IBM has reported the fabrication of a multi-stage RF receiver made using graphene, the monolayer form of carbon atoms packed in a honeycomb lattice that has been touted as potential replacement for silicon.
The mobility of electrons in graphene is about a factor of 40 higher than that of silicon-based structures partly because of quantum mechanical effects of containing the electrons within two dimensions. However, the monolayer nature of the material makes it prone to damage during IC fabrication.
IBM reported a previous graphene circuit, a frequency mixer, in June 2011 but that was a single graphene transistor integrated with two inductors. IBM reported a 2GHz frequency doubler RF circuit in a CMOS-compatible manufacturing process technology at International Electron Device Meeting, in December 2011.
And now the company has gone a stage further with the construction of an RF IC using three graphene transistors four inductors, two capacitors and two resistors. All the circuit components were monolithically integrated in 0.6 square millimeters fabricated on a 200mm silicon wafer production line, according to Shu-Jen Han of IBM Research, writing on the company's website.
The graphene IC has 10,000 times better performance than previously reported and the highest level of graphene integration and of silicon CMOS manufacturing compatibility so far, Han claims. The development is reported in a paper "Graphene Radio Frequency Receiver Integrated Circuit" authored by Han, Alberto Valdes Garcia, Satoshi Oida, Keith Jenkins and Wilfried Haensch, and published by Nature Communications.
Graphene operated at gigahertz frequencies has the potential to transmit and receive signals over greater distances and more energy efficiently than silicon equivalents Han said.
The circuit operates with multigigahertz carrier frequencies and consumes less than 20mW while demonstrating the highest conversion gain of any graphene RF circuit, Han said. It was used to receive the digital message I-B-M over a 4.3-GHz carrier.
IBM's approach construction of the circuit was broadly similar to that employed with the frequency doubler. Which was to invert the usual manufacturing process and define gate structures first on silicon/silicon-carbide wafers and then to transfer graphene layers fabricated using chemical vapor deposition to the silicon. After defining the areas of graphene IBM was able to attach source and drain contacts to the graphene to complete FET structures.
Han said that the latest demonstration highlights the potential to include graphene-on-silicon RF devices within low-cost silicon circuits to provide superior and pervasive wireless communications, allowing such things as smart sensors and RFID tags that send data over significant distances.
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