Min Kyu Yang

Bipolar resistive switching behavior in Ti/MnO2/Pt structure for nonvolatile memory devices

This study examined the electrical properties of Ti/MnO2/Pt devices with stable and reproducible bipolar resistive switching behavior. The dependency of the memory behavior on the cell area and operating temperature suggest that the conducting mechanism in the low resistance states is due to the locally conducting filaments formed. X-ray photoelectron spectroscopy showed that nonlattice oxygen ions form at the MnO2 surface. The mechanism of resistance switching in the system examined involves the generation and recovery of oxygen vacancies with the nonlattice oxygen ions.

Influence of oxygen content on electrical properties of NiO films grown by rf reactive sputtering for resistive random-access memory applications

NiO films were prepared on Pt∕Ti∕SiO2∕Si substrates by rf reactive sputtering. The voltage-current characteristics of the Pt∕NiO∕Pt structures showed reproducible resistive switching behaviors at room temperature. The high- and low-resistance states were retained without applying an external bias voltage; the high- to low-resistance ratio was greater than 10. To investigate the influence of the oxygen content on the electrical properties, voltage-current characteristics of NiO films grown at various oxygen contents were investigated. As oxygen content increased from 5% to 10%, the resistance value of the NiO film drastically increased, and a resistive switching behavior was observed. However, as the oxygen content increased to 20%, the resistive switching behavior disappeared. The change in switching behavior was discussed in terms of Ni vacancies and compensating holes inside the NiO film. In addition, the memory properties of NiO-based resistive random-access memory were also investigated.

Resistive switching characteristics and set-voltage dependence of low-resistance state in sputter-deposited SrZrO3:Cr memory films

60-nm-thick Cr-doped SrZrO3 thin films with polycrystalline structure were fabricated on SrRuO3∕SrTiO3 (100) substrates at 450°C by off-axis radio-frequency sputtering. From room temperature current-voltage measurements of Pt∕Cr-doped SrZrO3∕SrRuO3 structures, reproducible bistable resistive switching behavior was observed. The dominant conduction mechanisms of the high-resistance state were Ohmic conduction in the low-electric-field region and Frenkel-Poole emission in the high-electric-field region, while the low-resistance state fully followed Ohmic conduction. These bulk-limited conduction mechanisms imply that resistive switching phenomena may be related to the conducting path in the SrZrO3:Cr film matrix. In addition, the initial-resistance value of as-deposited SrZrO3:Cr films was much higher than that of the high-resistance state, indicating that the first soft-breakdown behavior (defined as the resistance change from the initial-resistance state of as-deposited film to the low-resistance state) i...

Electrode Dependence of Bipolar Resistive Switching in SrZrO3:Cr Perovskite Film-Based Memory Devices

The electrode dependence of bipolar resistive switching in SrZrO 3 :Cr-based metal-oxide-metal (MOM) structures was investigated. The Pt/SrZrO 3 :Cr/SrRuO 3 structures showed bipolar resistive switching, and the polarities of external bias for set/reset processes were determined by the junction between SrZrO 3 :Cr film and SrRuO 3 electrode. The MOM structure consisting of noble metal electrodes (Pt/SrZrO 3 :Cr/Pt) did not show resistive switching, while the TiO x N y -inserted MOM structure (Pt/SrZrO 3 :Cr/TiO x N y /Pt) exhibited reproducible resistive switching behavior. The results suggest that resistive switching behaviors are related to the formation and annihilation of oxygen vacancies within local conduction paths by electric-field-induced oxygen ion migration.

Bipolar Resistive Switching Behavior of a Pt/NiO/TiN Device for Nonvolatile Memory Applications

Bipolar resistive switching behavior was observed in a Pt/NiO/TiN device. The device exhibited switching behavior that was stable over 100 cycles and did not degrade after 104 s. An electroforming process was required to obtain these bipolar resistive switching properties, and the conduction behavior of the low resistance state followed Ohms law, indicating that conductive filaments formed during the electroforming process. The conductive filaments consisted of oxygen vacancies and the Pt electrode behaved as an oxygen reservoir. The bipolar resistive switching of the Pt/NiO/TiN device was explained by the generation and annihilation of oxygen vacancies in the filaments.

