Relay device retains memory

The nanorelay has been designed to operate as a memory device in high-temperature applications

Researchers at the University of Bristol, in the UK, have developed a new type of electromechanical nanodevice that can be used as a non-volatile memory in high-temperature power systems in EVs and aircraft (writes Nick Flaherty).

The leakage current in transistors used as electronic memory devices increases with temperature, so an electromechanical relay built on a micromachined silicon process has been developed to act as a memory that can retain its state when powered off.

“Part of the challenge is the way electromechanical relays operate,” said Dr Dinesh Pamunuwa, the project’s lead investigator at the university. “When actuated, a beam anchored at one end moves under an electrostatic force. As the beam moves, the air gap between the actuation electrode and beam is rapidly reduced while the capacitance increases.“

At a critical voltage, called the pull-in voltage, the electrostatic force becomes much greater than the opposing spring force, and the beam snaps in.

“This inherent electromechanical pull-in instability makes precise control of the moving beam – which is critical for non volatile operation – very difficult.”

The rotating nano relay design maintains a constant air gap as the beam moves, eliminating this electromechanical pull-in instability.

“The nano relay operates with an actuation voltage as low as 1.6 V with a 120 nm actuation airgap, and can be built using a standard low-cost CMOS process, making it suitable for use with high-temperature electronic systems.

The Bristol team, along with researchers at the University of Southampton in the UK and the Royal Institute of Technology in Sweden, showed that the nanorelay works over 42 cycles at 200 C and retained data for up to six months.

“This relay operation is a significant step forward in developing electronics for all-electric vehicles and energy efficient, more-electric aircraft,” said Dr Pamunuwa.

“Electronics built from nano relays instead of transistors can work at much higher temperatures while also having zero standby power. All digital electronic systems need logic and memory, and this device makes it easier to build relay based memory that retains the stored state when powered off.”