Department of Electrical Engineering

Indian Institute of Technology Hyderabad (IITH) is a premier institute of science and technology established in 2008. IITH has been consistently ranked in the&nbsp;<a href="https://iith.ac.in/reports/" rel="noopener noreferrer">top 10 institutes</a>&nbsp;in India for Engineering&nbsp;<a href="https://www.nirfindia.org/2021/EngineeringRanking.html" rel="noopener noreferrer" target="_blank">according to NIRF</a>&nbsp;making it one of the most coveted schools for science and technology in the country.

IITH offers&nbsp;<a href="https://iith.ac.in/academics/under-graduate/">undergraduate programs</a>&nbsp;in all the classical engineering disciplines, applied sciences, design, as well as several modern interdisciplinary areas. Students are given a flexibility to explore a broad set of areas, and potentially pursue a minor or double major in a discipline that is not their own. Students who wish to seek a deeper understanding of their own discipline are strongly encouraged to get involved in cutting-edge research with the help of a faculty to mentor them, and earn an Honors in their own field.

The very foundation of IIT Hyderabad is based on&nbsp;<a href="https://iith.ac.in/research/">research and innovation</a>. The vibrant research culture is evident from the number of patents and publications that IITH produces consistently every year. IITH offers&nbsp;<a href="https://iith.ac.in/academics/programmes-offered/">graduate programs</a>&nbsp;at both a masters, and a doctoral level, in several diverse areas. There are separate programs for technology, design, science, and liberal arts. The&nbsp;<a href="https://iith.ac.in/academics/post-graduate/">MTech program</a>&nbsp;is offered in various modes and durations to cater to the ever-growing need of postgraduate level professionals in the country.

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IITH creates a unique holistic ecosystem for education that offers interactive learning, a very flexible academic structure, cutting-edge research, strong industry collaboration, and entrepreneurship. This is an environment which enables students and faculty to translate their dreams into realities.

IIT Hyderabad

Indoor localization has a wide range of applicability in personal health applications. There is a need for specialized indoor localization methods [1] like Time of Arrival (TOA), Time Difference of Arrival (TDOA), Angle of Arrival (AOA) and Received Signal Strength Indicator (RSSI) due to limited usability of global positioning system (GPS). The proposed work uses a novel commensal radar system (inspired by biological inter-species coexistence where one system exploits other without detrimental effect) which uses communication radiation as the illuminator, called CommSense[2]. It uses LTE communication infrastructure due to its wide availability in indoor environments. Therefore, we call this system LTE-CommSense [3]. We believe, utilization of orthogonal frequency division multiplexing (OFDM) and multiple input and multiple output (MIMO) may provide better resolution for this scenario. LTE signal provides high range resolution due to its wide bandwidth ranging from 1.4 to 20 MHz. Following this principle, the proposed system uses only passive receiver nodes that uses existing LTE communication signal. Communication receiver modules extracts information which is affected by the channel condition. It uses the same spectrum of the communication system without any detrimental influence on it. The communication signal strength between LTE (user equipment (UE)) and (eNodeB) gets affected by the span of the channel. Following the CommSense principle, we use three passive nodes (PN) for two dimensional (2D) indoor localization. These PNs determine respective distances of the (UE) by measuring incident signal power at the PNs with which it communicates with the (eNodeB). After the respective distances are calculated, we use these distances for trilateration to determine the co-ordinate of the UE. Depending on the PN placements, the trilateration algorithm is modified to have less calculation complexity. The calibration of the system to calculate the distance of the UE from a PN is performed. We setup a testbed to calculate the accuracy of our proposed method in a indoor laboratory environment. Without any loss of generality, we place the PNs at right angle to each other to reduce the computational complexity for trilateration. Use of LTE for RSSI based indoor localization and demonstration on SDR platform is a novel effort. First we evaluated the accuracy of distance calculation of individual PNs. The evaluated distance values using our proposed approach along with the actual distance values are compared with the ground truth measurements. © 2018 The Institute of Electronics, Information and Communication Engineers (IEICE).

