Giessen, Universiẗat, Diss., 1999.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 125 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 121-125).

The (1-x)SrBi2Ta2O9-xBi3TaTiO9 thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi2Ta2O9: a leading candidate material for memory applications. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600 oC and grain size was found to be considerably increased for the (1-x)SrBi2Ta2O9-xBi3TaTiO9 compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the thin films was in the range 180-225 for films with 10-50 mol % of Bi3TaTiO9 content in the solid solution. Ferroelectric properties of (1-x)SrBi2Ta2O9-xBi3TaTiO9 thin films were significantly improved compared to SrBi2Ta2O9. For example, the observed 2Pr and Ec values for films with 0.7SrBi2Ta2O9-0.3Bi3TaTiO9 composition, annealed at 650 oC, were 12.4 micro C/cm2 and 80 kV/cm, respectively. The solid solution thin films showed less than 5 % decay of the polarization charge after 10^10 switching cycles and good memory retention characteristics after about 10^6 s of memory retention. The size and temperature effect of 0.7SrBi2Ta2O9-0.3Bi3TaTiO9 thin films were studied by determining how the ferroelectric properties vary with film thickness and temperature. It was found that the ferroelectric properties were determined by the grain size, and not by the thickness of the film in our studied thickness range of 80-350 nm. A 80 nm thick film showed good ferroelectric properties similar to the 350 nm thick film. Thermal stability of the 0.7SrBi2Ta2O9-0.3Bi3TaTiO9 thin film was found to be much better compared to the SrBi2Ta2O9 and Pb(Zr,Ti)O9 thin films due to its higher Curie temperature and lower Schottky activation energy according to temperature changes. Also, 0.7SrBi2Ta2O9-0.3Bi3TaTiO9 thin films has shown good ferroelectric properties on multilayer system such as PtRh/PtRhOx/poly-Si suggest their suitability for high density FRAM applications. / Ph. D.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: William. Alan Doolittle; Committee Member: Jeffrey Nause; Committee Member: Linda S. Milor; Committee Member: Shyh-Chiang Shen; Committee Member: Stephen E. Ralph.

Techn. Hochsch., Diss., 2003--Aachen.

As technology advances, mechanical and electrical systems are subjugated to intense temperature fluctuations through their service life. Designing coatings that operate in extreme temperatures is, therefore, a continuing challenge within the tribology community. Silver tantalate was chosen for investigation at the atomic level, the physical and chemical properties that influence the thermal, mechanical, and tribological behavior for moving assemblies in high temperature tribological applications. By correlating behavior of internal physical processes to the macro tribological behavior, the tribological community will potentially gain improved predicative performance of solid lubricants in future investigations. Three different approaches were explored for the creation of such materials on Inconel substrates: (1) powders produced using a solid state which were burnished on the surface; (2) monolithic silver tantalate thin films deposited by magnetron sputtering; and, (3) an adaptive tantalum nitride/silver nanocomposite sputter-deposited coating that forms a lubricious silver tantalate oxide on its surface when operated at elevated temperatures. Dry sliding wear tests of the coatings against Si3N4 counterfaces revealed friction coefficients in the 0.06 - 0.15 range at T ~ 750 °C. Reduced friction coefficients were found in nanocomposite materials that contained primarily a AgTaO3 phase with a small amount of segregated Ag phase, as suggested by structural characterization using X-ray diffraction. The presence of nanoparticles of segregated Ag in the thin films further enhanced the performance of these materials by increasing their toughness. Additional characterization of the AgTaO3 films at 750 °C under normal loads of 1, 2, 5, or 10 N revealed that the friction monotonically increased as the load was increased. These results were complemented by molecular dynamics simulations, which confirmed the increase of friction with load. Further, the simulations support the hypothesis that this trend can be explained in terms of decreased presence of Ag clusters near the sliding surface and the associated decreased porosity. The results suggest that the relative amount of Ag in a TaN or Ta2O5 mastrix may be used to tune film performance for a given application.

Des poudres de LiNbO₃ ou de LiTaO₃ ont été préparées par la méthode sol-gel à partir d'alcoolates de lithium et de niobium ou de tantale. Des céramiques de bonne compacité ont été frittées à des températures de 1075 et 1150°C respectivement. Divers paramètres ont été considérés : structure, état d'association et concentration du précurseur, rapport eau/alcoolate, nature du solvant. Leur influence sur la compacité, la microstructure des céramiques et sur les propriétés diélectriques et ferroélectriques a été déterminée.

