THESIS
2018
xviii, 130, that is, xix, 130 pages : illustrations ; 30 cm
Abstract
Infrared radiation sensors, which can detect infrared electromagnetic radiations (0.7 μm to
1mm), have been widely used in numerous applications. Among the different infrared detectors, thermoelectric (TE) infrared sensors are passive sensors and require no complex cooling system;
therefore, they have much less complex structures and are more energy and cost-efficient,
making them an attractive solution for infrared detection. However, the conventional planar TE
sensor structures are generally quite bulky and they need to make a tradeoff between a high
responsivity and a fast response, rendering them unsuitable for high-speed and high-resolution
infrared detection.
In this work, we proposed a vertical design based on free-standing micropillars, which can
achieve a high responsiv...[
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Infrared radiation sensors, which can detect infrared electromagnetic radiations (0.7 μm to
1mm), have been widely used in numerous applications. Among the different infrared detectors, thermoelectric (TE) infrared sensors are passive sensors and require no complex cooling system;
therefore, they have much less complex structures and are more energy and cost-efficient,
making them an attractive solution for infrared detection. However, the conventional planar TE
sensor structures are generally quite bulky and they need to make a tradeoff between a high
responsivity and a fast response, rendering them unsuitable for high-speed and high-resolution
infrared detection.
In this work, we proposed a vertical design based on free-standing micropillars, which can
achieve a high responsivity, a short response time and a small device size simultaneously.
Theoretical modeling and numerical simulations were conducted to evaluate the effects of
various key design parameters such as the nanowire diameter, length to diameter ratio, absorber
area, thermoelectric properties of the TE element, and the number of nanowires, on the
performance of the TE sensors. The modeling results show that the vertical design can
potentially provide superior performance.
With the optimized device design and absorber structure, we developed the first TE infrared
sensing structure based on vertically standing SiGe nanowires and the corresponding
fabrication process. We successfully demonstrated the TE infrared sensors with selectively
doped nanowires of 1 μm and 300 nm diameters, which have a footprint of 28×28 μm
2and are the smallest TE infrared sensors reported in the literature. To achieve a high selective infrared absorption, based on “multi-layer integration” theory, an atmospheric-window matched
broadband absorber has been developed and integrated with the developed sensor. Laser and
blackbody radiation measurements were conducted to characterize the performance of the
fabricated TE infrared sensors. The measured performance of the devices with 1-μm-thick and
2-μm-long nanowires is close to the theoretical predictions, with a responsivity reaching 160
V/W and a response time down to 0.6 ms, which is the fastest response for thermal infrared
sensors and may enable high-speed infrared detection using TE sensors. Meanwhile, the devices
with 300-nm-thick nanowires show a response time of 6 ms and a responsivity of more than
4000 V/W, achieving both high spatial and temporal resolutions as well as a high responsivity.
These findings demonstrate that it is possible to achieve superior responsivity as well as
high spatial and temporal resolutions using a free-standing structure integrated with vertical
nanowires. More importantly, these TE infrared sensors can be fabricated using IC-compatible
fabrication process and Si-based materials, paving the way for large-scale integration for high
performance infrared applications such as high-speed infrared imaging.
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