Mechanical and electrical characterization of CVD-grown graphene transferred on chalcogenide Ge2Sb2Te5 layers.

Non volatile memories based on Phase Change Materials, e. g. Ge2Sb2Te5 .are considered possible candidates in the present market scenario. The Extreme Ultraviolet Lithography (EUVL) technology, actually, allows to scale the memory device structures in the node of 18-20 nm. The capability of increasing the bits in the storage devices is one of the most important requests of the market for Non-Volatile Memory that remains one of key product segment for the mass production. The scaling possibilities of PCM must be coupled to the need of increasing the device characteristics also in the terms of power performances. The reduction in power consumption for each bit transcription implies also a reduction of the power losses. In the present work we investigate the physical properties of the mechanically transferred CVD-grown graphene layer on 50 nm thick Ge2Sb2Te5 and the possible utilization of graphene as scaled contact. Different authors [1-2] showed that carbon nanotubes and carbon nanoribbons can be used as electric contacts in a planar PCM with a relevant reduction in Joule losses. Moreover, it was shown [3] that the interposition of a graphene layer between the PCM active material and the metallic via increases the thermal confinement, due to the weak van der Waals interactions at the interface [4-5], thus reducing the programming current. Here we reported the mechanical and electrical characterization of CVD-grown graphene transferred on Chalcogenide Ge2Sb2Te5. The graphene layer was synthesized by C-CVD technique using a Cu foil as catalyst and it was then transferred on the GST layer by standard Cu foil wet-etching and subsequent release of the polymer-supported graphene layer. The physical characterizations show a multi domain nature of the graphene grown and transferred on chalcogenide layer. The bonding forces between the graphene and GST layer in a complete multilayer stack, namely Ni/Au layer - CVD graphene – GST layer, were characterized using the Nano-scratch Tester (CSM instruments). Every sample was tested with the CSM equipment setting a progressive linear scratch using an initial load of 0.05 mN and ending with a load of 11 mN. The indentation and the scratches was performed using a diamond spherical tip with a radius 1 μm. The electrical contact resistance of the same type of complete multilayers was investigated using the Circular Transmission Line Method (CTLM).The preliminary physical and electrical characterizations indicate the possible advantages of graphene utilization as contacts.