JT8D and JT9D jet engine performance improvement program. Task 1: Feasibility analysis

JT8D and JT9D component performance improvement concepts which have a high probability of incorporation into production engines were identified and ranked. An evaluation method based on airline payback period was developed for the purpose of identifying the most promising concepts. The method used available test data and analytical models along with conceptual/preliminary designs to predict the performance improvements, weight, installation characteristics, cost for new production and retrofit, maintenance cost, and qualitative characteristics of candidate concepts. These results were used to arrive at the concept payback period, which is the time required for an airline to recover the investment cost of concept implementation

Schottky power diodes designed for improved breakdown characteristics

Silicon carbide (SiC) is a semiconductor material sold as substrates (like silicon is) for making semiconductor devices. It has advantages (compared to other semiconductors like silicon) regarding making devices that operate at high temperature, high electric fields and high current density. Overall, the semiconductor industry continues to expand and SiC products are a growing part of this. In 2016, global semiconductor sales reached nearly US340 billion (the highest ever) according to The Semiconductor Industry Association (SIA). Market growth is driven by the ever-increasing amount of semiconductor technology in devices the world depends on for working (as reported by SIA). Power electronic components such as semiconductor SiC power diodes used in cars for example are among the numerous areas where improvements in performance are continually sought. ‘Increasing electrification in vehicles generally – and in hybrid and electric vehicles specifically is energizing the market for power semiconductors in vehicles’ (IHS Markit report). The HIS report shows that the total market for power semiconductors (including discrete SiC power diodes) will increase from US5.5 billion in 2016 to more than US$8.5 billion in 2022. An increasing trend towards electric cars in the coming years is expected to drive the demand for electronic components made from suitable semiconductor materials, including SiC. The advantage of SiC semiconductor chips is that they have high-reliability in harsh environments like the environment of the drive train of vehicles which includes the engine and connected components to deliver power to the wheels of vehicles. Moreover, the car industry is just one area where improvements in power semiconductor devices are sought. Anywhere where there is control, or high transmission voltage and current and voltage conversion, will benefit from improvement in diode performance. Two important aspects of Schottky diode performance are how much current it can deliver when in the forward bias mode and how much voltage it can withstand when in current blocking mode. Too much current (forward bias) or too much voltage (typically a reverse bias consideration) across the diode will cause it to break down. Considering the value of the power semiconductor device market, the industry push for performance, and the possibilities that improvements in SiC materials bring to semiconductor research, SiC Schottky diodes (also called Schottky Barrier Diodes, SBD) were investigated to determine the influence of several factors that affect device performance. Minimising the loss of energy and maximising the possible delivered electric current and also blocking voltage capability by improving SiC Schottky diode electrical performance is an important area of semiconductor research and of value to industry. Breakdown in the forward and reverse bias modes will be the focus of this research but the other aspects will also be reported on too. For example, high forward current is desired but if it comes at the expense of high forward voltage then there will be high power loss in the diode which should ideally act as a switch with no power loss. Similarly, a high reverse bias is desired but if leakage current (reverse bias current) is high then again there is power loss. This study uses finite element modelling and experimental investigation of different metals for forming improved Schottky contacts. Contact geometry and electrode edge isolation techniques are investigated to optimise designs. Schottky contact geometry is optimised in order to minimise the incidents of maximum current density within the diode structure, where breakdown occurs. Surface preparation and surface treatment prior to Schottky formation and in particular the surface treatments used to give a carbon-rich SiC surface, which in this research has been found to reduce the turn-on voltage of SiC Schottky diodes, is also investigated. Optimised geometry and electrode edge isolation improvements are demonstrated using silicon substrates and this improvement can be applied to any metal-to-semiconductor combination. A diode requires an Ohmic contact and this is also studied here with the approach of using selective etching to prepare the SiC surface. SiC diodes were fabricated and used for electrical testing to determine the electrical characteristics. Moreover, the effects of the quality of the SiC itself on the breakdown voltage was investigated (the major qualifier for crystal quality is the value of the density of the defect known as a micropipe and this value is called MPD (for micropipe density) and given in SiC wafer specifications from suppliers

The Development of Microdosimetric Instrumentation for Quality Assurance in Heavy Ion Therapy, Boron Neutron Capture Therapy and Fast Neutron Therapy

This thesis presents research for the development of new microdosimetric instrumentation for use with solid-state microdosimeters in order to improve their portability for radioprotection purposes and for QA in various hadron therapy modalities. Monte Carlo simulation applications are developed and benchmarked, pertaining to the context of the relevant therapies considered. The simulation and experimental findings provide optimisation recommendations relating to microdosimeter performance and possible radioprotection risks by activated materials. The first part of this thesis is continuing research into the development of novel Silicon-on-Insulator (SOI) microdosimeters in the application of hadron therapy QA. This relates specifically to the optimisation of current microdosimeters, development of Monte Carlo applications for experimental validation, assessment of radioprotection risks during experiments and advanced Monte Carlo modelling of various accelerator beamlines. Geant4 and MCNP6 Monte Carlo codes are used extensively in this thesis, with rigorous benchmarking completed in the context of experimental verification, and evaluation of the similarities and differences when simulating relevant hadron therapy facilities. The second part of this thesis focuses on the development of a novel wireless microdosimetry system - the Radiodosimeter, to improve the operation efficiency and minimise any radioprotection risks. The successful implementation of the wireless Radiodosimeter is considered as an important milestone in the development of a microdosimetry system that can be operated by an end-user with no prior knowledge

Tunable Copper Microstructures in Blanket Films and Trenches Using Pulsed Electrodeposition

