Department of Electrical Engineering

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IIT Jodhpur

A computationally efficient analytical model to accurately predict the electrical characteristics of wrap-gate carbon nanotube FETs (CNTFETs) is proposed and described in this paper. A wrap-gate structure offers an ideal geometry with minimum body thickness and maximum control over the channel as well as improved device scalability. The parasitic effects present in a real device are incorporated into an ideal wrap-gate device model, and the Poisson-Schrödinger equations are solved self-consistently to obtain the potential and carrier density at the top of the barrier. Exact analytical expressions, such as CNTFET density-of-states are used for approximately evaluating the integral expressions. Finally, the drain current is obtained for near-ballistic transport in the device. The electrical characteristics from our model are validated with recently reported experimental results from the literature, demonstrating good accuracy when the device is on. The subthreshold characteristics are underestimated and offer scope for improvement. Various performance metrics, including threshold voltage and subthreshold swing, and on-current are within 2-11% error. The proposed model can thus be used to study the performance of wrap-gate CNTFETs under various parametric conditions, and extended to circuit simulation models, such as SPICE. © 1963-2012 IEEE.

World University root node

IEEE Transactions on Electron Devices

Analytical Modeling of Wrap-Gate Carbon Nanotube FET with Parasitic Capacitances and Density of States

The effect of structural dissimilarity of the additive solvent from the main solvent on the properties of the solution and resulting crystals for solution processed organic field-effect transistors (OFETs) is comprehensively studied. Organic semiconductor TIPS-Pentacene was explored with toluene as the main solvent and benzene, cyclohexane, and hexane as additives for making semiconductor solutions. The solution formation with various solvents is explained by Hansen's solubility theory, according to which the binary solvent with higher structural dissimilarity between constituent solvents is a weaker solvent of the organic semiconductor; which eventually supports better molecular aggregation and crystallinity in the resulting crystallites. As investigated by XRD, the degree of crystalline order systematically increased with rising dissimilarity in component solvents; integrated intensity ratio rising from 0.52 for toluene to 0.54, 0.69 and 0.72 respectively for toluene/benzene, toluene/cyclohexane, and toluene/hexane. The variation in degree of crystallinity is also reflected in electrical properties of OFETs, where the field-effect mobility improved from 0.05 cm2/(V.s) for toluene solvent to higher than 0.1 cm2/(V.s) for toluene/hexane. © 2016 Elsevier B.V. All rights reserved.

Synthetic Metals

Crystallinity and performance improvement in solution processed organic field-effect transistors due to structural dissimilarity of the additive solvent

Falls have always been source of injuries and fatalities. There can be various reasons for falls from medical conditions to loss of balance. Fall detection in the labs is based on video recordings while ubiquitous methods utilize inertial sensors. These methods require a lot of data processing consequently much power is utilized. In this paper, we propose a fall detection method which does not require inertial sensing nodes thus reduces computation and power requirements. Previous methods have either used received signal strength as monitoring parameter which is quite unstable or uses ambient monitoring points sensing through which remains disturbed by environmental noise and obstacles. We are proposing a novel ubiquitous wireless nodes deployment on the subject's body to minimize noise interferences. Fall has been detected using wireless sensing physical layer channel state information (CSI). The human body acts as an obstacle for the wireless signals generating unique signature with respect to the activity performed which can be estimated using CSI. This CSI information is available in new 802.11n WLAN NICs. We argue that this signature should be best observed when both the sender and receiver nodes are deployed on the body due to minimum environmental interference. We have trained the system to identify these signatures and detect falls. We have also been able to differentiate falls from fall like activities such as squatting and sitting on chair with sufficient accuracy. © 2015 IEEE.

2015 International Conference on Computing and Network Communications, CoCoNet 2015

Ubiquitous fall detection through wireless channel state information

This paper for the first time presents a comprehensive computational modeling approach for AlGaN/GaN high electron mobility transistors. Impact of the polarization charge at different material interfaces on the energy band profile as well as parasitic charge across the epitaxial stack is modeled and studied. Furthermore, impact of surface and bulk traps on two-dimensional electron gas, device characteristics, and gate leakage is accounted in this paper. For the first time, surface states modeled as donor type traps were correlated with gate leakage. Moreover, a new approach to accurately model the forward gate leakage in Schottky gate devices is proposed. Finally, impact of lattice and carrier heating is studied, while highlighting the relevance of carrier heating, lattice heating, and bulk traps over the device characteristics. In addition to this, modeling strategy for other critical aspects like parasitic charges, quantum effects, S/D Schottky contacts, and high field effects is presented. © 2016 IEEE.

