffraction (TED), and the local coordination symmetries of the Hf atoms in the films are revealed by the profile of electron energy-loss near-edge structure (ELNES) taken at oxygen K-edge. These ELNES spectra are then simulated using real-space multiple-scattering (RSMS) method. We find a good agreement between the experimental and the simulated result of pure HfO2. The incorporation of Y indeed stabilizes HfO 2 to a cubic structure, but it also contributes to possible lattice distortion and creation of complex defect states, causing discrepancies between the experimental and the simulated result. As a comparison, the local coordination symmetry of Hf is largely degraded upon the incorporation of Al, which not only amorphorizes HfO2, but also introduces significantly amount of O vacancies in the film. We have further investigated the interfacial structures of HfO2 and Al-incorporated HfO2 thin films on Si using spatially resolved ELNES, which a series of the oxygen K-edge spectra is acquired when a 0.3 nm electron probe scanning across the film/Si interface. We find that interfaces are not atomically sharp, and variation in the local coordination symmetry of Hf atoms lasts for a couple of monolayers for both the HfO2 and the Al-incorporated HfO2 samples. Annealing of the HfO2 film in the oxygen environment leads to the formation of a thick SiO2/SiOx stack layer in-between the original HfO2 and the Si substrate. As a comparison, the interfacial stability is significantly improved by incorporating Al into the HfO 2 film to form HfAlO, which effectively reduces/eliminates the interfacial silicon oxide formation during the oxygen annealing process. The interfacial structure of SiTiO3 (STO) dielectric and Si is significant different from that between Hf-based dielectric and Si, as the crystalline STO is epitaxially grown on the Si. Together with the high resolution high-angle annular-dark-field (HAADF) image, the spatially resolved ELNES acquired across the STO/Si interface reveal an amorphous interfacial region of 1-2 monolayer thickness, which is lack of Sr, but contains Ti, Si, and O. Based on these experimental evidences, we propose a classical molecular dynamic (MD) interface model, in which the STO is connected to Si by a distorted Ti-O layer and a complex Si-O layer. The simulated results, based on the MD interface model, generally agree with the experimental results, disclosing a gradual change of the local atomic coordination symmetry and possible defect incorporation at the interface. / Wang, Xiaofeng = Si衬底上高k介电薄膜的结构研究 / 王晓峰. / Adviser: Li Quan. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 103-112). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Wang, Xiaofeng = Si chen di shang gao k jie dian bo mo de jie gou yan jiu / Wang Xiaofeng.

The scaling of integrated circuits requires the use of alternative dielectric materials as the replacement for silicon dioxide in the submicron devices. The scaling limit for silicon dioxide used in MOSFETs is 1.2nm and the Oxide Nitride Oxide (ONO) stack used in flash memory applications is 13.0nm. The use of alternative dielectrics with high- κ value will alleviate the problem of charge retention and also would help to decrease the programming voltage in case of flash memory cells. Many alternative high- κ dielectric materials such as TaO2, TiO2, Al2O3 etc., have been examined for this purpose previously. Recently the metal oxides such as ZrO2 and HfO2 have been found to be viable replacements for the existing oxide. The high- κ value along with high bandgap motivates this replacement. A complete modeling of the reactively sputtered HfO2 films in the thickness range of 294Å to 480Å is attempted using the data obtained by one of the group members at the Sharp Laboratories of America, Inc. The IV and CV data is used to characterize the material properties and conduction mechanism in HfO2 films used as a control dielectric. The slope of the Poole-Frenkel plot is close to the theoretical value in the intermediate region however it starts to deviate at high field regions. Temperature dependent data also suggests that there are two types of vii traps active in the intermediate and high field regions. However the origin of these traps is not known. Temperature dependent data indicates that there is a rapid increase in the leakage current at elevated temperatures in the high field region further suggesting that the charge retention capability of the device would be adversely affected under such conditions.

The chemistry of hafnium oxide based and materials are described in the context of ion exchange and lithography. HafSOx, represented by the composition HfO₂₋[subscript x](SO₄)x, is described to possess a significant capacity towards ion exchange in acidic and basic solutions, enabling films of HafSOx to be cleanly and readily be converted to oxide films by neutralization. The optical properties, composition and morphology of these oxide films are characterized. The fabrication of mixed metal oxide films is demonstrated via solution and ion exchange routes. This thesis also explores the photoresist chemistry of HafSOx resists. A photoreaction mechanism based on the decomposition of peroxide is proposed. In addition, the patterning of HafSOx films by 193 nm, extreme ultraviolet (EUV) and electron beam radiation is described, and the influence of composition on its photoresist properties is studied. / Graduation date: 2012

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

This study is focuses on the resistance switching physical mechanism in hafnium oxide (HfO2) of resistive random access memory (RRAM). HfO2 was taken as the resistance switching layer because HfO2 is extremely compatible with the prevalent complementary metal oxide semiconductor (CMOS) process. The detail physical mechanism is studied by the stable RRAM device (Ti/HfO2/TiN), which is offered from Industrial Technology Research Institute (ITRI). In this study, the resistance switching property of two different forming conductions are compared, including DC sweeping forming and AC pulse forming. In general, forming is a pivotal process in resistance random access memory (RRAM) to activate the resistance switching behavior. However, over forming would lead to device damage. The overshoot current has been considered as a degradation reason during the forming process. The circuit design is used to obtain the overshoot effect of DC sweeping forming by oscilloscope and semiconductor parameter analyzer system. The quantity of charge through the switching layer has been proven as the key element in the formation of the conduction path. Ultra-fast pulse forming can form a discontinuous conduction path to reduce the operation power.