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Resistive switching (RS) device behavior is highly dependent on both insulator and electrode material properties. In particular, the bottom electrode (BE) surface morphology can strongly affect RS characteristics. In this work, Ru films with different thicknesses grown on a TiN layer by radical-enhanced atomic layer deposition (REALD) are used as an inert BE in TaOx-based RS structures. The REALD Ru surface roughness is found to increase by more than 1 order of magnitude with the increase in the reaction cycle number. Simultaneously, a wide range of RS parameters, such as switching voltage, resistance both in low and high resistance states, endurance, and so forth, monotonically change. A simplified model is proposed to explain the linkage between RS properties and roughness of the Ru surface. The field distribution was simulated based on the observed surface morphologies, and the resulting conducting filament formation was anticipated based on the local field enhancement. Conductive atomic force microscopy confirmed the theoretical expectations.

This work reports a radical-enhanced atomic layer deposition (REALD) process using WH2(Cp)2–O*–H* reaction cycles (Cp = cyclopentadienyl group) to grow WO3–x films with a wide range of tunable oxyg...

Hf0.5Zr0.5O2 thin films are one of the most appealing HfO2-based ferroelectric thin films, which have been researched extensively for their applications in ferroelectric memory devices. In this work, a 1 mol % La-doped Hf0.5Zr0.5O2 thin film was grown by plasma-assisted atomic layer deposition and annealed at temperatures of 450 and 500 °C to crystallize the film into the desired orthorhombic phase. Despite the use of a lower temperature than that used in previous reports, the film showed highly promising ferroelectric properties—a remnant polarization of ∼30 μC/cm2 and switching cycle endurance up to 4 × 1010. The performance was much better than that of undoped Hf0.5Zr0.5O2 thin films, demonstrating the positive influence of La doping. Such improvements were mainly attributed to the decreased coercive field (by ∼30% compared to the undoped film), which allowed for the use of a lower applied field to drive the cycling tests while maintaining a high polarization value. La doping also decreased the leakage...

The growth per cycle saturation behaviors depending on the precursor pulse duration, reactant pulse duration, and reactant concentration were examined for hydrogen radical enhanced atomic layer deposition (REALD) of TaOx using tantalum-ethoxide as the precursor and plasma-activated hydrogen as the reactant. The chemical state of the TaOx film was dependent on the active hydrogen pulse duration and hydrogen volume fraction in the H2/Ar plasma mixture. The density of the electronic states in the dielectric band gap increased with the increase in the plasma exposure time (6–50 s) and hydrogen volume fraction (7–70%) whereas Ta4f core-level X-ray photoelectron spectroscopy indicated that the observed defects in the TaOx band gap are related to the oxygen deficiency. The ab initio calculations of oxygen deficiency concentrations and the energy spectrum satisfactorily correlated with the experimental data. The demonstrated combination of the growth saturation availability with the precise control of oxygen deficiency concentrations in the PEALD process could be highly useful in fields in which oxide dielectrics with adjustable oxygen deficiencies are required.

The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp) 2 and O 2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH 3 /Ar plasma pretreatment. It was demonstrated that NH 3 /Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20 A) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuO x (x ≈ 2) layer with thickness of ∼8 A after O 2 pulse (first half-cycle). It was also shown that oxygen of RuO x layer combusts Ru(EtCp) 2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34 A per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

The plasma-enhanced atomic layer deposition (PEALD) process using Ta(OC2H5)5 as a Ta precursor and plasma-activated hydrogen as a reactant for the deposition of TaOx films with a controllable concentration of oxygen vacancies (VO) is reported herein. The VO concentration control was achieved by varying the hydrogen volume fraction of the hydrogen–argon mixture in the plasma, allowing the control of the leakage current density in the tantalum oxide films within the range of 5 orders of magnitude compared with the Ta2O5 film grown via thermal ALD using the identical Ta precursor and H2O. Temperature-dependent current–voltage measurements combined with Poole-Frenkel emission modeling demonstrated that the bulk trap depth decreases with the increasing hydrogen volume fraction, which could be attributed to the increase of the VO concentration. The possible chemical change in the PEALD TaOx films grown under different hydrogen volume fractions was confirmed by the in situ X-ray photoelectron spectroscopy (XPS) ...

