Ti Buffer Layer Research Articles

Performance improvement of bilayer memristor based on hafnium oxide by Ti/W synergy and its synaptic behavior

Bilayer and multi-layer structures can effectively improve the performance of memristors, but the oxide/metal interface during the resistance switching process affects its reliability and stability. In this work, the Pt/HfO2/HfOx/W and Pt/HfO2/HfOx/Ti/W memristors with a homogeneous bilayer structure are compared to systematically investigate the effect of interface engineering on bilayer hafnium oxide devices by inserting Ti buffer layer to construct Ti/W composite electrode. Compared with the stimulated oxidation of the W electrode, the device under the synergy of Ti/W composite electrode showed better switching uniformity (The resistance of the high-resistance state and reset voltage variation coefficient decreased from 83.1 % to 31.9 % and from 9.5 % to 5.6 %, respectively.) and robust endurance (>104 cycles). Meanwhile, some essential synaptic behaviors such as nonlinear transmission characteristics, paired-pulse facilitation, and spike-timing-dependent plasticity were mimicked by using different pulse stimuli. Subsequently, the resistance switching mechanism of the device under the Ti/W synergy was explored by combining the results of I–V curve fitting and material analysis. These results provided important experimental guidance and a theoretical basis for further optimization of electrode interfacial effect in the future.

Study of the Long-Range Exchange Coupling in Nd-Fe-B/Ti/Fe Multilayered Structure

The exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions.

High corrosion resistance and through-plane electrical conductivity of C/Ti and C/Cr coated metal bipolar plates used in PEMFC

To improve the corrosion resistance and enhance the electrical conductivity in a simulated proton exchange membrane fuel cell, carbon bound SS316L stainless steel plates were modified with titanium (Ti) or chromium (Cr). The SS316L interfacial contact resistance of 312.38 mΩ·cm2 was reduced to 1.59 mΩ·cm2 when modified with Ti and to 1.32 mΩ·cm2 when modified with Cr. The increase in potential enhanced the shedding of C films and the oxidation and dissolution of Ti and Cr buffer layers. The corrosion current density in the C/Ti coating was lower than C/Cr coating under high voltage polarization. The oxidation of Ti and Cr buffer layers led to poor appetency between the C film and the SS316L and to degradation of the through-plane electrical conductivities in the C/Ti and C/Cr coated metal bipolar plates.

Cu2O Heterojunction Solar Cell with Photovoltaic Properties Enhanced by a Ti Buffer Layer

In this study, semiconductor oxide cuprite (Cu2O) and indium tin oxide (ITO) heterojunction solar cells with and without a 10 nm thick titanium (Ti) thin film as the buffer layer were fabricated and characterized for comparison. The Cu2O film was formed by low-cost electrodeposition, and Ti and ITO layers were deposited on a glass substrate by sputtering. The interfacial microstructures, surface topology, and electrical and photovoltaic properties of both solar cells were investigated. The test results showed that the Ti buffer layer changed the surface morphology, resistivity, and contact potential of the electrodeposited Cu2O film. With these changes, the photovoltaic performances of the Cu2O/Ti/ITO solar cell including open-circuit voltage (VOC) and short-circuit current (ISC) were all enhanced compared to the Cu2O/ITO solar cell, and the power conversion efficiency was improved from 1.78% to 2.54%. This study offers a promising method to improve the efficiency of Cu2O-based solar cells for sustainability in material resource, environment and eco-system, and energy production.

