Professor Chongwu Zhou of the Ming Hsieh Department of Electrical Engineering at USC likes to think small – very small. Dr. Zhou and his team in the Nanolab research carbon nanotubes, two-dimensional (2D) materials, lithium/sodium ion batteries, and bio nanotechnology.
Most recently, Dr. Zhou is applying his work to portable electronics, like smartphones. Today’s smartphones use low-noise amplifiers and power amplifiers for signal processing. Linearity is a major determining factor in the quality of the phone conversations and the speed of the 4G access. A low linearity will induce distortions, causing the degradation of phone conversation quality and internet-exploring speed.
Carbon nanotubes are inherently more linear than the materials for the devices in smartphones today. In addition, this tiny material is only 1–2 nanometers in diameter. To put that in perspective, a single strand of human hair is a full 50 THOUSAND nanometers in diameter. In order to use carbon nanotubes in smartphones, the cut-off frequency of the carbon nanotube transistors needs to be several tens of the smartphone operation frequency (~2 GHz), and the higher the better.
Previous research with nanotubes has been able to make carbon nanotube transistor cut-off frequency of ~20 GHZ. In a recent paper that Dr. Zhou and his team published, they were able to significantly improve the cut-off frequency to greater than 70 GHZ, getting us one step closer to the applications of carbon nanotubes in portable electronic products. They’re now focusing on perfecting their technique and developing their new transistors with a cut-off frequency greater than 100 GHz. Achieving that goal will make their technology suitable for a broad range of electronics other than smartphones.
“Today’s smartphones are not slow, and the quality of conversation is good by any means,” Dr. Zhou says. “But what we’re talking about with carbon nanotubes is going from a BMW to a Ferrari.”
In addition to increasing the speed and improving the conversation quality, Dr. Zhou is quick to point out that there are other exciting possibilities. “There has been a lot of talk of flexibility as the future of smartphones,” Dr. Zhou says. “One of the main challenges to achieving this is that the widely used silicon transistors are simply too rigid. Replacing the rigid transistors with these carbon nanotube transistors would be a big first step towards truly flexible phones.”
Smartphones have reached the stage in their development where they are now a vital tool in nearly everyone’s life. Their functions, and the jobs we expect them to do, is growing at a rate that our current materials simply cannot keep up with. At this point, Dr. Zhou’s research has taken us one step closer to that future.
Ph.D. Student Yu Cao holds a film with carbon nanotubes.