Improvements in the detectivity of infrared pyroelectric detectors

Abstract

We have constructed a pyroelectric detector with a 100 μm TGS plate and a silicon window to check a simple theory leading to the calculation of the detectivity, and to the definition of a figure of merit for pyroelectric materials used in the construction of infrared detectors. We have measured a NEP (7 mm 2, 0.1 mm, 320°K, 5 cps, 500°K) = 10 -9 Watt cps -1/2, in good accordance with calculations assuming 30% absorption in the target. A figure of merit is defined as M = λ( c') -1(ϵ“ T) -1/2 where λ, c' and ϵ” are respectively the pyroelectric coefficient, the specific heat per unit volume, and the imaginary part of the dielectric constant. Using this figure of merit, triglycine selenate appears as one of the best materials with a detectivity three times higher than for TGS. It would lead to the background limit at room temperature ( D ∗ ≈ 3 x 10 10 W -1 cm cps 1/2) for a 1 μm thick plate. The NEP when optimized by the choice of a high enough bias resistor is shown to increase as the square root of frequency.