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Plan view scanning transmission electron microscopy was used to investigate the microstructural connections to device resistance in inline phase change switch devices. It was revealed that massive structural changes occur in GeTe during switching, most notably the formation of an assembly of voids along the device centerline and large GeTe grains on either side of an "active region." Restructuring of this variety was tied to changes in ON-state resistance with increasing pulse number, where initially porous and fine-grained (10-20 nm) GeTe was converted to large crystalline domains comprising the majority of the RF gap (400-700 nm). A phenomenological model for this microstructure is presented in which the OFF pulse melts a given width of GeTe, and upon cooling crystalline material outside the melt region acts as a template for an inward-propagating crystalline growth front. The voids observed along the device centerline were correlated to increasing OFF state resistance and a relatively stable ON state with increasing pulse number via a series resistance model. As a result of this analysis, OFF state resistance was suggested as an early indicator of device reliability. An improved GeTe deposition process was implemented to limit void formation, which is shown to have a more stable OFF-state resistance with increasing pulse number. [ABSTRACT FROM AUTHOR]

Degeneratively doped conductive oxides represent a unique host for exploring the inter-relationship between the properties of charge carriers and their collective plasmonic response. These materials often lack interband transitions that obfuscate interpretation of spectral response in elemental metals, and unlike metals, the electronic transport properties of conductive oxides are easily tunable. This work explores the process-structure-property relationships that regulate surface plasmon resonance (SPR) in sputter deposited indium tin oxide (ITO) thin films. Film deposition conditions are used to regulate film microstructure and tune the electronic mobility to between 7 and 40 cm2 V-1 s-1. Postdeposition annealing in low oxygen partial pressure atmospheres is used to engineer the ITO defect equilibrium and modulate carrier concentrations to between 1020 and 1021 cm-3. These electronic transport properties are modulated with near independence enabling straightforward interpretation of their influence on the SPR response observed in the infrared reflectivity spectrum. Higher electronic mobilities favor narrower surface plasmon absorption bands, while higher carrier concentrations favor higher absorption band frequencies. A simple free electron model, having only electronic carrier density and electronic mobility as variables, can be used to describe ITO’s dielectric response. Calculations that combine this dielectric function and the Fresnel equations provide simulated reflectivity spectra that match experimental data with remarkable accuracy. Because these spectra use no fitting parameters and are calculated with well-studied material properties, it opens the opportunity for future design of plasmonic response in advanced material systems including degeneratively doped semiconductors, silicides, and nitrides. [ABSTRACT FROM AUTHOR]

The refractory nature of BaTiO3 leads to limited densification and grain growth for films processed at low temperatures and a modest nonlinear dielectric response due to a marked sensitivity to physical scale and material quality. Adding liquid-forming sintering aids, common in bulk ceramics, to thin films enhances mass transport, leading to enhanced grain growth at lower temperatures. This work explores the effectiveness of a sputtered CuO buffer layer with BaO-B2O3 (BBO) fluxes to engineer the microstructure of BaTiO3 films. Grain size and homogeneity increase in the presence of even a ~1 nm CuO layer. In general, grain size increases from 75 to 370 nm with an addition of 2.2% BBO and 8 nm CuO. Room temperature capacitance in fluxed films increases by a factor of 5 over pure films, and ferroelectric phase transitions are clearly observable in dielectric measurements. CuO-BBO proves effective on (0001) Al2O3 and (100) MgO substrates, although all microstructures are notably finer for the latter. [ABSTRACT FROM AUTHOR]

The microstructure of polycrystalline barium titanate (BaTiO3) thin films processed with a liquid-phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close-packed c-plane modifies the orientation, morphology, and relative amount of an interfacial BaAl2O4 second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO3. As the substrate orientation transitions from c-plane, to r-plane, to a-plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously. [ABSTRACT FROM AUTHOR]

A low-temperature thin-film processing method for BaTiO3 is studied to understand microstructure development in the presence of a liquid-forming phase. The addition of a eutectic barium borate flux is found to prevent nucleation of BaTiO3 during pulsed-laser deposition on sapphire substrates at 400 °C. Subsequent thermal annealing above the flux's eutectic temperature dramatically enhances the film's microstructural development and crystallinity. A secondary reaction phase of barium aluminate is identified at the substrate interface in both unfluxed and fluxed films, although it is more pronounced in the fluxed films. This barium aluminate phase in conjunction with the liquid flux serves to nucleate {111} twins in the barium titanate, which subsequently lead to enhanced grain growth. The resulting large-grained and dense thin films result in markedly improved dielectric properties. [ABSTRACT FROM PUBLISHER]

