Solution-based and Solution Combustion-based Processing Techniques for Metallic and Metal Oxide Thin Films for Optoelectronic Applications

Abstract

Despite the enormous dependency of human life on silicon-based electronic devices, there exists a constant urge for new materials and processing techniques for targeted applications. The specific areas demanding mechanical flexibility and optical transparency in the devices require a new set of materials and processing methodologies; thin films of metal oxides are of one such category of materials depicting the properties mentioned above. In the present study, a series of functional metal oxides along with their applications in Thin Film Transistors (TFTs) is addressed. Initially, two distinct transparent conducting oxides, namely, titanium-doped indium oxide (ITiO: In14TiO23) and zinc and tin co-doped indium oxide (IZTO: In1.4Sn0.3Zn0.3O3) are fabricated at low temperatures using solution combustion technique. The method involves molecular precursors of fuel, oxidizer and the exothermicity of the reaction between them. The film of IZTO deposited via low-temperature (200 °C) solution combustion is found to be electrically conductive (102 Scm-1) and optically transparent (~83 %) in the visible spectrum. Similarly, thin films of ITiO have shown an electrical conductivity of 20 Scm-1 and optical transparency of ~100 %. However, the molecular precursor-based depositions are advantageous over nano-dispersion based ones. The morphological irregularities of the films deposited via nano-dispersions is addressed by a simple technique of tailoring the dwell-time: the time-elapse between the drop-casting and the thermal annealing. A uniform silver deposit is achieved at a temperature of 200 °C with a dwell-time of 10 min. Also, spraying of combustible precursors of silver resulted in the uniform and electrically conductive (107 Sm-1) films at 160 °C. The applications of transparent and conducting IZTO as a gate electrode with pentacene-semiconductor has shown saturation mobility (µsat), on:off ratio (Ion:Ioff), and the threshold voltage (Vth) of 0.44 cm2V-1s-1, 103 and -12.5 V respectively. In addition, the fuel-free solution combustion is realized in fabricating thin film of semiconducting IZTO (In4Sn4ZnO15) at 200 °C. The TFTs with SiO2 dielectric and IZTO (~45 nm) semiconductor has shown µsat, Ion:Ioff, and the Vth of 0.50 ± 0.02 cm2 V-1 s-1, 1.25 × 104and 6.6 ± 0.79 V respectively. In addition, the voltage operation (< 3 V) is realized by replacing conventional SiO2 by ~106 nm thick solution processed high dielectric permittivity (~21) sodium β-alumina and the TFTs have revealed a µsat, Ion:Ioff and Vth of 4.21 ± 0.18 cm2 V-1 s-1, 1.4 × 102 and 0.47 ± 0.08 V respectively.