MEMS are essential components that send and receive signals and data. With an expanding number of cell phones and wireless devices, there is an urgent need for more reliable and robust MEMS switches, says Binghamton University’s Assistant Professor Sherry Towfighian.
Traditional switches open and close numerous times during just one hour, but their current lifespan is limited by their electrode number: Two.
When the two electrodes come into contact – after several repetitions – the surface of the bottom electrode becomes damaged, leading to a MEMS switch that has to be discarded and replaced.
Along with graduate student Mark Pallay, Towfighian developed a switch that uses more than the traditional two electrodes. By upping the electrode number to four, and changing the usual electrode configuration, the team designed a switch that can limit the damage caused by surface contact.
The new MEMS switch features three electrodes on the bottom and one electrode parallel to the others. The two bottom electrodes on the right and left side are charged while the middle and top electrodes are grounded.
“This type of MEMS switch is normally closed, but the side electrodes provide a strong upward force that can overcome the forces between the two middle electrodes and open the switch,” said Towfighian.
That strong upward force – known as electrostatic levitation – enables a reliable bi-directional switch.
Professor Towfighian spoke with Tech Briefs about how the new design will improve our cell phones and power lines.
Tech Briefs: What was the inspiration for this work?
Professor Sherry Towfighian: The inspiration for this work was exploring possibilities to go beyond the conventional MEMS switches that suffer from a major instability limitation. Often designers of MEMS switches try to mitigate this problem, but cannot avoid it, which ultimately results in failure. The new mechanism enables avoiding this problem completely. The result is reliable switches that last longer and save significant costs.
Tech Briefs: What are the limitations of traditional MEMS switches, and how does your new device improve upon those limitations?
Prof. Towfighian: Current switches consist of two electrodes that pull together when charged. Thus, the force between them is always in one direction and toward each other. We added two more electrodes in a creative configuration that caused a force in the opposite direction. This leads to an easier release of the switch, which was not possible in the conventional switches. The result is a bi-directional and robust switch that can last longer.
Tech Briefs: What is electromagnetic levitation?
Prof. Towfighian: Electrostatic levitation permits the charged electrodes to push apart rather than pull together. This is enabled using four electrodes, instead of two as in the conventional switch design.
Tech Briefs: What is possible, because of this new MEMS switch design? What kinds of cell phone applications?
Prof. Towfighian: Often we purchase cell phones, whose hardware does not work properly either immediately or after some time. Sometimes, the cause of these failures is because MEMS switches stop working properly because of their inherent limitations. These MEMS switches exist in wireless communication circuits inside a cell phone. Thanks to the new design, many of these failures can be avoided. That means facing fewer hardware problems and more cost saving.
Tech Briefs: Any other applications?
Prof. Towfighian: The other application of these switches can be in powerlines. When the voltage goes beyond a certain limit because of sudden events such as earthquakes or lightning, the proposed switch can immediately shut off the powerline before it causes any threat to the public safety.
Other applications of this mechanism can be in MEMS filters that are used for signal processing. The filters enable noise performance improvements in many devices such as radio or TV.
Tech Briefs: What’s next regarding this research?
Prof. Towfighian: We plan to operate these switches autonomously from mechanical shock or impact. This can be possible using triboelectric transducers that convert mechanical impact to electric voltages. This concept opens up possibilities for many safety switches such as those in airbag deployment devices. When they experience shock beyond a limit, the switch can trigger the airbag without any power source.
What do you think? Will electromagnetic levitation improve our cell phones and power lines? Share your comments and questions below.