TiN Thin Films Research Articles

Room-temperature ferromagnetism in epitaxial titanium nitride thin films

Localized charge injection by formation of vacancies provides an attractive platform for the development of multifunctional nanomaterials with direct implications in spintronics. However, further progress in spintronics critically depends on a deeper understanding of polaronic interactions between the localized charge states. This report is focused on TiN metallic system, which exhibits Pauli paramagnetism due to the absence of unpaired localized spin states. Here, nitrogen vacancies (VN) are used as a variable to tune the magnetic properties of epitaxial TiN thin films by thermal annealing in high-vacuum and N2 environment. Systematic introduction of VN generates robust magnetic ordering in vacuum-annealed TiN1-x films, with Curie temperature (TC) ∼700 K, and saturation magnetization (Ms) at absolute zero of 13.6 emu g−1. The signature spin-glass behavior below the irreversibility temperature (Tir ∼40 K) indicates the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling interactions between the unpaired localized spin-states. Through spatially resolved electron energy-loss spectroscopy, we have determined the generation of unpaired localized spins at Ti+2 polarons with ∼12 ± 2 at.% VN in TiN1-x films. Such a large concentration of VN results in increased spin stiffness and high TC. These findings open a definitive pathway for tuning the magnetic nature of metallic materials for spintronic applications.

Synthesis and characterization of TiN / Ti / AISI 410 coatings

The synthesis and characterization of Ti and TiN thin films of different thicknesses was carried out on a martensitic stainless steel AISI 410 substrate used for tool manufacturing. The mechanical parameters between the interacting surfaces such as thickness, adhesion and hardness were measured. By means of the scanning electron microscope (SEM) the superficial morphology of the Ti/TiN interface was observed, finding that the growth was of columnar grains and by means of EDAX the existence of titanium was verified. Using X-ray diffraction (XRD) it was possible to observe the presence of residual stresses (~ -3.1 GPa) due to the different crystalline phases in the coating. Under X-ray photoemission spectroscopy (XPS) it was possible to observe the molecular chemical composition of the coating surface, being Ti-N, Ti-N-O and Ti-O the predominant ones.

Deposition Pressure Dependent Electric Properties of (Hf, Zr)O2 Thin Films Made by RF Sputtering Deposition Method

To study the applications for ferroelectric non-volatile memory and ferroelectric memristor, etc., deposition pressure dependent electric the properties of (Hf, Zr)O2 thin films by RF sputtering deposition method were investigated. The bottom electrode was TiN thin film to produce stress effect on the formation of orthorhombic phase and top electrode was Pt thin film by DC sputtering deposition. Deposition pressure was varied along with the same other deposition conditions, for example, sputtering power, target to substrate distance, post-annealing temperature, annealing gas, annealing time, etc. The structural and electric properties of the above thin films were investigated. As a result, it is confirmed that the electric properties of the (Hf, Zr)O2 thin films depend on the deposition pressure which affects structural properties of the thin films, such as, structural phase, ratio of the constituents, etc.

A facile growth control of perovskite SrTiO3 thin films by tailoring surface morphologies of TiN seeding layers in the hydrothermal-galvanic couple synthesis

Growth control of cubic perovskite structure strontium titanate (SrTiO3) thin films was facilely achieved by tailoring surface morphologies of the TiN seeding layer in the hydrothermal-galvanic couple (HT-GC) synthesis. Two types of TiN thin films with pyramidal (P-TiN) and granular (G-TiN) surface morphologies were deposited on Si substrates by sputtering. The TiN-coated Si working electrodes were then directly connected to the Pt counter electrode without applying any external power source and soaked in 0.1 M Sr(CH3COOH)2 mixed with 2 M NaOH at 80 °C for 1–60 min. Significant galvanic currents were detected during the HT-GC synthesis. Directional oriented cubic SrTiO3 thin films grew over the two types of highly preferred oriented TiN seeding layers. The growth kinetics of SrTiO3 was deduced by fitting the coverage of the oxide over the two types of TiN at different reaction times to a modified Avrami equation. It was shown that galvanic currents, relative peak integrated intensities, and growth rates of SrTiO3 over the P-TiN were much higher than those on the G-TiN, while the grain sizes of SrTiO3 over the P-TiN were smaller. The faceted surfaces with fewer phase boundaries for P-TiN could yield a different rate-limiting step during the HT-GC synthesis and enhance significantly the growth of the oxide. This facile growth control could also be applied to similar perovskite oxide/conductive nitride systems.

