Youngjune Cho

Low temperature synthesis of PbTiO3 thin films by MOCVD without carrier gas

Abstract A new MOCVD (metal–organic chemical vapor deposition) technique employing the precursor delivery without carrier gas was developed in the deposition of PbTiO 3 thin films, which enables low temperature (450°C) synthesis and high grow rates (∼6.0 μ m/h). Substrates used were bare Si, TiO 2 buffered Si, and platinized Si. Tetraethyl lead, titanium tetra-isopropoxide, and oxygen were used as precursors. Perovskite PbTiO 3 thin films were successfully grown on all kinds of substrates investigated at the substrate temperature of 450°C. However, the C–V characteristics of perovskite thin films prepared at low temperature did not always show normal ferroelectric behavior. Without carrier gas, impinging of non-adsorbing species with substrates would be suppressed as much as possible. The difference in growth behaviors with or without carrier gas was compared with each other.

Mixing and Simplex Search for Optimal Illumination in Machine Vision

Mixed-color illumination affects the quality of images in industrial vision system and it is important to optimize color and intensity for image acquisition. This study used simplex search to find the optimal illumination in a short amount of time. A typical color mixer synthesized various color of lights by changing the inputs of RGB power LEDs and passing the lights through an optical system. The image quality under mixed-color illumination was calculated according to the sharpness. For the purpose of optimal illumination using simplex search, a probe network was organized with N + 1probing points for N inputs. The shape of the probe network, simplex, was varied through procedures of extension, contraction, and shrinkage. The inputs of the color mixer were changed until the size of the simplex became smaller than a threshold. The simplex search was tested for commercial semiconductor patterns, and was useful for finding the optimal illumination.

A review of light intensity control and quick optimum search in machine vision

Optimum searching methods were applied to find optimal illumination of a single color to enhance the quality of a monochrome image and reduce searching time. The problem was defined as 1D searching optimization between light intensity and image sharpness. The image sharpness is the degree of distinctness and is a non-linear function of the input voltage, which can be used to adjust the light intensity. We considered conventional optimum search methods, such as steepest descent, conjugate gradient, Newtons method, bisection, and golden section. These derivative methods and direct searches were tested for a sample pattern using single color lights under coaxial illumination. The iteration for the optimal condition was 6.7% of full scanning in average. The test results show that the steepest descent and golden search are recommended. We checked the possibility of applying these search methods to automatic lighting in machine vision.

Region-based Q-learning using convex clustering approach

For continuous state space applications, a novel method of Q-learning is proposed, where the method incorporates a region-based reward assignment being used to solve a structural credit assignment problem and a convex clustering approach to find a region with the same reward attribution property. Our learning method can estimate a current Q-value of an arbitrarily given state by using effect functions, and has the ability to learn its actions similar to that of Q-learning. Thus, our method enables robots to move smoothly in a real environment. To show the validity of our method, the proposed Q-learning method is compared with conventional Q-learning method through a simple two dimensional free space navigation problem, and visual tracking simulation results involving a 2-DOF SCARA robot are also presented.

Automatic focus control for assembly alignment in a lens module process

This study proposes an auto focusing method for multi-focus images in assembling lens modules in digital camera phones. A camera module in a camera phone is composed of a CCD sensor, an IR glass, a lens and a PCB board. The alignment of the components is one of the most important factors in determining the product quality. Auto-focus is essential to adjust the image quality of the IR glass, but there are two focal points in the captured image, due to the thickness of the IR glass. Therefore, the sharpness, probability and scale factor are used to find the desired focus from a multi-focus image. The sharpness is defined as the clarity of the image. The variation of the probability and scale factors are analyzed to find the focus after pattern recognition with a registered image. The presented algorithm was applied to a lens assembly machine which has 5 axes, two vacuum chucks and an inspection system. The desired focus can be determined on the local maximum of the sharpness, the probability and the scale factor in the experiment.

Optical distance control for a multi focus image in camera phone module assembly

Camera phones are very popular these days and mass production is essential for manufacturing the camera modules used in the phones. This study aims at developing a focusing method for use in the camera module assembly process. The camera module is composed of small components and machine vision is necessary to align them before their assembly. The inspected images usually have multiple areas with different focal distances, due to the different thicknesses of the components. Sharpness is the evaluation of focus, calculated by determining its absolute derivative and used for determining the focal point. A dynamic focus region(DFR) is defined to find the object of interest to be focused on. The DFR is built from the edge fragments detected using several narrow ROIs across the vision screen. An assembly machine was constructed to attach lens mounts to a PCB for the experiment. The distance between the lens mount and vision camera was adjusted to find the focus position by means of the sharpness and DFR. The result shows that the desired object is brought into focus and the proposed method can be applied to the camera module assembly process.

The new insertion method of liquid powders using the electrode array for e-paper applications

In this paper, the new particle insertion method was proposed and experimentally demonstrated. In the proposed method, the electrode array was adopted to insert the liquid powders into each cell of the liquid powder display panel. The each electrode pattern size was 140 times 140 mum and the size of the electrode pattern array was fabricated on the glass wafer. The each square cell size of the base panel was 220 times 220 mum and the width of the rib on the panel was 20 mum. The voltage range applied to the electrode array was about from 0 to 600 V DC. To monitor the operation characteristics of the liquid powder under the various applied voltage conditions, the computer vision system was also used. The experimental results showed the strong capability of the noble method to manipulate the charged tiny particles for the mass production applications of the e-paper.

Experimental Study on Fabrication of AZO Transparent Electrode for Organic Solar Cell Using Selective Low-Temperature Atomic Layer Deposition

AZO (aluminum-doped zinc oxide) is one of the best candidate materials to replace ITO (indium tin oxide) for TCOs (transparent conductive oxides) used in flat panel displays, organic light-emitting diodes (OLEDs), and organic solar cells (OSCs). In the present study, to apply an AZO thin film to the transparent electrode of an organic solar cell, a low-temperature selective atomic layer deposition (ALD) process was adopted to deposit an AZO thin film on a flexible poly-ethylene-naphthalate (PEN) substrate. The reactive gases for the ALD process were di-ethyl-zinc (DEZ) and tri-methyl-aluminum (TMA) as precursors and H2O as an oxidant. The structural, electrical, and optical characteristics of the AZO thin film were evaluated. From the measured results of the electrical and optical characteristics of the AZO thin films deposited on the PEN substrates by ALD, it was shown that the AZO thin film appeared to be comparable to a commercially used ITO thin film, which confirmed the feasibility of AZO as a TCO for flexible organic solar cells in the near future.

The effects of SCM and PWM on the chromaticity and the spectrum of PC white LEDs

When phosphor converted white light emitting diodes were operated under stepwise current modulation (SCM) and pulse width modulation (PWM), the change in chromaticity and spectrum were investigated. In the chromaticity diagram, yellow shift was observed with increasing forward current in SCM while blue shift with increasing duty ratio in PWM In SCM, the peak wavelength around blue color band moved to shorter wavelengths and the efficiency of blue-to-yellow conversion also increased as forward current increased. Meanwhile, a peak wavelength in PWM was almost fixed but the light conversion efficiency decreased as duty ratio increased. The average Δuv was 0.004193 in SCM and 0.003210 in PWM.

The Embedded Vision System for Portable Applications

Abstract A simple and cost-effective time switching method is to connect two camera modules into one camera interface port. The suggested embedded vision system is implemented and the image taken as expected. The design requirements for the hardware and the device driver are also considered. The captured image quality proves our suggestion could be a good candidate for two camera interface solutions without using complicated DSPs or FPGAs.