Devices could help improve mobile phone performance

According to a statement, the devices are designed to ease congestion over the airwaves to improve the performance of mobile phones and other portable devices.

‘There is not enough radio spectrum to account for everybody’s handheld portable device,’ said Jeffrey Rhoads, an associate professor of mechanical engineering at Purdue University.

The overcrowding results in dropped calls, busy signals, degraded call quality and slower downloads. To counter the problem, industry is trying to build systems that operate with more sharply defined channels so that more of them can fit within the available bandwidth.

‘To do that you need more precise filters for cell phones and other radio devices — systems that reject noise and allow signals only near a given frequency to pass,’ said Saeed Mohammadi, an associate professor of electrical and computer engineering who is working with Rhoads, doctoral student Hossein Pajouhi and other researchers.

The Purdue team has created nanoelectromechanical resonators that contain a tiny beam of silicon that vibrates when voltage is applied. Researchers have shown that the new devices are produced with a nearly 100 per cent yield, meaning nearly all of the devices created on silicon wafers were found to function properly.

‘We are not inventing a new technology; we are making them using a process that’s amenable to large-scale fabrication, which overcomes one of the biggest obstacles to the widespread commercial use of these devices,’ Rhoads said.

Findings are detailed in a research paper appearing online in the journal IEEE Transactions on Nanotechnology. The paper was written by doctoral students Lin Yu and Pajouhi as well as Rhoads, Mohammadi and graduate student Molly Nelis.

The devices are created using silicon-on-insulator (SOI) fabrication — the same method used by industry to manufacture other electronic devices. The resonators can be readily integrated into electronic circuits and systems because SOI is compatible with complementary metal-oxide-semiconductor technology (CMOS).

The new device, in a class of devices called nanoelectromechanical systems (NEMS), is said to be highly tuneable, enabling researchers to overcome manufacturing inconsistencies that are common in nanoscale devices.

‘Because of manufacturing differences, no two nanoscale devices perform the same rolling off of the assembly line,’ Rhoads said. ‘You must be able to tune them after processing, which we can do with these devices.’

The heart of the device is a silicon beam attached at two ends. The beam, which vibrates in the centre, is about two microns long and 130nm wide. Applying alternating current to the beam causes it to selectively vibrate side to side or up and down and also allows the beam to be finely tuned.

The nanoresonators were shown to control their vibration frequencies better than other resonators and it is thought the devices might replace electronic parts to achieve higher performance and lower power consumption.

The researchers, funded in this project by the US National Science Foundation, have filed a patent application for the concept.