Matching Items (17)

Simulation models for programmable metallization cells

Description

Advances in software and applications continue to demand advances in memory. The ideal memory would be non-volatile and have maximal capacity, speed, retention time, endurance, and radiation hardness while also

Advances in software and applications continue to demand advances in memory. The ideal memory would be non-volatile and have maximal capacity, speed, retention time, endurance, and radiation hardness while also having minimal physical size, energy usage, and cost. The programmable metallization cell (PMC) is an emerging memory technology that is likely to surpass flash memory in all the listed ideal memory characteristics. A comprehensive physics-based model is needed to fully understand PMC operation and aid in design optimization. With the intent of advancing the PMC modeling effort, this thesis presents two simulation models for the PMC. The first model is a finite element model based on Silvaco Atlas finite element analysis software. Limitations of the software are identified that make this model inconsistent with the operating mechanism of the PMC. The second model is a physics-based numerical model developed for the PMC. This model is successful in matching data measured from a chalcogenide glass PMC designed and manufactured at ASU. Matched operating characteristics observable in the current and resistance vs. voltage data include the OFF/ON resistances and write/erase and electrodeposition voltage thresholds. Multilevel programming is also explained and demonstrated with the numerical model. The numerical model has already proven useful by revealing some information presented about the operation and characteristics of the PMC.

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Date Created
  • 2013

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Cu-Silica Based Programmable Metallization Cell: Fabrication, Characterization and Applications

Description

The Programmable Metallization Cell (PMC) is a novel solid-state resistive switching technology. It has a simple metal-insulator-metal “MIM” structure with one metal being electrochemically active (Cu) and the other one

The Programmable Metallization Cell (PMC) is a novel solid-state resistive switching technology. It has a simple metal-insulator-metal “MIM” structure with one metal being electrochemically active (Cu) and the other one being inert (Pt or W), an insulating film (silica) acts as solid electrolyte for ion transport is sandwiched between these two electrodes. PMC’s resistance can be altered by an external electrical stimulus. The change of resistance is attributed to the formation or dissolution of Cu metal filament(s) within the silica layer which is associated with electrochemical redox reactions and ion transportation. In this dissertation, a comprehensive study of microfabrication method and its impacts on performance of PMC device is demonstrated, gamma-ray total ionizing dose (TID) impacts on device reliability is investigated, and the materials properties of doped/undoped silica switching layers are illuminated by impedance spectroscopy (IS). Due to the inherent CMOS compatibility, Cu-silica PMCs have great potential to be adopted in many emerging technologies, such as non-volatile storage cells and selector cells in ultra-dense 3D crosspoint memories, as well as electronic synapses in brain-inspired neuromorphic computing. Cu-silica PMC device performance for these applications is also assessed in this dissertation.

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Date Created
  • 2017

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Development of novel sensor devices for total ionization dose detection

Description

Total dose sensing systems (or radiation detection systems) have many applications,

ranging from survey monitors used to supervise the generated radioactive waste at

nuclear power plants to personal dosimeters which measure the

Total dose sensing systems (or radiation detection systems) have many applications,

ranging from survey monitors used to supervise the generated radioactive waste at

nuclear power plants to personal dosimeters which measure the radiation dose

accumulated in individuals. This dissertation work will present two different types of

novel devices developed at Arizona State University for total dose sensing applications.

The first detector technology is a mechanically flexible metal-chalcogenide glass (ChG)

based system which is fabricated on low cost substrates and are intended as disposable

total dose sensors. Compared to existing commercial technologies, these thin film

radiation sensors are simpler in form and function, and cheaper to produce and operate.

The sensors measure dose through resistance change and are suitable for applications

such as reactor dosimetry, radiation chemistry, and clinical dosimetry. They are ideal for

wearable devices due to the lightweight construction, inherent robustness to resist

breaking when mechanically stressed, and ability to attach to non-flat objects. Moreover,

their performance can be easily controlled by tuning design variables and changing

incorporated materials. The second detector technology is a wireless dosimeter intended

for remote total dose sensing. They are based on a capacitively loaded folded patch

antenna resonating in the range of 3 GHz to 8 GHz for which the load capacitance varies

as a function of total dose. The dosimeter does not need power to operate thus enabling

its use and implementation in the field without requiring a battery for its read-out. As a

result, the dosimeter is suitable for applications such as unattended detection systems

destined for covert monitoring of merchandise crossing borders, where nuclear material

tracking is a concern. The sensitive element can be any device exhibiting a known

variation of capacitance with total ionizing dose. The sensitivity of the dosimeter is

related to the capacitance variation of the radiation sensitive device as well as the high

frequency system used for reading. Both technologies come with the advantage that they

are easy to manufacture with reasonably low cost and sensing can be readily read-out.

