Color photoresist

Color photoresist is a liquid that can be turned into a solid pattern with light. It's the ink LCD color filters are printed with, except the printing is done with ultraviolet light through a mask instead of with a press.

Its backbone is acrylate resin. A typical recipe mixes acrylate monomers (small molecules with reactive ends), a binder polymer, a photoinitiator that breaks into reactive fragments under UV, a solvent and a finely ground pigment. It's coated onto glass as a thin, even film and dried. Under a mask, UV light falls only where the pattern should be. There, the photoinitiator starts a chain reaction that links the acrylates into a tight, solid network. Elsewhere the film stays soluble, and a mild alkaline solution washes it away. A bake hardens what's left. This is called a negative resist: what the light hits, stays.

With carbon black mixed in, it becomes the black matrix. With red pigment, green pigment or blue pigment, it forms the windows of the color filter, each layer about 2 micrometers thick. The resist used to pattern transistors is a different, positive type that is stripped off after use. Color resist stays in the panel for good.