Linear thermopile array for fast searching

A linear thermopile array with characteristics of high responsivity, fast response and low cost has been developed for use in searching for and detecting heat-radiating objects. The thermopile is fabricated by means of a silicon surface micromachining, compatible Si CMOS process and a lift-off technique, which results in a precisely patterned Au black absorption layer. The dynamic signal-to-noise ratio is proposed as a new figure of merit for evaluating thermal infrared sensors and is used to design the thermopile configuration so as to obtain optimum responsivity and thermal time constant. The newly fabricated thermopile array is composed of a zigzag arrangement of two rows of seven infrared sensing elements and achieves responsivity of 230 V/W and a thermal time constant of 0.5 msec. The array, incorporating an optical system with a 30-mm-diameter lens and an focal ratio (F/#) of 0.74, provides a dynamic S/N ratio of 6.9 at a scanning speed of 1,000 m/s and a distance of 80 m for a target with a background temperature difference of 25 °C.