Measurement of inkjet droplet size based on Fraunhofer diffraction

Dong Yeol Shin; Yoon Jae Moon; Jun Young Kim; Kyung-Tae Kang

doi:10.1063/5.0159472

Measurement of inkjet droplet size based on Fraunhofer diffraction

Rev Sci Instrum. 2023 Oct 1;94(10):105106. doi: 10.1063/5.0159472.

Authors

Dong Yeol Shin^{1

2}, Yoon Jae Moon¹, Jun Young Kim³, Kyung-Tae Kang¹

Affiliations

¹ Digital Transformation R&D Department, Korea Institute of Industrial Technology (KITECH), Sangnok-gu, Ansan-si 15588, South Korea.
² Micro/Nano System Department, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, South Korea.
³ Organic Semiconductor Laboratory, Department of Semiconductor Engineering, Gyeongsang National University, Jinju 52828, South Korea.

PMID: 37796099
DOI: 10.1063/5.0159472

Abstract

Inkjet printers have started to manufacture OLED/QLED pixel arrays for the display industry, and the precise measurement and control of ink droplet volume during the printing process has become important. We investigated the feasibility of Fraunhofer diffraction analysis as a volume measurement tool for fast-moving inkjet droplets. To confirm the basic idea, two Fraunhofer diffraction-based methods were used to calculate the wire diameters of well-known sized and steady-positioned metal wires. The first method was to curve-fit the whole measured diffraction intensity curve with the extensive Fraunhofer diffraction equation. The second one was to use the simple approximate diameter calculation equation with the measured position data of minimum diffraction intensity. The metal wire diameters calculated by the two methods showed less than 1.17% error. For the size measurement of fast-moving inkjet droplets, the first method showed 24.5 µm diameter and 7.7 pL volume, while the second method showed 25.4 µm diameter and 8.58 pL volume. We found that the second method was more suitable for real-time inkjet monitoring because its average computer calculation time was 33 ms, and the first method took an average of 34 ms, about 1000 times more CPU time. Hence, Fraunhofer diffraction analysis as an inkjet droplet volume measurement tool was feasible with a good balance of measurement time and measurement accuracy.