Stoichiometric TiN Research Articles

Effect of substrate bias on microstructure and properties of Ni–TiN nanocomposite thin films deposited by reactive magnetron co-sputtering

The effect of substrate bias variation on structure and properties of the Ni–TiN nanocomposite thin films deposited on Si (100) substrates by magnetron sputtering has been investigated. Deposition has been carried out by reactive co-sputtering of high purity Ti and Ni targets as RF and DC sources, respectively in an atmosphere with Ar:N2=1:2. The microstructures of the as-deposited films have been examined using grazing incidence X-ray diffraction and transmission electron microscopy. It has been observed that with an increase in negative substrate bias from 0 to −80V, the TiN volume fraction increases from 36 to 50%, whereas the average grain sizes of both Ni (≈10–17nm) and TiN (≈6–9nm) decrease. Moreover, the biaxial compressive residual stress as estimated by sin2ψ technique scales with negative substrate bias. The surface roughness determined using atomic force microscopy appears to be the least in the nanocomposite film deposited with substrate bias of −60V. Furthermore, X-ray photoelectron spectroscopy studies have confirmed the formation of oxygen-free stoichiometric TiN in this film. Hardness (≈12.6–16.9GPa), elastic modulus (≈208–233GPa) and scratch-resistance determined by nanoindenter, as well as electrical resistivity (≈26–47μΩ·cm) measured using dc four-probe method, are found to scale with TiN content. An increase in hardness and electrical resistivity with an increase in negative substrate bias is also attributed to a decrease in Ni grain size and an increase in point defect density.

First-principles quantum molecular dynamics study of TixZr1−xN(111)/SiNy heterostructures and comparison with experimental results

The heterostructures of five monolayers B1–TixZr1−xN(111), x = 1.0, 0.6, 0.4 and 0.0 (where B1 is a NaCl-type structure) with one monolayer of a Si3N4-like Si2N3 interfacial layer were investigated by means of first-principles quantum molecular dynamics and a structure optimization procedure using the Quantum ESPRESSO code. Slabs consisting of stoichiometric TiN and ZrN and random, as well as segregated, B1–TixZr1−xN(111) solutions were considered. The calculations of the B1–TixZr1−xN solid solutions, as well as of the heterostructures, showed that the pseudo-binary TiN–ZrN system exhibits a miscibility gap. The segregated heterostructures in which Zr atoms surround the SiyNz interface were found to be the most stable. For the Zr-rich heterostructures, the total energy of the random solid solution was lower compared to that of the segregated one, whereas for the Ti-rich heterostructures the opposite tendency was observed. Hard and super hard Zr–Ti–Si–N coatings with thicknesses from 2.8 to 3.5 μm were obtained using a vacuum arc source with high frequency stimulation. The samples were annealed in a vacuum and in air at 1200 °C. Experimental investigations of Zr–Ti–N, Zr–Ti–Si–N and Ti–Si–N coatings with different Zr, Ti and Si concentrations were carried out for comparison with results obtained from TixZr1−xN(111)/SiNy systems. During annealing, the hardness of the best series samples was increased from (39.6 ± 1.4) to 53.6 GPa, which seemed to indicate that a spinodal segregation along grain interfaces was finished. A maximum hardness of 40.8 GPa before and 55 GPa after annealing in air at 500 °C was observed for coatings with a concentration of elements of Si  (7–8) at.%, Ti  22 at.% and Zr  70 at.%.

Dual-Polarization-Sensitive Kinetic Inductance Detectors for Balloon-borne Sub-millimeter Polarimetry

We are developing arrays of kinetic inductance detectors for sub-millimeter polarimetry that will be deployed on the BLAST balloon-borne instrument. The array is feedhorn-coupled, and each pixel contains two lumped-element kinetic inductance detectors (LEKIDs) made of TiN. The absorbing, inductive sections of the LEKID-pair are orthogonal, which allows simultaneous measurement of both horizontal and vertical polarizations within one spatial pixel. In this paper, we show efficient absorption in TiN films when coupled to waveguide at room temperature and present dark measurements of single polarization devices with varying capacitor geometries. We show that it will be difficult to achieve background-limited performance in BLAST with stoichiometric TiN films with T\(_{c}=4.5\) K, and that non-stoichiometric films with lower T\(_{c}\) will be required.