In March 2012, a group of researchers met to discuss emerging topics in ceramic science and to identify grand challenges in the field. By the end of the workshop, the group reached a consensus on eight challenges for the future:-understanding rare events in ceramic microstructures, understanding the phase-like behavior of interfaces, predicting and controlling heterogeneous microstructures with unprecedented functionalities, controlling the properties of oxide electronics, understanding defects in the vicinity of interfaces, controlling ceramics far from equilibrium, accelerating the development of new ceramic materials, and harnessing order within disorder in glasses. This paper reports the outcomes of the workshop and provides descriptions of these challenges. [ABSTRACT FROM AUTHOR]

The authors report a study of molecular beam deposition of MgO films on amorphous SiO2 and (0001) GaN surfaces over a large range of temperatures (25–400 °C) and molecular oxygen growth pressures (10−7–10−4 Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO3), all components of MgO become volatile at normal epitaxial growth temperatures (=250 °C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10−5 Torr O2 is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source. [ABSTRACT FROM AUTHOR]

The addition of a liquid-forming flux to barium titanate thin films promotes densification and grain growth, improves nonlinear dielectric properties, and allows residual strain to be sustained in polycrystalline films without cracking at thicknesses relevant to device fabrication. Relative tuning, an excellent indicator of crystalline quality and an important material property for tunable microwave devices, increases from 20% to 70%. Films exhibit 0.15% residual differential thermal expansion mismatch strain, resulting in a shift to the paraelectric-ferroelectric phase transition of 50 °C. This result is in excellent agreement with theory, demonstrating the ability to tune ferroic transitions without epitaxial approaches. [ABSTRACT FROM AUTHOR]

In situ residual gas analyzer techniques were used to identify process-property relationships that regulate microstructure evolution in chemical solution-deposited BaTiO3 films. In situ analysis of furnace exhaust gasses enabled quantitative exploration of thermolysis and crystallization reactions and an ability to identify processing parameters that influence the temperature ranges over which they occur. The atmospheric analysis was instrumental in identifying heat treatments that produced optimally consolidated precursor gels that crystallized into BaTiO3 layers with optimized structure and properties. Slow ramp rates resulted in higher porosity, larger grain size, and a dramatic drop in the capacitor yield. Fast ramp rates produced similar trends; however, the mechanisms were distinct. The effects of oxygen partial pressure were also explored. BaTiO3 grain size increased with increasing pO2, whereas there was no appreciable influence on density and capacitor yield. Optimal firing parameters, i.e., 20 °C/min ramp rate at a pO2 of 10-13 atm, were identified as those that produced an overlap in the temperature ranges of thermolysis and crystallization reactions and thus a precursor gel with a density and compliance that supports crystallization and densification while tolerating the associated volume contraction. This in situ approach to analyze downstream furnace gas is shown to be a generically applicable means to understand synthesis methods that are complicated by simultaneous mechanisms of precursor decomposition, extraction of volatile components, and crystallization. [ABSTRACT FROM AUTHOR]

Spinodal decomposition can improve a number of essential properties in materials, especially hardness. Yet, the theoretical prediction of the onset of this phenomenon (e.g., temperature) and its microstructure (e.g., wavelength) often requires input parameters coming from costly and time-consuming experimental efforts, hindering rational materials optimization. Here, we present a procedure where such parameters are not derived from experiments. First, we calculate the spinodal temperature by modeling nucleation in the solid solution while approaching the spinode boundary. Then, we compute the spinodal wavelength self-consistently using a few reasonable approximations. Our results show remarkable agreement with experiments and, for NiRh, the calculated yield strength due to spinodal microstructures surpasses even those of Ni-based superalloys. We believe that this procedure will accelerate the exploration of the complex materials experiencing spinodal decomposition, critical for their macroscopic properties. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructure of polycrystalline barium titanate (BaTiO3) thin films processed with a liquid-phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close-packed c-plane modifies the orientation, morphology, and relative amount of an interfacial BaAl2O4 second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO3. As the substrate orientation transitions from c-plane, to r-plane, to a-plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously. [ABSTRACT FROM AUTHOR]