Hadi Teguh Yudistira

Flight behavior of charged droplets in electrohydrodynamic inkjet printing

Flight behaviors of charged droplets are presented for electrohydrodynamic (EHD) inkjet printing. Three different kinds of EHD spraying techniques, pulsed dc, ac, and single potential (SP) ac, have been investigated and both conductive and dielectric target surfaces were considered. Experimental results show that the flight paths of charged droplets may deviate from their regular straight route, i.e., directly from the nozzle to the substrate. Depending on the droplet charge and applied electric field, droplets may deflect, reflect, or retreat to the meniscus. We can solve these drawbacks by SP EHD printing.

Ag dot morphologies printed using electrohydrodynamic (EHD) jet printing based on a drop-on-demand (DOD) operation

Electrohydrodynamic (EHD) jet printing technology is an attractive method for micro-scale electronic device fabrication. The primary advantage of EHD jet printing compared with conventional inkjet printing is the capability to print at resolutions below 10 µm and to eject high-viscosity ink. In this study, by using drop-on-demand (DOD) jetting, we printed silver (Ag) dots onto a silicon (Si)-wafer and evaluated the dot uniformity. Furthermore, we investigated the effects of substrate surface energy and substrate temperature on the dot morphology. We also investigated the effects of overprinting on the dot morphologies. Our results show that we successfully created uniform dot patterns under 10 µm by using EHD jet printing. In addition the dot diameter approached 14 µm while the substrate was heated up to 40 °C. We also found that on the hydrophobic Si-wafer, increasing the substrate temperature and the number of overprinting could be used as an alternative method for increasing the aspect ratio of dot and suppressing the coffee-stain effect.

Directly Drawn Poly(3-hexylthiophene) Field-Effect Transistors by Electrohydrodynamic Jet Printing: Improving Performance with Surface Modification

In this study, direct micropatterning lines of poly(3-hexylthiophene) (P3HT) without any polymer binder were prepared by electrohydrodynamic jet printing to form organic field-effect transistors (OFETs). We controlled the dielectric surface by introducing self-assembled monolayers and polymer thin films to investigate the effect of surface modifications on the characteristics of printed P3HT lines and electrical performances of the OFETs. The morphology of the printed P3HT lines depended on the surface energy and type of substrate. The resulting OFETs exhibited high performance on octadecyltrichlorosilane-modified substrates, which was comparable to that of other printed P3HT OFETs. In order to realize the commercialization of the OFETs, we also fabricated a large-area transistor array, including 100 OFETs and low-operating-voltage flexible OFETs.

Retreat behavior of a charged droplet for electrohydrodynamic inkjet printing

The charged droplet retreat phenomenon in electrohydrodynamic inkjet printing is experimentally observed and theoretically explained. If the charge concentration of a droplet generated from a nozzle is high enough, Coulomb fission is generated a second time and the main droplet retreats to the meniscus on the nozzle. The retreat phenomenon is due to interactions between the charged droplet, the meniscus, and charges on the substrate. The Rayleigh limit is used to give a theoretical estimate of the amount of charge on the droplet and the meniscus during the retreat.

Fabrication of terahertz metamaterial with high refractive index using high-resolution electrohydrodynamic jet printing

Metamaterial is an engineered material whose electromagnetic properties can be determined by the unit structure. Lithography is one of main methods to fabricate metamaterials for fine patterning which has limitations in large-area fabrication. We present a direct fabrication method for metamaterial using the electrohydrodynamic jet printing. An electrical pulse was controlled to make drop-on-demand operation, through which flexible high refractive-index metamaterial could be fabricated in the form of I-shaped silver electrodes with 10-μm widths and 5-μm gaps on polyimide substrate. The peak value of the refractive index was 18.4 at a frequency of around 0.48 THz.

Semianalytical study of hemispherical meniscus oscillation with an anchored edge on a conductive flat plate under an ac electric field

This paper presents an experimental observation and a semianalytical simulation of the oscillations of an anchored hemispherical liquid meniscus on a conductive flat plate under an ac electric field. For the simulation, the liquid is assumed to be an incompressible, inviscid, and perfectly conductive fluid in a zero-gravity environment. The mutual interaction between the electric field and the hydrodynamics is iteratively solved. As a result, the simulation can follow the oscillating meniscus shapes and contours of the electric field outside the meniscus according to the applied frequency. The velocity profile of the liquid inside the meniscus is also presented. The present theory can be used to predict the oscillation shape of a liquid droplet on a plate with a certain applied frequency. The simulated oscillation shape is in agreement with the experimental result. The effects of the liquid density, the liquid surface tension, and the radius of the hemispherical meniscus on the oscillation are investigate...