Development of GaN transducer and on-chip concentrator for galvanic current sensing

Gallium nitride (GaN) magnetic high electron mobility transistors (MagHEMTs) with different gate lengths intended for integration with magnetic flux concentrator for galvanic isolation are presented. Detailed discussions on the physical mechanisms behind the sensitivity change at room temperature with respect to gate geometry are given. The relative sensitivity of dual-drain GaN MagHEMTs with a device length of L = 65 μm and a width of W = 20 μm is measured at the highest of S = 17.21%/T and the lowest of S = 7.69%/T at VGS= -2 V and VGS= 0 V, respectively. In addition, a novel spiral magnetic flux concentrator with the conversion factor of up to FC= 96 mT/A is designed for improving the performance of the optimized MagHEMTs in ICs. It is predicted that a spiral configuration is a necessity to enhance the conversion factor for a long MagHEMT

Evaluation of the impact of urban water systems on railways: The scenario of track flooding caused by a water main burst

Failures and disruption scenarios can reveal inherent but little known dependencies that exist between technical infrastructure systems. Whereas the dependencies between infrastructures in their normal state of operation are usually obvious and mutually correlated, interdependencies, when systems are disrupted, show a great deal of variety, depending on the specific scenario. The literature reveals the lack of a proper tool that can evaluate and quantify the scenario of track flooding caused by a water main burst, a cross-sectoral failure that can impact the operation of two urban infrastructure systems: the railways and the water supply. This work presents an approach to investigate the impact of urban water systems on railways and applies it to the case study of the Thameslink railway and Thames Water assets in London. The developed tool can be integrated into city level water supply GIS systems to facilitate the understanding of external risks (transport disruption) caused by an internal failure (water main bursts). Also, the results can help railway system operators facilitate the decision-making process in terms of drainage policy and maintenance activities

Insulated gate and surface passivation structures for GaN-based power transistors

Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Si- and GaAs-based devices counterparts. Metal–insulator–semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator materials have been applied to GaN-based transistors, the properties of insulator/III-N interfaces are still not fully understood. This is mainly due to the difficulty of characterizing insulator/AlGaN interfaces in a MIS HEMT because of the two resulting interfaces: insulator/AlGaN and AlGaN/GaN, making the potential modulation rather complicated. Although there have been many reports of low interface-trap densities in HEMT MIS capacitors, several papers have incorrectly evaluated their capacitance–voltage (C–V) characteristics. A HEMT MIS structure typically shows a 2-step C–V behavior. However, several groups reported C–V curves without the characteristic step at the forward bias regime, which is likely to the high-density states at the insulator/AlGaN interface impeding the potential control of the AlGaN surface by the gate bias. In this review paper, first we describe critical issues and problems including leakage current, current collapse and threshold voltage instability in AlGaN/GaN HEMTs. Then we present interface properties, focusing on interface states, of GaN MIS systems using oxides, nitrides and high-κ dielectrics. Next, the properties of a variety of AlGaN/GaN MIS structures as well as different characterization methods, including our own photo-assisted C–V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology

Analysis of GaN MagHEMTs

The simulations, calibration, measured output currents and relative sensitivity of the first-ever fabricated gallium nitride (GaN) magnetic high electron mobility transistors (MagHEMTs) are given in this work. The current imbalance and relative sensitivities obtained from simulations are calibrated against the experimental data measured at room temperature (RT). The average calculated relative sensitivity of the 60 fabricated devices measured is 11.98%T−1. We present three-dimensional simulation results of GaN split-current magnetic sensors for different geometrical and biasing parameters at various ambient temperatures. The detailed analysis of device behaviour is given for each scenario. The relative sensitivity degrades at 400 K (S r = 6.78%T−1) and 500 K (S r = 4.91%T−1) compared to the sensitivity measured at 300 K (S r = 11.98%T−1). The GaN MagHEMTs show promising predicted relative sensitivities at 400 K and 500 K compared to silicon magnetic field effect transistors (MagFETs) operating at much lower temperatures. Moreover, device geometrical parameters are optimised to enhance the relative sensitivity from 11.98%T−1 to 23.29%T−1 using the commercial simulation toolbox Atlas, by Silvaco

Device simulation and optimization of i-GaN capped AlGaN/AlN/GaN HEMT

No abstract available

Device simulation and optimization of i-GaN capped AlGaN/AlN/GaN HEMT

No abstract available