Quartz Crystal Cuts: Angles and Properties (AT, BT, etc.)

Many quartz crystal-based products are chosen according to the required electrical values of the design or the known properties of an existing product. Frequency is the most critical element, but stability, load capacitance, tolerance, ESR, etc., may also be factors.

If these values are known, then the Digi-key search filters are useful. For example, the keyword “crystal” can be searched from the Digi-key home page [click here https://www.digikey.com/ ], Product Index > Crystals, Oscillators, Resonators > Crystals > “Crystals”, or go directly to the main category where those are found [click here https://www.digikey.com/en/products/filter/crystals/171 ]. From that point, values may be selected from the filter titles.

In some cases, though, there may only be partial electrical values known, or the crystal is described using a short label such as “AT”, “BT”, “SC”, etc., or any of these along with the word “Cut” as in “AT Cut”. That label is not currently searchable on our site, so it helps to understand what this short description indicates for a crystal product.

Example:

These Silicon Dioxide (SiO2) quartz crystals are anisotropic. Anisotropy is the property that allows for variations in physical behavior along different molecular axes of the substance. In the drawing below, for example, a quartz crystal exhibits different properties when viewed from, or energy is applied to, any one of the three axes.

Crystal3Axes

Because the quartz crystal has a predictable, ordered structure, the effects of different angles of cuts other than the direct axes can be predetermined. This would not be possible in an amorphous structure such as common glass where no semblance of molecular order exists. In that case, the properties are the same in all directions (isotropic).

The properties that are relevant to quartz crystals are piezoelectricity, dielectricity, and elasticity, and these in turn are relevant to the electric dipole along the silicon axis within a SiO2 crystal. Thus, cutting the quartz bar at different angles results in different orientations of the SiO2 dipole. This, in turn, is what gives the different quartz cuts their inherent properties. A graphical representation of the piezoelectric effect is shown below.

The full effects of every type of quartz cut is a complex matter—an area of research that is not yet static—so the scope of this article is to simply establish the connection between the crystal cut label (AT, BT, CT, etc.) and the properties of the crystal. Many examples of these angled cuts are shown in the following diagram.

CrystalCutAngles.PNG

Using various reference materials, some crystal products might be included or excluded from qualifying as a particular cut type. A guide to the frequency range is helpful in that regard since some cuts are used for the kilohertz range and others are used for the megahertz range. Sites may vary slightly on the reported frequency range, but they will still be useful.

For example, a basic list such as that shown below would separate some of the products on our site.

AT = 0.5 – 300 MHz
BT = 0.5 – 200 MHz
CT = 300 – 900 kHz
DT = 75 – 800 kHz

The previous information answers the most basic question of whether or not a specific crystal cut is available on the Digi-key site. The answer is ‘maybe’, but that label plus many other crystal features are not searchable with the filters that are in place. If the actual cut of a particular crystal (part number or series) must be verified, or if the question is regarding the availability of a specific cut, it is best to check the manufacturer’s documentation or contact them directly.

Further Reading/References and Guides:

Epson Technical Info – Crystal: [click here https://www5.epsondevice.com/en/information/technical_info/crystal/ ]

TXC Corporation – Technical Terminology: [click here http://www.txccrystal.com/term.html#03 ]

Jauch Quartz – It’s All About the Angle: [click here https://www.jauch.com/blog/en/its-all-about-the-angle-the-at-cut-for-quartz-crystals/ ].

Find quartz crystals and related products in the links, below:

[Main] Crystals, Oscillators, Resonators: [click here https://www.digikey.com/en/products/category/crystals-oscillators-resonators/12 ]

Crsytals: [click here https://www.digikey.com/en/products/filter/crystals/171 ]. Product Index > Crystals, Oscillators, Resonators > Crystals

Oscillators: [click here https://www.digikey.com/en/products/filter/oscillators/172 ]. Product Index > Crystals, Oscillators, Resonators > Oscillators

Resonators: [click here https://www.digikey.com/en/products/filter/resonators/174 ]. Product Index > Crystals, Oscillators, Resonators > Resonators

VCOs (Voltage Controlled Oscillators): [click here https://www.digikey.com/en/products/filter/vcos-voltage-controlled-oscillators/173 ]. Product Index > Crystals, Oscillators, Resonators > VCOs (Voltage Controlled Oscillators)

1 Like