TiN Buffer Layer Research Articles

Texture and phase transition hysteresis in epitaxially integrated VO2 films on TiN/Si(100)

Vanadium oxide (VO2), which exhibits a metal-to-insulator (MIT) transition at 68∘C, has been of immense technological interest for many applications such as sensor, electro-optic, and memory devices. In this work, we demonstrate the epitaxial integration of VO2 onto Si(100) via a TiN buffer layer, which is compatible with complementary metal–oxide–semiconductor (CMOS) technology. Our study revealed that the growth of epitaxial VO2 on TiN was mediated by a thin layer of epitaxial TiO2. The orientation relationship between various layers was established to be (011)V O2M∥ (110)TiO2∥ (100)TiN∥ (100)Si and [100]V O2M∥ [001]TiO2∥ [011]TiN∥ [011]Si. Through pole figures, reciprocal space maps (RSM), and transmission electron microscopy (TEM), we confirmed the presence of tilted rotational domains. We quantified the degree of misorientation in various VO2 films by introducing a relevant parameter, η, determined by analyzing the (011) pole figures. We found a correlation indicating that the thermal hysteresis of the phase transition, determined from in-situ temperature-dependent XRD, decreases with the degree of misorientation. This decrease in misorientation suggests the presence of more geometrically compatible grain boundaries, leading to a decrease in thermal hysteresis.

X-ray reciprocal space mapping analysis of ferromagnetic GdN films grown by pulsed laser epitaxy

Epitaxial thin films of ferromagnetic rare-earth nitride, GdN, were synthesized using pulsed laser deposition (PLD) on (001) MgO, pseudo-cubic (001) YAlO3, and (001) TiN buffered (001) MgO substrates. X-ray high-resolution reciprocal space mappings confirmed the epitaxial relationship between GdN and the substrates. The use of a TiN buffer layer changed the growth direction of the GdN films from (001) to (111). The ferromagnetic behavior of the films was characterized, and it was found that the magnetic easy axis could be tuned according to the crystal growth direction. These results suggest that PLD is a viable method for synthesizing epitaxial GdN films with tunable magnetic properties. The ability to control the crystal growth direction and magnetic easy axis of GdN films could be useful for developing spintronic devices.

Arc Ion Plating 법으로 형성된 TiAlN 박막의 버퍼층에 따른 특성 연구

In this study, using the AIP method, a TiAlN thin film was grown on a WC-5Co alloy using the buffer layer as TiAl, TiN, and CrN. The preferred orientation according to the XRD analysis showed a pattern with the growth directions of (111) and (110) in almost coating conditions. In the case of the thin film using TiN and CrN as buffer layers, (220) was more prominent than that of other specimens. The adhesion of the TiAlN layer showed a tendency to be affected by the buffer layer and surface roughness. The TiN buffer layer showed the highest adhesion of 130 [N], while the TiAl buffer layer showed a low adhesion of 20[N]. And to examine the high-temperature oxidation resistance, heat treatment was performed. In the case of the specimen using TiN and CrN as buffer layers and coating the TiAlN upper layer for 60 minutes, nitrogen was not replaced with oxygen even at 900[℃] and the nitride thin film was maintained as it is.

Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate

Improving the coherence of superconducting qubits is a fundamental step towards the realization of fault-tolerant quantum computation. However, coherence times of quantum circuits made from conventional aluminum-based Josephson junctions are limited by the presence of microscopic two-level systems in the amorphous aluminum oxide tunnel barriers. Here, we have developed superconducting qubits based on NbN/AlN/NbN epitaxial Josephson junctions on silicon substrates which promise to overcome the drawbacks of qubits based on Al/AlOx/Al junctions. The all-nitride qubits have great advantages such as chemical stability against oxidation, resulting in fewer two-level fluctuators, feasibility for epitaxial tunnel barriers that reduce energy relaxation and dephasing, and a larger superconducting gap of ~5.2 meV for NbN, compared to ~0.3 meV for aluminum, which suppresses the excitation of quasiparticles. By replacing conventional MgO by a silicon substrate with a TiN buffer layer for epitaxial growth of nitride junctions, we demonstrate a qubit energy relaxation time {T}_{1}=16.3;{{upmu }}{{{{{rm{s}}}}}} and a spin-echo dephasing time {T}_{2}=21.5;{{upmu }}{{{{{rm{s}}}}}}. These significant improvements in quantum coherence are explained by the reduced dielectric loss compared to the previously reported {T}_{1}approx {T}_{2}approx 0.5;{{upmu }}{{{{{rm{s}}}}}} of NbN-based qubits on MgO substrates. These results are an important step towards constructing a new platform for superconducting quantum hardware.

Low-Power Artificial Neurons Based on Ag/TiN/HfAlOx/Pt Threshold Switching Memristor for Neuromorphic Computing

Threshold switching (TS) devices are promising candidates to build highly compact and energy efficient artificial neurons. Here, we present a Pt/Ag/TiN/HfAlOx/Pt (PATHP) device with excellent TS characteristics, including a large selectivity(1010), a wide range of operation current from 10 nA to 1 mA, an extremely steep slope (0.63 mV/dec) and fast turn-on speed (50 ns). The stable TS performance can be ascribed to the introduction of TiN buffer layer and the alternate atomic layer deposited HfAlOx layer. Further, we experimentally demonstrate the functions of leaky-integrate-and-fire neurons with low power feature based on a RC circuit and a single device, respectively, which are essential for constructing spiking neuromorphic systems.

Epitaxial growth of (111) BaTiO3 thin films on (0002) GaN substrates with SrTiO3/TiN buffer layers

High-quality perovskite (111) BaTiO3 (BTO) ferroelectric thin films were epitaxially grown on wurtzite (0002) GaN substrates with the rationally designed SrTiO3 (STO)/TiN buffer layers by pulsed laser deposition. Particularly, TiN thin films with excellent conductivity could also be served as the bottom electrodes. The epitaxial relationship of the BTO/STO/TiN/GaN heterostructures was proved to be (111)[1 $$\bar{1}$$ 0] BTO//(111)[1 $$\bar{1}$$ 0] STO//(111)[1 $$\bar{1}$$ 0] TiN//(0002)[11 $$\bar{2}$$ 0] GaN by reflection high-energy electron diffraction and high resolution X-ray diffraction. Furthermore, the detailed interface structure and epitaxial relationship of the BTO/STO/TiN/GaN heterostructures were identified on atomic scale by high resolution transmission electron microscopy. The epitaxial (111) BTO ferroelectric thin films on GaN substrates exhibited the favorable ferroelectric properties with the remnant polarization of 12.97 μC cm−2. The high-quality epitaxial integration of perovskite BTO thin films on wurtzite GaN substrates could promote the potential applications in the advanced GaN-based integrated ferroelectric devices.

Epitaxial growth mechanism of perovskite (1 1 1) SrTiO3 on wurtzite (0 0 0 2) GaN with single unit-cell TiN buffer layers

Epitaxial integration of SrTiO3 (STO) with GaN plays a key role in exploring monolithic and multifunctional GaN-based devices. Herein, high quality perovskite (1 1 1) STO thin films were epitaxially grown on wurtzite (0 0 0 2) GaN substrates with novel designed single unit-cell TiN buffer layers by pulsed laser deposition. Epitaxial relationship model is proposed to be (1 1 1) [1 1¯ 0] STO//(1 1 1)[1 1¯ 0] TiN//(0 0 0 2)[1 1 2¯ 0] GaN. Furthermore, interfacial structure and epitaxial relationship of STO/TiN/GaN heterostructure is directly confirmed on atomic scale by high-resolution transmission electron microscopy. With the insertion of TiN, lattice mismatch between (1 1 1) STO and (0 0 0 2) GaN is reduced tremendously from 13.3% to 7.9%. More significantly, relaxation process and N atom vacancies in surface atom layer of single unit-cell (1 1 1) TiN could further release lattice mismatch strain between STO and GaN, and thus enormously facilitates epitaxial growth of STO. Moreover, the formation mechanism of twin domain structures and tilted twin grain-boundaries in STO is also discussed to clarify the epitaxial growth process of perovskite (1 1 1) STO on wurtzite (0 0 0 2) GaN.

