Ferroelectric materials for uncooled thermal imaging

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 reviews the properties of PST in relation to those of other materials which have been considered for use in this role and discusses how dopants, including K/Bi, Nb, Ti and Zr, 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 for cooling. F_D figures-of-merit of over 20 × 10^-5Pa^{- 1/2} are reported. A concern for the user of devices under electrical bias is the possible change in the properties of the active material with time. This is particularly so in the case of dielectric bolometers where they are subject to high bias fields (up to 5 V μm^-1) for extended periods. The results of measurements of the properties of PST after aging under such fields are presented.