Review of recent research towards power cable life cycle management

Power cables are integral to modern urban power transmission and distribution systems. For power cable asset managers worldwide, a major challenge is how to manage effectively the expensive and vast network of cables, many of which are approaching, or have past, their design life. This study provides an in-depth review of recent research and development in cable failure analysis, condition monitoring and diagnosis, life assessment methods, fault location, and optimisation of maintenance and replacement strategies. These topics are essential to cable life cycle management (LCM), which aims to maximise the operational value of cable assets and is now being implemented in many power utility companies. The review expands on material presented at the 2015 JiCable conference and incorporates other recent publications. The review concludes that the full potential of cable condition monitoring, condition and life assessment has not fully realised. It is proposed that a combination of physics-based life modelling and statistical approaches, giving consideration to practical condition monitoring results and insulation response to in-service stress factors and short term stresses, such as water ingress, mechanical damage and imperfections left from manufacturing and installation processes, will be key to success in improved LCM of the vast amount of cable assets around the world

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Gate oxide failure in MOS devices

The thesis presents an experimental and theoretical investigation of gate oxide breakdown in MOS networks, with a particular emphasis on constant voltage overstress failure. It begins with a literature search on gate oxide failure mechanisms, particularly time-dependent dielectric breakdown, in MOS devices. The experimental procedure is then reported for the study of gate oxide breakdown under constant voltage stress. The experiments were carried out on MOSFETs and MOS capacitor structures, recording the characteristics of the devices before and after the stress. The effects of gate oxide breakdown in one of the transistors in an nMOS inverter were investigated and several parameters were found to have changed. A mathematical model for oxide breakdown, based on physical mechanisms, is proposed. Both electron and hole trapping occurred during the constant voltage stress. Breakdown appears to take place when the trapped hole density reach a critical value. PSPICE simulations were performed for the MOSFETs, nMOS inverter and CMOS logic circuits. Two models of MOSFET with gate oxide short were validated. A good agreement between experiments and simulations was achieved

Yield and Reliability Analysis for Nanoelectronics

As technology has continued to advance and more break-through emerge, semiconductor devices with dimensions in nanometers have entered into all spheres of our lives. Accordingly, high reliability and high yield are very much a central concern to guarantee the advancement and utilization of nanoelectronic products. However, there appear to be some major challenges related to nanoelectronics in regard to the field of reliability: identification of the failure mechanisms, enhancement of the low yields of nano products, and management of the scarcity and secrecy of available data [34]. Therefore, this dissertation investigates four issues related to the yield and reliability of nanoelectronics. Yield and reliability of nanoelectronics are affected by defects generated in the manufacturing processes. An automatic method using model-based clustering has been developed to detect the defect clusters and identify their patterns where the distribution of the clustered defects is modeled by a new mixture distribution of multivariate normal distributions and principal curves. The new mixture model is capable of modeling defect clusters with amorphous, curvilinear, and linear patterns. We evaluate the proposed method using both simulated and experimental data and promising results have been obtained. Yield is one of the most important performance indexes for measuring the success of nano fabrication and manufacturing. Accurate yield estimation and prediction is essential for evaluating productivity and estimating production cost. This research studies advanced yield modeling approaches which consider the spatial variations of defects or defect counts. Results from real wafer map data show that the new yield models provide significant improvement in yield estimation compared to the traditional Poisson model and negative binomial model. The ultra-thin SiO2 is a major factor limiting the scaling of semiconductor devices. High-k gate dielectric materials such as HfO2 will replace SiO2 in future generations of MOS devices. This study investigates the two-step breakdown mechanisms and breakdown sequences of double-layered high-k gate stacks by monitoring the relaxation of the dielectric films. The hazard rate is a widely used metric for measuring the reliability of electronic products. This dissertation studies the hazard rate function of gate dielectrics breakdown. A physically feasible failure time distribution is used to model the time-to-breakdown data and a Bayesian approach is adopted in the statistical analysis

Prognostics for Electronics Components of Avionics Systems

Electronics components have and increasingly critical role in avionics systems and for the development of future aircraft systems. Prognostics of such components is becoming a very important research filed as a result of the need to provide aircraft systems with system level health management. This paper reports on a prognostics application for electronics components of avionics systems, in particular, its application to the Isolated Gate Bipolar Transistor (IGBT). The remaining useful life prediction for the IGBT is based on the particle filter framework, leveraging data from an accelerated aging tests on IGBTs. The accelerated aging test provided thermal-electrical overstress by applying thermal cycling to the device. In-situ state monitoring, including measurements of the steady-state voltages and currents, electrical transients, and thermal transients are recorded and used as potential precursors of failure

