Precise Detection of Short-Circuit Defects on TFT Substrate by Infrared Image Matching

摘要

A technique is developed which detects short circuits in the TFT substrate for liquid-crystal displays by matching of radiated infrared images. The technique is based on heating of the short-circuit point by the leak current. In this study, the position of the heating on the substrate is identi- fied with high precision by the proposed method, which specifies the line pattern in the infrared image containing the short circuit, and can determine the short-circuit posi- tion relative to the line pattern. The following two elements are included in the system: (1) a radiated infrared image detection system, synchronized to the impressed voltage, in order to manifest a small heated point; (2) a high-precision positioning system for the line pattern, based on subpixel template matching which extracts the template for each TFT substrate to be tested. The systems are evaluated by experiments, and it is verified that a detection accuracy of ± 5 μm is obtained for the short-circuit position relative to the line pattern. The accuracy is sufficient to discriminate malfunctioning TFTs, which helps to remedy unsatisfac- tory TFT substrates.