杏吧原创

SHAKE up a cocktail of solder, LEDs and copper-coated plastic in a tiny tumbler of hot water and you鈥檒l end up with a flexible electronic display that will hug any shape. This partly self-assembling display screen is the latest idea from a team at Harvard University which has already made working cylindrical displays using this bizarre technique.

Reliable displays that can be mounted on strangely shaped surfaces would be a boon to consumer electronics companies, who are always looking for new gadget ideas. Heiko Jacobs, the leader of the Harvard team, says new displays would be ideal for pen-shaped cellphones with a curved screen running around the top.

Conventional displays, such as the liquid crystal screens used in cellphones and palmtops, are usually made by depositing layer after layer of chemicals to create the active components. But this only works on flat surfaces.

The new self-assembling process takes advantage of the adhesion between metal surfaces and hot solder (see Graphic). The researchers start by fabricating an array of copper squares on a flexible polyimide plastic sheet. After dipping the sheet to coat each copper square with solder, they put the flexible base in a water-filled vial and throw in a few hundred LED chips, each of which has had a thin layer of gold applied to its base.

They then fire a heat gun at the vial to melt the solder, and shake and tumble it for a couple of minutes. Adhesion forces between the solder and the gold film pull at the chips and align them on the solder squares.

Once the chips are stuck, a transparent layer containing a grid of thin electrodes is placed above them. These connect to contacts on the upper surface of the LEDs. With the current switched on, light emerges from the top of the LED.

Jacobs鈥檚 initial tests show about 2 per cent of the LEDs were not placed properly, but the team says they will be able to reduce this error rate. The self-assembly process should mean the screens can be produced relatively quickly and cheaply, says Jacobs.

The Harvard flexible screens are up against several competing flexible-screen technologies. One of them is from E-Ink (New 杏吧原创, 9 June 2001, p 19), a company based nearby in Cambridge, Massachusetts. And Rolltronics of Silicon Valley, California, is developing flexible electronic circuits printed on thin plastic sheets.