DEVELOPMENT OF SMALL SIZE UNCOOLED INFRARED MICROBOLOMETER PIXEL

2021-9
Tekin, Baran utku
This thesis reports the development of 12 µm pixel pitch single layer microbolometer structures for use in the 8-12 µm wavelength regions, following recent trends in the last decade in microbolometers. Various pixel structures are designed, simulated, fabricated, and characterized to obtain acceptable detector performance in these small pixels. The pixel structures are improved by reducing the pixel thermal conductance and by using planar type electrode structures where the active material is selected as VWOx (Vanadium-Tungsten Oxide). Predictive modeling with electro-thermal simulations has aided in attaining the best possible pixel structures. Besides that, absorptance is optimized using the cascaded transmission line (CTL) simulation method to improve the pixel absorption between 8-12 µm spectral region show that more than 85% level. Designed detector pixels are fabricated using a CMOS compatible process flow. Each fabrication step is optimized considering a possible array fabrication on CMOS wafers. Then, pixels are characterized electrically, thermally, and optically. These characterizations include temperature coefficient of resistance (TCR), noise, thermal conductance, absorption, responsivity, and thermal time constant measurements. The TCR of the active material, VWOx, is measured around -4 %/K with an optimum resistance value. The thermal conductance values of pixels are measured as low as 20 nW/K. Additionally, the corner frequency is measured 0.85 kHz at 10 μA bias current. Finally, a responsivity value of 37 kV/W at 473 µV is measured for the best-performed fabricated pixel with a low thermal time constant of less than 2 ms, suitable for applications that require high frame rates. Fabrication of 640x480 format FPAs is conducted in the framework of this thesis with the optimized detector structure. Among measured FPAs, the responsivity and operability are measured as high as 10 mV/K and >99%, respectively. Using these measurement results, the lowest NETD value of a 640x480 FPA measured minimum is 200 mK. The success of the developed detector structures is verified through the images obtained from the detectors that are monolithically built on the CMOS readout circuit. It should be noted that this thesis reports the first successfully fabricated 640x480 FPA array using a 12 µm pixel pitch single layer microbolometer in Turkey. The development in this small size FPA production may open a path to different applications to be developed and used in Turkey in the future.

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Citation Formats
B. u. Tekin, “DEVELOPMENT OF SMALL SIZE UNCOOLED INFRARED MICROBOLOMETER PIXEL,” M.S. - Master of Science, Middle East Technical University, 2021.