TiN Layer Research Articles

Corrosion and wear behavior of TiN PVD coated 304 stainless-steel

Ti/TiN multilayered physical vapor deposition (PVD) coatings were deposited on stainless-steel by cathodic arc deposition method. Bare sample of stainless steel 304 was compared with monolithic TiN coating and TiN coating having 2, 4, 6 and 8 Ti interlayers. The properties like corrosion and wear resistance were studied and analyzed comparatively. Potentiodynamic polarization curves showed that highest corrosion resistance was indicated by TiN coating with 8 Ti interlayers. Sample having 8 Ti interlayers have high corrosion potential (Ecorr) and low corrosion current density (Icorr) as compared to other samples. This may be attributed to the arrangement of interlayers that prevents the corrosive agents to penetrate surface. All multi-layered coatings show better results than the substrate material. Pin on disk wear test revealed that coating having monolithic TiN layer have the lowest coefficient of friction and consequently have less wear volume and wear rate as compared to other coatings with Ti interlayers. These results made the investigated coated stainless steel 304 valuable for wide range of industrial applications that required wear and corrosion resistance.

The influence of near service environmental conditions on the corrosion and LCF behaviour of a beta-stabilized γ-TiAl alloy

The damage behaviour of the TiAl alloy Ti-43.5Al-4Nb-1Mo-0.1B was investigated by isothermal thermogravimetric-analysis (TGA) and strain controlled low-cycle-fatigue (LCF) experiments at high temperature. Aluminium depletion and the formation of a continuous brittle layer in the subsurface zone takes place in synthetic exhaust gas. Contrary, a continuous ductile γ-phase forms in the subsurface zone in air. Since a continuous TiN layer as diffusion barrier is not formed in the early stages of corrosion, strong hardening is observed in LCF test samples in exhaust gas and a strain amplitude of 0,6 %, leading to a significant reduction of the cycles to failure.

Effect of nitriding conditions of Ti6Al7Nb on microstructure of TiN surface layer

Presented experiments were aimed at comparing microstructure of the TiN layer produced on Ti6Al7Nb alloy being gas nitrided (GN) or glow discharge nitrided with either active screen (GD-ASN) or at cathode potential (GD-CPN). They were treated at 620 °C, 680 °C, 740 °C and 830 °C for 6 h. The transmission electron microscopy investigations showed that thickness of the TiN layer depends less on average temperature of nitrided piece, but more on temperature of its surface, being the highest for the GD-CPN process. The growth of TiN layer during the GN treatment proceeds mainly towards the core and to a lesser extent at the surface. The former process is controlled by chemisorption and inward diffusion of nitrogen atoms, while the latter by outward diffusion of titanium. The factor controlling the growth of TiN during the GD-ASN treatment is exclusively the flux of the titanium atoms sputtered from the active screen. The thickness of the TiN layer produced during the GD-CPN process in the temperature range between 680 °C and 830 °C is controlled in the same way as during the GN, except the fact that bombardment of the processed material with nitrogen ions strongly raises the surface temperature.

Multilayered conductive films of semiconductor devices and integrated circuits

The stress-migration phenomenon in films of alloy Al–Si which is observed at a current of high density (an order 105 А/mm2) is investigated. By results of researches the technical decision which allows quality raise of obtained film structures is offered. Its essence consists in formation in films the traps for migrating atoms of aluminium at course of a current of high density at the expense of formation the passive layer of TiN on the metal layer surface, for example, Al–1,5 %Si. In the presence of advanced relief of a surface of modern integrated circuits, for example with sub-micron sizes of the topology elements, the thickness and structure of metal current-carrying films on relief steps differs from what are located on planar sites. It leads to occurrence of essential gradients of mechanical pressure which are stress-migration motive power. As it is known, that temperature factor of linear expansion of aluminium is approximately 20 times, than SiO2, that causes active generation of dot defects in a layer of the alloy on the base of aluminium which is much more plastic than SiO2. Under the influence of a gradient of residual pressure, dot defects, existed in films, for example vacancies, come to movement mainly on border of metal - dielectric and in due course under the influence of a current of high density lead to formation of group defects in an alloy film, in particular emptiness, hills etc. Since stress-migration processes on these sites occur most intensively, as a result there is a rupture of films mainly on steps of a topological relief. Results of the research have passed approbation and can be used at manufacturing of silicon semi-conductor devices and integrated microcircuits.

