A silicon-thermopile-based infrared sensing array for use in automated manufacturing

This paper describes a new low-cost infrared detector array that has been realized using standard silicon MOS process technology and micromachining. This array uses thermopiles as infrared detecting elements and multiple layers of silicon oxide and silicon nitride for diaphragm windows measuring 0.4 mm × 0.7 mm × 1.3 µm. Each thermopile consists of 40 polysilicon-gold thermocouples. A high fill factor for this array structure has been achieved by using the boron etch-stop technique to provide 20-µm thick silicon support rims. The array shows a response time of less than 10 ms, a responsivity of 12 V/ W; and a broad-band input spectral sensitivity. The process is compatible with silicon MOS devices, and a 16 × 2 staggered array with on-chip multiplexers has been designed for applications in process monitoring. The array theoretically achieves an NETD of 0.9°C and an MRTD of 1.4°C at a spatial frequency of 0.2 Hz/mrad in a typical imaging system.