Ferroelectric ceramics and thin films for uncooled thermal imaging arrays

The pyroelectric effect in ferroelectric materials has long been used for the detection and imaging of long wavelength infra-red radiation. Lead scandium tantalate (PST) has been shown to have exceptionally good pyroelectric figures of merit, especially for small detectors of the type involved in the large arrays needed for uncooled solid state thermal imaging. This paper will review the properties of PST in relation to those of other materials which have been considered for use in this role and discuss how the inclusion of dopants can be used to modify the properties of the material in a way which would be beneficial to certain modes of detector operation, particularly with respect to the elimination of the requirement of cooling. Single element detectors and linear and two dimensional arrays have been made using PST. Their properties are compared with those of similar devices made using conventional pyroelectric ceramics. Ferroelectric thin films can now be made using sol-gel techniques whose figure-of-merit are comparable with those of bulk ceramic materials and the properties of these will be reviewed in relation to those of the ceramics discussed above and their potential for device applications discussed.