Graphene as a Diffusion Barrier in Galinstan-Solid Metal Contacts

Abstract

Abstract-This report presents the use of graphene as a diffusion barrier to a eutectic Ga-In-Sn alloy, i.e., galinstan, for electrical contacts in electronics. Galinstan is known to be incompatible with many conventional metals used for electrical contacts. When galinstan is in direct contact with Al thin films, Al is readily dissolved leading to the formation of Al oxides present on the surface of the galinstan droplets. This reaction is monitored ex-situ using several material analysis methods as well as in-situ using a simple circuit to follow the time-dependent resistance variation. In the presence of a multilayer graphene diffusion barrier, the Al-galinstan reaction is effectively prevented for galinstan deposited by means of drop casting. When deposited by spray coating, the high impact momentum of the galinstan droplets causes damage to the multilayer graphene and the Al-galinstan reaction is observed at some defective spots. Nonetheless, the graphene barrier is likely to block the formation of Al oxides at the Al/galinstan interface leading to a stable electrical current in the test circuit.

Review of Graphene as a Solid State Diffusion Barrier

“…Graphene has been reported as a diffusion barrier on eutectic Ga–In–Sn alloys . This alloy reacts with Al, Ni, and Pt even at room temperature and, when it is in direct contact with the Al thin films common in microelectronics, the Al decomposes into Al oxides.…”

“…This alloy reacts with Al, Ni, and Pt even at room temperature and, when it is in direct contact with the Al thin films common in microelectronics, the Al decomposes into Al oxides. Figure shows that the presence of a 4‐layer graphene interlayer significantly reduces the reaction of the Ga–In–Sn with Al and provides an effective diffusion barrier to this alloy …”

“…c) Schematic illustration of the galinstan deposited on the Al thin film, with the interlayer of 4‐layer SLG stack represented by a solid back bold line by means of spray coating where the part of graphene under the galinstan is partially damaged, which is represented by the dashed bold line (left) and the subsequent dissolution of Al in the galinstan where no Al‐oxide layer forms at the interface (right). Reproduced with permission . Copyright 2009, IEEE.…”

Sliding Interconnection for Flexible Electronics with a Solution‐Processed Diffusion Barrier against a Corrosive Liquid Metal

“…[34,35] However, the imperfect structural integrity of a graphene layer usually allows the infiltration of a liquid metal, eventually destroying the underlying metallic layer. [36] As for now, the seamlessly formed thin nickel layer is known to effectively stop the penetration of gallium [37] but it necessitates an environmentally hazardous electroplating process.…”

A Low-Cost Fluid Switch for Frequency-Reconfigurable Vivaldi Antenna

“…In RF fluid research, the most popular fluid antenna systems use fluids like EGaIn [9] or Galinstan [10]. However, these materials react when in contact with many conventional metals such as Al, Ni, and Pt at room temperature [11]. Furthermore, these are expensive materials that are not suitable for low-cost systems.…”