@article{aygun_daniels_borland_maria_2010, title={In situ methods to explore microstructure evolution in chemically derived oxide thin films}, volume={25}, ISSN={["0884-2914"]}, DOI={10.1557/jmr.2010.0066}, abstractNote={In situ residual gas analyzer techniques were used to identify process-property relationships that regulate microstructure evolution in chemical solution-deposited BaTiO3films. 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 BaTiO3layers 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. BaTiO3grain 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 pO2of 10−13atm, 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.}, number={3}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Aygun, Seymen M. and Daniels, Patrick and Borland, William J. and Maria, Jon-Paul}, year={2010}, month={Mar}, pages={427–436} }
 @article{ihlefeld_daniels_aygun_borland_maria_2010, title={Property engineering in BaTiO3 films by stoichiometry control}, volume={25}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2010.0151}, abstractNote={BaTiO3 thin films were prepared on metallic foil substrates using chemical solution deposition. The impact of A to B site cation ratios on the phase assemblage and microstructural and dielectric properties was investigated by characterizing a sample set that includes stoichiometric BaTiO3 and 1, 2, 3, 4, and 5 mol% excess BaO. Each composition was subjected to a high-temperature anneal step with maximum dwell temperatures of 1000, 1100, and 1200 °C for 20 h. Excess barium concentrations greater than 3% lead to dramatic grain growth and average grain sizes exceeding 1 μm. Despite the large deviations from stoichiometry and the 20 h dwell time at temperature, x-ray diffraction, and high-resolution electron microscopy analysis were unable to detect secondary phases until films with 5% excess barium were annealed to 1200 °C. Thin films with 3% excess barium were prepared on copper substrates and annealed at 1060 °C, the practical limit for copper. This combination of BaO excess and annealing temperature produced an average lateral grain size of 0.8 μm and a room-temperature permittivity of 4000. This is in comparison to a permittivity of 1800 for stoichiometric material prepared using identical conditions. This work suggests metastable solubility of BaO in BaTiO3 that leads to enhanced grain growth and large permittivity values. This technique provides a new solid-state means of achieving grain growth in low thermal budget systems.}, number={6}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Ihlefeld, J. F. and Daniels, P. R. and Aygun, S. M. and Borland, W. J. and Maria, J-P.}, year={2010}, month={Jun}, pages={1064–1071} }
 @article{laughlin_ihlefeld_daniels_maria_2008, title={Flexible and lithography-compatible copper foil substrates for ferroelectric thin films}, volume={516}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2007.08.093}, abstractNote={A process has been developed for preparing a low surface roughness copper foil by evaporation and subsequent peel-off of copper metal layers on glass slides. These 15 micron thick substrates exhibited roughness values between 1 and 2 nm root-mean-square (RMS) and 9 nm RMS over 25 μm2 and 100 μm2 analysis areas, respectively. The deposition and crystallization of barium strontium titanate layers were demonstrated on these smoother variant foils. The fully processed dielectric layers exhibited field tunability greater than 5:1, and could withstand fields in excess of 750 kV/cm. High field loss tangents below 0.007 were observed, making these materials excellent candidates for microwave devices. Finally, a process of lamination and contact lithography was used to demonstrate patterning of micron-scale features suitable for microwave circuit element designs.}, number={10}, journal={THIN SOLID FILMS}, author={Laughlin, B. and Ihlefeld, J. F. and Daniels, Patrick and Maria, J. -P.}, year={2008}, month={Mar}, pages={3294–3297} }
 @article{aygun_daniels_borland_maria_2008, title={Hot sputtering of barium strontium titanate on nickel foils}, volume={103}, ISSN={["0021-8979"]}, DOI={10.1063/1.2909920}, abstractNote={The relationships linking temperature and voltage dependent dielectric response, grain size, and thermal budget during synthesis are illustrated. In doing so, it was found that maximizing thermal budgets within experimental bounds leads to electrical properties comparable to the best literature reports irrespective of the processing technique or microstructure. The optimal film properties include a bulk transition temperature, a room temperature permittivity of 1800, a voltage tuning ratio of 10:1 at 450 kV/cm, and a loss tangent less than 1.5% at 450 kV/cm. The sample set illustrates the well-known relationship between permittivity and crystal dimension, and the onset of a transition temperature shifts at very fine grain sizes. A brick wall model incorporating a high permittivity grain and a low permittivity grain boundary is used to interpret the dielectric data. However, the data show that high permittivity and tunability values can be achieved at grain sizes or film thicknesses that many reports associate with dramatic reductions in the dielectric response. These differences are discussed in terms of crystal quality and maximum processing temperature. The results collectively suggest that scaling effects in ferroelectric thin films are in many cases the result of low thermal budgets and the consequently high degree of structural imperfection and are not from the existence of low permittivity phases at the dielectric-electrode interface.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Aygun, Seymen M. and Daniels, Patrick and Borland, William and Maria, Jon-Paul}, year={2008}, month={Apr} }
 @article{daniels_ihlefeld_borland_maria_2007, title={Smart electrodes for ultralarge-area thin film capacitors}, volume={22}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.2007.0272}, abstractNote={A process suitable for preparing metal-insulator-metal thin film capacitors with submicron insulating layers and top electrodes with cm-scale dimensions is presented. Most importantly, this process does not require sophisticated deposition equipment or a clean room environment. The key to large area yield is co-firing the insulator film with a non-dewetting electrode during the dielectric crystallization/densification anneal. We propose a mechanism of electrode dewetting during the high temperature anneal where the metal laterally retreats from geometric asperities that compromise the integrity of the insulating layer. This behavior is driven by surface energy minimization, which promotes metal migration away from the regions of high curvature. This methodology is not material specific, and only requires a top electrode with a large contact angle to the dielectric in question. Using this technique, functional thin film capacitors with 2.5 cm lateral dimensions and 1 μm dielectric thicknesses can be routinely prepared.}, number={7}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Daniels, Patrick and Ihlefeld, Jon and Borland, William and Maria, Jon-Paul}, year={2007}, month={Jul}, pages={1763–1766} }