Crystal blank is present inside every quartz oscillator. It is the resonating element of the oscillator which starts to vibrate when a voltage is applied. The performance of the oscillators depends on the way the crystal blank is manufactured. One of the major steps in manufacturing crystal is the orientation of the quartz when once the crystal blank is cut. The internal structure can create various cuts of crystal blanks. Two common forms of cuts are AT cuts and SC cuts. In AT cut, the temperature coefficients of the internal structure of the crystal or lattice will have minimum impact on the performance of the crystal. Whereas, the SC-cut is a stress compensated. Whether to choose AT cuts or SC cuts depend on three factors.
Frequency vs. Temperature
It describes how the frequency output of the oscillator changes with temperature. The SC cut will have improved performance because of the slope of the curve near the crystal’s turning point, which is 1/3rd of the AT. It also performs well at increased temperature ranges.
It describes how the crystal’s frequency changes over the life of the crystal. Aging of the crystal takes place due to impurities within the oscillator. SC cuts are less sensitive to the aging effects of crystal blank plating stress, crystal mount stress, etc.
It describes how the frequency output of the oscillators is affected due to shock and vibration. As the quartz crystal is an electromechanical device, adding a vibration can cause the characteristics of the electrical output to change.
You must consider these factors when choosing the type of cut for your crystal oscillator. Whichever type of cut you want must improve the performance of your oscillator.