QFT Ltd has spun out from the Dundee University Amorphous Materials Group which 25
years ago started a revolution with its pioneering work on thin film electronics
that underpins today’s large area electronics sector.
This is one of the first
active matrix LCDs produced by the group in the early 1980s.
The basic technology of field emission has been known for several years, and there are many materials and forms that have been used to create the electron-emitting sources. Field emission is regarded as the most likely candidate to challenge the dominance of liquid crystal in display applications. In principle FEDs retain many of the desirable attributes of the cathode ray tube in that the image is created by phosphors being excited by the energy of electron impact. In the case of FE though, the electrons originate from many millions of emission sites, uniformly distributed across the field of the display, rather than from a single cathode.
QFT's novel process requires the laser irradiation of hydrogenated amorphous silicon (a-Si:H) to produces a high density of emission sites both on the a-Si:H surface as well as within the film. The resulting structure shows a high uniformity of electron emission. A typical surface structure is shown below.
The field emission is caused by proximity effects of highly conducting particles in an insulating matrix where the resulting morphology enhances the internal electric field. Surface morphology resulting from the laser processing gives additional enhancement.
The resulting films show a low threshold, high output current, high uniformity and no evidence of hysteresis
This layer then acts as an electron source for conventional phosphor materials. A third gate electrode is added using self-aligned techniques that rely only on thin film processing.
A micrograph of a 3-terminal backplane structure showing individual emitter sites surrounded by gate metal.