Graphene passivation effect on copper cavity resonator preserves Q-factor

Proposed resonator design and measurement technique is a promising solution to estimate the value of materials surface conductivity. In the developed device, there are no mechanical connections, that interrupt the flowing microwave currents, which eliminates losses due to poor metal contact and related measurement errors. The main losses (60%) in the resonator are concentrated in a small sample under study - resonance element sample, which ensures high sensitivity to changes in surface conductivity. The influence of annealing the copper cavity resonator surface conducting microwave currents, as well as the effect of graphene coating on its intrinsic quality factor and frequency, was experimentally studied. Technological procedures for modifying a copper surface such as annealing in an H₂/Ar atmosphere at a temperature of 1070 °C and subsequent coating with graphene by chemical vapor deposition method are studied. The modification of copper resonator surface texture during heat treatment in hydrogen and argon atmospheres has been studied. It is shown that during annealing, the resonator quality factor increases. The increase of the quality factor was associated with a decrease of resistance of copper, with the growth of crystalline grains, this effect disappears when the resonator is exposed to an air atmosphere. It was found that the graphene coating does not make a significant contribution to the change in the quality factor, but prevents the active growth of the oxide layer and prevents impurities deposition on the copper surface from the atmosphere. Thus, after annealing in hydrogen atmosphere and subsequent coating with graphene, the increased quality factor is retained. The considered procedures can be used to increase and stabilize the resonators quality factor, to eliminate oxidation and contamination of their surface. The results of this work can be used in the designing of microwave devices to study the thin films surface impedance.