• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.969-974
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• 2022

In order to maximize dynamic range and to minimize image lag in digital X-ray imaging, diminishing residual parasitic capacitance in photodiode in pixels is critically necessary. These requirements are more specifically requested in dynamic X-ray imaging with high frame rate and low image lag for industrial 2D/3D automated X-ray inspection and medical CT imaging. This study proposes duoPIX^TM X-ray imaging sensor for the first time that is composed of reset thin film transistor, readout thin film transistor and photodiode in a pixel. To verify duoPIX^TM X-ray imaging sensor, designing duoPIX^TM pixel and imaging sensor was executed first then X-ray imaging sensor with 105 ㎛ pixel pitch, 347 mm × 430 mm imaging area and 3300 × 4096 pixels (13.5M pixels) was fabricated and evaluated by using module tester and image viewer specifically for duoPIX^TM imaging sensor.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.8
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• pp.47-54
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• 2012

In this paper, we have fabricated the Schottky diode for THz applications by heterogeneous resist patterning method. The Schottky diode was developed using electron beam lithography and photolithography to connect the anode and the anode pad for a simple process. The measured performance of developed Schottky diode are $11.2{\Omega}$ of series resistance, 25.96 fF of junction capacitance, 1.25 of ideality factor and 547.6 GHz of cut-off frequency.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.244-245
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• 2010

최근 광전자 분야에서는 미래 에너지 자원에 대한 관심과 함께 GaN 기반 발광다이오드 및 태양전지 연구가 활발히 진행되고 있다. GaN는 높은 전자 이동도와 높은 포화 속도 등의 광전자 소자에 유리한 특성을 가지고 있으나, 고 인듐 함유량과 막질의 우수한 특성을 동시에 구현하는 것은 매우 어렵다. 이를 극복하기 위한 방법으로써 선택 영역 박막 성장법(Selective Area Growth)은 마스크 패터닝을 통해 제한된 영역에서만 박막을 성장하는 방법으로써 GaN의 막질을 향상 시킬 수 있는 방법으로 주목받고 있다. 본 논문에서는 대면적 기판에서 GaN의 막질 향상뿐만 아니라 고인듐 InGaN 박막 성장을 위하여 서브마이크로미터 주기와 크기를 갖는 홀 패턴을 포토리소그라피 공정 최적화를 통해 구현할 수 있는 방법에 대해 논의한다. 그림. 1은 사파이어 기판 위에 선택 영역 박막 성장법을 이용하여 성장한 n-GaN/활성층/p-GaN의 구조를 나타낸 그림이다. 이를 통하여 서브마이크로미터 스케일의 반극성 InGaN면 위에 높은 인듐 함유량을 가지면서도 우수한 특성을 갖는 박막을 얻을 수 있다. 본 실험을 위하여 사파이어 기판 위에 SiO2를 증착한 후 포토레지스트(AZ5206)을 도포하고 포토리소그라피 공정을 진행하여 2um 크기 및 간격을 갖는 패턴을 형성했다. 그림. 2는 AZ5206에 UV를 조사(5초)하고 현상(23초)한 패턴을 윗면(그림. 2(a))과 $45^{\circ}$ 기울인 면(그림. 2(b)) 에서 본 SEM(Scanning Electron Microscope) 사진이다. 이를 통해 약 2.2um의 홀 패턴이 선명하게 형성 됨을 볼 수 있다. 그 후 수백나노 직경의 홀을 만들기 위해서 리플로우 공정을 수행한다. 그림. 3은 리플로우 온도에 따른 패턴의 홀 모양을 AFM(Atomic Force Microscope)을 이용하여 측정한 표면의 사진이다. 이를 통해 2차원 평면에서 리플로우 온도 및 시간에 따른 변화를 볼 수 있다. 그림.3의 (a)는 리플로우 공정을 진행하기 전 패턴이고, (b)는 $150^{\circ}C$에서 2분, (c)는 $160^{\circ}C$에서 2분 (d)는 $170^{\circ}C$에서 2분 동안 리플로우 공정을 진행한 패턴이다. $150^{\circ}C$와 $160^{\circ}C$에서는 직경에 큰 변화가 없었고, $160^{\circ}C$에서는 시료별 현상 시간 오차에 따라 홀의 크기가 커지는 경향이 나타났다. 그러나 $170^{\circ}C$에서 2분간 리플로우 한 시료 (그림. 3(d))의 경우는 홀의 직경이 ~970nm 정도로 줄어든 것을 볼 수 있다. 홀의 크기를 보다 명확히 표현하기 위해 그림.3에 대응시켜 단면을 스캔한 그래프가 그림.4에 나타나 있다. 그림.4의 (a) 및 (b)의 경우 포토레지스트의 높이 및 간격이 일정하므로, 리플로우에 의한 영향은 거의 없었다. 그림. 4(c)의 경우 포토레지스트의 높이가 그림.4(a)에 비해 ~25nm 정도 낮은 것으로 볼 때, 과도 현상 및 약간의 리플로우가 나타났을 가능성이 크다. 그림. 4(d)에서는 ~970nm의 홀 크기가 나타나서 본 연구에서 목표로 하는 나노 홀 크기에 가장 가까워짐을 확인할 수 있었다. 따라서, $170^{\circ}C$ 이상의 온도와 2분 이상의 리플로우 시간 조건에서 선택 영역 성장을 위한 나노 홀 마스크의 크기를 제어할 수 있음을 확인하였다.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.10 no.3
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• pp.237-242
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• 2016

