Hf- and Ti-Based Organic/Inorganic Hybrid Dielectrics Synthesized via Chemical Vapor Phase for Advanced Gate Stack in Flexible Electronic Devices

Abstract

To achieve the low power operation required by various high performance flexible electronics, such as switching and memory devices, advanced gate dielectrics should be ultra-thin, flexible, with low gate leakage current. Organic-inorganic hybrid dielectrics are proposed to realize this combination of attributes, where the organic matrix contributes outstanding mechanical flexibility and the inorganic component provides the required electrical characteristics. Among candidate inorganic components, HfOx and TiOx are particularly attractive because of their high dielectric constant (high-k) and wide/narrow energy bandgap. Flexible Hf and Ti hybrid high-k dielectrics are synthesized in this work via an initiated chemical vapor deposition (iCVD) process, where 2-hydroxyethyl-methacrylate (HEMA) and tert-butyl peroxide (TBPO) are used as monomers and initiators, respectively. The synthesized Hf hybrid dielectrics exhibit a high-k value of 9.6, leakage currents below 1.0 x 10(-6) A cm(-2) at 2 MV cm(-1), bandgaps of 5.9 eV, and electrical breakdown fields over 3 MV cm(-1). The synthesized Ti hybrid dielectrics exhibit the highest k-value of 13.0 and decent currents below 1.0 x 10(-4) A cm(-2) at 2 MV cm(-1) due to its narrow bandgap of 3.8 eV, making it suitable for use as a charge trapping layer for flexible memory devices, rather than as a gate dielectric. n-type and p-type organic thin film transistors (OTFT) prepared with the Hf hybrid dielectrics exhibit typical transfer and output characteristics, even under tensile stresses as high as 2.0% strain. Under the mechanical stress condition of 2.0% tensile strain, no noticeable degradation is observed in the Hf hybrids in terms of saturation mobility (mu(sat)), subthreshold swing (S.S.), interface trap density (D-it), threshold voltage (V-T), or hysteresis. These results show that the Hf and Ti hybrid dielectrics can enhance the performance of flexible electronics.