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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Silicon X-ray smart sensor micromodule and microsystem

Wang, H. (Hongbo) 26 July 2002 (has links)
Abstract Research on X-ray imaging sensors and systems have been carried out for several decades. To make these X-ray scanners smaller with better performance and higher operating speed is an important subject for scientific research and industrial applications. This thesis covers a whole X-ray line-scan camera system. Special attention is given to the smart sensor micromodule design and processing technology. The smart sensor micromodule is an integrated sensor card that includes both silicon X-ray sensor array and signal-processing integrated circuits, which can perform the functions of both an optical sensor and an analog signal processor. Digital signal processing (DSP) made by application specific integrated circuits (ASICs) is also covered in this thesis. Processing technology of the photodiode array, design of the integrated circuit, design and packaging of the micromodules are presented in this thesis. The mechanism of photodiode leakage current is studied in detail. Measured results show that the leakage current level of the photodiode array achieves 80 pA/cm2 under zero bias condition, which outperforms the best photodiode reported so far. The algorithm of the digital signal processing is also studied. The X-ray scanning system can achieve 2 m/s scanning speed with a spatial resolution of 400 mm.
2

Multi-mode Pixel Architectures for Large Area Real-Time X-ray Imaging

Izadi, Mohammad Hadi January 2010 (has links)
The goal of this work is to extend the state-of-the-art in digital medical X-ray imaging as it pertains to real-time, low-noise imaging and multi-mode imager functionality. One focus of this research in digital flat-panel imagers is to increase the detective quantum efficiency, particularly at low X-ray exposures, in order to enable low-noise imaging applications such as fluoroscopy or tomographic mammography. Another focus of this research is in the creation of a multi-mode imager, such as a combined radiographic and fluoroscopic (R&F) imager, which will reduce hospital costs, both in terms of equipment acquisition and storage space. To that end, we propose a novel three-transistor multi-mode digital flat-panel imager with a dynamic range capable for use in R&F applications, with a particular focus on noise optimization for low-noise real-time digital flat-panel X-ray fluoroscopy. This work involves the derivation and optimization of the total input referred noise of an active pixel sensor (APS) in terms of the on-pixel thin-film transistor device dimensions. It is determined that in order to minimize noise, all non-transistor capacitances at the pixel sense node needed to be minimized. This leads to a design where the on-pixel storage capacitance is eliminated; and instead the gate capacitance of the sense-node transistor is used to store the incoming X-ray converted charge. This work allows researchers to gain insight into the fundamental noise operation of active pixels used in medical imaging, and to appropriately choose device dimensions. Due to the inherent large feature sizes of thin-film transistors, active pixel flat-panel X-ray medical imagers offer lower resolution than their film-screen counterparts. By demonstrating the desirability of smaller device dimensions for reduced noise and the elimination of a storage capacitor, this research frees some of the area constraints that exist in active pixel flat-panel imagers, allowing for smaller pixels, and thus higher resolution medical imagers. The noise analysis and optimization as a function of pixel TFT device dimensions in this work is applicable to any amorphous silicon (a-Si) based charge-sensitive pixel, and is easily extended to other device technologies such as polysilicon (poly-Si). iv In addition, experimental results of a 64x64 pixel four-transistor APS imaging array fabricated in a-Si technology and mated with an a-Se photoconductor for use in medical X-ray imaging is presented. MTF results and transient response in the presence of X-rays (image lag) for the APS array are poor, which is ascribed to high charge trapping at the silicon nitride/a-Se interface. Improvements to the silicon nitride passivation layer and pixel layout are suggested to reduce this charge trapping. The prototype imager is compared directly with a state-of-the-art a-Si PPS imaging array and demonstrates good SNR performance for X-ray exposures down to 1.5μR. Pixel design and fabrication process improvements are suggested for low-exposure APS testing and improved low-noise performance.
3

