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Pradhan S.K.,National Tsing Hua University | Barik R.,Indian Central Electronics Engineering Research Institute
Applied Materials Today | Year: 2017

In this work, we report clean, surface protected and high quality topological insulator (TI) thin film Hall bar device of millimeter size long, without using any resist and lithography techniques. The pronounced effect of weak anti-localization (WAL) behavior has been observed in the magneto-transport measurements at low temperatures over the range T = 4–10 K and in the low field regions and as we go from 10 K onwards to higher temperatures the WAL cusp disappears, also we find that the high field magenetoresistance (MR) is linear in field. The MR behavior with respect to magnetic field (B) seems to be symmetric. We also report thickness dependent weak-anti localization (WAL) behavior in topological insulator Bi2Te3 thin film Hall bar device. Our systematic magneto-transport measurements for varying thickness reveal WAL signals obtain in thicker films, where as a sudden diminishment of the surface transport below the critical thickness of ∼4 nm has been observed by suppression of WAL behavior. The pronounced behavior of this effect is also found to be dependent on the temperatures, where the WAL cusps are observed at low temperatures in the low-field regions. © 2017 Elsevier Ltd

Islam T.,Jamia Millia Islamia University | Khan A.U.,Jamia Millia Islamia University | Akhtar J.,Indian Central Electronics Engineering Research Institute | Rahman M.Z.U.,Jamia Millia Islamia University
IEEE Transactions on Industrial Electronics | Year: 2014

A microcontroller-based digital hygrometer system using a low-cost moisture sensor in the range of 3.7-100 ppm has been developed. The sensor is of capacitive type and consists of nanoporous thin film of alumina γ - Al2O3 dip coated in between two parallel gold electrodes onto an alumina substrate. The behavior of the sensor has been modeled with an object to develop a signal processing circuit to convert capacitance change into frequency. The detection electronics circuit is based on a relaxation oscillator whose output is suitable for interfacing with a digital device. The sensor has been characterized with the circuit and then output frequency is calibrated in terms of ppm. The accuracy of the digital hygrometer when compared with the commercial dew point meter is found to be ±;1 PPM. © 2014 IEEE.

Mittal M.,Indian Central Electronics Engineering Research Institute | Mittal M.,Indian Institute for Plasma Research | Kumar A.,Indian Central Electronics Engineering Research Institute | Kumar A.,Academy of Scientific and Innovative Research AcSIR
Sensors and Actuators, B: Chemical | Year: 2014

Fossil fuels endow wide applications in industrial, transportation, and power generation sectors. However, smoke released by burning fossil fuels contains toxic gases, which pollutes the environment and severely affects human health. Carbon nanotubes (CNTs) are potential material for gas sensors due to their high structural porosity and high specific surface area. Defects present on the CNT sidewalls and end caps facilitate adsorption of gas molecules. The chemical procedures adopted to purify and disperse carbon nanotubes create various chemical groups on their surface, which further enhance the adsorption of gas molecules and thus improve the sensitivity of CNTs. Present review focuses on CNT chemiresistive gas sensing mechanisms, which make them suitable for the development of next generation sensor technology. The resistance of carbon nanotubes decreases when oxidizing gas molecules adsorb on their surface, whereas, adsorption of reducing gas molecules results in increasing the resistance of CNTs. Sensing ability of carbon nanotubes for the gases namely, NO, NO2, CO, CO2 and SO2, released on burning of fossil fuels is reviewed. This review provides basic understanding of sensing mechanisms, creation of adsorption sites by chemical processes and charge transfer between adsorbed gas molecules and surface of CNTs. In addition, useful current update on research and development of CNT gas sensors is provided. © 2014 Elsevier B.V. All rights reserved.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Nanoscience and Nanotechnology Letters | Year: 2012

