Vu Dat Nguyen

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.

Mechanism of electrohydrodynamic printing based on ac voltage without a nozzle electrode

The electrohydrodynamic (EHD) spraying technique has been applied to inkjet printing technology for fabrication of printed electronics. The conventional EHD inkjet device is based on dc voltage and requires two electrodes: a nozzle electrode and an extractor electrode. This study notes several drawbacks of the dc-based EHD printing device such as electrical breakdown and demonstrates stable jetting by using the extractor electrode alone without the nozzle electrode and ac voltage. The continuous ejection of droplets can be obtained only by ac voltage, showing consistent ejection at every peak of electrical signal. The suggested EHD inkjet device prevents electrical breakdown.

Non-contact printing of high aspect ratio Ag electrodes for polycrystalline silicone solar cell with electrohydrodynamic jet printing

This paper presents a non-contact printing mechanism for high aspect ratio silver (Ag) electrodes fabricated by an electrohydrodynamic (EHD) jet printing technique. Using high viscosity Ag paste ink, we were able to fabricate narrow and high aspect ratio electrodes. We investigated the effect of the surface energy of the substrate and improved the aspect ratio of printed lines through multiple printing. We fabricated the polycrystalline silicone solar cell with the Ag electrode and achieved cell efficiency of around 13.7%. The EHD jet printing mechanism may be an alternative method for non-contact fabrication of solar cells electrodes.

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.

Metal-mesh based transparent electrode on a 3-D curved surface by electrohydrodynamic jet printing

Invisible Ag mesh transparent electrodes (TEs), with a width of 7 μm, were prepared on a curved glass surface by electrohydrodynamic (EHD) jet printing. With a 100 μm pitch, the EHD jet printed the Ag mesh on the convex glass which had a sheet resistance of 1.49 Ω/. The printing speed was 30 cm s−1 using Ag ink, which had a 10 000 cPs viscosity and a 70 wt% Ag nanoparticle concentration. We further showed the performance of a 3-D transparent heater using the Ag mesh transparent electrode. The EHD jet printed an invisible Ag grid transparent electrode with good electrical and optical properties with promising applications on printed optoelectronic devices.

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.

A Hybrid Inkjet Printer Utilizing Electrohydrodynamic Jetting and Piezoelectric Actuation

This paper reports a hybrid electrohydrodynamic (EHD) inkjet printing technique that offers better uniformity and stable operation in drop-on-demand (DOD) patterns compared to the conventional methods. This hybrid technique takes advantage of both electrohydrodynamic and piezoelectric methods where a piezoelectric actuator is used to supply a fixed volume of ink to the nozzles exit for every jetting period, and the electrohydrodynamic technique is used to form ink droplets. Experimental results show that the print quality improves significantly when ink was supplied to the nozzle exit at a controlled rate using piezoelectric actuation.

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.