The frequency of a quartz crystal is required to stay within specified tolerances over the operating temperature range and over a given period of time. This first property is called the temperature characteristic or T/C. The change in frequency versus time relation is commonly called aging.

Although many processes can be controlled in a manufacturing facility to improve aging, the driving force is cleanliness. By having clean facilities and handling techniques, the impurities which cause aging are kept to a minimum. Figure 3 shows the typical aging characteristics of resistance weld crystals. To insure that our crystals meet your aging specification, high temperature burn-in is used for pre-conditioning. If the aging tolerances required are more rigid than those illustrated in Figure 3, additional conditioning will be performed to meet tighter requirements.

In order to maintain the cleanliness needed for the best aging, VI CINOX crystals are assembled in a clean room. The best aging is accomplished with SC-cut crystals.

The graphs on the following page show the change in frequency with respect to temperature. The various curves are dependent on the angle at which the quartz is cut from the original crystal with respect to the crystallographic axes. By controlling the angle of cut and applying the correct tolerances, crystals can be produced which are within the required T/C tolerance over the range of operating temperatures.

The angle of cut is controlled by X-ray diffraction techniques with tolerances frequently being as tight as 1/4 minute of arc. Tolerances as loose as ± 2 minutes of arc are used in less demanding applications. Tolerances looser than this are rarely encountered by the manufacturers of precision crystals.

The curves following show that as the T/C requirements become tighter, the operating temperature range over which the T/C can be met is reduced. There is a compromise which must be made between T/C and temperature range. If this is unsatisfactory, other techniques can be used to meet wider temperature ranges and/or tighter tolerances.