Recently, several SiGe HBT devices fabricated on CMOS-compatible silicon on insulator (SOI) substrates (SiGe HBTs-on-SOI) have been demonstrated, combining the well-known SiGe HBT performance with the advantages of SOI substrates. These new devices are especially interesting in the context of extreme environments - highly challenging surroundings that lie outside commercial and even military electronics specifications. However, fabricating HBTs on SOI substrates instead of traditional silicon bulk substrates requires extensive modifications to the structure of the transistors and results in significant trade-offs. The present work investigates, with measurements and TCAD simulations, the performance and reliability of SiGe heterojunction bipolar transistors fabricated on silicon on insulator substrates with respect to operation in extreme environments such as at extremely low or extremely high temperatures or in the presence of radiation (both in terms of total ionizing dose and single effect upset).

Many legacy nuclear facilities exist with the number of such facilities due to increase in the future. For a variety of reasons, some of these facilities have poorly documented blueprints and floor plans. This has led to many areas within such facilities being left unexplored and in an unknown state for some considerable time. The risk to health that these areas might pose has in some cases precluded human exploration and facilities have been maintained in a containment state for many years. However, in more recent years there has been a move to decommission such facilities. The change of strategy from containment to decommissioning will require knowledge of what it is that needs to be decommissioned. It is hoped that an autonomous or semi- autonomous robotic solution can satisfy the requirement. For successful mapping of such environments, it is required that the robot is capable of producing complete scans of the world around it. As it moves through the environment the robot will not only need to map the presence, type and extent of radioactivity, but do so in a way that is economical from the perspective of battery life. Additionally, the presence of radioactivity presents a threat to the robot electronics. Exposure to radiation will be necessary but should be minimised to prolong the functional life of the robot. Some tethered robots have been developed for such applications, but these can cause issues such as snagging or the tether inadvertently spreading contamination, due to being dragged along the floor. Nuclear environments have very unique challenges, due to the radiation. Alpha and beta radiation have a short emission distance and therefore cannot be detected until the robot is in very close proximity. Although the robot will not become disabled by these forms of radiation, it may become contaminated which is undesirable. Radiation from gamma sources can be detected at range, however pinpointing a source requires sensors to be taken close to the emitter, which has adverse effects on the robot's electronics, for example gamma radiation damages silicon based electronics. Anything entering these environments is deemed to be contaminated and will eventually require disposal. Consequently the number of entries made should ideally be minimised, to reduce the production and spread of potential waste/contamination. This thesis presents results from an investigation of ways to provide complete scans of an environment with novel algorithms which take advantage of common features found in industrial environments and thereby allow for gaps in the data set to be detected. From this data it is then possible to calculate a minimum set of way points required to be visited to allow for all of the gaps to be filled in. This is achieved by taking into account the sensor's parameters such as minimum and maximum sensor range, angle of incidence and optimal sensor distance, along with robot and environmental factors. An investigation into appropriate exploration strategies has been undertaken looking at the ways in which gamma radiation sources affect the coverage of an environment. It has discovered undesired behaviours exhibited by the robot when radiation is present. To overcome these behaviours a novel movement strategy has been presented, along with a set of linear and binary battery modifiers, which adapt common movement strategies to help improve overall coverage of an unknown environment. Collaborative exploration of unknown environments has also been investigated, looking into the specific challenges radiation and contamination offer. This work has presented new ways of allowing multiple robots to independently explore an environment, sharing knowledge as they go, whilst safely exploring unknown hazardous space where a robot may be lost due to contamination or radiation damage.

