Biased Films Research Articles

Investigation of substrate bias effects on the reactively sputtered ZrN diffusion barrier films

ZrN diffusion barrier films were prepared by DC reactive magnetron sputtering under different negative substrate bias. The composition, microstructure, resistivity and diffusion barrier properties of ZrN films, with respect to substrate bias, were studied by means of X-ray diffraction, electron probe microanalyzer, Auger electron spectroscopy, and four point probe method. Results showed that the deposition rate and impurity oxygen content of ZrN films were substantially influenced by the resputtering effects due to the ion bombardment on the film surface. The competition between surface energy and strain energy made the preferred orientation of ZrN films change from (1 1 1) to (2 0 0) and then back to highly (1 1 1) preferred orientation as a function of substrate bias. The application of negative substrate bias could effectively decrease the electrical resistivity due to the decrease of impurity oxygen content and the densification of films, resulting from the moderate-energy ion irradiation. The biased ZrN films could successfully be used as a diffusion barrier layer, between Cu and SiO 2, even up to the high temperature of 800 °C for 30 min.

Superconducting and microstructural studies on sputtered niobium thin films foraccelerating cavity applications

The aim of the present research activity was to verify the influence of the applied biasvoltage on the microstructural and functional properties of magnetron sputtering physicalvapour deposition (MS-PVD) niobium thin films for use in superconducting resonantcavities for particle accelerators.Four different sets of samples were produced, by varying both the applied biasvoltage and the nature of the substrate (copper or quartz). The morphological,microstructural, and mechanical properties of the coatings were experimentallydetermined by focused ion beam scanning electron microscopy (FIB-SEM), atomic forcemicroscopy (AFM), transmission electron microscopy (TEM), and nanoindentationtechniques, and then correlated to the applied bias and nature of the substrate.The superconducting properties (critical temperatureTc and residual resistivity) were determined by a calibrated four-contact probe and acryogenic apparatus.The microstructures and surface properties of biased films grown on copper and quartzwere compared. The observed differences are likely connected to the low conductivity ofquartz that induces a re-sputtering effect and a consequent modification of thesuperconducting performances.

Magnetic memory in ferromagnetic thin films via exchange coupling

We show the possibility of creating magnetic domain memory in thin ferromagnetic films by inducing spatially varying exchange coupling interactions. We evidence this phenomenon in a perpendicular exchange bias film made of [Co/Pd] IrMn multilayers. Our coherent x-ray magnetic scattering speckle correlation study shows that the film exhibits no memory at room temperature but acquires a very high degree of magnetic memory, above 80% with subsequent field cycling when the sample is zero-field cooled below the blocking temperature of the IrMn layers $(T<275\text{ }\text{K})$.

Structural investigation by the Rietveld method of sputtered tungsten carbide thin films

Thin films of tungsten carbides deposited by reactive radio-frequency sputtering were investigated by X-ray diffraction using the Rietveld method. Two films were selected for the structural refinement. One was biased, the other unbiased. The unbiased film was found to consist of a cubic phase WC 1 − x (C 0.9) in the space group Fm3 m with a lattice parameter of 4.263 (5) Å. A negative substrate bias of − 40 V leads to a multiphasic film: a cubic phase WC 1 − x with a lattice parameter of 4.301 (6) Å and a hexagonal phase W 2C ( P-3 m1) with lattice parameters of a = b = 2.787 (1) and c = 4.549 (2) Å. The domain size was found to be of ~ 5 nm. The coexistence of nanocrystalline phases WC 1 − x and W 2C is in accordance with the decrease of the carbon content (WC 0.7) in the biased film.

Linear chirp control of infrared signal in a biased semiconductor thin film

Ultrashort light–matter interactions between a linear chirped pulse and a biased semiconductor thin film GaAs are investigated. Using different chirped pulses, the dependence of infrared spectra on chirp rate is demonstrated for a 5 fs pulse. It is found that the infrared spectra can be controlled by the linear chirp of the pulse. Furthermore, the infrared spectral intensity could be enhanced by two orders of magnitude via appropriately choosing values of the linear chirp rates. Our results suggest a possible scheme to control the infrared signal.

Wide-Tunable Low-Field Interdigitated Barium Strontium Titanate Capacitors

This letter reports low-field wide-tunable interdigitated barium strontium titanate (BST) capacitors. The capacitors consisting of BST thin film dielectric, silicon substrate, and gold metallization have been fabricated. The capacitance exhibits 0.2 pF at zero-bias and shows a tunability of 63% with an applied electric field of 1.4 V/mum. This corresponds to a 3.5 mum electrode gap width and a 5 V dc bias. Microwave measurements reveal a zero bias film quality of 50 around 30 GHz.

Contact potential measurement using a heated atomic force microscope tip

This letter reports contact potential measurement between the tip of a heated atomic force microscope cantilever and a biased gold film. Force-distance experiments were performed with tip temperature, tip potential, and substrate potential independently controlled. Experiments were conducted for probe temperatures of 23 to 200 °C and tip potentials of −1 V to 1 V. The measured contact potential was a function of temperature, due to the thermoelectric properties of the tip and substrate. The Seebeck coefficient for the combined system was close to −4.30mV∕K, consistent with the tip and substrate materials. The technique is scalable to arrays suitable for large area imaging.

