Variation Reduction for Signal-to-Noise Ratios and Low-Frequency Noise of Far-Infrared Imaging Pixels Using an Array of Schottky Diode Detectors in CMOS and Postfabrication Selection

To mitigate the low frequency noise variability in Schottky barrier diodes (SBD’s) fabricated in a 110-nm foundry CMOS process and its effect on the performance of electromagnetic-thermal far-infrared (FIR) detectors, post-CMOS-fabrication selection of a subset of an array of parallel connected SBD detectors that form a pixel to reduce the noise and to increase the signal-to-noise ratio (SNR) is demonstrated. This technique at 20 THz reduces the SNR variation by ~4 dB compared to using all detectors in 5×5 arrays of FIR detectors with a 3.5 μm × 2.5 μm patch antenna. Furthermore, this technique is used to increase the worst-case SNR by ~5 dB. The sub-array combination of the 5×5 detector array with the highest SNR is utilized to create a thermal image of two 10-Ω carbon resistors with peak temperatures of 420 K and 380 K, respectively. The structural similarity index (SSIM) is employed to demonstrate that switching off varying subset combinations of detectors within a pixel does not degrade the image quality. The highest specific detectivity, D* of the pixels at 20 THz reported in this paper is 2.1 × 104, which is the highest reported D* for detectors not employing a thermal isolation cavity and operating at ~10 THz and above.