Jaeyong Choi

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.

Design and Fabrication of Electrostatic Inkjet Head using Silicon Micromachining Technology

This paper presents design and fabrication of optimized geometry structure of electrostatic inkjet head. In order to verify effect of geometry shape, we simulate electric field intensity according to the head structure. The electric field strength increases linearly with increasing height of the micro nozzle. As the nozzle diameter decreases, the electric field along the periphery of the meniscus can be more concentrated. We design and fabricate the electrostatic inkjet heads, hole type and pole type, with optimized structure. It was fabricated using thick-thermal oxidation and silicon micromachining technique such as the deep reactive ion etching (DRIE) and chemical wet etching process. It is verified experimentally that the use of the MEMS inkjet head allows a stable and sustainable micro- dripping mode of droplet ejection. A stable micro dripping mode of ejection is observed under the voltages 2.5 kV and droplet diameter is 10 μm.

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.

Satellite/spray suppression in electrohydrodynamic printing with a gated head

During electro-hydrodynamic printing, part of discharged jets may be broken into tiny satellites/sprays, making patterns scattered. This paper presents a method of suppressing these satellites/sprays based on a ring-shaped gate electrode placed in between nozzle and substrate. We discover, by simulation and experimentation, that the maximum satellite/spray suppression can be achieved when the diameter of gate hole and the distance from nozzle to gate are, respectively, about 5, and 2.5 times the outer diameter of nozzle and when the gate voltage applied has a waveform of a negative and positive pulse pair mixed with a fixed gate bias.

Microelectromechanical systems print heads for industrial printing

Abstract With the recent prospect of microelectromechanical systems (MEMS) print heads broadening their applications beyond digital printing for office use into industrial printing for the direct patterning of micro/nano devices and circuits, MEMS print heads have attracted renewed attention as a key player for realizing printed electronics. Cost-effectiveness, flexibility, and environmental friendliness in fabrication are the main drivers of industrial printing. This chapter introduces MEMS print heads—especially, a new type referred to here as the electrohydrodynamic (EHD) print head. This has emerged recently as a viable and even better alternative to the conventional piezoelectric MEMS print heads for industrial printing, as it offers a higher resolution and thickness of patterning and can eject a high viscosity of ink. Nowadays, not only EHD droplet ejection but also the EHD printing system for industrial applications is being investigated intensively with commercialization in mind. Furthermore, performance indices such as repeatability and stability are becoming a major issue to solve. This chapter also addresses briefly the effort to improve such reliability related indices.

MEMS print heads for industrial printing

Abstract: With the recent prospect of micro electro mechanical systems (MEMS) print heads broadening their applications beyond digital printing for office use into industrial printing for the direct patterning of micro/nano devices and circuits, MEMS print heads have attracted renewed attention as a key player for realizing printed electronics. Cost-effectiveness, flexibility and environmental friendliness in fabrication are the main drivers of industrial printing. This chapter introduces MEMS print heads – especially, a new type referred to here as the electro hydro dynamics (EHD) print head. This has emerged recently as a viable and even better alternative to the conventional piezoelectric MEMS print heads for industrial printing, as it offers a higher resolution and thickness of patterning and can eject a high viscosity of ink. Nowadays, not only EHD droplet ejection, but also the EHD printing system for industrial applications is being investigated intensively with commercialization in mind. Furthermore, performance indices such as repeatability and stability are becoming a major issue to solve. This chapter also addresses briefly the effort to improve such reliability related indices.