Role of reactive gas on the structure and properties of titanium nitride films grown by plasma enhanced atomic layer deposition

The authors report on the role of various reactive gases on the structure and properties of TiN thin films prepared by plasma enhanced atomic layer deposition (PEALD) from tetrakis(dimethylamido)titanium. The reactive gas plays an important role determining the film structure and properties. Nitrogen-based plasma (N­2 and NH3) resulted in low oxygen (∼3%) and carbon (∼2%) contamination and well-defined columnar grain structure. A nitrogen excess (∼4%) was found in the films deposited using N2 plasma. The stoichiometric films and lowest resistivity (∼80 μΩ cm) were achieved using NH3 plasma. Deposition using H2 plasma resulted in higher carbon and oxygen contamination (∼6% for each element). The reactive gas also plays an important role in determining the grain size and preferential orientation. By varying the plasma chemistry, either (111) or (100) oriented films can be obtained. A mechanism determining the PEALD TiN preferential orientation is proposed. Finally, plasma induced degradation of the underlying dielectric layer is evaluated.

Experimental and analytical investigation into boiling induced thermal stress: Its impact on the stress state of oxide scales of nuclear components

Abstract This paper experimentally and theoretically investigates thermal stress of materials caused by non-uniform surface temperature fields due to bubble dynamics of nucleate boiling. The surface temperature of Calcium fluoride (CaF2) on a thin-film indium tin oxide (ITO) heater was measured by an Infrared high-speed camera. Then, the obtained temperature fields were used to calculate boiling induced thermal stresses. An analytical model was developed to predict thermal stress due to nucleate boiling. The localized cold spot under a growing bubble gives rise to the peak tensile stress. The magnitude of the peak stress is predominantly determined by liquid and solid properties, and applied heat flux to a limited extent. Nevertheless, higher heat flux is observed to result in a higher probability of material fracture due to an increased number of nucleation sites, which gives a larger effective surface area under stress. Newly discussing another cause of stresses for oxide layer mechanical integrity, the presented discovery of boiling induced stress implies potential effects on break-away of oxide scales under boiling conditions, including reactor fuel claddings and steam generator U-tubes. Moreover, the boiling stress can be potentially used to design self-cleaning surfaces by breaking unwanted deposits.

Energetic particle irradiation study of TiN coatings: are these films appropriate for accident tolerant fuels?

Coating nuclear fuel cladding alloys with hard thin films has been considered as an innovative solution to increase the safety of nuclear reactors, in particular during a of loss-of-coolant accident (LOCA). In this context, and due to its suitable mechanical properties and high corrosion resistance, titanium nitride thin films have been proposed as candidate coatings for zirconium alloys in new accident tolerant fuels for light water reactors. Although the properties of TiN hard coatings are known to be adequate for such applications, the understanding of how the exposure to energetic particle irradiation changes the microstructure and properties of these thin films is still not fully understood. Herein, we report on heavy ion irradiation in situ within a Transmission Electron Microscopy (TEM) of magnetron-sputtered TiN thin films. The coatings were irradiated with 134 keV Xe + ions at 473 K to a fluence of 6.7 × 1015 ions⋅cm−2 corresponding to 6.2 displacements-per-atom where significative microstructural alterations have been observed. Post-irradiation analytic characterisation with Energy Filtered TEM and Energy-Dispersive X-ray spectroscopy carried out in a Scanning Transmission Electron Microscope indicates that TiN thin films are subjected to radiation-induced segregation. Additionally, the nucleation and growth of Xe bubbles appears to play a major role in the dissociation of the TiN thin film.

Structural and morphological properties of TiN deposited by magnetron sputtering

This work studied the simultaneous effect of multiple parameters on the microstructure and topography of TiN thin films deposited by reactive unbalanced DC magnetron sputtering. The simultaneous influence of deposition parameters including pressure, temperature, and power on crystallite size, texture coefficient, microstructure, and roughness parameters was investigated using design of experiments (DoE): the Taguchi method. The results showed that the mean crystallite size of (111) and (200) planes increase when the temperature and cathode power increase. Furthermore, the increase of cathode power from 50 to 150 W augments the mean of root mean square height (Sq) from 2 to 10 nm. However, the substrate temperature has no considerable effect on the roughness parameters of the surface. Cathode power has also a prominent influence on the skewness of deposited layers in which it abruptly decreases when the power changes from 100 W to 150 W. In other words, all samples deposited at 150 W have negative skewness. It was also shown that the deposition rate is mainly controlled by the cathode power.

