Sang Uk Son

Drop-on-demand printing of conductive ink by electrostatic field induced inkjet head

Recently, inkjet printing technology has become crucial in many industrial fabrication fields mainly due to its advantages of noncontact and fast pattern generation. In this paper, we investigate an electrostatic field induced inkjet printing system, which is based on an electrohydrodynamic process, for drop-on-demand jetting. In order to locate the optimal jetting conditions, we tested jetting performance for various bias voltages and pulse signals. To investigate the characteristics of drop-on-demand operation and micropatterning, we used conductive silver ink and examined the drops and lines patterned on a substrate.

Electrostatic droplet formation and ejection of colloid

This paper presents a novel mechanism of electrostatic micro droplet formation and ejection using charged colloid as fluid. Unlike conventional electrostatic jetting which requires a high operating voltage, we offer a commercially viable, low operating voltage for droplet-on-demand operation based on a layered electrode structure of nozzle. The layered electrode structure of nozzle allows the formation, acceleration, and ejection of a droplet to be controlled by the voltage signals applied to individual electrodes. A simulation study indicates that the proposed mechanism allows less than 100 volt of operating voltage for the formation and ejection of a few pico-liter volume of droplet. Investigation includes the effects of the following factors on the droplet formation and ejection: 1) The shape of meniscus inside the nozzle. 2) The electric field distribution. 3) The density of charged nano particles in colloid.

Comparative Study on Ejection Phenomena of Droplets from Electro-Hydrodynamic Jet by Hydrophobic and Hydrophilic Coatings of Nozzles

An electro-hydrodynamic (EHD) jet from an electrostatic inkjet head shows advantages in printing microsize patterns because it can generate submicron droplets and can use highly viscous inks. Since the basic principle of the EHD jet is to form a droplet from the apex of a meniscus at the end of a nozzle, the stable ejection of the droplet greatly depends on the shape of the meniscus, which is affected by surface characteristics of the nozzle, electric potential, and ink properties. Hence, experiments have been performed using nozzles with hydrophobic and hydrophilic coatings to investigate the droplet ejection.

The study on the optimal operating voltage and pressure for the stable ejection using the electrostatic field induced MEMS inkjet head

Inkjet technology is already used in the manufacture of many electronic devices. During recent years, electrostatic induced inkjet print technology has turned theoretical research into a practical manufacturing solution. This paper presents a novel electrostatic field induced inkjet device featured by a MEMS fabricated nozzle with ring shaped control electrode and investigates the feasibility of applying the inkjet device to flexible electronics, micro bio chips and sensor devices manufacturing process. The electric voltage signal applied to a ring shaped electrode plate against the inside the nozzle allows a jet ejection to take place. This demonstrates a feasibility of electrostatic induced inkjet device as a disruptive alternative to conventional print heads.

Efficient Control of Electrospray Emission for Colloid Microthruster with Laminated Electrodes

(Abstract) In this paper, MEMS based colloid micro-thruster, feature by MEMS fabricated nozzle with a conductive pole inside, is developed by bulk silicon processing. This paper also investigates the effect of the laminated electrodes on the efficiency and stability for forming jets from the liquid meniscus. Unlike conventional colloid microthruster, which is composed of conductive nozzle and single external extractor electrode, we offer more efficient mechanism for controllable operation based on layered electrodes and pole type nozzle. The layered electrodes allow the cone and jet formation, and acceleration of spray to be controlled by the voltage signals applied to individual electrodes. It is experimentally verified that the use of the pole type nozzle and the layered electrodes allow the stable and sustainable cone jet mode for an applied voltage as low as 800 V.

Fabrication and performance analysis of electrostatic micro droplet ejector

This paper proposes a monolithic fabrication and performance analysis electrostatic micro-droplet ejector. Unlike conventional electrostatic jetting which requires a high operating voltage, we offer a commercially viable, low operating voltage for droplet-on-demand operation based on a nozzles monolithic electrode structure. The monolithic electrode structure of the nozzle allows the formation, acceleration, and ejection of a droplet to be controlled by the voltage signals applied to control electrodes. The ground electrode is designed to have hole-tip shape. A hole-tip type ground electrode gives the electric field stronger than that for the bottom ground electrode. And ejection hole is coated a hydrophobic material (Teflon). So the liquid formed convex geometric shape of the meniscus between the hydrophilic and hydrophobic surfaces through the hydrophilic microchannel by capillary attraction. Formation and ejection in hydrophobic coating channel shows that stable D-type jetting property compared with hydrophilic coating channel.