Optimization of design and technology for uncooled poly-SiGe microbolometer arrays

Abstract

The performance characteristics of polycrystalline SiGe microbolometer arrays are the subject of both design and technological optimizations performed in this work to move the arrays towards the production. An NETD of 90 mK at a time constant of 11 ms is already achievable for the best non-optimized 60 µm pixel, 0.26 µm thick bolometer design in a linear 128 pixel array according to the results of LWIR characterization. The performance of linear 32, 64 and 128 element arrays of 50-, 60-and 75-µm pixel bolometers made with 0.26…0.13 µm thin poly-SiGe on several wafer runs was the starting point for the computer simulation of detector features and evolution of its characteristics under reading bias pulses. The material properties and parameters of read-outs are taken into account in the optimization of the design parameters of arrays as well. The typical bolometer characteristics achieved on the latest wafer run if processed with the PC-program accounting for the read-out and heating effects, result in an average NETD of 70 mK at a time constant of 17 ms for 50 µm pixels in a 320×240 array. Despite less TCR-to-1/f noise ratio as compared with VO x arrays, the several advantages make poly-SiGe a very attractive candidate for an uncooled array, i.e. full compatibility with CMOS technology, better characteristics/price ratio, resistance nonuniformity σ/mean <0.2%, and a possibility to release extrathin structures.

Micromachined poly-SiGe bolometer arrays for infrared imaging and spectroscopy

“…The example can be found in the recent publication 3 . A 100%-operability together with 100% yield obtained this year with the requirements of ±2% resistance deviation, or 99.9% yield at ±1% deviation are, probably, the best reported wafer-scale parameters as well 3 . Therefore, usually, only 5 -10% of the pixels on our 8″ wafers are the subject of probing.…”

“…The previous study of SiGe bolometers has shown a necessity of design improvement in order to obtain NETD less than 100 mK with 50 µm pixels 3 . The design optimization is performed in this work taking into account the measured microbolometer characteristics, i.e.…”

“…Therefore, usually, only 5 -10% of the pixels on our 8″ wafers are the subject of probing. It is quite enough to characterize precisely the resistance and TCR of all arrays since the wafer-scale nonuniformity of these parameters is investigated well 3 . The summarized resistance nonuniformity over the last 7 most intensively probed wafers containing more than 500,000 pixels in total is shown in Fig.7.…”

“…The Belgian tandem IMEC -XenICs has already reported on a possibility of reaching the signal-to-noise ratio on 60-µm pixels corresponding 90 mK Noise Equivalent Temperature Difference (NETD) if the array is supplied with f/0.86-objective 3 . However, at that time, an attempt to decrease the size of pixel to 50 µm had led to a drastic rise of NETD in about 4 times.…”

Uncooled IR focal plane arrays: worldwide review and state-of-the-art at ULIS

“…In Belgium, IMEC, using a strong expertise in silicon technology developed a Si-Ge polycrystalline bolometer technology industrialized by XeniC's [7] which is manufacturing linear arrays.…”