Huai-Yuan Tseng

High-Speed Printing of Transistors: From Inks to Devices

The realization of a high-speed printing technique with high resolution and pattern fidelity is critical to making printed electronics a viable technology for electronics manufacturing. The printing requirements of printed electronics are substantially different that those of graphic arts. To make printed electronics a reality, it is necessary to deliver high resolution, good reproducibility, excellent pattern fidelity, high process throughput, and compatibility with the requisite semiconductor, dielectric, and conductor inks. In this paper, we review the physics of pattern formation from pixelated primitives, such as those that exist during inkjet and gravure printing, and will show how control of drop merging and drying can be used to produce high-fidelity shapes, including lines, squares, and intersections. We additionally discuss the physical underpinnings of gravure printing and inkjet printing, and show how these techniques can be scaled to produce high-fidelity highly scaled patterns, including sub-2 micron features at printing speeds of ~1 m/s. Finally, in conjunction with high-performance materials, we describe our realization of high-performance fully printed transistors on plastic, offering high-switching speed, excellent process throughput, and good fidelity over large areas.

All inkjet printed self-aligned transistors and circuits applications

We fabricate devices and circuit blocks using a novel, fully-printed transistor process that self-aligns source/drain electrodes to gates, resulting in improved overlap capacitance. These are used with a self-aligned interconnect to realize fully-printed transistor arrays and inverters showing performance suitable for use in a range of low-cost electronics applications.

Printing and scaling of metallic traces and capacitors using a laboratory-scale rotogravure press

In this paper we demonstrate the design and development of a small-size, sheet-fed gravure printer which can achieve 10µm alignment of multiple layers and requires less than 200µL of ink per print. Using this printer we demonstrate highly-scaled metallic silver lines, 20µm wide, printed with nano-particle and precursor based inks. We describe some scaling trends which are specific to the printing technique, and the inks used. We also demonstrate the use of rotogravure for printing poly-vinyl phenol dielectric layers and describe how ink formulation and gravure roll design affect thickness and uniformity of these layers. Finally, we describe printed capacitors fabricated using a hybrid gravure/ink-jet process presenting some of the challenges of printing multiple layer devices and the need for hybrid-technique printing processes.

All printed self-aligned organic transistors for low cost RFID applications

The lack of self-alignment between the gate and the source/drain electrodes is significant problem for printed transistors, since alignment is typically limited by the layer-to-layer registration capabilities of the printer. This in turn necessitates the use of design rules specifying large gate-to-source/drain overlaps, resulting in degraded switching speed due to the large overall capacitance [1]. Here, for the first time, we demonstrate the realization of self-aligned transistors in a fully inkjet-printed process, without the need for any lithography or vacuum processing. With self-aligned printing of the source/drain to the gate, we achieve a minimum overlap of 0.78um between the gate the source/drain, contrasted to the >10um typically required in conventional printed transistors. As a result, the cut-off frequency of the printed transistor is significantly enhanced since parasitic overlap capacitances are minimized. Moreover, variations of the channel length can be reduced since the channel length is now defined by self-alignment. In contrast to previous reports on self-aligned printed devices [2], we achieve self-alignment in a fully-printed process without using any lithographic steps.