Cryogenic monolithic sapphire-rutile temperature compensated resonator oscillator

We have tested a new temperature-compensated sapphire resonator as frequency determining element for high-stability microwave oscillator. Temperature compensation has been obtained by coating the sapphire resonator with a thin rutile film. A 2-µm rutile thickness is sufficient to reach turnover temperature higher than 40 K, and a 2 x 10-12 short-term frequency stability has been obtained.