The effect of incomplete ionization on the turn-off behavior of FS IGBTs

This letter demonstrates for the first time the effect of the incomplete ionization (I.I.) of the transparent p-anode layer on the static and dynamic characteristics of the field-stop insulated gate bipolar transistors (FS IGBTs). This effect needs to be considered in FS IGBTs TCAD modeling to match accurately the device characteristics across a wide range of temperatures. The acceptor ionization energy (EA) governing the I.I. mechanism for the p-anode is extracted via matching the experimental turn-off waveforms and the static performance with Medici simulator. © 1980-2012 IEEE.

Direct detection of molecular biorecognition by dipole sensing mechanism.

This work investigates the feasibility of transducing molecular-recognition events into a measurable potentiometric signal. It is shown for the first time that biorecognition of acetylcholine (ACh) can be translated to conformational changes in the enzyme, acetylcholine-esterase (AChE), which in turn induces a measurable change in surface potential. Our results show that a highly sensitive detector for ACh can be obtained by the dilute assembly of AChE on a floating gate derived field effect transistor (FG-FET). A wide concentration range response is observed for ACh (10(-2)-10(-9)M) and for the inhibitor carbamylcholine CCh (10(-6)-10(-11)M). These enhanced sensitivities are modeled theoretically and explained by the combined response of the device to local pH changes and molecular dipole variations due to the enzyme-substrate recognition event.

High-performance nanowire oxide photo-thin film transistor.

A gate-modulated nanowire oxide photosensor is fabricated by electron-beam lithography and conventional dry etch processing.. The device characteristics are good, including endurance of up to 10(6) test cycles, and gate-pulse excitation is used to remove persistent photoconductivity. The viability of nanowire oxide phototransistors for high speed and high resolution applications is demonstrated, thus potentially expanding the scope of exploitation of touch-free interactive displays.

Highly efficient detector of the neurotransmitter ACh and AChE inhibitors

Among the variety of applications for biosensors one of the exciting frontiers is to utilize those devices as post-synaptic sensing elements in chemical coupling between neurons and solid-state systems. The first necessary step to attain this challenge is to realize highly efficient detector for neurotransmitter acetylcholine (ACh). Herein, we demonstrate that the combination of floating gate configuration of ion-sensitive field effect transistor (ISFET) together with diluted covalent anchoring of enzyme acetylcholinesterase (AChE) onto device sensing area reveals a remarkable improvement of a four orders of magnitude in dose response to ACh. This high range sensitivity in addition to the benefits of peculiar microelectronic design show, that the presented hybrid provides a competent platform for assembly of artificial chemical synapse junction. Furthermore, our system exhibits clear response to eserine, a competitive inhibitor of AChE, and therefore it can be implemented as an effective sensor of pharmacological reagents, organophosphates, and nerve gases as well. © 2007 Materials Research Society.

Electron-beam patterning of polymer electrolyte films to make multiple nanoscale gates for nanowire transistors

We report an electron-beam based method for the nanoscale patterning of the poly(ethylene oxide)/LiClO4 polymer electrolyte. We use the patterned polymer electrolyte as a high capacitance gate dielectric in single nanowire transistors and obtain subthreshold swings comparable to conventional metal/oxide wrap-gated nanowire transistors. Patterning eliminates gate/contact overlap, which reduces parasitic effects and enables multiple, independently controllable gates. The method's simplicity broadens the scope for using polymer electrolyte gating in studies of nanowires and other nanoscale devices. © 2013 American Chemical Society.

200V superjunction lateral IGBT fabricated on partial SOI

A 200V lateral insulated gate bipolar transistor (LIGBT) was successfully developed using lateral superjunction (SJ) in 0.18μm partial silicon on insulator (SOI) HV process. The results presented are based on extensive experimental measurements and numerical simulations. For an n-type lateral SJ LIGBT, the p layer in the SJ drift region helps in achieving uniform electric field distribution. Furthermore, the p-pillar contributes to the on-state current. Furthermore, the p-pillar contributes to sweep out holes during the turn-off process, thus leading to faster removal of plasma. To realize this device, one additional mask layer is required in the X-FAB 0.18μm partial SOI HV process. © 2013 IEEE.

