Hyun Woo Dang

Hybrid Surface Acoustic Wave- Electrohydrodynamic Atomization (SAW-EHDA) For the Development of Functional Thin Films

Conventional surface acoustic wave - electrostatic deposition (SAW-ED) technology is struggling to compete with other thin film fabrication technologies because of its limitation in atomizing high density solutions or solutions with strong inter-particle bonding that requires very high frequency (100 MHz) and power. In this study, a hybrid surface acoustic wave - electrohydrodynamic atomization (SAW-EHDA) system has been introduced to overcome this problem by integrating EHDA with SAW to achieve the deposition of different types of conductive inks at lower frequency (19.8 MHZ) and power. Three materials, Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV), Zinc Oxide (ZnO), and Poly(3, 4-ethylenedioxythiophene):Polystyrene Sulfonate (PEDOT:PSS) have been successfully deposited as thin films through the hybrid SAW-EHDA. The films showed good morphological, chemical, electrical, and optical characteristics. To further evaluate the characteristics of deposited films, a humidity sensor was fabricated with active layer of PEDOT:PSS deposited using the SAW-EHDA system. The response of sensor was outstanding and much better when compared to similar sensors fabricated using other manufacturing techniques. The results of the device and the films’ characteristics suggest that the hybrid SAW-EHDA technology has high potential to efficiently produce wide variety of thin films and thus predict its promising future in certain areas of printed electronics.

Electrohydrodynamic Spray Deposition of ZnO Nanoparticles

This paper presents the electrospray deposition of solution-based ZnO nanoparticles. Transparent thin film transistors in active matrix displays have become the most interested research area. Electrospray assures direct deposition by eliminating etching steps required after deposition by other techniques. Uniform layers of minimum thickness 87 nm on glass and 356 nm on polyimide using electrospray experiment is achieved. Contact angle analyzer has been used for finding properties like wetting energy, spreading coefficient and work of adhesion of the ink on glass and polyimide substrates. All experiments were performed in ambient conditions.

Characterization of flexible temperature sensor fabricated through drop-on-demand electrohydrodynamics patterning

The fabrication and characterization of a temperature sensor on flexible poly(ethylene terephthalate) (PET) substrate is discussed. The device was printed by drop-on-demand (DOD) electrohydrodynamic (EHD) Patterning method using silver nanoparticles ink on a roll-to-roll (R2R) system on a mass scale. EHD patterning was performed at atmospheric pressure and room temperature in a single step. The ink viscosity was 300 cps and it contained 55 wt % of silver nanoparticles. The parameters for printing head speed, and DOD were optimized to create connected lines. The printed temperature sensor has the resistivity of 25.35 µΩcm and the temperature coefficient of resistance (TCR) is 0.0007687 °C−1. The micro sensor can be applied to many applications to measure temperature accurately of flat or curved surfaces.

A Study of Micro Stencil Printing based on Solution Atomization Process

In this study, experiments were conducted for micro pattern printing to combine solution atomization process and stencil printing based on electrospray deposition. The stencil mask fabricated by etching the photosensitive glass placed below 0.3 mm distance to substrate has 100 um line width. The process parameters of electrospray deposition system for the atomization of the solution are applied voltage and supply flow rate of the solution. Meniscus angle of cone-jet was optimized by varying the supply flow rate from 0.3 ml/hr to 0.7 ml/hr. Voltage condition was verified having symmetric cone-jet angle and no pulsation at 8.5 kV applied voltage. In addition, a number of micro patterns are printed using a single 1 step process by solution atomization process. Variable line width of approximate 100 um was confirmed by changing conditions of solution atomization regardless of the pattern size of stencil mask.

Resistive behaviour of silver nanoparticle films on ultra-low modulus polydimethylsiloxane with trench type roughness

The resistive behaviour of silver (Ag) nanoparticle based thin films at different loading conditions (axial stretching, bending and repeated bending) has been studied on rough ultra-low modulus polydimethylsiloxane substrates with scratch or trench type roughness. These films have been fabricated using a non-vacuum and scalable thin film deposition technique, rod coating. The fabricated films showed minute changes in their resistance when stretched up to an average of almost 27% axial strain, and when bent on circular surfaces with diameters in the range 10–30 mm. The films were also found to remain conductive even after 1000 bending cycles. These results suggest that the as-fabricated silver nanoparticle films could be potentially useful in areas like stretchable, flexible and epidermal electronics.

Effect of different ground hole size on stable meniscus in electrostatic integrated deposition inkjet head

There have been growing interests in direct patterning of metallic contents on the surface of the substrate without including complex steps of the micro fabrication lithography process. The direct fabrication process using ink-jet printing can be expected to be a powerful tool for both nanotechnology research and applications such as micro electronics. The electrostatic inkjet system has a huge number of applications in terms of cost and time effected manufacturing of printed electronics like RFID, electronic devices and flexible display, solar cell, sensors etc. Inkjet printers operate by propelling various size droplets of conductive ink onto the non conductive substrate. For experimental purpose, an integrated electrostatic inkjet nozzle head was fabricated. For the charging of ink meniscus, an electrode is inserted inside the nozzle head containing conductive ink. The difference between the charge meniscus and ground electrode is depended on the ink properties like surface tension, viscosity and number of metallic pigments. Therefore, for the extraction of droplets, a ring type ground terminal with internal diameter of 1.5mm, 1mm. 0.5mm with a fixed distance of 500um from the meniscus is employed. The paper is focused on the different meniscus shape and extractions in meniscus before dripping is evaluated through experiments. And optimal ground is proposed. This study will help to develop and analysis the integrated electrostatic nozzle head and aspects of the nozzle head.