Influence of nitride buffer layers on superconducting properties of niobium nitride

Niobium nitride thin films were deposited using reactive magnetron sputtering simultaneously on sapphire substrates with TiN, VN, and AlN buffer layers. Deposition temperature was varied from 400 to 840 °C. It was found that the crystal structure, surface roughness, and transition temperatures of the resulting NbN films depend strongly on both the growth temperature and the type of the buffer layer. The use of VN and TiN buffer layers for growing NbN at 400 °C improved transition temperatures compared to NbN grown at 840 °C on sapphire. While increasing the temperature improved the superconducting performance of films grown directly on sapphire, it caused hexagonal δ′-NbN and ε-NbN phases to emerge on the buffered films. A highly oriented hexagonal ε-NbN film was achieved by using a TiN buffer and an 840 °C deposition temperature. The ability to deposit high performance NbN at a lower temperature will improve and simplify the fabrication of advanced superconducting devices such as superconducting single photon detectors.

Improvement of HfOx-Based RRAM Device Variation by Inserting ALD TiN Buffer Layer

In this letter, the impacts introduced by oxygen-scavenging metal (Ti), including forming voltages variation and resistances dispersion in high/low states of HfO x -based RRAM devices, were investigated. Based on experiments, it is concluded that Ti atoms during physical vapor deposition process can randomly penetrate into the bulk of HfO x and are intended to randomly create the initial oxygen vacancies, thus causing the performance degradation. Moreover, a novel structure with an atomic layer deposition-TiN buffer layer inserted between oxygen-scavenging Ti and HfO x layers was proposed and experimentally demonstrated to reduce the impacts of Ti penetration, which further improves vacancy-creating approach. It was experimentally verified that with the help of incorporating a TiN buffer layer, the uniformity of switching parameters, such as forming voltage and resistance, was effectively improved. The understanding and improvement of device variation caused by oxygen-scavenging metal in oxides-based resistive random access memory (RRAM) are useful for further development of highly reliable RRAM technology.

Heteroepitaxial growth of ferroelectric films on Si substrates and their applications in waveguides and electro-optics

We introduce a general route to integrate epitaxially ferroelectric Sr1.9Ca0.1NaNb5O15 (SCNN) thin films on Si(001) substrates by pulsed laser deposition. The In:Mg0.8Zn0.2O (In:MZO)/TiN buffer layer is induced to overcome the large lattice mismatch between SCNN films and Si(001) substrates. The In:MZO layer acts as the buffer layer to bridge the Si and ferroelectric, the buffer layer with low refractive index for waveguide structure and the bottom electrode for electro-optic (EO) modulators. Waveguide and EO properties of the epitaxial integrated heterostructure were characterized by a prism coupler technique. The observed sharp and distinguishable TM and TE propagation mode lines revealed that favorable light confinements were achieved within the SCNN waveguide layer. The extraordinary and ordinary refractive indices were measured to be ne = 2.1802 and no = 2.2164 at 633 nm, respectively, implying a birefringence of 0.0362 was obtained. This large birefringence indicates that a large optically anisotropic property existed in the epitaxial SCNN films. An angular shift of guided mode was observed under applied electric field along with c-axis direction. The linear EO coefficient tensor r33 was measured to be about 860 pm/V. All of these results indicate that the integrated SCNN/In:MZO/TiN/Si epitaxial heterostructure has great potential for integrated optical EO and waveguide applications.