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Created

Date Created
  • 2017

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Analysis and Modeling of Foundry Compatible Programmable Metallization Cell Materials

Description

Programmable Metallization Cell (PMC) devices are, in essence, redox-based

solid-state resistive switching devices that rely on ion transport through a solid electrolyte (SE) layer from anode to cathode. Analysis and modeling

Programmable Metallization Cell (PMC) devices are, in essence, redox-based

solid-state resistive switching devices that rely on ion transport through a solid electrolyte (SE) layer from anode to cathode. Analysis and modeling of the effect of different fabrication and processing parameter/conditions on PMC devices are crucial for future electronics. Furthermore, this work is even more significant for devices utilizing back-end- of-line (BEOL) compatible materials such as Cu, W, their oxides and SiOx as these devices offer cost effectiveness thanks to their inherent foundry-ready nature. In this dissertation, effect of annealing conditions and cathode material on the performance of Cu-SiOx vertical devices is investigated which shows that W-based devices have much lower forming voltage and initial resistance values. Also, higher annealing temperatures first lead to an increase in forming voltage from 400 °C to 500 °C, then a drastic decrease at 550 °C due to Cu island formation at the Cu/SiOx interface. Next, the characterization and modeling of the bilayer Cu2O/Cu-WO3 obtained by annealing the deposited Cu/WO3 stacks in air at BEOL-compatible temperatures is presented that display unique characteristics for lateral PMC devices. First, thin film oxidation kinetics of Cu is studied which show a parabolic relationship with annealing time and an activation energy of 0.70 eV. Grown Cu2O shows a cauliflower-like morphology where feature size on the surface increase with annealing time and temperature. Then, diffusion kinetics of Cu in WO3 is examined where the activation energy of diffusion of Cu into WO3 is calculated to be 0.74 eV. Cu was found to form clusters in the WO3 host which was revealed by imaging. Moreover, using the oxidation and diffusion analyses, a Matlab model is established for modeling the bilayer for process and annealing-condition optimization. The model is built to produce the resulting Cu2O thickness and Cu concentration in Cu-WO3. Additionally, material characterization, preliminary electrical results along with modeling of lateral PMC devices utilizing the bilayer is also demonstrated. By tuning the process parameters such as deposited Cu thickness and annealing conditions, a low-resistive Cu2O layer was achieved which dramatically enhanced the electrodeposition growth rate for lateral PMC devices.

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Date Created
  • 2020

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Programmable metallization cell devices for flexible electronics

Description

Programmable metallization cell (PMC) technology is based on an electrochemical phenomenon in which a metallic electrodeposit can be grown or dissolved between two electrodes depending on the voltage applied between

Programmable metallization cell (PMC) technology is based on an electrochemical phenomenon in which a metallic electrodeposit can be grown or dissolved between two electrodes depending on the voltage applied between them. Devices based on this phenomenon exhibit a unique, self-healing property, as a broken metallic structure can be healed by applying an appropriate voltage between the two broken ends. This work explores methods of fabricating interconnects and switches based on PMC technology on flexible substrates. The objective was the evaluation of the feasibility of using this technology in flexible electronics applications in which reliability is a primary concern. The re-healable property of the interconnect is characterized for the silver doped germanium selenide (Ag-Ge-Se) solid electrolyte system. This property was evaluated by measuring the resistances of the healed interconnect structures and comparing these to the resistances of the unbroken structures. The reliability of the interconnects in both unbroken and healed states is studied by investigating the resistances of the structures to DC voltages, AC voltages and different temperatures as a function of time. This work also explores replacing silver with copper for these interconnects to enhance their reliability. A model for PMC-based switches on flexible substrates is proposed and compared to the observed device behavior with the objective of developing a formal design methodology for these devices. The switches were subjected to voltage sweeps and their resistance was investigated as a function of sweep voltage. The resistance of the switches as a function of voltage pulse magnitude when placed in series with a resistance was also investigated. A model was then developed to explain the behavior of these devices. All observations were based on statistical measurements to account for random errors. The results of this work demonstrate that solid electrolyte based interconnects display self-healing capability, which depends on the applied healing voltage and the current limit. However, they fail at lower current densities than metal interconnects due to an ion-drift induced failure mechanism. The results on the PMC based switches demonstrate that a model comprising a Schottky diode in parallel with a variable resistor predicts the behavior of the device.

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Date Created
  • 2011

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Fractal properties and applications of dendritic filaments in programmable metallization cells

Description

Programmable metallization cell (PMC) technology employs the mechanisms of metal ion transport in solid electrolytes (SE) and electrochemical redox reactions in order to form metallic electrodeposits. When a positive bias

Programmable metallization cell (PMC) technology employs the mechanisms of metal ion transport in solid electrolytes (SE) and electrochemical redox reactions in order to form metallic electrodeposits. When a positive bias is applied to an anode opposite to a cathode, atoms at the anode are oxidized to ions and dissolve into the SE. Under the influence of the electric field, the ions move to the cathode and become reduced to form the electrodeposits. These electrodeposits are filamentary in nature and persistent, and since they are metallic can alter the physical characteristics of the material on which they are formed. PMCs can be used as next generation memories, radio frequency (RF) switches and physical unclonable functions (PUFs).

