Study of Pyroelectric Devices. Part I

摘要

This report summarizes work done on the theory of ferroelectric detectors, sources of noise in ferroelectrics and dielectrics, and characteristics and limitations of capacitive bolometers. In addition, results of other work including theory of thermal diffusion in pyroelectric detectors as well as techniques used for material preparation, problems encountered in device fabrication and measurements of D* at 100Hz of PLZT samples are summarized. The main results are that the parameters of the thermodynamical theory of pyroelectric detectors can be expressed in terms of independent fundamental molecular parameters which yield a lossless material figure of merit p/sq root of epsilon in close agreement with experimental valves. This approximate model based on the molecular field approximation predicts that P/sq root of epsilon is almost independent of the material parameters over a wide range of pyroelectric materials. Further improvement in detectivity must come from lowering the material loss parameter tan delta. Theoretical work on the noise sources in ferroelectrics led to the conclusion that the thermal noise is caused by the partition noise in a two-level system. A capacitive bolometer operating in the paraelectric region near the Curie temperature exhibited a very low noise equivalent power which is comparable with that of a pyroelectric detector. It is concluded that an understanding of the fundamental loss mechanisms in ferroelectric pyroelectric detectors is needed before improvement in a materials-limited device detectivity can be attained. (Author)