Reusable TiN Substrate for Surface Plasmon Resonance Heterodyne Phase Interrogation Sensor.

A TiN-based substrate with high reusability presented high-sensitivity refractive index measurements in a home-built surface plasmon resonance (SPR) heterodyne phase interrogation system. TiN layers with and without additional inclined-deposited TiN (i-TiN) layers on glass substrates reached high bulk charge carrier densities of 1.28 × 1022 and 1.91 × 1022 cm−3, respectively. The additional 1.4 nm i-TiN layer of the nanorod array presented a detection limit of 6.1 × 10−7 RIU and was higher than that of the 46 nm TiN layer at 1.2 × 10−6 RIU when measuring the refractive index of a glucose solution. Furthermore, the long-term durability of the TiN-based substrate demonstrated by multiple processing experiments presented a high potential for various practical sensing applications.

Release behavior of metals from tin-lined copper cookware into food simulants during cooking and cold storage.

The copper pots with an inner coating layer of tin have been remarkably used in many countries for a long time. In this study, leaching of some metals from tin-lined copper pots into food simulators at different pHs (4, 5.5, 7, and 8.5) during boiling processing (95 °C for 1, 2, and 3 h) or refrigerated storage (4 °C for 1, 2, and 3 days) was investigated. Citric acid and sodium hydroxide were used to adjust the pH of food simulators. The leaching concentrations of metals were analyzed by inductively coupled plasma optical emission spectrometers (ICP-OES). Scanning electron microscopy (SEM) was used to indicate the surface morphological properties of cookware. Based on the preliminary experiments, metals including Al, Sn, Cu, Mn, Fe, Ca, Na, Cr, Mg, and Zn were selected to analyze in acidic treatments. Furthermore, Al, Cu, Sn, Na, and Ca were analyzed for neutral and alkaline ones. Results showed that the boiling temperature for 3 h resulted in a much higher migration of metals compared with cold storage for 3 days. Mn and Cr showed the lowest metal concentration during cooking and cold storage, respectively. The concentration of Sn in acidic simulators was remarkably higher than the other metals during both cooking and refrigerated storage. However, Ca during cold storage, as well as Na during both cooking and cold storage, showed the most migration in alkaline solutions, among the other pHs. An acidic simulator with pH 4 showed the most considerable release of metals from copper pots. SEM results indicated more intense surface corrosion by acidic solution (pH 4) than alkaline one. In general, longer cooking and cold storage durations led to increasing metals release. The migration of the studied metals demonstrates the impurities of the tin layer of these cookwares that may lead to acute and/or chronic diseases.

Fabrication of high-photoresponsivity BaSi2 films formed on conductive layers by radio-frequency sputtering

We fabricated randomly oriented polycrystalline BaSi2 films on TiN metal layers by sputtering for the deployment of BaSi2 solar cells on a flexible substrate. The formation of BaSi2 films was demonstrated by X-ray diffraction and Raman spectroscopy. Photoresponsivity increased at wavelengths <1000 nm, corresponding to the band gap of BaSi2, and reached 1.6 A W−1 at a wavelength of 650 nm under a bias voltage of 0.5 V applied to the front ITO electrode with respect to the TiN layers. This value is equivalent to the highest value ever achieved for undoped BaSi2 epitaxial films grown by MBE.

