A Low Temperature Aqueous Solution Processing Route for IGZO Thin Films Employing Electrochemically Synthesized InGaZn Clusters

Abstract

Owing to the growth of its applications, including solar cells, electrochromatic windows, and especially active channel layers in thin film transistors (TFTs), amorphous indium gallium zinc oxide (IGZO) has become an area of significant research interest. In particular, a low temperature solution based fabrication route for IGZO would enable greater application as it would decrease manufacturing costs, enable large area deposition, and make IGZO compatible with low temperature substrates. Here, a previously unreported nanocluster was synthesized in solution. In addition to characterizing the solution with dynamic light scattering, it was used as an inorganic aqueous precursor for solution deposition of IGZO thin film. Scanning electron microscopy and X-ray reflectometry revealed that films were dense and that solution precursors had sufficient metal concentration to yield films up to 15 nm thick per layer. Quartz crystal microbalance analysis and infrared transmittance spectroscopy revealed that processing temperatures of 200-250°C were sufficient to remove counter ions from the film, a significant improvement over existing sol-gel routes that necessitate the removal of organic ligands. Finally, TFT devices that were fabricated using IGZO as the active channel layer displayed high performance. In particular, a composition of In:Ga:Zn=69:12:19 yielded an average channel mobility of 15.2 cm²V⁻¹s¹, a turn-on voltage of ∼-40 V, and an on/off current ratio of> 10⁶.