Pyroelectric ceramics and thin films

11 Pyroelectric Ceramics and Thin Films Characterization, Properties and Selection 

The following discussion separates pyroelectric materials into 3 groups intrinsic pyroelectrics which are operated well below Tc, dielectric bolometer materials which are operated close to Tc, but with an electrical bias applied and ferroelectric thin films. 

There are many different types of pyroelectric, including single crystals, polymers, ceramics and thin films and several reviews [2,3,28,29] have considered the properties of many pyroelectric materials in detail, so the discussion here will be confined to a brief review of pyroelectric ceramics and thin films. 

For these materials, it has been possible to quote the dielectric properties at 1 kHz and 33 Hz, to illustrate the differences in figures-of-merit (especially FD) which are obtained by going to the frequency range of interest for device applications. The Fd figures are reduced 

The control of electrical resistivity in these ceramics is, as noted above, very desirable. There has been considerable success in the use of uranium as a dopant for this function in a variety of compositions [36-38], Recently, chromium has also been shown to exhibit some promise for this [39], 

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In conclusion, it has been demonstrated that the pyroelectric properties of polar materials can be compared relatively simply through the measurement of a few key physical parameters (pyroelectric,dielectric and thermal coefficients) and the judicious use of appropriate figures-of-merit. It is essential that the dielectric properties are measured in the frequency range appropriate for device use, and this is typically in the range of a few to 100 Hz. The properties of many pyroelectric ceramics and thin films have been compared and it has been shown that good pyroelectric properties can be obtained from this films manufactured at relatively low temperatures, a fact that bodes well for their future applications in fully-integrated arrays. 

WhatniOTe RW (2004) Pyroelectric arrays ceramics and thin films. J Electroceram 13 139-147... 

Pyroelectric sensors utilize a wide range of material forms crystals, bulk ceramics, thick layers, and thin films. Noteworthy among new compositions with improved performance is the class of relaxor pyroelectrics. Many novel pyroelectric sensors utilize thin and thick films. Bulk pyroelectric ceramics for room temperature, and pyroelectric sensors, are widely available. New compositions with higher permittivity are available now. 

SBN pyroelectric detector (Liu and Maciolek [3.27]) to Plessey production ceramic pyroelectric detector it Thin film bolometer (Bessonneau [3.15])... 

Ca, Ba, Sr ) into PT ceramics is reported to enhance the pyroelectric properties. Substitution of these ions results in the reduction of lattice anisotropy leading to hard and dense ceramics with high mechanical strength. From the standpoint of thermal responsivity, the performance of a pyroelectric detector is enhanced when it is in the form of a thin film. In recent device applications, it has become increasingly necessary to consider the improvement of these films in then-performance in addition to the large component area and connection to many circuit elements. Recently, calcium- and lanthanum-doped lead... 

Ferroelectric crystals (especially oxides in the form of ceramics) are important basic materials for technological applications in capacitors and in piezoelectric, pyroelectric, and optical devices. In many cases their nonlinear characteristics turn out to be very useful, for example in optical second-harmonic generators and other nonlinear optical devices. In recent decades, ceramic thin-film ferroelectrics have been utilized intensively as parts of memory devices. Liquid crystal and polymer ferroelectrics are utilized in the broad field of fast displays in electronic equipment. 

Both, piezoelectric and pyroelectric behavior is possible only in ferroelectric ceramics, or in otherwise polar materials that are deposited as textured thin films. 

Table 27.3 Heterostructural characteristics and electrical properties (dielectric, ferroelectric, and pyroelectric) of two (Ca, Pb)Ti03 thin films prepared from the same precursor solutions but crystallized with different thermal annealing rates for the ceramic conversion.

Some LB films exhibit a temperature-dependent pyroelectric coefficient that makes them candidates for thermal imaging applications (1). Both X- and Z-type films and alternating Y-type films (Fig. 6) can be built with permanent polarization, whose magnitude is often temperature-dependent. Their pyroelectric coefficient p is small relative to standard semiconducting and ceramic materials, but so is their permittivity e this makes their ratio p/s, the figure of merit, comparable to that as for currently employed inorganic materials. The advantage of LB methods is that they can be used to prepare very thin, very uniform films. 

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