Kye-Si Kwon

Waveform Design Methods for Piezo Inkjet Dispensers Based on Measured Meniscus Motion

Waveform design methods for piezo inkjet dispensers based on measured meniscus motion are presented. The meniscus motion is measured from charge-coupled-device camera images wherein strobe lights from light-emitting diodes are synchronized with the jetting signal. Waveforms for the piezo dispenser are designed such that the number of experiments can be significantly reduced compared to conventional methods. Furthermore, the designed waveform can also be evaluated by the measured meniscus motion since the motion is directly related to jetting behavior.

A fully roll-to-roll gravure-printed carbon nanotube-based active matrix for multi-touch sensors.

Roll-to-roll (R2R) printing has been pursued as a commercially viable high-throughput technology to manufacture flexible, disposable, and inexpensive printed electronic devices. However, in recent years, pessimism has prevailed because of the barriers faced when attempting to fabricate and integrate thin film transistors (TFTs) using an R2R printing method. In this paper, we report 20 × 20 active matrices (AMs) based on single-walled carbon nanotubes (SWCNTs) with a resolution of 9.3 points per inch (ppi) resolution, obtained using a fully R2R gravure printing process. By using SWCNTs as the semiconducting layer and poly(ethylene terephthalate) (PET) as the substrate, we have obtained a device yield above 98%, and extracted the key scalability factors required for a feasible R2R gravure manufacturing process. Multi-touch sensor arrays were achieved by laminating a pressure sensitive rubber onto the SWCNT-TFT AM. This R2R gravure printing system overcomes the barriers associated with the registration accuracy of printing each layer and the variation of the threshold voltage (Vth). By overcoming these barriers, the R2R gravure printing method can be viable as an advanced manufacturing technology, thus enabling the high-throughput production of flexible, disposable, and human-interactive cutting-edge electronic devices based on SWCNT-TFT AMs.

Experimental analysis of waveform effects on satellite and ligament behavior via in situ measurement of the drop-on-demand drop formation curve and the instantaneous jetting speed curve

In situ techniques to measure the drop-on-demand (DOD) drop formation curve and the instantaneous jetting speed curve are developed such that ligament behavior and satellite behavior of inkjet droplets can be analyzed effectively. It is known that the droplet jetting behavior differs by ink properties and the driving waveform voltage. In this study, to reduce possible droplet placement errors due to satellite drops or long ligaments during printing, waveform effects on drop formation are investigated based on the measured DOD drop formation curve and the instantaneous jetting speed curve. Experimental results show that a dwell time greater than the so-called efficient dwell time was effective in reducing placement errors due to satellite drops during the printing process.

Investigation of pulse voltage shape effects on electrohydrodynamic jets using a vision measurement technique

In this paper, we present a vision measurement technique to evaluate electrohydrodynamic (EHD) inkjet behavior, and discuss the effects of the pulse voltage shape on the EHD jets for drop-on-demand printing, including the falling and rising time in the pulse voltage. Sequential images acquired by a charge-coupled device (CCD) camera with a strobe light-emitting diode (LED) were used to visualize EHD jet behavior with respect to time. A vision algorithm was implemented in an EHD jet system to enable in situ measurement and analysis of EHD jets. A guideline for selecting pulse shape parameters is also presented, to enable the achievement of high-frequency reliable jets for drop-on-demand printing. Printing results are presented to demonstrate the drop consistency of jets.

Rheological properties of Ag suspended fluid for inkjet printing

Rheological characterization of inks for the inkjet printing application has been considered to be essential with dissemination of applying the inkjet printing technology into many related industries. In this study, the high concentrated Ag suspension was prepared using poly(acrylic acid) as both a polyelectrolyte and a polymeric dispersant, and rheological properties of the suspension such as shear stress, shear viscosity, and dynamic moduli were examined using a rotational rheometer. The difference of rheological properties was investigated with different concentrations of the polyelectrolyte. The shear thinning effects and yield behavior of suspension were analyzed using rheological constitutive equations of state.

An inkjet vision measurement technique for high-frequency jetting.

Inkjet technology has been used as manufacturing a tool for printed electronics. To increase the productivity, the jetting frequency needs to be increased. When using high-frequency jetting, the printed pattern quality could be non-uniform since the jetting performance characteristics including the jetting speed and droplet volume could vary significantly with increases in jet frequency. Therefore, high-frequency jetting behavior must be evaluated properly for improvement. However, it is difficult to measure high-frequency jetting behavior using previous vision analysis methods, because subsequent droplets are close or even merged. In this paper, we present vision measurement techniques to evaluate the drop formation of high-frequency jetting. The proposed method is based on tracking target droplets such that subsequent droplets can be excluded in the image analysis by focusing on the target droplet. Finally, a frequency sweeping method for jetting speed and droplet volume is presented to understand the overall jetting frequency effects on jetting performance.

Measurement of inkjet first-drop behavior using a high-speed camera

Drop-on-demand inkjet printing has been used as a manufacturing tool for printed electronics, and it has several advantages since a droplet of an exact amount can be deposited on an exact location. Such technology requires positioning the inkjet head on the printing location without jetting, so a jetting pause (non-jetting) idle time is required. Nevertheless, the behavior of the first few drops after the non-jetting pause time is well known to be possibly different from that which occurs in the steady state. The abnormal behavior of the first few drops may result in serious problems regarding printing quality. Therefore, a proper evaluation of a first-droplet failure has become important for the inkjet industry. To this end, in this study, we propose the use of a high-speed camera to evaluate first-drop dissimilarity. For this purpose, the image acquisition frame rate was determined to be an integer multiple of the jetting frequency, and in this manner, we can directly compare the droplet locations of each drop in order to characterize the first-drop behavior. Finally, we evaluate the effect of a sub-driving voltage during the non-jetting pause time to effectively suppress the first-drop dissimilarity.

Electrohydrodynamic Inkjet Printing System for Ultrafine Patterning

The application of inkjet technology has been broadening from home printers to manufacturing tools. Recently, there have been demands for high-resolution printing, especially in the field of printed electronics applications. To improve upon the conventional inkjet printing patterning method, electrohydrodynamic (EHD) inkjet technology has recently attracted attention because droplets smaller than the nozzle diameter can be ejected and materials with wider viscosity range can be used for jetting. In this study, an EHD jet printing system for fine patterning is presented. To print various patterns based on drop on demand printing, vector and raster printing algorithm are implanted in the printing software. Fine conductive patterns with line width of less than can be easily achieved via EHD jet using a nozzle with inner diameter of .

Development of Inkjet Printing System for Printed Electronics

An inkjet printing system for printed electronics was developed. In this study, a printing algorithm was mainly discussed. In order to print a pattern image at a target location, we developed a hardware and software algorithm for determining the distances between a substrate camera and the selected nozzles. We implemented a vector-printing algorithm where AutoCAD dxf file was used for XY motion control and for printing. We also developed printing method using bitmap images. The technical issues in using CAD drawings and bitmap images were discussed.

Application of Taguchi Method to Identify Damage in Cantilever Beam

A robust damage identification technique is presented such that the location and severity of damages can be identified in presence of random errors in measured data as well as systematic errors in analytical model. In order to identify damage efficiently, the concept of design of experiment using orthogonal array is used for screening main effects of each parameter which corresponds to possible damage location in FE model. Then, Taguchi method, which has been widely used for robust design in industry, is applied to the optimization of the objective function, which is defined by the difference between measured and analytical modal data, by updating the parameters in analytical FE model in an iterative way. The numerical simulation of cantilever beam shows that various types of damages can be identified effectively with reasonable accuracy.Copyright