Conduction In Low Resistance State Research Articles

Impact of Stack Engineering on HfOₓ/Al:HfOₓ-Based Flexible Resistive Memory Devices and Its Synaptic Characteristics

The effect of stack engineering of HfO_x/ Al-doped HfO_x(Al:HfO_x)-based flexible resistive random access memory (ReRAM) devices including its synaptic characteristic has been investigated. The flexible Al/HfO_x/Al:HfO_x/HfO_x/ITO/PET resistive memory device shows outstanding switching performance in terms of repeatability, statistical variation of parameters even in bending condition up to 5 mm. The switching mechanism has been explained by ohmic conduction in low resistance state (LRS) and the trap-controlled space charge limited conduction (SCLC) in high resistance state (HRS). The improved synaptic characteristics, such as long-term potentiation (LTP), long-term depression (LTD), spike-rate-dependent plasticity (SRDP), paired-pulse facilitation (PPF), and post-tetanic potentiation (PTP), are effectively mimicked with Al/HfO_x/Al:HfO_x/ITO/PET ReRAM, which is suitable for neuromorphic computing application.

Functional bipolar resistive switching in AlN/Ni–Mn–In based magnetoelectric heterostructure

This report explores the influence of temperature on resistive switching characteristics in the AlN/Ni–Mn–In magnetoelectric (ME) heterostructure-based resistive random access memory (ReRAM) device. The fabricated Cu/AlN/Ni–Mn–In/Si device exhibits a sharp transition from a high resistance state (HRS) to low resistance state (LRS) at a SET voltage. The rupture of the filament from its weakest point at a RESET voltage turn the device back to its HRS. The stable bipolar resistive switching behavior is described by the current–voltage (I–V) characteristic. The HRS and LRS are explained by the trap-controlled space charge limited conduction mechanism and a well-known Ohmic conduction mechanism, respectively. The temperature-dependent resistance has been observed to further confirm the conduction mechanism in HRS and LRS. The current conduction in LRS is explained by an analytical model based on copper metallic filament formation via Cu+ migration from the top to the bottom electrode. A significant change in the SET voltage has been observed with the decrease in temperature. This variation in the SET voltage is explained via strain-mediated coupling in interfacially connected AlN/Ni–Mn–In ME heterostructure. The fabricated device displays an appreciable OFF/ON ratio of the order ∼3 × 103 with good endurance and retention of ∼1000 cycles and ∼900 s, respectively. A slight variation (<40%) in SET and RESET voltages has been observed for total endurance cycles. This study demonstrates the importance of ME heterostructure for futuristic tuneable ReRAM applications.

Improved resistive switching performance of graphene oxide-based flexible ReRAM with HfOx buffer layer

Flexible electronic devices have generated large research interest in recent years. Herein, we demonstrate a resistive random access memory (ReRAM) device fabricated on a flexible polyethylene terepthalate (PET) substrate using a bilayer of graphene oxide (GO) and HfOx films. The physical properties of GO and HfOx were characterized by a number of techniques such as X-ray diffraction (XRD), UV–Visible absorption spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The GO/HfOx-bilayered ReRAM devices exhibited good switching behavior at low SET/RESET voltages and showed improved cell-to-cell uniformity of switching parameters compared to the devices without HfOx layer, due to the oxygen vacancies within the HfOx film as confirmed by XPS. The switching mechanism was explained by the formation/rupture of the conductive filament through the migration-induced oxidation/reduction reaction of the oxygen vacancies at the interface of GO/HfOx. From the I–V curve fitting, the conduction in low resistance state (LRS) was found to be governed by the Ohmic mechanism and the trap-controlled space charge limited current (SCLC) in high resistance state (HRS) was observed for both the cycles.

Effect of Aluminum Doping on Performance of HfOₓ-Based Flexible Resistive Memory Devices

The Al-doped HfO x -based resistive memory devices have been fabricated on indium tin oxide (ITO)-coated polyethylene terephthalate (PET) flexible substrate at room temperature. X-ray photoelectron spectroscopy is used to extract the different doping percentage of Al which allows optimizing the switching performance. It improves the cycle-to-cycle and cell-to-cell uniformity of switching parameters by tuning the oxygen vacancies in HfO x layers. The 7.5% Al-doped HfO x -based flexible resistive memory device shows excellent switching characteristics such as resistance ratio ( $> 10^{3}$ ) and retention ( $\sim 10^{4}$ s). There is no degradation of memory window under the mechanical strain with bending radius ranging from 25 to 5 mm. The temperature-dependent resistive switching characteristics have also been studied. There is sufficient memory window ( $> 10^{2}$ ) till $\sim 10^{4}$ s at elevated temperature. The ${I}$ – ${V}$ curve fitting shows the ohmic (hopping) conduction in low resistance state (LRS) and the trap-controlled space charge limited conduction (SCLC) in high resistance state (HRS), supported by Arrhenius plot.

