AT Cut vs. SC Cut Quartz Crystals: Key Differences Explained

This page explains the differences between AT cut and SC cut quartz crystals, helping you choose the right crystal cut for applications like Oven Controlled Crystal Oscillators (OCXOs).

About Quartz Crystals

Quartz-based crystal devices serve as reference frequency oscillator sources for frequency synthesizers and fixed local oscillators.

AT Cut Crystal

AT cut image

The AT cut is a widely used type in the industry. As illustrated in Figure 2 (not provided here, but presumably a graph), it delivers good performance over a broad temperature range.

The AT cut is derived from a Y-bar with a 35° theta rotation, as depicted in Figure 1 (again, not provided). It exhibits symmetrical behavior around 25°C, known as the inflection temperature. With precise angle adjustments, good stability can be achieved across a temperature range from -55°C to 125°C.

SC Cut Crystal

This SC cut type utilizes double rotation, defined by a theta value of 34.11 degrees and a phi value of 21.93 degrees.

The letters “SC” stand for “Stress Compensated.” Since quartz crystal is anisotropic, the stresses observed in the AT cut are reduced or eliminated through the second rotation in the phi direction.

The SC cut has an inflection temperature around 92°C. An operating temperature of approximately 80 to 100°C is required for OCXO designs. The cutting method for SC cuts is complex and results in higher labor costs due to the double rotations. Vacuum-sealed enclosures are also necessary. Furthermore, SC cuts necessitate a more rigorous calibration process.

Other Crystal Cut Types

• BT Cut: Angle from the Z-axis is 49 degrees. It operates in the frequency range of 0.5 to 200 MHz and is similar to the AT cut.
• XY Cut: Widely used for low-frequency applications, ranging from 5 to 100 KHz. A common frequency is 32.768 KHz, often used as a clock reference in microcontrollers.
• GT Cut: This type has an angle of 51° 7’. Its frequency range is from 0.1 to 2.5MHz.
• IT Cut: Similar to the SC cut, with an operating frequency range from 0.5 to 200 MHz.

AT Cut vs. SC Cut: Temperature Performance

AT cut vs SC cut temperature performance

Comparison Table: AT Cut vs. SC Cut

The following table highlights the differences between AT cut and SC cut crystals concerning various performance parameters:

This information is valuable when choosing a crystal cut for OCXO design.