AT cut vs SC cut | difference between AT cut and SC cut of Quartz crystal

This page AT cut vs SC cut covers difference between quartz crystal AT cut and SC cut. This helps choose proper crystal cut for OCXO as per application.

About Quartz Crystal: This quartz based crystal devices are used as reference frequency oscillator source for frequency synthesizer as well as fixed local oscillators. Refer Quartz Crystal page for more information. There are different types of crystal cuts which have different performance characteristics. The crystal devices are used for various frequency control applications.

AT cut

AT cut

This AT cut type is used widely in the industry. It delivers good performance over wide temperature range as shown in the figure-2. The AT cut is made from Y bar at 35o theta rotation. The same has been shown in the figure-1.

As shown in the figure-2, AT cut is symmetrical around 25 degreeC(known as inflection temperature). Angles with good stability can be produced with temperature in the range from -55 degreeC to 125 degreeC.

SC cut

This SC cut type has double rotation and have been defined by theta of value 34.11 degrees and phi of value 21.93 degrees. The letters SC refers to "Stress Compensated". As quartz crystal is an-isotropic the stresses that have been observed in the AT cut will be reduced or eliminated using second rotation in phi direction.

SC cut will have inflection temperature of about 92 degreeC. Operating temperature of about 80 to 100 degreeC is needed for OCXO design.

Cutting method of operation in SC cut is difficult and need high labor cost. This is because of double rotations. Vacuum seal enclosures are also needed for this type of cut. It requires tighter calibration method.

Other crystal cut types

BT cut:
Angle from z axis is 49 degree. It has operating frequency range from 0.5 to 200 MHz. It is similar to AT cut type.
XY cut:
This crystal cut type is widely used for low frequency of operation. It has range from 5 to 100 KHz. One common frequency used is 32.768KHz as used in many of micro-controllers as clock reference source.
GT cut:
This type has angle of 51o 7'. It has frequency range from 0.1 to 2.5MHz.
IT cut:
It is similar to SC cut type. It has operating frequency range from 0.5 to 200 MHz.

Difference between AT cut and SC cut crystal

AT cut vs SC cut temperature performance

Following table mentions difference between AT cut and SC cut with respect to various performance parameters.

Specification AT cut SC cut
Temperature stability Good Best (<10PPB)
Aging Good Best (<2PPB/Day)
Drive level sensitivity Good Best
G-sensitivity Good Best
Frequency Over-shoot Good Best
Volume/Availability Best Good
Delivery/lead time Best Good
Cost Lower Higher
Q factor lower higher (it will achieve low phase noise)
Operating frequency About 0.5 to 300 MHz About 0.5 to 200 MHz
Mode of vibration Thickness shear Thickness shear

This page is very useful to choose cut type for OCXO design.

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