Multi-mode Pixel Architectures for Large Area Real-Time X-ray Imaging

Izadi, Mohammad Hadi January 2010 (has links)
The goal of this work is to extend the state-of-the-art in digital medical X-ray imaging as it pertains to real-time, low-noise imaging and multi-mode imager functionality. One focus of this research in digital flat-panel imagers is to increase the detective quantum efficiency, particularly at low X-ray exposures, in order to enable low-noise imaging applications such as fluoroscopy or tomographic mammography. Another focus of this research is in the creation of a multi-mode imager, such as a combined radiographic and fluoroscopic (R&F) imager, which will reduce hospital costs, both in terms of equipment acquisition and storage space. To that end, we propose a novel three-transistor multi-mode digital flat-panel imager with a dynamic range capable for use in R&F applications, with a particular focus on noise optimization for low-noise real-time digital flat-panel X-ray fluoroscopy. This work involves the derivation and optimization of the total input referred noise of an active pixel sensor (APS) in terms of the on-pixel thin-film transistor device dimensions. It is determined that in order to minimize noise, all non-transistor capacitances at the pixel sense node needed to be minimized. This leads to a design where the on-pixel storage capacitance is eliminated; and instead the gate capacitance of the sense-node transistor is used to store the incoming X-ray converted charge. This work allows researchers to gain insight into the fundamental noise operation of active pixels used in medical imaging, and to appropriately choose device dimensions. Due to the inherent large feature sizes of thin-film transistors, active pixel flat-panel X-ray medical imagers offer lower resolution than their film-screen counterparts. By demonstrating the desirability of smaller device dimensions for reduced noise and the elimination of a storage capacitor, this research frees some of the area constraints that exist in active pixel flat-panel imagers, allowing for smaller pixels, and thus higher resolution medical imagers. The noise analysis and optimization as a function of pixel TFT device dimensions in this work is applicable to any amorphous silicon (a-Si) based charge-sensitive pixel, and is easily extended to other device technologies such as polysilicon (poly-Si). iv In addition, experimental results of a 64x64 pixel four-transistor APS imaging array fabricated in a-Si technology and mated with an a-Se photoconductor for use in medical X-ray imaging is presented. MTF results and transient response in the presence of X-rays (image lag) for the APS array are poor, which is ascribed to high charge trapping at the silicon nitride/a-Se interface. Improvements to the silicon nitride passivation layer and pixel layout are suggested to reduce this charge trapping. The prototype imager is compared directly with a state-of-the-art a-Si PPS imaging array and demonstrates good SNR performance for X-ray exposures down to 1.5μR. Pixel design and fabrication process improvements are suggested for low-exposure APS testing and improved low-noise performance.
4

TFT-Based Active Pixel Sensors for Large Area Thermal Neutron Detection

January 2014 (has links)
abstract: Due to diminishing availability of 3He, which is the critical component of neutron detecting proportional counters, large area flexible arrays are being considered as a potential replacement for neutron detection. A large area flexible array, utilizing semiconductors for both charged particle detection and pixel readout, ensures a large detection surface area in a light weight rugged form. Such a neutron detector could be suitable for deployment at ports of entry. The specific approach used in this research, uses a neutron converter layer which captures incident thermal neutrons, and then emits ionizing charged particles. These ionizing particles cause electron-hole pair generation within a single pixel's integrated sensing diode. The resulting charge is then amplified via a low-noise amplifier. This document begins by discussing the current state of the art in neutron detection and the associated challenges. Then, for the purpose of resolving some of these issues, recent design and modeling efforts towards developing an improved neutron detection system are described. Also presented is a low-noise active pixel sensor (APS) design capable of being implemented in low temperature indium gallium zinc oxide (InGaZnO) or amorphous silicon (a-Si:H) thin film transistor process compatible with plastic substrates. The low gain and limited scalability of this design are improved upon by implementing a new multi-stage self-resetting APS. For each APS design, successful radiation measurements are also presented using PiN diodes for charged particle detection. Next, detection array readout methodologies are modeled and analyzed, and use of a matched filter readout circuit is described as well. Finally, this document discusses detection diode integration with the designed TFT-based APSs. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2014
5

Readout Circuitry for a Logarithmic CMOS Active Pixel Sensor That Facilities High Speed Image Processing

Vatte, Madhu Latha Reddy 19 August 2010 (has links)
No description available.
6

CMOS Photodetectors for Low-Light-Level Imaging Applications

Faramarzpour, Naser 04 1900 (has links)
Weak optical signals have to be measured in different fields of sciences including chemistry and biology. For example, very low levels of fluorescence emission should be detected from the spots on a DNA microarray that correspond to weakly expressed genes. High sensitivity charge-coupled devices (CCDs) are used in these applications. CCDs require special fabrication and are difficult to integrate with other circuits. CMOS is the technology used for fabrication of CPUs and other widely used digital components. CMOS is not optimized for light detection. CMOS circuits are however cheap, low power and can integrate several components. Active pixel sensor (APS) is the most common pixel structure for CMOS photodetector arrays. In this work we provide an accurate analysis of the APS signal using new models for the capacitance of the photodiode. We also provide a complete noise analysis of the pixel to calculate the SNR of the pixel and provide optimum operation points. We propose a new mode of operation for APS that can achieve at least l 0 dB higher SNR, than conventional APS, at light levels of less than 1 μW/cm^2. We fabricated several APS pixels in CMOS 0.18 μm technology and measured them to confirm the proposed analyzes. There are applications like fluorescence lifetime imaging that require both sensitivity and fast response. Photomultiplier tubes (PMTs) are commonly used in these applications to detect single photons in pico- to nano-seconds regime. PMTs are bulky and require high voltage levels. Avalanche photodiodes (APDs) are the semiconductor equivalent of PMTs. We have fabricated different APDs along with different peripheral circuitries in CMOS 0.18 μm technology. Our APDs have a 5.5 percent peak probability of detection of a photon at an excess bias of 2 V, and a 30 ns dead time, which is less than the previously reported results. The low price of CMOS makes modem diagnosis devices more available. The low power of CMOS leads to battery-driven hand-held imaging solutions, and its high integration leads to miniaturized imaging and diagnosis systems. A low-light-level CMOS imager paves the way for the future generation of biomedical diagnosis solutions. / Thesis / Doctor of Philosophy (PhD)
7

