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Yuyang Research Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Scanned by CamScanner Parasitic Capacitance Definition In electrical circuits, parasitic capacitance, is an unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. All actual circuit elements such as inductors, diodes, and transistors have internal capacitance, which can cause their behavior to depart from that of 'ideal' circuit elements. Additionally, there is always non-zero capacitance between any two conductors; this can be significant at higher frequencies with closely spaced conductors, such as wires or printed circuit board traces. The parasitic capacitance between the turns of an inductor or other wound component is often described as self-capacitance. However, self-capacitance of a conductive object is a different phenomenon, referring to the capacitance of the object without reference to another object. Mechanism When two conductors at different potentials are close to one another, they are affected by each other's electric field and store opposite electric charges like a capacitor. Changing the potential v between the conductors requires a current i into or out of the conductors to charge or discharge them. where C is the capacitance between the conductors. For example, an inductor often acts as though it includes a parallel capacitor, because of its closely spaced windings. When a potential difference exists across the coil, wires lying adjacent to each other are at different potentials. They act like the plates of a capacitor, and store charge. Any change in the voltage across the coil requires extra current to charge and discharge these small 'capacitors'. When the voltage changes only slowly, as in low-frequency circuits, the extra current is usually negligible, but when the voltage changes quickly the extra current is larger and can affect the operation of the circuit. Coils for high frequencies are often basket-wound to minimize parasitic capacitance. OVERSHOOT Abstract A Kinetic Monte Carlo (KMC) numerical simulator is developed for metal oxide resistive random access memory (RRAM). Improvements made on the stochastic model: 1. multiple conduction mechanisms 2. local field and local temperature profile 3. tracking of the individual oxygen migration path. I. Introduction The simulations suggest: 1.eliminating the forming process and decreasing the parasitic capacitance is required for minimizing the overshoot effect and reducing the reset power consumption; 2. the degradation of endurance can be explained by oxygen escaping from the electrode during cycling 3. the oxygen migration barrier can be extracted from the retention baking test over a suitable temperature range. To uses stochastic model to optimize RRAM characteristics, must understand: 1. The switching mechanism has been attributed to the formation/rupture of conductive filament (CF) with oxygen vacancies. 2. The variability originates from the random oxygen vacancy (Vo) generation/ recombination and oxygen ion (O2-) migration processes. 3. The set/forming current overshoot 4. The retention/endurance degradation mechanisms Scanned by CamScanner Scanned by CamScanner Objectives of the study& experiment : 1. further improve our stochastic model by taking more physical effects into account 2. gain insights on the evolution of CF configuration during the overshoot transient period and during the endurance cycling and retention baking tests. II. Model and Simulation Description 1. During the forming/set process (transition from high resistance state (HRS) to low resistance state (LRS)), O2- are pulled out from lattice and Vo are generated and form CF connecting both electrodes. 2. During the reset process (transition from LRS to HRS), CF is ruptured by the recombination of Vo with the O2- that migrate from the oxygen reservoir at the electrode/oxide interface. 3. Thus a tunneling gap is formed between the electrode and the residual CF. 4. The trap-assisted-tunneling (TAT) is the dominant conduction mechanism at low bias regime for the high resistance state (HRS) in HfOx RRAM, 5. Add two more mechanisms into the simulator: 1) The FN tunneling at high bias regime for HRS 2) The metallic conduction at LRS Trap-assisted-tunneling(TAT): The metallic conduction at LRS: • electrons are in localized state. • The electrons are partially in the extended states. • Vo are very far apart form each other. • Vo are close to each other. The characteristics of a conductive filament in HfO2 RRAM: 1. dependent on the duration of the current compliance overshoot, (which may occur during the filament formation process) 2. filament resistance is found to be affected by the duration of the overshoot caused by the parasitic capacitance. Forming Process: 1.involves the application of a relatively high voltage to “form” the conducting filament connecting the electrodes in the capacitor 2.determines the SET/RESET characteristics of the device. 3. forming current compliance limit determines the overall resistance of the formed filament * It is hard to practically control the current compliance because the current during a fast transient forming process may exceed the compliance limit (aka overshoot) due to discharge of the parasitic capacitance upon resistance change variations of the maximum RESET current. To limit overshoot: 1. utilizing a constant voltage high temperature forming method 2.employing a 1T1R device configuration, where each memory cell is connected in series with a transistor controlling the maximum passing current. * the source of the overshoot variation is strongly linked not only to the overshoot amplitude, but also to the duration of the overshoot. Biasing: Establishing predetermined voltages or currents at various points of an electronic circuit for the purpose of establishing proper operating conditions in electronic components. Coulomb blockade (CB) named after Charles-Augustin de Coulomb's electrical force, is the increased resistance at small bias voltages of an electronic device comprising at least one low-capacitance tunnel junction. Because of the CB, the resistances of devices are not constant at low bias voltages, but increase to infinity for biases under a certain threshold (i.e. no current flows). Intro: Artificial synapse Neuromorphic computing ( refer to Chapter 25) Conduction mechanism Methodology: Sample preparation Materials Feature size Sputtering system Mention how to use the sputtering system to grow the device Pressure, temperature, gas used Characterisation: DC measurement Pulse measurement Use of heater Performance of the device Energy dispersive X Ray (element analysis) Check the stoichiometry of the sample Complementary Metal Oxide Semiconductor List of literature reading: 1. Resistive Random Access Memory (RRAM) From Devices to Array Architectures 2. RRAM switching statistics 3. Effects of RRAM Stack Configuration on Forming Voltage and Current Overshoot 4. RRAM textbook 5. Statistical Fluctuations 6. Thin Film growth of Solid State materials 7. Understanding Metal Oxide RRAM Current Overshoot and Reliability 8. Dependence of the Filament Resistance on the Duration of the Current Overshoot.
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