Nonprecious NiFe, CoFe oxyhydroxide are among the most active materials for oxygen evolution reaction (OER) in basic media. However, phase separation in these composites during water oxidation rema...

Operando Raman Spectroscopy Reveals Cr-Induced-Phase Reconstruction of NiFe and CoFe Oxyhydroxides for Enhanced Electrocatalytic Water Oxidation

A glucose biosensor has been fabricated by immobilizing glucose oxidase (GOx) on unhybridized titanium dioxide nanotube arrays using an optimized cross-linking technique. The TiO2 nanotube arrays were synthesized directly on a titanium substrate by anodic oxidation. The structure and morphology of electrode material were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the glucose biosensor were conducted by cyclic voltammetry and chronoamperometry measurements. It gives a linear response to glucose in the 0.05 to 0.65 mM concentration range, with a correlation coefficient of 0.9981, a sensitivity of 199.6 μA mM−1 cm−2, and a detection limit as low as 3.8 µM. This glucose biosensor exhibited high selectivity for glucose determination in the presence of ascorbic acid, sucrose and other common interfering substances. This glucose biosensor also performed good reproducibility and long-time storage stability. This optimized cross-linking technique could open a new avenue for other enzyme biosensors fabrication.

Glucose biosensor based on glucose oxidase immobilized on unhybridized titanium dioxide nanotube arrays

Solution-Processed Rad-Hard Amorphous Metal-Oxide Thin-Film Transistors

As the major redox couple and nonprotein thiol source in human tissues, the level of glutathione (GSH) has been a concern for its relation with many diseases. However, the similar physical and chemical properties of interference molecules such as cysteine (Cys) and homocysteine (Hcy) make discriminative detection of GSH in complex biological fluids challenging. Here we report a novel surface-enhanced Raman scattering (SERS) platform, based on silver-nanoparticle-embedded porous silicon disks (PSDs/Ag) substrates for highly sensitive and selective detection of GSH in biofluids. Silver nanoparticles (AgNPs) were reductively synthesized and aggregated directly into pores of PSDs, achieving a SERS enhancement factor (EF) up to 2.59 × 107. Ellman’s reagent 5,5′-ditho-bis (2-nitrobenzoic acid) (DTNB) was selected as the Raman reactive reporting agent, and the GSH quantification was determined using enzymatic recycling method, and allowed the detection limit of GSH to be down to 74.9 nM using a portable Raman sp...

Silver-Nanoparticle-Embedded Porous Silicon Disks Enabled SERS Signal Amplification for Selective Glutathione Detection

Flexible electronics is rapidly evolving towards devices and circuits to enable numerous new applications. The high-performance, in terms of response speed, uniformity and reliability, remains a sticking point. The potential solutions for high-performance related challenges bring us back to the timetested silicon based electronics. However, the changes in the response of silicon based devices due to bending related stresses is a concern, especially because there are no suitable models to predict this behavior. This also makes the circuit design a difficult task. This paper reports advances in this direction, through our research on bendable piezoelectric oxide semiconductor field effect transistor (POSFET) based touch sensors. The analytical model of POSFET, complimented with Verilog- A model, is presented to describe the device behavior under normal force in planar and stressed conditions. Further, dynamic readout circuit compensation of POSFET devices have been analyzed and compared with similar arrangement to reduce the piezoresistive effect under tensile and compressive stresses. This approach introduces a first step towards the systematic modeling of stress induced changes in device response. This systematic study will help realize high-performance bendable microsystems with integrated sensors and readout circuitry on ultra-thin chips (UTCs) needed in various applications, in particular, the electronic skin (e-skin).

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Device Modelling for Bendable Piezoelectric FET-Based Touch Sensing System

The carrier mobility of Si material can be enhanced under strain, and the stress magnitude can be measured by the Raman spectrum. In this paper, we aim to study the penetration depths into biaxially-strained Si materials at various Raman excitation wavelengths and the stress model corresponding to Raman spectrum in biaxially-strained Si. The experimental results show that it is best to use 325 nm excitation to measure the material stress in the top strained Si layer, and that one must pay attention to the distortion of the buffer layers on measuring results while 514 nm excitation is also measurable. Moreover, we established the stress model for Raman spectrum of biaxially-strained Si based on the Secular equation. One can obtain the stress magnitude in biaxially-strained Si by the model, as long as the results of the Raman spectrum are given. Our quantitative results can provide valuable references for stress analysis on strained materials.

