Reverse‐Offset Printing of Metal‐Nitrate‐Based Metal Oxide Semiconductor Ink for Flexible TFTs

Reverse‐offset printing (ROP) is a novel printing technique capable of forming electronics‐industry‐relevant linewidths (≈1 µm) with good thickness control and sharp edge definition. It is demonstrated that through a controlled oxygen‐plasma treatment, the energy of the surfaces related to the process steps of ROP can be optimized to allow the patterning of metal‐oxide semiconductor layers using a simple printing ink based on metal nitrates dissolved in an organic solvent. The steps of the ROP process are analyzed using surface‐energy measurements and Fourier transform infrared spectra of the ink during drying. Thin‐film transistors (TFTs) fabricated using a roll‐to‐plate ROP of In2O3 semiconductor and evaporated Al source/drain (S/D) contacts show, on average, mobilities of 3.1 and 3.5 cm2 V−1 s−1, and ON/OFF‐ratios up to 108 and 107 on a Si/SiO2 substrate and on a flexible polyimide‐type substrate, respectively. TFTs on the flexible substrate with also the S/D‐contacts printed with ROP using Ag nanoparticle ink exhibit a 1.4 cm2 V−1 s−1 mobility. To demonstrate the scalability of the process, continuous lines of In2O3 are printed using a roll‐to‐roll‐compatible (R2R) ROP with linewidths down to ≈2 µm. This process is expected to lead to miniaturized metal‐oxide circuits as required by flexible high‐resolution sensor arrays and displays. Reverse‐offset printing (ROP) alleviates common problems associated with conventional printing methods, such as inkjet and gravure, including large linewidths and uneven print profiles. It is demonstrated that ROP can be applied using a simple metal‐nitrate‐based ink and allows high‐resolution metal oxide patterns with ≈2 µm linewidths. Thin‐film transistors are fabricated on Si/SiO2 and flexible substrates with ROP‐processed In2O3 semiconductor.