Experimental Study on Tool Wear and Delamination in Milling CFRPs with TiAlN- and TiN-Coated Tools

Carbon fiber-reinforced polymers (CFRPs) have very good mechanical properties, such as extremely high tensile strength/weight ratios, tensile modulus/weight ratios, and high strengths. CFRP composites need to be machined with a suitable cutting tool; otherwise, the machining quality may be reduced, and failures often occur. However, as a result of the high hardness and low thermal conductivity of CFRPs, the cutting tools used in the milling process of these materials complete their lifetime in a short cycle, due to especially abrasive wear and related failure mechanisms. As a result of tool wear, some problems, such as delamination, fiber breakage, uncut fiber and thermal damage, emerge in CFRP composite under working conditions. As one of the main failure mechanisms emerging in the milling of CFRPs, delamination is primarily affected by the cutting tool material and geometry, machining parameters, and the dynamic loads arising during the machining process. Dynamic loads can lead to the breakage and/or wear of cutting tools in the milling of difficult-to-machine CFRPs. The present research was carried out to understand the influence of different machining parameters on tool abrasion, and the work piece damage mechanisms during CFRP milling are experimentally investigated. For this purpose, cutting tests were carried out using a (Physical Vapor Deposition) PVD-coated single layer TiAlN and TiN carbide tool, and the abrasion behavior of the coated tool was investigated under dry machining. To understand the wear process, scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) was used. As a result of the experiments, it was determined that the hard and abrasive structure of the carbon fibers caused flank wear on TiAlN- and TiN-coated cutting tools. The best machining parameters in terms of the delamination damage of the CFRP composite were obtained at high cutting speeds and low feed rates. It was found that the higher wear values were observed at the TiAlN-coated tool, at the feed rate of 0.05 mm/tooth.

Deformation behavior of a novel sandwich-like TiNb/NiTi composite with good biocompatibility and superelasticity

In this study, a novel sandwich-like TiNb/NiTi superelastic composite was designed and fabricated to achieve a combination of good biocompatibility and superelasticity. Experimental results revealed that the good biocompatibility of the TiNb/NiTi composite was attributed to the outer non-cytotoxic TiNb layer insulating the direct contact between the inner NiTi layer and cells, and the excellent superelasticity of the composite was mainly ascribed to two different kinds of fully reversible stress-induced martensitic (SIM) transformations, involving B2↔B19′ and β↔α″ transformations. Based on the in situ high-energy synchrotron X-ray diffraction (SXRD) technique, the deformation mechanism of TiNb/NiTi composite, involving the elastic elongation and recovery of B2, β, B19′, and α″ phases, reversible B2↔B19′ and β↔α″ SIM transformations, was clearly clarified. These results could shed some light on the design and development of novel superelastic composites for biomedical applications.

Growth mechanism of MnS/Fe on TiN surface: First principle investigation

It is an important way for TiN inclusions to play the role of oxide metallurgy to induce inclusions or ferrite heterogeneous nucleation, while MnS and Fe precipitate on TiN are two typical growth modes. Understanding the formation process of TiN–MnS/Fe composite interface is extremely important for the control of TiN containing composite inclusions in steel and the effectiveness of catalyst. Based on the thermodynamic characteristics of TiN induced precipitation of MnS and Fe in steel, the bond structure, charge and energy of TiN crystal structure, TiN (111) N terminal surface structure and TiN–MnS/Fe interface structure are calculated by the first principle method. The growth mechanism of MnS/Fe on TiN surface at atomic scale is analyzed. The results show that TiN is a semi-metallic crystal with a band gap of 3.0 eV; Mn and Fe atoms will be adsorbed on the TiN (111) N terminal surface in the form of face-center cubic (FCC) stacking; MnS and Fe will grow on the TiN surface to form an interface system, and the influence distances of TiN template effect are 12.587 Å and 10.588 Å, respectively. The growth part (MnS and Fe) affected by TiN can be divided into two layers: coherent epitaxial layer (CEL) and transition layer (TL), in which the CEL and TL of TiN–MnS interface are both four layers, while the two and four layers of TiN–Fe interface.

