Orientation dependence of thermal conductivity in copper-graphene composites

Abstract

Copper and graphene multilayer films were deposited on a copper substrate. The surface of the multilayer film was covered with another film of copper by electrochemical deposition. An electrically insulating film of polymer followed by films of silicon and yttria-stabilized zirconia were deposited to isolate the sample electrically from a gold heater line deposited on the top. The three-omega method was used to determine the cross-plane thermal conductivity in the sample. The effective planar thermal conductivity in the sample was determined from two gold heater lines deposited adjacent to each other on the surface. The gradient of temperature between the heater lines was evaluated under steady state to determine the planar thermal conductivity. The results show that the cross-plane thermal conductivity in the copper-graphene layers is reduced as a result of the lower thermal conductivity normal to the graphene planes. The planar thermal conductivity in the copper-graphene layers was not reduced below that in copper. The interface thermal resistance between copper and graphene was evaluated from the planar thermal conductivity. The interface thermal resistance either in the cross plane direction or in the planar direction is found to be not a limiting factor for the improvement in the thermal conductivity in the copper-graphene composite films.