Flexible, stretchable and bendable electronic devices and technologies may soon flood the market. Thin film technology forms the backbone to these kind of applications. At present, their exploitation is ongoing as the various capabilities they possess continue to be unearthed. Flexibility and transparency is the deterministic factor for the various desired applications. Quality assurance of the thin films is essential for successful fabrication. Consequently, offline sampling and inspection at times become impracticable thereby necessitating the use of online techniques. There exist several characterization techniques, however, a majority of them is intended for use on small area samples. Synchronized thermography is an infrared imaging based characterization techniques which has already proven to be versatile when employed to inspect the uniformity of large area thin films and evaluate the features of more complex structures such as solar cells. So far, this technique has only been studied with stationary samples.
University of Oulu researchers in Finland: Mr. Kari Remes, Dr. Kimmo Leppänen and professor Tapio Fabritius evaluated the performance and applicability of the synchronized thermography technique in a realistic roll-to-roll production environment with continuously moving samples. They hoped to build a characterization system which would be able to detect possible defects and uniformity of moving conductive thin films. Their work is published in the research journal, Optics Express.
The research team commenced their experimental procedure by selecting two differently handled indium tin oxide on polyethylene terephthalate as sample materials to represent the conductive films. Next, the two samples were placed to the measurement setup in turn and thermal imaging procedure conducted. The designed online thermography measurement system followed roll-to roll fabrication principles.
The authors configured the data capturing so, that all unnecessary data processing features such as averaging were set off to ensure the fastest possible analysis and feedback loop. The synchronized thermography based analysis was able to reveal defects on both samples where the researchers noted that the intentionally damaged sample displayed more imperfections with different types while the defects of the cautiously handled sample seemed to be smaller and fewer.
Kari Remes and colleagues study demonstrated a novel roll-to-roll compatible synchronized thermography based online measurement system as an auspicious assessment tool that will enable determine quality of films. The applicability of this system has been proven by its incorporation and use during the characterization of a moving plastic film with conductive indium tin oxide on top. Altogether, the results obtained have indicated that synchronized thermography has unbounded potential to be exploited in the online homogeneity characterization and sheet resistance approximation of large area thin films which are impractical with other existing techniques.
Kari Remes, Kimmo Leppänen, Tapio Fabritius. Thermography based online characterization of conductive thin films in large-scale electronics fabrication. Volume 26, No. 2 | 2018 | Optics Express 1219
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