THE INVESTIGATION OF WEAR PROPERTIES OF TIN COATINGS ON THE H13 TOOL STEEL UNDER DIFFERENT DEPOSITION PARAMETERS

The present paper reports the influence of working pressure and nitrogen flow rate on the mechanical and wear properties of TiN thin films deposited by DC reactive magnetron sputtering with RF bias voltage. The process of PVD coating is conducted in a nitrogen-argon gaseous mixture at a temperature of 150°C and a DC power of 200W for 90 min. The micro hardness and the wear resistance of the TiN are determined prior to and after the PVD coating. The wear volumes of samples were evaluated using optical profilometre. Worn surfaces were observed using scanning electron microscopy. It was observed that coated samples showed considerable higher mechanical properties and wear resistance compare to uncoated samples. Abrasive wear mechanism was observed on the surface of worn surfaces.

57Fe Mössbauer study of epitaxial TiN thin film grown on MgO (1 0 0) by magnetron sputtering

The properties and performance of TiN thin films are closely related to the concentration and mobility of lattice defects in the thin film structures of TiN. This makes a local atomic scale study of TiN thin films an ever-growing demand. Emission 57Fe Mössbauer spectroscopy (eMS) is a powerful tool in this regard, which we apply here to study an ultrathin TiN film epitaxially grown on MgO (1 0 0). With the help of theoretical calculations, our results show that most implanted Fe ions adopt a 2+ valence state and locate at the Ti sublattice in the bulk-like single crystalline grains, with the rest Fe residing at the grain boundaries as interstitials. A small percentage of nitrogen point defects (vacancy VN and interstitial NI) are observed in the bulk-like crystalline grains. A temperature-dependent, interstitial NI mediated site-exchange between NI and VN inside the crystal grain are deduced via a N2 dimmer like diffusion of NI through the crystal grains in the temperature range of 540–620 K. This is interesting in the perspective of exploring the catalytic property of TiN nanostructures. The titanium vacancy (VTi) is only detected at the grain boundaries. Annealing up to 813 K, both the VN and NI are annihilated in the crystalline grains and the VTi is fully recovered with healing of the grain boundaries. However, no evidence of ferromagnetism due to dilute implantation of 57Mn/57Fe and or structural defects in the film is obtained. This suggests that the so far reported dilute magnetism and defect-induced ferromagnetism in TiN nanostructures requires a further systematic investigation.

Ion-beam based characterization of TiN back contact interlayers for CZTS(e) thin film solar cells

Time-of-Flight Elastic Recoil Detection Analysis (ToF-ERDA) and Time-of-Flight Medium-Energy Ion Scattering (ToF-MEIS) have been employed to investigate the potential of TiN thin films as intermediate layers on Mo back contact in CZTS(e) solar cells. TiN films of various thicknesses (20, 50 and 200 nm) were prepared with reactive DC magnetron sputtering and atomic layer deposition on Mo/SLG (soda-lime glass) substrates and annealed ex situ in either S or Se atmosphere. In situ annealing of the samples to different temperatures was also performed in the MEIS setup together with subsequent ToF-MEIS and ERDA analysis.The results of the sample and interlayer composition profiles, layer quality and thickness distributions are discussed in context with complementary experimental findings partially obtained previously by X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy and Scanning Transmission Electron Microscopy – Electron Energy Loss Spectroscopy (STEM – EELS).

Effect of heating and resistance on emission properties of carbon nanotubes

We have studied the effect of the series resistance on the heating of the cathode, which is based on carbon nanotubes and serves to realize the field emission of electrons into the vacuum. The experiment was performed with the single multi-walled carbon nanotube (MCNT) that was separated from the array grown by CVD method with thin-film Ni-Ti catalyst (nickel 4 nm / Ti 10 nm). The heating of the cathode leads to the appearance of a current of the thermionic emission. The experimental voltage current characteristic exhibited the negative resistance region caused by thermal field emission. This current increases strongly with increasing voltage and contributes to the degradation of the cold emitter. The calculation of the temperature of the end of the cathode is made taking into account the effect of the phenomenon that warms up and cools the cathode. We have developed a method for processing of the emission volt-ampere characteristics of a cathode, which relies on a numerical calculation of the field emission current and the comparison of these calculations with experiments. The model of the volt-ampere characteristic takes into account the CNT’s geometry, properties, its contact with the catalyst; heating and simultaneous implementation of the thermionic and field emission. The calculation made it possible to determine a number of important parameters, among which the voltage and current of the beginning of thermionic emission, the temperature distribution along the cathode, the resistance of the nanotube. The phenomenon of thermionic emission from CNT’s was investigated experimentally and theoretically. The conditions of this type emission occurrence were defined. The results of the study could form the basis of theory of CNT emitter’s degradation.

