Pyroelectric linear array infrared sensors made of c-axis-oriented La-modified PbTiO3 thin films

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Abstract
High sensitive pyroelectric linear array infrared sensors have been fabricated by using highly c‐axis‐oriented and spontaneous polarized La‐modified PbTiO3 (PLT) thin films. The PLT thin films were deposited on (100)‐oriented Pt thin film on (100)‐cleaved MgO single crystals by rf magnetron sputtering. The PLT thin films have high figures of merit for voltage responsivity (Rv) and specific detectivity (D*) without a poling treatment. Two types of linear array sensors, reticulated and nonreticulated ones, were fabricated. The reticulated and nonreticulated sensors have 64 elements with 200‐μm pitch and 128 elements with 100‐μm pitch, respectively. Ni‐Cr electrodes of approximate area 1.9×10−4 or 3.0×10−4 cm2 were deposited by vacuum evaporation on the PLT thin films with a thickness of 3–4 μm. Pyroelectric coefficients and their uniformity increased upon decreasing the deposition area of an element. Therefore, the elements of reticulated sensors have considerably larger Rv and D* compared with the nonreticulated ones. The nonreticulated sensors have a very high resolution of 10 elements/mm, a large Rv of 900 V/W at 100 Hz, and a high D* (500 K, 100, 1) of 1.5×108 cm Hz1/2/W. Furthermore, the reticulated ones have a very large Rv of 2200 V/W, a remarkably high D* of 6×108 cm Hz1/2/W, and a very low thermal cross talk of <3% at 100 Hz.