TaO x films with controlled ratio of Ta4+ and Ta5+ atoms were prepared at different hydrogen concentrations in plasma. As shown by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, the chemical state of Ta4+ corresponds to oxygen vacancies in the TaO x film. Electrophysical studies of the metal–dielectric–metal structures revealed an increase in the leakage current by four orders of magnitude as the hydrogen concentration in the plasma was increased from 7 to 70%, which is due to an increase in the concentration of oxygen vacancies in TaO x . A test structure of a resistive memory cell was made on the basis of the nonstoichiometric TaO x obtained. It withstood more than 106 rewriting cycles. The suggested atomic layer deposition process shows promise for solving one of the main problems of resistive memory: extension of its working life.

The mechanism responsible for the charge transport in thin ferroelectric Hf0.5Zr0.5O2 films has been studied. It is shown that in these films the transport mechanism is phonon-assisted tunneling between the traps. The optimal thickness of dielectric film for TiN/Hf0.5Zr0.5O2/Pt structures is determined. As a result of comparing the experimental current–voltage (I–V) characteristics of TiN/Hf0.5Zr0.5O2/Pt structures with the calculated ones, the thermal and optical energies of the traps are determined and the concentration of the traps is estimated. A comparison between the transport properties of ferroelectric and amorphous Hf0.5Zr0.5O2 films is carried out. It is shown that the charge transport mechanism in this dielectric does not depend on its crystalline phase. A method for decreasing leakage currents in Hf0.5Zr0.5O2 is proposed. A study of the resource of repolarization cycles for TiN/Hf0.5Zr0.5O2/TiN metal-dielectric-metal (MDM) structures fully grown by atomic layer deposition (ALD) has been carried out.

The structural and electrical properties of materials based on hafnium oxide grown by atomic layer deposition (ALD) are analyzed. The possibility and prospects of the use of their nanoscale films in nonvolatile memory are considered. The possibility of scaling Ferroelectric random access memory (FRAM) to subμm dimensions while preserving the ferroelectric properties is shown.

The multilevel resistive switching effect in Pt/HfxAl1−xOy/TiN stacks has been studied by hard X-ray photoelectron spectroscopy (HAXPES). Atomic layer deposition was used to grow HfxAl1−xOy films with graded Al depth profile, where the engineered Al concentration across the film facilitates the desired oxygen vacancies' profile. The method to derive the electrical potential profile across dielectric from the HAXPES spectra is proposed. By combining the information on the chemical state at both interfaces with the extracted potential distribution, a qualitative model for the resistive switching effect in the Pt/HfxAl1−xOy/TiN metal–insulator–metal stack is proposed. According to this model, the conductive filaments controlling the resistivity are formed by the electric field driven condensation of the charged oxygen vacancies in the oxide.

A nonvolatile memory cell prototype based on the effect of resistive switching in thin Hf x Al1 − x O y oxide films grown by atomic layer deposition (ALD) with a Al depth-graded profile has been developed. This prototype imitates the arrangement of memory cells between the metallization layers of integral circuits. The obtained results are much superior to the parameters of conventional flash memory cells in increasing the reset speed and decreasing the reset voltage.

This work demonstrates by in vacuo X-ray photoelectron spectroscopy and grazing-incidence X-ray diffraction that Ru(EtCp)2 and O* radical-enhanced atomic layer deposition, where EtCp means the ethylcyclopentadienyl group, provides the growth of either RuO2 or Ru thin films depending on the deposition temperature (Tdep), while different mechanisms are responsible for the growth of RuO2 and Ru. The thin films deposited at temperatures ranging from 200 to 260 °C consisted of polycrystalline rutile RuO2 phase revealing, according to atomic force microscopy and the four-point probe method, a low roughness (∼1.7 nm at 15 nm film thickness) and a resistivity of ≈83 µΩ cm. This low-temperature RuO2 growth was based on Ru(EtCp)2 adsorption, subsequent ligand removal, and Ru oxidation by active oxygen. The clear saturative behavior with regard to the precursor and reactant doses and each purge time, as well as the good step coverage of the film growth onto 3D structures, inherent to genuine surface-controlled atomic layer deposition, were confirmed for the lowest Tdep of 200 °C. However, at Tdep = 260 °C, a competition between film growth and etching was found, resulted in not-saturative growth. At higher deposition temperatures (300-340 °C), the growth of metallic Ru thin films with a resistivity down to ≈12 µΩ cm was demonstrated, where the film growth was proved to follow a combustion mechanism known for molecular oxygen-based Ru growth processes. However, this process lacked the truly saturative growth with regard to the precursor and reactant doses due to the etching predominance.