Critical Temperature Tuning of Ti/TiN Multilayer Films Suitable for Low Temperature Detectors

We present our current progress on the design and test of Ti/TiN multilayer for use in kinetic inductance detectors. Sensors based on sub-stoichiometric TiN film are commonly used in several applications. However, it is difficult to control the targeted critical temperature \(T_c\), to maintain precise control of the nitrogen incorporation process and to obtain a production uniformity. To avoid these problems we investigated multilayer Ti/TiN films that show a high uniformity coupled with high quality factor, kinetic inductance and inertness of TiN. These features are ideal to realize superconductive microresonator detectors for astronomical instruments application but also for the field of neutrino physics. Using pure Ti and stoichiometric TiN, we developed and tested different multilayer configurations, in terms of number of Ti/TiN layers and in terms of different interlayer thicknesses. The target was to reach a critical temperature \(T_c\) around \((1{\div } 1.5)\) K in order to have a low energy gap and slower recombination time (i.e. low generation–recombination noise). The results prove that the superconductive transition can be tuned in the \((0.5{\div } 4.6)\) K temperature range by properly choosing the Ti thickness in the \((0{\div } 15)\) nm range, and the TiN thickness in the \((5{\div } 100)\) nm range.

Effect of Stoichiometry of TiN Electrode on the Switching Behavior of TiN/HfOx/TiN Structures for Resistive RAM

ABSTRACTTwo types of TiN/HfOx/TiN devices have been fabricated where the top 200nm TiN electrode has been deposited by two different sputtering methods; reactive, using a titanium target in a nitrogen environment, and non-reactive, using a titanium nitride target. Characterization of the materials shows that the reactive TiN is single-phase stoichiometric TiN with a sheet resistance of 7Ω/square. The non-reactive TiN has a sheet resistance of 300Ω/square and was found to contain significant amounts of oxygen. The resistive switching behavior differs for both devices. The reactive stoichiometric TiN device results in bipolar switching with a Roff/Ron ratio of 50. The non-reactive TiN results in unipolar switching with a Roff/Ron ratio of more than 103, however this device shows poor reproducibility. These results show that an oxygen rich layer between the top electrode and insulator affects the Roff value. It supports the theory of oxygen vacancies leading to the formation of conductive filaments.

Influence of seed layer orientation on the growth and physical properties of SnS nanostructures

Stoichiometric tin (II) sulfide (SnS) nano-structures were synthesized on SnS(010)/glass substrates using a simple and low-temperature chemical solution method, and their physical properties were investigated. The as-synthesized SnS nanostructures exhibited orthorhombic crystal structure and most of the nanocrystals are preferentially oriented along the direction. These nanostructures showed p-type electrical conductivity and high electrical resistivity of 93 Omega cm. SnS nanostructures exhibited a direct optical band gap of 1.43 eV. While increasing the surrounding temperature from 20 to 150 degrees C, the electrical resistivity of the structures decreased and exhibited the activation energy of 0.28 eV.

Effect of thickness on the structure, composition and properties of titanium nitride nano-coatings

Titanium nitride (TiNx) coatings were grown by magnetron sputtering onto Si(100) substrates by varying time of deposition to produce coatings with variable thickness (dTiN) in the range of 20–120nm. TiNx coatings were characterized by studying their structure, composition, and mechanical properties. Nuclear reaction analysis (NRA) combined with Rutherford backscattering spectrometry (RBS) analyses indicate that the grown coatings were stoichiometric TiN. Grazing incidence X-ray diffraction (GIXRD) measurements indicate that the texturing of TiN coatings changes as a function of dTiN. The (111) and (002) peaks appear initially; (111) becomes intense while (002) disappears with increasing dTiN. Dense, columnar grain structure was evident for all the coatings in electron microscopy analyses. The residual stress for TiN coatings with dTiN~120nm was 1.07GPa in compression while thinner samples exhibit higher values of stress.