Interdiffusion behaviors observation in TiN/ZrOxNy bilayer by XAS and ToF-SIMS

Interface behavior plays an important role in multilayer structure. The deep understanding of interface diffusion and reaction is necessary to improve the performance of device with multilayer structure. In the present work, we perform a detailed systematic study on interdiffusion and interaction between the TiN and ZrOxNy layers in the TiN/ZrOxNy bilayer system. A series of TiN/ZrOxNy bilayers with reverse deposition orders or with varied composition have been prepared by radio-frequency reactive magnetron sputtering. Synchrotron radiation x-ray absorption spectroscopy (XAS) and time of flight secondary ion mass spectrometry (ToF-SIMS) are both used to understand well interface diffusion behavior. The XAS results indicate that interaction and interdiffusion extent between TiN and ZrO2 (ZrOxNy) layers depend on deposition order of both layer. Herein the O atoms enter easily into the TiN layer by substituting the N atoms when the ZrO2 or ZrOxNy layer is deposited onto the TiN layer. No significant interaction between TiN and ZrN layers takes place in the TiN/ZrN sample. Both XAS results and ToF-SIMS depth profiles reveal that the interaction between TiN and ZrOxNy layers depends on the deposition order of the layers.

Mechanisms of TiN Effective Workfunction Tuning at Interfaces with HfO2 and SiO2

By use of a combination of electrical measurements and internal photoemission interface barrier characterization, the effective workfunction (EWF) changes of nm-thin TiN layer deposited on top of o...

Selective Lithium Deposition on 3D Porous Heterogeneous Lithiophilic Skeleton for Ultrastable Lithium Metal Anodes

AbstractLithium (Li) metal batteries (LMBs) have been deemed as the next promising high‐energy battery systems for ultrahigh energy densities. However, serious Li dendrites and low Coulombic efficiency issues still impede the practical application of LMBs. Herein, a common three‐dimensional (3D) copper foam partially decorated by a thin lithiophilic tin (Sn) layer (CF@Sn) has been constructed as the current collector of a Li metal anode. The large Li ions prefer to be induced by a Sn layer to produce Li−Sn alloy and selectively deposit on the alloy layers of the composite matrix. Due to the excellent confinement of the growth of metallic Li, the 3D porous heterogeneous lithiophilic skeleton can effectively improve uniform Li deposition, inhibit Li dendrite formation, reduce electrolyte consumption and enhance the electrochemical performance. The composite matrix leads to a high Coulombic efficiency (98.5%) over 400 cycles and ultrastable Li charging/discharging behavior for 1000 h for the symmetric cell at 1 mA cm−2. For the low energy barrier of alloy layer, small potential polarization (20 mV in symmetric cell) and nucleation overpotential (10.5 mV) can be obtained as expected. Especially, full cells paired with LiFePO4 cathodes and CF@Sn@Li anodes deliver an enhanced rate capability and a great discharging capacity of 140 mAh g−1 with high capacity retention of 95.2% after 300 cycles at 0.5 C. The proposed 3D lithiophilic skeleton demonstrates an effective strategy to realize stable and practical Li metal anodes.

Investigation on the performance of SnS solar cells grown by sputtering and effusion cell evaporation

SnS is an earth-abundant, non-toxic, and low-cost absorber material for solar cell applications. In this work, the physical properties of SnS thin films and efficiency of SnS solar cells were investigated for different tin metal layer thicknesses of 300 nm (Sn-300), 500 nm (Sn-500), and 700 nm (Sn-700) deposited by DC sputtering followed by the sulfurization using effusion cell evaporation method. The XRD and Raman characterizations confirmed the formation of single-phase SnS compound with orthorhombic structure for the case of Sn-500. The sulfurized films of Sn-500 had remarkable and homogeneous morphology with the optical band gap energy of 1.35 eV. The fabricated device showed an efficiency of 0.74% with an open-circuit voltage of 267mV, short circuit current density of 8.47 mA/cm2, and fill factor of 54.16. By varying the different metal tin layer thicknesses, this is the first report with device efficiency for SnS solar cells grown via effusion cell evaporation technique.