Ti/HfO2-Based RRAM with Superior Thermal Stability Based on Self-Limited TiOx

HfO2-based resistive random-access memory (RRAM) with a Ti buffer layer has been extensively studied as an emerging nonvolatile memory (eNVM) candidate because of its excellent resistive switching (RS) properties and CMOS process compatibility. However, a detailed understanding of the nature of Ti thickness-dependent RS and systematic thermal degradation research about the effect of post-metallization annealing (PMA) time on oxygen vacancy distribution and RS performance still needs to be included. Herein, the impact of Ti buffer layer thickness on the RS performance of the Al/Ti/HfO2/TiN devices is first addressed. Consequently, we have proposed a simple strategy to regulate the leakage current, forming voltage, memory window, and uniformity by varying the thickness of the Ti layer. Moreover, it is found that the device with 15 nm Ti shows the minimum cycle-to-cycle variability (CCV) and device-to-device variability (DDV), good retention (105 s at 85 °C), and superior endurance (104). In addition, thermal degradation of the Al/Ti(15 nm)/HfO2/TiN devices under different PMA times at 400 °C is carried out. It is found that the leakage current increases and the forming voltage and memory window decrease with the increase in PMA time due to the thermally activated oxidation of the Ti. However, when the PMA time increases to 30 min, the Ti can no longer capture oxygen from HfO2 due to the formation of self-limited TiOx. Therefore, the device shows superior thermal stability with a PMA time of 90 min at 400 °C and no degradation of the memory window, uniformity, endurance, or retention. This work demonstrates that the Ti/HfO2-based RRAM shows superior back-end-of-line compatibility with high thermal stability up to 400 °C for over an hour.

Effect of Ti and Au buffer layers on controlling the density and wettability of well-aligned ZnO nanorod arrays grown on different substrates.

ZnO nanorod arrays (NRAs) have potential applications as building blocks for nanoscale electronic, optoelectronic, and sensing applications. The density of ZnO NRAs is controlled by a simple low-cost hydrothermal growth process. It is shown that Ti and Au thin buffer layers can be used to control ZnO NRA density up to an order of magnitude on a wide variety of substrates including bare glass AZO, ZnO seeded AZO, FTO and ITO substrates, respectively. We investigate surface morphological, structural and optical properties of ZnO NRAs by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, and photoluminescence spectroscopy measurements, respectively. To highlight the importance of NRA density, wettability measurements show large dependence on density and static water contact angles range from as low as ∼23° to as large as ∼142°. These results indicate that the capability to control the density of ZnO NRAs, and thus their wettability, can have additional implications such as in their use in biosensors, field emission, dye-sensitized solar-cells (DSSCs), and photocatalytic activity in addition to potential light trapping effects over wide spectral ranges.

Anomalous critical supercurrent and half-integer Shapiro steps based on Josephson junction of topological insulator nanowires

Topological insulator-based Josephson junction, as a candidate device for searching for Majorana zero energy modes, has attracted much attention. One of the key issues along this direction is to fabricate Josephson junctions with high-quality interfaces, hoping to searching for 4π-period current-phase relation in topologically non-trivial Josephson junction. In this work, the Josephson junctions based on three-dimensional topological insulator nanowires Bi<sub>2</sub>Te<sub>3</sub> and Bi<sub>2</sub>(Se<sub><i>x</i></sub>Te<sub>1–<i>x</i></sub>)<sub>3</sub> are fabricated to study their superconducting proximity effects, multiple Andreev reflections, and current-phase relations. A number of interesting phenomena are observed, including the anomalous enhancement in junctions’ critical supercurrent with magnetic field, and the appearance of half-integer Shapiro steps in the ac Josephson effect. And, we discuss the possible origins of the observed anomalous behaviors in general, and their relation with the ferromagnetic layer of TiTe alloy formed at the interface between the topological insulator nanowires and the Ti buffer layer of the metallic electrodes, in particular. We provide the experimental evidence for the formation of a ferromagnetic TiTe alloy layer at the interface of our device. And, we believe that the formation of such a layer in our Josephson device breaks the time reversal symmetry, leading to the observed anomalous enhancement of the critical supercurrent with magnetic field, as well as the appearance of half-integer Shapiro steps. Our results suggest that to study the topologically non-trivial behaviors such as 4π-period current-phase relation, one still needs to improve the interface quality of the superconductor-normal metal-superconductor type of Josephson junction devices.

