High-purity quartz crystal blank (cultured quartz for resonators)

01

Set the cultured quartz grade

Sawyer's general material specification covers single-crystal cultured quartz bars for piezoelectric elements in timing, frequency control and frequency selection. It grades material Q through infrared alpha (α₃₅₀₀ = (1/t) log(T₃₈₀₀/T₃₅₀₀), measured by FTIR on a Y-cut slice from the largest bar of each autoclave run) with the correlation 10⁶/Q = 0.114 + 7.47α − 0.45α²: IEC grade C (electronic) at α 0.060 for Q 1.8 × 10⁶, grade B (premium Q) at 0.045 for 2.2 × 10⁶ and grade A (special premium Q) at 0.033 for 3.0 × 10⁶. [1]

It grades inclusions into IEC grades Ib, I and II by their count and size in a sampled volume, and dislocations by etch channel density on an etched AT-cut slice (IEC grade 1 ≤ 10, 2 ≤ 30, 3 ≤ 100, 4 ≤ 300 per cm²), requires freedom from electrical and optical twinning, cracks and gross imperfections in the useful volume, and supplies right-handed quartz unless otherwise specified; it notes that swept quartz needs ultra-low inclusion density so sweeping does not start cracks. [1] Sawyer lists high-Q quartz (minimum Q ≥ 3.0 million), low etch channel quartz (≤ 10/cm² before sweeping) and swept quartz for radiation hardness and etch processing. [3]

Editorial calculation: for grade B, 0.114 + 7.47 × 0.045 − 0.45 × 0.045² ≈ 0.450, so Q ≈ 10⁶ ÷ 0.450 ≈ 2.2 × 10⁶, matching the table. [1]

Give the supplier the quartz grade (IEC alpha/Q, inclusion and etch channel grades), handedness, swept or unswept, the cut and angle with tolerance, blank shape and dimensions (diameter or rectangle, thickness or target frequency), flatness, parallelism and surface finish, edge treatment, inspection and sampling plan, packaging and quantity.

02

Fix orientation, cut and dimensions

For lumbered bars, Sawyer's specification sets X and Z dimension tolerances of ±0.13 mm, seed centring within a 3.0 mm band, orientation verified by X-ray diffraction before and after lumbering, and a maximum deviation of ±15′ on the minus-X reference surface (and on the Z surfaces for seed-free bars, ±1° for seed-centred bars), with the reference surface flat within 0.1 mm so that all but the principal wafer-cutting angle is set by that surface; properties are verified by sampling to MIL-STD-1055D and it cites IEC 758. [1]

Sawyer's hydrothermal growth note describes quartz grown on seed crystals in steel autoclaves from a nutrient of natural quartz in an alkali hydroxide or carbonate solution, at operating conditions between 300 and 400 °C, with the temperature difference between dissolving and growing chambers as the chief control of growth rate, and lithium added at 0.01–0.10 mol/L. [2] It also lists lumbered bar stock for doubly rotated cuts and seed-free bars with Z = 10–28 mm and X = 100 mm. [3]

Editorial note: the blank's cut angle, thickness and diameter follow from the resonator design — frequency, overtone and temperature behaviour — so give the supplier the resonator target as well as the blank drawing. [1]

03

Work out blank thickness and contour from frequency

US patent 4,124,809 A, filed in 1972 by the Swiss watch group SSIH, summarises how a thickness-shear blank is cut and sized. Rotating the cut about the X-axis by +35° (AT-cut) or −49° (BT-cut) reduces, and at certain temperatures nullifies, the thermal coefficients of frequency. For the AT-cut the frequency constant K is about 1,670 kHz per mm and the fundamental-mode range is about 1–20 MHz; blank thickness is K divided by the desired frequency. The BT-cut constant is about 2,550 kHz per mm. For circular blanks of a set diameter, the patent gives a bi-convex contour for 1–3 MHz, plano-convex for 3–10 MHz and plane-parallel above 10 MHz, and notes that low-frequency units perform poorly unless a minimum diameter-to-thickness ratio is kept; central electrodes trap the vibration energy so it decays towards the edge. [4]

Editorial calculation from K ≈ 1,670 kHz·mm: an AT-cut fundamental blank is about 1.67 mm thick at 1 MHz, 0.167 mm at 10 MHz and 0.0835 mm at 20 MHz; a BT-cut blank at 10 MHz is about 0.255 mm, about 1.5 times the AT-cut thickness. Final thickness is set by the resonator maker's frequency adjustment, so give the blank supplier the target frequency, overtone and tolerance rather than a thickness alone. [4]

Editorial note: confirm the cut angle tolerance, contour (bevel or convex radius) and diameter on the blank drawing, and that the bar orientation report from the quartz supplier covers the angle you need. [4] [1]

04

Compare what suppliers offer

The companies in the manufacturer list below show this product on their own websites. Confirm the legal seller, factory and scope for your order.

Ask each supplier for the material certificate with infrared alpha, inclusion and etch channel grades for the autoclave run, the X-ray orientation report and the dimensional inspection for the blanks you order. [1]

05

Trace what each property controls

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your resonator

A quartz blank quotation needs values for your resonator. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the material, cut and dimension data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Material: [IEC alpha grade; inclusions; etch channels]
Handedness/sweeping: [right; swept]
Cut: [type; angle; tolerance]
Target: [MHz; overtone; temperature range]
Shape/size: [Ø or L×W; thickness]
Surface: [lapped; polished; flatness]
Inspection: [X-ray; sampling plan]
Quantity: [pcs]

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