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Posted: Jun 09, 2011
Scientists build first wafer-scale graphene integrated circuit
(Nanowerk News) In a just-published work in the magazine Science ("Wafer-Scale Graphene Integrated Circuit"), IBM researchers announced the first integrated circuit fabricated from wafer-size graphene, and demonstrated a broadband frequency mixer operating at frequencies up to 10 gigahertz (10 billion cycles/second). This result opens up possibilities of achieving practical graphene technology with more high-performance, radio-frequency communication devices and is also a major milestone for the Carbon Electronics for RF Applications (CERA) program, funded by DARPA.
Graphene, the thinnest electronic material consisting of a single layer of carbon atoms packed in a honeycomb structure, possesses outstanding electrical, optical, mechanical and thermal properties that make it an ideal for a number of applications including high-frequency, flexible, and transparent electronics.
Despite significant scientific progress in the understanding of this novel material and the demonstration of high-performance graphene-based devices, the challenge of integrating graphene transistors with other components on a single chip had not been realized until now, mostly due to poor adhesion of graphene with metals and oxides and the lack of reliable fabrication schemes to yield reproducible devices and circuits.
Optical image of a completed graphene integrated circuit (IC) including contact pads. The probes for testing the circuit (P1-P4) are also shown. The scale bar is 100 µm.
This new integrated circuit, consisting of a graphene transistor and a pair of inductors compactly integrated on a silicon carbide (SiC) wafer, overcomes these design hurdles by developing wafer-scale fabrication procedures that maintain the quality of graphene and, at the same time, allow for its integration to other components in a complex circuitry.
How it Works
In this demonstration, graphene is synthesized by thermal annealing of SiC wafers to form uniform graphene layers on the surface of SiC. The fabrication of graphene circuits involves four layers of metal and two layers of oxide to form top-gated graphene transistor, on-chip inductors and interconnects.
The circuit operates as a broadband frequency mixer, which produces output signals with mixed frequencies (sum and difference) of the input signals. Mixers are fundamental components of many electronic communication systems. Frequency mixing up to 10 GHz and excellent thermal stability up to 125°C has been demonstrated with the graphene integrated circuit.
The fabrication scheme developed can also be applied to other types of graphene materials, including chemical vapor deposited (CVD) graphene films synthesized on metal films, and are also compatible with optical lithography for reduced cost and throughput.
Previously, the team has demonstrated standalone graphene transistors with a cut-off frequency as high as 100 GHz and 155 GHz for epitaxial and CVD graphene, for a gate length of 240 and 40 nm, respectively.