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Artificial Neuron using MoS2/Graphene Threshold Switching Memristor
Title
Artificial Neuron using MoS2/Graphene Threshold Switching Memristor.
Creator
Kalita, Hirokjyoti, Roy, Tania, Sundaram, Kalpathy, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description
With the ever-increasing demand for low power electronics, neuromorphic computing has garnered huge interest in recent times. Implementing neuromorphic computing in hardware will be a severe boost for applications involving complex processes such as pattern recognition. Artificial neurons form a critical part in neuromorphic circuits, and have been realized with complex complementary metal(-)oxide(-)semiconductor (CMOS) circuitry in the past. Recently, insulator-to-metal-transition (IMT)...
Show moreWith the ever-increasing demand for low power electronics, neuromorphic computing has garnered huge interest in recent times. Implementing neuromorphic computing in hardware will be a severe boost for applications involving complex processes such as pattern recognition. Artificial neurons form a critical part in neuromorphic circuits, and have been realized with complex complementary metal(-)oxide(-)semiconductor (CMOS) circuitry in the past. Recently, insulator-to-metal-transition (IMT) materials have been used to realize artificial neurons. Although memristors have been implemented to realize synaptic behavior, not much work has been reported regarding the neuronal response achieved with these devices. In this work, we study the IMT in 1T-TaS2 and the volatile threshold switching behavior in vertical-MoS2 (v-MoS2) and graphene van der Waals heterojunction system. The v-MoS2/graphene threshold switching memristor (TSM) is used to produce the integrate-and-fire response of a neuron. We use large area chemical vapor deposited (CVD) graphene and MoS2, enabling large scale realization of these devices. These devices can emulate the most vital properties of a neuron, including the all or nothing spiking, the threshold driven spiking of the action potential, the post-firing refractory period of a neuron and strength modulated frequency response. These results show that the developed artificial neuron can play a crucial role in neuromorphic computing.
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Date Issued
2018
Identifier
CFE0007203, ucf:52291
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007203
HIGH QUALITY GATE DIELECTRIC/MoS2 INTERFACES PROBED BY THE CONDUCTANCE METHOD
Title
HIGH QUALITY GATE DIELECTRIC/MoS2 INTERFACES PROBED BY THE CONDUCTANCE METHOD.
Creator
Krishnaprasad Sharada, Adithi Pandrahal, Roy, Tania, Abdolvand, Reza, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description
Two-dimensional materials provide a versatile platform for various electronic and optoelectronic devices, due to their uniform thickness and pristine surfaces. We probe the superior quality of 2D/2D and 2D/3D interfaces by fabricating molybdenum disulfide (MoS2)-based field effect transistors having hexagonal boron nitride (h-BN) and Al2O3 as the top gate dielectrics. An extremely low trap density of ~7x10^10 states/cm2-eV is extracted at the 2D/2D interfaces with h-BN as the top gate...
Show moreTwo-dimensional materials provide a versatile platform for various electronic and optoelectronic devices, due to their uniform thickness and pristine surfaces. We probe the superior quality of 2D/2D and 2D/3D interfaces by fabricating molybdenum disulfide (MoS2)-based field effect transistors having hexagonal boron nitride (h-BN) and Al2O3 as the top gate dielectrics. An extremely low trap density of ~7x10^10 states/cm2-eV is extracted at the 2D/2D interfaces with h-BN as the top gate dielectric on the MoS2 channel. 2D/3D interfaces with Al2O3 as the top gate dielectric and SiOx as the nucleation layer exhibit trap densities between 7x10^10 and 10^11 states/cm2-eV, which is lower than previously reported 2D-channel/high-k-dielectric interface trap densities. The comparable values of trap time constants for both interfaces imply that similar types of defects contribute to the interface traps. This work establishes the case for van der Waals systems where the superior quality of 2D/2D and 2D/high-k dielectric interfaces can produce high performance electronic and optoelectronic devices.