The morphology of the filaments is impacted by the biasing conditions. Under a relatively high applied electric field, they form as dendritic elements with a low fractal dimension (FD), whereas a low electric field leads to high FD features. Ion depletion effects in the SE due to low ion diffusivity/mobility also influences the morphology by limiting the ion supply into the growing electrodeposit.

Ion transport in SE is due to hopping transitions driven by drift and diffusion force. A physical model of ion hopping with Brownian motion has been proposed, in which the ion transitions are random when time window is larger than characteristic time. The random growth process of filaments in PMC adds entropy to the electrodeposition, which leads to random features in the dendritic patterns. Such patterns has extremely high information capacity due to the fractal nature of the electrodeposits.

In this project, lateral-growth PMCs were fabricated, whose LRS resistance is less than 10Ω, which can be used as RF switches. Also, an array of radial-growth PMCs was fabricated, on which multiple dendrites, all with different shapes, could be grown simultaneously. Those patterns can be used as secure keys in PUFs and authentication can be performed by optical scanning.

A kinetic Monte Carlo (KMC) model is developed to simulate the ion transportation in SE under electric field. The simulation results matched experimental data well that validated the ion hopping model.

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Created

Date Created
  • 2015

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Modeling and Simulation of the Programmable Metallization Cells (PMCs) and Diamond-Based Power Devices

Description

This PhD thesis consists of three main themes. The first part focusses on modeling of Silver (Ag)-Chalcogenide glass based resistive memory devices known as the Programmable Metallization Cell (PMC). The

This PhD thesis consists of three main themes. The first part focusses on modeling of Silver (Ag)-Chalcogenide glass based resistive memory devices known as the Programmable Metallization Cell (PMC). The proposed models are examined with the Technology Computer Aided Design (TCAD) simulations. In order to find a relationship between electrochemistry and carrier-trap statistics in chalcogenide glass films, an analytical mapping for electron trapping is derived. Then, a physical-based model is proposed in order to explain the dynamic behavior of the photodoping mechanism in lateral PMCs. At the end, in order to extract the time constant of ChG materials, a method which enables us to determine the carriers’ mobility with and without the UV light exposure is proposed. In order to validate these models, the results of TCAD simulations using Silvaco ATLAS are also presented in the study, which show good agreement.

In the second theme of this dissertation, a new model is presented to predict single event transients in 1T-1R memory arrays as an inverter, where the PMC is modeled as a constant resistance while the OFF transistor is model as a diode in parallel to a capacitance. The model divides the output voltage transient response of an inverter into three time segments, where an ionizing particle striking through the drain–body junction of the OFF-state NMOS is represented as a photocurrent pulse. If this current source is large enough, the output voltage can drop to a negative voltage. In this model, the OFF-state NMOS is represented as the parallel combination of an ideal diode and the intrinsic capacitance of the drain–body junction, while a resistance represents an ON-state NMOS. The proposed model is verified by 3-D TCAD mixed-mode device simulations. In order to investigate the flexibility of the model, the effects of important parameters, such as ON-state PMOS resistance, doping concentration of p-region in the diode, and the photocurrent pulse are scrutinized.

The third theme of this dissertation develops various models together with TCAD simulations to model the behavior of different diamond-based devices, including PIN diodes and bipolar junction transistors (BJTs). Diamond is a very attractive material for contemporary power semiconductor devices because of its excellent material properties, such as high breakdown voltage and superior thermal conductivity compared to other materials. Collectively, this research project enhances the development of high power and high temperature electronics using diamond-based semiconductors. During the fabrication process of diamond-based devices, structural defects particularly threading dislocations (TDs), may affect the device electrical properties, and models were developed to account of such defects. Recognition of their behavior helps us understand and predict the performance of diamond-based devices. Here, the electrical conductance through TD sites is shown to be governed by the Poole-Frenkel emission (PFE) for the temperature (T) range of 323 K ˂ T ˂ 423 K. Analytical models were performed to fit with experimental data over the aforementioned temperature range. Next, the Silvaco Atlas tool, a drift-diffusion based TCAD commercial software, was used to model diamond-based BJTs. Here, some field plate methods are proposed in order to decrease the surface electric field. The models used in Atlas are modified to account for both hopping transport in the impurity bands associated with high activation energies for boron doped and phosphorus doped diamond.

