Drop-on-demand (DOD) electrohydrodynamic (EHD) jet printing uses a nozzle and pulsated electric fields to eject small ink droplets of functional material to the appointed spot of a substrate at the appointed time, which offers solutions of high resolution patterning for fabrication of printed electronics, bioengineering, and display. Because the EHD jet connects fine drops to yield a fine pattern, it is essential to realize high throughput by generating drops quickly and reliably. In this study, the characteristics of jetting frequency were experimentally investigated as a function of nozzle dimensions by measuring response of jetting frequency to pulsating frequency which is varying from 1 Hz to 2000 Hz. The results showed that, even when the nozzle diameter is the same, the other dimensions of the nozzle significantly change the response of jetting to high pulsating frequency. Using a linear damping model describing hydrodynamic motion of ink inside the nozzle, the different behavior of the jetting frequency was explained via the different damping ratio of the oscillating ink: contrary to an underdamped system, an overdamped system supports a jetting frequency higher than the natural frequency.

We proposed a micro electrode fabrication method by a metal inkjet printing technology for the bio-applications of dielectrophoresis (DEP). The electrodes are composed of bottom planar gold (Au) electrodes and three dimensional (3D) silver (Ag) electrodes fabricated locally on the Au electrode through metal inkjet printing. We observed the negative DEP characteristics of the 4 μm polystyrene beads on the both electrodes at the 500 kHz, AC 20 V_pp point. The number of beads trapped on the printed Ag electrode is 79 and 25 on the planar Au electrode because of spatially larger electric field in a 3D electrode system.

Area-selective atomic layer deposition (AS-ALD) has been studied as an alternative method for metal oxide ALD film patterning in the microelectronics industry. To perform AS-ALD, area-deactivation or -activation processes should be implemented in advance using selective surface modification through a photography-based lift-off process and printing techniques. This study introduces a novel approach for Al₂O₃ AS-ALD using inkjet-printed inhibition patterns. ALD-inhibition patterns with two-layer structures of fluorocarbon (FC) thin film and photoresist (PR) were patterned by inkjet printing. Low surface energy FC thin films were used to block the Al₂O₃ nucleation and growth during the ALD process, and PR was patterned to easily remove ALD-inhibition patterns using a lift-off process. To demonstrate AS-ALD, an Al₂O₃ thin film approximately 10 nm thick was deposited via an in-house built system with a multiple-slit gas source. The proposed AS-ALD method was evaluated for topological analysis using atomic force microscopy and surface composition analysis using a time of flight secondary ion mass spectrometry after Al₂O₃ deposition and a lift-off process. Finally, a 6 nm thick Al₂O₃ film was selectively patterned by the lift-off process using an inkjet-printed 1.28 μm thick FC-covered PR inhibition pattern.

This study proposes the unique method to analyze the cleanliness of the fine metal mask (FMM) used in OLED display manufacturing after FMM cleaning process. We developed a FMM-mimic microstructure as a substitute for the FMM, which can be used for the evaluation of cleaning efficiency. The FMM-mimic microstructure was fabricated using a combination of photolithography, reactive ion etching, anodic bonding and sand blasting processes. To demonstrate the proposed cleanliness analytical method, a 1.4 μm-thick Tris-(8-hydroxyquinoline) aluminum (Alq₃) film was deposited on the FMM-mimic microstructure as a contaminant by vacuum thermal evaporation. The Alq₃-deposited FMM-mimic microstructure was cleaned by N-methyl-2-pyrrolidone (NMP) with changing cleaning time. We analyzed the residual contaminants on the FMM-mimic microstructure using a fluorescence microscope. The developed FMM-mimic microstructure proves very convenient for inspecting the residual contaminant inside the gap through the transparent glass by general optical and fluorescence microscopy.