Disposable Wearable Sensors Based on Nanocellulose for Biomedical Applications

Monitoring of human motor and muscle activity is used in many areas, from prosthetics during rehabilitation to training monitoring of athletes. Sensors for these tasks are usually made of flexible polymers and require recycling after the expiration date. Nanocellulose (NC) can be used as a biodegradable base for this type of sensor. The development of low-cost disposable sensors that do not require disinfection and cleaning is relevant. NC is a composite nanoscale structure of cellulose fibers (fibrils) with a high aspect ratio. The paper aim is to develop disposable wearable biodegradable bend sensors based on nanocellulose using vacuum synthesis methods and the study of their characteristics. Nanocellulose was synthesized by the TEMPO method. The sensors were created by means of magnetron sputtering of Ti/Ni or Cr/Ni thin films at the surface of nanocellulose. Measuring stand was developed to determine the change in resistance due to the bending of the sensor. It’s mechanical part consists of an elastic deformation plate made of high-alloy steel, which can be bent using a micrometric screw. The change in resistance is linearly related to the elongation of the measured sample. A Wheatstone bridge and a 24-Bit ADC HX711 were used to measure the change in resistance. During testing of the sensor for analysis of muscle activity, the sensor element was attached to the human skin with the help of medical glue BF-6. The obtained sensors were tested for biodegradability. The samples were placed in the ground at a depth of 20-30 mm. The mass of nanocellulose samples was measured using a high-precision digital balance EDIS 50 (50/0.001 g) with a built-in level. The optimal ratio of the value of sensitivity and reversibility is observed in the range of the nominal resistance of the nickel film from 10 to 100 Ohms. This is due to an increase in the surface area of ​​the Ni film, which leads to an increase in sensitivity, but at the same time there is a decrease in the repeatability of the characteristics due to a greater influence of the heterogeneous structure of nanofibrillated cellulose. In addition, sensors with different buffer layer materials - Ti and Cr - were selected for testing. For titanium-based sensors, the maximum sensitivity coefficient is 0.312%, while the deviation of the sensor signal after one bending-unfolding cycle (reversibility) is less than 0.001%. Chromium-based sensors have significantly higher sensitivity (0.9753%), but worse reversibility (7.14%). Sensors based on the Cr buffer layer showed poorly reproducible results in the cyclic mode of operation, namely: there are significant fluctuations in the signal amplitude (up to 50-60%) already after the second bending-unfolding cycle. Therefore, despite the high sensitivity of such sensors, they are unsuitable for analyzing human motor and muscle activity/ The sensors based on the Ti buffer layer showed good response (2.5-3%) and good repeatability and resistance to cyclic bending (30 times). It can be seen that the obtained dependencies are approximated by a linear law. Some deviation from linearity is obviously related to the inhomogeneity of the Ni thin film. Also, the sensors showed a good loss of mass (40% in 9 weeks) during the biodegradability test, which confirms their ability to decompose under the influence of atmospheric phenomena. So, in this work, disposable wearable sensors on a nanocellulose substrate were synthesized for the evaluation of motor and muscle activity of a person. It was found that such sensors can be used to test of finger and biceps movement during at least 10-30 full flexion-extension cycles. For test of elbow movement, it is planned to synthesize a high-elastic composite material based on nanocellulose and bioelastic material (for example, polyvinyl alcohol). Thus, the proposed sensor manufacturing technology makes it possible to obtain cheap, light, flexible disposable wearable sensors that do not require further disposal after the end of operation.