Predictive control for spacecraft rendezvous in an elliptical orbit using an FPGA

A field programmable gate array (FPGA)-based predictive controller for a spacecraft rendezvous manoeuvre is presented. A linear time varying prediction model is used to accommodate elliptical orbits, and a variable prediction horizon is used to facilitate finite time completion of manoeuvres. The resulting constrained optimisation problems are solved using a primal dual interior point algorithm. The majority of the computational demand is in solving a set of linear equations at each iteration of this algorithm. To accelerate this operation, a custom circuit is implemented, using a combination of Mathworks HDL Coder and Xilinx System Generator for DSP, and used as a peripheral to a MicroBlaze soft core processor. The system is demonstrated in closed loop by linking the FPGA with a simulation of the plant dynamics running in Simulink on a PC, using Ethernet. © 2013 EUCA.

Progress in the understanding of Ni silicide formation for advanced MOS structures

Metallic silicides have been used as contact materials on source/drain and gate in metal-oxide semiconductor (MOS) structure for 40 years. Since the 65 nm technology node, NiSi is the preferred material for contact in microelectronic due to low resistivity, low thermal budget, and low Si consumption. Ni(Pt)Si with 10 at.% Pt is currently employed in recent technologies since Pt allows to stabilize NiSi at high temperature. The presence of Pt and the very low thickness (<10 nm) needed for the device contacts bring new concerns for actual devices. In this work, in situ techniques [X-ray diffraction (XRD), X-ray reflectivity (XRR), sheet resistance, differential scanning calorimetry (DSC)] were combined with atom probe tomography (APT) to study the formation mechanisms as well as the redistribution of dopants and alloy elements (Pt, Pd.) during the silicide formation. Phenomena like nucleation, lateral growth, interfacial reaction, diffusion, precipitation, and transient phase formation are investigated. The effect of alloy elements (Pt, Pd.) and dopants (As, B.) as well as stress and defects induced by the confinement in devices on the silicide formation mechanism and alloying element redistribution is examined. In particular APT has been performed for the three-dimensional (3D) analysis of MOSFET at the atomic scale. The advances in the understanding of the mechanisms of formation and redistribution are discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Articulating current service development practices: a qualitative analysis of eleven mental health projects.

BACKGROUND: The utilisation of good design practices in the development of complex health services is essential to improving quality. Healthcare organisations, however, are often seriously out of step with modern design thinking and practice. As a starting point to encourage the uptake of good design practices, it is important to understand the context of their intended use. This study aims to do that by articulating current health service development practices. METHODS: Eleven service development projects carried out in a large mental health service were investigated through in-depth interviews with six operation managers. The critical decision method in conjunction with diagrammatic elicitation was used to capture descriptions of these projects. Stage-gate design models were then formed to visually articulate, classify and characterise different service development practices. RESULTS: Projects were grouped into three categories according to design process patterns: new service introduction and service integration; service improvement; service closure. Three common design stages: problem exploration, idea generation and solution evaluation - were then compared across the design process patterns. Consistent across projects were a top-down, policy-driven approach to exploration, underexploited idea generation and implementation-based evaluation. CONCLUSIONS: This study provides insight into where and how good design practices can contribute to the improvement of current service development practices. Specifically, the following suggestions for future service development practices are made: genuine user needs analysis for exploration; divergent thinking and innovative culture for idea generation; and fail-safe evaluation prior to implementation. Better training for managers through partnership working with design experts and researchers could be beneficial.

