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

Lead based relaxor ferroelectric thin films can become very useful due to their excellent electrical properties, provided the growth difficulties and high cost of fabrication which have stymied their applications are overcome. Our work describes a systematic study of establishing a set of process conditions for reproducible depositions of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) thin films on La0.67Ca0.33MnO3 (LCMO) seeded Pt/TiO2/Glass substrates. Films were grown at ambient temperature using RF- magnetron sputtering. Single phase PMN-PT films could be obtained by ex situ thermal annealing in air for 2 h at temperatures of 550 and 650 °C. Films annealed at temperatures lower than 550 °C and films deposited without the LCMO buffer layer showed presence of pyrochlore phase. Effect of annealing temperature, on the microstructure, dielectric and ferroelectric properties of the PMN-PT films has been investigated. Scanning electron micrographs of single phase PMN-PT films show a bimodal grain size distribution for the thin films annealed at 550 and 650 °C. The films annealed at 650 °C yielded a dielectric constant of 1300 and a remnant polarization (2Pr) of 17 μC cm-2. © 2018 IOP Publishing Ltd.

GENERAL

Department of Metallurgical Engineering & Materials Science

Department of Physics

School of Advanced Sciences

Vellore Campus

Materials Research Express

PMN-PT thin films on La0.67Ca0.33MnO3 seeded platinized glass substrate: Phase formation, dielectric and ferroelectric studies

The magneto-dielectric response in multiferroic ZnFe2O4/PMN-PT bilayer thin films prepared on a glass substrate using RF magnetron sputtering has been investigated in this work. PMN-PT thin films (i.e. PMN-PT/LCMO/Pt/Ti/glass) deposited on glass were used as a substrate for deposition of ZnFe2O4 thin films. ZnFe2O4 thin films were annealed ex situ at different temperatures. Structural, magnetic, ferroelectric, dielectric and magneto-dielectric studies were carried out on these multiferroic bilayer thin films. Structural studies revealed the presence of each layer in its respective single phase. Magnetic and ferroelectric studies revealed the ferromagnetic and ferroelectric behaviors of these bilayers. To quantify the magnetoelectric coupling, the dielectric constant of the bilayer was measured at room temperature as a function of frequency with and without the applied magnetic field. The magneto-dielectric response MD(%) was calculated by finding the relative change in dielectric constant at 1 kHz as a percentage. The observed MD response was correlated with magnetization of the ferrite layer. An MD response of 2.60% was found for a bilayer film annealed at 350 °C. At this particular annealing temperature, the ZnFe2O4 layer also has the highest saturation magnetization of 1900 G. © 2016 IOP Publishing Ltd.

World University root node

Smart Materials and Structures

Room-temperature magneto-dielectric response in multiferroic ZnFe2O4/PMN-PT bilayer thin films

The paper describes the fused floating-point Add-Subtract Unit using IEEE-754 standard 32 bit floating point number representation. In fused add-subtract unit, both add unit and subtract unit perform parallel operation and this approach of fused unit reduces the hardware required and also the cost of designed unit. Besides addition and subtraction if one more operation suppose multiplication is to be performed then a multifunctional design is required. The multi-functional floating-point unit includes a multiplier unit above a Fused Add-Subtract Unit which uses hardware more efficiently in comparison to the separate unit blocks for each operation. This method reduces the area of the designed block but the speed of operation is also reduced. The blocks are reduced based on the common operation between each designed unit. For example, in every unit rounding operation is done after each operation for floating point number. If a common block for rounding is designed then the hardware is reduced. The paper also compares one add unit with fused floating point add-subtract unit and one multifunctional unit. © 2015 IEEE.

VIT Unitversity

Department of Micro and Nanoelectronics

School of Electronics Engineering

2015 Online International Conference on Green Engineering and Technologies (IC-GET)

Fused floating-point add and subtract unit

Operational stability of organic devices at above-room-temperatures in ambient environment is of imminent practical importance. In this report, we have investigated the charge transport and degradation mechanisms in pentacene based organic field effect transistors (OFETs) operating in the temperatures ranging from 25 °C to 150 °C under ambient conditions. The thin film characterizations techniques (X-ray photoelectron spectroscopy, X-ray diffraction and atomic force microscopy) were used to establish the structural and chemical stability of pentacene thin films at temperatures up to 150 °C in ambient conditions. The electrical behavior of OFETs varies differently in different temperature bracket. Mobility, at temperatures below 110 °C, is found to be thermally activated in presence of traps and temperature independent in absence of traps. At temperatures above 110 °C mobility degrades due to polymorphism in pentacene or interfacial properties. The degradation of mobility is compensated with the decrease in threshold voltage at high temperatures and OFETs are operational at temperatures as high as 190 °C. 70 °C has been identified as the optimum temperature of operation for our OFETs where both device behavior and material properties are stable enough to ensure sustainable performance. © 2015 Elsevier B.V. All rights reserved.