Effect of multi-interfacial structure on fracture resistance of composite TiSiN/Ag/TiSiN multilayer coating

A composite TiSiN/Ag/TiSiN multilayer coating was deposited on a Ti6Al4V substrate by multi-arc ion plating system. The coating had a special structure with a TiN buffer layer, TiSiN/Ag multilayers that possess alternating TiSiN (45 nm) and Ag (12 nm) layers, and TiSiN coating interlayers of 120 nm thickness for a total thickness of 1.7 μm. The TiSiN layers had a nanocrystalline/amorphous microstructure of nc-TiN, nc-Ag and amorphous Si3N4, with amorphous Si3N4 present around nanocrystal TiN and Ag boundaries, and Ag layers consisting of ductile nanocrystal silver. We have shown that this design of the composite TiSiN/Ag/TiSiN multilayer coating can effectively hinder crack propagation and increase fracture resistance of the coating.

Epitaxial integration of CoFe2O4 thin films on Si (001) surfaces using TiN buffer layers

Epitaxial cobalt ferrite thin films with strong in-plane magnetic anisotropy have been grown on Si (001) substrates using a TiN buffer layer. The epitaxial films have been grown by ion beam sputtering using either metallic, CoFe2, or ceramic, CoFe2O4, targets. X-ray diffraction (XRD) and Rutherford spectrometry (RBS) in random and channeling configuration have been used to determine the epitaxial relationship CoFe2O4 [100]/TiN [100]/Si [100]. Mössbauer spectroscopy, in combination with XRD and RBS, has been used to determine the composition and structure of the cobalt ferrite thin films. The TiN buffer layer induces a compressive strain in the cobalt ferrite thin films giving rise to an in-plane magnetic anisotropy. The degree of in-plane anisotropy depends on the lattice mismatch between CoFe2O4 and TiN, which is larger for CoFe2O4 thin films grown on the reactive sputtering process with ceramic targets.

Influence of multi-interfacial structure on mechanical and tribological properties of TiSiN/Ag multilayer coatings

The TiSiN/Ag multilayer coatings with bilayer periods of ~50, 65, 80, 115, 150, and 410 nm have been deposited on Ti6Al4 V alloy by arc ion plating. In order to improve the adhesion of the TiSiN/Ag multilayer coatings, TiN buffer layer was first deposited on titanium alloy. The multi-interfacial TiSiN/Ag layers possess alternating TiSiN and Ag layers. The TiSiN layers display a typical nanocrystalline/amorphous microstructure, with nanocrystalline TiN and amorphous Si3N4. TiN nanocrystallites embed in amorphous Si3N4 matrix exhibiting a fine-grained crystalline structure. The Ag layers exhibit ductile nanocrystalline metallic silver. The coatings appear to be a strong TiN (200)-preferred orientation for fiber texture growth. Moreover, the grain size of TiN decreases with the decrease of the bilayer periods. Evidence concluded from transmission electron microscopy revealed that multi-interfacial structures effectively limit continuous growth of single (200)-preferred orientation coarse columnar TiN crystals. The hardness of the coatings increases with the decreasing bilayer periods. Multi-interface can act as a lubricant, effectively hinder the cracks propagation and prevent aggressive seawater from permeating to substrate through the micro-pores to some extent, reducing the friction coefficient and wear rates. It was found that the TiSiN/Ag multilayer coating with a bilayer period of 50 nm shows an excellent wear resistance due to the fine grain size, high hardness, and silver-lubricated transfer films formed during wear tests.

Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100) substrates with a TiN buffer layer. A 50-nm-thick (200)-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large IcRN product of 3.8 mV, a sharp quasiparticle current rise with a ΔVg of 0.4 mV, and a small subgap leakage current. The junction quality factor Rsg/RN was about 23 for the junction with a Jc of 47 A/cm2 and was about 6 for the junction with a Jc of 3.0 kA/cm2. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200)-orientated TiN buffer layer and had a highly crystalline structure with the (200) orientation.

