• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.597-597
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• 2013

The resistive switching behaviors of Pt nanodisk on Nb-doped SrTiO3 single-crystal have been studied with conductive atomic force microscopy in ultra-high vacuum. The nanometer sizes of Pt disks were formed by using self-assembled patterns of silica nanospheres on Nb-doped SrTiO3 single-crystal semiconductor film using the Langmuir-Blodgett, followed by the metal deposition with e-beam evaporation. The conductance images shows the spatial mapping of the current flowing from the TiN coated AFM probe to Pt nanodisk surface on Nb：STO single-crystal substrate, that was simultaneously obtained with topography. The bipolar resistive switching behaviors of Pt nanodisk on Nb：STO single-crystal junctions was observed. By measuring the current-voltage spectroscopy after the forming process, we found that switching behavior depends on the charging and discharging of interface trap state that exhibit the high resistive state (HRS) and low resistive state (LRS), respectively. The results suggest that the bipolar resistive switching of Pt/Nb:STO single-crystal junctions can be performed without the electrochemical redox reaction between tip and sample with the potential application of nanometer scale resistive switching devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.285-285
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• 2016

Resistive random access memory devices have been widely studied due to their high performance characteristics, such as high scalability, fast switching, and low power consumption. However, fluctuation in operational parameters remains a critical weakness that leads to device failures. Although the random formation and rupture of conducting filaments (CFs) in an oxide matrix during resistive switching processes have been proposed as the origin of such fluctuations, direct observations of the formation and rupture of CFs at the device scale during resistive switching processes have been limited by the lack of real-time large-area imaging methods. Here, a novel imaging method is proposed for monitoring CF formation and rupture across the whole area of a memory cell during resistive switching. A hybrid structure consisting of a resistive random access memory and a light-emitting diode enables real-time monitoring of CF configuration during various resistive switching processes including forming, semi-forming, stable/unstable set/reset switching, and repetitive set switching over 50 cycles.

• Journal of the Semiconductor & Display Technology
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• v.20 no.1
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• pp.54-58
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• 2021

The RGO with controllable oxygen functional groups is a novel material as the active layer of resistive switching memory through a reduction process. We designed a nanoscale conductive channel induced by local oxygen ion diffusion in an Au / RGO+GQD / Al resistive switching memory structure. A strong electric field was locally generated around the Al metal channel generated in BIL, and the local formation of a direct conductive low-dimensional channel in the complex RGO graphene quantum dot region was confirmed. The resistive memory design of the complex RGO graphene quantum dot structure can be applied as an effective structure for charge transport, and it has been shown that the resistive switching mechanism based on the movement of oxygen and metal ions is a fundamental alternative to understanding and application of next-generation intelligent semiconductor systems.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.77-81
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• 2020

Resistive RAM (ReRAM) is a strong candidate for the next-generation nonvolatile memories which use the resistive switching characteristic of transition metal oxides. The resistive switching behaviors originate from the redistribution of oxygen vacancies inside of the oxide film by applied programming voltage. Therefore, controlling the oxygen vacancy inside transition metal oxide film is most important to obtain and control the resistive switching characteristic. In this study, we introduced an applying electric field into photochemical metal-organic deposition (PMOD) process to control the oxidation state of metal oxide thin film during the photochemical reaction by UV exposure. As a result, the surface oxidation state of FeOx film could be successfully controlled by the electric field-assisted PMOD (EFAPMOD), and the controlled oxidation states were confirmed by x-ray photoelectron spectroscopy (XPS) I-V characteristic. And the resistive switching characteristics with the oxidation-state of the surface region could be controlled effectively by adjusting an electric field during EFAPMOD process.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.257-261
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• 2010

A non-volatile resistive random access memory (RRAM) device with a Cr-doped $SrZrO_3/SrRuO_3$ bottom electrode heterostructure was fabricated on $SrTiO_3$ substrates using pulsed laser deposition. During the deposition process, the substrate temperature was $650^{\circ}C$ and the variable ambient oxygen pressure had a range of 50-250 mTorr. The sensitive dependences of the film structure on the processing oxygen pressure are important in controlling the bistable resistive switching of the Cr-doped $SrZrO_3$ film. Therefore, oxygen pressure plays a crucial role in determining electrical properties and film growth characteristics such as various microstructural defects and crystallization. Inside, the microstructure and crystallinity of the Cr-doped $SrZrO_3$ film by oxygen pressure were strong effects on the set, reset switching voltage of the Cr-doped $SrZrO_3$. The bistable switching is related to the defects and controls their number and structure. Therefore, the relation of defects generated and resistive switching behavior by oxygen pressure change will be discussed. We found that deposition conditions and ambient oxygen pressure highly affect the switching behavior. It is suggested that the interface between the top electrode and Cr-doped $SrZrO_3$ perovskite plays an important role in the resistive switching behavior. From I-V characteristics, a typical ON state resistance of $100-200\;{\Omega}$ and a typical OFF state resistance of $1-2\;k{\Omega}$, were observed. These transition metal-doped perovskite thin films can be used for memory device applications due to their high ON/OFF ratio, simple device structure, and non-volatility.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.32-43
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• 2023

