A team led by Roman Sordan of the Politecnico di Milano and Eric Pop of the University of Illinois says it has made the first integrated graphene oscillators – with the added bonus that the devices operate at 1.28 GHz. The graphene ring oscillators also appear to be less sensitive to fluctuations in the supply voltage compared with both conventional silicon CMOS devices and earlier oscillators made from the 2D materials.
The circuits are ring oscillators and the work could be an important step towards realizing all-graphene microwave circuits.
Ultimately it is expected that graphene will enable chips at terahertz operation.
ABSTRACT – Ring oscillators (ROs) are the most important class of circuits used to evaluate the performance limits of any digital technology. However, ROs based on low-dimensional nanomaterials (e.g., 1-D nanotubes, nanowires, 2-D MoS2) have so far exhibited limited performance due to low current drive or large parasitics. Here we demonstrate integrated ROs fabricated from wafer-scale graphene grown by chemical vapor deposition. The highest oscillation frequency was 1.28 GHz, while the largest output voltage swing was 0.57 V. Both values remain limited by parasitic capacitances in the circuit rather than intrinsic properties of the graphene transistor components, suggesting further improvements are possible. The fabricated ROs are the fastest realized in any low-dimensional nanomaterial to date and also the least sensitive to fluctuations in the supply voltage. They represent the first integrated graphene oscillators of any kind and can also be used in a wide range of applications in analog electronics. As a demonstration, we also realized the first stand-alone graphene mixers that do not require external oscillators for frequency conversion. The first gigahertz multitransistor graphene integrated circuits demonstrated here pave the way for application of graphene in high-speed digital and analog circuits in which high operating speed could be traded off against power consumption.
SOURCE – Physics World, ACS Nano
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