Effect of buffer layer on oxidation and corrosion resistance of CrN coatings on Zr alloy prepared by FCVAD technology

To improve the oxidation resistance of fuel cladding in case of nuclear accidents, CrN coatings with different metal buffer layers (Cr, Ti, Al) were deposited on Zr 702 alloy via filtered cathode vacuum arc deposition (FCVAD) technology. The phase composition, microstructure, mechanical properties, oxidation resistance and corrosion resistance of the coatings were systematically investigated. CrN coating with Cr buffer layer showed excellent oxidation resistance at 800–1000 °C in air. Cr buffer layer effectively retarded the diffusion of oxygen and the decomposition of CrN by generating a Cr2O3 layer. CrN coating with Cr buffer layer had the lowest mass gain and the thinner oxide scale after oxidation at 800–1000 °C compare with that of Ti and Al buffer layer. The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization test revealed that Cr buffer layer effectively improved the corrosion resistance of CrN coating by generating Cr2O3 passive film. In addition, Cr/CrN coating showed excellent mechanical properties. Cr buffer layer made more contribution to the comprehensive properties of CrN coatings than Ti and Al, which illustrated utilization potentiality for the protection of fuel cladding.

Effect of buffer layer and substrate growth temperature on the microstructural evolution of hexagonal boron nitride thin films

Hexagonal boron nitride (hBN) thin films have excellent optical, electrical, and corrosion resistance properties that can enable a wide range of applications. The current study explores pulsed laser deposition technique for synthesizing hBN thin films. The microstructure, mechanical, and wetting properties of hBN thin films were analyzed as a function of substrate growth temperature (25 °C, 300 °C, 500 °C, and 800 °C) and buffer layer addition (Cu or Ti). The microstructure of hBN thin films was found to be influenced by the deposition temperature. This study revealed that the layered growth (for samples deposited at 25 °C) and layer plus island growth (for samples deposited at ≥300 °C) to be the primary growth modes of the thin films regardless of the buffer layer. The roughness of hBN thin films with the Cu buffer layer, in general, increased with the increase in deposition temperature, whereas no significant differences in roughness were observed for films deposited on Si and Ti buffer layer. Grazing Incidence X-ray diffraction results showed the presence of hexagonal close packed crystal structure for all the deposited thin films. These results were corroborated with Raman spectroscopy. The hBN thin films exhibited the hardness and modulus values of ~10–14 GPa and ~120–180 GPa, respectively. No considerable differences in mechanical properties were observed for hBN thin films deposited at various temperatures except for the films deposited with the Cu buffer layer, which showed lower mechanical properties. The wettability of hBN thin films was analyzed using contact angle measurements. The wettability was found to be directly influenced by the surface roughness of hBN thin films. Characterization of hBN thin films indicates that the deposition temperature and buffer layer addition had an influence on the growth and microstructural evolution of hBN thin films.

Electronic synaptic plasticity and analog switching characteristics in Pt/TiOx/AlOx/AlTaON/TaN multilayer RRAM for artificial synapses

In this work, electronic synaptic plasticity and analog bipolar switching behavior by using a Pt/TiOx/AlOx/AlTaON/TaN multilayer resistive random-access memory (RRAM) device were examined. By using high-resolution transmission electron microscopy (HRTEM), the oxidation–reduction reaction occurs between the Ti buffer layer and the high-k Al2O3 layer at the top interface, and the high-k Al2O3 layer and the TaN bottom electrode at the bottom interface, resulting in the formation of the Pt/TiOx/AlOx/AlTaON/TaN multilayer RRAM structure. According to X-ray photoelectron spectroscopy (XPS) studies, different proportions of oxygen vacancies in TiOx/AlOx/AlTaON multilayer film play a key role in increasing RS properties uniformity. This multilayer structure-based RRAM device exhibits a stable RS behavior with a very large on/off resistance window (∼104), excellent durability (500 DC endurance cycles), and 104 s retention period with virtuous uniformity during the cycling operation. Furthermore, the device mean value (μ) set-and reset-voltage is −2.82 V, and +1.5 V, resulting in a low-operating voltage that is beneficial for neuromorphic systems. Besides, by adjusting the reset voltage, the device achieved a progressive transition from the low resistance state (LRS) to the high resistance state (HRS). To develop the artificial neural networks, basic biological properties such as potentiation, depression, and paired-pulse facilitation were efficiently mimicked. Ohmic conduction in the LRS and Schottky emission in the HRS are the two types of current transport conduction mechanisms. The analog bipolar switching behavior is governed by the redox reaction, which promotes the formation and rupture of oxygen vacancy-based conical shape conductive filaments. These findings show that multilayer RRAM devices have the potential to be used for future information storage and neuromorphic computing of artificial synapses.

