Fraunhofer FEP Integrable Solution for 2D Inline Process Monitoring

Joint project KODOS – Fabricated Thin Glass Composite for Optoelectronic System (13N14607), funded by the German Federal Ministry of Education and Research, developed an integrable solution for in-line process monitoring and mapping of process parameters. 
 
Until now electrical properties of the coating were determined and analyzed at defined measuring points. For the first time, SURAGUS GmbH at Fraunhofer FEP has created a unique solution that enables in-situ 2D monitoring that uses traversable eddy current measuring heads resulting in more detailed process optimization during coating. 
 
A significant contribution to the service life and functionality of subsequent products is made by the coatings of flexible materials such as ultra-thin glass or web, and roll-to-roll (R2R) manufacturing processes allows for high volume production of flexible devices. 
 
Until now, the analysis of coatings has been carried out subsequently via various inspection systems and characterization methods, and process control is then tailored according to the findings. The inline monitoring process allows for an analysis directly during the coating process, with this process fluctuations or inhomogeneities can be detected directly, avoiding a high reject rate. 
 
Fraunhofer FEP has multiple pilot facilities and laboratories for the development of functional coatings on ultra-thin glass, or other flexible materials. The KODOS project brings innovative material thin glass into finished products along the whole value chain. In working with SURAGUS, researchers have developed efficient coating technologies for electrodes and OLEDs.
 
Sheet resistivity can now be monitored in-situ with the option of 2D traversability of sensors in the R2R process. The x-y traversability of the sensors enables mapping in 2D to make coating thickness fluctuations visible over the coating width or defects during coating.
 
The measurement system in Fraunhofer FEP’s RC300 system is used for sheet resistance measurement on thin TCOs or metallic layers. Now the system can be used to coat, wind, and simultaneously measure ultra-thin glass and films. 
 
Fraunhofer FEP developed a self-sufficient instillation variant for a traverse that was integrated into the RC300 vacuum R2R system. Project manager Jacqueline Hauptmann explained, “our R2R system has a very small installation capacity, i.e., there was very little space as well as only limited possibilities to install further components in the system. Thanks to our in-house expertise in systems and hardware development, a traverse that could be easily integrated was now designed, drawn in 3D and constructed for this purpose. Particular attention was paid to developing a concept that could be adopted to any existing vacuum coating system and equipped with a wide variety of sensors.”
 
“When integrating our eddy current sensors into the new solution for R2R vacuum systems, attention had to be paid to the vacuum suitability of the individual components and overheating during operation has to be avoided in order not to impair the vacuum,” said SURAGUS GmbH managing director Marcus Klein. “In addition, special algorithms for compensation of signal changes caused by the movement of the sensors had to be developed to achieve high accuracies. In the meantime, we have jointly designed an overall solution on the facility at Fraunhofer FEP, where our sensors provide reliable values for sheet resistance of metallic, organic and inorganic layers.”
 
Non-contact high-frequency eddy current testing as a monitoring technology can ensure process stability and coating quality for new volume and established manufacturing processes, and support improvements in manufacturing yields. With the new traverse, transferable solutions were developed for process control or pure data acquisition to adjust process parameters during coating.
 
Researchers are currently working on a pilot scale with still low winding speeds. This is now being optimized and faster winding and measuring modes are being tested.