Efficient and stable tin perovskite solar cells enabled by amorphous-polycrystalline structure

Tin perovskite solar cells (TPSCs) have triggered intensive research as a promising candidate for lead-free perovskite solar cells. However, it is still challenging to obtain efficient and stable TPSCs because of the low defects formation energy and the oxidation of bivalent tin; Here, we report a TPSC with a stable amorphous-polycrystalline structure, which is composed of a tin triple-halide amorphous layer and cesium-formamidinium tin iodide polycrystals. This structure effectively blocks the outside oxygen, moisture and also suppresses the ion diffusion inside the devices. In addition, its energy level benefits the charge extraction and transport in TPSCs. This design enabled us to obtain the certified quasi-steady-state efficiency over 10% for TPSCs from an accredited certification institute. The cell was stable, maintaining 95% of the initial PCE after operation at the maximum power point under AM 1.5 G simulated solar light (100 mWcm−2) for 1000 hours.

Demonstration of an Equivalent Material Approach for the Strain-Induced Reliability Estimation of Stacked-Chip Packaging

A huge shift in classical system integration composed of heterogeneous and homogeneous substances from 2D to 2.5D or even 3D assembly is a promising solution to satisfying the requirements of electronic packages, such as high operating speed, multifunctionality, and low form factor, under the physical limits of nanoscaled transistors and bottlenecks in related fabrication technologies. However, considerable dimension mismatch is introduced into the entire packaging by numerous microbumps ( ${\mu }$ -bumps) with complicated compositions in existing frameworks. In addition, failure location and precise reliability estimation are difficult to achieve when the layout of high-density ${\mu }$ -bump arrays is considered. To solve this urgent issue, an equivalent material characteristic methodology for ${\mu }$ -bump arrays based on finite element analysis (FEA) is developed in this study. A test vehicle for chip-on-chip packaging with wafer-level underfill is set up to obtain the mechanical characteristics of equivalent materials for the portion with internal ${\mu }$ -bump arrays. The equivalent plastic strain generation of the tin layer is simulated by systematically comparing the numerical convergence of FEA under the assumption that the lead-free solder forms ${\mu }$ -bumps within after the assembly process. Analytic results indicate that at least four rows of actual ${\mu }$ -bumps from the outermost edge of the ${\mu }$ -bump array are required to ensure numerical accuracy in contrast with the result obtained from the actual model of the present packaging structure.

The Surface Morphology of a Ti–6Al–4V Fiber-Lasered Nitride Layer

A fiber laser was used to nitride Ti–6Al–4V titanium alloy the effect of the process parameters on the surface morphology was studied. The surface chemical composition of the nitride layer and the phase of black powder on the surface were analyzed, the two-dimensional and three-dimensional surface topography of the nitride layer surface were measured, and the cross-section microstructure of the nitride layer was photographed. The effects of laser power, laser scanning speed, nozzle distance, and nitrogen flow rate on the surface morphology were studied. The experiments show that the laser power mainly affects the surface oxidation, the laser scanning speed mainly affects the surface roughness, and the nozzle distance has a great influence on the surface morphology. The gas flow rate, however, had a slight effect on the surface morphology. A large heat input and a high nitrogen flow rate caused an increase in TiN and TiO2 black powders. Surface oxidation did not affect the formation of a continuous TiN layer nor surface roughness. Finally, the critical energy density leading to increased surface roughness was calculated.

Enhancing biocompatibility of NiTi shape memory alloys by simple NH3 treatments

This paper presents the treatment of NiTi shape memory alloys (SMAs) in flowing ammonia at 700 °C as a simple and cost-effective nitriding process to provide a protective surface layer hindering Ni ion release in biological environments. Experimental results demonstrated that a smooth protective TiN layer on the NiTi SMAs along with TiOxNy and TiO2 formed on the surface upon treating the as-received NiTi SMA in ammonia at 700 °C. The protective TiN layer and the smooth surface hinder the amount of Ni ion release to artificial saliva (AS) after 28 days of immersion, while the dry air treatment at similar conditions results in a significantly rough surface, leading to about 20 times higher Ni ion release. Overall, the findings presented herein demonstrate that NH3 nitriding is an effective method to eliminate the Ni presence from the surface and to obtain a smooth final surface, which, in turn, restricts the Ni ion release from the NiTi SMA into AS. Consequently, nitriding the surface of NiTi under NH3 at 700 °C turned out as a promising method to lower Ni ion release and thereby contribute to the biocompatibility of NiTi SMAs, which, however; needs to be further validated through further experimentation.

