Development of high fill factor and high performance uncooled infrared detector pixels

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2011
Küçük, Şeniz Esra
This thesis presents the design, fabrication and characterization of high performance and high fill factor surface micromachined uncooled infrared resistive microbolometer detectors which can be used in large format focal plane arrays (FPAs). The detector pixels, which have a pixel pitch of 25 μm, are designed and fabricated as two-level structures using the enhanced sandwich type resistor while the active material is selected as Yttrium Barium Copper Oxide (YBCO). First level of the pixel structure is allocated for the formation of the support arms in order to obtain longer support arms hence lower thermal conductance values to get the desired high performance levels. The pixel body is built in the second level such that the fill factor and absorption of the detector is maximized. Structural and sacrificial layer thicknesses are also optimized in order to increase the absorption coefficient of the pixel in the 8-12 μm wavelength range. The thermal simulations are conducted using finite element method (FEM) by CoventorWare software. The designed pixel has a fill factor of 92 % together with the thermal conductance and thermal time constant values calculated as 16.8 nW/K and 19.3 ms in the simulations, respectively. The pixels are fabricated at METU MEMS facilities after the design of a CMOS compatible process flow. All process steps are optimized individually to obtain the expected high performance. Characterization step of the pixels includes the measurements of temperature coefficient of resistance (TCR), noise and thermal conductance value together with the thermal time constant. Effective TCR of the pixel is measured as -2.81 %/K for a pixel with a support arm resistance of 8 kΩ and total resistance of 55 kΩ. The corner frequency of 1/f noise in the pixel is 9.5 kHz and 1.4 kHz under 20 μA and 10 μA current bias, respectively. The total rms noise is 192 pA within 8.4 kHz bandwidth for a current bias of 20 μA. Thermal conductance, Gth, of the pixel is measured as 17.4 nW/K with a time constant of 17.5 ms. The measurement results indicate that the single pixels designed and fabricated in the scope of this thesis are applicable to large format FPAs in order to obtain a high performance imager. The expected NETD values are 33 mK and 36 mK for 384x288 and 640x480 format FPAs, respectively

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Citation Formats
Ş. E. Küçük, “Development of high fill factor and high performance uncooled infrared detector pixels,” M.S. - Master of Science, Middle East Technical University, 2011.