Effects of substrate bias and nitrogen flow ratio on the resistivity and crystal structure of reactively sputtered ZrNx films at elevated temperature

ZrNx films were sputtered in an Ar+N2 atmosphere, with different substrate biases (zero to −200V) at a 2% nitrogen flow ratio and various nitrogen flow ratios (%N2=0.5%–24%) under −200V of substrate bias. The resistivity, crystal structure, and compositional depth profiles of ZrNx films, before and after vacuum annealing at 500–900°C, were investigated. At 2% N2, the resistivity of ZrNx films decreases with increasing substrate bias due to reduction of incorporated oxygen and porosity. Additionally, the resistivity of −200V biased ZrNx films (%N2=2%) are about the same before and after annealing, but the resistivities of zero and −100V biased ZrNx films increase with increasing annealing temperature. In addition, the ZrO2 phases (monoclinic and tetragonal) are found in ZrNx films deposited with 2% N2 and no substrate bias after annealing at 900°C; however, ZrN and tetragonal ZrO2 phases are revealed in ZrNx films sputtered with a substrate bias at the same temperature. On the other hand, the resistivities...

Factors Affecting Microhardness of Ti/TiN Multilayer Films Deposited by Pulsed Bias Arc Ion Plating

Ti/TiN multilayer films were deposited on high-speed-steel (HSS) substrates using pulsed-bias arc ion plating. Orthogonal experiments were used to analyze factors affecting microhardness of the films. The results show that of all the pulsed bias related parameters including pulsed bias magnitude, duty ratio, frequency, and film geometry parameters including modulation period, TiN/Ti thickness ratio, and grain size of TiN, the pulsed bias magnitude is the major factor affecting the microhardness. The maximum microhardness of 34.1 GPa was obtained with pulsed bias magnitude 900 V, duty ratio 50%, frequency 30 kHz, and modulation period 84 nm.

Exchange bias energy in Co/Pt/IrMn multilayers with perpendicular and in-plane anisotropy

The magnetization reversal process in perpendicularly biased [ Pt / Co ] 3 / d Pt Pt/IrMn and in-plane biased Co / d Pt Pt/IrMn multilayers with 0 nm ⩽ d Pt ⩽ 1.2 nm was investigated using Kerr magnetometry and Kerr microscopy. For the system with in-plane magnetic anisotropy, the exchange bias field decreases monotonically with Pt insertion layer thickness, while its coercivity remains constant. The samples with perpendicular magnetic anisotropy, on the other hand, exhibit maximum exchange bias and minimum coercivity for d Pt = 0.1 nm . In both cases, the existence of large exchange bias fields correlates with a high domain density during magnetization reversal. The interface exchange coupling energy is larger for the in-plane biased films than for the perpendicularly biased multilayers.

X-ray Diffraction Study of Electric Field-Induced Metal–Insulator Transition of Vanadium Dioxide Film on Sapphire Substrate

An X-ray diffraction study of the electric field-induced metal–insulator transition (MIT) of a vanadium dioxide (VO2) film on a sapphire (001) substrate, which exhibited MIT at a temperature of approximately around 68 °C with a three-order change in resistivity, was performed. A simple device fabricated using a VO2 film having aluminum electrodes as ohmic contacts with a gap separation of 1.0 mm showed current jump at an applied voltage of 48 V. The X-ray diffraction of an in situ electrically biased VO2 film in transition state showed a crystalline structure change from monoclinic VO2 to tetragonal VO2 when compliance current was higher than a certain value. We found that this macroscopic crystalline structure change is not induced by electric field in the case of the lowest compliance current, indicating the significance of the current for fast and durable operation of VO2-based devices.

A note on constrained shape memory alloys upon thermal cycling

In this paper, we present a systematical study on the constrained shape memory alloys upon thermal cycling. The focuses are the transformation temperature interval and hysteresis. Closed-form expressions are obtained for biased actuators and thin films atop an elastic substrate.

Magnetization depth dependence in exchange biased thin films

The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet (AF/FM) exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF2∕FM (FM=Fe, Ni, and Py) bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature (TN) is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above TN have also been discussed.

Structural analysis of cubic boron nitride films by ultraviolet Raman spectroscopy

Cubic boron nitride (BN) films with improved crystallinity are deposited by physical vapor deposition at an extremely low substrate bias (−35V). The films are characterized by UV Raman in association with Fourier transformed infrared (FTIR) spectroscopy. The influences of bias voltage and film thickness on the characterizations are investigated. UV Raman, in contrast to FTIR, is demonstrated to be a more powerful tool with high sensitivity for quantitative and/or qualitative evaluation of the phase purity and crystallinity, especially as the film thickness increases. Hexagonal BN inclusions (less than 1%), not evident in FTIR, are clearly revealed by UV Raman analysis.