An Extended-Gate Ion-Sensitive Field-Effect Transistor with CMOS Technology-Intrinsic TiN Sensing Layer

The extended-gate ion-sensitive field-effect transistor (EGISFET) has promising potentials in chemical and biological sensing due to flexibility for array arrangement, less light-sensitivity, and compatibility with CMOS standard fabrication process [1-2]. An EGISFET is consisted of a MOSFET and a floating-gate structure separated from analyte solutions by a sensing layer. Because charges adjacent to the sensing layer change the floating-gate potential, the channel current of the EGISFET can be modulated through the electrical field effect. In a general CMOS process, the EGISFET can be achieved by using metal/VIA/polysilicon layers as the extended gate material and the passivation nitride layer on top of the metal as the sensing layer. For the EGISFET operation, a solution gate voltage is provided in the analyte solution and a capacitive voltage divider can be obtained based on a series connection of the electrical double layer capacitance (CEDL), the sensing layer capacitance (CS) and the gate oxide capacitance (COX). Due to the capacitive coupling nature, a higher CS/(CS+COX) ratio can have a larger part of solution gate voltage transferred to COX, and thus can have a higher EGISFET transconductance [3], which promises a better sensing response, e.g. channel-current change for a given charge change. However, CS is decreasing because of scaling down for realizing high spatial resolution sensing array. Then EGISFETs become less sensitive due to a weaker capacitive coupling.In order to ameliorate this scaling effect, we developed a TiN-EGISFET based on a CMOS 0.35 μm standard fabrication process. Instead of using the 1-2 μm thick passivation/intermediate dielectric layer as the sensing layer, we took advantage of an intrinsic extra-thin TiN layer within the VIA structure as the sensing layer. To expose the TiN layer, the metal/VIA layout was placed in a special manner to form a hanging micro-structure after a one-step wet etching. Followed by sonication, the micro-structure was broken at a mechanical weak point, e.g. the metal/VIA interface, and the ultra-thin TiN was successfully exposed. To have a control group, a traditional EGISFET was also implemented on the same chip. In the EGISFET measurement, a Ag/AgCl electrode was used to provide solution gate voltage, and the electric characteristic curve for each device was measured in pH solutions with different values.Compared to the traditional EGISFET occupying the same chip area, transconductance for the TiN-exposed EGISFET was improved up to 240%. This enhancement is possibly attributed to the conductivity and chemical stability of TiN, which make CS in the TiN-exposed region disappeared, only left CEDL and COX in series. As a result, a larger portion of solution gate voltage is dropped across COX because CEDL>>COX. Furthermore, the pH sensitivity of TiN-exposed EGISFET reaches 51 mV/pH without obvious hysteresis and drift (Figure 1). This is also supported by the previous literatures [4-5]. At 0.5V overdrive voltage, the current variation of TiN-exposed EGISFET is -9.12 mA/pH, which is 275% as high as that of the traditional EGISFET (Figure 2). These results suggest that a TiN-exposed EGISFET with a smaller footprint can possess the same sensitivity of a traditional EGISFET with a larger footprint.In conclusion, we developed a method to fabricate EGISFETs with TiN sensing layers in a commercialized CMOS process. This is the first time to have the in-situ TiN EGISFET in the CMOS process without extrinsic TiN deposition. This method can be employed to realize EGISFETs with higher density in a given area without sacrificing sensitivity, thus potentially beneficial to the development of high performance and high spatial resolution ISFET sensing array.

