Browsing by Author "Yang, Kei-Hsiung"

Now showing 1 - 17 of 17

A Novel Composite Bump Design for Chip-on-Glass Package Using Non-Conductive Adhesive Film
(2009-01-01)
Tang, Pao-Yun
;
Sun, Wei-Hao
;
Yang, Kei-Hsiung
;
交大名義發表
;
National Chiao Tung University
A novel composite bump, Smart bump, structure has been successfully developed for chip-on-glass (COG) package using non-conductive adhesive film (NCF). We have successfully verified the low contact resistance and high reliabilities using Smart bump and COG NCF process for the packages of 17"W, 12.1" and 2.4" TFT-LCD modules. We have realized that COG NCF process with Smart bump is simpler and lower cost in consumable materials than the conventional COG ACF process with Au bump. The COG NCF process also allows fine-pitch-driver package for high-resolution TFT-LCDs, and has a higher process yield in pilot production.
A Simple Method to Measure Pretilt Angles of Inverse Twisted Nematic Liquid Crystal Cells
(2014-12-01)
Wang, Sheng-Ya
;
Lin, Chia-Yi
;
Yang, Kei-Hsiung
;
交大名義發表
;
National Chiao Tung University
We have developed a simple optical method based on measurements of phase retardation[1] versus out-of-plane cell rotation angle and data analyzed by extended Jones matrix method to obtain pretilt angles of inverse twisted nematic (ITN) and tilted homeotropic liquid crystal (LC) cells. In our Jones-matrix calculations, we have assumed a constant pretilt angle as the LC-director tilt angles throughout the ITN cell as well as the tilted homeotropic cell. We have compared the measured pretilt angles of the ITN cell with those of an accompanying tilted homeotropic (ATH) cell. The results showed increasing discrepancies between them with increasing rubbing depth for LC alignments. However, these discrepancies could be explained by assuming that the surface-LC tilt angle of the ITN cell was equal to the measured pretilt angle of the ATH cell to generate a convex-type LC-director-deformation profile within the ITN cell based on Oseen-Frank elastic continuum theory with infinite anchoring energies. The average of the LC-director tilt angles over this profile was equivalent to the measured pretilt angle of the ITN cell.
Computations of the Signal-to-Noise Ratio for Medical X-Ray Imagers
(2014-08-01)
Lo, Yu-Chen
;
Huang, Kuan-Chieh
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
If the signal in a medical X-ray imaging detector is formed by integrating the scintillation (or electrical) pulses, rather than by counting them, the signal-to-noise ratio is reduced by a factor which depends on the pulse height distribution. Formulas are expanded from Swank\'s publication to derive the signal-to-noise ratio for any given optical or electrical pulse-size distribution. A new quantity called noise-equivalent absorption is defined which bears a simple relationship to the signal-to-noise ratio of integrated X-ray imaging as the quantum absorption to the signal-to-noise ratio of photon-counting X-ray imaging.
Determination of Ion Concentrations and Mobilities from High- and Low-Ionization-Rate Impurities in TN LCDs
(2011)
Kuo, Chih-Hao
;
Yang, Kei-Hsiung
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
Ion concentration and mobility are two most important parameters to affect the display qualities of LCDs in terms of flickers, image-sticking, and Mura. Prior publications on the measurement of ion concentration and mobility did not distinguish ions either from high- or low-ionization-rate impurities. For the first time, we have developed experimental and analytic methods to determine both mobilities and ion concentrations of high- and low-ionization-rate impurities perpendicular to liquid crystal directors in TN LCDs aligned by rubbed polyimide films. Our methods can also be extended to measure the ion mobilities and concentrations parallel to nematic liquid crystal directors by applying a high voltage on the TN cell or preparing samples with homeotropic LC alignments.
Entanglement-free determination of pretilt angles of twisted nematic liquid-crystal cells by phase measurement
(2017-08-10)
Chiang, Che-Wen
;
Lin, Ping-Chun
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
The pretilt angle of a twisted nematic (TN) liquid crystal display has a strong effect on viewing angles and response times of the display as well as shifting the light-leaking disclination lines into the black-matrix area within pixels of a thin-film-transistor driven TN panel for a high contrast ratio. In this Letter, we develop an optical method to determine the TN pretilt angle based on heterodyne measurements of the phase versus the incident angle of a thin TN cell subjected to out-of-plane rotations. We believe that our method of measuring phases has advantages of simpler setup and calculations, better stability, and less sensitive to ambient electromagnetic interference than the commonly used method of measuring intensities.
Flaw detection and measurement for 4K Ultra HD thin-film-transistor array panel
(2014-05-01)
Wang, Yao-Chin
;
Lin, Bor-Shyh
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
Display pixels of liquid-crystal-display televisions (LCD TVs) on thin-film-transistor (TFT) array are getting smaller. This paper introduced the method of voltage imaging technique, which developed and provides initial insight into the thin-film-transistor array flaw detection and measurement for ultra-high-definition (Ultra HD, UHD) LCD TV application. We proposed the measurement of flaw detection, based on TFT array testing and characterization with respect to opto-electric transformation measurement. (C) 2014 Elsevier Ltd. All rights reserved.
