TPT July 2020

G LOBA L MARKE T P L AC E

G LOBA L MARKE T P L AC E

standby power,” Dr Pamunuwa said. “Any digital electronic system needs logic and memory and this relay makes it easier to build relay-based memory that retains the stored state when powered off, by using stiction [the friction which tends to prevent stationary surfaces from being set in motion]. Maintaining a constant air gap as the relay switches allows very precise electrostatic control, and greatly improves reliability.” The relays were designed by Dr Sunil Rana and nanoscale prototypes were fabricated by Dr Joao Mouro, both senior postdoctoral researchers in the microelectronics group at Bristol. Dr Jamie Reynolds, a senior postdoctoral researcher at the University of Southampton carried out contact material deposition, testing and characterisation under the supervision of Professor Harold Chong. Microscale prototypes were fabricated by Dr Simon Bleiker of the Royal Institute of Technology under the supervision of Professor Frank Niklaus. Sourcing power in the shadows Solar panels need precision placing to receive maximum sunlight, and to prevent one panel from shading another; this limits the number of panels in a given area and, as a consequence, the amount of power generated. However, a recent paper from Q Zhang et al, writing in Energy & Environmental Science, reports a device capable of generating energy in shadowy areas where solar cells are ineffective, potentially even inside the home or office. Swee Ching Tan, and his colleagues from the National University of Singapore, have developed a device that can harvest energy, even when considerably shaded. Mr Tan said: “To make this device is much cheaper and easier than silicon solar cells. [Our device] only needs a piece of silicon substrate coated with a thin piece of [gold] metal film.” The device could boost power generation indoors, as well as on solar farms, as the device is sensitive in shadows cast by even low light intensities. The team has demonstrated that optical illumination contrasts create work function contrasts on metal films coated onto a semiconductor (silicon, in this case). Tan explained that, due to this work function contrast, “electrons can flow from the light region into the dark region, as they are being generated, in the silicon substrate”. Connecting this generator with an external circuit will convert the flow of electrons into electrical power. Each cell contains a gold film deposited on a silicon wafer. Several cells of the same size are arranged on a flexible and

Research Developing electronics for the highest efficiency in electric vehicles and aircraft Researchers at the UK’s University of Bristol have developed a new type of nanoelectromechanical relay to enable high temperature, non-volatile memory. The work, which was reported in Nature Communications, was carried out in collaboration with the UK’s University of Southampton and the Royal Institute of Technology, Sweden. The devices could prove an important development for all- electric vehicles and more-electric aircraft, both of which demand energy-efficient electronics with integrated data storage capable of operating in extreme temperatures. Transistor leakage current increases with temperature, and nanoelectromechanical relays have emerged as a possible alternative to transistors for these applications. However, until now, a reliable and scalable non-volatile relay to implement memory, but that retains its state when powered off, has not been available. “Part of the challenge is the way electromechanical relays operate; when actuated, a beam anchored at one end moves under an electrostatic force,” explained Dr Dinesh Pamunuwa, lead investigator of the Microelectronics research group at the University of Bristol. “As the beam moves the air gap between the actuation electrode and beam rapidly reduces, 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, critical for non-volatile operation, very difficult.” Now, Dr Pamunuwa’s team has demonstrated a rotational relay that maintains a constant air gap as the beam moves, eliminating the electromechanical pull-in instability. Using this relay, they have successfully demonstrated the first high temperature non-volatile nanoelectromechanical relay operation at 200°C. Dr Pamunuwa describes the discovery as “…a truly exciting development, as the need to develop technology that reduces our dependency on fossil fuels increases.” It could mark a significant stride toward developing electronics for all-electric vehicles and energy-efficient more-electric aircraft and for creating zero-standby power intelligent nodes for the IoT. “Electronics built from nano relays instead of transistors can work at much higher temperatures, while also having zero

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JULY 2020