Transfer-free multi-layer graphene as a diffusion barrier.

Graphene is a promising ultra-thin barrier against undesired mass transport, however, the high deposition temperatures or the defect inducing post-deposition transfer processes limit its widespread applicability. Herein we report on the successful blocking of copper (Cu) ion diffusion by large area multi-layer graphene (MLG) membranes deposited directly on silicon oxide (SiO2) via low temperature plasma-enhanced chemical vapor deposition. The barrier strength of MLG is compared to evaporated tantalum (Ta) by applying positive bias-temperature stress (BTS) to Cu/barrier/SiO2/Si test structures. After constant BTS of 4 × 106 V cm-1 at 400 K for 50 min, the MLG barrier device exhibits a negligible flat band voltage shift in capacitance-voltage measurements and no discernible current peak in triangular voltage scans, whereas the Ta barrier allows significant Cu ion transport. Highly limited Cu ion diffusion through MLG suggests that lower energy diffusion paths, like grain boundaries and defects of individual graphene layers, do not align in the direction of an applied stress field. In general, the presented low-temperature direct growth MLG membranes can block undesirable diffusion in many applications, and are especially suitable as Cu diffusion barriers in integrated circuit chips, photovoltaic cells and flexible electronic devices.