The major advantage of slip-ring technology in Spiral CT is that it facilitates continuous rotation of the x-ray tube, so that volume data can be acquired from a patient quickly. Not only for such a fast scan, but also for the dose reduction purpose, high signal-to-noise ratio and fast data acquisition system is required. In this study, we have built a multi-channel photodetector and multi-channel data acquisition system for CT application. The detector module consisted of CdWO4 crystal and Si photodiode in 16 channels. For the performance test of the preamplifier stage, both the transimpedance and switched integrator types are optimized for the photodetector modules. Switched integrator showed better noise performance in the limited bandwidth which is suitable for the current CT application. The control sequence for data acquisition and 20 bit ADC is designed with VHDL(Very High Speed Integrated Circuit Hardware Description Language) and implemented on FPGA(Field Programmable Gate Array) chip. Our Si photodiode detector module coupled to CdWO4 crystal showed comparable signal with other commercially available photodiode for CT. Switched integrator type showed higher SNR but narrower bandwidth compared to transimpedance preamplifier. Digital hardware is designed by FPGA, so that the control signal could be redesigned without hardware alteration.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.115-122
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• 2012

In this paper, we demonstrate that indoor wireless optical communication is possible with lighting LEDs without a photo diode or a solar cell. A LED is used for both light emitting and light signal detection. This scheme is very useful because transmission is possible without any additional communication systems. In experiments, wireless optical communication will be carried out at a higher signal frequency of 5MHz using a lighting LEDs with both light emitting and light detection characteristics in the future.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.7
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• pp.17-22
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• 2008

This paper presents a low-power and small-area pulse width modulator by light intensity for photoflash. Light intensity controller is achieved by using capacitor, photodiode, and comparator. The proposed circuit designs digital circuit to reduce static power consumption except comparator. And IGBT driver has short circuit protection using delay cell. The pulse width modulator has the operating range of $V_{MS}$ from 0.5V to 2.5V and pulse width of output from 0.14ms to 1.65ms at 300Hz. The pulse width modulator fabricated in $0.35-{\mu}m$ CMOS technology occupies $0.85mm{\times}0.56mm$. This circuit consumes 3.0mW at 300Hz and 3.0V.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.2
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• pp.309-314
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• 2012

In this paper, we present surface-to-underwater visible light communication systems using white LEDs. Pulse position modulation (PPM)-based analogue data communications and on-off keying-based digital data communications systems are developed. Inexpensive and commercial power-LEDs and photo-diodes are used to construct two types of systems. We report the experimental results obtained from the prototype systems to show the possibility of an optical underwater visible light transceiver as a basis for short range underwater wireless network. Their performance deteriorates more than the atmosphere's one because of attenuation and scattering of the light in water, but these results are promising for the potential to create more robust network interface that improve medium performance such as a LED modulation and a photo-detector demodulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.66-71
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• 2004

Airborne contaminant particles are intruded into optical disk drive(ODD) due to the flow caused by disk rotation and can be adhered to objective lens, which causes read/write errors. Such a phenomenon can be a serious problem for high-density storage devices. The purpose of this paper is to understand the effect of particle contamination of objective lens in a CD-ROM drive on laser diode power and photo diode RF signal. The measurements of laser power and readout RF signal were carried out by using a laser power meter and a time interval analyzer, respectively. The parameters for estimating a readout-signal' distortion were its jitter and amplitude. Alumina(Al$_2$O$_3$) particles were used as test dust particles. The results show that the failure for data access happened as the degree of lens contamination was greater than 20％.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.623-631
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• 2011

Light emitting diodes (LEDs) which can produce uniform luminescence need a very difficult and complex procedure because LEDs have strong and straight optical property. One of the major parameters for LED production is the determination of the viewing angle. However, in the present, there is still no available production technology to measure LED viewing angle and optical property. In this study, we developed a five-side LED viewing angle and optical property measurement system, having a source meter that uses a high speed switching photo relay instead of a mercury relay. This new measurement system can measure the viewing angle at a very high accuracy of ${\pm}0.66^{\circ}$. This new technology presents a great potential for fast and reliable LED mass production, which can significantly cut down the cost from savings in production time.

• Journal of IKEEE
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• v.22 no.3
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• pp.742-746
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• 2018

In this paper, we implemented a VLC(Visible Light Communication) system capable of transmitting/receiving data on a 30MHz clock based on On/Off keying modulation/demodulation. The data rate of the implemented system can be verified by functional verification of VLC channel composed of LED/photodiode driver and VLC transmitting/receiving signal of Tx/Rx platform. But, In the experimental results with the VLC transmitting/receiving for combined module, the maximum transmission rate was measured at 15 MHz. Therefore, we describe the problems that can occur when implement the VLC system using the LED module with output power of 15W or more and propose ways to improve it.