THESIS
2010
xx, 120 p. : ill. ; 30 cm
Abstract
Rapid advances in semiconductor industry complementary metal oxide semiconductor (CMOS) fabrication process have enabled the integration of a camera onto a single silicon chip. Referred to as CMOS image sensor, a camera-on-a-chip offers significant cant advantages in terms of system miniaturization and
manufacturing cost. Like the vast majority of commercially available camera
systems, CMOS image sensors are essentially designed to image the world in
terms of intensity and color. However, they are "blind" to the third characteristic of light that is polarization. Capturing the polarization state of light
reflected or emitted by objects in a scene can not only reveal valuable information about their geometrical, physical, chemical, physiological, and/or
metabolic properties but also...[
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Rapid advances in semiconductor industry complementary metal oxide semiconductor (CMOS) fabrication process have enabled the integration of a camera onto a single silicon chip. Referred to as CMOS image sensor, a camera-on-a-chip offers significant cant advantages in terms of system miniaturization and
manufacturing cost. Like the vast majority of commercially available camera
systems, CMOS image sensors are essentially designed to image the world in
terms of intensity and color. However, they are "blind" to the third characteristic of light that is polarization. Capturing the polarization state of light
reflected or emitted by objects in a scene can not only reveal valuable information about their geometrical, physical, chemical, physiological, and/or
metabolic properties but also greatly simplify a number of important machine
vision tasks such as autonomous navigation or automatic target detection.
Commercially available CMOS cameras can be made polarization-sensitive
by coating individual pixels with micrometer-scale polarizer elements. A micropolarizer array (MPA) is thus formed on top of the photosensitive pixel
array. Previously reported micropolarizer implementations suffer from two main limitations: (i) use of selective etching to pattern polarizer elements at
the pixel pitch, which is a difficult process to control at the micrometer scale,
and (ii) incomplete polarization signature since the circular polarization component cannot be extracted. This circularly polarized component is crucial to
fully determine the polarization state of light since, in general, a ray will be
elliptically polarized, that is, it can be decomposed into a linear and circular
polarization vector. This thesis addresses the above limitations to enable the
development of miniature CMOS single-chip polarization cameras capable of
capturing simultaneously all possible polarization states of light reflected or
emitted by objects in a scene.
This thesis investigates and demonstrates a number of novel MPA design
and fabrication technologies, which completely remove the need for selective
etching and enable the extraction of all possible polarization states of incident light. The well-controlled-process of ultraviolet (UV) photolithography is
used, for the first time, for the patterning of high resolution pixel-level MPAs
with submicron thicknesses. Another unique feature of the developed MPAs is
that they can be fabricated using standard and well-established CMOS manufacturing flows, enabling low-cost mass production. Both absorptive-type
and reflective-type linear polarizers are explored for applications with both
natural passive light source (e.g. polarization difference imaging and partial-linear polarization imaging) and artificial collimated active light source for full
Stokes imaging. The proposed implementations significantly scale the MPA
pitch size down to 2μm. Reported experimental results validate the concept
of high performance photo-aligned MPAs with major principal transmittance
and extinction ratio as high as ~80% and ~3200 (35dB), respectively.
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