High aperture ratio TFT array structures for IPS mode with low crosstalks
(2004)
Lin, Jiunn-Shyong
;
Chen, Shu-Hsia
;
Yang, Kei-Hsiung
;
光電工程學系
;
Department of Photonics
The replacement of CRT by TFT-LCD in TV application requires the implementation of LC modes with wide viewing angles and excellent video-display quality. IPS mode has been known as an excellent technology to realize wide viewing angles. In this paper, we report the designs of two novel TFT electrode structures that not only increase the aperture ratio but also reduce the crosstalks. We have improved IPS mode in aperture ratio by 1.5 times and effectively reduced the coupling ratio from 4.2% to 2.1%.
Intra-cell ionic properties of twisted nematic liquid crystal cells
(2019-01-01)
Chen, Po-An
;
Yang, Kei-Hsiung
;
光電學院
;
College of Photonics
Under 1-kHz and low-frequency driving, we report our investigation of intra-cell ionic properties of two twisted nematic (TN) liquid crystal (LC) cells made of same LC mixture but different polyimide (PI) materials for LC alignments. A heterodyne interferometry system was used to measure the phase retardations of the TN cells versus applied voltages at 1kHz. We also measured the phase retardations and currents of the TN cells versus time by applying a mid-grayscale voltage of 1.3V at 0.1Hz to the cells. Related to the above-measured data, we have developed equations to characterise the field-driven transports of mobile charge carriers within the PI films independently from that within the LC medium of same TN cell to obtain time-dependent in-cell voltages of mobile charge carries across the LC mixture and across two PI-alignment films, respectively. Our experimental methods can be used to optimise LC mixtures and PI materials for low-refresh-rate thin-film-transistor-driven liquid crystal displays (LCDs) for low power and provide bases for further investigations on mobile-charge-carrier generation and transport within thin in-cell PI-alignment films as well as within the LC mixture of same LC cell. [GRAPHICS] .
Investigation of Curtain Mura in TFT-TN panels after COG ACF process
(2012-10-01)
Wang, Sheng-Ya
;
Liao, Wei-Hsiang
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
We have utilized a transmission ratio (TR) between curtain-shaped (Curtain) Mura and non-Mura zones as a key parameter to characterize the optical appearance of Curtain Mura occurred on a 13.3-in TFT-TN panel (Mura sample) after bonding process to place silicon-based driver-IC chips on one of the panel substrates using anisotropic conductive film as a binder (COG ACF process). Our measured TRs of the Mura sample at zero applied voltage were in good agreement with calculated TRs using optical parameters of the Mura sample derived from the measured Stokes parameters of the liquid crystal (LC) medium in that sample. We conclude that the occurrence of Curtain Mura is dominant by the stress-induced change in the twist angle, less sensitive and insensitive to the corresponding induced changes in the cell gap and pretilt angle of the in-panel-LC medium, respectively. By simulation, we also point out a way to reduce the occurrence of Curtain Mura by designing the cell gap for a 90 degrees-twsit TN panel to satisfy the condition of Gooch-Terry first minimum. (C) 2012 Elsevier B.V. All rights reserved.
Ionic effects on electro-optics and residual direct current voltages of twisted nematic liquid crystal cells
(2018-01-01)
Chen, Po-An
;
Yang, Kei-Hsiung
;
光電學院
;
College of Photonics
By using electro-optical and dielectric absorption [1-4] measurements, we report our investigations of ionic effects on electro-optics and residual direct current voltages (VrDCs) of two polyimide (PI)-aligned twisted nematic (TN) cells with same liquid crystal mixture but different PI-alignment materials. We have also carried out new experimental methods to find out that the observed VrDCs were caused by LC-PI-interfacial trapped ions generated and transported from the LC medium for one TN cell, and from the PI layers for the other TN cell. Our measured VrDCs indicated that the former had two different exponential-decay rates similar to the published results by M. Mizusaki et al. [2] but the latter had only a single exponential-decay rate. [GRAPHICS] .
My Three-Decade Investigation of Ions in EPDs and LCDs
(2011)
Yang, Kei-Hsiung
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
Ion concentration and its ionization activation energy and mobility are important parameters to affect flickers, image-sticking, Mura, panel assembly yield and reliabilities of TFT-LCDs. Prior publications to measure these parameters did not distinguish ions either from high (HIR) or low ionization rate (LIR) impurities. After persistent investigation for past three decades, I conclude that both ions of HIR and LIR impurities existed in EPDs, FLCDs and TN LCDs, and their ion generation and transport equations have been unified and described in our publications. For the first time, we have recently developed methods of measurement and analysis to obtain the ion concentration, mobility and activation energy of LIR impurities in a TN cell. Our recent results showed that most of ions existing in our TN cells came from ions of LIR impurities. Our experimental results on charge-trapping phenomena by uv-irradiated polyimide alignment layers seemed to indicate that the ions of LIR impurities were more likely to get trapped to produce image-sticking of LCDs.
