Researchers from the University of California, Riverside (UCR) and the University of Georgia have made use of three 2D materials – graphene, tantalum sulphide and boron nitrate – to create a simple, compact and fast voltage controlled oscillator (VCO). According to the team, this 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. But graphene’s potential has been limited by its inability to function as a semiconductor, and the researchers attempted to overcome this by adding tantalum sulphide (TaS2), which has been shown to act as an electrical switch at room temperature. The researchers then coated TaS2 with hexagonal boron nitrate 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. Also, the team said that “There are many charge-density wave materials that have interesting electrical switching properties; 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”. The integrated system is said to be the first example of a functional VCO comprising 2D materials that operates at room temperature.