Engineers at Fujitsu say they have developed a manufacturing process for thin film transistors (TFTs) that will help them realise their goal of building a PDA (personal digital assistant) inside a sheet of glass possibly as early as 2003.
It has been possible to build integrated circuits directly onto glass for some time, but the technology has thus far only allowed relatively simple devices to be produced on a glass substrate. This is because the speed at which electrons move, called their mobility, is relatively slow on glass.
Current polysilicon displays have a mobility fast enough to enable some chips, such as driver chips, to be produced directly onto the same piece of glass as the LCD they control. The electrons in anything more complex, such as a system LSI (large scale integrated circuit) or microprocessor, have to move at much higher speeds and so require either glass with higher mobility or separate silicon-based components. These are then packaged in plastic, inserted into circuit boards and then connected with wires to the glass panel.
Engineers have known how to increase glass mobility for some time — crystals used in the display need to have a larger grain size. But doing that at below 550 degrees Celsius, the point at which the glass substrate begins to melt or become distorted, has been a problem. The new manufacturing process developed by engineers at Fujitsu creates crystals with a faster mobility while keeping the temperature below 450 degrees.
"There are many problems to overcome before commercial production but this is the most basic problem — and it has been overcome," said Nobuo Sasaki, an engineer working on the process at Fujitsu Laboratories.
In the labs, Sasaki has been able to produce a polysilicon TFT LCD panel with faster mobility on a 30cm-square glass substrate using the new method and he said the technology could easily be applied to substrates of one square metre. A substrate is typically used to produce several LCDs at once and is then cut up after manufacturing is complete.
Engineers want to mount components directly onto glass because of potentially large savings in manufacturing costs. "We can make both (display) pixels and integrated circuits in the same production process. If we can make many functions at the same time, the systems become cheaper," said Sasaki. "(Our goal is) to make it more than 50 percent cheaper than current production."
Also, PDAs or computers made using the new technology won't be much larger than the displays they now house, he said. "At the moment I am thinking about integrating (the components) in the peripheral regions, around two or three millimetres wide, around the display edge."
If engineers like Sasaki are successful, the time could be just around the corner when PDAs look little different from a small panel of glass.