Over the past decade, inkjet technology has been well recognized for the manufacturing of products that include “printing beyond colors.” This micrometer‐scale precise technology provides a straightforward approach toward judicious deposition of electronically functional material inks on various substrates over relatively large areas, for printed/flexible electronics. The technology promotes upscalability and has become a renowned process tool for fabricating electronic devices in the field of printed/flexible electronics. Here, the fabrication of printed thin‐film transistors (TFT) on cheap coated paper substrate using inkjet technology is reported. For developing the TFT layer stack conductive nanoparticle inks, a polymeric dielectric ink and a p‐type organic semiconductor ink are employed. The coating on the paper provides several advantages for fabrication process of TFTs; for example, control over ink spreading. This control of ink spreading can directly influence the fabrication of interdigitated source/drain (S/D) electrodes for TFTs, when a top gate bottom contact architecture is considered. This results in better manufacturing yields and promising electrical performance, which are also the focus of this research. The all inkjet‐printed TFTs on paper exhibit electrical performance with maximum S/D current ranging to 170 nA, charge carrier mobility of 0.087 cm2 V−1 s−1, and current on/off ratio of 330.
Inkjet and screen printing technologies are well known in the graphic arts industry for the reproduction of texts, images, and graphics. During the last decades, these printing technologies have been attracting increasing interest for the deposition of functional materials, e.g., in the field of printed electronics and for biological applications. However, their usage is mainly limited to 2D applications, i.e., rather flat deposits ranging from nanometers to several tens of micrometers in thickness. For 3D applications, sophisticated additive manufacturing technologies are developed to manufacture structures with high shape complexities. Herein, the potential of standard inkjet and screen printing technology as tools for the development of functional 3D objects is demonstrated. 3D functional structures printed by inkjet and screen printing technology combining conductive and nonconductive materials to a multi-material structure are shown. A metal nanoparticle ink formulation is applied to inkjetprint conductive metal pillars with a high aspect ratio (in the range of 50) used as vertical interconnects. The interconnects are encapsulated with an inkjet-printed polymeric ink formulation and finally used as conductive tracks to light up a solidstate light-emitting diode (LED). Screen printing is applied to print primary batteries used as the power source for the LED.
The inside front cover shows a top‐gated thin‐film transistor and its respective array, processed on a paper substrate using inkjet printing, as described by Kalyan Yoti Mitra and co‐workers in article number https://doi.org/10.1002/aelm.201700275. These printed devices have been developed with the goal of constructing circuits that can be used for expendable flexible paper electronics.
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