Effect of Substrate Roughness on Adhesion and Structural Properties of Ti-Ni Shape Memory Alloy Thin Film.

Ti-Ni shape memory alloy (SMA) thin films are very attractive material for industrial and medical applications such as micro-actuator, micro-sensors, and stents for blood vessels. An important property besides shape memory effect in the application of SMA thin films is the adhesion between the film and the substrate. When using thin films as micro-actuators or micro-sensors in MEMS, the film must be strongly adhered to the substrate. On the other hand, when using SMA thin films in medical devices such as stents, the deposited alloy thin film must be easily separable from the substrate for efficient processing. In this study, we investigated the effect of substrate roughness on the adhesion of Ti-Ni SMA thin films, as well as the structural properties and phase-transformation behavior of the fabricated films. Ti-Ni SMA thin films were deposited onto etched glass substrates with magnetron sputtering. Radio frequency plasma was used for etching the substrate. The adhesion properties were investigated through progressive scratch test. Structural properties of the films were determined via Feld emission scanning electron microscopy, X-ray diffraction measurements (XRD) and Energy-dispersive X-ray spectroscopy analysis. Phase transformation behaviors were observed with differential scanning calorimetry and low temperature-XRD. Ti-Ni SMA thin film deposited onto rough substrate provides higher adhesive strength than smooth substrate. However the roughness of the substrate has no influence on the growth and crystallization of the Ti-Ni SMA thin films.

Valley-Selective Linear Dichroism in Layered Tin Sulfide

Valley-related physics, optics, and electronics have been extensively investigated in transition metal dichalcogenides with a honeycomb lattice such as molybdenum disulfide. Their photoemission properties exhibit a circular dichroism due to energy degenerate but inequivalent valleys located at K and K′ in momentum space. Recently linear dichroism was observed in few-layer black phosphorus with highly anisotropic in-plane optical properties. Here, we report a novel valley-selective linear dichroism of the photoluminescence in layered thin-film tin sulfide (SnS). We identified two PL emission peaks, exhibiting an orthogonal linear dichroism, arising from two inequivalent valleys in the energy band. The photon emission from the Γ-X valley is completely x-polarized, while in contrast, the photon emission from the Γ-Y valley is purely y-polarized. This unique valley-selective linear dichroism in SnS is further confirmed by the band-edge absorption measurements along the Γ-X and Γ-Y directions, respectively. Ou...

(Invited) Using Amorphous Carbon to Enable Area-Selective Atomic Layer Deposition for Advanced Patterning Applications

The demand for transistors and memory devices with smaller feature sizes and increasingly complex architectures furthers the need for advanced thin film patterning techniques. A pre-patterned, sacrificial layer can be used as a template for bottom-up fill of new materials which would otherwise be difficult to pattern using traditional top-down lithographic methods. This work investigates initial growth of TiN, TiO2, and HfO2 thin films during thermal atomic layer deposition (ALD) onto a high density, amorphous carbon (aC) sacrificial layer. ALD of TiN by TiCl4/NH3 at 390oC, TiO2 by Ti(OCH3)4/H2O at 250oC, and HfO2 by HfCl4/H2O at 300oC on as-deposited aC films resulted in uninhibited, continuous thin film growth. We find that carbon surface reduction and passivation using a H2 plasma resulted in delayed film coalescence for TiN, TiO2, and HfO2 on the aC. After 200 TiN cycles on H2 plasma-treated aC, Rutherford backscattering spectrometry shows Ti levels below the detection limit (8×1013 at/cm2), whereas SiO2 or Si3N4 substrates show TiN growth of ~6 nm, corresponding to a selectivity of ~200:1. Exposing plasma-treated aC to H2O induces nucleation for TiN ALD, consistent with favorable nucleation on hydroxyl sites. Therefore, the H2O co-reagent in TiO2 and HfO2 ALD contributes to loss of selectivity compared to TiN ALD using NH3. Furthermore, we demonstrate the use of the Avrami Equation to model the nucleation behavior on plasma-treated aC, providing useful insights into process improvements for increased selectivity. We confirm scaling of selectivity to sub 50 nanometer patterns using 45 nm aC/Si3N4 line/space patterns, where 3.5 nm TiO2 and 5.8 nm TiN films are deposited on Si3N4 with minimal particle formation on aC, with selectivity loss primarily on feature corners and edges. We conclude that improved scaling of selectivity to nanometer scale patterns can be achieved by optimizing surface loading and extent of plasma exposure, and by further understanding shape effects in nanoscale surface plasma modification.