Random Telegraph Signal Noise in CMOS Image Sensor (CIS) and Use of a CIS in a Low-Cost Digital Microscope

Majumder, Sumit 10 1900 (has links)
<p>The introduction of the digital image sensor has triggered a revolution in the field of imaging. It has not only just replaced the conventional silver halide film based imaging system, but has also enormously widened the scope of imaging applications. Previously, charge-coupled devices (CCDs) were the most popular technology for image sensors. But in the past decade, they have been rapidly replaced by the CMOS image sensor (CIS) technology. The CCD image sensors offers higher sensitivity, wider dynamic range and better resolution compared to its CMOS imager counterparts. However, the lower power performance, higher speed of operation, easier integration with signal control and processing circuitries, and the use well-established mainstream fabrication process of CMOS technology, are key advantages that have served to propel CMOS imagers beyond CCDs in the market.</p> <p>However, CIS suffers from higher temporal noise compared to that of CCDs. One of the major noise sources in CIS is the 1/ noise generated from the in-pixel active amplifier. Due to continuous shrinking of MOS devices, the random telegraph signal (RTS) noise is emerging as a dominant noise source over other low frequency noise in CMOS imagers, resulting into reduced imaging performance.</p> <p>The RTS noise which evolves from trapping and de-trapping of electrons by the defects in the oxide, causes fluctuation in the drain current of the MOSFET. In this work, we have carried out time-domain measurement of RTS noise in CIS pixels. The time domain RTS measurements provide useful information about its characteristics in different operating conditions, which can be further used to extract the trap parameters and determine the optimum settings of operation of CIS.</p> <p>The capability of integrating various on-chip operations, higher speed and lower fabrication cost has made the CIS a good choice for various imaging applications. In order to demonstrate the extent of possible applications of CIS, we have developed an imaging system using a CIS. Two major concerns of biomedical imaging systems are their speed and cost. The system presented here is implemented using a CIS and FPGA (field programmable gate array) that provides a low-cost and high frame rate solution for biomedical microscopy.</p> / Master of Applied Science (MASc)
8

CMOS Active Pixel Sensors for Digital Cameras: Current State-of-the-Art

Palakodety, Atmaram 05 1900 (has links)
Image sensors play a vital role in many image sensing and capture applications. Among the various types of image sensors, complementary metal oxide semiconductor (CMOS) based active pixel sensors (APS), which are characterized by reduced pixel size, give fast readouts and reduced noise. APS are used in many applications such as mobile cameras, digital cameras, Webcams, and many consumer, commercial and scientific applications. With these developments and applications, CMOS APS designs are challenging the old and mature technology of charged couple device (CCD) sensors. With the continuous improvements of APS architecture, pixel designs, along with the development of nanometer CMOS fabrications technologies, APS are optimized for optical sensing. In addition, APS offers very low-power and low-voltage operations and is suitable for monolithic integration, thus allowing manufacturers to integrate more functionality on the array and building low-cost camera-on-a-chip. In this thesis, I explore the current state-of-the-art of CMOS APS by examining various types of APS. I show design and simulation results of one of the most commonly used APS in consumer applications, i.e. photodiode based APS. We also present an approach for technology scaling of the devices in photodiode APS to present CMOS technologies. Finally, I present the most modern CMOS APS technologies by reviewing different design models. The design of the photodiode APS is implemented using commercial CAD tools.
9

