OPTICAL CHARGE-SENSING METHOD FOR TESTING AND CHARACTERIZING THIN-FILM-TRANSISTOR ARRAYS

Improved methods for testing thin-film transistor (TFT) arrays are bec oming increasingly important as TFT liquid-crystal flat-panel displays become the first choice for many applications, The optical charge-sen sing method for testing TFT arrays described in this paper uses interf ace reflections to sense accumulative free carriers and to generate ma ps showing the type and location of line and point defects, The method is nondestructive and provides data which can be used to repair certa in types of array defects, It can also be used to measure such paramet ers as threshold voltage and channel conductance of TFT's, and frequen cy response of driver circuits, Optical charge sensing depends not onl y on charge density but also on the structure of the TFT arrays, Charg e-sensing sensitivity is reduced by reflections from the metal interco nnects, An improvement in the net reflectance change is obtained by us ing polarized and angled incident light in spite of reduced reflectanc e changes compared with normal incidence.