Papers by Guru Subramanyam
International Workshop on Thin Films for Electronics, Electro-Optics, Energy, and Sensors 2019, 2019
International Conference on Neuromorphic Systems 2020
As computer networks become more advanced, the necessity for reliable intrusion detection at extr... more As computer networks become more advanced, the necessity for reliable intrusion detection at extreme efficiency has vastly increased. Thus, in this work we present a one shot learning system capable of online learning for network intrusion detection. Adaptive resonance theory is implemented in custom low power memristor-based neuromorphic hardware. The system is capable of discriminating with existing knowledge to learn incrementally. The winner take all circuitry is implemented with a capacitor and CMOS timing circuit that finds the winning neuron and controls the weight update for only the winning neuron. The time required to find a winning neuron was determined to be in the nanosecond range. The performance of the system was evaluated on both previously known and zero-day datasets. The detection accuracy using zero-day packets is 99.97%, and 99.99% for the known attacks. Furthermore, the system was tested using various vigilance parameters and learning rates. The variation of threshold voltage across the capacitor was also investigated to observe the effect on learning and detection accuracy. CCS CONCEPTS • Hardware; • Emerging technologies; • Analysis and design of emerging devices and systems; • Emerging architectures;
MRS Advances
V1−xWxO2 is known to be a reliable thermochromic material for multiple practical applications due... more V1−xWxO2 is known to be a reliable thermochromic material for multiple practical applications due to its insulator to metal transition temperature controlled by W dopping. In this paper, we present electrical and optical properties of V1−xWxO2 thin films synthesized by PLD technique. In this respect, the electrical resistance, the refractive index (n), and extinction coefficient (k) as a function of temperature from 25 to 80 °C and wavelength ranging from 500 to 3000 nm were obtained using conventional 4-probe resistance and ellipsometry methods. The direct and indirect bandgap values at different doping levels and temperatures have been calculated using n and k versus energy data and compared with thermally activated bandgap from electrical resistance. A decrease in direct and indirect bandgaps with temperature and wavelength was observed with doping and temperature. Comparison between thermal and optical bandgap demonstrates that activated thermal bandgap is only comparable with t...
International Journal of Antennas and Propagation, 2012
A novel printed antenna with a frequency reconfigurable feed network is presented. The antenna co... more A novel printed antenna with a frequency reconfigurable feed network is presented. The antenna consists of a bowtie structure patch radiating element in the inner space of an annulus that is on a nongrounded substrate with a ferroelectric (FE) Barium Strontium Titanate (BST) thin film. The bowtie patch is fed by a coplanar waveguide (CPW) transmission line that also includes a CPW-based BST shunt varactor. Reconfiguration of the compact 8 mm × 8 mm system has been demonstrated by shifting the antenna system's operating frequency 500 MHz in the 7-9 GHz band by applying a DC voltage bias.
Modeling of memristor devices is essential for memristor based circuit and system design. This ch... more Modeling of memristor devices is essential for memristor based circuit and system design. This chapter presents a review of existing memristor modeling techniques and provides simulations that compare several existing models to published memristor characterization data. A discussion of existing models is presented that explains how the equations of each relate to physical device behaviors. The simulations were completed in LTspice and compare the output of the different models to current–voltage relationships of physical devices. Sinusoidal and triangular pulse inputs were used throughout the simulations to test the capabilities of each model. The chapter is concluded by recommending a more generalized memristor model that can be accurately matched to several different published device characterizations. This generalized model provides the potential for more accurate circuit simulation for a wide range of device structures and voltage inputs. 12.
2021 IEEE Cognitive Communications for Aerospace Applications Workshop (CCAAW), 2021
Advances in Condensed Matter Physics, 2018
This paper presents tunable inductors designed with vanadium dioxide (VO2) thin film to implement... more This paper presents tunable inductors designed with vanadium dioxide (VO2) thin film to implement tunability. Two types of configurations, a single line coil inductor and a dual line coil inductor, are proposed. Tunable inductance is realized by thermally controlling VO2 thin film stub to be an insulator or a conductor. The measurements of inductors are taken in the frequencies range from 0.01 GHz to 10 GHz. The electrical model has been developed to derive the corresponding inductance. The results show that the tuning range is about 69% when the temperature changes from room temperature to above the critical temperature of 68°C.
