Jun Ho Yu

Accurate and rapid evaluation of thickness uniformity in inkjet-printed organic layers is critical for the reliable fabrication of thin-film encapsulation (TFE) structures used in flexible organic light-emitting diode devices. In this study, we present a wide-field light extinction imaging method as a non-destructive, high-throughput technique for mapping the thickness distribution of ultraviolet (UV)-curable organic layers printed on glass substrates. Utilizing the optical properties of glass and organic materials, thickness information was extracted from two-dimensional light attenuation images acquired under 300 nm UV illumination. The proposed method enabled micron- to sub-micron-scale characterization of surface morphology, revealing edge bead formation, corner-thickening effects, and periodic waviness artifacts. Surface roughness parameters remained below 0.1 μm across printing densities ranging from 40% to 80%, demonstrating stable morphological control through halftoning-based layer deposition. These results confirm the method’s effectiveness for high-resolution, large-area thickness inspection, with practical relevance for process monitoring and quality control in printed electronics manufacturing. The technique also facilitates early detection of surface contamination or defects, offering a promising tool for inline inspection in industrial TFE production lines.

In this study, we propose an optimized inkjet printing process to improve the insertion loss of inkjet-printed coplanar waveguide (CPW) transmission lines. The process involves varying the drying temperature and adjusting the number of printing steps to investigate their effects on the electrical characteristics of the printed CPW. The relationships between surface roughness, surface cavities, morphological changes, and insertion loss are studied by conducting atomic force microscopy analysis and by examining the insertion loss up to 3 GHz. The printed CPW that underwent low-temperature drying after the first printing and high-temperature drying after the second printing before sintering showed improved results in terms of insertion loss, surface microcavities, and surface morphology compared to the CPWs prepared under different drying conditions. In particular, the proposed process led to an improvement in the insertion loss from 0.167 dB to 0.082 dB at 3 GHz. These findings provide valuable insights for improving the reliability and efficiency of printed electronics used in high-frequency applications.

Organic thin layers are highlighted as crucial components of flexible and printed electronic products due to their ability to provide mechanical flexibility in various applications, such as flexible displays and wearable electronics. The thickness and uniformity of these layers are crucial factors that influence surface planarization, mechanical stress relief, and the enhancement of optical performance. Therefore, accurate measurement of their thickness distribution is essential. In this study, the two-dimensional thickness distributions of spin-coated and inkjet-printed organic microlayers on glass substrates were measured using a light extinction image method. Using a 300 nm wavelength light source and a camera, images with an area of 4872 × 3640 μm² and an XY resolution of 3.5 μm were obtained through single measurements. The precision of the measured thickness could be enhanced to several nanometers through pixel binning and image overlaying. Using this light extinction measurement system, we measured and analyzed the thickness distribution of the center and edge of the spin-coated and inkjet-printed organic layers with thicknesses of several micrometers.