Study of high precision cell gap measurement and optical properties of liquid crystal displays

• Main Authors: Min-Tzung Shiu, 許民宗
• Other Authors: Ya-Wei Hsueh
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/83677740525625268357

碩士 === 國立中央大學 === 物理研究所 === 91 === The most popular method of measuring the cell gap of LCD devices is using Fabry-Perot interference principle. Using spectrum-analyzer and light sources of different wavelength, empty cells can thus be analyzed. However, the cost is quite high. Other methods can be performed if some electrical-optical parameters of the liquid crystals are already available. Information of a LCD device''s rubbing direction is also required. By measuring the difference in the transmittance due to phase delays, one can estimate the gap of a LCD cell. The drawback of this method is that the computation for cell gap estimation varies with rubbing direction, and its computation complexity is relatively high. With respect to measuring optical characteristics of LCD devices, ellipsometers have been widely utilized to accurately measure the ordinary reflectivity(no) and extraordinary reflectivity(ne) of unknown LCD cells. This method has several drawbacks of high computation complexity, diffucult technical operation, and more cost. This thesis provides a different method measuring these parameters, having the advantage of easier hardware implementation for LCD cell gap measurement. Furthermore, the computation for cell gap estimation does not vary with the rubbing direction, and it can be applied to both transmission-type and reflection-type LCD devices. The proposed method also has several outstanding characteristics: wider range of measurement, high precision compared to other methods, and its performance can be upgraded by improving hardware or using our computer programs to compare all the relative positions of possible intereference stripes A novel method has also been proposed to measure the optical characteristics of LCD devices. Using the same equipment for cell gap measurement, as well as the developed programs, optical parameters such as ordinary reflectivity, extraordinary reflectivity, and pretilt angle can be easily measured. Although the precision of the proposed method is limited to error propagation, yet the cost and computational complexity are lower than those ellipsometer-facilitated methods. Without any related optical characteristics of the unspecified liquid crystal, we can still apply our method, but the estimation error is larger. We can always decrease the estimation error if some optical parameters are available. The precision of measurement can also be increased by matching estimated parameters of different cell gaps. The proposed method focuses on providing a different way of measuring cell gap of LCD cells. Because the error-propagation effect, the precision of the estimated cell gap will directly influences the precision of other parameters. At the end of our thesis, we compared our estimated parameters with those obtained by simulation. The comparison shows the accuracy and outstanding performance of our proposed method.