1.1 - Pyroelectric single-element detectors with very small responsive elements

Abstract

Pyroelectric detectors are used in very large numbers in devices for non-contact temperature measurement, in motion detectors and in gas analysers. Detectors with small responsive elements are necessary, in particular for the realisation of small measuring spots. On the other hand, the signal-tonoise ratio should be as large as possible. A mathematical-physical model of the detector demonstrates that the responsivity is, in particular for low modulation frequencies, influenced by heat conduction processes into the ambient pyroelectric material and the ambient gas layer. For high responsivities it is therefore inevitable to provide good thermal insulation to the responsive element. The article describes the principal layout and the essential properties of pyroelectric single-element detectors on the basis of lithium tantalate. The detectors have a 3D-patterned pyroelectric chip which ensures good thermal insulation of the responsive element. The self-supporting responsive element is of a few micrometres thickness. It is shown that it is possible to obtain a specific detectivity D* (500K, 10Hz, 1Hz, � W = 1) � 4 x 10 8 cmHz 1/2 W -1 for a responsive area of [0.5 x 0.5] mm 2 with a special chip layout. At the same time, the acceleration sensitivity of the detectors could be drastically reduced. The detector properties obtained are compared with the properties of detectors with unpatterned chips.