Fabrication of quantum dots (QDs) by two plasma-assisted techniques, namely, ion sputtering and plasma-enhanced chemical vapour deposition (PECVD) is reviewed. Relative advantages of these techniques compared to colloidal synthesis and lithography are pointed out. Mechanisms of self-organized quantum dot formation are elucidated. While in sputtering, surface instability is the basis of self-organized quantum dot formation, Stranski-Krastanov (SK) growth is the growth mode responsible for the transition to 3-D islands in heteroepitaxial growth. Salient features of ion sputtering systems and plasma reactors used for QD growth are introduced. Deposition parameters are briefly presented for specific cases of growth of quantum dots of CuInSe2, ZnO, Si, SiC, GaAs, GaSb, by sputtering, as well as Si, Ge, GaN, and InP by PECVD. Of no less significance is the use of plasma for surface modification of quantum dots. Because improvement of QD characteristics by plasma exposure is being increasingly practiced, such usage of plasma is also touched upon. CNT quantum dot formation is also explained. Undeniably, the overall scenario of plasma-assisted techniques in quantum dot formation and modification constitutes an important research area, which has attracted considerable attention due to ever-escalating applications of QDs in several fields. On these considerations, the present paper deals with the fundamental aspects of QD formation and also attempts to provide an overview of the state of the art. Copyright © 2012 American Scientific Publishers.

Khanna V.K.,Indian Central Electronics Engineering Research Institute | Khanna V.K.,Academy of Scientific and Innovative Research AcSIR
Sensors and Actuators, B: Chemical | Year: 2015

An early paper [1] proposed the virtual pore widening model to explain the temporal drift in the characteristics of porous aluminum oxide humidity sensor. It is shown here that this model does not provide a plausible mechanism for the decrease in sensitivity caused by aging. Instead, it predicts the contradictory behavior of an increase in sensitivity with aging, which is not true. Alternatively, hydration of the aluminum oxide on exposure to moisture provides a more cogent explanation of the aging process, as observed in an alumina-gate ion-sensitive field-effect transistor (ISFET). In this paper, the monotonic decrease in capacitance of Al2O3 humidity sensor with the extent of hydration has been established, both by equivalent circuit approach and by modeling the sensor as a heterogeneous dielectric. Capacitance calibration characteristics of the humidity sensor have been simulated by employing the theory of alumina humidity sensor. Similarities and dissimilarities of aging of this sensor with ISFET drift have been elucidated. Whereas in ISFET, a thin hydrated layer is formed only at the surface of the gate dielectric, in Al2O3 sensor, hydration of inner layers in the porous film is highly likely. Unification of aging mechanisms in sensors is briefly discussed. © 2015 Elsevier B.V.. All rights reserved.

Agarwal P.B.,Indian Central Electronics Engineering Research Institute | Kumar A.,Indian Central Electronics Engineering Research Institute
Microelectronics Journal | Year: 2011

This paper presents an octal-to-binary encoder that is designed using capacitive single-electron transistors (C-SETs). The design parameters are calculated by considering each C-SET as a switching device in pull-up configuration. Logic circuit is based on voltage state logic. The designed circuit was simulated using SIMON 2.0, which is based on Monte Carlo and master equation (MC-ME) methods. The simulation results verify the operation of octal-to-binary encoder. © 2010 Elsevier Ltd. All rights reserved.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Journal of Physics D: Applied Physics | Year: 2011

Physico-chemical mechanisms of adhesion and debonding at the various surfaces and interfaces of semiconductor devices, integrated circuits and microelectromechanical systems are systematically examined, starting from chip manufacturing and traversing the process stages to the ultimate finished product. Sources of intrinsic and thermal stresses in these devices are pointed out. Thin film ohmic contacts to the devices call for careful attention. The role of an adhesion layer in multilayer metallization schemes is highlighted. In packaged devices, sites facing potential risks of delamination are indicated. As MEMS devices incorporate moving parts, there are additional issues due to adhesion of suspended structures to surfaces in the vicinity, both during chip fabrication and their subsequent operation. Proper surface treatments for preventing adhesion together with design considerations for overcoming stiction pave the way to reliable functioning of these devices. Adhesion-delamination issues in microelectronics and MEMS continue to pose significant challenges to both design and process engineers. This paper is an attempt to survey the adhesion characteristics of materials, their compatibilities and limitations and look at future research trends. In addition, it addresses some of the techniques for improved or reduced adhesion, as demanded by the situation. The paper encompasses fundamental aspects to contemporary applications. © 2011 IOP Publishing Ltd.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Sensors and Transducers | Year: 2012