Whisker Mitigation Mechanisms in Indium-Doped Tin Thin Films: Role of the Surface

The effect of indium doping on whisker mitigation in tin electroplated on copper has been investigated. Whisker growth studies show that indium addition to Sn effectively mitigates whisker growth. Cross-section images showed predominantly columnar grains in the thin film. X-ray photoelectron spectroscopy studies of the oxide revealed a mixture of In2O3 and SnO2, along with a stoichiometrically defective oxide that can serve as a vacancy source at the metal-oxide interface. In addition, Auger electron spectroscopy showed In segregation at the grain boundaries as well as In enrichment just below the oxide layer. Cyclic voltammetry tests showed that the anodic behavior of the thin films exhibits active/passive transition where the passive current increases significantly upon doping Sn with In. We interpret these surface-related results in terms of a less tenacious oxide that permits reduction of in-plane compressive residual stress, thereby minimizing the driving force for whisker formation and growth.

Hybrid rf SQUID qubit based on high kinetic inductance

We report development and microwave characterization of rf SQUID (Superconducting QUantum Interference Device) qubits, consisting of an aluminium-based Josephson junction embedded in a superconducting loop patterned from a thin film of TiN with high kinetic inductance. Here we demonstrate that the systems can offer small physical size, high anharmonicity, and small scatter of device parameters. The work constitutes a non-tunable prototype realization of an rf SQUID qubit built on the kinetic inductance of a superconducting nanowire, proposed in Phys. Rev. Lett. 104, 027002 (2010). The hybrid devices can be utilized as tools to shed further light onto the origin of film dissipation and decoherence in phase-slip nanowire qubits, patterned entirely from disordered superconducting films.

Study on the electronic structure and optical properties of TiN films based on the first-principle

Base on the first-principles, the energy band and optical properties of TiN thin films were modeled by the materials studio (MS) programm. The energy band, total density of states (DOS), dielectric function, absorption and reflectivity of TiN were studied. The results suggested that the Fermi energy (EF) passes through the energy band with dense distribution of energy levels, moreover, the total density of states crosses the EF, suggested that TiN belongs to metalloid, and determined by electronics in Ti-3d state. Meanwhile, the structure of energy band was affected by pressure, but the influence of temperatures is weak. The reflectivity of TiN to red light (1.63 eV to 1.97 eV) is lower than that of blue light (2.53 eV to 2.75 eV). Moreover, TiN has a higher reflectance in the infrared region, and showed translucent in the visible light region and the static permittivity of TiN is about 39.24 F/m.

Transmission Kikuchi diffraction from nano-crystalline Ti and TiN thin-films

Nano-crystalline Ti and TiN thin-films fabricated on <100> P-type Si wafers via magnetron sputtering are characterized by transmission Kikuchi Diffraction (TKD) in an FEI Sirion scanning electron microscope (SEM). A simple and cost-effective sample preparation combined with the TKD experiment at working distance of ∼ 3 mm and a tilt of 35° produced indexable Kikuchi patterns. Pole figures generated by automatic and manual indexing revealed <0001>|| normal direction (ND) fiber texture and <111>||ND fiber texture in monolithic Ti and TiN thin-films, respectively. Glancing angle x-ray diffraction results corroborated the texture in the samples. Spatial resolution of ∼ 60 nm is achieved that is close to the limit of resolution in conventional electron backscatter diffraction (EBSD). It is demonstrated that a simple sample preparation method in TKD technique combined with selected area electron diffraction (SAED) in transmission electron microscope (TEM) may reveal fundamental knowledge about different mechanisms occurring during fabrication and processing of the thin-film systems.

Combined effects of surface oxidation and interfacial intermetallic compound growth on solderability degradation of electrodeposited tin thin films on copper substrate due to isothermal ageing

We report new insights into the solder wettability degradation of Sn thin films on Cu under 155 °C isothermal ageing. A multiscale wettability degradation model was established, reflecting quantitatively the surface oxidation and interfacial intermetallic compound (IMC) growth, on the basis of solder wetting behaviour. The thermal oxidation of Sn exhibited heterogeneous inward thickening, lateral expanding and outward platelet-like growth, forming nanocrystalline, oxygen-deficient SnO2 with pronounced voiding/cracking propensity. Unlike a commonly held belief that the initial wettability loss is due to surface-exposing and oxidation of IMCs, it was found from dual combined effects of inward surface oxidation and outward IMC growth.