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Materials Science and Engineering: Electrical Ceremics
^ Fabrication and Characterization of Ferroelectric Thin Films by the MOCVD Method
H. Chen,* C. H. Lin, P. Friddle, A. Daga
U.S. Department of Energy, DE-FG02-91ER45439

(In cooperation with the Frederick Seitz Materials Research Laboratory)

This work encompasses the fabrication and characterization of ferroelectric thin films fabricated by metal-organic chemical vapor deposition (MOCVD) techniques. For infrared detector applications, researchers grow Pb(Sc0.5Ta0.5)O3-PbT:O3 (PSTT) thin films and perform noise, blackbody responsivity, spectral response, and frequency response measurements. The PSTT detectors' performance will be compared with commercial state-of-the-art pyroelectric detectors. The ultimate goal of this work is to develop a room-temperature infrared radiation detector. Researchers base this work on the ferroelectric PSTT system and a novel detection approach which utilizes both the ferroelectric and the pyroelectric properties. Researchers also fabricate other perovskite thin films and multilayers such as PT, PZT, and BST on various types of substrates and investigate the structure-property-processing relationships.

^ Oxide Thin Films for Electronic and Optical Applications
H. Chen,* S. W. Lee
U.S. Department of Energy, DE-FG02-91ER45439; Nippon Steel Co. Gift

(In cooperation with the Frederick Seitz Materials Research Laboratory)

The primary objective of this research is to produce oxide thin films for electronic applications. One example is a flammable gas sensor using SnO2 and the other is Ta2Os as dielectric material or thermal barrier. These oxide thin films are grown by the MOCVD technique. Microstructural analysis is also carried out on the grown films using XRD, SEM, TEM, AES, and XPS. Sensing tests are done for SnO2 using resistivity measurements with reducing gases such as H2, alcohol, and so forth. Dielectric constant, C-V, optical transmittance, and film conductance measurements are made. Models are suggested to explain the measured electrical and optical properties.

^ Additive Patterning of Sol-Gel Thin Layers: Shrinkage, Decohesion, and Lift-off
D. A. Payne,* E. A. Mikalsen
U.S. Department of Energy, DE-FG02-91ER45439

An investigation is under way on the additive patterning of thin layers by use of monolayer-mediated deposition. Microcontact printing is used to selectively transfer an ultrathin molecular film to the surface of a substrate. Subsequent chemical solution deposition is mediated by the underlying molecular resist to achieve decohesion exclusively above patterned areas. This investigation identifies three critical processes that facilitate this novel additive patterning technique: film densification, stress release by decohesion wherever the monolayer is present, and facile lift-off over the microcracked regions. Current efforts are focused on the influence of the functionalized molecular resist on feature resolution and edge roughness.

^ Densification and Stress Development in Sol-Gel-derived PZT Coatings
D. A. Payne,* R. J. Ong, L. H. Allen
U.S. Department of Energy, DE-FG02-91ER45439

(In cooperation with the Frederick Seitz Materials Research Laboratory)

Sol-gel-derived PZT thin layers deposited on silicon were examined for their shrinkage behavior using in situ ellipsometry. This research involves correlating densification data with thermal analysis (DTA, TGA). The effect of pyrolysis and crystallization on layer shrinkage is observed as experimental parameters, such as layer thickness and substrate type, are varied. The resulting stresses in the coating are measured as a function of heat treatment by a laser reflectance technique and related to associated densification phenomena and substrate/layer thermal expansion mismatch.

^ Effects of Atmospheric Moisture on the Structure of Sol-Gel Thin Layers
D. A. Payne,* E. A. Mikalsen, K. L. Holverson
U.S. Department of Energy, DE-FG02-91ER45439

This study investigates the structural consequences of humidity control on the spin-coating deposition of PZT thin layers. Film thickness, density, and refractive index are affected through variations in the film deposition conditions. In polymeric gels, hydrolysis and condensation reactions prescribe the structure during spin coating. By controlling the atmospheric moisture during the spin coating process, researchers can investigate the effect on film density and uniformity, crystallization behavior, and dielectric, ferroelectric, and optical properties. The sensitivity of different chemical routes to atmospheric moisture is under investigation.

^ Patterning of Sol-Gel Thin Layers Using Soft-Lithography
D. A. Payne,* E. A. Mikalsen
U.S. Department of Energy, DE-FG02-91ER45439

Research is directed at the patterning of curved surfaces. Soft lithographic methods, including micromolding in capillaries (MIMIC) and microcontact printing (μCP), are under investigation for the selective deposition of solution-derived oxide thin films. This approach is to develop soft lithographic methods and sol-gel deposition processes to achieve additive patterning on both planar and non-planar surfaces. Materials under investigation include pyroelectric and ferroelectric lead zirconium titanate and barium strontium titanate. Current efforts are aimed at achieving high-quality patterns for film thicknesses ranging from 30 to 1000 nm by novel application of soft lithographic techniques.

^ Preparation and Characterization of Ta2O5-TiO2 Ceramics
D. A. Payne,* S. Hemjinda
U.S. Department of Energy, DE-FG02-91ER45439

(In cooperation with the Frederick Seitz Materials Research Laboratory)

Ta2O5 is widely studied for possible application in VLSI technology as the next generation of higher dielectric constant (K) gate oxide materials. In this project, researchers have shown that the dielectric constant of Ta2O5 can be significantly improved by small substitutions of TiO2. At 1 MHz, 0.944Ta2O5-0.056TiO2 exhibited K=245 with tanδ=0.01, more that five times the value for Ta2O5 alone (K=35, tanδ=0.008). The enhancement was attributed to the formation and stabilization of a high temperature structure (monoclinic). Increasing additions of TiO2 lowered the orthorhombic to monoclinic phase transformation temperature from 1360°C to 1200°C (that is, for 0.92 Ta2O5-0.08TiO2). Monoclinic Ta2O5-TiO2 ceramics exhibited a unique microstructure, with highly oriented columnar grains. Work in progress includes temperature-dependent dielectric property measurements, sintering, and phase transformation behavior.

^ Single Crystals and Thin Films of Doped Rare Earth Manganese Perovskites
D. A. Payne,* B. A. Clothier
U.S. Department of Energy, DE-FG02-91ER45439

(In cooperation with the Frederick Seitz Materials Research Laboratory)

Rare earth manganese perovskites doped with divalent cations, such as Ca, Sr, Ba, and Pb, have been shown to exhibit greatly enhanced magnetoresistive properties when compared with metallic heterolayers. Improved magnetoresistive behavior is greatly desired for sensor applications, such as magnetic read heads, or advanced computer memories, such as MRAM cells. Current research is concerned with the electronic behavior and morphological characterization of doped rare earth manganese perovskite single crystals. Resulting candidate materials are deposited by low-temperature solution processing and self-assembled patterning to form integrated structures for devices.

^ Phase Separation and Charge Ordering in Complex Oxides
J. M. Zuo*
Department of Energy, DE-FG02-91ER45439; University of Illinois

(In cooperation with the Frederick Seitz Materials Research Laboratory)

This project is to investigate charge ordering and nanoscale phase separation in complex oxides, such as colossal magnetoresistive manganites and high-Tc superconductors. The goal is to understand nanostructures in these complex materials and their relationship to the unusual properties of each material. The project involves synthesis, property measurements, and the electron beam characterization. A nanometer-sized electron probe is used for structural characterizations, which allows researchers to probe an individual structural domain and obtain unique structural information not available from other sources.


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