THE INFLUENCE OF HEAT-EXCHANGE BETWEEN A SENSITIVE ELEMENT AND ITS SURROUNDINGS ON THE SPECIFIC DETECTIVITY OF PYROELECTRIC DETECTORS

The specific detectivity of pyroelectric sensors at low frequencies is mainly influenced by the thermal conditions within the sensor. The temperature noise caused by heat exchange between the sensitive element and its surroundings is transformed into an increase of the dielectric loss due to electrothermal coupling. The complex normalized current responsivity is used to calculate the influence of thermal conditions. While the absolute value \T(R)\ gives the frequency response of the sensitivity, the additional dielectric loss tan delta(T) is deduced from the imaginary part. The loss due to electrothermal coupling tan delta(T) exceeds the dielectric intrinsic loss tan delta(i) for most sensor structures within the frequency range up to 100 Hz. Thus, the maximum attainable specific detectivity of a pyroelectric sensor at normal operation frequencies is dependent on its construction rather than on the material parameter dielectric intrinsic loss tan delta(i) which is frequently referred to. The effect of electrothermal coupling can be employed in sensors with reduced sensitivity at low frequencies as used for FTIR-devices.