A Dielectric Bolometer Behavior of BST Thin Film Prepared by Metal-Organic-Decomposition with Excellent Reproducibility in Thermal Cycling Test

Abstract

We have proposed a new type of simple detector pixel circuit and device structure for application of dielectric bolometer mode (DB) of infrared (IR) image sensor. The DB mode has merits such as uncooled room temperature operation, chopperless, low power dissipation, and high-sensitivity. A stable Ba_1划xSr_xTiO₃ (BST) thin film has been successfully developed as a dielectric bolometer material for IR detector by Metal-Organic-Decomposition (MOD) method. The film was prepared on both Pt/Ti/SiO₂/Si-bulk and Pt/Ti/NSG/Si₃N₄/SiO₂ membrane structures, where an IR light is detected at the membrane as a change in dielectric constant (ε). So, the important issue for realizing a reliable IR sensor with high-sensitivity has been achieved to have a good thermal stability in ε against change in the detector temperature. XRD patterns and D-E hysteresis curves were measured and revealed that the BST film has a good perovskite structure and shows an adequate ferroelectric loops, especially for final annealing temperature higher than 700 °C. Temperature Coefficient of Dielectric constant (TCD), which decides the IR sensitivity, of the MOD made BST film is about 1 %/K. The reproducibility in ε, namely IR detector capacitance, was found to be very good in temperature ranging from about 10 to 80 °C within a relative change of 2 %. Finally, the stabilities in both the temperature dependence of ε and the output level have been obtained with a fairly large IR detectivity, where voltage sensitivity(Rv) and specific detectivity(D*) were about 1.2 kV/W and 2.9e8 cmHz ^1/2/W, respectively.