New Experimental Results on Electro-Optical Effects of Ionic Impurities in Twisted Nematic Liquid Crystal Displays
(2011)
Chen, Hsin-Hsu
;
Yang, Kei-Hsiung
;
照明與能源光電研究所
;
影像與生醫光電研究所
;
Institute of Lighting and Energy Photonics
We report new experimental results on electro-optical effects of a twisted nematic (TN) liquid crystal cell caused by ionic impurities within the cell. By using a published ion-generation equation that took both field-assisted and thermal-activated behaviors into consideration, for the first time, we have identified methods of measurement and analysis to obtain the ion concentration and the activation energy of low-ionization-rate impurities within a TN cell.
Optics of light scattering caused by liquid-crystal-director fluctuations
(2019-01-02)
Chiang, Che-Wen
;
Yang, Kei-Hsiung
;
光電學院
;
College of Photonics
We have applied the light-scattering equation caused by liquid-crystal (LC)-director fluctuations as derived by De Gennes [1] to the case where the polarization direction of the incident light is at an arbitrary angle with respect to the LC directors within the cell. Based on the De Gennes's equation, we have used an out-of-plane (OPR) cell-rotation method to measure the pretilt angles of a tilted-homogeneously aligned LC cell. Our measured pretilt angles are in good agreement with that obtained by the published OPR-rotation method [2] based on a different mechanism. Our method is simple in setup and requires no complicated data-fitting calculations when the pretilt angles are below about 30 degrees. In addition, there is no need to know cell parameters except the ordinary and extraordinary refractive indices of the LC medium at the wavelength of incident light. [GRAPHICS] .
Simple and direct measurements of pretilt angles in hybrid-aligned nematic liquid-crystal cells
(2013-07-20)
Wang, Sheng-Ya
;
Wu, Huang-Ming
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
We have developed a general approach to perform direct measurements of the pretilt angles from 0 degrees to 75 degrees in hybrid-aligned nematic (HAN) liquid-crystal cells whose cell gaps can also be accurately determined with the help of known pretilt angles. In this paper, we have used a Zeeman laser system to measure the angular-dependence phase retardation of the HAN cells and MATLAB mathematical software to carry out theoretical calculations and fit the measured data to derive the pretilt angles. In general, pretilt angles adjacent to opposite substrates of a HAN cell are different. Our measured pretilt angles of the HAN cell were in good agreement with the measured pretilt angles of two accompanying homogenous cells whose alignment methods were the same as applied to opposite substrates of the HAN cell, respectively. The advantage of direct measurement is easily applicable to measure the pretilt angles of aged HAN cells. (C) 2013 Optical Society of America
Simple method to obtain accurate pretilt angles for thin twisted nematic liquid-crystal cells
(2013-01-10)
Wang, Sheng-Ya
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
;
Institute of Photonic System
Modern thin-film-transistor-driven twisted nematic (TN) products on the market require thin cell gaps below the value to satisfy the condition of the Gooch-Tarry first minimum in transmission for fast response times and wide viewing angles. For the first time to our knowledge, we have developed a simple experimental method based on a new configuration of out-of-plane cell rotation and analyzed our data by extended Jones matrix method to obtain accurate pretilt angles for such thin TN cells where the well-accepted configuration of the out-of-plane cell rotation method analyzed by Birecki and Kahn [ The Physics and Chemistry of Liquid Crystal Devices (1980), p. 115] was insufficient to address. (C) 2013 Optical Society of America
The Application of the Sawtooth Photonic Crystal on Producing Polarized Light
(2011-09-15)
Pei, Ting-Hang
;
Chen, Wei-Chou
;
Yang, Kei-Hsiung
;
光電學院
;
College of Photonics
We have proposed a sawtooth photonic crystal formed by Si-SiO(2) periodic layers designed on a planar medium as a polarizer. The polarizer can produce H-polarized light very efficiently because the frequency of E-polarized light is chosen at the photonic band gap but that of H-polarized light at the photonic conduction band. The best polarization ratio is as high as 2.56 x 10(5) : 1 when the normalized frequency a/lambda is 0.24 and the incident angle is about 13 degrees. Highly polarized light can be produced in a normalized frequency range from 0.23 to 0.25, and this can possibly be applied to an LED with a certain bandwidth.
Thermally induced light leakage in in-plane-switching liquid crystal displays
(2009-02-01)
Hsu, Jy-Shan
;
Lin, Yi-Hsin
;
Lin, Hung-Chun
;
Yang, Kei-Hsiung
;
光電工程學系
In this paper, we report the thermally induced light leakage in in-plane-switching liquid crystal displays (IPS LCDs) that have a built-in small-angle deviation (< 4 deg) between the polarization axis of a polarizer and the rubbing directions for liquid crystal (LC) alignment. We have found that the thermally induced light leakage depends strongly on the phase retardation which is a function of cell gap, wavelength, and birefringence of LCs used in the IPS LC cells. In addition, we have measured the light leakage of vertically aligned LC cells, which is independent of temperature and the deviation angle. A temperature-scanning method is proposed to reduce the light leakage of the IPS LCDs.