Mura, mura on the wall, whos the fairest of us all?

07/01/1997

Mura, mura on the wall, who`s the fairest of us all?

The addition of liquid crystal during cell assembly of thin-film transistor (TFT) arrays often introduces subtle smears, termed "mura" in Japan and "alluk" in Korea. Muras are mid-to-low (0.5-10 cycles/degree) spatial frequency defects with varying forms of low contrast display discoloration, which are very difficult to detect, identify, and distinguish visually (see "Tradeoffs in panel designs for cell testing," August 1995, p. S17, and "Plate design and cost of ownership for in-process FPD test systems," January 1997, p. 87). Often, as TFT array quality improves, mura detection and classification determine the performance of different AMLCD manufacturing lines and their long term acceptance by end-users. Replacing subjective human inspection with automated cell inspection systems has partially solved the problem, but a system that judges display quality independently to resolve differences between inspectors (human and automated) and manufacturers has yet to appear.

At the recent Society for Information Display (SID`97) meeting in Boston, MA, officials from Photon Dynamics revealed a plan to introduce an inspection system that can detect muras in a standardized fashion and adapt to each manufacturer`s definition of acceptable display quality. The plan was slated to begin with the June introduction of image processing software containing test libraries of muras. Over the years, engineers at Photon Dynamics have compiled and classified images of rubbing muras, edge port muras, alignment muras, block muras, and many other process defects. Based on this information, they have developed algorithms to identify muras with objective criteria. Using their N-Aliasing imaging technology, a new inspection system then processes multiple amplified and enhanced images of the entire panel. Classification of image defects against the system library offers consistent and quantitative evaluations of test panel muras. Users can specify different acceptance levels of detected muras and can add their own tests. This feature allows different users to specify accepted levels of defects for flexible cost saving strategies. When asked if Photon Dynamics believes this library will become an industry standard, company representative C.J. Meurell said, "Certainly." - M.Y.M.L.