Effects of deposition method and conditions for IGZO film and thermal annealing on composite film quality, surface roughness, microstructural defects, and electrical properties of Ti/IGZO/graphene/polyimide specimens

Abstract

The depositions of a thin graphene as the inter layer of the indium gallium zinc oxide (IGZO) film and polyimide substrate and a Ti film bellow the IGZO layer to induce the IGZO crystallizations have been reported by the authors' study [1] to have a significant reduction in the electrical resistivity (R) and increases in carrier mobility (Mb) and concentration (Cc) via the annealing as compared to those created in the specimens without graphene. In the present study, Ti/IGZO/graphene/polyimide specimens were fabricated using Ti as the top layer, with the IGZO film prepared using e-beam evaporation and radio-frequency magnetron sputtering, in order to compare the ability of preserving the structure integrity of graphene after the IGZO deposition. When sputtering was used, the thicknesses of the Ti and IGZO films were controlled by the deposition power; when e-beam evaporation was used, the thicknesses were controlled by the deposition time. Rapid thermal annealing (RTA) was further applied to some specimens to investigate the combined effects of the IGZO deposition method and heat treatment on the microstructure defects, electrical and mechanical properties, and surface morphology of the specimens. The quantities of bulges and microvoid defects increase after the RTA, and become the governing factors for increasing surface roughness (Ra). The X-ray photoelectron spectroscopy spectra for O1s were deconvoluted to evaluate the peak intensity ratio, IRO2, defined for the evaluation of the oxygen vacancies in the microstructure. When sputtering was used, IRO2 increased after RTA; in contrast, when e-beam evaporation was used, IRO2 decreased after RTA. For all specimens without RTA, an increase in either the deposition power or time of IGZO has decreased IRO2. TiO2, ZnO, and Ga2O3 are the three oxides created in the specimens. The ways of increasing the TiO2 grains result in a rise of IRO2. The electrons released from the TiO2 formations are available to raise the quantity of ZnO. The peak intensity (PIZnO) of ZnO is lowered by annealing, irrespective of the IGZO deposition method. With sputtering and without RTA, increasing the IRO2 value increased the carrier mobility (Mb), but decreased the resistivity (R) and carrier concentration (Cc), irrespective of the deposition power. After the RTA, carrier concentration and resistivity are lowered, and carrier mobility is risen. With e-beam evaporation and without RTA, the vague interface between Ti and IGZO films and the void defects in IGZO make these electrical properties more complicated in behavior and dependent on IGZO deposition time. Specimen's resistivity was lowered and carrier concentration was elevated by applying the RTA. The deposition of the Ti film as top layer can result in a much bigger reduction of R and further increases in Mb and Cc for these two IGZO deposition methods as compared to those shown in Ref. [1].