Performance of a 350 character TFT-LC display panel

The problems encountered in increasing the resolution of a 6" × 6" TFT addressed liquid crystal display from 20 lpi to 30 lpi are described, together with the solutions developed. The major problem relates to the reduced capacitance of the LC element resulting in a lack of frame period storage. Two approaches were utilized: the first consisted of a systematic effort to analyze the factors that influence off "leakage" current in the TFT. As a consequence of this a TFT with leakage current of less than one nanoampere was achieved. The alternate approach was to incorporate an extra 5 pF capacitor in each display element. A layout of the matrix circuit was developed which incorporated the capacitor under the gate bus bar, thereby avoiding a sacrifice in the active area of the display element. Both approaches were successful and good quality displays fabricated. Electrical design considerations, TFT fabrication principles and performance of the resulting 6" × 6" 30 lpi TFT-LC panel will be presented.