IEEE Transactions on Electron Devices, 2015
The 2013 International Joint Conference on Neural Networks (IJCNN), 2013
The 2010 International Joint Conference on Neural Networks (IJCNN), 2010
As semiconductor devices have shrunk further into the nanoscale regime, a new device, the memrist... more As semiconductor devices have shrunk further into the nanoscale regime, a new device, the memristor, has been discovered that has the potential to transform neuromorphic computing systems. This device is considered as the fourth fundamental circuit element. It was first theorized by Dr. Leon Chua in 1971 and has been discovered by HP labs in 2008. This paper describes initial efforts at fabricating the memristor devices and examining their properties. Two versions of memristor devices have been fabricated at the University of Dayton and the Air Force Research Laboratory utilizing varying thicknesses of the Ti02 dielectric layers. Our results show that the devices do exhibit the characteristic hysteresis loop in their I-V plots. Further refinement in the devices to achieve stronger hysteresis will be carried out as future work.
The 2011 International Joint Conference on Neural Networks, 2011
A memristor based write circuit is presented that can update multiple memristors using a neuron s... more A memristor based write circuit is presented that can update multiple memristors using a neuron spike generated by the Izhikevich model. A memristor read circuit is also presented that is capable of quantizing the resistance into 5 discrete values that could be digitally decoded. Together, these circuits provide the basic block for a memristor based neuromorphic architecture. The memristors were modeled using published device characterization data.
International Journal of Antennas and Propagation, 2012
A novel printed antenna with a frequency reconfigurable feed network is presented. The antenna co... more A novel printed antenna with a frequency reconfigurable feed network is presented. The antenna consists of a bowtie structure patch radiating element in the inner space of an annulus that is on a nongrounded substrate with a ferroelectric (FE) Barium Strontium Titanate (BST) thin film. The bowtie patch is fed by a coplanar waveguide (CPW) transmission line that also includes a CPW-based BST shunt varactor. Reconfiguration of the compact 8 mm × 8 mm system has been demonstrated by shifting the antenna system’s operating frequency 500 MHz in the 7–9 GHz band by applying a DC voltage bias.
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2013
This paper presents a SPICE model for memristive devices. It builds on existing models and is cor... more This paper presents a SPICE model for memristive devices. It builds on existing models and is correlated against several published device characterization data with an average error of 6.04%. When compared to existing alternatives, the proposed model can more accurately simulate a wide range of published memristors. The model is also tested in large circuits with up to 256 memristors, and was less likely to cause convergence errors when compared to other models. We show that the model can be used to study the impact of memristive device variation within a circuit. We examine the impact of nonuniformity in device state variable dynamics and conductivity on individual memristors as well as a four memristor read/write circuit. These studies show that the model can be used to predict how variation in a memristor wafer may impact circuit performance.
IEEE Electron Device Letters, 2011
This letter proposes a new mathematical model for memristor devices. It builds on existing models... more This letter proposes a new mathematical model for memristor devices. It builds on existing models and is correlated against several published device characterizations. This letter identifies significant discrepancies between the existing models and published device characterization data. The proposed model addresses these discrepancies. In particular, it allows modeling of memristor-based neuromorphic systems.
Crystals, 2021
Ba0.5Sr0.5TiO3 (BST-0.5) thin films (600 nm) were deposited on single crystal MgO, SrTiO3 (STO), ... more Ba0.5Sr0.5TiO3 (BST-0.5) thin films (600 nm) were deposited on single crystal MgO, SrTiO3 (STO), and LaAlO3 (LAO) substrates by pulsed laser deposition at an oxygen partial pressure of 80 mTorr and temperature of 720 °C. X-ray diffraction and in situ reflection high-energy electron diffraction routinely ascertained the epitaxial quality of the (100)-oriented nanocrystalline films. The broadband microwave (1–40 GHz) dielectric properties were measured using coplanar waveguide transmission line test structures. The out-of-plane relative permittivity (ε⏊/) exhibited strong substrate-dependent dielectric (relaxation) dispersions with their attendant peaks in loss tangent (tanδ), with the former dropping sharply from tens of thousands to ~1000 by 10 GHz. Although homogeneous in-plane strain (ϵǁ), enhances ε⏊/ with εMgOBST−0.5⏊/>εSTOBST−0.5⏊/>εLAOBST−0.5⏊/ at lower frequencies, two crossover points at 8.6 GHz and 18 GHz eventually change the trend to: εSTOBST−0.5⏊/>εLAOBST−0.5⏊/...