Improved optical and electrical properties of rf sputtered Al doped ZnO films on polymer substrates by low-damage processesa)

Three types of low-damage radio-frequency (rf) magnetron sputtering processes—an interruptive process, a rotating cylindrical holder method, and an off-axis sputtering method—were designed and studied to reduce the film surface temperature during deposition. Low-damage sputtering processes were investigated to improve the resistivity and optical transmittance in the visible range of Al doped ZnO (AZO) thin films deposited on polymer substrates. In the case of the polyethersulfone substrate, AZO films with a resistivity of 1.0×10−3 Ω cm and an optical transmittance of 75% were obtained by the rotating repeat holder method during rf sputtering.

Low-voltage resistive switching of polycrystalline SrZrO3:Cr thin films grown on Si substrates by off-axis rf sputtering

A polycrystalline Cr-doped SrZrO3∕SrRuO3 layered structure showing a reproducible resistive switching behavior with a resistive switching voltage of ±2.5V was successfully fabricated on commercial Si (100) substrate by off-axis rf sputtering. Typical resistance values of high- and low-resistance states were about 100 and 5kΩ, respectively, so that the ratio of high- to low-resistance value is about 20. These values are appropriate for memory applications, and the resistive switching voltage of ±2.5V is the lowest value among the switching voltages of Cr-doped SrZrO3 films on Si substrates reported in recent literature. We suggest that the low-voltage resistive switching of the polycrystalline Cr-doped SrZrO3 thin film is attributed to the reduction of resputtering effects and the formation of a clean interface between the Cr-doped SrZrO3 thin film and the SrRuO3 bottom electrode layer by the use of 90° off-axis sputtering.A polycrystalline Cr-doped SrZrO3∕SrRuO3 layered structure showing a reproducible resistive switching behavior with a resistive switching voltage of ±2.5V was successfully fabricated on commercial Si (100) substrate by off-axis rf sputtering. Typical resistance values of high- and low-resistance states were about 100 and 5kΩ, respectively, so that the ratio of high- to low-resistance value is about 20. These values are appropriate for memory applications, and the resistive switching voltage of ±2.5V is the lowest value among the switching voltages of Cr-doped SrZrO3 films on Si substrates reported in recent literature. We suggest that the low-voltage resistive switching of the polycrystalline Cr-doped SrZrO3 thin film is attributed to the reduction of resputtering effects and the formation of a clean interface between the Cr-doped SrZrO3 thin film and the SrRuO3 bottom electrode layer by the use of 90° off-axis sputtering.

Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaO(x) Thin Film.

A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS.

Effects of Switching Parameters on Resistive Switching Behaviors of Polycrystalline

Polycrystalline SrZrO3:Cr-based metal-oxide-metal (MOM) structures were fabricated on Si substrates by RF sputtering for commercial memory applications. From current-voltage measurements of the MOM structures, reproducible and bistable resistive switching behaviors were observed. In this paper, the effects of switching parameters, such as set power and voltage sweep rate, on the resistive switching characteristics of SrZrO3:Cr-based MOM structures were investigated. With increasing set power (= int I(V)dV, set voltage les V les 0) during set process [resistance change from a high-resistance state to a low-resistance state (LRS)], the LRS current was increased, and the shape of the LRS curve was changed from nonlinear to linear. Also, as the voltage sweep rate was decreased from 50 to 0.5 V/s, the current level of the LRS was increased, and the resistive switching behavior was more clearly observed. The results suggest that the change in switching behaviors is attributed to the variation of local conduction paths and that resistive switching behaviors are energy dependent.

\hbox{SrZrO}_{3}

NiO films were grown on a Pt substrate by radio frequency (RF) magnetron sputtering using a NiO ceramic target. A crystalline NiO phase with the [111] preferred orientation was formed for the films grown above 100 °C. Resistance switching behavior was not observed in the NiO films annealed in the air or in ambient O2 after film deposition. However, the NiO films annealed in ambient N2 exhibited resistance switching properties. The stability of the switching voltage was considerably influenced by the oxygen to argon ratio during film growth. In particular, the NiO film grown under an 8.0 mTorr oxygen partial pressure exhibited stabilized switching voltages (Vset~1.45±0.20 V and Vreset~0.62±0.09 V). Therefore, the control of the ambient gas pressure during the growth and annealing of the NiO films was important for obtaining good resistance switching properties.