Thin-film transistor array

The thin-film transistor array is the back glass of an LCD panel. Magnified, it shows a fine grid of metal lines, with a transistor and a clear electrode in every cell. One cell is one subpixel.

It's built up layer by layer on a sheet of display glass in a clean room. Each layer follows the same cycle: deposit a thin film over the whole sheet, coat it with light-sensitive resist, expose a pattern through a mask, then etch away what isn't wanted. First comes copper for the gate lines that run along the rows. Then silicon nitride and silicon for the thin-film transistors, followed by more copper for the data lines that run down the columns. Another layer of silicon nitride protects everything, and finally indium tin oxide forms the clear electrode in each subpixel.

In the LCD panel, the array is a huge grid of switches. One row at a time, a gate line turns on every transistor in its row, and the data lines charge each electrode to the voltage for its brightness. The transistors then switch off and hold that charge until the next frame. The biggest factories work on glass about 3 meters across.