In-cell touch sensors are built directly into the LCD layers. On-cell touch sensors are near the top of the LCD stack just below the top polarizer. Out-cell touch sensors are built separately from the LCD then adhered to the LCD either with an optical bond layer or with a perimeter seal. There are a variety of material stack up options for out-cell sensors including GG, GGG, GG2, GFF, GF, and OGS. The topmost layer is often a cover lens which can be adhered with a dry or liquid optical bond material. Liquid optical bonding is a complicated process requiring dams and UV curing from multiple angles.