Effect of substrate roughness and material selection on the microstructure of sputtering deposited boron carbide thin films

Amorphous boron carbide (B4C) thin films are by far the most popular form for the neutron converting layers in the 10B-based neutron detectors, which are a rising trend in detector technologies in response to the increasing scarcity and price of 3He, the standard material for neutron detection. The microstructure of the B4C films is closely related to the important properties, e.g. density and adhesion, for the converting layers, which eventually affect the detection efficiency and the long-term stability of the detectors. To study the influence from substrates of different roughness and materials, the B4C films were deposited on polished Si substrates with Al, Ti, and Cu buffer layers and unpolished Si, Al, Ti, and Cu substrates by direct current magnetron sputtering at a substrate temperature of 623 K. The tapered columnar grains and nodular defects, generally observed in SEM images, indicated a strong shadowing effect where voids were introduced around the grains. The change in the grain size did not show a direct dependence to the substrate roughness, acquired from the surface profile, nor to the mass density of the films, obtained from reflectivity patterns. However, films with non-uniform size of columnar grains were deposited on substrates with high skewness, leading to a drop of mass density from ~95% down to ~70% of tabulated bulk density. On the other hand, similar microstructures and mass density were obtained from the films deposited on Al, Ti, and Cu of different roughness and good adhesion were observed from cross-cut adhesion tests, showing the reliability of sputtering deposited B4C films on common structural materials in neutron detectors.

Strain Control of Phase Transition and Exchange Bias in Flexible Heusler Alloy Thin Films.

The practical applications for the distinctive functions of metamagnetic Heusler alloys, such as magnetic shape memory effect, various caloric effects, etc., strongly depend on the phase transition temperatures. Here, flexible Heusler alloy Ni-Mn-Sn films have been deposited on mica substrates by pulsed laser deposition with a Ti buffer layer. Clear ferromagnetic (FM) transition followed by the martensitic transformation at around room temperature and exchange bias (EB) with a blocking temperature of 70 K are observed. Under the application of both tensile and compressive strains by bending the mica substrates, all the characteristic temperatures of Ni-Mn-Sn films, including the FM transition temperature, martensitic transformation temperature, and blocking temperature of EB, are significantly increased by about 10 K. Furthermore, EB field and coercivity are both strongly strengthened, which is mainly caused by the simultaneous enhancement of FM and anti-FM Mn-Mn coupling because of their shortened separations by strain and verified by the Monte Carlo simulation results. The strain controlling for structural and magnetic properties provides efficient manipulation for Heusler alloy-based magnetic devices.

Suppressed Stochastic Switching Behavior and Improved Synaptic Functions in an Atomic Switch Embedded with a 2D NbSe2 Material.

We investigated chemical vapor-deposited (CVD) two-dimensional (2D) niobium diselenide (NbSe2) material for the resistive switching and synaptic characteristics. Three different atomic switch devices with Ag/HfO2/Pt, Ag/Ti/HfO2/Pt, and Ag/NbSe2/HfO2/Pt were studied as both memory and neuromorphic devices. Both the inserted Ti and NbSe2 buffer layers effectively control the stochastic Ag-ion diffusion, leading to suppressed variation of switching characteristics, which is a critical issue in an atomic switch device. Especially, the device with the 2D NbSe2 buffer layer strikingly enhanced the device reliability in both endurance and retention. In conjunction with scanning transmission electron microscopy (STEM) and energy-dispersive spectrometry (EDS) analysis of the control of the Ag-ion migration, it was understood that filament connection is interrelated with the SET and RESET processes. Besides resistive behaviors in the memory device, various synapse functions such as spike-rate-dependent plasticity (SRDP), forgetting curve, potentiation, and depression were demonstrated with an atomic switch with the 2D NbSe2 buffer layer. Furthermore, the emulated long-term synaptic property was simulated using the MNIST 28 × 28 pixel database. Using adopting a CVD 2D NbSe2 blocking layer, the stochastic Ag-ion diffusion behavior is well-controlled and therefore stable switching and synapse functions are attained.

