Cut is the term applied to the orientation (rotation) of the wafer or blank in relation to one or more of the three crystallographic atomic axis of the quartz material. By adjusting the rotation of the blank around one or more of these axes, the frequency vs. temperature characteristic of the blank can be adjusted. The most common cuts used today for quartz crystals are AT, BT and SC.
AT & BT Cut quartz resonators are the most commonly used and they are shear-vibrators typically in a disk configuration. Frequency is adjusted by the thickness of the quartz disk and the temperature is adjusted by controlling the rotation/angle at which the disk is cleaved from the quartz bar in processing. For and AT cut, the frequency to thickness relationship can be approximated using the following equation.
Frequency (MHz.) = .0665 / Thickness (inches)
SC Cut resonators get their name from the term "Stress Compensated". An SC Cut crystal is especially resistant to any mechanical stresses placed on it. The temperature vs. frequency characteristics of an SC Cut resonator is determined by the rotation/angle of two of the three crystallographic atomic resonators or DRATS. DRATs are typically operated above ambient temperature in oven controlled crystal oscillators (OCXO) allowing them to exhibit very small frequency excursions over a narrow operating temperature range.
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