Low drive level sensitivity (DLS) of quartz crystal resonators

This work is a contribution to a better understanding of the DLS mechanism. The paper describes an experimental set-up allowing resonator´s motional parameter measurements with variable drive level as low as - 100 dBm in a controlled temperature enclosure. As the drive level becomes very low, measurement becomes more and more noisy and difficult to exploit. Specific experimental procedures and data processing required to improve the signal-to-noise ratio are described. Resistance vs. drive level curve of several crystals exhibiting DLS reveal different behaviours that have been investigated. Phase noise measurement of resonators exhibiting DLS by using a high performance interferometric instrument developed in our lab are currently being performed at the idea of answering the question of the correlation between the two phenomena. Eventually, by using a submicron resolution scanning electron microscope, a number of surface defects have been observed on the surface of the resonators exhibiting DLS. The responsibility of these defects for the DLS is discussed.