Active matrix development

The active matrix LCD (AMLCD) offers a great potential for making colour displays capable of operation at video rates. The display contains a matrix of non-linear devices on one plate of the liquid crystal cell, which act as switches, allowing current to flow when addressing a given row of pixels but not when addressing other rows. The two most common implementations involve the use of either amorphous silicon or polycrystalline silicon (polysilicon) thin film transistors (TFTs). Ordinary polysilicon, as used as an interconnect in VLSI, is not suitable for use as an active layer. A deposition process operating at much lower pressures, which produces material of high quality (high mobility, low threshold voltage, low off current), was developed. Another critical consideration when making active matrix displays, is that of yield. The capacitively coupled transistor (CCT) architecture developed solves problems associated with other technologies by putting the gate lines and transistors on one plate of glass and the data lines on the other plate. The two are therefore separated by a high resistance medium, the liquid crystal