[Paper Review] A breakthrough toward wafer-size epitaxial graphene transfer

Ayako Hashimoto, Hiromitsu Terasaki+3 more|arXiv (Cornell University)|May 26, 2010

Graphene research and applications3 citations

TL;DR

This paper presents a novel transfer technique for wafer-scale epitaxial graphene grown on SiC substrates, using a titanium (Ti) capping layer deposited via electron-beam evaporation to enable large-area exfoliation and transfer onto SiO2/Si substrates. Raman spectroscopy and low-energy electron microscopy confirm successful transfer of monolayer and bilayer graphene with high quality, marking a critical step toward scalable graphene electronics beyond CMOS.

ABSTRACT

The formation of graphene on any desirable substrate is extremely essential for the successful replacement of Si with graphene in all technological applications in the beyond-CMOS era. Recently, we observed that a Ti layer formed on epitaxial graphene by electron-beam evaporation has the sufficiently large area of contact with the surface of epitaxial graphene for the exfoliation process to take place. We also observed that the exfoliated FLG on the Ti layer can be easily transferred onto a SiO2/Si substrate. In this paper, we have proposed a new technique for transferring graphene having a large area of several square mm from the graphitized vicinal SiC substrate. Raman scattering spectroscopy and low-energy electron microscopy analysis have revealed that we can transfer mono-layer and bi-layer graphene onto the SiO2/Si substrate by using the proposed transfer process. The initial size of epitaxial graphene formed on the SiC substrate is the only limitation of the new transfer process. The transfer process is expected to become an extremely important technology that will mark the beginning of a new era in the field of graphene electronics.

Motivation & Objective

• To develop a scalable method for transferring large-area epitaxial graphene from SiC substrates to arbitrary substrates for device integration.
• To overcome the challenge of transferring graphene without damaging its structure or electronic properties.
• To enable the use of epitaxial graphene in practical electronic devices by facilitating reliable, large-area transfer.
• To demonstrate the feasibility of transferring graphene with minimal defects using a Ti interlayer.

Proposed method

• A titanium (Ti) layer is deposited via electron-beam evaporation onto epitaxial graphene grown on vicinal 4H-SiC substrates.
• The Ti layer forms a strong interfacial contact with the graphene surface, enabling mechanical exfoliation of the graphene-Ti stack from the SiC substrate.
• The exfoliated graphene-Ti stack is then transferred onto a SiO2/Si substrate using a polymer-assisted transfer process.
• The Ti layer is subsequently removed via wet etching, leaving free-standing graphene on the target SiO2/Si substrate.
• Raman spectroscopy and low-energy electron microscopy are used to characterize the transferred graphene's layer count and structural quality.
• The process is scalable, limited only by the initial size of the epitaxial graphene on SiC.

Experimental results

Research questions

• RQ1 Can a Ti capping layer enable large-area, damage-free exfoliation and transfer of epitaxial graphene from SiC substrates?
• RQ2 What is the quality of transferred monolayer and bilayer graphene after transfer to SiO2/Si substrates?
• RQ3 Can the transfer process be scaled to wafer-level dimensions while preserving graphene's electronic properties?
• RQ4 How does the interfacial adhesion between Ti and graphene influence the exfoliation efficiency?

Key findings

• The Ti capping layer enables effective exfoliation of epitaxial graphene from SiC substrates due to strong interfacial contact.
• Monolayer and bilayer graphene were successfully transferred onto SiO2/Si substrates with high structural integrity.
• Raman spectroscopy confirmed the presence of single- and few-layer graphene with minimal defects after transfer.
• Low-energy electron microscopy verified the uniformity and crystallinity of the transferred graphene layers.
• The transfer process is scalable and limited only by the initial size of the epitaxial graphene on SiC.
• The method represents a significant advancement toward wafer-scale integration of epitaxial graphene in electronics.