Polycrystalline lead selenide x– y addressed uncooled focal plane arrays

Abstract

A technology for processing low-density uncooled focal plane arrays (FPAs) of polycrystalline PbSe has been developed. PbSe is deposited, processed and sensitised on substrates with two levels of metal separated by a thin dielectric layer of SiO 2. The design allows an x– y addressed type read out with a reduced number of leads and high filling factors. Unlike standard polycrystalline PbSe processing methods, we deposited PbSe by sublimation in vacuum. As-deposited PbSe is not sensitive to infrared light. In order to make it photosensitive it is necessary to expose the films to specific thermal treatments. We have developed a very efficient sensitisation process during which substrates withstand temperatures as high as 450 °C. A very low-density (8 × 8 elements) PbSe FPA has been processed as a technology demonstrator. Electro-optical characterisation was performed using electronics which allows reading every single photoconductive element of the 8 × 8 array. Room temperature detectivities typically yield values of D ∗ λ∼3×10 9 cm Hz 1/2 W −1 at 330 Hz modulation frequency and 1.2 Hz bandwidth. The capabilities of the developed technology can be easily extended to more dense arrays. The main applications of these devices are missions where fast response (less than a few ms) and high detectivities at room temperature are mandatory at the 3–5 μm spectral range.