Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

This work presents a metal-insulator-semiconductor (MIS) structure based on nickel oxide (NiO) showing negative differential resistance (NDR) properties. The Ni / NiO / HfO 2/ Ni layers structure was obtained by multiple sputtering steps and was then characterized by electrical measurements and other relevant methods. The electrical characteristics of the MIS structure were studied as a function of the oxide layer thickness. The observed NDR behavior could be attributed to a combination of the band-bending and a tunneling current contribution. © 2019, The Minerals, Metals & Materials Society.

World University root node

Department of Sensor and Biomedical Technology

School of Electronics Engineering

Vellore Campus

Journal of Electronic Materials

Negative Differential Resistance (NDR) Behavior of Nickel Oxide (NiO) Based Metal-Insulator-Semiconductor Structures

This work reports on the fabrication of microbump structures on nickel (Ni) films by single-pulse, localized laser irradiation. Conditions for the reproducible formation of such microstructures have been identified in terms of laser-irradiation and film parameters after systematic studies involving a relevant parameter space. Ni films deposited by vacuum evaporation were found to be better suited for reproducible laser microstructuring because they lack the typical cracks and voids morphology of sputtered films. The continuous and smooth nature of the evaporated films facilitated a radially symmetric heat flow propagation upon laser irradiation, which then resulted in a complex combination of thermal expansion, deformation, and other processes leading to a high yield of microstructures. An improvement in the inductance and the quality factor of on-chip spiral inductors, incorporating such laser-microstructured ferromagnetic nickel thin films was observed, which demonstrates the potential of such a laser-based method for fabrication or fine tuning of various micro-/nano-electric/electronic sensor and other components and systems. © 2002-2012 IEEE.

IEEE Transactions on Nanotechnology

Laser-Based Fabrication of Microstructures on Nickel Thin Films and Its Applications in On-Chip Thin Film Inductors

This paper presents a computational study of non-stoichiometric nickel oxide in a 64-cell NiO system to model and validate localized heating effects due to nanosecond laser irradiation. Variation in the Bandgap of NiO is studied as a function of varying concentrations of native defects, ranging from 0 to 25%. It is observed that there is a slight increase in the bandgap from 3.80 eV for stoichiometric NiO to 3.86 eV for Ni-rich NiO and to 3.95 eV for O-rich NiO. It is hence deduced that the experimental laser irradiation leads to simultaneous reduction of Ni2+ ions and the oxidation of NiO as the number of laser pulses increase. As well, a detailed study on the effects of doping nickel family elements, i.e., palladium (Pd) and platinum (Pt), in stoichiometric NiO is presented. A bandgap decrease from 3.8 eV for pure NiO to 2.5 eV for Pd-doping and 2.0 eV for Pt-doping for varying doping concentrations ranging from 0–25% Pd, Pt, respectively, is observed. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

Fulltext

Condensed Matter

A computational study on the variation of bandgap due to native defects in non-stoichiometric nio and pd, pt doping in stoichiometric nio

This work reports on the effect of ultraviolet (UV) laser irradiation on the structural, electrical, and optical properties of nickel oxide (NiOx) thin films, deposited by reactive sputtering of nickel in an oxygen containing atmosphere. It was found that the conduction type can be changed from p-type to n-type and the resistivity decreased as the number of laser pulses is increased and then increases again. The as-deposited films are polycrystalline, while laser irradiation renders the films amorphous. The observed transition from O-rich NiOx as-deposited films to Ni-rich laser-irradiated NiOx can be significant to electrochromic, resistive switching, and other applications. The band gap of the as-deposited and the laser irradiated NiOx films was obtained from spectroscopic ellipsometry measurements and was found to slightly increase upon laser irradiation. It is also observed that the surface roughness increases slightly. Aging effects or instabilities in the structure and composition of the films are also observed under normal conditions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Physica Status Solidi (A) Applications and Materials Science

Modification of reactively sputtered NiOx thin films by pulsed UV laser irradiation

