Researchers at Stanford University have made a three-dimensional circuit made from carbon nanotubes.
While it seems that graphene, nanotubes’ upstart younger cousin, has been taking more and more of the limelight of late, the Stanford University researchers led by H.S. Philip Wong are still making inroads in applying carbon nanotubes to electronics.
Carbon nanotubes have tantalized researchers for years now with their favorable characteristics for creating circuits five times faster than a silicon circuit, but one of the obstacles has been scaling beyond a single nanotube transistor. The problem has been primarily controlling the quality and purity of the carbon nanotubes.
In an ingenious engineering approach, the Stanford researchers started from the premise that they are never going to get a set of pure carbon nanotubes, they will just work around it. What they would have to do is come up with a way to separate semiconducting nanotubes from metallic nanotubes after they’ve both been aligned on a silicon wafer and metal electrodes laid on top of them.
To do this they used the insulating layer between the silicon and the nanotubes as a back gate that would allow the switching off of the semiconducting nanotubes so they could then apply an electric charge through the metal electrodes that would burn off the metallic nanotubes.
The researchers have been able to apply this method to making 3D circuits that can make simple circuits capable of making and storing small calculations. The Stanford researchers have managed to make nanotube arrays with five to 10 nanotubes per micrometer, but they will need to reach 100 nanotubes per micrometer to start seeing substantial performance.
Where will this end up? Hard to say, whenever you see a story start with “Such a computer is still at least 10 years off”, you can pretty much say, “maybe never.”
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.