Browsing by Author "Berco, Dan"

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A comprehensive study of bipolar operation in resistive switching memory devices
(2016-06)
Berco, Dan
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Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The authors present a new numerical analysis method to investigate the conduction filament dynamics of a resistive switching nonvolatile metal-insulator-metal structured memory device. This comprehensive method, utilizing the Gibbs free energy criteria as a leading indicator and allowing simulation of all resistive memory operational phases (forming, set and reset), is presented for the first time. The formation and rupture of an oxygen vacancies based conduction filament are simulated to demonstrate a cycle of operation in a hafnium oxide based resistive forming layer. Starting from a random initial distribution of defect states, on to a formed conduction filament and ending in a ruptured state. Detailed plots of the physical parameters within the resistive layer are provided to gain deeper understanding of the conduction filament kinetics and introduce the concept of "hot spots", referring to random localized initial agglomeration of oxygen vacancies in which temperature surges is favored and contribute to initiate the conductive filament formation. By basing the method on well known thermodynamic properties and the Metropolis algorithm, simulation reliability and efficiency are obtained. The presented results confirm previously published data demonstrating the switching characteristics of hafnium based resistive random access memory.
A numerical analysis of progressive and abrupt reset in conductive bridging RRAM
(2016-06)
Berco, Dan
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The authors investigate the conduction filament (CF) properties of a Cu- based conductive bridging resistive memory device by implementing a numerical simulation of the low and high resistive states, starting from a random initial distribution of oxygen vacancies (OV) defects states in the resistive switching layer (RSL) to a formed CF and ending in a ruptured state. A calculation approach which accounts for both the statistical nature of the system and the synergetic effect of OV and Cu species on the overall conductance is presented. By defining a disorder parameter, the correlation between the OV initial distribution and the CF reset behavior is analyzed. A dependence of the reset transition, being either abrupt or progressive, on the physical shape of the CF which in turn is affected by this disorder is shown to exist based on the simulation results.
A numerical study of forming voltage and switching polarity dependence on Ti top electrode thickness in Zr RRAM
(2016-06)
Berco, Dan
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The authors investigate the conduction filament (CF) formation voltage and reset polarity dependence of a Ti/Zr/Pt resistive switching memory device on the Ti top electrode (TE) thickness by means of numerical simulation. A calculation method which accounts for both the initial statistical nature of the resistive switching layer (RSL) and the interaction of oxygen vacancies with oxygen species (O) on the overall conductance is used. The results show a correlation between the TE thickness and the density profile of O species both along the RSL-TE interface and within the TE, and indentify the causes for the previously observed not yet fully comprehended TE thickness dependent functionality of this device. The authors demonstrate that accumulation and reduction of O, during forming, result in a charged interfacial layer which decreases the effective oxide thickness and determines the forming voltage and switching polarity. In addition, local temperature profiles within the CF during forming promote O diffusion into the TE material which reduces the local conductivity and affects the forming voltage magnitude as well. In addition the authors provide forming and reset calculations for TE thicknesses of 5, 20 and 40 nm which are in good agreement with published experimental data.
A numerical study of multi filament formation in metal-ion based CBRAM
(2016-02-01)
Berco, Dan
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This study investigates the underlying mechanisms of multiple conductive filaments (CF) creation in metal-ion based conductive bridge RRAM (CBRAM) by using the Metropolis Monte Carlo algorithm and suggests a possible explanation for this phenomenon. The simulation method is demonstrated over a Cu/HfO2 structure, starting from a random initial distribution of oxygen vacancies (OV) defects in the resistive switching layer, to a formed CF and ending in a ruptured state. the results indicate that "Hot Spots" (HS), where agglomeration of OV trap like states for electron hopping based conduction induce local heating, create favorable energy conditions to attract diffused metal species originating from the top electrode. While HS may be created and annihilated by random OV generation and recombination processes, the precipitated metal forms a stem out of which a CF could evolve. The CF stem's final growth stage is mainly driven by drift and diffusion. This process may lead to the formation of one or more CFs as a function of the forming bias voltage. This bias dependence is demonstrated over a large range, where the creation of a single, double and multiple CFs are shown. In addition, the reset process of the multi CF device is presented, and the experimentally observed, step like, gradual CBRAM reset is verified. The simulated results are in good agreement with experimental data and promote the idea that OV defect engineering may be used to improve CBRAM performance. (C) 2016 Author(s).
A stochastic simulation method for the assessment of resistive random access memory retention reliability
(2015-12-21)
Berco, Dan
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This study presents an evaluation method for resistive random access memory retention reliability based on the Metropolis Monte Carlo algorithm and Gibbs free energy. The method, which does not rely on a time evolution, provides an extremely efficient way to compare the relative retention properties of metal-insulator-metal structures. It requires a small number of iterations and may be used for statistical analysis. The presented approach is used to compare the relative robustness of a single layer ZrO2 device with a double layer ZnO/ZrO2 one, and obtain results which are in good agreement with experimental data. (C) 2015 AIP Publishing LLC.
A stochastic simulation method for the assessment of resistive random access memory retention reliability
(2015-12-21)
Berco, Dan
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This study presents an evaluation method for resistive random access memory retention reliability based on the Metropolis Monte Carlo algorithm and Gibbs free energy. The method, which does not rely on a time evolution, provides an extremely efficient way to compare the relative retention properties of metal-insulator-metal structures. It requires a small number of iterations and may be used for statistical analysis. The presented approach is used to compare the relative robustness of a single layer ZrO2 device with a double layer ZnO/ZrO2 one, and obtain results which are in good agreement with experimental data. (C) 2015 AIP Publishing LLC.