Preparation and characteristics of pyroelectric infrared sensors made of <i>c</i>-axis oriented La-modified PbTi03 thin films

Abstract

Highly c-axis oriented La-modified PbTiO3 (PLT) thin films were deposited on (100) oriented Pt thin film or (100) cleaved MgO single crystals by rf-magnetron sputtering. Figures of merit for infrared detector were studied on the PLT thin films. It was found that a composition Pb1−xLaxTi1−x/4O3 where x=0.10 (PL10) was the most suitable for the infrared detector. The films have the advantage of having pyroelectric effect and polarization with the same direction even without a poling treatment. The films have high figures of merit Fv(=γ/cvεr) of 0.83×10−10 (C cm/J) and Fm(=γ/cv(εr tan δ)1/2) of 1.2×10−8 (C cm/J) because of relative low-dielectric constant εr of 200 and high-pyroelectric coefficient γ of 5.3×10−8 C/cm2 K. Both the Fv and the Fm of the films are 3 times as large as those of PbTiO3 ceramics. High sensitive pyroelectric infrared sensors were fabricated by using the PL10 films. The thickness of the films is 2 μm, and the electrodes were vacuum evaporated Ni-Cr of approximate area 7×10−4 cm2. The MgO substrate under the sensing area is etched off by phosphoric acid. The sensors have a large voltage responsivity of 2400 (V/W) at 25 Hz. A high specific detectivity D*(500,25,1) of 5×108 (cm(Hz)1/2 /W) has been attained.