Low Microphony Pyroelectric Arrays

It is well known that pyroelectric infra-red detectors can exhibit high levels of piezoelectric microphony. Microphonic signals manifest themselves as an unwanted source of noise when the devices are subjected to accelerations or vibrations from the environment. Accurate models have been developed to describe the strains occurring in an active pyroelectric layer mounted on a substrate as an IR detector, from which piezoelectric microphony levels can be predicted. It has been shown that the main source of noise is generated by the lateral strain in the pyroelectric, caused by a flexing of the substrate mounting. This strain engenders a microphonic voltage via the piezoelectric d3, coefficient. The noise voltage is thus critically dependent upon the nature of the mechanical mounting. A second, much smaller, source of microphony is caused by the self-loading of the pyroelectric elements when subjected to accelerations parallel to the polar axis. This generates a thickness-mode noise signal via the piezoelectric d33 coefficient which is independent of the mounting arrangement.