Inkjet printing of homogeneous and green cellulose nanofibril dielectrics for high performance IGZO TFTs

Abstract

Inkjet printing of environmentally friendly functional nanomaterials for high performance indium–gallium–zinc oxide (IGZO) thin film transistors (TFTs) is highly in demand for the development of inexpensive and green electronics. However, it remains challenging to obtain nanomaterial inks with desirable physicochemical properties for inkjet printing and finally to achieve homogeneous in-plane patterns. Here, we present biodegradable and uniform cellulose dielectric films for high performance IGZO TFTs via inkjet printing. Firstly, an oxidized cellulose nanofibril (CNF) was selected due to its stable dispersion in water, and additives were added to obtain CNF ink suitable for our printing system. Moreover, it was found that adding additives also increased the interactions inside the solution, so the obtained CNF ink exhibited a gel-like behavior with a rapidly increasing viscosity after high-speed shearing. Such behavior was defined as fast-self-gelation properties, which were beneficial for improving the uniformity of the printed films by inhibiting the outward capillary flow. Based on these properties, we further added surfactants to regulate the internal flow, and then obtained a homogeneous morphology. Besides the excellent uniformity, the prepared CNF film was a candidate for transparent dielectrics, with excellent transparency (above 95%) and a low leakage current density (3.68 × 10⁻⁶ A cm⁻²). Finally, IGZO-TFTs with a mobility of more than 10 cm² V⁻¹ s⁻¹ and an on/off current ratio of higher than 5 × 10⁴ were fabricated using the printed CNF films as dielectrics, thus shedding light on the use of CNF dielectrics obtained by inkjet printing for the fabrication of high-performance, inexpensive, and environmentally friendly electronics.