NEC has printed
carbon nanotube transistors on a plastic substrate, and claimed
superior performance to other printed devices.
"The channel materials of conventional research organic
transistors generally demonstrate little mobility and are therefore
considered unsuitable for electronic devices with high-speed
operation," said NEC. "The carbon nanotube
(CNT) channel material allows 100 times greater mobility than
regular organic transistors."
How much mobility? "Some devices exceed over 100cm²/Vs," NEC
told Electronics Weekly.
Electron and hole mobility respectively around 1,500 and
450cm²/Vs in silicon. Printed organics rarely hit 5cm²/Vs.
Tested on polyethylene naphthalate
(PEN) substrates, "the CNT ink can be printed by such as ink-jet
printing methods. We used a spin-coating method in this case", said
NEC. "We fabricated thin film bottom-gate bottom-contact
transistors."
Printed nanotube semiconductors can achieve
100cm²/Vs.
The firm has established a model which relates transistor
characteristics and the length and density of nanotubes in the
channel, and said it will use this to increase performance.
It also has a channel coating-process "capable of accurately
controlling the density of the CNT", although it admits there was
performance variation between prototype transistors.
Reducing carbon footprint by printing semiconductors is one of
NEC's aims. "Manufacturing processes can be dramatically simplified
in comparison to conventional semiconductors waste materials
generated can be reduced, and CO2 emissions can be reduced by more
than 90 per cent."