Active Matrix

Active matrix is a type of addressing scheme used in flat panel displays. In this method of switching individual elements (pixels) of a flat panel display, each pixel is attached to a transistor and capacitor which actively maintain the pixel state while other pixels are being addressed. This is to be contrasted with the older passive matrix technology in which each pixel must maintain its state passively, without being driven by circuitry.

The active matrix technology was invented and first demonstrated by Hungarian emigré T Peter Brody and his Thin-Film Devices department at Westinghouse Electric Corporation in 1968, and the term was introduced into the literature in 1975.

Given an m × n matrix, the number of connectors needed to address the display is m + n (just like in passive matrix technology). Each pixel is attached to a switch-device, which actively maintains the pixel state while other pixels are being addressed, which also prevents crosstalk from inadvertently changing the state of an unaddressed pixel. The most common switching devices use Thin Film Transistors (TFT), i.e. a FET based on either the cheaper non-crystalline thin-film silicon (a-Si), polycrystalline silicon (poly-Si), or CdSe semiconductor material.

Another variant is to use diodes or resistors, but neither diodes (e.g. Metal insulator metal diodes), nor non-linear voltage dependent resistors (i.e. varistors) are currently used. The latter of these is not yet economical when compared to TFT.

The Macintosh Portable (1989) was perhaps the first consumer laptop to employ an active matrix panel. Today virtually all TVs, computer monitors and smartphone screens that use LCD or OLED technology employ active matrix technology.