Flexible Circuits
March 21, 2014

Flexible Circuits

As much as I go on about new technologies and their positive impacts on us both as a species as well as culturally, there is one new technology I have been very slow to adapt to. E-readers. As a writer, I adore books. I would much rather have a physical copy on hand, able to flip through the pages at my pleasure, than have an electronic device that does it for me. Yes, I do have one. I was given a Kindle as a gift a while back, and I have made some use out of it, but I use it more for having pdf’s on hand than I do for reading books. Still, I must admit, anything that encourages reading in this time of television/movies on demand and video games that can take as much as 40 or more hours to play is a step in the right direction. While I might not care for them personally, I do like what they do overall.

Currently, the biggest problem with e-readers is transporting them. You either need a bag/purse or really, really big pockets to carry them comfortably. Thankfully, a recent innovation has helped a team at Stanford University come up with an answer to this problem, and many others, using carbon nanotubes.

Making circuits out of carbon nanotubes (CNT) gives both flexibility and resilience, but what it has always lacked is the reliability and power-efficiency of the more rigid silicon circuits. This is because CNT circuits were not complementary circuits – those with both P-type and N-type transistors, which are what allow a circuit to handle random electronic “noise” (fluctuations). Electricity travels through semiconductors in two different ways. It either jumps from positive hold to positive hole or it can simply push through them. Semiconductors able to utilize the first type of movement are called P-type, and those that use the second are N-type. By being able to efficiently handle both, electronics are able to maintain reliability despite any random fluctuations. Until now, CNT circuits were only P-type semiconductors and there was no known way of making them also N-type without sacrificing the strength or flexibility that CNT’s provided.

The Stanford team overcame this by treating the CNTs with a chemical dopant they created called DMBI and applied it by using an ink-jet printer to accurately deposit it in very precise locations on the circuit. This substance allowed for CNTs to act as N-type semiconductors and marked the first time that a CNT circuit could work reliably despite any power fluctuations, as well as with lower energy consumption.

Because CNTs are still a relatively new technology, they are still a ways behind plastics in terms of mass-market applications for things like bendable display screens for tablets or e-readers. However, with their newfound ability to create a P-N type blend, they have moved up the running a great deal. According to Professor Zhenan Bao of Standord University, one of the heads of the project, “CNTs offer the best long term electronic and physical attributes.” They are strong enough to flex and stretch while still being capable of delivering a faster performance than plastic circuitry. While there is still work to be done, the innovations of Professor Bao and her team mark a great step forward in the field of flexible circuits.

Image Credit: Bao Lab / Stanford University

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