World University root node

Progress in Electromagnetics Research Symposium

Indoor Localization System Using Commensal Radar Principle

This paper presents dynamic spectrum sharing protocol, in which operators lease or borrow their spectrum depending on traffic load condition over unit time. To achieve this, a spectrum sharing rule is proposed, which guides the operator when to lease or borrow spectrum with respect to current traffic load condition. The spectrum sharing rule presented here depends on both user arrival rate and service rate which contribute to the traffic load experienced by the operator over a unit time. Further, we analyze the impact of presented spectrum sharing rules on the multi-operator system in terms of probability of blocking. © 2018 IEEE.

2018 10th International Conference on Communication Systems and Networks, COMSNETS 2018

Impact of spectrum sharing rules in multioperator communication system

WLAN and Body Area Networks (BAN) are rapidly advancing as high data rate wireless communication systems using UWB spectrum. UWB spectrum offers 7 GHz wide bandwidth which ranges over 57 to 64 GHz. In this UWB communication systems Antenna design plays a crucial role for signal transmission and reception. However Antenna design at UWB spectrum is more challenging than narrow band design Beam forming Antenna arrays play an important role at these frequencies. In this paper A novel embroidery broadside dipole array is proposed. The proposed antenna array is designed and analyzed using High Frequency Structure Simulator (HFSS). © 2018 The Institute of Electronics, Information and Communication Engineers (IEICE).

A Millimetre Wave Embroidary Beam Forming Antenna Array for UWB Applications

Recent improvements in the understanding and fabrication of GaN have led to its application in high frequency communication and high voltage switching systems. Requirement for operation at even higher frequency and voltages is driving the research currently on design of GaN based devices. In this paper, we present the result of our study of two-dimensional (2-D) High Electron Mobility Transistors (HEMTs) based on GaN/AlGaN/GaN heterostructure using Sentaurus TCAD tools. Exhaustive RF simulations were performed to study the effect of various device parameters such as Gate length, Gate-to-Source spacing, Gate-to-Drain spacing, etc. as well as the effect of various Gate shapes such as T-Gate, Y-Gate, etc., on the high frequency performance of the Transistor. Simulation result shows very promising result with fT and fMAX value of 1691.43 GHz and 2650.84 GHz respectively. © 2018 IEEE.

Proceedings of International Conference on 2018 IEEE Electron Device Kolkata Conference, EDKCON 2018

Dependency of fT and fMAX on Various Device Parameters of AIGaN/GaN HEMT

Diffusion of atoms across the boundary between two bonding layers is the key for achieving excellent thermocompression Wafer on Wafer bonding. In this paper, we demonstrate a novel mechanism to increase the diffusion across the bonding interface and also shows the CMOS in-line process flow compatible Sub 100 °C Cu–Cu bonding which is devoid of Cu surface treatment prior to bonding. The stress in sputtered Cu thin films was engineered by adjusting the Argon in-let pressure in such a way that one film had a compressive stress while the other film had tensile stress. Due to this stress gradient, a nominal pressure (2 kN) and temperature (75 °C) was enough to achieve a good quality thermocompression bonding having a bond strength of 149 MPa and very low specific contact resistance of 1.5 × 10−8 Ω-cm2. These excellent mechanical and electrical properties are resultant of a high quality Cu–Cu bonding having grain growth between the Cu films across the boundary and extended throughout the bonded region as revealed by Cross-sectional Transmission Electron Microscopy. In addition, reliability assessment of Cu–Cu bonding with stress engineering was demonstrated using multiple current stressing and temperature cycling test, suggests excellent reliable bonding without electrical performance degradation. © 2018, The Korean Institute of Metals and Materials.

