High Resistance State Conduction Research Articles

Conduction mechanism and impedance analysis of HfO[formula omitted]-based RRAM at different resistive states

Conduction mechanism and impedance analysis of both the low resistance state (LRS) and high resistance state (HRS) are performed on TiN/HfOx/Pt resistive-switching memory devices at various temperatures. The dc conduction mechanism in LRS is dictated by Ohmic conduction, whereas by trap controlled space-charge-limited current conduction in HRS. The XPS analysis results on the surface of the HfOx film indicated the presence of oxygen deficiencies. The equivalent physical model under various resistance states is established by using ac impedance spectroscopy method, that is related to oxygen vacancies in the HfOx film. We further discussed the activation energy of dc and ac in the HRS and found the conduction occurs at the grain boundary. Through analysis of different resistance states of HfOx-based resistive switching memories, the conduction mechanism correlation between time and frequency domain is established.

Resistive switching in reactive electrode-based memristor: engineering bulk defects and interface inhomogeneity through bias characteristics

A novel work on several aspects of current conduction mechanism for resistive switching (RS) of a reactive electrode-based memristor (Al/ZnO/Al) against generally used inert electrode–based devices has been illustrated. Compliance current (Icc), i.e. maximum current through device and stop voltage (Vstop), i.e. maximum Vstop upon device, has been used as bias characteristics to evaluate the effect upon conduction behavior. Effect of change in Icc for constant Vstop and vice-versa upon high resistance state (HRS) and low resistance state (LRS) has been evaluated in terms of change in bulk defects, i.e. oxygen vacancy and interface inhomogenity, i.e. AlOx formation/dissolution. The device shows unipolar resistive switching (URS) at lower Icc (< = 0.1 mA) and transits irreversibly into bipolar resistive switching (BRS) at higher Icc (> = 1 mA). The dominant conduction behavior of the device is found to be homogenous resistive switching (HoRS). The conduction in HRS and LRS is found to be space-charge limited current conduction. Conductive atomic force microscopy results of the thin film switching layer support the HoRS mechanism and also illustrate the role of interfacial oxide in attributing BRS behavior in the Al/ZnO/Al resistive switch. Studies can be utilized in future to further understand the RS conduction mechanism in reactive electrode–based RS and can be applied for multi-state memory applications.

Resistive Switching in Reduced Graphene Oxide Incorporated Polyvinyl Alcohol Films

Reduced graphene oxide (rGO) nanoparticle incorporated thin films of polyvinyl alcohol (PVA) were spin coated on ITO coated glass substrates. I-V characteristics revealed resistive switching in these films. The ON/OFF switching ratio values varied with voltage sweep cycles. The largest switching ratios obtained were 8 orders between the high resistance state (HRS) to low resistance state (LRS) and 7 orders for the LRS to HRS. In the LRS, the electrical conduction was initially space charge limited which turned to ohmic behavior that persisted till switching occurred to HRS. In the reverse voltage sweep, the conduction in HRS was initially ohmic, which then turned into a hopping type of conduction which persisted till switching occurred to the LRS. These conduction mechanisms in LRS and HRS are qualitatively different from that of pure rGO and other PVA composite films investigated earlier.

Biocompatible and Flexible Chitosan‐Based Resistive Switching Memory with Magnesium Electrodes

A flexible and transparent resistive switching memory based on a natural organic polymer for future flexible electronics is reported. The device has a coplanar structure of Mg/Ag‐doped chitosan/Mg on plastic substrate, which shows promising nonvolatile memory characteristics for flexible memory applications. It can be easily fabricated using solution processes on flexible substrates at room temperature and indicates reliable memory operations. The elucidated origin of the bipolar resistive switching behavior is attributed to trap‐related space‐charge‐limited conduction in high resistance state and filamentary conduction in low resistance state. The fabricated devices exhibit memory characteristics such as low power operation and long data retention. The proposed biocompatible memory device with transient electrodes is based on naturally abundant materials and is a promising candidate for low‐cost memory applications. Devices with natural substrates such as chitosan and rice paper are also fabricated for fully biodegradable resistive switching memory. This work provides an important step toward developing a flexible resistive switching memory with natural polymer films for application in flexible and biodegradable nanoelectronic devices.

Nonvolatile unipolar resistive switching behavior of amorphous BiFeO3 films

Amorphous BiFeO3 thin films were grown on an indium tin oxide glass substrate using RF magnetron sputtering at room temperature. The resistive switching behavior of amorphous BiFeO3 thin films was investigated. The Au/amorphous BiFeO3/indium tin oxide device exhibited the stable unipolar resistive switching behavior with a substantial resistance ratio (larger than 102) between low and high resistance states and the excellent retention performance. The low resistance state exhibited a linear Ohmic behavior, while the high resistance state conduction could be ascribed to the trap controlled space-charge limited conduction mechanism. Based on the X-ray photoelectron spectroscopy, the observed resistive switching behavior was mainly attributed to the electric field induced migration of oxygen vacancies.