Characterization and in-situ monitoring of sub-stoichiometric adjustable superconducting critical temperature titanium nitride growth

The structural and electrical properties of Ti–N films deposited by reactive sputtering depend on their growth parameters, in particular the Ar:N2 gas ratio. We show that the nitrogen percentage changes the crystallographic phase of the film progressively from pure α-Ti, through an α-Ti phase with interstitial nitrogen, to stoichiometric Ti2N, and through a substoichiometric TiNx to stoichiometric TiN. These changes also affect the superconducting transition temperature, TC, allowing, the superconducting properties to be tailored for specific applications. After decreasing from a TC of 0.4K for pure Ti down to below 50mK at the Ti2N point, the TC then increases rapidly up to nearly 5K over a narrow range of nitrogen incorporation. This very sharp increase of TC makes it difficult to control the properties of the film from wafer-to-wafer as well as across a given wafer to within acceptable margins for device fabrication. Here we show that the nitrogen composition and hence the superconductive properties are related to, and can be determined by, spectroscopic ellipsometry. Therefore, this technique may be used for process control and wafer screening prior to investing time in processing devices.Contribution of the U.S. government, not subject to copyright.

Low Power and Improved Switching Properties of Selector-Less Ta2O5 Based Resistive Random Access Memory Using Ti-Rich TiN Electrode

The effects of TiN top electrode composition (TiN vs Ti-rich TiN) on the resistive switching characteristics of selector-less TiN/TiOx/Ta2O5/TiN resistive random access memory (ReRAM) are investigated. Ti-rich TiN enables TiOx to have a higher concentration of oxygen vacancy and reduce barrier height between top electrode and TiOx. This leads to higher on/off current ratio and lower operation voltage without degradation of non-linearity which is the important factor for selector-less type ReRAM, compared to the stoichiometric TiN resistor stack. Consequently, it is verified that the switching mechanism is hybrid combination of filament formation and redox reaction in switching operation. This work is applicable to both high density and cost-effective ReRAM.

Effective electron mean free path in TiN(001)

The measured resistivity ρ of smooth stoichiometric epitaxial TiN(001) is 13 and 3.0 μΩ cm at 298 and 77 K for bulk layers but is 8 and 25 times higher when the layer thickness d is reduced to 2 nm. The increase in ρ with decreasing d is attributed to diffuse electron-surface scattering and is well described by the classical Fuchs-Sondheimer (F-S) model. This is unexpected because the F-S model is based on the nearly free electron model, while TiN exhibits a highly non-spherical Fermi surface and three bands crossing the Fermi-level. The measured room temperature effective electron mean free path λ for bulk scattering is 45 ± 4 nm, which is an order of magnitude larger than the free-electron prediction. This deviation is attributed to ∼93% of charge transport in TiN being due to two slightly filled bands which represent only 4% of conduction electrons. The F-S model is applicable to TiN because these two bands are nearly parabolic and nearly degenerate, yielding a single value for λ, which is estimated based on the published band structure to be 49 nm, in excellent agreement with the experimental 45 nm. These results demonstrate that the F-S model is applicable to metals with non-spherical Fermi-surfaces as long as the charge transport is dominated by a single (or multiple degenerate) band(s).

Synthesis route and mechanical properties of reactive hot pressed TiN–TiB2 ceramics

Reaction process and phase formation mechanisms in reactive hot pressing (RHP) of titanium and boron nitride blend powders have been investigated in vacuum. In temperatures of up to 1300°C, chemical reactions in the Ti–BN blend powder proceed via a solid-state diffusion process. Intermediate phases of hexagonal α-TiN0.3, tetragonal Ti2N, nonstoichiometric cubic TiN0.9 and orthorhombic TiB are found before they finally transform to the stoichiometric cubic TiN and hexagonal TiB2. Both the TiN–TiB2 ceramics reactive hot-pressed at 1600 and 1800°C represent intragranular/intergranular distributions of TiB2 in TiN. In contrast with monolithic TiN and TiB2 ceramics, the reactive hot-pressed TiN–TiB2 exhibits a significant enhancement on flexural strength and fracture toughness. TiN–TiB2 ceramics reactive hot-pressed at 1800°C have a Vickers hardness of 17.8GPa, an elastic modulus of 475GPa, a flexural strength of 732MPa and a fracture toughness of 8.5MPa·m1/2.

