  We developed a theoretical model for the calculation of the main
characteristics of pyroelectric response of pyroactive multilayer structures,
which are basic elements of modern pyroelectric detectors of radiation and
other transducers. In the framework of the proposed model, the dependences of
the pyroelectric response frequency spectra on the ferroelectric film thickness
have been investigated. It was found that a pronounced extrinsic size effect is
inherent to the pyroelectric response frequency spectra, such as the strong
thickness dependence of the response maximal value and its frequency position.
Thickness dependences of the frequency position of the pyroelectric response
maximum and the optimal thickness of the pyroactive ferroelectric film are
calculated. The frequency spectra of the pyroelectric current and voltage
calculated theoretically are in quantitative agreement with experimental ones
for Al/P(VDF-TrFE)/Ti/Si pyroactive structure. Developed procedure is important
for improving the sensitivity of pyroelectric devices. Obtained analytical
expressions allow us to optimize the performances of pyroactive elements using
the existence of the size effect, which depend on pyroactive layer and
substrate thicknesses, as well as on the conditions of heat transfer and
exchange at corresponding boundaries of the pyroactive structure.
