Noise measurements of 10 MHz LGT crystal Oscillators

Our aim is to estimate the potential of LGT resonators to built oscillators of good stability in the short term domain. This objective needs two conditions: 1) The manufacturing of high Q-factor resonators with a process similar to that used for high stability quartz crystal resonators. 2) The realization of a scheme of an oven controlled oscillator specifically designed for these resonators. A batch of langatate (LGT) crystal resonators has been manufactured in our laboratory. A satisfying machining and polishing process is now ready. These resonators are optimized in terms of curvature radius and electrode diameter. They are available in an electrode-deposited version as well as in the electrodeless version, the so-called BVA structure. The energy trapping should still be optimized but here and now good quality factors, closed to 1.4 10⁶, are achieved for 10 MHz, 5th overtone resonators. Presently, their motional parameters are quite different from those of quartz crystal resonators. Classic topologies of quartz crystal oscillators are not well suited for LGT crystal resonators. Further, the high thermal sensitivity of LGT crystal resonators (parabolic f-T curve) requires a particular attention on the oven thermal stability. As a consequence, a specific oscillator topology has been designed for an appropriate use of these LGT crystal resonators. Resulting frequency stabilities are described in terms of Allan variance or power spectral density of frequency fluctuations.