Large volume continuous synthesis of metal oxide nanoparticle inks toward inkjet printed TFT devices

P.N. Gooden, C. Crawshaw, S. Butterworth, S. Oertel, M.P.M. Jank
Promethean Particles Ltd, UK

Keywords: inkjet, nanoparticles, metal oxide

Summary:

In contrast to lab-scale approaches, industrial manufacturing requires large-volume, inexpensive, and well-controllable processes. Mixed metal oxide nanoparticle based thin films offer a wide range of functionalities and electrical properties tuneable by composition. An ink for solution processed semiconducting thin films is developed based on a continuous solvothermal synthesis process. IZO nanoparticles inks with an average size of 50 nm showing intrinsic stabilization in a mixed polyol / alcohol solvent have been produced, which are further modified for spin and inkjet processing. Bottom-gate top-contact thin-film transistors (TFTs) were fabricated by spin coating and inkjet printing on to a p+- Si/SiO2 substrate. S / D electrodes were either inkjet printed with a conductive silver ink or evaporated aluminium. Annealing of the semiconducting layer in air yields TFT devices with an ON/OFF ratio between 1x105 and 1x106 and a saturation mobility of 0.6 cm2/Vs. Due to the unpatterned semiconductor layer, the observed gate leakage is only two orders of magnitude below the ON current (1x10-5 A). Inkjet printed TFTs show a gate leakage reduction of four decades and an ON / OFF ratio between 1x106 and 1x107 at a reduced saturation mobility of 0.014 cm2/Vs (Vd = 40 V). The controlled and continuous production of metal oxide nanoparticles delivers a versatile and facile basis for industrial-scale solution processing of inorganic semiconductors. The presented approach yields performance values close to amorphous silicon and has a high potential for further improvements.