The development of the reference samples SPAM-20 and SPAM-100 for the spatial characteristics of nanostructures, based on periodic multilayer Al2O3/TiO2 coatings and intended for monitoring measurement accuracy and certification of x-ray reflectometry measurement techniques, is discussed. The metrological characteristics of these standard samples are examined.

Comparative analysis of atomic-layer deposition of titanium dioxide in precursor systems Ti(OCH3)4-H2O and Ti(OC2H5)4-H2O demonstrated that the growth rate of titanium dioxide produced by atomic-layer deposition in the Ti(OCH3)4-H2O system can be adequately estimated using a model taking into account the number and size of ligands in the metal-containing precursor. Studies in simulated body fluids demonstrated that polycrystalline anatase TiO2 coatings are capable of accelerated osteointegration, which makes this precursor promising for development of new biomedical articles.

Bioactive materials are of great interest due to a strong bond between bioactive surface and bone material. Materials and techniques, used for pretreatment of implant surfaces, have a number of considerable disadvantages. Bioactive thin films, grown by Atomic Layer Deposition, can solve a number of problems of pretreatment, increase the quality and lifetime of implant. The article describes a structural approach to theoretical prediction of bioactive materials as well as experiments performed on new bioactive TiO2 surfaces with a different crystalline structure.

The atomic layer deposition of titanium oxide in the precursor systems Ti(OCH3)4-H2O and Ti(OC2H5)4-H2O was compared. The growth rate of titanium oxide formed by the atomic layer deposition in the Ti(OCH3)4-H2O system can be adequately estimated with due to regard for the number and size of ligands of a metal-containing precursor. The study in simulated body fluid solutions showed that polycrystallin TiO2 coatings with anatase structure are prone to accelerated osseointegration and, consequently, promising for the development of new biomedical products.

Quaternary alloyed HfAlTiO thin (~ 4–5 nm) films in the wide range of Ti content have been grown on Si substrates by Atomic Layer Deposition technique, and the effect of both the film composition and the interfacial reactions on the electrical properties of HfAlTiO films is investigated. It is shown that depending on the Ti content, the permittivity and the leakage current density Ileak in HfAlTiO films vary in the range k = 18 ÷ 28 and 0.01–2.4 A cm− 2, respectively. The incorporation of ultra thin SiN interlayer in Al/HfAlTiO/SiN/Si stack gives rise to the sharp (× 103) decrease of the Ileak ~ 6 · 10− 5 A/cm2 at the expense of the rather low capacitance equivalent thickness ~ 0.9 nm.

TiO 2 coatings were grown on Ti and Si by Atomic Layer Deposition (ALD) from titanium ethoxide and water at 300 °C in a wide range of the reaction cycles number N = 100–2000. TiO 2 coatings were found to be amorphous at low value of N N ≥ 300 revealed anatase polycrystalline structure. The TiO 2 coatings bioactivity was evaluated by hydroxyapatite forming ability by the technique of soaking in Simulated Body Fluid (SBF). Correlation between bioactivity and structural properties of TiO 2 was determined. X-ray diffraction and scanning electron microscopy with electron probe microanalysis showed that amorphous TiO 2 coating did not induce the hydroxyapatite growth whereas anatase resulted in the hydroxyapatite forming on the samples surfaces which confirmed TiO 2 anatase bioactivity.

