Better gold alloys for communications tech

Dec 03, 2013 by Matt Shipman
How Changing the Way We Study Gold Could Boost Communication Tech
This graph shows just how much softer solid gold was in the experiment.

( —Under the right circumstances, pushing on nothing is harder than pushing on something – at least when that "something" is gold. That's the finding from a new materials science paper, and it's a finding that could expedite the development of new wireless communication technologies.

The Problem

At issue are ohmic radio frequency microelectricalmechanical systems switches (RF-MEMS switches). That's an extremely long name for an extremely small object. RF-MEMS switches are basically just metal on-off switches. And they're tiny – only micrometers, or millionths of a meter, long. But they're key to the next generation of low-energy, devices, such as satellites and cell phones.

But RF-MEMS switches can be unreliable, often breaking or getting stuck in the "on" position. And, as you can imagine, fixing micrometer-long switches in a cell phone is problematic – virtually impossible in a satellite.

"Solving the problem of reliability for RF-MEMS switches is a challenge due to the complex environment in which these switches have to operate," says Doug Irving, senior author of the paper and a researcher at NC State. "We need a material that won't lose conductivity (when exposed to oxygen, due to oxidation, AKA rust), but that is strong enough to handle changes in and temperature while being repeatedly flipped back and forth."

Gold meets most of these requirements. But gold is soft. If you push on it hard enough, or often enough, it will get bent out of shape – and your RF-MEMS switch won't work anymore.

So researchers have spent years trying to find out how to make a gold alloy that retains gold's good properties (like conductivity) but is hard enough to take a beating.

Most, if not all, of the researchers working on this problem have tested the hardness of their experimental gold alloys by pushing on them without running an electrical current through the probe they're pushing with. Remember that probe because, as it turns out, the lack of current makes a big difference.

The Study

This is where Doug Irving's research team comes in. Irving is a computational materials design expert. That means he develops complex computer models to see how a wide range of variables (e.g. heat or electricity) can influence how different materials behave.

And when the problem of gold alloys for RF-MEMS switches landed on his desk, he wanted to see if running an electrical current through the probe would make a difference. After all, these switches would only be operating when a current was being run through them.

Irving's team designed a model to evaluate the hardness of gold when the probe was running a constant voltage of 0.2 volts. (If that doesn't sound like much power, it's not. These are low-energy, remember?)

They then ran the model with the nanometers-wide probe making contact in three ways: with the probe flush against the gold surface; with the probe making contact with some gold, but also covering a "void" or empty gap in the surface (such voids are common at the nanometer scale); and with the probe making contact with some gold, but also covering a pocket of hydrocarbons (because these contaminants are also fairly common).

The researchers found that the gold became much softer when the probe was flush with the gold's surface, as opposed to when the probe covered a void or came into contact with hydrocarbons.

"Voltage leads to current, and current leads to heat," Irving says. "When the probe was flush with the gold's surface it conducted heat deep into the material, making it easier for the pressure of the probe to deform the metal. Hydrocarbons and empty space don't conduct current, so the current – and  its related heat – spread out at the edges. The heat didn't extend much beyond the surface of the material."

To put this finding in context, Irving's team performed the same tests again, but without running 0.2V through the probe. In those tests, the was much harder when the probe was flush with the surface.

"Voltage makes a huge difference," Irving says. "This highlights the necessity for testing materials in 'in use' conditions, as close as possible to the conditions the material will face in its final application."

This doesn't solve the problem of finding the perfect alloy for RF-MEMS switches, but it does suggest better strategies. "And by incorporating current into the equation, we should find the right material much more quickly," Irving says.

And the sooner they find the right material, the sooner engineers can use that material to develop resilient RF-MEMS switches and related technologies.

Explore further: World's most complex crystal simulated

More information: Christopher Freeze, Xiaoyin Ji, Angus Kingon. "Impact of Joule heating, roughness, and contaminants on the relative hardness of polycrystalline gold," Journal of Physics: Condensed Matter, 2013. DOI: 10.1088/0953-8984/25/47/472202

Related Stories

Building bridges between nanowires

Sep 20, 2013

Place a layer of gold only a few atoms high on a surface bed of germanium, apply heat to it, and wires will form of themselves. Gold-induced wires is what Mocking prefers to call them. Not 'gold wires', as ...

Hybrid material as gold-leaf substitute

Jun 18, 2013

( —A team of researchers headed by Professor Raffaele Mezzenga has created a hybrid material out of gold and milk proteins that looks like a wafer-thin gold leaf. Thanks to its properties, it could ...

Recommended for you

Controlling core switching in Pac-man disks

Dec 24, 2014

Magnetic vortices in thin films can encode information in the perpendicular magnetization pointing up or down relative to the vortex core. These binary states could be useful for non-volatile data storage ...

World's most complex crystal simulated

Dec 24, 2014

The most complicated crystal structure ever produced in a computer simulation has been achieved by researchers at the University of Michigan. They say the findings help demonstrate how complexity can emerge ...

Atoms queue up for quantum computer networks

Dec 24, 2014

In order to develop future quantum computer networks, it is necessary to hold a known number of atoms and read them without them disappearing. To do this, researchers from the Niels Bohr Institute have developed ...

New video supports radiation dosimetry audits

Dec 23, 2014

The National Physical Laboratory (NPL), working with the National Radiotherapy Trials Quality Assurance Group, has produced a video guide to support physicists participating in radiation dosimetry audits.

Ultrasounds dance the 'moonwalk' in new metamaterial

Dec 23, 2014

Metamaterials have extraordinary properties when it comes to diverting and controlling waves, especially sound and light: for instance, they can make an object invisible, or increase the resolving power of ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.