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

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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.