Conduction Mechanisms in Resistance Switching Memory Devices Using Transparent Boron Doped Zinc Oxide Films.

In this work, metal/oxide/metal capacitors were fabricated and investigated using transparent boron doped zinc oxide (ZnO:B) films for resistance switching memory applications. The optical band gap of ZnO:B films was determined to be about 3.26 eV and the average value of transmittance of ZnO:B films was about 91% in the visible light region. Experimental results indicated that the resistance switching in the W/ZnO:B/W structure is nonpolar. The resistance ratio of high resistance state (HRS) to low resistance state (LRS) is about of the order of 105 at room temperature. According to the temperature dependence of current-voltage characteristics, the conduction mechanism in ZnO:B films is dominated by hopping conduction and Ohmic conduction in HRS and LRS, respectively. Therefore, trap spacing (1.2 nm) and trap energy levels in ZnO:B films could be obtained.

Conduction mechanism of resistive switching films in MgO memory devices

In this work, nonpolar resistance switching behavior was demonstrated in Pt/MgO/Pt structure. The resistance ratio of high resistance state (HRS) and low resistance state (LRS) is about on the order of 105 for the compliance current (Icomp) of 1 mA at 300 K. Using enough Icomp (≥0.5 mA) during SET processes, the LRS resistances reach a minimum of about 102–103 Ω and the RESET currents reach a maximum of about 10−4–10−3 A. Experimental results indicate that the conduction mechanism in MgO films is dominated by the hopping conduction and the Ohmic conduction in HRS and LRS, respectively. Therefore, the electrical parameters of trap energy level, trap spacing, Fermi level, electron mobility, and effective density of states in conduction band in MgO films were obtained.

Experimental investigation of the reliability issue of RRAM based on high resistance stateconduction

In this paper, reliability issues of robustHfOx-based RRAM are experimentally investigated in terms of cycling ageing, temperatureimpact and voltage acceleration. All reliability issues can be estimated by the conduction ofthe high resistance state (HRS). The conduction current of the HRS exponentiallyincreases as the square root of the applied voltage, which is well explained by‘quasi-Poole–Frenkel-type’ trap assistant tunneling. Further experiments on HRS conductionat different temperatures show that the depth of the potential well of the trap inHfOx film is about 0.31 eV. The degradation induced by the cycling ageing ispossibly ascribed to the increase of the amount of oxygen ions in theTiOx layer ofthe TiN/TiOx/HfOx/TiN device. The retention times with various stress voltages at different temperatures alsoexhibit an exponential relationship to the square root of the applied voltage, indicatingthat stress current plays a dominant role for the degradation of the HRS. Anoxygen-release model is proposed to explain the relationship of retention time to HRSconduction current.

Conduction behavior change in amorphous LaLuO3 dielectrics based on correlated barrier hopping theory

Unipolar switching behaviors have been revealed in amorphous LaLuO3, which makes it suited for not only logic but memory applications using the conventional semiconductor or the emerging nano/CMOS architectures. Such switching is comprehended with regard to the conduction behavior transition between high- and low-resistance states. The conduction in high-resistance state follows the Poole’s law, whereas the conduction in low-resistance state is dominated by percolation. The transition between these resistance states is attributed to the change in the separation between oxygen vacancy sites in the light of the correlated barrier hopping theory.

Temperature Dependence of Electrical Properties of NiO Thin Films for Resistive Random Access Memory

AbstractTemperature dependence of electrical properties in NiO thin films for ReRAM applications has been investigated. I-V measurements have been carried out in the temperature range from 100K to 523K. The resistance in the high resistance state (HRS) is almost independent of temperature below 250K, whereas it decreases with an activation energy of 300 meV above 250K. Hopping conduction and band conduction may be dominant in the low- and high-temperature range, respectively. Admittance spectroscopy on the NiO/n+-Si structure¡¡reveals the existence of a high density of traps, which may contribute to the conduction in HRS. In the low resistance state (LRS), however, the resistance slightly increased in the whole temperature range and the trend is similar to that of metallic Ni film, indicating the metallic Ni defects is related to the conduction in LRS. The Pt/NiO/Pt structure demonstrated stable resistance switching even at temperature as high as 250°C or higher. Since other competitive nonvolatile memories will face severe difficulty in high-temperature operation, the present ReRAM shows promise for high-temperature application.