2D materials enable ‘first useful’ charge-density wave based device

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Researchers from the University of California, Riverside (UCR) and the University of Georgia have used three 2D materials – graphene, tantalum sulphide and boron nitride – to create a simple, compact and fast voltage controlled oscillator (VCO). According to the team, the part is the first useful device that exploits the potential of charge density waves to modulate an electrical current through a 2D material.

Apart from having the potential of being an ultralow power alternative to silicon based devices, the device is thin and flexible, making it suitable for use in wearable technologies.

Graphene’s potential has been limited by its inability to function as a semiconductor. To overcome this, the researchers added tantalum sulphide (TaS2), which has been shown to act as an electrical switch at room temperature. The researchers then coated TaS2 with hexagonal boron nitride to prevent oxidation. In the design, graphene functions as an integrated tunable load resistor, which enables precise voltage control of the current and VCO frequency.

Prototype devices are said to operate at MHz frequencies, but the team suggests that operational frequency could increase to the THz region.

“There are many charge-density wave materials that have interesting electrical switching properties,” said UCR’s Professor Alexander Balandin, who led the research team. “However, most reveal these properties at very low temperature only. The particular polytype of TaS2 that we used can have abrupt changes in resistance above room temperature. That made a crucial difference.”

Prof Balandin said the integrated system is the first example of a functional VCO comprising 2D materials that operates at room temperature.

“It is difficult to compete with silicon, which has been used and improved for the past 50 years. However, we believe our device … can potentially become a low-power alternative to conventional silicon technologies in many different applications,” he added.