Continuous-Wave Green Laser Activation of Transparent InZnO Electrodes for Fully Solution-Processed Oxide Thin-Film Transistors

Thin-film electronics integration onto large-scale flexible substrates is making huge advancements in many sectors, which include display technology and health care. This requires both large-area deposition and low-temperature fabrication strategies to be suitable for heat-sensitive substrates. In this context, solution processing is preferred over conventional vacuum techniques as it eliminates the use of complex and high-energy equipment and is compatible with atmospheric processing, making it favorable for high throughput roll-to-roll processing. In this work, we demonstrate a full solution approach for oxide thin-film transistor (TFT) fabrication using a spin-coating technique. Amorphous InZnO (a-IZO) is used for both the semiconductor and electrode layers, while fluorinated polysilsesquioxane is used as the gate insulator. By utilization of a top-gate self-aligned structure, the channel and electrode regions in a single a-IZO layer can be defined. In order to achieve a functional TFT, a continuous-wave green laser with a wavelength of 532 nm is irradiated onto the device to modify the electrical properties of a-IZO and transform regions of the semiconductive oxide into a conductive electrode. The fully solution-processed a-IZO TFT reaches a linear mobility of 14.6 cm 2 V –1 s –1 and an on–off current ratio in the order of 10 8, which rivals the performance of vacuum-processed oxide TFTs. Our analyses show the retention of the amorphous structure of IZO accompanied by changes in the chemical bonding in the metal-oxide network. The enhancement in the conductivity of a-IZO is proposed to be related to oxygen vacancy generation and formation of In–In bonds, as suggested by the observed shift of the XPS O 1s spectra to a higher binding energy and of the XPS In 3d spectra to a lower binding energy. These findings demonstrate the suitability of continuous-wave green laser irradiation to tailor the electrical properties of metal oxides and its potential for low-temperature device fabrication.