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Date Issued
2018
Identifier
CFE0007214, ucf:52209
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007214
Experimental confirmation of ballistic nanofriction and quasiparticle interference in Dirac materials.
Title
Experimental confirmation of ballistic nanofriction and quasiparticle interference in Dirac materials.
Creator
Lodge, Michael, Ishigami, Masahiro, Kaden, William, Schelling, Patrick, Del Barco, Enrique, Roy, Tania, University of Central Florida
Abstract / Description
This dissertation is broadly divided into two parts. The first part details the development and usage of an experimental apparatus to measure the dry nanofriction for a well-defined interface at high sliding speeds. I leverage the sensitivity of a quartz crystal microbalance (QCM) to determine the drag coefficient of an ensemble of gold nanocrystals sliding on graphene at speeds up to 11 cm/s. I discuss the theories of velocity-dependent friction, especially at high sliding speeds, and QCM...
Show moreThis dissertation is broadly divided into two parts. The first part details the development and usage of an experimental apparatus to measure the dry nanofriction for a well-defined interface at high sliding speeds. I leverage the sensitivity of a quartz crystal microbalance (QCM) to determine the drag coefficient of an ensemble of gold nanocrystals sliding on graphene at speeds up to 11 cm/s. I discuss the theories of velocity-dependent friction, especially at high sliding speeds, and QCM modeling. I also discuss our synthesis protocols for graphene and molybdenum disulfide, as well as our protocol for fabricating a clean, graphene-laminated QCM device and nanocrystal ensemble. The design and fabrication of our QCM oscillator circuit is presented in detail. The quantitatively-measured the drag coefficient is compared against molecular dynamics simulations at both low and high sliding speeds. We show evidence of a predicted ultra-low friction regime and find that the interaction energy between gold nanocrystals and graphene is lower than previously assumed. In the second part of this dissertation, I detail the band structure measurement of a novel semimetal using scanning tunneling microscopy. In particular, I measured the energy-dependenceof quasiparticle interference patterns at the surface of zirconium silicon sulfide (ZrSiS), a topological nodal line semimetal whose charge carrier quasiparticles possess a pseudospin degree offreedom. The aims of this study were to (1) discover the shape of the band structure above the Fermi level along a high-symmetry direction, (2) discover the energetic location of the line node inthe same high-symmetry direction, and (3) discover the selection rules for k transitions. This study confirms the predicted linearity in E(k) of the band structure above the Fermi level. Additionally,we observe an energy-dependent mechanism for pseudospin scattering. This study also provides the first experimentally-derived estimation of the line node position in E(k).
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Date Issued
2018
Identifier
CFE0007218, ucf:52222
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007218
GaN Power Devices: Discerning Application-Specific Challenges and Limitations in HEMTs
Title
GaN Power Devices: Discerning Application-Specific Challenges and Limitations in HEMTs.
Creator
Binder, Andrew, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Roy, Tania, Kapoor, Vikram, Chow, Lee, University of Central Florida
Abstract / Description
GaN power devices are typically used in the 600 V market, for high efficiency, high power-density systems. For these devices, the lateral optimization of gate-to-drain, gate, and gate-to-source lengths, as well as gate field-plate length are critical for optimizing breakdown voltage and performance. This work presents a systematic study of lateral scaling optimization for high voltage devices to minimize figure of merit and maximize breakdown voltage. In addition, this optimization is...
