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Roll up for the flexible transistor

Roll up for the flexible transistor

作者:舜丶  时间:2019-03-01 12:07:00  人气:

By JULIAN BROWN TV screens that roll up like blinds, smart cards that are really flexible and electronic displays that can be embedded in car windscreens could flow from the invention by French scientists of the flexible transistor. Francis Garnier and colleagues at the CNRS Laboratory for Molecular Materials near Paris have developed ways to replace all the structures in a transistor with polymers. What is more, they are able to lay down these components without the complex high-temperature, high-vacuum techniques needed in silicon chip foundries. In 1990, Garnier’s team unveiled a transistor made mostly from plastics; but this still needed some metallic components, such as gold and silver for the electrodes (Technology, 15 December 1990). Even these have now been dispensed with, replaced by conducting contacts made of graphite-based polymer ink. The contacts are deposited either side of a thin layer of insulating polyester. The whole structure is supported by adhesive tape, which lies beneath the bottom electrode, or gate (see Figure). With the help of a precision-made mask, Garnier’s team lays down a 40-nanometre film of a polymer semiconductor between the two top contacts, the source and drain. The plastic is a modified form of a sulphur-based polymer, sexithiophene, which has semiconducting properties similar to those of silicon. The device works in a similar way to a field-effect transistor. The field produced by a voltage applied between a top electrode and gate modifies any current flowing between the source and drain. The device, which is described in last week’s issue of Science, can work as a simple switch or an analogue amplifier. Garnier’s device is about 50 micrometres in size, more than ten times larger than conventional transistors that are etched onto silicon chips. So it is unlikely that manufacturers will see the polymer transistor as a cheap way to make complex devices such as microprocessors. However, the great advantage of the new devices is that they are completely flexible and can be made virtually transparent. Their size is still small enough to make them suitable for large flat-panel screens. They could also help to solve a major problem with electronic smart cards – when the cards bend, their chips can fly off. By ‘printing’ plastic transistors onto the card instead, banks could issue cards that are much more robust. If made transparent, the transistors could be ideal for head-up displays in cars. By incorporating the devices with liquid crystal displays into glass windscreens,