Effective Approaches for Low Temperature Polysilicon TFT LCD Post-Mapping Yield Control Problem

Abstract

Low-temperature polysilicon (LTPS) technology has drawn the attention of many display manufacturers because it has several potential advantages over amorphous thin-film-transistor liquid crystal display TFT LCD). The mapping operation matches one TFT and one color-filter (CF) glass plate together to form one LCD plate. Each plate contains a certain number of cells that are independent devices. The matched LCD cell is good only when the TFT and CF cell match is good. When only a TFT or CF cell is good, there is a yield loss. The sorter is a robot used in LCD manufacturing systems to achieve higher yield in matching TFT and CF plates. This sorter contains several ports that can transfer CF glasses from CF cassettes to match TFT glasses. This is an important determinant for post-mapping yield. This study first proposes a linear programming formulation to optimize the plates-matching problem for the various ports. Next, we propose an algorithm to reduce the number of ways for choosing different matched objects when the number of matched cassettes is large. This algorithm avoids computer overload and provides an excellent solution. The empirical results illustrate the efficiency and effectiveness of the proposed approaches. Note to Practitioners - Yield is an important competitiveness determinant for thin-film-transistor liquid crystal display (TFT LCD) factories. TFT-LCD contains three major manufacturing sectors: the array, cell and module assembly processes. The yield loss from the cell process is one of the most critical steps. This study first formulates a linear programming for the TFT color-filter plates-matching problem in the cell process and a reduction algorithm then is developed to reduce the computational efforts. Our proposed approach is workable and it does not require a significant investment to produce yield improvement by applying the proposed matching algorithm.