Electronic Materials Letters

Direct, CMOS In-Line Process Flow Compatible, Sub 100 °C Cu–Cu Thermocompression Bonding Using Stress Engineering

The molten salt of Strontium Iodide (SrI2) and Europium Iodide (EuI2) was filtered by specially designed dual chamber quartz ampoule using micro frit filter. Eu2+ doped SrI2 single crystal was grown by modified transparent vertical Bridgman technique. Photoluminescence (PL) excitation and emission (PLE) were recorded for the grown crystal. The characteristic emission of Eu2+ was observed at 432 nm. Similar emission was observed at 435 nm, when the sample was excited by X-ray source also. Scintillation properties of the SrI2:Eu2+ crystal were checked by the gamma ray spectrometer using 137Cs, 57Co and 60Co gamma sources. The energy resolutions of the grown crystal were found to be 4.6% at 662 KeV, 7.5% at 122 KeV and 9.8% at 1332 KeV. The Scintillation decay profile was also analyzed. The scintillation decay time of Eu2+ ion was calculated to be 1.26 μs for SrI2:Eu2+ single crystal. © 2018 Elsevier B.V.

Journal of Alloys and Compounds

Difficulties and improvement in growth of Europium doped Strontium Iodide (SrI2:Eu2+) scintillator single crystal for radiation detection applications

The main aim of this work is to report an alternative technique of creating vanadium pentoxide (V2O5) based uncooled infrared (IR) detector, by a state-of-the-art V2O5 nanofibers, manufactured by facile and economical electrospinning process. The nanofibers were thermally and electrically characterized to determine their bolometric performance. The nanofibers show maximum voltage responsivity of (Rv) 6987.3 V/W at 100 mA DC bias, under normal room temperature and pressure condition. Nanofibers show very good thermal response (τs) and recovery time (τr) when subjected to a periodic On-Off cycle of IR lamp (150W) illumination. Temperature dependent resistance measurement reveals that nanofibers are exhibiting semiconductor to metallic phase transition at 67°C with maximum TCR% -1.6%/K at the transition temperature. V2O5 nanofibers characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman Spectroscopy confirms their crystallinity and elemental composition. The optical band gap of the nanofibers is analyzed by UV-Visible spectroscopy. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images confirms their microstructural dimensions and surface homogeneity. The entire analysis reaffirms the suitability of V2O5 nanofibers as one of the futuristic sensing material for IR imaging applications. © The Electrochemical Society.

ECS Transactions

Vanadium pentoxide nanofibers as IR sensors for bolometer applications

In the present modern era of electronic industry has motivated for high performance integration by vertically stacked three dimensional integrated circuits (3D ICs). Electronic interconnections at packaging and die levels, Pb-free solder micro bumps are intended to replace conventional Pb-containing solder joints due to increasing awareness of an environmental conservation, and processing at low thermal budgets. The better alternative for solder is copper, due to its high electrical and thermal properties. But the surface oxidation was the major bottleneck. In this work, we have demonstrated low temperature and low-pressure copper to copper interconnect bonding using optimized thin gold passivation layer. Here the passivation layer over the copper surface was optimized to a thickness of 3nm there by helps in preventing Cu surface oxidation and makes lower surface RMS roughness. High-density surface plane orientations that have been studied using XRD helped in faster diffusion through an interface. Majorly in this work, we have discussed the time taken for copper atoms to diffuse over the ultra-thin passivation layer of gold using Fick's second law approximation. These conditions have been used while bonding. Bonded samples were subjected to various reliability studies in order to confirm the efficacy of the proposed Au passivation based bonded structure. Also, we have observed the Interface quality using TEM, and C-SAM (mode C-Scanning acoustic microscopy) imaging resulting in good quality of bonding. The diffusion of copper atomic species movement across the interface is confirmed by EDS analysis. Low and stable specific contact resistance (~1.43 × 10-8 ?- cm2) at robust conditions are confirmed to be effective and front runner for low temperature, low pressure Cu-Cu bonding for 3D IC packaging and heterogeneous integration. © 2018 IEEE.

2018 IEEE 20th Electronics Packaging Technology Conference, EPTC 2018

Gold passivated Cu-Cu bonding at 140ºC for 3D IC packaging and heterogeneous integration applications.

