Memristors are basically a fourth class of passive electrical circuit, joining the resistor, the capacitor, and the inductor, which exhibit their unique properties primarily at the nanoscale and represent one of the most promising circuit elements for information storage and processing in future computing technologies. But one major problem with current memristors is their inability to perform effectively at extremely high temperatures, such as those in aircraft engine control systems or in wearable electronics for firefighters. Now a crack team of researchers, collaborating between the University of Massachusetts Amherst and Nanjing University in China, has created memristors that can function efficiently at temperatures far exceeding 300 degrees Centigrade.
The research team – led by Professor Feng Miao of the Physics Department at Nanjing University, Professor Joshua Yang of the Electrical and Computer Engineering Department at UMass Amherst, and Professor Peng Wang of the Engineering and Applied Sciences Department at Nanjing University – has just achieved memristors that can function above 300 degrees Centigrade, even after thousands of bending cycles.
The research team built and tested the groundbreaking memristors by using stacked, fully two-dimensional materials to form van der Waals heterostructures known as graphene/MoS2-xOx/graphene. The group has just published this work in Nature Electronics.
Memristive devices are electrical resistance switches that can alter their resistance based on the history of applied voltage and current. These devices can store and process information and offer several key performance characteristics that exceed conventional integrated circuit technology.
In a variety of situations, electronic devices need to be operated in harsh environments. For instance, aircraft engine control systems and drilling data acquisition systems are usually required to operate in high-temperature environments greater than 200 degrees Centigrade. Although the integration of a cooling system might be utilized under certain circumstances, it is not a solution for general applications.
As Yang explained, “Among various electronic devices, the memristor is considered as one of the most promising circuit elements for information storage and processing in future computing technologies. However, traditional memristors also face issues of robustness, especially at elevated temperatures encountered in a number of applications. Therefore, there is a strong demand for ultra-robust and high-performance memristors in harsh environments.”
These harsh performance requirements call for new materials to be adopted in memristors. Van der Waals heterostructures based on layered, two-dimensional materials offer great opportunities to build memristors from stacks of material with atomic precision by design. By combining the superior properties of each component in the stack, the heterostructure can provide possible solutions to address various challenges of electronic devices, especially those with vertical multilayered structures.
In this study, the team led by Miao and Yang developed robust memristors based on a van der Waals heterostructures of fully layered two-dimensional materials (graphene/MoS2-xOx/graphene), leading to unprecedented thermal stability lacking in traditional memristors.
For the first time anywhere, these new devices have been switched more than 10-million times at an operating temperature of up to 340 degrees Centigrade. “The operating temperature of 340 degrees Centigrade is a record-high for memristors, suggesting potential applications of such devices as high-density memory or computing units for high-temperature electronics,” Miao said.
Through careful microscopic studies, the team found that the switching layer in their device has an excellent thermal stability at temperatures up to 800 degrees Centigrade. “Compared with traditional amorphous metal-oxide switching layers used in previous memristors,” Miao said, “the layered crystal structure of the new memristor is considered to be responsible for the high thermal stability of the devices.”
In addition to the superior thermal stability, the two-dimensional-layer-based memristors also exhibit great mechanical flexibility if they are made on a flexible substrate. The device maintains its switching performance after being bent mechanically more than 1,000 times.
“Designing electronic devices with good flexibility and simultaneously high thermal stability is challenging because inorganic memristive materials usually lack mechanical flexibility, while organic memristive materials usually lack good thermal stability,” Yang said. “Fortunately, the two-dimensional memristive materials we utilized here have both.”
Yang concluded that “Memristive electronics with both high thermal stability and mechanical flexibility are highly valuable for many special applications, such as wearable electronics for fire fighters.” (February 2018)