Uncooled microbolometer infrared focal plane array in standard CMOS

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Abstract
This paper reports implementation of a low-cost microbolometer focal plane array using n-well layer in a CMOS process as the microbolometer material. N-well microbolometer structures are suspended for thermal isolation by post-etching of fabricated CMOS dies using silicon bulk-micromachining techniques. Although n-well has a moderate TCR of 0.5-0.65%/K at 300K, it still provides a reasonable performance due to its single crystal structure which contributes low 1/f noise. Detailed thermal simulations in ANSYS were performed to obtain an optimized structure. Various prototype FPAs with 16x16 array sizes have been implemented with 80 mm x 80 mm and 50 mm x 50 mm pixel sizes. The measurements and calculations show that the n-well microbolometers can provide a responsivity of 8.5 x 106 V/W, a detectivity of 5.5 x 109 cmHz1/2/W, and an NETD of 260 mK at 30 frames per second using a simple, fully-serial readout approach with an integrator output. The performance of the array can be increased with advanced readout techniques and improved pixel structures. The CMOS n-well microbolometer approach seems very cost-effective to produce large focal plane arrays for uncooled infrared imaging with reasonable performance.

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