Lithium Tantalate Substrates for Pyroelectric Detectors

Lithium Tantalate ( LiTaO₃ ) belongs to class of ferroelectric crystals which possess intrinsic spontaneous electric polarization. Usually crystal volume is divided into many microscopic domains with randomly oriented polarizations. However ,it is possible to align all domains in one direction parallel to so called polar axis by applying high external electric field near the Curie temperature. After such poling procedure crystal will stay in single domain state with uniform polarization direction if operation temperature does not exceed Curie temperature. Pyroelectric effect is change of polarization with temperature resulting in a polarization current within a crystal. In practice, the effect can be measured if electrodes are applied to crystal surfaces normal to polar axis and connected through an external circuit. So pyroelectric substrate ( thin plate of pyroelectric material with proper electrodes) is a heart of pyroelectric detectors featuring very broad operation wavelength with extremely fast response time. LiTaO₃ is the most popular material for pyroelectric detector substrates due to it’s very high pyroelectric coefficient, chemical and mechanical stability and wide temperature range defined by high Curie temperature.

ELAN produces standard and custom substrates made of high optical quality, fully poled LiTaO₃ crystals. Standard specs are as follows:

Orientation: Z-cut +/- 15 arc. min.

Diameter:
Standard: 10 mm +/- 0.1 mm
Available: from 2x2 mm to 30x30 mm, depending on thickness
 
Thickness:
Standard: 50 microns +/- 5 microns
Available: from 20 microns to 200 microns , depending on diameter

Polish: both sides polished with 20/10 Scratch/Dig
Parallelism < 5 arc. Sec.

Electrodes: 25-30 nm Cromium
or 25-30 nm Cromium overcoated with 50-60 nm gold

Other specs are available on request.

Pyroelectric substrates made of Lithium Niobate (LiNbO₃) are available also.
This crystal has less pyroelectric coefficient as compared to LiTaO₃ but it’s Curie temperature is even higher ( 1150 deg. C as compared to 610 deg. C of LiTaO₃) and better temperature stability of the detector. This material is cheaper and available in larger sizes.