Plastic pixels will position Bell Labs onto big screen

Plastic pixels will position Bell Labs onto big screenPotential route for Bell Labs to big screen printed displays via smarter plastic active semiconductor pixel. Steve Bush
Bell Labs is close to revealing details of a smarter all-‘plastic’ active semiconductor display pixel, a potential route to big-screen printed displays.
“The new smart pixel design includes the circuitry to allow for variations in the pixel and drive components to be compensated for,”said Ananth Dodabalapur, an emissive device physicist at Lucent’s Bell Labs. Plastic: What’s in a name?
There is currently a bit of a problem with naming the new breed of semiconductors based on organic material, those not predominantly metal or semi-metal in nature.
Essentially there are two types, polymer and short-molecule. These could usefully be summed-up by the term ‘organic’ if some device physicists had not started to use it specifically for short molecule materials. Much as I know it is inaccurate, I shall continue to use the term ‘plastic’ until the dust settles.
If you have a view, or know the proper term to use, feel free to contact me. steve.bush@rbi.co.uk  
 
Bell Labs has already demonstrated active all-plastic pixels which combine a drive transistor and a photo-emissive structure (see diagram above).
The new pixel-driver combination enables parameters that drift during operation to be brought back into line. “If a transistor needs more voltage, it gets more voltage,”said Dodabalapur.
Until Dodabalapur presents his findings at a forthcoming physics symposium in San Francisco, few more details are available.
The circuit, developed by Dodabalapur’s colleagues, is analogue and has six transistors, but according to Dodabalapur needs little space in the pixel. “Only two of the transistors need to be of any size,” he said.
The other disclosed detail is that the pixel does not work totally alone. It sends information back to the drive circuitry which modifies drive signals accordingly.
The smart pixel is destined for future large area displays. Larger than those currently made using LCD technology. “LCDs do not scale up well,”said Dodabalapur.
And when will we see these large emissive displays. “Several years,”he said, “certainly not less than five. Say five to ten years.” Plastic: Which type?
Bell Labs is making both transistors and light emitters in polymer and short-molecule (‘organic’) materials.
Both materials make emitters with similar characteristics, but display polymers can be deposited in an ink form and therefore lend themselves to printing. Also, single layer emissive structures are possible with polymers, but not short-molecules – according to Bell Lab’s Ananth Dodabalapur.
CDT, the Cambridge-based display company, and its licensees champion polymer emitters whereas Kodak and FED Corp in the US and Pioneer in Japan are actively following the short-molecule route. Products including short-molecule technology are available in the market.
Interestingly, as Bell Lab’s sees plastic pixels as a way of making big displays, FED Corp is using short-molecule materials to make miniature silicon-backplane displays.
Both polymer and short-molecule transistors can be printed.


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