Graphene-based Crack-Free Ceramic Coatings for High-Performance Passive RF Devices

Abstract: Dielectric resonators coated with highly conductive metallic layers are widely used in radio frequency (RF) applications. The quality factor (Q-factor) of resonators is a key figure-of-merit that describes the loss and the energy efficiency of the resonators. Significant advances in minimizing losses of dielectric materials and enhancing conductivity of metal coatings have been made in the past decades. Hence, this project puts more emphasis on the relationship between the surface roughness of the resonators and their Q-factors. Through adding a TiO2/graphene intermediate layer between the resonator substrate and the conductive silver coating, there is an obvious improvement in the surface smoothness of the resonator samples. The surface roughness level has been reduced for 54.4%. The Vector Network Analyzer (VNA) test results also show an increase in its Q-factor of 11.5% around the resonator fundamental resonance frequency of 3.8 GHz. The graphene was mainly designed to reduce the number and scale of cracks in the TiO2 layer during the annealing and cooling process. The results show the potential to enhance the Q-factor of dielectric resonators at high frequencies by reducing the surface roughness. However, there are still some problems that need to be solved in future research. The adhesion condition of the silver coating needs to be improved. The contact resistance in the test process can be reduced. And the defective rate should also be reduced. These problems exist in this project, but the theoretical prediction is able to be basically proven by the test results.