The potential of NiO sublayers for whisker growth mitigation has been examined. A thin NiO film was applied on a Cu-coated substrate before the deposition of a thicker Sn layer. The growth of Sn whiskers was then followed by optical and scanning electron microscopy and was compared with the whisker growth on a control sample without the NiO sublayer. No whiskers were observed on the sample with the NiO layer even after 12 months, whereas the control sample developed whiskers of size and density that is generally expected, based on the vast amount of published work on the topic. The mechanisms of whisker growth and whisker growth suppression are briefly discussed as well. © 2017 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Sn whisker growth mitigation by using NiO sublayers

We have demonstrated the NiO/ZnO based rectifying diode for LED application for substituting GaN for optoelectronics applications. We have systematically studied the current-voltage (I-V) characteristics of NiO based Metal-Insulator-Semiconductor (MIS) devices under forward and reverse bias for its use in LED applications. The results obtained show that the current increases exponentially with the voltage after a critical turn-on-voltage. The mechanism of carrier transport responsible for the rectifying behavior of the MIS structure as well as the light emission is discussed in relation to the experimental results. MRS Advances © 2016 Materials Research Society.

MRS Advances

Rectifying behavior and light emission from nickel oxide MIS structures

The present work accentuates the effect of UV laser irradiation on the conductivity ofnickel oxide (NiO) thin films, deposited at various temperatures by radio-frequency reactive sputtering ofNi in oxygen containing atmosphere. The effect of UV irradiation on zinc oxide - nickel oxide heterostructures, obtained by sputtering, was examined as well. It was found that the resistivity of NiO changes from 12 Ω-cm to 0.62 Ω-cm, and the majority carrier concentration from3.95 × 1017 holes/cm3 to 4.22 × 10 20 electrons/cm . The current-voltage (I-V) characteristics ofthe ZnO/NiO heterostructure shows an improved p-n diode behavior with the forward bias current increasing for the laser-irradiated ZnO/NiO compared to the as-deposited stack. The observed improvement in diode-like behavior suggests that laser irradiation can be an important technique to controllably change the structural, electrical and optical properties of metal oxide thin films. MRS Advances © 2016 Materials Research Society.

Effect of UV laser irradiation on the properties of NiO films and ZnO/NiO heterostructures

In this work, we examine the potential improvement in inductance (L) and quality factor (Q) of on-chip ferromagnetic thin film inductors through the formation of conical microstructures by localized ultraviolet laser irradiation on ferromagnetic thin film. Parameters affecting L and Q, and arising from the surface modification upon laser irradiation include thickness of the film, size, and density of the structures. The thickness of the film is optimized to 0.2 μm, and at least 18% increase in inductance and 25% increase in Q-factor for NiFe thin film in comparison to the conventional spiral inductor is expected. L and Q values of NiFe films with and without microstructuring are compared, and a 7% increase is predicted for the microstrucired film. The proposed fabrication process, including the laser microstructuring technique, is likely to provide a significant flexibility, cost effectiveness and even better parameters, if other material systems are considered. © 2015 Taylor and Francis.

Journal of Electromagnetic Waves and Applications

Improvement in inductance and Q-factor by laser microstructuring of ferromagnetic on-chip thin film inductors

In this work, we propose a wideband multi-section transforming coupled-line balun using near equal length transmission line elements. The resulting design is realized by cascading several coupled-lines with minimal discontinuities. The multi-section Chebyshev matching optimizes bandwidth at the expense of passband ripple. The proposed design delivers good impedance matching and consistent 180° phase shift over 0.8-8 GHz frequency spectrum. Furthermore, the need for vias in conventional balun designs is relaxed by replacing the short-circuited (SC) terminal by its equivalent dual open-circuited (OC) element. The proposed design is simulated, fabricated, and measured. Both simulated and measured results are in a good agreement, and show an input port matching of below −9.7 dB over the design bandwidth, with a maximum phase and amplitude imbalance of 2.1° and 0.9 dB, respectively. © 2015 by the authors; licensee MDPI, Basel, Switzerland.