In this paper, we report a low temperature, fine-pitch, bump-less, damascene compatible Cu-Cu thermocompression bonding, using an optimized ultra-thin passivation layer, Constantan, which is an alloy (Copper-Nickel) of 55% Cu and 45% Ni. Surface oxidation and its roughness are the major bottlenecks in achieving high quality, low temperature, and fine-pitch Cu-Cu bonding. In this endeavor, we have used Cu rich alloy (Constantan) for passivation of Cu surface prior to bonding. We have systematically optimized the constantan passivation layer thickness for high quality low temperature, low pressure, bump-less Cu-Cu bonding. Also, we have studied systematically the efficacy of Cu surface passivation with optimized ultra-thin constantan alloy passivation layer. After rigorous trial and optimization, we successfully identified 2 nm passivation layer thickness, at which very high quality Cu-Cu bonding could be accomplished at sub 200 °C with a nominal contact pressure of 0.4 MPa. Post-bonding, electrical and mechanical characterization were validated using four-probe IV measurement and bond strength measurement respectively. Furthermore, Cu-Cu bonding interface was analyzed using IR wafer bonder inspection tool. Very high bond strength of 163 MPa and defect free interface observed by WBI-IR clearly suggests, Cu-Cu finepitch bonding with optimized ultra-thin alloy of 2 nm thick constantan, is of very high quality and reliable. Moreover, this novel bonding approach with alloy based interconnect passivation technique is the prime contestant for future heterogeneous integration. © 2018 IEEE.

Proceedings - Electronic Components and Technology Conference

Metal-alloy Cu surface passivation leads to high quality fine-pitch bump-less Cu-Cu bonding for 3D IC and heterogeneous integration applications

Detailed experimental study involving flow boiling of water in microchannel is discussed in this chapter. The work aims to study the different aspects of the problem such as pressure drop, heat transfer coefficient, pressure instability, and void fraction. Flow visualization has also been performed. Experiments have been conducted in silicon microchannels with trapezoidal or rectangular cross-section of hydraulic diameter 45-140 μm, and a microheater fabricated on the reverse side of the silicon wafer to provide well controlled and metered input power. The experimental data is compared with the annular flow model and various empirical correlations, and complemented with clear discussion of the observed phenomenon. In the two-phase regime, the average pressure drop increases with a decrease in the flow rate and reaches a maximum (with a minimum on either side), while in the dryout regime the pressure drop decreases with flow rate. Our results suggest that there are up to four mass flow rate values with same pressure drop penalty and the operating point can be chosen with the maximum heat transfer coefficient. The average pressure drop is found to have a strong dependence on the channel aspect ratio and becomes minimum in rectangular microchannel for width-to-depth ratio of about 1.5. The instability in pressure drop has been quantified and linked to the underlying flow regime. The minimum PRMS/Pavg is found to occur when the flow transitions to annular. For the first time, a flow regime map is also obtained for such systems. The flow is found to be predominately annular at high heat flux and flow rate. A breakup of the flow frequency suggests that the flow is bistable in the annular regime. At a fixed location, the flow periodically switches from single phase liquid to annular, and vice-versa. Otherwise, all three regimes: single phase liquid, bubbly and slug are obtained. An image analysis technique has also been developed and utilized to estimate the void fraction as a function of position in the microchannel, heat flux and mass flow rate. The technique has been extended to obtain heat transfer coefficient purely from image analysis. Both void fraction and heat transfer coefficient are found to increase monotonically with position in the microchannel. There are several novel aspects of this study. For example, effect of microchannel aspect ratio on pressure drop is studied for the first time. Some guidelines for choosing the operating point with desired constraints have been proposed. Ways to reduce instability have also been explored. Development of flow regime map and flow visualization technique is not available in the literature currently. Pressure drop data near CHF condition have been presented. The results are interesting from both fundamental and electronic cooling point of view. © 2012 Bentham Science Publishers.