NbN/AlN/NbN/TiN Tunnel Junctions on Si (100) Substrate for Superconducting Devices

We developed a technique for fabricating (100)-oriented NbN thin films on Si (100) wafers by dc magnetron sputtering using TiN as a buffer layer. The lattice constant of the TiN buffer layer measured using X-ray diffraction was 0.4242 nm, which is relatively close to the NbN lattice constant of 0.446 nm. Therefore, NbN on the TiN buffer layer was epitaxially grown along the (100) direction. The junctions consisted of epitaxial NbN/AlN/NbN tunnel junctions using a TiN buffer layer fabricated on single-crystal Si (100) substrates. The NbN/AlN/NbN trilayer with the TiN buffer layer exhibited a single-crystal structure with a (200) orientation without other orientations. The gap voltage and the ratio of R sg /R N were approximately 4.9 mV and 100, respectively, for a junctions size of 1.4 × 1.4 μm 2 and J C = 8 A/cm 2 . Here, R sg is the gap resistance at 4 mV, and R N is the junction resistance at 10 mV. These results suggest that the NbN films using the TiN buffer technique offers significant promise for applications in several superconducting devices.

Effects of deposition temperature and quenching rate on the surface morphology and magnetic properties of FePt/TiN films

FePt thin films have been deposited on Si substrate with a TiN buffer layer. The effects of deposition temperature and the quenching rate on the magnetic properties and microstructure of the FePt/TiN films have been investigated. Out-of-plane anisotropy can be achieved for the film deposited at room temperature followed by annealing at 600°C and quenching in air. It is observed that a small fraction of L10-FePt in the room temperature deposited film is well-aligned in the perpendicular direction which is due to the large surface energy of the TiN buffer layer, which contracts the lattice of L10-FePt during the ordering process. However, by increasing the deposition temperature from room temperature to 450°C, both the L10-ordering parameter and the in-plane anisotropy can be enhanced. The microstructure and phase structural results indicate that a high quenching rate is beneficial to refine the FePt grains despite the high deposition temperature. The highest in-plane coercivity (915.6kA/m) is obtained by depositing at 300°C and quenching in air. However, when the film is deposited at 300°C followed by quenching in ice water, the average FePt grain size dramatically decreases to 22nm and the in-plane coercivity still maintains at about 875.8kA/m. The results indicate that the high rate quenching can effectively separate the grains and result in the high coercivity due to the reduced exchange coupling effect.

Structural and resistance switching properties of epitaxial Pt/ZnO/TiN/Si(001) heterostructures

We report the bi-epitaxial growth of ZnO and resistance switching characteristics of Pt/ZnO/TiN-based heterojunction devices fabricated on Si(001) substrates by pulsed laser deposition. The structural properties of the heterostructures characterized by XRD (θ-2θ, φ scans) and TEM confirm that the ZnO films having hexagonal wurtzite structure (six-fold symmetry) grow bi-epitaxially on the TiN buffer layer (four-fold symmetry). The Pt(111) grows epitaxially on ZnO(0001). The epitaxial relationship between the various films is given as (111)Pt ‖ (0001)ZnO ‖ (001)TiN ‖ (001)Si and [100]TiN ‖ [100]Si, [21¯1¯0]ZnO ‖ [110]TiN or [101¯0]ZnO ‖ [110]TiN, and [101¯]Pt ‖ [21¯1¯0]ZnO. The effect of ZnO growth temperature on the electrical properties of Pt/ZnO/TiN devices is studied and correlated with the microstructure of the ZnO/TiN interface. The Pt/ZnO/TiN devices exhibited good bi-polar resistance switching characteristics at voltages as low as ±1 V.