A dependence of structural properties of TiO 2 films grown on both Si- and Ti-substrates by atomic layer deposition (ALD) at the temperature range of 250–300 °C from titanium ethoxide and water on the number of reaction cycles N was investigated using Fourier-transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). TiO 2 films grown on both Si- and Ti-substrates revealed amorphous structure at low values of N N up to values 400–3600 resulted in the growth of polycrystalline TiO 2 with structure of anatase on both types of substrates and according to XRD-measurements the sizes of crystallites rose with the increase of N . The maximum anatase crystallite size for TiO 2 grown on Ti-substrate was found to be on ∼35% lower in comparing with that for TiO 2 grown on Si-substrate. A use of titanium methoxide as a Ti precursor with the ligand size smaller than in case of titanium ethoxide allowed to observe an influence of the ligand size on both the growth per cycle and structural properties of TiO 2 . The average growth per cycle of TiO 2 deposited from titanium methoxide and water (0.052 ± 0.01 nm/cycle) was essentially higher than that for TiO 2 grown from titanium ethoxide and water (0.043 ± 0.01 nm/cycle). Ligands of smaller sizes were found to promote the higher crystallinity of TiO 2 in comparison with the case of using the titanium precursor with ligands of bigger sizes.

The structure and chemical composition of the titanium dioxide thin films formed by atomiclayer deposition (ALD) from tetraethoxytitanium and water precursors were studied by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy. The deposited films were demonstrated to have good stoichiometry and anatase type polycrystalline structure. The growth per cycle of titanium dioxide was calculated by an ALD model taking into account the sizes and number of ligands in reactant molecules.

Using the methods of Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction in the geometry of the grazing beam, and Fourier transform infrared spectroscopy, we studied the chemical composition and structure of thin films of titanium dioxide formed by atomic layer deposition from tetraethoxytitanium and water. It is shown that the films obtained are characterized by a high stoichiometry of composition and by amorphous or polycrystalline structure of the anatase modification, depending on the number of reaction cycles. Using a model of the process of atomic layer deposition that takes into account the size and number of ligands of the reacting molecules, we calculated the amount of titanium dioxide deposited in a single reaction cycle.

We report the possibility of employment of low temperature (≤330 °C) plasma-enhanced atomic layer deposition for the formation of both electrodes and hafnium-oxide based ferroelectric in the metal-insulator-metal structures. The structural and ferroelectric properties of La doped HfO2-based layers and its evolution with the change of both La content (2.1, 3.7 and 5.8 at. %) and the temperature of the rapid thermal processing (550–750 °C) were investigated in detail. Ferroelectric properties emerged only for 2.1 and 3.7 at. % of La due to the structural changes caused by the given doping levels. Ferroelectric properties were also found to depend strongly on annealing temperature, with the most robust ferroelectric response for lowest La concentration and intermediate 650 °C annealing temperature. The long term wake-up effect and such promising endurance characteristics as 3 × 108 switches by bipolar voltage cycles with 30 μs duration and ± 3 MV/cm amplitude without any decrease of remnant polarization value were demonstrated.

Recently proposed novel neural network hardware designs imply the use of memristors as electronic synapses in 3D cross-bar architecture. Atomic layer deposition (ALD) is the most feasible technique to fabricate such arrays. In this work, we present the results of the detailed investigation of the gradual resistive switching (memristive) effect in nanometer thick fully ALD grown TiN/HfO2/TiN stacks. The modelling of the I-V curves confirms interface limited trap-assisted-tunneling mechanism along the oxygen vacancies in HfO2 in all conduction states. The resistivity of the stack is found to critically depend upon the distance from the interface to the first trap in HfO2. The memristive properties of ALD grown TiN/HfO2/TiN devices are correlated with the demonstrated neuromorphic functionalities, such as long-term potentiation/depression and spike-timing dependent plasticity, thus indicating their potential as electronic synapses in neuromorphic hardware.

A mild N2O plasma treatment technique (low power and low substrate temperature) for carbon materials' (including graphite and carbon nanotubes) functionalization followed by subsequent high-k dielectric atomic layer deposition (ALD) was developed. It was shown that N2O plasma carbon functionalization leads to the formation of epoxide and carboxylic groups on the carbon surface which act as active centers for ALD and, as a result, conformal and uniform Al2O3 and TixAl1−xOy films' growth occurred on the carbon surfaces. It was shown that the electrical properties of multinary TixAl1−xOy oxides are more promising in comparison to single Al2O3 oxide. Some electrical properties of the TixAl1−xOy films observed were a high dielectric constant ∼19, low leakage current density (