Effect of Mg content in Ag/Zn1-XMgXO/Cu structure for bipolar resistive switching performances

In this study, the bipolar resistive switching behavior of Pulsed Laser Deposited Zn1-xMgxO (x= 0, 0.1) thin films in Ag/Zn1-XMgxO/Cu structure has been investigated. The XRD pattern of Zn1-XMgxO exhibits the presence of (002) and (103) reflection. The cross-sectional field emission scanning electron microscopy (FE-SEM) studies were further carried out to examine the thickness of the film. In order to analyze the bipolar resistive switching behavior of the Zn1-xMgxO thin films, an I-V measurement was performed at room temperature. The memory cell Ag/Zn0.9Mg0.1O/Cu exhibits set voltage (ON state) at 2.57V and reset voltage (OFF state) at -3.15 V, excellent OFF to ON resistance ratio (~10 5 ) for 200 DC sweep cycles and exhibits good retention (>10 3 s). The physical mechanism responsible for exhibiting switching behavior in the Zn1-xMgxO thin films was explained by formation and rupture of the nano-scale conduction filament due to Oxygen vacancies. Ohmic conduction and Poole-Frenkel emission are responsible for current conduction in Low Resistance State (LRS) and High Resistance State (HRS) regions respectively. Enhanced switching behavior is observed by substitution of Mg in ZnO thin film. Nonvolatile two resistance states of the Zn1-XMgxO thin film could prove useful in future power efficient memory devices.

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.

Multilevel resistive switching effect in sillenite structure Bi12TiO20 thin films

Multilevel resistive switching effect has been demonstrated in Pt/Bi12TiO20/Pt structures, in which the sillenite structure Bi12TiO20 thin films were prepared by a chemical solution deposition method. The non-volatile multilevel resistive switching can be easily realized by changing either the compliance current during set process or reset voltage during reset process. The Pt/Bi12TiO20/Pt devices show excellent switching parameters such as reproducible switching effect, low set/reset voltage, high cell yield, good endurance, and long retention time (up to 104 s). The dominated conduction mechanisms were Ohmic conduction in low resistance state (LRS) and lower voltage region of high resistance state (HRS), and Schottky emission in higher voltage region of HRS. In the reset process, the switching from LRS to HRS consists of two parts: an abrupt transition due to thermal effect and a gradual transition owing to electric field-induced migration of oxygen vacancies. On the basis of the measurements of the resistance-temperature dependence in different resistance states and analysis of current-voltage characteristics, we explained the resistive switching behavior using a conductive filament-related model.

Resistive Switching and Current Conduction Mechanisms in Amorphous LaLuO3 Thin Films Grown by Pulsed Laser Deposition

The unipolar resistive switching characteristics of the amorphous LaLuO3 thin films deposited by pulsed laser deposition have been studied. Reliable and repeatable nonvolatile switching of the resistance of LaLuO3 films was obtained between two well defined states of low and high resistance with nearly constant resistance ratio ∼107 and non-overlapping switching voltages in the range of 0.66-0.83 V and 1.9-2.7 V respectively. The temperature dependent measurement revealed metallic and semiconducting behavior in low and high resistance states respectively. The switching between low and high resistance states was attributed to the change in the separation between oxygen vacancies in light of the correlated barrier hopping theory. The current conduction mechanism of the device in high-resistance state followed the Poole's law, whereas the conduction in low-resistance state was found to be dominated by percolation. The resistance of low and high resistance states of the film showed no obvious degradation for up to ∼104 seconds indicating good retention. The achieved characteristics of the resistive switching in LaLuO3 thin films seem to be promising for futuristic nonvolatile memory applications.

An Empirical Model for RRAM Resistance in Low- and High-Resistance States

We present a simple empirical expression describing hafnium-based RRAM resistance at different reset voltages and current compliances. The model that we propose describes filament resistance measured at low ( ~ 0.1 V) reading voltage in both low-resistance state (LRS) and high-resistance state (HRS). The proposed description confirms that conduction in LRS is ohmic (after forming with a sufficiently high current compliance) and is consistent with the earlier description of HRS resistance as controlled by a trap-assisted electron transfer via traps in the oxidized portion of the filament. The length of the nonohmic part of the filament is found to be directly proportional to reset voltage. Moreover, low-frequency noise measurements at different reset voltages evidence a tradeoff between HRS resistance and noise in reading conditions.

Bipolar resistive switching characteristics of Al-doped zinc tin oxide for nonvolatile memory applications

Resistive random access memory using Al-doped zinc tin oxide (AZTO) as resistive switching layer was prepared by radio-frequency magnetron sputtering at room temperature. The Ti/AZTO/Pt device exhibits reversible and robust bi-stable resistance switching behavior over hundreds of switching cycles within 2 V sweep voltage. The Ti/AZTO/Pt device showed stable retention characteristics for over 104 s under read disturb stress condition. Besides, the electrical conduction mechanism was dominated by ohmic conduction in low resistance state, while the current transport behavior followed a trap-controlled space-charge-limited conduction process in high resistance state.

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.