Three-dimensional quantum simulation of multigate nanowire field effect transistors

Detailed numerical methods for the three-dimensional quantum simulation of the multigate nanowire field effect transistors in the ballistic transport regime are presented in this work. The device has been modeled based on the effective mass theory and the non-equilibrium Green’s function formalism, and its simulation consists of solutions of the three-dimensional Poisson’s equation, two-dimensional Schrödinger equations on the cross-sectional planes, and one-dimensional transport equation. Details on numerical techniques for each of the simulation steps are described, with a special attention to the solution of the most CPU demanding two-dimensional Schrödinger equation.     

High temperature field effect hydrogen and hydrocarbon gas sensors based on SiC MOS devices

The growing need for reliable, efficient, high temperature hydrogen and hydrocarbon monitoring has fueled research into novel structures for gas sensing. Metal oxide semiconductor (MOS) devices employing a catalytic metal layer have emerged as one of the leading sensing platforms for such applications, owing to their high sensitivity and inherent capability for signal amplification. The limited operating temperature of such devices employing silicon as the semiconductor has led research efforts to focus on replacing them with devices based on silicon carbide (SiC). More recently, MOS devices having different oxide layers exhibiting improved sensing performance have emerged. Considering the amount of research that has been carried out in this area in recent times, it is important to elucidate the new findings and the gas interaction mechanisms that have been ascribed to such devices, and bring together several theories proposed by different research groups. In this paper we first highlight the needs which have driven research into SiC based field effect hydrogen and hydrocarbon sensors, illustrate the various structures being investigated, and describe the device evolution and current status. We provide several sensing examples of devices that make use of different oxide layers and demonstrate how their electrical properties change in the presence of the gases, as well as presenting the hydrogen gas interaction mechanisms of these sensors.     

Semiconducting metal oxides as sensors for environmentally hazardous gases

This article extensively reviews the recent development of semiconductor metal oxide gas sensors for environmentally hazardous gases including NO₂, NO, N₂O, H₂S, CO, NH₃, CH₄, SO₂ and CO₂. The gas sensing properties of differently-prepared metal oxides and loaded metal oxides towards nine environmentally hazardous gases have been individually compared and digested. Promising materials for sensitive and selective detection of each hazardous gas have been identified. For instance, unloaded WO₃ nanostructures are the most promising candidates for NO₂ sensing while metal catalyst loaded WO₃ and gold-loaded SnO₂ sensors are among the most effective for NO and N₂O sensing, respectively. Moreover, related gas-sensing mechanisms are comprehensively discussed.     

Three-dimensional simulation studies on electrostatic predictions for carbon nanotube field effect transistors

Analysis of the electrostatic characteristics and the gate capacitance of typical nanostructured carbon nanotube field effect transistors (CNTFETs) were performed numerically. A previously developed parallelized electrostatic Poisson's equation solver (PPES) is employed, coupled with a parallel adaptive mesh refinement (PAMR) to improve the numerical accuracy near the region where variation of potentials are significant. CNTFETs with four typical configurations of the gate electrode, the bottom gate (BG), the double gate (DG), the top gate (TG), and the surrounding gate (SG) were simulated. Effects of the nanotube arrangement and the gate length on the gate capacitance are presented and discussed. The simulation results show that SG-CNTFET possesses the largest gate capacitance among various structures. However, TG-CNTFET is recommended for practical applications by taking into account both the device performance and the difficulty of fabrication. According to the simulated gate capacitance, estimation of the on-state current of CNTFETs is possible.     

Accurate distributed and semidistributed models of field effect transistors for millimeter wave applications

An accurate distributed model of field effect transistors, including the parasitic impedances of the electrodes and the mutual coupling between them for analyzing the propagation effects along the electrodes working at millimeter wave frequencies, is presented. A numerical method is used to calculate the S‐parameters of the distributed model. Then, a corresponding simpler semidistributed model, which avoids solving coupled differential equations, is then presented. A GaAs pHEMT example is given to show the well agreement of the S‐parameters of the measurement and the distributed model ranging from 1 to 60 GHz. The S‐parameters of the semidistributed model agree well with that of the distributed model up to 100 GHz, and both of the models can be applied for S‐parameters prediction out of the measurement equipment range. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Analysis of the noble metal catalytic additives introduced by impregnation of as obtained SnO2 sol–gel nanocrystals for gas sensors

In order to clarify the role of the noble metal additives in the gas sensing mechanisms, three of the most common catalytic additives, such as Pd, Pt and Au, have been introduced in a sol–gel obtained tin oxide base material. The additives nominal weight concentrations used were 0.2% and 2%, and they were introduced in the precipitated tin oxide. A posterior calcination treatment was carried out, during 8 h, at the temperatures of 250°C, 400°C, 450°C, 600°C, 800°C and 1000°C. Structural and surface analysis of these nanopowders have been performed. Identification and localisation of metallic, 2+ and 4+ oxidised states of the used noble metals are discussed, and experimental evidences about their effects on the sensor performance are presented. Likewise, effects of their presence on the nanoparticle characteristics, and also on the material sensitivity to CO and CH₄, are analysed and discussed.     

Novel technique for estimating metal semiconductor field effect transitor parasitics

A novel technique is developed for extracting the gate resistance, parasitic inductances, and pad capacitances for metal semiconductor field effect transistor devices. The parameters are extracted from two sets of S‐parameter measurements: cold measurements and pinch‐off measurements. The proposed technique gives rise to reliable results and it is insensitive to the unavoidable measurement errors over any frequency range. The technique is tested on hypothetical data and applied to S‐parameter measurements of a few metal semiconductor field effect transistor devices on the same wafer to provide a unique solution. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 62–73, 2003.