Gerd Grau

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.

Printed unmanned aerial vehicles using paper-based electroactive polymer actuators and organic ion gel transistors

We combined lightweight and mechanically flexible printed transistors and actuators with a paper unmanned aerial vehicle (UAV) glider prototype to demonstrate electrically controlled glide path modification in a lightweight, disposable UAV system. The integration of lightweight and mechanically flexible electronics that is offered by printed electronics is uniquely attractive in this regard because it enables flight control in an inexpensive, disposable, and easily integrated system. Here, we demonstrate electroactive polymer (EAP) actuators that are directly printed into paper that act as steering elements for low cost, lightweight paper UAVs. We drive these actuators by using ion gel-gated organic thin film transistors (OTFTs) that are ideally suited as drive transistors for these actuators in terms of drive current and frequency requirements. By using a printing-based fabrication process on a paper glider, we are able to deliver an attractive path to the realization of inexpensive UAVs for ubiquitous sensing and monitoring flight applications.

Fabrication of a high-resolution roll for gravure printing of 2μm features

High-resolution features are key to achieve high performance printed electronics devices such as transistors. Gravure printing is very promising to achieve high resolution in combination with high printing speeds on the order of 1m/s. High-speed gravure has recently been shown to print high resolution features down to linewidths and spacing of 2μm. Whilst this was a tremendous improvement over previous reports, these results had been obtained using silicon printing plates. These silicon printing plates are fabricated using microfabrication techniques which offer several advantages over traditional metal gravure cylinders where the features are defined by techniques such as stylus engraving, laser engraving or etching. This offers much greater precision and design freedom in terms of feature size, surface roughness, cell placement and cell shape. However, rigid silicon printing plates cannot be used in a roll-to-roll printing process that would truly enable low-cost printed electronics. Here we demonstrate for the first time a gravure printing roll that combines the precision of silicon printing plates with the form factor of a metal cylinder. The fabrication process starts with a silicon master whose pattern is replicated by polymer molding. The actual metal printing plate is then built up on the polymer negative of the pattern by a combination of electroless and electroplating. After separation of the polymer and the metal, the metal printing plate can be mounted on a magnetic roll for printing. Printing of highly scaled 2μm features is demonstrated. Different metal surfaces were explored to optimize printing performance and wear during printing.

A computational model for doctoring fluid films in gravure printing

The wiping, or doctoring, process in gravure printing presents a fundamental barrier to resolving the micron-sized features desired in printed electronics applications. This barrier starts with the residual fluid film left behind after wiping, and its importance grows as feature sizes are reduced, especially as the feature size approaches the thickness of the residual fluid film. In this work, various mechanical complexities are considered in a computational model developed to predict the residual fluid film thickness. Lubrication models alone are inadequate, and deformation of the doctor blade body together with elastohydrodynamic lubrication must be considered to make the model predictive of experimental trends. Moreover, model results demonstrate that the particular form of the wetted region of the blade has a significant impact on the models ability to reproduce experimental measurements.

Low-cost fabrication of paper-based systems: Microfluidics, sensors, electronics and deployment

Paper is a very interesting substrate material for sensing systems due to its porous nature, low cost, light weight and biodegradability. Low-cost sensing platforms can be created by combining paper substrates with low-cost printed fabrication methods. Here, recent progress is reviewed in the areas that will be needed to create powerful paper-based sensing systems: pump-free microfluidics to manipulate fluids of interest, biosensors to detect analytes, printed microelectronics for signal processing and novel methods of deploying paper-based systems such as printed gliders.

High-resolution gravure printed lines: proximity effects and design rules

Gravure printing is a very promising method for printed electronics because it combines high throughput with high resolution. Recently, printed lines with 2μm resolution have been demonstrated at printing speeds on the order of 1m/s. Here we build on these results to study how more complex patterns can be printed that will ultimately lead to printed circuits. We study how the drag-out effect leads to proximity effects in gravure when multiple lines are printed close to each other. Drag-out occurs as the doctor blade passes over the roll surface to remove excess ink from the land areas in between the cells that make up the pattern. In addition to this desirable removal of excess ink, some ink from the cells also wicks up the doctor blade and is removed from the cells. This ink is subsequently deposited on the land area behind the cells leading to characteristic drag-out tails. If multiple lines, oriented perpendicular to the print direction, are printed close to each other, the ink that has wicked up the doctor blade from the first line will affect the drag-out process for subsequent lines. Here we show how this effect can be used to enhance print quality of lines as well as how it can deteriorate print quality. Important variables that will determine the regime for printing optimization are ink viscosity, printing speed, cell size, cell spacing and relative placement of lines. Considering these factors carefully allows one to determine design rules for optimal printing results.