No abstract

New, stable aqueous solutions have been developed for the deposition of high-quality HfO2 thin films. The low ionic strength of the solution relative to a stoichiometric salt provides the means to directly spin coat a film without organic additives. Peroxide mediates particle interaction in the solution, while enabling relatively low-energy pathways for condensation of the precursor species to a film. Film structure, chemistry, and density are investigated by X-ray diffraction, FT-IR, electron-probe microanalysis, SEM, and X-ray reflectivity. Results from these measurements collectively reveal that smooth and dense HfO2 films are readily produced from the precursors with annealing at moderate temperatures. Optical properties of the films are studied by spectroscopic ellipsometry and transmission/reflection measurements. The observed refractive indices (1.89−1.93) are comparable to those achieved via vapor deposition techniques. Dielectric properties are evaluated through integration of the films into capacitors and thin film transistors. Performance as capacitor dielectrics is characterized by leakage current densities <10 nA/cm2 (at 1 MV/cm) and breakdown fields up to 5.5 MV/cm. As gate dielectrics in thin film transistors with amorphous indium gallium zinc oxide channels, the films exhibit small gate leakage, enabling transistor performance with incremental mobilities near 13 cm2/V·s.

No abstract

An indium–gallium–zinc oxide or a zinc–tin oxide thin‐film transistor (TFT) fabricated when the relative humidity in the laboratory is less than 50% is found to exhibit good electrical performance, with an abrupt, distortion‐free transfer curve and a turn‐on voltage close to 0 V. In contrast, when such an amorphous oxide semiconductor (AOS) TFT is fabricated at a relative humidity greater than 50%, its “as‐fabricated” electrical performance is very poor, typically characterized by a large amount of hysteresis, a strongly negative turn‐on voltage, and a kink‐like distortion in the subthreshold region of its transfer curve. However, the electrical performance of such a poor‐quality TFT is observed to improve over time, if it is simply stored in the dark at room temperature without being subjected to electrical stress. This recovery usually requires weeks (months) for an unpassivated (passivated) AOS TFT. Recovery is tentatively ascribed to the gradual removal of moisture from the AOS TFT channel layer.

Low-Energy Path to Dense HfO 2 Thin Films with Aqueous Precursor.-High-quality, smooth and dense HfO2 thin films are deposited by spin coating using an aqueous H2O2/HNO3 solution of the precipitate obtained from an aq. pH 8.5 solution of HfOCl2 and NH3 as a precursor. The films are characterized by XRD, FTIR, SEM, and X-ray reflectivity. Dielectric properties are evaluated through integration of the films into capacitors and thin film transistors. The performance as capacitor dielectrics is characterized by leakage current densities <10 nA/cm 2 (at 1 MV/cm) and breakdown fields up to 5.5 MV/cm. The optical and dielectric properties of the films substantively exceed those produced by any other solution technique and in most respects rival those produced via advanced vapor methods, enabling their use as a high-performance dielectric. -(JIANG, K.; ANDERSON, J. T.; HOSHINO, K.; LI, D.; WAGER, J. F.; KESZLER*, D. A.; Chem. Mater. 23 (2011) 4, 945-952, http://dx.doi.org/10.1021/cm102082j ; Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USA; Eng.) -W. Pewestorf 16-006