The selection of material is crucial for the performance of a pyroelectric sensor. The material must exhibit a strong pyroelectric effect (a large pyroelectric coefficient) and ideally have other favorable properties like low dielectric constant, low specific heat capacity, and high thermal stability. Several types of materials are commonly used:
- Single Crystals:
- Lithium Tantalate (LiTaO3): One of the most widely used materials due to its high pyroelectric coefficient, high Curie temperature (meaning it retains its pyroelectric properties up to high temperatures, >600°C), chemical stability, and relatively low cost compared to other single crystals. It’s common in high-performance PIR sensors.
- Triglycine Sulfate (TGS): Exhibits a very high pyroelectric coefficient, especially near its Curie temperature (around 49°C). However, its low Curie temperature, water solubility, and mechanical fragility limit its use to specific laboratory or specialized applications, often requiring temperature stabilization.
- Ceramics:
- Lead Zirconate Titanate (PZT) Variants: These are ferroelectric ceramics belonging to the perovskite family. By adjusting the composition (Zr/Ti ratio) and adding dopants (like Lanthanum – PLZT, or Uranium), their properties can be tailored. PZT-based ceramics offer good pyroelectric coefficients, can be formed into various shapes, and are relatively cost-effective to produce in large quantities. They are common in many commercial PIR sensors.
- Other ceramics like Lead Titanate (PT) or Lead Germanate (PGO) derivatives are also used.
- Polymers:
- Polyvinylidene Fluoride (PVDF) and its copolymers (e.g., P(VDF-TrFE)): These are flexible, lightweight, and relatively inexpensive polymer films that can be made pyroelectric through stretching and poling processes. While their pyroelectric coefficients are generally lower than those of crystals or ceramics, their mechanical flexibility, low thermal conductivity (leading to better thermal isolation), and potential for large-area fabrication make them suitable for specific applications like tactile sensors, hydrophones, or low-cost IR detectors.
The choice depends on the specific application requirements, balancing factors like sensitivity, operating temperature range, cost, durability, and required frequency response.