Fundamental Studies of Aging in Quartz Resonators

Absfracf-A study of the effects of impurities in quartz, along with an examination of the role of sorption phenomena and thermally-induced strains, is directed toward the goal of a nonaging quartz crystal, Le., the production of a crystal unit whose frequency change with time is less than its short time stability of a few parts in 10. A fundamental approach has been adopted, consisting of the separation and measurement, as far as possible, of each factor contributing to frequency change. The methods of the kinetic theory of rate processes have been applied to assist in the evaluation and identification of the various processes responsible for frequency aging. Studies of frequency change related to the adsorption and desorption of mass have been carried out in an environmental test chamber using methods capable of resolving mass changes of 10 pg/cm2. Frequency changes associated with thermally-induced strain have been reduced by the use of special parallel-field electrodes. Evidence of the role of impurities, particularly alkali ions, in the change of the frequency determining parameters of the quartz material is presented, and the role of ionizing radiation and of water vapor is discussed. The significance of the results obtained so far are discussed, and the indicated approach to an optimum crystal unit design is presented.