Journal Science -Electromechanical Computing at 500°C with Silicon Carbide the nanoelectromechanical system (NEMS) could be used in microcontrollers embedded in hot machinery such as jet engines or oil-drilling rigs.
Logic circuits capable of operating at high temperatures can alleviate expensive heat-sinking and thermal-management requirements of modern electronics and are enabling for advanced propulsion systems. Replacing existing complementary metal-oxide semiconductor field-effect transistors with silicon carbide (SiC) nanoelectromechanical system (NEMS) switches is a promising approach for low-power, high-performance logic operation at temperatures higher than 300°C, beyond the capability of conventional silicon technology. These switches are capable of achieving virtually zero off-state current, microwave operating frequencies, radiation hardness, and nanoscale dimensions. Here, we report a microfabricated electromechanical inverter with SiC complementary NEMS switches capable of operating at 500°C with ultralow leakage current.
At 550 °C Lee’s team managed to get the inverter to switch on and off 500,000 times a second – performing a computation with each cycle. The faster the switching speed, the zippier the computing. Lee predicts that switching speeds of a billion times a second (1 gigahertz) are possible.
To build its device, the team coated a silicon wafer with a thin layer of silicon oxide and then a 400 nm thick layer of SiC. The researchers then used electron beam lithography to make a simple switch comprising two SiC electrodes (the gate and drain) that are spanned by a SiC cantilever beam (the source). The SiC switch was released from the wafer by using a chemical to etch away the silicon oxide.
When a voltage was applied between the gate and source, the electrostatic force was found to pull the beam into contact with the drain (but not the gate). This allows current to flow between source and drain, making the device a NEMS field-effect transistor. Mehregany and colleagues were then able to make a NOT logic gate by combining two such switches.
The team operated the device at 500 °C at a frequency of 500 kHz and with logical input voltages of ±6 V. While this voltage is much higher than silicon logic devices – which work at 3 V or less – the NEMS logic of ±6 V is in line with other high-temperature devices, according to the team. And because the switching voltage is not an intrinsic property of the device – as it is in a semiconductor – the device’s voltage could in principle be further reduced by making the component switches smaller.
The team was able to operate a typical switch for about 21 billion cycles at room temperature before the cantilever beam fractured. At 500 °C, however, the switches only lasted about 2 billion cycles
By refining the design of the switch, it is possible to reduce the bending stress on the switch and as a result, improve the switch reliability and lifetime significantly. Lee believes that these and other improvements could result in devices that could deliver a trillion cycles of reliable operation at gigahertz speeds – which would exceed the speed and lifetime requirements of a typical microcontroller circuit.
In addition to boosting the performance of individual switches, the team is working on integrating the devices into more complex circuit elements such as an adder or register
Megahertz MEMS Oscillator Chip
SiTime Corp. has fielded what it says is the first kilohertz-range microelectromechanical system (MEMS) oscillator chip. The SiT8503 covers the 200-kHz to 1,000-kHz range with claimed five-decimal-place accuracy.
The SiT8503 runs on supply voltages of 1.8 to 3.3 V, can withstand shocks to 50,000 G and vibrations up to 70 G, has configurable frequency stability of +/–20 to +/–50 ppm and consumes 10 microamps in standby mode. Packages measure as small as 2.5 x 2 mm.