Seoul National University Researchers Develop Graphene Solutions for Use with Photolithographic Techniques to Make Graphene Semiconductor Devices

Seoul National University (Seoul, KR) researchers have developed a method for manufacturing a graphene structure solution and a graphene semiconductor device using nano photolithographic techniques. A uniform graphene nanostructure solution is produced by applying anisotropic etching on multi-layered graphene using an oxide nanowire as a mask.
A graphene device is manufactured by dipping a substrate with a pattern of a molecule layer in a graphene nanostructure solution so that graphenes are aligned with the pattern on the substrate say inventors Biophysics and Chemical Biology, College of Natural Sciences  Professor Seunghun Hong and Koh Juntae in U.S. Patent 20100035186. The molecule layer pattern is formed by utilizing a photolithography process
Graphene shows stable characteristics and high electric mobility, and has accumulated considerable interest as a material for use in next generation semiconductor devices. However, in order to show semiconductor characteristics, the graphene is typically required to be formed as a channel having a nanoscale line width. This is because the graphene basically has a metallic characteristic.

Graphene nanostructures are typically synthesized in a form of a solution or powder. Therefore, in order to manufacture a device using a graphene nanostructure, a process of aligning a graphene nanostructure on a solid surface with a desired directivity is required.

Recently, in order to commercialize a device utilizing a graphene nanostructure, techniques for selectively adhering graphene nanostructures on a substrate at desired positions have been widely studied. Among them, a technique in which a solution with dispersed graphenes is spread on a silicon substrate so that graphenes may be adhered on the substrate is being studied.

However, when a nanoscale graphene device is manufactured using a graphene-dispersed solution according to conventional schemes, including the aforementioned schemes, it is difficult to fabricate devices having uniformly good characteristics since the nanostructure graphenes dispersed in the solution are not uniform in their widths. In addition, a technique that positions graphenes at desired positions for mass production has not yet been developed.

Techniques for manufacturing a graphene device and a graphene nanostructure solution were developed by Hong and Juntae to overcome the above problems. One of their methods of manufacturing a graphene nanostructure solution comprises: forming a target nanostructure on a multi-layered graphene; forming a multi-layered graphene nanostructure by performing anisotropic etching using the target nanostructure as a mask; and forming a solution having graphene nanostructures dispersed therein by dispersing the multi-layered graphene nanostructure in a dispersion solvent.
For a dispersion solvent o-dichlorobenzene is used. However, other materials such as 1,2-dichloroethane or poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) may also be used as dispersion solvent.
A hydrophilic molecule layer may help adhesion of the graphene nanostructure to the substrate by increasing affinity between them. In further detail, graphene nanostructures may be adhered to the hydrophilic molecule layer by applying a positive voltage to the substrate after forming the hydrophilic molecule layer in the region where the graphene is adhered.  
Aminopropyltriethoxysilane (APTES), 3-mercaptopropyl trimethoxysilane (MPTMS), etc., may be used for the hydrophilic molecule layer.

As shown in FIGS. 1(A) and 1(B), an oxide nanowire (20) having a diameter of several nanometers is adhered on a multi-layered graphene (10)  utilizing a van der Waals force. In the present example embodiment, highly oriented pyrolytic graphite (HOPG) that is currently commercially available is used as the multi-layered graphene that includes a plurality of graphene layers (11). 

A a van der Waals force is utilized to attach the oxide nanowire (20) to the graphene (10). However, it is notable that the oxide nanowire may be adhered to the graphene in various other ways, for example by utilizing an electrostatic force. A vanadium oxide nanowire, by way of example, may be used as the oxide nanowire. FIG. 2 is a flowchart that shows a method of manufacturing a dispersion solution of graphene nanostructure.