A direct method for measuring pyroelectric coefficients is described. The method is more straightforward than either the dynamic method or the charge integration technique. Pyroelectric coefficients measured by the direct measurement technique are applied to the design of pyroelectric detectors. A SrxBa1-xNb2O6 detector is described with variable response times from 1 msec to 4 nsec.

Pyroelectric coefficient direct measurement technique and application to a nsec response time detector

Ferroelectric films of lead zirconate titanate (PZT) have been fabricated by rf planar magnetron sputtering. Films having a resistivity >106 Ω cm and a dielectric constant >800 at 300 K have been achieved using 100% oxygen as a sputtering medium, 10% excess PbO added to the target, and appropriate post‐deposition annealing. The sputtering rate is in the range 0.2–1.0 μm/h and varies with sputtering pressure and substrate temperature. Post‐deposition annealing affects both crystallinity and grain size, but incipient crystallization formed only in as‐grown films deposited at substrate temperatures >400 °C is essential for this process to be effective. A clear ferroelectric transition is observed at 350 °C, while the activation energy for dc conductivity of around 0.8 eV is consistent with bulk properties of PZT. The spontaneous polarization and coercive field measured from ferroelectric hysteresis loops is 20.75 μC/cm2 and 10 kV/cm, respectively. The optical transmittance of the films is determined by a Pb–Pb charge transfer band near 400 nm and this is a sensitive test of film stoichiometry.

rf planar magnetron sputtering and characterization of ferroelectric Pb(Zr,Ti)O3 films

The principles of operation of a pyroelectric detector are summarized and responsivity, noise, noise equivalent power and detectivity are derived. The relationship between responsivity and frequency is discussed as are the various sources of noise. There follows a discussion of the relative merits of the five principal pyroelectric materials in common use: Triglycine Sulphate, Lithium Tantalate, Strontium Barium Niobate, Pyroelectric Ceramics and Polyvinylidene Fluoride. Factors influencing the choice of material are outlined and summarized in performance curves for three sizes of detector. Mention is made of a variety of detector types currently available and some of the current applications. A very brief summary of possible future developments is included.

A brief guide to pyroelectric detectors

The recently reported permanent poling effects in triglycine sulphate (TGS) containing some α-alanine additive is further investigated by pyroeiectric and dielectric measurements. The probable role of an L-alanine molecule in the lattice of TGS is examined in terms of the atomic motions normally required to reverse the polarity of the ferroelectric crystal. The observations can be explained by a model which relates the lack in α-alanine of the prototypic symmetry possessed by glycine I to the inhibition of the ferroelectric switching mechanism. Substituted α-alanine molecules are shown to lead to local irreversible dipoles which can “pole” a TGS crystal in a single sense provided that only one optically active form (L) is used. In this case crystals grown either below or above Tc behave similarly. Thus crystals can be grown in the non-polar phase, which become spontaneously, fully poled when cooled below Tc. Using dl-alanine as the additive for crystals grown below Tc, large permanently poled regions of e...

Structural inhibition of ferroelectric switching in triglycine sulphate—I. additives

Ferroelectric thin films are playing a growing role as key elements in variety of devices. For various techniques of ferroelectric thin film preparation, the sol-gel processing is one of the most promising. In comparison with different deposition techniques, we survey the intrinsic advantages and the recent improvements of the sol-gel processing. In this review paper, several interesting topics, including epitaxial growth and grain-orientation, symmetric and asymmetric P-E hysteresis loops, heterojunction effect of the interface between film and substrate, to attest pyroelectricity of the films, electrooptic coefficients in poled and unpoled films, possibility of amorphous ferroelectrics, etc., are introduced.

Ferroelectric thin films prepared by sol-gel processing

Pyroelectric infrared radiation detectors of triglycline sulfate (TGS), triglycine fluoberyllate (TGFB), lithium sulfate, strontium barium niobate (SBN), and polycrystalline TGS are compared for responsivity, noise, and detectivity as a function of temperature. TGS, which currently exhibits the highest responsivity and detectivity at ambient temperature from 0.01 Hz to at least 10 KHz, is still one order of magnitude away in detectivity from an ideal thermal detector. Under ambient operating or storage conditions between 35° and 60°C, TGFB is the choice over TBS. Some spectral data is also presented.

Improvement in the pyroelectric infrared radiation detector

An ultrasonic transducer concept is described where a plurality of different focal lengths, within a unitary structure, are the result of combining the one-dimensional focusing by individual zones of a piezoelectric spiral-shaped cylindrical surface with orthogonal focusing due to individual Fresnel zone electrode patterns.

Henry P. Beerman

Papers

Improvement in the pyroelectric infrared radiation detector

Multi-focus ultrasonic transducer