Talking about flexible electronics...

Stanford engineers have developed an improved process for making flexible circuits that use carbon nanotube transistors, a development that paves the way for a new generation of bendable electronic devices. Credit: Bao Lab, Stanford University

Doping of single-walled carbon nanotube (SWNT) thin-film transistors- Credit: Huiliang Wang et al./PNAS

Just yesterday I posted a news on the creation of a stretchable and bendable antenna and I mentioned that it represents an important component in wearable electronics. These latter have been improved considerably resulting in circuits on a plastic substrata that can be easily bended. The "density" of these "plastic circuits" (the number of transistors per square unit), however, is pretty low and the reason is that whilst normal semiconductor circuits are designed using both P and N type transistors alternating one with the other, in the case of plastic based transistors only P-type can be used. Just to refresh the electronic courses we took too many years ago, a P type transistor has electrons jumping from one positive hole to the next whilst a N type transistor has the electron bouncing along a series of electrons (Negative) like beads in a necklace. As it happens, by mixing N type and P type transistors one can have a circuit that is robust to noise and use very little power. This is not the case if you were to use only one type or the other. By the way, the "C" in CMOS means "complementary" exactly to indicate this mixing.

Now researchers at Stanford University have created a CNT (Carbon Nano Tubes) that can be used for producing flexible chip and that has the "complementary circuit" characteristics, having both N and P type junctions. 

CNT are basically P type but they have managed to create N type by adding a chemical dopant. They used an ink jet printer to inserted the dopant at the right place.

It is still a lab result but it shows that it is possibile to create flexible electronics with the same kind of robustness and density of silicon based electronics. It is (just) a matter of moving from the lab to the industrial production.  It won't be easy but the first step has been made.


Author - Roberto Saracco

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