Low‐Temperature‐Processed Printed Metal Oxide Transistors Based on Pure Aqueous Inks

Abstract

Additive patterning of transparent conducting metal oxides at low temperatures is a critical step in realizing low cost transparent electronics for display technology and photovoltaics. In this work, inkjet printed metal oxide transistors based on pure aqueous chemistries are presented. These inks readily convert to functional thin films at lower processing temperatures (T ≤ 250 °C) relative to organic solvent-based oxide inks, facilitating the fabrication of high-performance transistors with both inkjetprinted transparent electrodes of aluminum-doped cadmium oxide (ACO) and semiconductor (InO x ). The intrinsic fluid properties of these water-based solutions enable the printing of fine features with This article is protected by copyright. All rights reserved. 2 coffee-ring free line profiles and smoother line edges than those formed from organic solvent-based inks. The influence of low temperature annealing on the optical, electrical, and crystallographic properties of the ACO electrodes is investigated, as well as the role of aluminum doping in improving these properties. Finally, we characterize the all-aqueous printed TFTs with inkjet-patterned semiconductor (InO x ) and source/drain (ACO) layers, which show ideal low contact resistance (R c < 160 Ω-cm) and competitive transistor performance (µ lin up to 19 cm 2 V -1 s -1 , SS ≤ 150 mV dec -1 ) with only low temperature processing (T ≤ 250 °C).

A Review of Low‐Temperature Solution‐Processed Metal Oxide Thin‐Film Transistors for Flexible Electronics

“…e) Schematic diagram and optical microscope image of oxide TFT with inkjet‐printed channel and source/drain electrodes and f) their transfer characteristics and linear mobility. e,f) Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…In 2017, inkjet‐printed oxide TFTs based on pure aqueous inks are achieved at low‐temperature of 250 °C by Subramanian and co‐workers The pure aqueous inks could be converted to oxide films at lower processing temperature compared with organic solvent‐based inks. Figure e shows a diagram of oxide TFT structure with the all‐aqueous‐printed TFTs with inkjet‐patterned channel and source/drain layers.…”

“…Holbery and co‐workers demonstrated an increase in electrode conductivity at low annealing temperatures, which minimized cracks originating from thermal stress and chemical diffusion between layers during the annealing process. An approach for lowering the fabrication temperature of conductive oxides in oxide TFTs was reported the following year …”

Recent Progress in Inkjet‐Printed Thin‐Film Transistors

“…In particular, the concentration of flocculation agent (NaCl in this work) was carefully determined to realize improved long‐term stability of the inks and better nanoparticle dispersion ability. Aqueous chemistries involving sol–gel metal oxide inks are also well‐known approaches for low‐temperature processing ( Figure ), which allow oxide films to be converted at 250 °C for both conductive electrodes and semiconductors. Additionally, Al doping could improve the transparency and conductivity, such that electrical and optical performances competitive to those of oxide TFTs fabricated using organic solvent‐based oxide inks were achieved.…”

“…g) Transfer characteristics with linear mobility shown and h) output characteristics of aqueous InOx‐printed transistor with printed ACO contacts processed at ≤250 °C. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”