IEEE Transactions on Nanotechnology

A Comprehensive Computational Modeling Approach for AlGaN/GaN HEMTs

This paper deals with event-triggering based design of discrete-time sliding mode (DTSM) control for linear systems. Multirate output feedback based DTSM is designed with event-triggering strategy such that the system trajectories remain bounded in the vicinity of sliding manifold. An event-triggering rule is developed for DTSM which is evaluated only at periodic time intervals. The control is updated whenever the triggering instant is generated at these discrete time instants. It is shown that with this technique the system trajectories remain bounded. Also, in this triggering scheme there is always guaranteed Zeno free execution of triggering sequences as it is inherently discrete. Simulation results are shown to demonstrate the theoretical treatments of this paper. © 2016 IEEE.

Proceedings of IEEE International Workshop on Variable Structure Systems

Discrete event-triggered sliding mode control with fast output sampling feedback

For uncertain systems with relative degree two, a continuous homogeneous sliding-mode control algorithm is proposed. This algorithm ensures finite-time convergence to the third-order sliding set, using only information about the output and its first derivative. We prove the convergence of the proposed algorithm via a homogeneous, continuously differentiable and strict Lyapunov function. © 2016 Published by Elsevier Ltd.

Automatica

Continuous terminal sliding-mode controller

The paper presents an event-triggering based sliding mode control law for delta operator systems with disturbance. The discrete domain representation of a system using shift operator becomes numerically ill-conditioned at very high sampling rates. To circumvent this problem, the system is represented using delta operator. The delta operator creates a rapprochement between continuous-time and discrete-time system model at very high sampling rates. A discrete-time sliding mode (DTSM) control law is developed to achieve robustness against external disturbances. Further to reduce the resource utilization, an event-triggered DTSM control law is proposed such that the closed loop system is stable. Due to the inherent discrete nature of the control there is no accumulation of triggering instants at any instant of time. Hence the zeno free execution of the control updating instants is always guaranteed. Simulation results are also shown to illustrate the effectiveness of the proposed method. © 2016 IEEE.

IECON Proceedings (Industrial Electronics Conference)

Event-triggered sliding mode control for delta operator systems

This paper presents the implementation of super-twisting control (STC) on nth-order perturbed integrator system using higher order sliding mode observer (HOSMO). It is shown that if nth-order SMO is used, either super-twisting algorithm structure is not achieved using continuous controller or the resulting controller is discontinuous. The discontinuous control action is not desirable for practical applications. A method for implementing STC using (n+1) th-order SMO is proposed. The controller proposed based on this observer design is continuous. Sliding surface is designed for handling relative degree problem and the controller is designed such that second order sliding mode (SOSM) is achieved on the sliding surface. Simulation results are also shown using practical example of Insulin-Glucose regulation dynamical model to illustrate the effectiveness of the proposed method. © 2016

IFAC-PapersOnLine

Implementation of Super-Twisting Control on Higher Order Perturbed Integrator System using Higher Order Sliding Mode Observer

GaN nanocrystals were formed in a silicon matrix by sequential implantation of Ga+ and N2+ ions followed by either Furnace Annealing (FA) or Rapid Thermal Annealing (RTA). The formation of Ga-rich clusters and Ga-N bonds was confirmed by X-ray photoelectron and photoluminescence spectroscopy. A Schottky top contact and ohmic bottom contact were fabricated and current-voltage (I-V) characteristics of the implanted samples were studied. Current values were found to be higher in RTA samples and lower in FA samples. It is observed that the height of the Schottky barrier strongly depends on the kind of annealing and is found to be 0.65 ± 0.02 eV for FA and 0.56 ± 0.02 eV for RTA compared to the value of 0.61 ± 0.02 eV for the pristine Si sample. A carrier transport mechanism is discussed based on experimental results for both kinds of annealing. © The Royal Society of Chemistry 2016.

RSC Advances

Effect of annealing on carrier transport properties of GaN-incorporated silicon

Hydrogen gas sensing response of RF sputtered nano-crystalline ZnO thin film is improved by ∼ 34.73 % using swift heavy ion irradiation technique. X-ray diffraction reveals single crystalline wurtzite structure of ZnO thin films. Full width half maximum (FWHM) of (0002) diffraction peak is decreased with increase in ion fluences. However, at very high fluence 1 × 1013 ions/cm2, crystallinity is degraded while FWHM of diffraction peak increases. The ZnO films were grown under highly compressive stress, which was relaxed with incremental ion fluences up to 1 × 1013 ions/cm2. Cathodoluminenscence spectroscopy shows intense predominant peak around ∼ 3.23 eV, which indicates good optical quality of the films. As ion fluence increases, a blue shift appears in near band emission peak from 3.23 to 3.33 eV, which indicates that in-plane stress is decreased. Surface morphology shows generation of self-affine nanostructure and grain fragments as ion fluences were increased. Grain fragmentations had enhanced the surface reaction, and as a result, gas sensor's relative response has improved. It was observed that the gas sensor's sensitivity is strongly dependent on ion fluences and operating temperature. The sensitivity was enhanced from 66.68% to 89.84% with fluence variations from pristine to 1 × 1012 ions/cm2 at 175 °C operating temperature. © 2016 IEEE.