Characterization of titanium particles treated with N2 plasma using a barrel-plasma-treatment system

Metallic titanium (Ti) particles treated with N2 plasma via the barrel-plasma-treatment system were thoroughly evaluated, to investigate changes in physical and chemical properties resulting from the treatment. The color of the Ti particles changed from gray to uniform brown upon plasma-treatment, indicating good surface uniformity. Depth profiling using X-ray photoelectron spectroscopy showed that the nitrogen implanted by plasma-treatment formed Ti-N bonds at or near the surface of the particles, resulting in the formation of a stoichiometric TiN layer. It was determined from cross-sectional transmission electron microscopy and nanobeam diffraction measurements that the resulting TiN layer had two different structures. Nanoindentation data showed that the surface of a treated sample was about five times harder than that of untreated particles.

Characterization of TiN thin films grown by low-frequency (60 Hz) plasma enhanced chemical vapor deposition

The characteristics of TiN thin films grown on glass substrates by very low frequency (60Hz) PECVD were investigated along with the reactive plasma generated using a 60Hz power source. The TiN film depositions were performed using a gaseous mixture of H2, N2 and TiCl4 onto a substrate positioned between two electrodes using a floating substrate holder with a heating unit. The substrate is electrically floated to avoid sample damages due to ion bombardment. As-grown TiN films showed a NaCl-type fcc structure with a (200) crystallographic plane, low resistivity (∼60μΩcm) and gold-like color. Crystallinity was improved, impurities such as O and Cl were reduced, and the atomic ratio of N/Ti became stoichiometric with the increase of substrate temperature. Particularly, no chlorine component was detected above 500°C. Also, the N2 partial pressure strongly affected the deposition rate and ratio of N/Ti. Otherwise, impurities and crystallinity barely changed with the change of N2 pressure. The atomic ratio of N/Ti, impurities, and crystallinity of the films significantly affected the optical and electrical properties. Consequently, we produced stoichiometric Cl-free TiN films with golden color above 500°C at 60mTorr. The effects of temperature played an important role in controlling the film properties compared to the N2 partial pressure.

LaLuO3 higher-κ dielectric integration in SOI MOSFETs with a gate-first process

The chemical reactions at the higher-κ LaLuO3/Ti1NX/poly-Si gate stack interfaces are in detail investigated. Electrical and structural characterization methods are employed to explore the thermal stability of the gate stack. A Ti-rich TiN metal layer degrades the gate stack performance after high temperature annealing while the gate stack with a near stoichiometric TiN layer is stable during 1000°C, 5s anneals. Based on these results an integration process of TiN/LaLuO3 in a gate-first MOSFET process on SOI is shown.

Raman scattering from TiNx (0.67 ≤ x ≤ 1.00) single crystals grown on MgO(001)

Epitaxial NaCl-structure δ-TiNx(001) layers, with x ranging across the single-phase compound field from 0.67 to 1.00, are grown on MgO(001) and analyzed by Raman spectroscopy. All samples, including stoichiometric TiN(001), exhibit first-order Raman peaks, which are forbidden by the Oh symmetry of NaCl-structure compounds. Thus, even stoichiometric TiN contains point defects, primarily N and Ti vacancies, consistent with previous electronic transport measurements. However, the presence of a well-resolved second-order longitudinal acoustic line at 615 cm–1 shows that the defect concentration is relatively low. The positions of the first-order acoustic lines are in good agreement with values obtained from calculated phonon density of states. As the N/Ti ratio x in TiNx and, hence, the number n of valence electrons per formula unit (n = 9 for stoichiometric TiN) decreases, the first-order acoustic lines shift to higher frequencies, due to the corresponding decrease in phonon anomalies associated with the acoustic branch. This is in agreement with the observed increase in the intensities of the first-order acoustic phonon peak with decreasing x, characteristic of a higher average N vacancy concentration adjacent to Ti atoms. However, the presence of antisite defects is also required to explain the frequency shift of the optical modes in under-stoichiometric TiNx.

Formation of metallic nanoclusters in oxygen deficient indium tin oxide films

The composition, structure, microstructure, and properties of indium tin oxide films grown by pulsed laser deposition at room temperature and under vacuum were studied. The films are highly nonstoichiometric, with about 20% oxygen deficiency, and present a semiconductor behavior between 300 and 15 K, followed by a superconducting transition at about 7 K related to the presence of In or In-Sn nanoclusters embedded in a stoichiometric indium tin oxide matrix, i.e., nanocomposite films are formed by the phase separation of oxygen deficient metastable indium tin oxide. The solid-liquid and liquid-solid phase transitions of the metallic nanoclusters were evidenced by resistivity measurements in the 300 to 450 K range. The films grown at room temperature are partially crystallized. Actually, stoichiometric indium tin oxide crystallites are observed in the as grown films. After thermal treatment (<450 K), both stoichiometric indium tin oxide crystallites and the tetragonal phase of the metallic In are observed in the nanocomposite films. The size of nanoclusters (from 5 to 30 nm), which depends on the thermal treatments and crystallization, and the microstructure of the nanocomposite films were confirmed by HRTEM measurements.