The lithium tantalite [LiTaO3, abbreviated to LT] thin films were deposited on Pt/Ti/SiO2/Si substrates by spin coating with sol-gel technology and various rapid thermal processing in this thesis. By changing the annealed layers and heating temperature(500~800¢J), the effects of various thermal treatments on the thin films growth and the related properties are studied. Besides, the dynamic response of pyroelectric IR detector using LiTaO3 films was studied. In addition, the detector with back side etching was achieved by the anisotropic wet etching of back silicon substrate. The comparisons of detectors with and without backside etching were also investigated. Experimental results reveal that the annealed layers will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of LT thin films. With the increase of the annealed layers, the grain size of LT thin film increases slightly, and highly c-axis orientated LT films can be obtained for the twelve annealed layers. From 4 to 12 annealed layers, the relative dielectric constant of LT thin film increases from 35 up to 65, the dielectric loss (tand) decreases from 0.00637 to 0.00324, the coercive field (Ec) decreases from 84.79KV/cm to 46.23KV/cm, the remnant polarization (Pr) increases from 2.54 mC/cm2 to 7.36 mC/cm2, and the pyroelctric coefficient (g) increases from 2.18´10-8 C/cm2K up to 5.71´10-8 C/cm2K. In addition, the results also show that the LT thin film possesses the largest figures of merit Fv (3.02¡Ñ10-10 Ccm/J) and Fm (4.08¡Ñ10-8 Ccm/J) at heating temperature of 700¢J with twelve annealed layers. The voltage responsivities (Rv) measured at 70 Hz exists a largest value of 8398 V/W with twelve annealed layers. The specific detectivity (D*) measured at 200 Hz has the maximum value of 1.1¡Ñ108 cmHz1/2/W with twelve annealed layers. The results show that LT12 pyroelectric thin film detector exists both the maximums of voltage responsivity and specific detecivity. Therefore, optimizing the conditions of this study, LT12 thin film will be the most suitable for IR detector application. Finally, the voltage responsivities (Rv) of LT thin film increases from 8398 V/W to 9537 V/W, and the specific detectivity (D*) increases from 1.1¡Ñ108 cmHz1/2/W to 2.67¡Ñ108 cmHz1/2/W after backside etching. The results show that the detectivity can be improved after backside etching.

The Ta-modified niobate lithium [LiNb1-xTaxO3, abbreviated to LNT] thin films were deposited on Pt/Ti/SiO2/Si substrates by spin coating with sol-gel technology and rapid thermal processing in this thesis. 1,3 propanediol was used as solvent to minimize the number of cycles of spin coating and drying processes to obtain the desired thickness of thin film. By changing the Ta content (x=0~1), the effects of various processing parameters on the thin films growth are studied. The effects of various Ta content on the response of pyroelectric IR detector devices are studied also. Experimental results reveal that the Ta content will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of LNT thin films. With the increase of Ta content, the grain size of LNT thin film decreases slightly, and highly c-axis orientated LNT films have been obtained for x=0.2. With the increase of Ta content, The relative dielectric constant of LNT thin film increases from 33 up to 62. The dielectric loss (tand) increases from 0.00374 to 0.00686,Coercive Field (Ec) decreases from 81.09KV/cm to 32.07KV/cm, and Remanent polarization (Pr) decreases from 8.48 mC/cm2 to 2.2 mC/cm2, pyroelctric coefficient (g) increases from 2.76´10-8 C/cm2K up to 4.51´10-8 C/cm2K with an increase of Ta content. In addition, the results also show that the LNT thin film possesses the largest figures of merit Fv (2.66¡Ñ10-10 Ccm/J) and Fm (2.57¡Ñ10-8 Ccm/J) at the heating temperature of 700¢J and Ta content of 20mol%. The voltage responsivities (Rv) measured at 70 Hz has a largest value of 7020 V/W with the Ta content of 20mol%. The specific detectivity (D*) measured at 200 Hz has the maximum value of 7.76¡Ñ107 cmHz1/2/W with the Ta content of 20mol%. The results show that LNT(20) pyroelectric thin film detector exists both the maximums of voltage responsivity and specific detecivity. Therefore, optimizing the conditions of this study, LNT(20) thin film will be the most suitable for IR detector application.

<p>Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, and electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies.</p><p>Ferroelectric materials usually have high dielectric constants, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used in fabrication capacitors for electronic industry because of their high dielectric constants, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure, and electrically tunable microwave integrated circuits using ferroelectric thin films can be developed. Therefore, it is very important to characterize the dielectric constant and tunability of ferroelectric thin films.</p><p>This thesis shows experimental results for growth, crystalline properties and microwave characterization of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering of a stoichiometric, high density, ceramic NKN, ATN, BST target onto single crystal LaAlO3(LAO), Al2O3 (sapphire), and Nd:YAlO3, and amorphous glass substrates. By x-ray diffractometry, NKN, ATN, BST films on LAO substrates were found to grow epitaxially, whereas films on r-cut sapphire substrates were found to be preferentially (00l) oriented.</p><p>Coplanar waveguide interdigital capacitor (CPWIDC) structures were fabricated by standard photolithography processing and metal lift-off technique. Microwave properties of the NKN/Sapphire and ATN/Sapphire with CPW structures were characterized using on-wafer microwave measurement technique. Measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field through the connection between network analyzer and power supply was applied to measure voltage tunability. Measured S-parameter were used for the calculation of capacitance, loss tanδ, tunability and K-factor.</p><p>The NKN films interdigital capacitors with 2 μm finger gap on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor = tunability/tanδ from 152% @ 10GHz to 46% @ 40GHz.</p><p>The microwave performance of ATN film CPWIDC with 2 μm finger gap on sapphire substrate in the microwave range from 1 to 40 GHz showed that frequency dispersion is about 4.3%, voltage tunability was 4.7% @ 20GHz and 200 kV/cm, loss tangent ∼ 0.068 @ 20GHz, K-factor = tunability/tanδ is ranged from 124% @ 10GHz to 35% @ 40GHz.</p><p>The BST films CPWIDC with 2μmfinger gap on Al2O3 substrate showed frequency dispersion of capacitance in the microwave range from 1 to 40 GHz about 17%, voltage tunability = 1 - C(40V)/C(0) ∼ 22.2%, loss tangent ∼ 0.137 @ 20GHz, and K-factor = tunability/tanδ from 281% @ 10GHz to 95% @ 40GHz.</p>