Active Pixel Sensor Architectures for High Resolution Large Area Digital Imaging

Taghibakhsh, Farhad 08 April 2008 (has links)
This work extends the technology of amorphous silicon (a-Si) thin film transistors (TFTs) from traditional switching applications to on-pixel signal amplification for large area digital imaging and in particular, is aimed towards enabling emerging low noise, high resolution and high frame rate medical diagnostic imaging modalities such as digital tomosynthesis. A two transistor (2T) pixel amplifier circuit based on a novel charge-gate thin film transistor (TFT) device architecture is introduced to shrink the TFT based pixel readout circuit size and complexity and thus, improve the imaging array resolution and reliability of the TFT fabrication process. The high resolution pixel amplifier results in improved electrical performance such as on-pixel amplification gain, input referred noise and faster readouts. In this research, a charge-gated TFT that operates as both a switched amplifier and driver is used to replace two transistors (the addressing switch and the amplifier transistor) of previously reported three transistor (3T) APS pixel circuits.. In addition to enabling smaller pixels, the proposed 2T pixel amplifier results in better signal-to-noise (SNR) by removing the large flicker noise source associated with the switched TFT and increased pixel transconductance gain since the large ON-state resistance of the switched TFT is removed from the source of the amplifier TFT. Alternate configurations of 2T APS architectures based on source or drain switched TFTs are also investigated, compared, and contrasted to the gate switched architecture using charge-gated TFT. A new driving scheme based on multiple row resetting is introduced which combined with the on-pixel gain of the APS, offers considerable improvements in imaging frame rates beyond those feasible for PPS based pixels. The novel developed 2T APS architectures is implemented in single pixel test structures and in 88 pixel test arrays with a pixel pitch of 100 µm. The devices were fabricated using an in-house developed top-gate TFT fabrication process. Measured characteristics of the test devices confirm the performance expectations of the 2T architecture design. Based on parameters extracted from fabricated TFTs, the input referred noise is calculated, and the instability in pixel transconductance gain over prolonged operation tine is projected for different imaging frame rates. 2T APS test arrays were packaged and integrated with an amorphous selenium (a-Se) direct x-ray detector, and the x-ray response of the a-Se detector integrated with the novel readout circuit was evaluated. The special features of the APS such as non-destructive readout and voltage programmable on-pixel gain control are verified. The research presented in this thesis extends amorphous silicon pixel amplifier technology into the area of high density pixel arrays such as large area medical X-ray imagers for digital mammography tomosynthesis. It underscores novel device and circuit design as an effective method of overcoming the inherent shortcomings of the a-Si material . Although the developed device and circuit ideas were implemented and tested using a-Si TFTs, the scope of the device and circuit designs is not limited to amorphous silicon technology and has the potential to be applied to more mainstream technologies, for example, in CMOS active pixel sensor (APS) based digital cameras.
10

Active Pixel Sensor Architectures for High Resolution Large Area Digital Imaging

Taghibakhsh, Farhad 08 April 2008 (has links)
This work extends the technology of amorphous silicon (a-Si) thin film transistors (TFTs) from traditional switching applications to on-pixel signal amplification for large area digital imaging and in particular, is aimed towards enabling emerging low noise, high resolution and high frame rate medical diagnostic imaging modalities such as digital tomosynthesis. A two transistor (2T) pixel amplifier circuit based on a novel charge-gate thin film transistor (TFT) device architecture is introduced to shrink the TFT based pixel readout circuit size and complexity and thus, improve the imaging array resolution and reliability of the TFT fabrication process. The high resolution pixel amplifier results in improved electrical performance such as on-pixel amplification gain, input referred noise and faster readouts. In this research, a charge-gated TFT that operates as both a switched amplifier and driver is used to replace two transistors (the addressing switch and the amplifier transistor) of previously reported three transistor (3T) APS pixel circuits.. In addition to enabling smaller pixels, the proposed 2T pixel amplifier results in better signal-to-noise (SNR) by removing the large flicker noise source associated with the switched TFT and increased pixel transconductance gain since the large ON-state resistance of the switched TFT is removed from the source of the amplifier TFT. Alternate configurations of 2T APS architectures based on source or drain switched TFTs are also investigated, compared, and contrasted to the gate switched architecture using charge-gated TFT. A new driving scheme based on multiple row resetting is introduced which combined with the on-pixel gain of the APS, offers considerable improvements in imaging frame rates beyond those feasible for PPS based pixels. The novel developed 2T APS architectures is implemented in single pixel test structures and in 88 pixel test arrays with a pixel pitch of 100 µm. The devices were fabricated using an in-house developed top-gate TFT fabrication process. Measured characteristics of the test devices confirm the performance expectations of the 2T architecture design. Based on parameters extracted from fabricated TFTs, the input referred noise is calculated, and the instability in pixel transconductance gain over prolonged operation tine is projected for different imaging frame rates. 2T APS test arrays were packaged and integrated with an amorphous selenium (a-Se) direct x-ray detector, and the x-ray response of the a-Se detector integrated with the novel readout circuit was evaluated. The special features of the APS such as non-destructive readout and voltage programmable on-pixel gain control are verified. The research presented in this thesis extends amorphous silicon pixel amplifier technology into the area of high density pixel arrays such as large area medical X-ray imagers for digital mammography tomosynthesis. It underscores novel device and circuit design as an effective method of overcoming the inherent shortcomings of the a-Si material . Although the developed device and circuit ideas were implemented and tested using a-Si TFTs, the scope of the device and circuit designs is not limited to amorphous silicon technology and has the potential to be applied to more mainstream technologies, for example, in CMOS active pixel sensor (APS) based digital cameras.

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