Optimising the dynamic performance of an all-wide-bandgap cascode switch

A SPICE simulation model of a novel cascode switch that combines a high voltage normally-on silicon carbide (SiC) junction field effect transistor (JFET) with a low voltage enhancement-mode gallium nitride field effect transistor (eGaN FET) has been developed, with the aim of optimising cascode switching performance. The effect of gate resistance on stability and switching losses is investigated and optimum values chosen. The effects of stray inductance on cascode switching performance are considered and the benefits of low inductance packaging discussed. The use of a positive JFET gate bias in a cascode switch is shown to reduce switching losses as well as reducing on-state losses. The findings of the simulation are used to produce a list of priorities for the design and layout of wide-bandgap cascode switches, relevant to both SiC and GaN high voltage devices. © 2013 IEEE.

High performance non-volatile ferroelectric copolymer memory based on a ZnO nanowire transistor fabricated on a transparent substrate

A high performance ferroelectric non-volatile memory device based on a top-gate ZnO nanowire (NW) transistor fabricated on a glass substrate is demonstrated. The ZnO NW channel was spin-coated with a poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) layer acting as a top-gate dielectric without buffer layer. Electrical conductance modulation and memory hysteresis are achieved by a gate electric field induced reversible electrical polarization switching of the P(VDF-TrFE) thin film. Furthermore, the fabricated device exhibits a memory window of ∼16.5 V, a high drain current on/off ratio of ∼105, a gate leakage current below ∼300 pA, and excellent retention characteristics for over 104 s. © 2014 AIP Publishing LLC.

High performance bilayer-graphene Terahertz detectors

© 2014 AIP Publishing LLC. We report bilayer-graphene field effect transistors operating as Terahertz (THz) broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity ∼1.2 V/W (1.3 mA/W) and a noise equivalent power ∼2 × 10-9 W/√Hz in the 0.29-0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.

Highly electron transparent Graphene for field emission triode gates

The enhanced emission performance of a graphene/Mo hybrid gate electrode integrated into a nanocarbon field emission micro-triode electron source is presented. Highly electron transparent gate electrodes are fabricated from chemical vapor deposited bilayer graphene transferred to Mo grids with experimental and simulated data, showing that liberated electrons efficiently traverse multi-layer graphene membranes with transparencies in excess of 50-68%. The graphene hybrid gates are shown to reduce the gate driving voltage by 1.1 kV, whilst increasing the electron transmission efficiency of the gate electrode significantly. Integrated intensity maps show that the electron beam angular dispersion is dramatically improved (87.9°) coupled with a 63% reduction in beam diameter. Impressive temporal stability is noted (<1.0%) with surprising negligible long-term damage to the graphene. A 34% increase in triode perveance and an amplification factor 7.6 times that of conventional refractory metal grid gate electrode-based triodes are noted, thus demonstrating the excellent stability and suitability of graphene gates in micro-triode electron sources. A nanocarbon field emission triode with a hybrid gate electrode is developed. The graphene/Mo gate shows a high electron transparency (50-68%) which results in a reduced turn-on potential, increased beam collimation, reduced beam diameter (63%), enhanced stability (<1% variation), a 34% increase in perveance, and an amplification 7.6 times that of equivalent conventional refractory metal gate triodes. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atom probe tomography of SRAM transistors: Specimen preparation methods and analysis

Different FIB-based sample preparation methods for atom probe analysis of transistors have been proposed and discussed. A special procedure, involving device deprocessing, has been used to analyze by APT a sub-30 nm transistor extracted from a SRAM device. The analysis provides three dimensional compositions of Ni-silicide contact, metal gate and high-k oxide of the transistor gate. © 2013 Elsevier B.V. All rights reserved.

Pt redistribution in N-MOS transistors during Ni salicide process

Atom probe tomography was used to study the redistribution of platinum during Ni(10 at.%Pt) silicidation of n-doped polycrystalline Si. These measurements were performed after the two annealing steps of standard salicide process both on a field-effect transistor and on unpatterned region submitted to the same process. Very similar results are obtained in unpatterned region and in transistor gate contact. The first phase to form is not the expected δ-Ni2Si but the non stoichiometric θ-Ni2Si. Pt redistribution is strongly influenced by this phase and the final distribution is different from what is reported in literature. © 2013 Elsevier B.V. All rights reserved.