Organic Electronics

Insight into the charge transport and degradation mechanisms in organic transistors operating at elevated temperatures in air

In this work, RF- magnetron sputtering technique has been employed to deposit nanocrystalline ZnFe2O4 thin films at room temperature. The as grown films were ex-situ annealed in air for 2 h at temperatures from 150°C to 650°C. X-ray diffraction, vibrating sample magnetometer and ferromagnetic resonance were used to analyze the phase formation, magnetic properties and microwave properties respectively. From the hysteresis loops and ferromagnetic resonance spectra taken at room temperature, a systematic study on the effect of O2 plasma on microwave properties with respect to processing temperature has been carried out. © 2014 AIP Publishing LLC.

AIP Conference Proceedings

Microwave properties of RF- sputtered ZnFe2O4 thin films

Synthesis of PMN-PT ceramics has been a challenge due to the undesirable pyrochlore phase formation. We have synthesized PMN-PT ceramics with varying PT content (x = 0.1, 0.15 and 0.3) using columbite precursor method. Influence of PT addition on the perovskite phase formation and microstructure has been studied using X-ray diffraction and scanning electron microscope respectively. © 2013 AIP Publishing LLC.

Influence of PbTiO3 addition on microstructure of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics

The observation and theory of a large remanent magnetoelectric (ME) coefficient and coercivity in the static field H dependence of the low-frequency ME effects are reported for bilayers of lead zirconate titanate (PZT) and a functionally graded ferromagnetic layer. The grading involves magnetization with the use of nickel zinc ferrite of composition Ni 0.7Zn 0.3Fe 2O 4 (NZFO) and pure Ni. In homogeneous bilayers of PZT-Ni or PZT-NZFO, the ME voltage coefficient (MEVC) vs H data do not show any hysteresis or remanence. Upon grading the ferromagnetic layer, significant changes including hysteresis and remanece are observed. In PZT-Ni-NZFO, MEVC vs H data show a positive remnant MEVC and a negative coercive field. When the grading is reversed, in samples of PZT-NZFO-Ni, the remnant MEVC is negative and the coercive field is positive. A theory is proposed for the low-frequency ME effects in the graded composites. According to the model, the grading in the magnetization leads to a built-in magnetic field in the ferromagnetic layer, and this field depends on the sequence of grading and the thickness of the NZFO and Ni layers. As a result, the total torque moment and flexural deformations in the composite and the bias field dependence of ME voltage coefficient becomes strongly hysteretic. Calculated MEVC vs H, remnant MEVC, and coercive field are in good agreement with the data. © 2012 American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Hysteresis and remanence in magnetoelectric effects in functionally graded magnetostrictive-piezoelectric layered composites

Tin oxide (SnO 2) thin films are of great interest in optoelectronics industries due to their promising properties such as conductivity and optical transparency in visible-infrared (VIS-IR) region. Improvement in these two key properties of SnO 2 is of technological importance. In order to find ways for these improvements in the present study, SnO 2 thin films have been prepared by Thermal Evaporation (TE) in oxygen (O 2) partial pressure and Plasma Assisted Thermal Evaporation (PATE) using RF (13.56 MHz) O 2 plasma. Optical, structural, compositional and electrical properties of the deposited films have been investigated by varying substrate temperature in range of 250-350 qC keeping other process parameters constant. The optical transmission spectra measured in VIS-IR region of films deposited by PATE have higher transparency (~80-90 %) in comparison to the films grown by TE (~60-70 %). X-ray Diffraction (XRD) study reveal SnO &amp; SnO 2 phases present in the film. Also X-ray Photoelectron Spectrosocpy (XPS) analysis showed Sno 2-x as the only content, which is in agreement to XRD results. Surface morphology study by Scanning Electron Microscopy (SEM) shows more needle shape grains in case of films deposited by TE as compared to PATE grown films. Both types of the films were subjected to Four-probe method for the measurement of resistivity, which is in the order of 10 -4 Ω-cm and 10 -3 Ω-cm for PATE and TE grown respectively. © 2011 SumDU.