Display of speed

Surrey University researchers claim to have made the first low-cost amorphous semiconductors with negative resistance. This could meet the increasing demand for high-speed electronics for large flat-display screens and mobile communications that are cheap enough to manufacture in volume.

Amorphous semiconductors — solids that are not crystalline — are relatively cheap to produce and deposit on to the plastic materials used in flat displays. However, to be useful, the switching has to be extremely fast. Previous attempts at using amorphous semiconductors to make diodes, which are needed to switch electric current to different areas of the display to form an image, have failed to produce the gigahertz switching speeds needed.

The crucial quality of a fast-switching semiconductor, said researcher Jeremy Allam from the university’s Advanced Technology Institute (ATI), is negative resistance: ‘The current passing through the material decreases, rather than increases, as the voltage across it rises.’ This can be achieved only with quantum-mechanical tunnelling, he said, whereby a specific voltage across the material allows electrons to ‘tunnel’ through energy barriers that would otherwise be impassible. Increasing the voltage past this value cuts off the tunnelling, hence the drop in current.