Show moreGaN power devices are typically used in the 600 V market, for high efficiency, high power-density systems. For these devices, the lateral optimization of gate-to-drain, gate, and gate-to-source lengths, as well as gate field-plate length are critical for optimizing breakdown voltage and performance. This work presents a systematic study of lateral scaling optimization for high voltage devices to minimize figure of merit and maximize breakdown voltage. In addition, this optimization is extended for low voltage devices ((<) 100 V), presenting results to optimize both lateral features and vertical features. For low voltage design, simulation work suggests that breakdown is more reliant on punch-through as the primary breakdown mechanism rather than on vertical leakage current as is the case with high-voltage devices. A fabrication process flow has been developed for fabricating Schottky-gate, and MIS-HEMT structures at UCF in the CREOL cleanroom. The fabricated devices were designed to validate the simulation work for low voltage GaN devices. The UCF fabrication process is done with a four layer mask, and consists of mesa isolation, ohmic recess etch, an optional gate insulator layer, ohmic metallization, and gate metallization. Following this work, the fabrication process was transferred to the National Nano Device Laboratories (NDL) in Hsinchu, Taiwan, to take advantage of the more advanced facilities there. Following fabrication, a study has been performed on defect induced performance degradation, leading to the observation of a new phenomenon: trap induced negative differential conductance (NDC). Typically NDC is caused by self-heating, however by implementing a substrate bias test in conjunction with pulsed I-V testing, the NDC seen in our fabricated devices has been confirmed to be from buffer traps that are a result of poor channel carrier confinement during the dc operating condition.
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Date Issued
2019
Identifier
CFE0007885, ucf:52786
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007885
Chemical Vapor Deposition Growth of Large Area 2D MoS2 Layers: Layer Orientation Control, Heterostructure Integration, And Applications for Stretchable Sensors.
Title
Chemical Vapor Deposition Growth of Large Area 2D MoS2 Layers: Layer Orientation Control, Heterostructure Integration, And Applications for Stretchable Sensors.
Creator
Islam, Md. Ashraful, Jung, YeonWoong, Sundaram, Kalpathy, Yuan, Jiann-Shiun, Roy, Tania, Cho, Hyoung Jin, University of Central Florida
Abstract / Description
Two-dimensional (2D)-layered MoS2 layers have exhibited a broad set of unusual and superior material properties unattainable in any traditional bulk materials, drawing significant research interests nowadays. For instance, they present excellent semiconducting properties accompanying high carrier mobility and large current ON/OFF ratio as well as extensive in-plane strain limit and thickness, projecting high suitably for emerging flexible and stretchable electronics. Such properties and...
Show moreTwo-dimensional (2D)-layered MoS2 layers have exhibited a broad set of unusual and superior material properties unattainable in any traditional bulk materials, drawing significant research interests nowadays. For instance, they present excellent semiconducting properties accompanying high carrier mobility and large current ON/OFF ratio as well as extensive in-plane strain limit and thickness, projecting high suitably for emerging flexible and stretchable electronics. Such properties and applications strongly depend on the physical orientation and chemical composition of constituent 2D layers. 2D MoS2 layers chemically grown in two distinct orientations, e.g., horizontal alignment for electronics and optoelectronics, and vertical alignment for electrochemical and sensing applications. Moreover, 2D heterostructure layers composed of vertically stacked dissimilar 2D TMDs held via weak van der Waals (vdW) attractions offer unique 2D/2D interfaces, envisioned to display exotic material properties, unattainable in their monocomponent counterparts. However, the underlying principle of their layer orientation-controlled growth and integrations are not well suited for scalable production, leaving their projected technological opportunities far from being realized for various novel applications. Herein, I study various aspects of 2D MoS2 layers that were studied from their large-area layer-orientation controlled growth and heterostructures integration to applications in stretchable electronic devices. I developed a chemical vapor deposition (CVD) synthesis, which can grow large-area ((>) cm2) 2D MoS2 layers in a layer-controlled manner and investigated their underlying growth mechanism. I then developed a viable transfer approach of the as-grown 2D layers and integrated them into secondary target substrates to realize a new type of 2D MoS2-layers based heterostructures. To further extend their layer-controlled CVD growth and integration approach, a high-performance stretchable 2D MoS2-based electrical sensors were demonstrated on the elastomeric substrates with unconventional structural layouts. This study paves the way to explore this emerging atomically-thin material in realizing a wide range of unusual device and technologies which have been foreseen to be impossible otherwise.
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Date Issued
2019
Identifier
CFE0007820, ucf:52812
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007820