Tampere University of Technology

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Self-Aligned Patterning Methods for Large-Area Electronics

Research output: Book/ReportDoctoral thesisCollection of Articles

Details

Original languageEnglish
PublisherTampere University of Technology
Number of pages43
ISBN (Electronic)978-952-15-3664-9
ISBN (Print)978-952-15-3607-6
Publication statusPublished - 11 Dec 2015
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University of Technology. Publication
PublisherTampere University of Technology
Volume1341
ISSN (Print)1459-2045

Abstract

Printed electronics is studied as an alternative to conventional electrics, especially for large-area applications, such as organic light emitting diode (OLED) lighting panels. The whole technology, however, suffers from a low resolution and registration accuracy in the printing process, limitations that directly affect the performance of the applications. Photolithography can overcome these limitations and provide both good registration accuracy and resolution, but it is a challenging process in high throughput fabrication. Thus new fabrication methods are being studied intensively to replace expensive lithography steps in the fabrication chain.

This thesis presents two alternative fabrication methods with a scale-up capacity for high volume production. The first combines fast low-resolution patterning with roll-to-roll scalable high resolution microcutting; the second was developed to accurately align dielectric patterns on conductors. The latter uses an electric current to heat metal lines and cure a polymer dielectric locally near the conductor. Uncured polymer is rinsed away, leaving an aligned dielectric on the lines. The method is well suited for passivating OLED anode grid lines, which require excellent registration accuracy to prevent significant losses in the device active area.

The layer-to-layer registration accuracy of Joule heating is defined by heat conduction in the substrate. Thus the accuracy can be increased either by selecting a thermally low conductive substrate or by using short current pulses. The latter method allows more freedom to design the other process parameters and materials. An optimal pulse length depends on the substrate material in that materials with high thermal conductivity require short heating pulses. Here though the pulse lengths are of the order of milliseconds, which are easy to produce. In addition to increased registration accuracy, pulsed heating significantly cuts down the processing time and required energy.

In this thesis, a dielectric registration accuracy of 2 µm was demonstrated on shadow- mask-evaporated silver lines on glass, a value similar to that reported for registration accuracy in roll-to-roll photolithography, 1 µm. Joule heating, however, does not require challenging alignment steps. To demonstrate the feasibility of Joule heating for passivation in an OLED device, a printed silver current distribution grid was passivated using pulsed Joule heating and fabricated as an OLED device.

The Joule heating work constituted not only an experimental study but involved extensive finite element simulations to obtain design rules for the current distribution grid and to study the heating selectivity. The idea of the pulsed heating was also a result of this work.

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