Hybrid Amorphous Selenium-CMOS Photon-Counting X-ray Imager

Many medical imaging modalities, such as mammography and micro-computed tomography, utilize digital X-ray imagers to observe human anatomy. Direct digital X-ray imagers rely on a sensor layer (typically a photoconductor) to convert X-ray photons to electrical charge, which can then be collected by pixel readout circuits. Whereas traditional integration-mode X-ray imagers typically integrate charge for long durations to acquire image frames, X-ray photon-counting imagers (PCI) resolve each incident photon as it arrives. This allows for equal energy-weighting of photons and multi-spectral image capture, both of which enhance contrast in images. Furthermore, PCIs also allow for higher dynamic range since count rates are not limited by integration well capacity. Many hybrid X-ray PCIs have been reported in the literature using photoconductors such as CdTe and HgI₂. However, these photoconductors are expensive to fabricate, suffer from low yield over large areas, and have limited spatial resolution. This thesis describes the design and characterization of the first hybrid X-ray amorphous selenium–CMOS PCI for mammography and micro-computed tomography. Amorphous selenium (a-Se) can be thermally deposited over large areas, allowing for cheaper and scalable fabrication as well as higher spatial resolution. Two arrays of 26 × 196 pixels are implemented in CMOS and interface directly to an a-Se sensor layer. Counter arrays neighbor the pixel arrays and have a one-to-one relationship with pixels, incrementing every time a photon is detected. Novel readout circuits allow for ultra high-resolution pixels, each occupying only 11.44 × 11.44 μm². Finally, the design of a custom PCB and FPGA system for characterizing the electronic performance of the PCI is described. The measured input-referred noise and threshold spread of the PCI are 41 e-rms and 107 e-rms, respectively, when operating the imager as a row scanner. This will enable an energy resolution of 5.7 keV, suitable for the proposed applications. Further analysis was done to identify methods of reducing threshold spread as well. Finally, the concluding chapter summarizes this work, compares its performance to other PCIs in the literature, and identifies future work to improve its performance

Biologically-Inspired Low-Light Vision Systems for Micro-Air Vehicle Applications

Various insect species such as the Megalopta genalis are able to visually stabilize and navigate at light levels in which individual photo-receptors may receive fewer than ten photons per second. They do so in cluttered forest environments with astonishing success while relying heavily on optic flow estimation. Such capabilities are nowhere near being met with current technology, in large part due to limitations of low-light vision systems. This dissertation presents a body of work that enhances the capabilities of visual sensing in photon-limited environments with an emphasis on low-light optic flow detection. We discuss the design and characterization of two optical sensors fabricated using complementary metal-oxide-semiconductor (CMOS) very large scale integration (VLSI) technology. The first is a frame-based, low-light, photon-counting camera module with which we demonstrate 1-D non-directional optic flow detection with fewer than 100 photons/pixel/frame. The second utilizes adaptive analog circuits to improve room-temperature short-wave infrared sensing capabilities. This work demonstrates a reduction in dark current of nearly two orders of magnitude and an improvement in signal-to-noise ratio of nearly 40dB when compared to similar, non-adaptive circuits. This dissertation also presents a novel simulation-based framework that enables benchmarking of optic flow algorithms in photon-limited environments. Using this framework we compare the performance of traditional optic flow processing algorithms to biologically-inspired algorithms thought to be used by flying insects such as the Megalopta genalis. This work serves to provide an understanding of what may be ultimately possible with optic flow sensors in low-light environments and informs the design of future low-light optic flow hardware

Technology 2001: The Second National Technology Transfer Conference and Exposition, volume 1

Papers from the technical sessions of the Technology 2001 Conference and Exposition are presented. The technical sessions featured discussions of advanced manufacturing, artificial intelligence, biotechnology, computer graphics and simulation, communications, data and information management, electronics, electro-optics, environmental technology, life sciences, materials science, medical advances, robotics, software engineering, and test and measurement

Proceedings of the 10th International Chemical and Biological Engineering Conference - CHEMPOR 2008

This volume contains full papers presented at the 10th International Chemical and Biological Engineering Conference - CHEMPOR 2008, held in Braga, Portugal, between September 4th and 6th, 2008.FC