Functional Ultrathin Films and Nanolaminates from Aqueous Solutions

Abstract

Nanolaminates composed of TiO2 and Al4O3(PO4)2 (AlPO) thin films have been fabricated from aqueous solution precursors. By adjusting precursor concentrations individual layers can be controlled to a thickness near 1 nm. Characterization by X-ray reflectivity and transmission electron microscopy (TEM) reveals near-atomically smooth interfaces and a high degree of regularity in the film stacks. X-ray diffraction is utilized to investigate the crystallization behavior of TiO2 layers under one-dimensional confinement of the glassy AlPO layers. TiO2–AlPO nanolaminates incorporated into capacitor structures exhibit low leakage current densities (<10 nA/cm2 at 1 MV/cm) and high breakdown fields up to 5.4 MV/cm with annealing temperatures as low as 350 °C. Tailorable dielectric constants have also been demonstrated by varying the relative thickness of the TiO2 and AlPO films. As gate dielectrics in thin-film transistors with solution-processed amorphous indium gallium zinc oxide channels, the nanolaminates exhibit small gate leakage, enabling ideal transistor performance with incremental mobilities near 3 cm2/V·s.