1998 IEEE MTT-S International Microwave Symposium Digest (Cat. No.98CH36192)
Trade names or manufacturers' names are used in this report for identification only. This usage d... more Trade names or manufacturers' names are used in this report for identification only. This usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.
Nanoscale research letters, Jan 29, 2013
Ferroelectric BaTiO3/SrTiO3 with optimized c-axis-oriented multilayered thin films were epitaxial... more Ferroelectric BaTiO3/SrTiO3 with optimized c-axis-oriented multilayered thin films were epitaxially fabricated on (001) MgO substrates. The microstructural studies indicate that the in-plane interface relationships between the films as well as the substrate are determined to be (001)SrTiO3//(001)BaTiO3//(001)MgO and [100]SrTiO3//[100]BaTiO3//[100]MgO. The microwave (5 to 18 GHz) dielectric measurements reveal that the multilayered thin films have excellent dielectric properties with large dielectric constant, low dielectric loss, and high dielectric tunability, which suggests that the as-grown ferroelectric multilayered thin films can be developed for room-temperature tunable microwave elements and related device applications.
Integrated Ferroelectrics, 2010
We report on the use of patterned ferroelectric films to fabricate proof of concept tunable one-p... more We report on the use of patterned ferroelectric films to fabricate proof of concept tunable one-pole microstrip filters with excellent transmission and mismatch/reflection properties at frequencies up to 24 GHz. By controlling the electric field distribution within the coupling region between the resonator and inputloutput lines, sufficiently high loaded and unloaded Q values are maintained so as to be useful for microstrip filter design, with low mismatch loss. In the 23-24 GHz region, the filter was tunable over a 100 MHz range, the loaded and unloaded Q values were 29 and 68, respectively, and the reflection losses were below-16 dB, which demonstrates the suitability of these films for practical microwave applications.
Integrated Ferroelectrics, 2002
The inclusion of voltage-tunable barium strontium titanate (BSTO) thin films into planar band pas... more The inclusion of voltage-tunable barium strontium titanate (BSTO) thin films into planar band pass filters offers tremendous potential to increase their versatility. The ability to tune the passband so as to correct for minor deviations in manufacturing tolerances, or to completely reconfigure the operating frequencies of a microwave communication system, are highly sought-after goals. However, use of ferroelectric films in these devices results in higher dielectric losses, which in turn increase the insertion loss and decrease the quality factors of the filters. This study explores the use of patterned ferroelectric layers to minimize dielectric losses without degrading tunability. Patterning the ferroelectric layers enables us to constrict the width of the ferroelectric layers between the coupled microstrip lines, and minimize losses due to ferroelectric layers. Coupled one-pole microstrip bandpass filters with fundamental resonances at ~7.2 GHz and well-defined harmonic resonances at ~14.4 and ~21.6 GHz, were designed, simulated and tested. For one of the filters, experimental results verified that its center frequency was tunable by 528 MHz at a center frequency of 21.957 GHz, with insertion losses varying from 4.3 to 2.5 dB, at 0 and 3.5 V/µm, respectively. These data demonstrate that the tuning-to-loss figure of merit of tunable microstrip filters can be greatly improved using patterned ferroelectric thin films as the tuning element, and tuning can be controlled by engineering the ferroelectric constriction in the coupled sections.
Integrated Ferroelectrics, 1999
Trade names or manufacturers' names are used in this report for identification only. This usage d... more Trade names or manufacturers' names are used in this report for identification only. This usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.
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Papers by Guru Subramanyam