Temperature Compensated Sapphire-Rutile Microwave Whispering Gallery Mode Resonator

A 2 µm-thick film of rutile (TiO2) was deposited on a sapphire disk using a sol gel method to realize a temperature compensated microwave resonator operating in whispering gallery mode configuration. The resonator, though not yet completely optimised, shows turnover temperatures rangin from 40 to 60K depending on the mode azimutal number. For the WGH(7,0,0) mode at 9.4 GHz, the Q-factor is of the order of 1.5 e6 at 46K. The technique appears easy to implement and can be used for the design of high-frequency stability microwave source.