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

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 degrees 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 angstrom per cycle at 105 degrees C to 0.3 angstrom per cycle at 195 degrees C. The measured density is approximate to 2.17gcm-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 degrees 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 +/- 0.6GPa for pure zircone MLD films, to n=1.86 and E= 97 +/- 5GPa for pure ZrO2 ALD films, respectively. In capacitor structures, the zircone films display low leakage currents and a dielectric constant of approximate to 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 -3V with an on/off current ratio of approximate to 103. The zircone and ZrO2/zircone alloy films provide a new class of hybrid organic/inorganic polymer films for many functional film applications.