Journal of Electrical Engineering & Technology, May 2, 2011
The current paper describes a simpler ground-type, single-plate electrowetting configuration for ... more The current paper describes a simpler ground-type, single-plate electrowetting configuration for droplet transport in digital microfluidics without performance degradation. The simplified fabrication process is achieved with two photolithography steps. The first step simultaneously patterns both a control electrode array and a reference electrode on a substrate. The second step patterns a dielectric layer at the top to expose the reference electrode for grounding the liquid droplet. In the experiment, a 5 µm thick photo-imageable polyimide, with a 3.3 dielectric constant, is used as the dielectric layer. A 10 nm Teflon-AF is coated to obtain a hydrophobic surface with a high water advancing angle of 116° and a small contact angle hysteresis of 5°. The droplet movement of 1 mM methylene blue on this simplified device is successfully demonstrated at control voltages above the required 45 V to overcome the contact angle hysteresis.
Development of an inspection system using an UV wavelength for defects on the thin electrode in a multilayer pattern
Journal of the Korean Physical Society, Sep 1, 2014
Generally, the Organic Light-Emitting Diode (OLED), Light-Emitting Diode (LCD), Touch Screen Pane... more Generally, the Organic Light-Emitting Diode (OLED), Light-Emitting Diode (LCD), Touch Screen Panel (TSP) glass and Thin Film Transistor (TFT) pattern consists of multiple layers of electrodes separated by thin insulating films. In multilayered devices, when using visible light to inspect the electrode pattern and the defect, the critical shapes of a specific layer are difficult to define. To increase the image contrast between the materials and the layers, this study uses a UV wavelength, which has larger selective differences in reflectance than a visible wavelength. The newly-developed optical system and image analysis units are made to focus on a specific UV range to precisely define a top electrode layer. Two types of magnification systems are developed. Direct side illumination is available in a magnification 1.2 (1.2x) system with a large back focal length (BFL). However, in a magnification 3 (3x) system, on-axis line beam illumination is needed. A multi-point LED source (custom-made) and an anamorphic optical system is used to increase the light efficiency and decrease the noise. Electric units and an algorithm for high-speed image processing and data transfer are also developed. The final images have good selective contrast between the layers despite the high-depth condition decided by the required NA for the target resolution. This system can be used for the inspection of general display panels, Printed Circuit Board (PCB) patterns, and mobile glasses that are composed of multilayered films.
Self-arrangement of solder balls by using the surface wettability difference
Materials Letters, Jun 1, 2010
ABSTRACT This letter describes a simple and efficient method of the solder ball placement for ele... more ABSTRACT This letter describes a simple and efficient method of the solder ball placement for electronic packaging. For self-arranging solder balls by using the surface wettability difference, the substrate surface was patterned into the hydrophilic Au solder ball land array with the hydrophobic Teflon passivation layer. Water droplets were formed only on the solder ball lands after dipping the patterned substrate into water. Then, the solder balls were placed on each of the wetted solder ball lands. After soldering two plates with 3 × 3, 4 × 4, and 5 × 5 arrayed solder balls, their average shear strengths were as high as 195, 220, and 251 MPa, respectively.
Synchronized Reverberatory Bursting Activity in Cultured Network of Rat Cortical Neurons
Journal- Korean Physical Society
We have investigated spatially distributed dynamics that arises in cultured networks of cortical ... more We have investigated spatially distributed dynamics that arises in cultured networks of cortical neurons of rats over two weeks by using a home-built multi-electrode array (MEA) plate recording system. The spiking dynamics detected through the MEA electrodes is typically a mixed signal of random single firing events and reverberating bursting events. The bursting activities seem to arise only when some degree of networking is established. Our analysis also indicates that the bursting activity spreads out in space gradually over days and becomes globally synchronized by the time the culture reaches approximately 10 days in vitro.
Bulletin of the American Physical Society, Mar 6, 2007
A new interdigit-type micro oil condition sensor was designed and fabricated for monitoring the d... more A new interdigit-type micro oil condition sensor was designed and fabricated for monitoring the deterioration of lubricating and insulating oils. The designed sensor operates based on the change of the dielectric constant and electrical conductivity. In order to improve sensor performance, an oil condition sensor was fabricated using MEMS technology and multi-wall carbon nanotube film. The experiment was performed with automobile engine oils with the same brand and quality so as to ensure measurement reliability. Capacitance changes were measured according to increasing mileage and the sensors' performance was improved. These results show that the proposed sensor could measure the degree of oil deterioration with a high sensitivity and it is applicable to other lubricating systems as well as insulating systems.
Fabrication of p-type poly-Si thin-film transistors using sequential lateral solidification and analysis of the device characteristics for various channel lengths
Journal of the Korean Physical Society, Dec 1, 2002
We present a micromachined NH3 chemiresistor sensor based on O2 plasma functionalized multiwall c... more We present a micromachined NH3 chemiresistor sensor based on O2 plasma functionalized multiwall carbon nanotube (MWCNT)/ conducting polymer (CP) composites, and discuss its gas sensing mechanism. The FTIR spectra of plasma-treated MWCNTs indicate that oxygenated groups are created on the surface of CNTs after the plasma treatment. The plasma-functionalized MWCNT/PANI sensor exhibits a linear response of 3.34% per ppm NH3 for concentrations ranging from 10 to 100 ppm, and a sensitivity of about 7 times higher than that from a corresponding pristine MWCNT sensor. This dramatic change in resistance is attributed to the fact that the binding of the functional group with the defective CNT is stronger than that with the perfect one.
With the development of smart devices supporting VR (Virtual Reality) and AR (Augmented Reality),... more With the development of smart devices supporting VR (Virtual Reality) and AR (Augmented Reality), users' input devices are changing to wearable devices. The existing input devices for gesture recognition were relatively rigid. In this research, we propose a gesture recognition device by using a flexible substrate to manufacture a device that can be used in close contact with a user's wrist. An array of flexible resistive strain gauge sensors was fabricated for sensing spatial muscle movements of the wrist. The fabricated strain sensors showed a linearly varying output characteristic, and a sensitivity of 0.05143 Ω/g was obtained for a load test from 0 to 500 g. A circuit board for processing sensor data was fabricated and a program was coded for collecting the sensor data from the circuit board. With this system, it was confirmed that the average recognition rate per gesture is 94.6% after applying these input devices directly to five basic wrists gestures on five test subjects.
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Papers by James Pak