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Date Created
  • 2017

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Defect Induced Aging and Breakdown in High-k Dielectrics

Description

High-k dielectrics have been employed in the metal-oxide semiconductor field effect transistors (MOSFETs) since 45 nm technology node. In this MOSFET industry, Moore’s law projects the feature size of MOSFET

High-k dielectrics have been employed in the metal-oxide semiconductor field effect transistors (MOSFETs) since 45 nm technology node. In this MOSFET industry, Moore’s law projects the feature size of MOSFET scales half within every 18 months. Such scaling down theory has not only led to the physical limit of manufacturing but also raised the reliability issues in MOSFETs. After the incorporation of HfO2 based high-k dielectrics, the stacked oxides based gate insulator is facing rather challenging reliability issues due to the vulnerable HfO2 layer, ultra-thin interfacial SiO2 layer, and even messy interface between SiO2 and HfO2. Bias temperature instabilities (BTI), hot channel electrons injections (HCI), stress-induced leakage current (SILC), and time dependent dielectric breakdown (TDDB) are the four most prominent reliability challenges impacting the lifetime of the chips under use.

In order to fully understand the origins that could potentially challenge the reliability of the MOSFETs the defects induced aging and breakdown of the high-k dielectrics have been profoundly investigated here. BTI aging has been investigated to be related to charging effects from the bulk oxide traps and generations of Si-H bonds related interface traps. CVS and RVS induced dielectric breakdown studies have been performed and investigated. The breakdown process is regarded to be related to oxygen vacancies generations triggered by hot hole injections from anode. Post breakdown conduction study in the RRAM devices have shown irreversible characteristics of the dielectrics, although the resistance could be switched into high resistance state.

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Created

Date Created
  • 2018

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NVM challenges in medical devices

Description

Electronic devices are gaining an increasing market share in the medical field. Medical devices are becoming more sophisticated, and encompassing more applications. Unlike consumer electronics, medical devices have far more

Electronic devices are gaining an increasing market share in the medical field. Medical devices are becoming more sophisticated, and encompassing more applications. Unlike consumer electronics, medical devices have far more limitations when it comes to area, power and most importantly reliability. The medical devices industry has recently seen the advantages of using Flash memory instead of Read Only Memory (ROM) for firmware storage, and in some cases to replace Electrically Programmable Read Only Memories (EEPROMs) in medical devices for frequent data storage. There are direct advantages to using Flash memory instead of Read Only Memory, most importantly the fact that firmware can be rewritten along the development cycle and in the field. However, Flash technology requires high voltage circuitry that makes it harder to integrate into low power devices. There have been a lot of advances in Non-Volatile Memory (NVM) technologies, and many Flash rivals are starting to gain attention. The purpose of this thesis is to evaluate these new technologies against Flash to determine the feasibility as well as the advantages of each technology. The focus is on embedded memory in a medical device micro-controller and application specific integrated circuits (ASIC). A behavioral model of a Programmable Metallization Cell (PMC) was used to simulate the behavior and determine the advantages of using PMC technology versus flash. When compared to flash test data, PMC based embedded memory showed a reduction in power consumption by many orders of magnitude. Analysis showed that an approximated 20% device longevity increase can be achieved by using embedded PMC technology.

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Created

Date Created
  • 2010

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Radiation sensing using chalcogenide glass materials

Description

The dissolution of metal layers such as silver into chalcogenide glass layers such as germanium selenide changes the resistivity of the metal and chalcogenide films by a great extent. It

The dissolution of metal layers such as silver into chalcogenide glass layers such as germanium selenide changes the resistivity of the metal and chalcogenide films by a great extent. It is known that the incorporation of the metal can be achieved by ultra violet light exposure or thermal processes. In this work, the use of metal dissolution by exposure to gamma radiation has been explored for radiation sensor applications. Test structures were designed and a process flow was developed for prototype sensor fabrication. The test structures were designed such that sensitivity to radiation could be studied. The focus is on the effect of gamma rays as well as ultra violet light on silver dissolution in germanium selenide (Ge30Se70) chalcogenide glass. Ultra violet radiation testing was used prior to gamma exposure to assess the basic mechanism. The test structures were electrically characterized prior to and post irradiation to assess resistance change due to metal dissolution. A change in resistance was observed post irradiation and was found to be dependent on the radiation dose. The structures were also characterized using atomic force microscopy and roughness measurements were made prior to and post irradiation. A change in roughness of the silver films on Ge30Se70 was observed following exposure. This indicated the loss of continuity of the film which causes the increase in silver film resistance following irradiation. Recovery of initial resistance in the structures was also observed after the radiation stress was removed. This recovery was explained with photo-stimulated deposition of silver from the chalcogenide at room temperature confirmed with the re-appearance of silver dendrites on the chalcogenide surface. The results demonstrate that it is possible to use the metal dissolution effect in radiation sensing applications.

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Created

Date Created
  • 2012