Low damping and small inhomogeneous linewidth broadening in [formula omitted] films

In this work we investigate structural, static and dynamics magnetic properties of Co2FeAl (CFA) films, deposited on Si (100) with Ti buffer and capping layers. We study the evolution of the coercive field, anisotropies, damping constant and linewidth broadening as a function of CFA film thickness in the range 5 nm to 200 nm. We obtain coercive fields weakly dependent on thickness, with values in the range 4.2 Oe to 7.8 Oe. All samples show roughly constant in-plane magnetic anisotropy, and out-plane anisotropy originated from the CFA/Ti interfaces. With increasing thickness we observe the emergence of rotatable anisotropy. We found magnetic damping parameters α between 2.56×10-3 and 3.45×10-3, and inhomogeneous linewidth ΔHo under 10.3 Oe for the whole range of CFA film thickness. These ΔH0 results are small when compared to the values reported for CFA in literature, specially for films with thickness above 100 nm. The present study contributes to a better understanding of the dynamic properties of magnetic CFA films, and open new potential applications in magneto-impedance sensors, RF shielding and others.

Transfer-Free, Large-Scale, High-Quality Monolayer Graphene Grown Directly onto the Ti (10 nm)-buffered Substrates at Low Temperatures

Graphene has attracted the interest of many researchers due to various its advantages such as high mobility, high transparency, and strong mechanical strength. However, large-area graphene is grown at high temperatures of about 1,000 °C and must be transferred to various substrates for various applications. As a result, transferred graphene shows many defects such as wrinkles/ripples and cracks that happen during the transfer process. In this study, we address transfer-free, large-scale, and high-quality monolayer graphene. Monolayer graphene was grown at low temperatures on Ti (10nm)-buffered Si (001) and PET substrates via plasma-assisted thermal chemical vapor deposition (PATCVD). The graphene area is small at low mTorr range of operating pressure, while 4 × 4 cm2 scale graphene is grown at high working pressures from 1.5 to 1.8 Torr. Four-inch wafer scale graphene growth is achieved at growth conditions of 1.8 Torr working pressure and 150 °C growth temperature. The monolayer graphene that is grown directly on the Ti-buffer layer reveals a transparency of 97.4 % at a wavelength of 550 nm, a carrier mobility of about 7,000 cm2/V×s, and a sheet resistance of 98 W/□. Transfer-free, large-scale, high-quality monolayer graphene can be applied to flexible and stretchable electronic devices.

Deposition and characterization of ZnO thin films on GaAs and Pt/GaAs substrates

This work reports the deposition and characterization of piezoelectric ZnO thin films on semi-insulating GaAs substrates for the fabrication of bulk acoustic waves sensors. ZnO films are deposited at 350 °C and low deposition rate using reactive radio frequency magnetron sputtering. The use of a Pt bottom electrode, between ZnO and GaAs, with and without Ti buffer layer, as well as the effect of the substrate crystallographic orientation are investigated. The characterization of the deposited films is performed to determine the optimal parameters for obtaining high-quality films and ZnO residual conductivity. ZnO films are textured along the c-axis for all GaAs cuts. The highest structural quality is obtained on (100) GaAs substrates. Moreover, the presence of the Ti buffer layer improves the texture quality, surface roughness and residual stresses. The lowest residual conductivity is determined for the ZnO/Pt/Ti/GaAs structure. However, a slight diffusion of Ga and Ti into Pt is observed, which may be of concern if Pt is used as a bottom electrode. Therefore, for thickness excitation functioning, further optimization of the Pt/GaAs interface has to be considered.

