Defective pixel

A defective pixel or a dead pixel is a pixel on a liquid crystal display (LCD) that is not functioning properly. The ISO standard ISO 13406-2 distinguishes between three different types of defective pixels, while hardware companies tend to have further distinguishing types.

Similar defects can also occur in charge-coupled device (CCD) and CMOS image sensors in digital cameras. In these devices, defective pixels fail to sense light levels correctly, whereas defective pixels in LCDs fail to reproduce light levels correctly.

A dark dot defect is usually caused by a transistor in the transparent electrode layer that is stuck "on" for TN panels or "off" for MVA, PVA, and IPS panels. In that state, the liquid crystal material does not do any rotation so that the light from the backlight does not pass through the RGB layer of the display.

A bright dot defect or hot pixel is a group of three sub-pixels (one pixel) all of whose transistors are "off" for TN panels or stuck "on" for MVA and PVA panels. This allows all light to pass through to the RGB layer, creating a bright pixel that is always on.

Another cause of bright dot may be the presence of impurities in the liquid crystal. On the one hand, impurities will affect the alignment of liquid crystal molecules, and on the other hand, they can reflect light to form bright spots.

A partial sub-pixel defect is a manufacturing defect in which the RGB film layer was not cut properly.

A tape automated bonding fault (TAB fault) is caused by a connection failure from the TAB that connects the transparent electrode layers to the video driver board of an LCD.

TAB is one of several methods employed in the LCD-manufacturing process to electrically connect hundreds of signal paths going to the rows and columns of electrodes in layer 6 (the transparent electrode layer) in the LCD to the video integrated circuits (ICs) on the driver board that drives these electrodes.