The conventional electronics industry is focusing a lot of effort on eliminating stochastic resonance (SR). SR is the hiss that generally hinders the detection of weak signals and degrades overall device performance. The electronics community is searching for a way to exploit SR to enhance single transmission for a new generation of devices—for example, bio-inspired sensors and computing processors whose design is based on the neural networks of the brain.
Researchers at Osaka University in Japan are working on achieving this with single-walled carbon nanotubes (SWNTs). The research team created a summing network SR device that detects subthreshold singles that are fabricated to include a self-noise component.
"The functional capabilities of our network SR device, which relies on dense nanomaterials and exploits intrinsic spontaneous noise at room temperature, offer a glimpse of future bio-inspired electronic devices," said Megumi Akai-Kasaya, assistant professor at Osaka University.
Researchers have known for decades that some animals use SR to enhance transmission or detection of signals below the detection threshold. Paddlefish live in muddy rivers, and they can detect and feed on the nearest plankton only when there is background electrical noise from the other plankton mass. The background noise is used to amplify the signals of the nearby plankton. Crayfish use SR to detect subtle movements of predators.
There is evidence that the human brain uses SR in visual processing. Undetectable light signals to the right eye become detectable through the addition of noise to the left eye. Researchers have discovered that adding random noise like SR to electronics devices can increase the detectability of signals and the efficiency of information transmission.
The two basic requirements for developing an SR-based electronic device are a signal detection threshold and the presence of additional noise. In order to satisfy these requirements in their SWNT device, the team created an SWNT network that had up to 300 carbon nanotubes aligned parallel to each other between chromium electrodes. This increased the signal detection ability.
The team functionalized the SWNTs with phosphomolybdic acid (PMo12) molecules that can firmly absorb on graphite materials before drying the device on a hot plate at 150° C under atmospheric pressure. The adsorption of the PMo12 molecules on the SWNTs generated additional noise.
"SWNTs can be generators of spontaneous noise, owing to their high sensitivity to external surface perturbation," Akai-Kasaya said. "What we found is that the introduction of an extra disruptor—molecular adsorption, and particularly with the adsorption of PMo12—generated a large and tunable type of electrical noise in addition to common environmental noise."
The team tested 10 different molecules adsorbed in the SWNTs as noise generators and found the SWNT/PMo12 combination was more than twice as effective as the other SWNT functionalized combinations.
"SWNTs offer a promising route to realizing a small-size summing network SR device that utilizes molecular thermal fluctuation as the noise source," Akai-Kasaya said.
A paper on this research was published in Applied Physics Letters.