| AVS 61st International Symposium & Exhibition | |
| 2D Materials Focus Topic | Friday Sessions |
| Session 2D+EM+MS+NS-FrM |
| Session: | 2D Materials: Device Physics and Applications |
| Presenter: | Nick Thissen, Eindhoven University of Technology, Netherlands |
| Authors: | N.F.W. Thissen, Eindhoven University of Technology, Netherlands R.H.J. Vervuurt, Eindhoven University of Technology, Netherlands J.J.L. Mulders, FEI Electron Optics, Netherlands J.W. Weber, Eindhoven University of Technology, Netherlands A.J.M. Mackus, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands A.A. Bol, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Graphene device fabrication on large-area graphene typically involves several patterning steps using electron beam or optical lithography, followed by graphene etching and metallization for application of metallic contacts. However, the resist films and lift-off chemicals used in lithography introduce compatibility issues, such as the difficulty of removing the resist from the graphene. This resist residue has a negative influence on the thermal and electrical properties of the graphene and interferes with functionalization of the graphene. This motivates the development of a ‘bottom-up’, direct-write, lithography-free fabrication method.
In this work, a lithography-free fabrication method for graphene-based devices was developed. As a first step, the method involves direct patterning of large-area graphene by focused ion beam (FIB) in order to isolate graphene from the bulk. The patterning of the graphene is performed in a DualBeam (SEM / FIB) system, in which a 30 kV FIB is used to locally remove graphene from the substrate. An in situ Raman microscope allows for direct observation of the graphene quality before and after FIB processing, from which it was determined that a low Ga-ion dose of 10 C/m2 is sufficient for complete graphene removal. By optimizing the pattern design, the ion beam current and the background pressure in the DualBeam system, unintentional damage of the graphene by scattered ions is almost completely prevented.
After FIB patterning, as a second step a direct-write atomic layer deposition (ALD) technique is applied in the same system to locally deposit contacts to the isolated graphene. In the direct-write ALD technique, the patterning capability of electron beam induced deposition (EBID) is combined with the material quality of ALD. A thin seed layer consisting of small Pt grains in amorphous carbon is deposited on the graphene by EBID in the desired contact pattern. Subsequently, a selective ALD process purifies the seed layers and builds them into high-quality Pt contacts. This combined approach yields virtually 100% pure Pt (resistivity of 12 μΩcm) with a lateral resolution of 10 nm[1]. This chemical approach to contact deposition is expected to yield lower contact resistances compared to conventional physical deposition techniques.
By combining patterning and direct contact deposition in the same system, graphene devices were fabricated from large-area graphene without the use of lithography. First results from sub-optimal devices demonstrate field-effect mobilities approaching 500 cm2/Vs and contact resistances as low as (40 ± 30) Ω.
[1] A.J.M. Mackus et al., Nanoscale 4, 4477 (2012)