Solution-Processed Ionically Polarized Oxide Dielectrics and Integrated Electronic Materials for Low-Voltage Transparent Transistors

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TECHNICAL SUMMARY:This project develops the transformative idea that fast ionic conductors exemplified by sodium beta-alumina (SBA) can act as high-capacitance gate dielectrics in transistors. The sodium, or other small inorganic cation, is intercalated between nonstoichiometric layers of Al (2-x) O3 (AlOx). The transistors can be solution-fabricated, transparent, and operable at battery voltages (1-5 V). They can employ organic semiconductors or inorganic oxide semiconductors with higher carrier mobility. While the ultimate technological goal is to produce improved electronic circuits, the project summarized here is to uncover fundamental solid state structures and ion transport mechanisms in this and related electronic oxide materials. This will be done by (a) uncovering the detailed structural intermediates traversed during their formation from sol-gel precursors, (b) studying the cation-dependent electric-field-induced ionic motions that are responsible for the high dielectric constants, and (c) deducing mechanisms by which the cations could conceivably migrate out of the dielectric films, resulting in undesired leakage currents and degradation in transistors, and with the aim of minimizing these effects. The first two tasks will be accomplished through combined experimental (synthesis, X-ray diffraction, scanning probe microscopy, frequency-dependent dielectric measurements) and theoretical (molecular dynamics) study. The third task will be carried out in part by considering conductors and semiconductors with which the BAs will be integrated, evaluating the possibilities that cations could penetrate such materials, and deriving conditions under which leakage currents would be minimized. Effort will therefore be devoted toward refining these accompanying materials, including newly discovered Al-Zn-Sn-O conductive compositions and ZnO-based semiconductors. Support from the Ceramics (CER) program in the Division of Materials Research (DMR) is gratefully acknowledged.NON-TECHNICAL SUMMARYThis proposal develops the transformative idea that a certain class of ceramic electrical conductors based on a compound known as sodium beta-alumina (SBA), can act as electrical insulators in certain devices. While the work of this proposal will be to uncover the fundamental scientific reasons why the SBA compounds can be so useful in electronics technologies, the ultimate impact will be to greatly advance the capabilities of printed, transparent, battery-powered circuits that can be applied to displays, photovoltaic systems, and sensors mounted on transparent substrates such as windshields and windows. The work will also lead to high school and undergraduate classroom modules that demonstrate the broad possibilities of electronics fabrication, physics, and application beyond silicon technology. These modules will be usable with apparatus readily available in educational laboratories with limited resources. This project is a strong fit with an ongoing nanomaterials collaboration of the PIs with minority institutions including Howard University and Prince Georges Community College that has already trained three African-American researchers, and that collaboration will be expanded. Graduate students and postdoctoral fellows will be trained in a synergistic combination of simulation, materials synthesis, physical characterization, and electronic integration techniques that can be applied to a broad range of future materials opportunities. Support from the Ceramics (CER) program in the Division of Materials Research (DMR) is gratefully acknowledged.