(Invited) Current and Voltage Control of Intermediate States in Bipolar Rram Devices for Neuristor Applications

Nowadays, there is an increasing interest in the fabrication of neuristors in which memristors are used to create a neuron-like behavior (1). Memristors based on resistive switching memories (RRAM) are promising candidates to implement artificial synaptic devices for their use in neuromorphic systems, due to their high number or reachable conductance levels.In a previous work (2) we show that TiN/Ti/ HfO2/W capacitors exhibit resistive switching behavior and that intermediate conductance states can be obtained by varying the voltage applied to the device (Voltage-control mode, VCM). We demonstrated that the conductance values vary near linearly when applying voltage depression pulses. During depression process, the conductance state depends on the amplitude and the duration of the voltage pulses length. Moreover, this process is accumulative: the conductance decreases when applying successive pulses of same amplitude and length. In contrast, the potentiation characteristic is not linear, as for other synaptic devices, as PRAMs: the transitions from high resistance state (HRS) to low resistance state (LRS) is very sharp and intermediate conductance state cannot be controlled. Decreasing the voltage pulse length or amplitude was not a choice. Additionally, we tried to use ramps where the voltage linearly increases and once again the characteristics remain very nonlinear. In summary, a very poor control of the potentiation state is obtained when using voltage as synapse stimulus.In the present work, we demonstrate that the potentiation process can be linearly controlled when using current as the synapse stimulus (Current-control mode, CCM).The devices used in this work are TiN/Ti/10-nm HfO2/W MIM capacitors. The high-k dielectric was deposited by the atomic layer deposition (ALD) technique at 225 ºC using TDMAH and water as hafnium and oxygen precursors respectively. Nitrogen was used as carrier and purge gas. The bottom electrode consists of a 200 nm W layer, and the top electrode consists of a 200 nm TiN layer and a 10 nm Ti layer. Metal electrodes were deposited by magnetron sputtering.An HP 4155B Semiconductor Parameter Analyzer was used to perform the voltage and the current measurements. In order to perform the pulsed measurements, we used an Agilent 33500B Series waveform generator which provides voltage pulses and ramps. The voltage waveforms are converted to mimic current waveforms using a home-made voltage to current converter. All the measurements were carried out at room temperature and the entire experimental setup was computer controlled.In figure 1 we show that the conductive path formation (electroforming) requires a very few nA current value. As the filament is formed, the devices reaches the low resistance state (LRS) and the voltage falls to a very low value. Once the filament is formed, we have measured the voltage-current (V-I) characteristic instead of the more usual current-voltage (I-V) characteristic. Figure 2 shows 50 consecutive bipolar switching V-I loops. It is important to point that in the CCM mode, a voltage compliance in the reset transition has to be used. Otherwise, irreversible oxide breakdown takes place due to the huge increase of the structure dissipated power. Departing from the HRS state we have applied current pulses of increasing amplitude. In Fig. 3 we plot the conductance of the device measured at 0.1 mA as a function of the amplitude of the current pulse previously applied. We see that the synaptic potentiation linearly depends on the pulse amplitude in the CCM mode. In Figure 4 we demonstrate that potentiation occurs at the very first current pulse. Successive pulses do not modify the conductance value. In summary, the potentiation process in CCM mode is very fast, non-accumulative and nearly linear. To confirm that this process is very fast we have obtained current transients in the VCM mode (Figure 5) which confirms that when a positive voltage is applied the current increases occurs at very short times (lower than the experimental setup time response).In contrast, the depression process is better controlled by applying voltage pulses (VCM mode) as described in ref. 2. Moreover, the depression process is slower and accumulative. That can be observed in Fig. 6 in which a train of -0.8 V voltage pulses is applied. The conductance decreases from pulse to pulse and show very long time rates (tens of ms for the showed voltage)In conclusion, CCM mode for potentiation and VCM mode for depression characteristic is the optimal combination to control the synaptic behavior of the studied bipolar RRAM devices.References Timmer, Nature Materials, 2012. DOI: 10.1038/NMAT3510García et al., Micr. Eng. 215, 110984 (2019). Figure 1