Detection of Physical Defects in Full Color Passive-Matrix OLED Display by Image Driving Techniques

Access to display pixels for the purpose of identification of a defect in a sealed display is difficult. Thus, it will be useful to investigate the physical defects in a passive-matrix organic light-emitting diode (PMOLED) display, such as electrically open anode or cathode, shorted anode or cathode or pixel short by driving the display as red, blue, green, white, or black image and observing the visual defects. In this paper, we associate a black horizontal line in a display with electrically open row, dark/dim horizontal line with shorted cathode, dead pixel or bright horizontal line or dark/dim vertical line with electrically shorted pixels and black vertical line with either electrically short or open anode. Further, we find a pixel short to be a complicated defect which manifests itself in a display in several ways depending on the image displayed. For example, a short in red pixel will result in bright horizontal line in a blue or green image but not in red image and its behavior in white or black image will be entirely different. However, by clearly understanding the cause of appearance of a defect, we also demonstrate that by a specific driving methodology, it is possible to identify a physical defect. We have used SPICE simulation to support the physical observations.