Resistive Random Access Memory (RRAM), based on resistive switching characteristics, is emerging as a next-generation memory device capable of efficiently processing large amounts of data through its fast operation speed, simple device structure, and high-density implementation. Interface type resistive switching offer the advantage of low operation currents without the need for a forming process. Especially, for RRAM devices based on transition metal oxides, various studies are underway to enhance the memory characteristics, including precise material composition control and improving the reliability and stability of the device. In this paper, we introduce various methods, such as doping of heterogeneous elements, formation of multilayer films, chemical composition adjustment, and surface treatment to prevent degradation of interface type resistive switching properties and enhance the device characteristics. Through these approaches, we propose the feasibility of implementing high-efficient next-generation non-volatile memory devices based on improved resistive switching properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.359-360
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• 2013

The effect of electrode and deposition methods on non-linear interfacial resistive switching in HfO2 based $250{\times}250$ nm2 cross-point device was studied. HfO2 based device has the interfacial resistive switching properties of non-linearity and self-compliance current switching. The operating current in HfO2 based device was increased with negatively increasing the heat of formation energy in top electrode. Also, it was investigated that the operating current in HfO2 based device was changed with deposition methods of O3 reactant ALD, H2O reactant ALD and dc reactive sputtering, resulting the magnitude of the operating current and on/off ratio in order of HfO2 films deposited by dc reactive sputtering, H2O reactant ALD, and O3 reactant ALD. To investigate the effect of electrode and deposition methods on operating current of non-linear interfacial resistive switching in the cross-point device, X-ray photoelectron spectroscopy was measured. Through the analysis of O 1s spectra, non-lattice oxygen concentration, which is closely related to oxygen vacancies, was increased in order of Pt, TiN, and Ti top electrodes and in order of O3 reactant ALD, H2O reactant ALD, and O3 reactant ALD, and dc reactive sputtering deposition method. From all results, non-lattice oxygen concentration in ultra-thin HfO2 films play a crucial role in the operating current and memory states (LRS & HRS) in the non-linear interfacial resistive switching.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.384-384
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• 2012

We report nonvolatile memory properties of poly (3, 4-ethylenedioxythiophene) (PEDOT) thin films grown by vapor phase polymerization using FeCl3 as an oxidant. Liquid-bridge-mediated transfer method was employed to remove FeCl3 for generation of pure PEDOT thin films. From the electrical measurement of memory device, we observed voltage induced bipolar resistive switching behavior with ON/OFF ratio of 103 and reproducibility of more than 103 dc sweeping cycles. ON and OFF states were stable up to 104 seconds without significant degradation. Cyclic voltammetry data illustrates resistive switching effect can be attributed to formation and rupture of conducting paths due to oxidation and reduction of PEDOT. The maximum current before reset process was found to be increase linearly with increase in compliance current applied during set process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.710-712
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• 2011

In this study, we fabricate resistive switching random access memory (ReRAM) devices constructed with a Al/$HfO_2$/ITO structure on glass substrates and investigate their memory characteristics. The hafnium oxide thin film used as a resistive switching layer is sputtered at room temperature in a sputtering system with a cooling unit. The Al/$HfO_2$/ITO device exhibits bipolar resistive switching characteristics, and the ratio of the high resistance (HRS) to low resistance states (LRS) is more than 60. In addition, the resistance ratio maintains even after $10^4$ seconds.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.66-79
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• 2008

Several oxides have recently been reported to have resistance-switching characteristics for nonvolatile memory (NVM) applications. Both binary and ternary oxides demonstrated great potential as resistive-switching memory elements. However, the switching mechanisms have not yet been clearly understood, and the uniformity and reproducibility of devices have not been sufficient for gigabit-NVM applications. The primary requirements for oxides in memory applications are scalability, fast switching speed, good memory retention, a reasonable resistive window, and constant working voltage. In this paper, we discuss several materials that are resistive-switching elements and also focus on their switching mechanisms. We evaluated non-stoichiometric polycrystalline oxides ($Nb_2O_5$, and $ZrO_x$) and subsequently the resistive switching of $Cu_xO$ and heavily Cu-doped $MoO_x$ film for their compatibility with modem transistor-process cycles. Single-crystalline Nb-doped $SrTiO_3$ (NbSTO) was also investigated, and we found a Pt/single-crystal NbSTO Schottky junction had excellent memory characteristics. Epitaxial NbSTO film was grown on an Si substrate using conducting TiN as a buffer layer to introduce single-crystal NbSTO into the CMOS process and preserve its excellent electrical characteristics.