Fabricated as a thin film of semiconductor and metal on glass or another substrate, this transistor gives every pixel in an active-matrix display its own switch. The panel selects one row, writes a new level into that pixel, and moves on. The pixel keeps its state until the scan returns.
That film is the backplane in an Active-Matrix Organic Light-Emitting Diode (AMOLED) panel and in many liquid-crystal panels. In the organic panel, the layer that emits light is an Organic Light Emitting Diode (OLED). The transistor does not produce the light or rotate the liquid crystal. It only lets each pixel be driven on its own. Spec sheets name this backplane TFT for both kinds of panel.
How Each Pixel Is Addressed
A passive grid ties many pixels to the same wires, so contrast falls as the panel grows. An active matrix places a transistor at the pixel and scans one row at a time.
- Select. A row line turns that pixel’s transistor on for a brief slice of the frame.
- Data. A column line delivers the level that sets the pixel’s brightness for the coming frame.
- Hold. A liquid-crystal pixel stores that voltage on a capacitor after the transistor turns off. An organic pixel is driven by current, so its circuit often uses more than one transistor to keep the current steady and to offset small differences between devices.
Backplane Role in the Panel
The backplane is the glass, or another substrate such as a flexible sheet, that carries the transistors, the select and data lines, and the storage elements. Liquid crystal between polarizers, or an organic emitting stack, sits on the viewing side of that circuit. Because every pixel has its own switch, a large panel can hold a sharp image without driving every row at once.
Semiconductor Films Compared
Panel makers deposit different semiconductor films on the substrate. The choice is about how easily charge moves in the film, how little leaks while the switch is off, and how large a sheet the process can coat.
| Film | Typical Use | Trade-Off |
| Amorphous silicon | Large liquid-crystal panels | Mature on big glass, with lower mobility that limits how much circuitry can sit beside the pixel |
| Low-temperature polycrystalline silicon | Smaller high-resolution panels, including many organic light-emitting modules | Higher mobility for faster switching and tighter pixel circuits, with more process steps |
| Oxide semiconductor, such as indium gallium zinc oxide | Large high-resolution panels that must hold a pixel level between scans | Mobility between the other two films, with low leakage while the switch is off |