A Program to Analyse the Origin of Noise in Ultra-Stable Quartz Crystal Resonators

In the mid 90s the quartz crystal oscillator attained a stability in the upper 10^-14 (flicker floor of the Allan deviation sigma_y(tau), which occurs at tau=1..10 s). As a matter of fact, the highest stability was obtained with bulk-acoustic-wave quartz crystal resonators at 5 MHz and at 10 MHz. Since, the research for higher stability seems to be at a standstill, while space applications are more and more demanding. FEMTO-ST Institute have started a research program on the origin of noise in 5 MHz and 10 MHz quartz crystal resonators, managed by The Centre National d´Etudes Spatiales (CNES). Several European manufacturers of high-stability resonators and oscillators participate. This article reports on the present status and on the future plans of this program. The first part consists in the analysis of the sensitivity of selected resonators to various externally-controlled parameters, like temperature, drive power, load impedance, series capacitance. The second part, planned, consists of listing the possible causes of noise, and of modeling their effects on frequency stability. Tests and measurements are mainly performed on an advanced phase noise measurement system, recently set up for this program. Of course, this program is a unique opportunity to test various batches of 5 MHz and 10 MHz resonators provided by the industrial partners.