Electronics

A 0.8-8 GHz multi-section coupled line balun

This paper presents the design of notched-band antenna with CPW - feed. The notched - band has been achieved by using the W-shape slot in ground plane. The antenna has been simulated using a 3D - Electromagnetic simulator. The experimental results of proposed antenna exhibit ultra wideband characteristics from 2.0-15.0 GHz except the notched-band frequency from 5.0-6.0 GHz. The slot is optimized with respect to width, length and position for a detailed study of notched-band characteristics. It is observed that the centre frequency and bandwidth of notched-band depend on the length and width of slot respectively. The experimental radiation patterns of this antenna are omnidirectional in H-plane and bidirectional in E-plane. This antenna can be useful for UWB system, medical imaging and vehicular radar. © 2012 SBMO/SBMag.

Journal of Microwaves, Optoelectronics and Electromagnetic Applications

On the design of UWB circular fractal antenna with notched-band characteristics using W-shape slot

A printed apollonian gasket monopole antenna with CPW-feed is proposed for ultra-wideband applications.The Ultra-wide bandwidth of this antenna is achieved by modified the CPW ground plane. The experimental result of this antenna exhibits the ultra-wideband characteristics from 2.8 to 15 GHz at VSWR 2:1. The simulated results calculated from high frequency structure simulator are in good agreement with experimental results. The measured radiation patterns of this antenna are omnidirectional in H-plane and bidirectional in E-plane. The radar cross section (RCS) of this antenna is also studied for structural mode and antenna mode scattering. This type of antenna can be useful for a number of applications such as ultrawideband system, radar, ground penetrating radar, medical imaging, and other military applications. © 2012 Wiley Periodicals, Inc.

Microwave and Optical Technology Letters

Design of apollonian gasket ultrawideband antenna with modified ground plane

Microwaves and RF

Fractal antenna aims at 2.9 To 14.6 GHz

A CPW feed guitar shaped ultra wide band antenna is designed on FR4 ((ε r=4.3) substrate of thickness 1.53 mm. This antenna exhibits the excellent measured impedeance matching over the frequency range of 2.99GHz to 18.0GHz and beyond. Critical design parameters have been optimized to achieve the UWB bandwidth as well as to observe the effect of design parameters on impedance bandwidth. The measured radiation patterns of this antenna are omnidirectional in H-plane and bidirectional in E-plane. The bandwidth and peak gain satisfy the FCC standard requirement. An extended impedance bandwidth is achieved by having the antenna of guitar shape. The proposed antenna can be used for medical imaging, vehicular radar and modern Ultra wideband systems, etc. © 2012 ISRAMT.

International Journal of Microwave and Optical Technology

On the design of a guitar shaped CPW - feed UWB antenna

Friction Stir Spot Welding (FSSW) is a solid state joining technology that has the potential to find applications in the automotive and aerospace industries. One of the FSSW approaches currently used is the refill method. Having numerical models capable to represent the physics of this process with reasonable accuracy can be useful to optimize process parameters and explore new tool designs. In this paper, a three-dimensional isothermal finite element model of the plunge phase of a refill FSSW process is presented. ABAQUS/Explicit is employed to obtain the deformations, stresses and strains induced in the plates being spot welded. Virtual tracers are also incorporated in the simulation in an attempt to visualize the material flow near the tool. A comparison of results provided by the simulation with previously reported experimental data shows that it gives an acceptable approximation but additional refinement of the model is needed.

SAE Technical Papers

Visualization of material flow in the refill friction stir spot welding process

Friction Stir Spot Welding (FSSW) has a strong potential to find applications in both the automotive and aerospace industries. At the present time, research efforts are taking place to gain a better understanding of the process, to explore different tool configurations, and to optimize the set of process parameters. In this regard, gaining an understanding of how the material flows under a given set of processing parameters is of particular importance for tool design and to validate numerical models aimed at simulating the process. In this paper, the results corresponding to an experimental study performed using markers are presented to provide insight about the material flow during the plunge phase of the fixed-position refill FSSW process. Copyright © 2005 SAE International.