Use of a Ti Buffer Layer to Improve the Mechanical Properties of Ge2Sb2Te5 Thin Films for Phase-Change Memory

The inclusion of a Ti inter-adhesion and electrode layer is important for the integration of Ge2Sb2Te5 (GST) phase-change materials into device fabrication. The microstructure and mechanical properties of Ge2Sb2Te5 thin films with a Ti buffer layer (GST/Ti) were investigated in this work. The results showed that the Ti layer affects the microstructure of GST thin films due to the diffusion of Ti atoms into the interface of the GST/Ti stack to form Te2Ti phase. A uniform grain distribution was observed in the GST/Ti thin films. Conversely, a nonuniform distribution and “abnormal” growth of {0001}-oriented grains were observed in GST thin films without a Ti buffer layer. Furthermore, the effect of the Ti transition layer on the grain growth mode of the GST, which has a significant influence on its mechanical properties, is discussed: a smaller unbalanced stress and more uniform grain distribution are evident in GST/Ti, thus the homogeneous grain distribution of GST with the addition of a Ti layer contributes to the higher hardness and elasticity modulus values. The improved mechanical properties of such GST/Ti thin films may be a factor ensuring the robustness of phase-change memory.

Interface roughness and texture in Co/Cu multilayers with Ti buffer layer

In this study, we investigate the effect of Ti buffer layer on surface/interface roughness and texture of the Co/Cu multilayers. The Ti(0, 3nm)/[Co(5nm)/Cu(5nm)]5 multilayers were deposited by direct current magnetron sputtering. Experimental results show that the rough interfaces and coarse three-dimensional island structure present in Co/Cu multilayers, while the interface roughness decreases and smooth surface emerges in Ti/Co/Cu multilayers. Simulaneously, the sharp {111} fiber texture exists in Ti/Co/Cu multilayers, while the Co/Cu multilayers reveal a weak texture. Compared with the Co/Cu multilayers, inserting Ti buffer layer could decrease the interface energy and increase the wettability. In addition, the {111} fiber texture in FCC metal films corresponds to the most densely packed plane and the minimizing surface energy. Accompanied by the process of film nucleation, it could be concluded that the degree of interface roughness is related to the texture intensity in Co/Cu multilayers. The analyses of magnetic properties suggestes that the higher magnetic properties of Ti/Co/Cu multilayers are caused by the smooth interface and sharp {111} fiber texture.

Switching Kinetics Control of W‐Based ReRAM Cells in Transient Operation by Interface Engineering

AbstractTungsten (W) is one of the most promising materials to be used in resistive random‐access memory electrodes due to its low work function and compatibility with semiconductors, which raises the possibility of device integration, scalability, and low power consumption. However, W has multiple oxidation states that affect device reliability, due to the formation of semistable oxides at the switching interface. W chemical interaction is modulated through the insertion of Al2O3 or Ti interfacial layers. The time‐dependent switching kinetics are investigated in transient Set/Reset operations. It is observed that a compact and stoichiometric atomic‐layer‐deposited Al2O3 barrier layer completely prevents W oxidation, resulting in a sharp current transient. The use of a sputtered Ti buffer layer allows a partial W oxidation, defining a tunable high‐resistance state by pulse rise time control. Notable improvements in endurance, power consumption, resistance state stabilization, and cycle‐to‐cycle and device‐to‐device variability are reported. Switching kinetics and conductive nanofilament evolution are studied in detail to understand the microscopic effect of the interface modifications. The tunability of multi‐HRS states by pulse timing control in Pt/HfO2/Ti/W is in the interest of network and brain‐inspired computing applications, adding a degree of freedom in the modulation of its resistance.