Penetration depth at various Raman excitation wavelengths and stress model for Raman spectrum in biaxially-strained Si

The tunnel field-effect transistor (TFET) is a potential candidate for the post-CMOS era. As one of the most important electrical parameters of a device, double gate TFET (DG-TFET) gate threshold voltage was studied. First, a numerical simulation study of transfer characteristic and gate threshold voltage in DG-TFET was reported. Then, a simple analytical model for DG-TFET gate threshold voltage V
 TG was built by solving quasi-two-dimensional Poisson equation in Si film. The model as a function of the drain voltage, the Si layer thickness, the gate length and the gate dielectric was discussed. It is shown that the proposed model is consistent with the simulation results. This model should be useful for further investigation of performance of circuits containing TFETs.

Double-gate tunnel field-effect transistor: Gate threshold voltage modeling and extraction

An analytical model for quasi-static C – V characteristics of strained-Si/SiGe pMOS capacitor is presented. By analyzing the model, the dependence of the C – V characteristics on the strained-Si layer thickness, doping concentration and Ge fraction is studied. Also, the reason of the shift of the plateau, observed in the gate C – V characteristics of the strained-Si pMOS capacitor, from the inversion region to the accumulation region as doping concentration increasing, has been explained. The results from the models show excellent agreement with the simulations and experimental data. The proposed models can be used to guide the design and has been implemented in the software for extracting the parameter of strained-Si MOSFET.

Analytical model for quasi-static C–V characteristics of strained-Si/SiGe pMOS capacitor

Germanium-tin films with rather high Sn content (28.04% and 29.61%) are deposited directly on Si (100) and Si (111) substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge1 −x Sn x films is investigated by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The x-ray diffraction (XRD) is also performed to determine the crystallinities of the Ge1−x Sn x films. The experimental results indicate that root mean square (RMS) values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400 °C. The diameter of the Sn three-dimensional (3D) island becomes larger than that of an as-grown sample when the annealing temperature is 700 °C. In addition, the Sn surface composition decreases when annealing temperature ranges from 400 °C to 700 °C. However, Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600 °C. The present investigation demonstrates that the crystallinity of Ge1−x Sn x /Si (111) has no obvious advantage over that of Ge1−x Sn x /Si (100) and the selection of Si (111) substrate is an effective method to improve the surface morphologies of Ge1−x Sn x films. We also find that more severe Sn surface segregation occurs in the Ge1−x Sn x /Si (111) sample during annealing than in the Ge1−x Sn x /Si (100) sample.

Effects of rapid thermal annealing on crystallinity and Sn surface segregation of ${\mathrm{Ge}}_{1-{\boldsymbol{x}}}{\mathrm{Sn}}_{{\boldsymbol{x}}}$ films on Si (100) and Si (111)

The conduction band structure of Si under uniaxial [100] stress is investigated by using the two band k·p perturbation theory. The conduction band parameters, including the conduction band minimum energy shift, split and electron effective mass change are quantitative described. Based on these band parameters, uniaxial stress induced electron mobility enhancment is systematically studied through Boltzmann transport theory. The results show that, when uniaxial [100] stress is applied to Si crystal, a gain of more than 50 % in electron mobility can be obtained. The electron mobility along the [100] increase with tensile stress and decrease with compressive stress, while does the opposite for the electron mobility along the [010] and [001]. The electron mobility along the [100], [010] and [001] tend to saturate for stress beyond a certain level. The stress induced the reduction of conductivity effective mass and the suppression of inter-valley scattering rate are responsible for the enhancement of electron mobility. The calculated results provide valuable reference for the optimum stress and orientation of the conduction channel in the uniaxial strained Si nMOS devices design. The electron mobility calculated model used in the present work is suitable for implementation in TCAD simulators.

He-Ming Zhang

Papers

Penetration depth at various Raman excitation wavelengths and stress model for Raman spectrum in biaxially-strained Si

Double-gate tunnel field-effect transistor: Gate threshold voltage modeling and extraction

Analytical model for quasi-static C–V characteristics of strained-Si/SiGe pMOS capacitor

Effects of rapid thermal annealing on crystallinity and Sn surface segregation of ${\mathrm{Ge}}_{1-{\boldsymbol{x}}}{\mathrm{Sn}}_{{\boldsymbol{x}}}$ films on Si (100) and Si (111)

Uniaxial Stress Induced Electron Mobility Enhancement in Silicon