Thermopile Area Array Readout

NASA/JPL thermopile detector linear arrays, wire bonded to Black Forest Engineering (BFE) CMOS readout integrated circuits (ROICs), have been utilized in NASA missions such as the Mars Climate Sounder and the Diviner Lunar Radiometer Experiment. Linear array thermopile detectors are fabricated by bulk micro-machining. Surface micro-machined thermopiles are desirable for area array thermopiles because the architecture provides both high detector fill factor and circuit fill factor in the pixel. The Phase I effort designs an area array ROIC compatible with surface micro-machined thermopile detectors to meet requirements of future NASA thermal instruments requiring D-Star > 4 x 109 Jones. Radiation hard-by-design will be utilized with 180 nm CMOS for low 1/f noise readout, operating temp 77-300 K, radiation hardness and noise immunity with on-ROIC ADC. Various pixel pitches and binning methods will be investigated to cover a desired wavelength detection range of 20 �m – 100 μm. The Phase I ROIC array design, in a 128x128 or larger format, will be fabricated on Phase II.

The technology developed on this SBIR will create improved thermopile readout to meet broadband infrared data collection. Thermal detectors (such as thermopiles), while typically less sensitive than quantum detectors, are useful when the combination of long wavelength signals and relatively high temperature operation (100-200K) makes LWIR and VLWIR quantum detectors unsuitable. Thermal detectors are also appropriate in applications requiring flat spectral response over a broad wavelength range. Thermopile area (2-D) arrays are required in future thermal instruments supporting infrared earth and planetary observing missions. A potential NASA application is a thermopile area array imaging capability with radiation tolerance to support missions to Jupiter.

Thermopile detectors require no electrical bias, and generate a voltage output that is proportional to the input radiation signal. They are also typically uncooled and are insensitive to substrate temperature variations, making temperature stabilization unnecessary. They are highly linear, which combined with their insensitivity to substrate temperature, broadband spectral sensitivity and low 1/f noise; make them ideal for accurate radiometry. A two-dimensional thermopile array built over CMOS readout circuitry in the substrate will allow large format staring imaging arrays that will compete and perhaps offer better performance than bolometer-based staring FPA imagers for radiometric imaging applications. Broadband IR area array sensors with filters allow spectral imaging.

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