Viruses are ubiquitous biological entities whose importance and role in aquatic habits is beginning to take form. However, several habitats have undergone limited to no examination with viral-geochemical parameters minimally examined and viral-mineral relationships in the natural environment and the role of mineralization on viral-host dynamic completely lacking. To further develop knowledge on the presence and abundances of viruses, how viruses impact aquatic systems, and how viral-host interactions can be impacted under mineralizing conditions, viruses were examined under a variety of habitats and experimental conditions. Water samples were collected from the deep subsurface (up to 450 m underground) and acid mine drainage (AMD) systems in order to determine the presence, abundance, and viral-geochemical relationships within the systems. Samples were also collected from a variety of freshwater habitats, which have undergone limited examination, to determine viral-geochemical and viral-mineral relationships. Lastly, bacteriophage-host dynamics were examined under authigenic mineral precipitation to determine how mineralization impacts this relationship. Results reveal that not only are viruses present in the deep subsurface and AMD systems, but they are abundant (up to 107 virus-like particles/mL) and morphogically diverse. Viruses are also the strongest predictor of prokaryotic abundance in southern Ontario freshwater systems where potential nutrients are rich. Geochemical variables, such as pH and Eh, were shown to have negative impacts of viral abundance indicting that AMD environments are detrimental for free viruses (i.e. not particle associated). Direct evidence of viral-mineral interactions was found using transmission electron microscopy as viral particles were shown attached to iron-bearing mineral phases (determined through elemental analysis). In addition, evidence of viral participation in mineralization events was found in both AMD and freshwater environments where inverse correlations were noted between viral abundance and jarosite saturation indices (r = -0.71 and r = -0.33, respectively), and goethite saturation indices were also noted to be the strongest predictor of VLP abundance in freshwater habitats explaining 78% of the variability in the data. Lastly, iron precipitation and/or metal ion binding to bacterial surfaces greatly reduced phage replication (~98%) revealing bacterial mineralization has a protective benefit strongly hindering viral replication.

Viruses are ubiquitous biological entities whose importance and role in aquatic habits is beginning to take form. However, several habitats have undergone limited to no examination with viral-geochemical parameters minimally examined and viral-mineral relationships in the natural environment and the role of mineralization on viral-host dynamic completely lacking. To further develop knowledge on the presence and abundances of viruses, how viruses impact aquatic systems, and how viral-host interactions can be impacted under mineralizing conditions, viruses were examined under a variety of habitats and experimental conditions. Water samples were collected from the deep subsurface (up to 450 m underground) and acid mine drainage (AMD) systems in order to determine the presence, abundance, and viral-geochemical relationships within the systems. Samples were also collected from a variety of freshwater habitats, which have undergone limited examination, to determine viral-geochemical and viral-mineral relationships. Lastly, bacteriophage-host dynamics were examined under authigenic mineral precipitation to determine how mineralization impacts this relationship. Results reveal that not only are viruses present in the deep subsurface and AMD systems, but they are abundant (up to 107 virus-like particles/mL) and morphogically diverse. Viruses are also the strongest predictor of prokaryotic abundance in southern Ontario freshwater systems where potential nutrients are rich. Geochemical variables, such as pH and Eh, were shown to have negative impacts of viral abundance indicting that AMD environments are detrimental for free viruses (i.e. not particle associated). Direct evidence of viral-mineral interactions was found using transmission electron microscopy as viral particles were shown attached to iron-bearing mineral phases (determined through elemental analysis). In addition, evidence of viral participation in mineralization events was found in both AMD and freshwater environments where inverse correlations were noted between viral abundance and jarosite saturation indices (r = -0.71 and r = -0.33, respectively), and goethite saturation indices were also noted to be the strongest predictor of VLP abundance in freshwater habitats explaining 78% of the variability in the data. Lastly, iron precipitation and/or metal ion binding to bacterial surfaces greatly reduced phage replication (~98%) revealing bacterial mineralization has a protective benefit strongly hindering viral replication.

This work evaluates two SiGe BiCMOS technology platforms as candidates for implementing extreme environment capable circuitry, with an emphasis on applications requiring high sensitivity and low noise. In Chapter 1, applications requiring extreme environment sensing circuitry are briefly reviewed and the motivation for undertaking this study is outlined. A case is then presented for the use of SiGe BiCMOS technology to meet this need, documenting the benefits of operating SiGe HBTs at cryogenic temperatures. Chapter 1 concludes with a brief description of device radiation effects in bipolar and CMOS devices, and a basic overview of noise in semiconductor devices and electronic components. Chapter 2 further elaborates on a specific application requiring low-noise circuitry capable of operating at cryogenic temperatures and proposes a number of variants of band-gap reference circuits for use in said system. Detailed simulation and theoretical analysis of the proposed circuits are presented and compared with measurements, validating the techniques used in the proposed designs and emphasizing the need for further understanding of device level low-temperature noise phenomena. Chapter 3 evaluates the feasibility of using a SiGe BiCMOS process, whose response to ionizing radiation was previously uncharacterized, for use in unshielded electronic systems needed for exploration of deep space planets or moons, specifically targeting Europa mission requirements. Measured total ionizing dose (TID) responses for both CMOS and bipolar SiGe devices are presented and compared to similar technologies. The mechanisms responsible for device degradation are outlined, and an explanation of unexpected results is proposed. Finally, Chapter 4 summarizes the work presented and understanding provided by this thesis, concluding by outlining future research needed to build upon this study and fully realize SiGe based extreme environment capable precision electronic systems.

The objective of this work is to investigate the performance of SiGe HBTs and scaled CMOS devices in extreme environments. In this work, the inverse mode operation of SiGe HBTs is investigated as a potential solution to the vulnerability of SiGe HBTs to single event effects. The performance limitations of SiGe HBTs operating in inverse mode are investigated through an examination of the effects of scaling on inverse mode performance and optimization schemes for inverse mode performance enhancements are discussed and demonstrated. In addition the performance of scaled MOSFETs, that constitute the digital backbone of any BiCMOS technology, is investigated under radiation exposure and cryogenic temperatures. Extreme environments and their effects on semiconductor devices are introduced in Chapter 1. The immunity of 90nm MOSFETs to total ionizing dose damage under proton radiation is demonstrated. Inverse mode operation of SiGe HBTs is introduced in Chapter 2 as a potential radiation hard solution by design. The effect of scaling on inverse mode performance of SiGe HBTs is investigated and the performance limitations in inverse mode are identified. Optimization schemes for improving inverse mode performance of SiGe HBTs are discussed in Chapter 3. Inverse mode performance enhancement is demonstrated experimentally in optimized device structures manufactured in a commercial third generation SiGe HBT BiCMOS platform. Further, a cascode device structure, the combines the radiation immunity of an inverse mode structure with the performance of a forward mode common emitter device is XIV discussed. Finally, idealized doping profiles for inverse mode performance enhancement is discussed through TCAD simulations. The cryogenic performance of inverse mode SiGe HBTs are discussed in Chapter 4. A novel base current behavior at cryogenic temperature is identified and its effect on the inverse mode performance is discussed. Matching performance of a 90nm bulk CMOS technology at cryogenic temperatures is investigated experimentally and through TCAD simulations in Chapter 5. The effect of various process parameters on the temperature sensitivity of threshold voltage mismatch is discussed. The potential increase of mismatch in subthreshold MOSFETs operating in cryogenic temperatures due to hot carrier effects is also investigated.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cressler, John; Committee Member: Deo, Chaitanya; Committee Member: Doolittle, Alan; Committee Member: Keezer, David; Committee Member: May, Gary; Committee Member: Papapolymerou, John. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D. in Chemical Engineering)--Vanderbilt University, Aug. 2008. / Title from title screen. Includes bibliographical references.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: John D. Cressler; Committee Member: John Papapolymerou; Committee Member: Shyh-Chiang Shen.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cressler, John D.; Committee Member: Papapolymerou, John; Committee Member: Ralph, Stephen; Committee Member: Shen, Shyh-Chiang; Committee Member: Zhou, Hao Min.