Doctoral Proposal Defense
Bryan Hall, Room 509c
Polarization Imaging Sensors in Advanced CMOS Technologies
Advisor: Dr. Viktor Gruev
Today’s CMOS and CCD imaging sensors capture intensity and color properties of the imaged environment with high resolution and low power sensors. The third property of light, namely polarization, has been ignored by the imaging industry partly because of the human inability to discriminate polarization. Nonetheless, polarization imaging has proven to be very useful in gaining additional visual information in many biomedical applications, such as imaging for early skin cancer, cervical cancer, and retinal surgery. In addition, polarization imaging has been used to enhance targets in scattered environments, such as underwater imaging and visibility in hazy conditions. One of the major challenges in the proliferation of polarization imaging technology is the lack of robust and compact sensors that capture accurate polarization properties of light in real-time and in high-resolution.
The scaling of CMOS technology, as predicted by Moore’s law, has allowed for realization of high resolution imaging sensors and for the emergence of multi-mega-pixel imagers. Designing imaging sensors in advanced CMOS technologies poses many challenges especially since transistor models do not accurately portray their performance in these technologies. Circuit designers have observed that transistors fabricated in advanced CMOS technologies no longer operate in the traditional modes of operation, such as: cut-off, sub-threshold, linear, and saturation modes. Instead, transistors are starting to operate in a new mode of operation, called velocity saturation mode. Traditionally analog designers have been discouraged from designing circuits in this mode of operation due to the low gain properties in single transistor amplifiers. Nevertheless, velocity saturation will become even more prominent mode of operation as transistors continue to shrink and warrants careful design of circuits that can exploit this mode of operation.
In this research endeavor, I plan to explore realization of imaging sensors fabricated in advanced CMOS technologies that exploit velocity saturation mode of operation in transistors and are capable of extracting polarization information from the imaged environment. In order to realize these imaging sensors, I will explore the following three research questions:
1. Can we utilize transistors operating in velocity saturation in order to design mixed-mode circuits and systems for imaging sensors? Can the performance of these new circuits be on par or perform better than current circuits used for imaging sensors?
2. Can we develop and fabricate carefully designed optical nano-structures that will behave as linear polarization filters with high contrast ratios? Can we design these structures from materials compatible with semiconductor fabs?
3. Can we develop hybrid sensors by monolithically integrating optical nano-structures with CMOS technology in order to enhance or filter the optical signals?
In order to explore these three research questions, I propose to design, fabricate and test a custom CMOS imaging sensor in 180 nm feature technology. The sensor will be composed of both analog and digital circuits allowing for imaging and signal processing at the focal plane. The circuits in the imaging sensor will be tailored to operate in velocity saturation mode. Furthermore, I will explore various nanofabrication techniques in order to realize optical filter structures composed of periodic metallic nanostructures with high contrast ratios. These nanostructures will be monolithically integrated with the custom CMOS imaging sensor in order to realize a hybrid system capable of extracting polarization information from the imaged environment.
The proposed imaging sensor will explore unique integration methods of nanostructures, which will be fabricated via upcoming nanofabrication methods, with standard CMOS technology. The methodology that will be developed as part of this proposal will not be limited only to polarization imaging sensors and will enable future realization of hybrid sensors by integrating various nanostructures with CMOS technology.
Computer Science & Engineering
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