Inkjet printing of sustainable ZTO/AlO_x thin film transistors

Abstract

Abstract Even though printed metal oxide thin film transistors (TFTs) have been a central topic of research in the past decade, the most notable results still require scarce elements such as gallium and indium, or high annealing temperatures (⩾400 °C) when using sustainable raw materials such as zinc and tin. In this work, safe, abundant and inexpensive materials such as zinc, tin and aluminum are explored to reach low-cost thin films and devices with both the semiconductor and dielectric layers deposited by inkjet printing and annealed at lower temperatures (300 °C). Alumina (AlO x ) and zinc tin oxide (ZTO) inks containing a theoretical optimal V % of ethylene glycol were optimized for production of uniform and reproducible AlO x /ZTO thin film layers. Common ink parameters (such as the reverse Ohnesorge, capillary, Webber and Reynolds numbers) were evaluated and compared with relevant literature on inkjet drop formation mechanisms. Inks within theoretical optimal parameter values were printing optimized in terms of drops per inch, number of layers, UV substrate surface activation, print speed, and post- annealing. A high-quality dielectric of two alumina layers was printed, having a breakdown field above 2.93 ± 0.33 MV cm −1 , and a dielectric constant of 7.74 ± 0.73 at 1 kHz. TFTs of inkjet printed (IJP) ZTO/AlO x layers were produced with a maximum I On / I Off ratio of 10 3 and a saturation mobility of 2.2 cm 2 V −1 s −1 . This approach not only advances the field of printed electronics but also addresses concerns related to material scarcity, thermal budget, and production costs.