Humidity sensors are required for diverse applications in low and high humidity ranges. Also, fast-response humidity sensors are sometimes needed. For this purpose, it is necessary to understand the hygroscopic influences and physico-chemical mechanisms underlying sensor operation as well as their correlation with the terminal properties of sensors. Several models and theories of sensors have been proposed for interpretation of their behaviour. This paper comprehensively surveys the available models and points out the utilization of selected models for tailoring sensor characteristics in accordance with intended application. Ionic salt doping is a useful technique for improving the sensitivity, linearity and hysteresis of humidity sensor characteristics. © 2012 IFSA.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Sensor Review | Year: 2013

Purpose - This paper aims to focus on the steps necessary to bolster marketability of ISFET-based sensors, keeping in view the present technological status of ISFET and its limitations. Design/methodology/approach - Technical problems inhibiting commercialization of ISFET-based sensors are highlighted. The problems considered include sensitivity, drift, cleaning, disposability, reference systems, chip structural designs, packaging, light, temperature, hysteresis and body effects, and instability of biosensors. Available solutions are prescribed, discussing both direct and indirect ways of addressing the problems of ISFET sensors. Findings - The history of progress of ISFET (Ion-sensitive Field-Effect Transistor) is synonymous with the ways and means devised by different researchers for surmounting (direct approach) or acclimatizing to the shortcomings of this device (indirect approach) . Signal conditioning hardware and software considerably help in obviating issues such as drift, hysteresis and thermal effects. Research limitations/implications - Reliable on-chip reference electrodes and ISFET packaging for continuous online applications are interesting research areas. Practical implications - Where a plausible solution exists, it should be readily availed; otherwise the device limitation should be understood and ingeniously bypassed. Compromising solutions targeted on the specific applications pave the way towards widespread utilization of these sensors in industrial, biomedical, food and environmental sectors. Originality/value - The study helps in understanding the problems besetting utilization of ISFETs, calling attention to essential remedies for ISFET-based products. It provides information of value to those involved in ISFET measurements. © Emerald Group Publishing Limited.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Indian Journal of Pure and Applied Physics | Year: 2012

The present paper describes the fabrication of ISFET (Ion-Sensitive Field-Effect Transistor) by a four-mask, thermal diffusion-based process. The sequence of physical and chemical processes for ISFET fabrication has been elaborated. In the first photomasking step, the regions for source and drain diffusion have been opened. The second photolithography defined the gate area. In the third photolithographic step, contact windows have been opened, and in the fourth photolithographic step, the metal pattern has been delineated. After completion of the fabrication process, the wafer has been diced into chips, which have been mounted on ceramic substrates to provide electrical connections for source, drain and substrate. Except for the gate region, the whole chip and wire bonds have been protected with insulating epoxy. For process characterization, current-voltage characteristics of MOSFET test devices simultaneously fabricated on the same wafer have been measured for gate-source voltages from -5 to +5 V. These were found to be N-channel, depletion-mode devices indicating similar behaviour for ISFETs. The pH-response of ISFET has been evaluated by drawing its I DS-V GS characteristics after immersion in standard buffer solutions and applying the gate-source voltage through Ag/AgCl reference electrode. From these transfer characteristics, pH-sensitivity of ISFET has been determined by finding the gate-source voltage necessary to ensure constant I DS, V DS condition. Technological shortcomings of this work have also been pointed out, and necessary remedial measures have been suggested.

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