Towards Prognostics for Electronics Components

Electronics components have an increasingly critical role in avionics systems and in the development of future aircraft systems. Prognostics of such components is becoming a very important research field as a result of the need to provide aircraft systems with system level health management information. This paper focuses on a prognostics application for electronics components within avionics systems, and in particular its application to an Isolated Gate Bipolar Transistor (IGBT). This application utilizes the remaining useful life prediction, accomplished by employing the particle filter framework, leveraging data from accelerated aging tests on IGBTs. These tests induced thermal-electrical overstresses by applying thermal cycling to the IGBT devices. In-situ state monitoring, including measurements of steady-state voltages and currents, electrical transients, and thermal transients are recorded and used as potential precursors of failure

The Role of Interface Effects and Minority Carriers in the Metal-Semiconductor Schottky Junction

The metal-semiconductor (MS) Schottky barrier junction, formed by putting a metal in contact with a semiconductor crystal, is the simplest form of electronic rectifier. Despite the simple structure, the MS junction shows a variety of anomalous electrical characteristics. The non-ideality is generally described as a linear bias-dependence of the energy barrier height at the MS junction, quantified by an ideality factor. As the physical origin of this bias-dependent barrier height, the presence of various interface effects, such as the Schottky barrier inhomogeneity, interface trap states and morphological defects, have been proposed. However, there is no consensus among the researchers about the extent to which each of these interface anomalies effect the ideality of the junction. Another intriguing aspect of the Schottky junction is its ability to inject minority carriers under certain conditions, as was demonstrated by the early works in the 1940s (e.g., the point contact transistor). However, the lack of physical understanding of this phenomenon, combined with poor reproducibility and the development of the p-n junction, inhibited technological progress of Schottky bipolar emitters. In recent years, the development of new material technologies, such as epitaxial graphene, has opened up possibilities for novel bipolar mode Schottky devices, reviving the interest in the theory of minority carrier injection in Schottky junctions. In this study, the role of non-ideal interface effects and minority carrier injection on the transport properties of the Schottky junction interface are explored in relation to experimental observations made in silicon carbide Schottky interfaces. Silicon carbide (SiC) is an indirect wide band gap material with electronic and thermal properties suitable for high power, high temperature and high frequency electronic applications. The electronic applications of SiC electronics include high power systems such a hybrid/electric vehicle and smart grid systems as well as high sensitivity sensors, such as nuclear radiation detectors. Many of these applications require large barrier Schottky junctions, which are obtained by using large work function metals, such as nickel (Ni) and platinum (Pt). As the Schottky junctions are formed on the surface of the semiconductor crystal, the crystal quality, and especially the surface characteristics are important regulators of the Schottky device performance. In this work, the epitaxial growth of 4H-SiC by CVD was optimized using dichlorosilane, a halogenated reactant gas as the silicon precursor. Large barrier (\u3e 1.6 eV) Ni/4H-SiC Schottky contacts were fabricated on lightly doped n-type SiC epitaxial layers. The as-deposited diodes showed non-ideal characteristics, Rapid thermal annealing of the contacts at \u3e 650oC improved the diode ideality. In this dissertation, the Schottky barrier inhomogeneity in the as-deposited diodes is studied using Tung’s inter-acting barrier model. It is shown that the Tung model was not applicable for the highly non-ideal (n \u3e 1.2) Schottky junctions. Rather, it is argued that interface trap states are responsible for the high level of non-ideality based on the observation of hysteresis patterns in the I-V and C-V characteristics. The trap density is estimated at 108~1010 cm-2 from the hysteresis results. In a parallel effort, the very large barrier (Фp ~2.6 eV) Schottky heterojunction between epitaxial graphene (EG) and p-doped SiC was studied in this work for its potential in sensing applications. Surprisingly, the junction showed the capability of high efficiency ( \u3e 99%) minority carrier injection. The theories of minority carrier injection in MS junctions are re-visited in this dissertation for explaining this result. It is shown analytically that highly efficient minority carrier injection is possible in large barrier Schottky junctions under a high injection level. An EG/p-SiC/n-SiC photo-transistor structure was developed that showed a bipolar gain in the order of 102 and a responsivity of 101~102 A/W under UV illumination. The bipolar EG/SiC Schottky junction, therefore, opens up unique possibilities in radiation detection and power switching applications