Copper interconnects in microelectronics have long been plagued with thermo-mechanical reliability issues. Control over the copper deposition process and resulting microstructure can dictate its material properties and reduce stresses as well as defects that form in the copper. In this thesis, pulse electrodeposition processing parameters were evaluated for their impact on the copper microstructure (grain size, texture, and twin density and stress state) through electron backscattering diffraction and wafer curvature measurements. Varying levels of constraint were also investigated for their effect on the copper microstructure to better understand the microstructures of more complex three-dimensional interconnects. Highly texture blanket copper films were deposited with various pulse frequencies and duty cycle, which was found to control grain size, orientation, and twin density. Higher twin densities were also observed in the films with lower residual stress. The findings from blanket film studies were carried over to trench deposited samples, where the influence of organic additives, typically used in the electrolytic bath to produce defect-free filling of advanced geometries, on the copper microstructure was studied. With the addition of organic additives, depositions produced finer grained structures with an increased contribution from the microstructure of the trench sidewall seed layer, especially with increasing trench aspect ratio. In addition, the increased constraint of the copper, resulted in larger stresses within the features and higher twin densities. The core of this dissertation demonstrated the ability to alter the resulting Cu microstructure through variations in pulse electrodeposition parameters

Study on High Energy Propellant Waste in the Processing of Fired Clay Bricks

Utilisation of propellant waste in fabrication of bricks is not only used as efficient waste disposal method but also to get better functional properties. In the present study, high energy propellant (HEP) waste additive mixed with soil and fly ash in different proportions during manufacturing of bricks has been investigated experimentally. X-ray diffraction (XRD) studies were carried out to confirm the brick formation and the effect of HEP waste. Ceramic bricks were fabricated with HEP waste additive in proper proportions i.e. 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3 wt %, 3.5 wt %, and 4 wt % and then evaluated for water absorption capability and compressive strength. Compressive strength of 6.7 N/mm2, and Water absorption of 22 % have been observed from modified fired bricks impregnated with HEM waste additive. Scanning electron microscopy (SEM) studies were carried out to analyze the effect of HEP waste additive on pore formation and distribution in the bricks. Further, the heat resulting from decomposition of propellants can cause a decrease in the energy required of baking process. The process of manufacturing of bricks with HEP waste additive is first of its kind till date

Microstructural evolution of epitaxial dielectric films derived from chemical precursors

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.Includes bibliographical references (leaves 138-150).by Man Fai Ngg.Ph.D

Effects of variable temperature and moisture conditions on respiration and nonstructural carbohydrate dynamics of tree roots

In warming climates, soil water content (SWC) may act as an important factor in determining belowground carbon dynamics in boreal forests. Here, we estimated the respiration and nonstructural carbohydrate (NSC) concentrations of tree roots in a mature Scots pine (Pinus sylvestris L.) stand in southern Finland during two growing seasons with contrasting weather conditions. Root respiration was estimated with four different methods: 1) incubating excised roots, 2) partitioning forest floor respirations with root exclusion, or 3) based on temperature response functions and 4) modelling with the whole-tree carbon model 'CASSIA'. In addition, we conducted a drought experiment in a greenhouse to determine the effect of reduced soil-water availability on respiration by incubating soil and roots of Scots pine saplings. We observed that the respiration of incubated roots of Scots pine saplings and soil decreased with drying after excluding the effect of temperature on respiration (RRES), soil being more sensitive to drought than roots. Similarly, RRES of incubated roots in the field was significantly decreased by lowered SWC, whereas respiration of the entire root system estimated with other methods was clearly higher in dryer and warmer than moister and cooler year. Nevertheless, incubated roots excavated from the topsoil are most affected by drying soil, which might not reflect the response of the entire root system. RRES of incubated roots was negatively associated with root fructose and glucose concentrations. At the same time, root fructose, glucose and sucrose concentrations were negatively associated with SWC due to their role in osmoregulation. Thereby it seems that RRES does not directly follow the changes in NSCs despite the apparent correlation. Our study highlights the responsive nature of root carbon dynamics in varying weather events that should be taken into account in estimating and modelling the impacts of warming climate.Peer reviewe

Development, Demonstration, and Device Physics of FET-Accessed One-Transistor GaAs Dynamic Memory Technologies

The introduction of digital GaAs into modem high-speed computing systems has led to an increasing demand for high-density memory in these GaAs technologies. To date, most of the memory development efforts in GaAs have been directed toward four- and six-transistor static RAM\u27s, which consume substantial chip area and dissipate much static power resulting in limited single-chip GaAs storage capacities. As it has successfully done in silicon, a one-transistor dynamic RAM approach could alleviate these problems making higher density GaAs memories possible. This dissertation discusses theoretical and experimental work that presents the possibility for a high-speed, low-power, one-transistor dynamic RAM technology in GaAs. The two elements of the DRAM cell, namely the charge storage capacitor and the access field-effect transistor have been studied in detail. Isolated diode junction charge storage capacitors have demonstrated 30 minutes of storage time at room temperature with charge densities comparable to those obtained in planar silicon DRAM capacitors. GaAs JFET and MESFET technologies have been studied, and with careful device design and choice of proper operating voltages experimental results show that both can function as acceptable access transistors. One-transistor MESFET- and JFET-accessed DRAM cells have been fabricated and operated at room temperature and above with a standby power dissipation that is only a small fraction of the power dissipated by the best commercial GaAs static RAM cells. A 2 x 2 bit demonstration array was built and successfully operated at room temperature to demonstrate the addressable read/write capability of this new technology

Wide Bandgap Based Devices

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits