Comparing Electronic Properties of Spin-Cast and Inkjet-Printed Indium Oxide Thin Films

Additive manufacturing is an emerging technology which enables relatively low-cost, high-volume device fabrication, with modest capital equipment requirements. Printable electronics refers to devices fabricated using different additive manufacturing processes such as inkjet printing, dispensing, and aerosol printing. The more traditional deposition techniques such as solution processing, vacuum deposition, sputtering, and evaporation currently offer higher quality, but at a higher cost due to material use and infrastructure investment. One of the challenges that printable electronics face is device quality optimization. While recent advances in solution-processed metal oxide thin film transistors (TFTs) have been impressive, most high-performance devices have been reported using spin-coating rather than additive manufacturing. Spin-coating is a useful technique for laboratory testing but is not industrially scalable. Ultimately, comparable performance needs to be achieved using techniques such as additive manufacturing for solution processed metal oxides to be commercially viable.<br/><br/>In this study, we compare device performance between inkjet printed and spin-coated metal oxide TFTs. The device under consideration is the indium oxide TFT, a material known to exhibit a high electron mobility in spin-cast TFTs. We study how conversion temperature, a critical parameter for compatibility with mechanically flexible substrates, affects performance in both sets of devices. We observe non-negligible differences in mobility and threshold voltage between the two deposition methods. For spin-coated devices, the mobility ranged from 5 cm^2/Vs to 9 cm^2/Vs going from thinner to thicker indium oxide layers. The thinner devices were more subject to defects which increased resistance against the carriers. The threshold voltage for solution processing ranged from -75 V to 10 V where the thickest layers have the lower voltages. This is likely due to trap states. This information will be critical for future efforts to optimize additive manufacturing processes for mechanically flexible electronics.