Molecular Layer Deposition of Zircone and ZrO2/Zircone Alloy Films: Growth and Properties

Authors

  • Byoung H. Lee,

    1. Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, 80309-0215 (USA)
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  • Virginia R. Anderson,

    1. Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, 80309-0215 (USA)
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  • Steven M. George

    Corresponding author
    1. Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, 80309-0215 (USA)
    2. Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado, 80309-0215 (USA)
    • Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, 80309-0215 (USA)
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  • This research was funded by the National Science Foundation (CHE-1012116) and DuPont Central Research and Development. Equipment utilized in this research was provided by the Air Force Office of Scientific Research (AFOSR). We thank Prof. Myung M. Sung at Hanyang University for obtaining the TEM images of the zircone MLD film. We also thank Noemi Leick at Eindhoven University of Technology for discussions regarding the refractive index of the zircone alloy films.

Abstract

Hybrid organic/inorganic polymer films based on zirconium are grown using molecular layer deposition (MLD) techniques. The zirconium alkoxide films, known as “zircones”, are grown using sequential exposures of zirconium tert-butoxide (ZTB) and ethylene glycol (EG) as the reactants at temperatures from 105 to 195°C. In-situ quartz crystal microbalance (QCM) and ex-situ X-ray reflectivity (XRR) experiments confirm linear growth versus the number of reaction cycles. The growth rates decrease versus temperature from 1.6 Å per cycle at 105°C to 0.3 Å per cycle at 195°C. The measured density is ∼2.17 g cm−3 for all the growth temperatures. Transmission electron microscopy (TEM) images reveal very uniform and conformal zircone films. ZrO2/zircone alloys are also fabricated by combining ZrO2 atomic layer deposition (ALD) and zircone MLD at 145°C. The composition of the ZrO2/zircone alloy is varied by adjusting the relative number of ZrO2 ALD and zircone MLD cycles in the reaction sequence. The ZrO2/zircone alloys display varying density, refractive index, elastic modulus, and hardness. The refractive index and elastic modulus change progressively from n = 1.63 and E= 27 ± 0.6 GPa for pure zircone MLD films, to n = 1.86 and E= 97 ± 5 GPa for pure ZrO2 ALD films, respectively. In capacitor structures, the zircone films display low leakage currents and a dielectric constant of ∼6.7. The zircone films are also utilized as the dielectric layer in pentacene-based thin film transistors (TFTs), which display a high field effect mobility of 2.11 cm2 V−1 s−1 operating at −3 V with an on/off current ratio of ∼103. The zircone and ZrO2/zircone alloy films provide a new class of hybrid organic/inorganic polymer films for many functional film applications.

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