Crystals for quartz resonators

This paper briefly describes the hydrothermal growth process and then discusses the important defects in quartz (twins, inclusions, dislocations, and impurities) and the correlations among them. The properties of quartz are reviewed and tabulated under the headings of intrinsic properties and defect-related properties. Resonator theory and fabrication techniques are outlined, with particular reference to aspects related to defects in the crystals. At this stage, it is possible to list the circuit design factors which must be taken into account when the application calls for very high performance. The paper then looks at the approach of a device maker faced with problems caused by impurities, inclusions, dislocations, and other nonideal properties of real crystals. This question leads to a specification of the crystals suitable for device use. The major parameter of this specification is the infrared $Q$, which must exceed about 1.8 million for satisfactory performance and yield. Acceptance test procedures are discussed, and finally the present state of the subject and the future prospects are briefly described.