Conductive-atomic force microscopy study of local electron transport in nanostructured titanium nitride thin films

Simultaneous local current and topography measurements were made on the surface of titanium nitride thin films by conductive-atomic force microscopy (C-AFM). Two compositions, stoichiometric TiN and sub-stoichiometric TiN 0.76 were investigated. Local variation of current at grain and grain boundaries was examined. The current flow is filamentary in nature, with the number of percolation paths being smaller for sub-stoichiometric titanium nitride. Current-voltage characteristics of stoichiometric TiN reveal that the grain interiors are electrically conductive, while in sub-stoichiometric TiN 0.76 thin film, grains are electrically resistive, i.e., a potential barrier to electron transport exists at the junction between the grain and the grain boundary in sub-stoichiometric TiN 0.76. Therefore, electron transport in this film is due to tunneling through the junction, which leads to increased resistivity. The total resistance of the samples measured using the four probe technique is 1 and 400 kΩ for TiN and TiN 0.76 respectively. In both type of compounds the grain and grain boundary resistances are of the order of MΩ. The grain and grain boundaries are connected in a manner that causes the total resistivity to be lower than the local resistivity.

Continuous multi cycle nanoindentation studies on compositionally graded Ti1−xAlxN multilayer thin films

Abstract Two types of Compositionally Graded Multilayer (CGM) films of Ti 1− x Al x N consisting of 21 layers were synthesized by reactive magnetron co-sputtering technique. The first one begins with a layer of Ti 0.4 Al 0.6 N from substrate and ends with TiN, whereas exactly a reverse order has been followed in the second one. As deposited CGM films are poly-crystalline with rocksalt structure similar to stoichiometric TiN. Secondary Ion Mass Spectrometry (SIMS) depth profile of the films showed the presence of 21 layers of equal thickness (50 nm) with varying aluminum content in steps. Continuous Multi Cycle (CMC) nanoindentation technique was used to analyze the failure modes of these films. Topographic examination of the indented zone revealed the presence of edge cracks inside and outside the indentation area when the load exceeds beyond 90 mN. The load–displacement profiles of CMC and single indentations exhibited the onset of pop-ins at a depth of ∼200 nm.

A molecular dynamics simulation of TiN film growth on TiN(0 0 1)

The growth of thin TiN films on the TiN(001) surface during reactive sputtering was simulated by molecular dynamics with the modified embedded-atom method potential. TiN3 is found to be the smallest epitaxial island and the film grows via the layer mode. Vacancy concentration in the deposited films decreases with increasing the substrate temperature and kinetic energy of incident atoms, resulting from the enhancement of the thermal diffusion and kinetic energy assisted athermal diffusion. To get the stoichiometric TiN film, the N:Ti flux ratio should be larger than unity and be increased with higher incident energy due to the weak adsorption of atomic N on TiN(001).

Nanocomposite indium tin oxide thin films: formation induced by a large oxygen deficiencyand properties

We report on the formation and properties of nanocomposite indium tin oxide thin filmswhich are grown by pulsed-electron beam deposition under a low oxygen pressure leadingto the formation of highly non-stoichiometric indium tin oxide films. For growth at roomtemperature these films are amorphous and insulating, while at higher temperatures, theoxygen deficiency leads to a disproportionation reaction with the formation of metallicclusters (indium or indium tin clusters) embedded in a stoichiometric crystallineindium tin oxide. This matrix is well crystallized and even epitaxial for growth onc-cut sapphire single crystal substrates. The presence of the metallic clusters induces specifictransport properties, i.e. a metallic conductivity at room temperature followed by asuperconducting transition at low temperature (about 6 K). Moreover, the solid–liquid andliquid–solid phase transitions in the metallic clusters can be clearly seen from the resistivitycurves as a function of temperature (in the room temperature to 450 K range),through specific changes in resistivity and the appearance of a hysteresis cycle.