Si incorporation in Ti1 − xSixN films grown on TiN(001) and (001)-faceted TiN(111) columns

Thin films consisting of TiN nanocrystallites encapsulated in a fully percolated SiNy tissue phase are archetypes for hard and superhard nanocomposites. Here, we investigate metastable SiNy solid solubility in TiN and probe the effects of surface segregation during the growth of TiSiN films onto substrates that are either flat TiN(001)/MgO(001) epitaxial buffer layers or TiN(001) facets of length 1–5nm terminating epitaxial TiN(111) nanocolumns, separated by voids, deposited on epitaxial TiN(111)/MgO(111) buffer layers. Using reactive magnetron sputter deposition, the TiSiN layers were grown at 550°C and the TiN buffer layers at 900°C. On TiN(001), the films are NaCl-structure single-phase metastable Ti1−xSixN(001) with N/(Ti+Si)=1 and 0≤x≤0.19. These alloys remain single-crystalline to critical thicknesses hc ranging from 100±30nm with x=0.13 to 40±10nm with x=0.19. At thicknesses h>hc, the epitaxial growth front breaks down locally to form V-shaped polycrystalline columns with an underdense feather-like nanostructure. In contrast, the voided epitaxial TiN(111) columnar surfaces, as well as the TiN(001) facets, act as sinks for SiNy. For Ti1−xSixN layers with global average composition values 〈x〉=0.16, the local x value in the middle of Ti1−xSixN columns increases from 0.08 for columns with radius r⋍2nm to x=0.14 with r⋍4nm. The average out-of-plane lattice parameter of epitaxial nanocolumns encapsulated in SiNy decreases monotonically with increasing Si fraction 〈x〉, indicating the formation of metastable (Ti,Si)N solid solutions under growth conditions similar to those of superhard nanocomposites for which the faceted surfaces of nanograins also provide sinks for SiNy.

Effect of conductive TiN buffer layer on the growth of stoichiometric VO2 films and the out-of-plane insulator–metal transition properties

A TiN buffer film is used with a conductive interfacial layer for stoichiometric vanadium dioxide (VO2) film growth, creating a layered device with a VO2 insulator–metal transition. Low-temperature growth (<250 °C) of the VO2 film on a Ti layer on a Si substrate is achieved using inductively coupled plasma-assisted sputtering. It is found that Ti diffusion and oxidation degrades the VO2 film quality at higher temperatures, but the introduction of a TiN buffer layer suppresses the degradation and enables growth of a stoichiometric VO2 film even at 400 °C. The high resistance of the VO2 film grown on the TiN layer suggests the benefit of using the intrinsic insulator–metal transition of VO2. The voltage-triggered switching properties of the layered devices are examined, and the cause of the high out-of-plane resistance in this layered structure is discussed based upon the dependence of the initial resistance as a function the electrode area.

Pressure Sensing Properties of AlN Thin Films Sputtered at Room Temperature

Aluminum nitride (AlN) thin films with a TiN buffer layer have been fabricated on SUS430 substrate by RF reactive magnetron sputtering at room temperature under 25~75% <TEX>$N_2$</TEX> /Ar. The characterization of film properties were performed using surface profiler, X-ray diffraction, X-ray photoelectron spectroscopy(XPS), and pressure-voltage measurement system. The deposition rates of AlN films were decreased with increasing the <TEX>$N_2$</TEX> concentration owing to lower mass of nitrogen ions than Ar. The as-deposited AlN films showed crystalline phase, and with increasing the <TEX>$N_2$</TEX> concentration, the peak of AlN(100) plane and the crystallinity became weak. Any change in the preferential orientation of the as-deposited AlN films was not observed within our <TEX>$N_2$</TEX> concentration range. But in the case of 50% <TEX>$N_2$</TEX> /Ar condition, the peak of (002) plane, which is determinant in pressure sensing properties, appeared. XPS depth profiling of AlN/TiN/SUS430 revealed Al/N ratio was close to stoichiometric value (45:47) when deposited under 50% <TEX>$N_2/Ar$</TEX> atmosphere at room temperature. The output signal voltage of AlN sensor showed a linear behavior between 26~85 mV, and the pressure-sensing sensitivity was calculated as 7 mV/MPa.