Graphensic AB is producing electronic grade graphene and related products

Graphene is a crystal plane built up of carbon (C) atoms with sp2 bonding in a honeycomb lattice in which carbon participates with three in-plane bonds while the forth one is unsaturated bond in the perpendicular direction. This crystal structure is responsible for the unique properties of graphene.

Graphene on SiC has attracted much interest owing to its potential as a viable candidate for electronic applications and sensors. Since it is epitaxially grown it possesses high quality crystal structure without grain boundaries while can be grown on an area as large as the SiC wafer (150 mm available on the SiC market presently).

On axis SiC wafers have two inequivalent faces: Si terminated and C terminated one. The general process conditions of thermal decomposition can be applied to both faces but the growth mechanism is proven to be epitaxial only on the Si face.

Graphensic AB is using patent protected process for epitaxial graphene growth on SiC. The process is realized in radio frequency inductively heated chamber in which a graphite crucible is placed. The graphene sample is mounted inside the crucible (Fig. 1). The graphene growth takes place at a temperature of 2000oC and argon atmosphere. When the temperature is raised above 1400oC, due to the thermodynamics of SiC, Si will sublimate leaving carbon atoms behind. They will move around via surface diffusion and will finally rearrange in a pattern that is given by an energetically driven surface reconstruction. The resulting lattice constant is commensurate to that of graphene and therefore it is said that graphene grows epitaxially. This has been confirmed only for graphene grown on the Si face of SiC. The reconstructed layer is called “buffer layer” or “zero layer”. Upon further heating the buffer layer converts to a true single layer graphene and more layers can be produced by adjusting the process conditions. Schematic illustration of graphene formation is presented in Fig. 2. Graphene area can be from 5×5 mm2 and up to a 4 inch wafer. Graphensic can provide graphene on all three SiC polytypes: 4H, 6H and 3C.

Fig. 1 Graphene growth set-up

Fig. 2 Schematics of graphene formation on SiC