1.3 - High Detectivity Uncooled Thermopile IRFPA Chip Prepared by Surface Micromachining

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings IRS² 2011
I1 - Photon and Thermal Detectors
U. Dillner, F. Hänschke, U. Schinkel, H. Meyer - Institute for Photonic Technology, Jena (Germany)
24 - 29


Thermopiles as thermal detectors are characterized by their simplicity and ruggedness of construction corresponding to low cost. They exhibit a uniform broadband response over the infrared spectrum, can be operated without cooling and generate a signal voltage, which is strictly proportional to the incoming radiation over many orders of magnitude and, moreover, insensitive to substrate temperature variations. In addition, they require neither an electrical bias nor an optical chopper and do not generate 1/f noise. Thermopile detectors are particularly well suited for spectral imaging, space science applications, track recording, presence detection and applications with low energy consumption. The purpose of this work is the fabrication of a surface-micromachined 2-D high detectivity thermopile array using a highly effective BiSb/Sb thermocouple materials combination. Surfacemicromachined sensor arrays offer a high responsivity and integration level, however, a vacuum packaging is indispensable due to the
small distance between absorber area and substrate surface. The thermoelectric array is built on 8x8 pixels with an active area of 100 microns in square, which are wired directly. Thermopile structure and absorber area are manufactured upon a sacrificial layer based on polyimide, which is removed at the end of the manufacturing process. Thermoelectric layers as well as wiring layers has been patterned almost exclusively by lift-off technique in order to obtain very small structure dimension with high reliability as well as high integration level. The active area of detectors can be equipped with two absorber types for different application, a broadband colloidal silver black layer as well as a quarter wavelength arrangement for the MIR wavelength range from 8 μm to 14 μm. The detectivity of a so manufactured FPA with silver black layer was about 109 cmHz1/2/W. The time constant was measured to be 40 ms.