Effects of substrate bias on CoCrPt-SiO2 magnetic recording media

CoCrPt and CoCrPt-SiO2 magnetic layers were investigated as a function of substrate bias. It was found that the use of substrate bias greatly modified the CoCrPt-SiO2 film microstructure. This was due to a large change in the SiO2 content during bias sputtering. Biasing had an effect of reducing the amount of oxide in the growing films and promoting the growth of larger grains, but it was also found to be very effective in decoupling the grains as determined by ΔM curves. In addition, in the biased films, a large dependence of the coercivity on film thickness was observed. The in-plane coercivity nearly doubled its value from 2400 to 4300 Oe as the thickness increased from 5 to 15 nm.

Influence of He-ion irradiation on thin NiMn∕FeNi exchange bias films

Using synchrotron x-ray diffraction and reflectivity, we studied the transition from the paramagnetic NiMn phase to the chemically ordered, antiferromagnetic L10 phase of NiMn∕Fe19Ni81 thin films deposited on a Si∕SiO2 substrate as a function of the annealing temperature. The transformation to a dominating L10-ordered NiMn film takes place between 300 and 400°C irrespective of the irradiation. This is also consistent with magnetization reversal measurements of the corresponding permalloy layers. The benefit of the ion irradiation is a reduction of the mosaicity for both the NiMn and the permalloy film, and a smoothening of internal interfaces.

Alloy Synthesis by Atomic Layer Laminations for Read Sensor Applications

ABSTRACTA novel method has been developed for synthesis of multi-element alloys by planetary magnetron sputter deposition techniques. The alloy is formed by alternating depositions of uniform ultra-thin component layers at a fraction of a mono-atomic layer, or atomic layer lamination. A minimal layer thickness of down to 0.1Å can be obtained such that the components can be mixed at atomic level forming a homogeneous alloy.A typical example is demonstrated here for the synthesis of CoxFe1−x alloys by alternating depositions of Co and Fe layers from pure element targets. The compositional dependence of the laminates basically reconstructs the well-known Slater-Pauling curve of the bulk CoxFe1−x alloys. The laminates exhibit a clear structural transition at Co compositions between 60 and 80 % from fcc phase to bcc phase, characteristic of bulk CoxFe1−x alloys. The novel atomic layer lamination has been successfully applied to the composition optimization of CoFe pinned layer with a best pinning strength at Co70Fe30 for exchange biased spin-valve films.

Modification of Sputter-Deposited Nanocrystalline LixMn2 − yO4 Thin-Film Cathodes by In Situ Substrate Bias and Postanneal

Thin films of lithium manganese oxides were deposited by radio frequency magnetron sputtering. Negative electric bias was applied on the substrates during deposition. The deposited films exhibited a defected spinel structure, , as characterized by X-ray diffraction and micro-Raman spectroscopy. As the substrate bias increased, the films developed stronger (111) orientation. At high substrate bias, the films tended to lose lithium and a second phase of manganese oxide developed. Postanneal was also carried out to fabricate well-crystallized spinel thin films for comparison. The film morphology also varied with substrate bias as observed by scanning electron microscope. By substrate bias and anneal, well-crystallized films with different morphologies can be obtained. Charge–discharge and cyclic voltammetry curves of these thin films were measured and compared. The different electrochemical characteristics of these films were attributed to the modified crystallography, morphology, and film stress. The films deposited with in situ substrate bias exhibited larger capacity without well-defined plateau. The postannealed films without substrate bias showed well-defined 4.1 and 3.9 V plateaus with slightly lower capacity. The biased and annealed films had low capacity but showed only 3.5% of capacity loss after 30 cycles.

The effects of plasma characteristics on the melting time at the front surface of a film on a substrate: An exact solution

Plasma heating of a film on a substrate is solved by using the Laplace transform method. The plasma is composed of a collisionless presheath and sheath on an electrically negative bias film partially reflecting and secondly emitting ions and electrons. The heating of the film from the plasma accounting for the presheath and sheath is determined from the kinetic analysis. This work proposes an analytical model to calculate the melting time and heating rate of the front surface of a film on the substrate, and provides quantitative results applicable to control the temperature evolution and the melting time in the film. The predicted surface temperature of the film on the substrate as a function of time is found to agree well with experimental data. The effects of dimensionless bias voltage, reflectivities of the ions and electrons on the wall, electron-to-ion source temperature ratio at the presheath edge, ion-to-electron mass ratio, charge number, plasma flow work-to-heat conduction ratios, substrate-to-film solid thermal conductivity ratios, and film-to-substrate solid specific heat ratios on the melting time and heating rate of the front surface are obtained. The contact Biot number between the film and substrate to simulate the heat conduction into substrate is also discussed. The results show that the melting time is strongly dependent on the plasma parameters and thermal properties of the material.

Effect of germanium addition on the properties of reactively sputtered ZrN films

For the first time, Zr–Ge–N films were deposited on silicon and steel substrates by sputtering a Zr–Ge composite target in reactive Ar– N2 mixture. The films were characterised by electron probe microanalysis, X-ray diffraction, micro-Raman spectroscopy and depth-sensing indentation. The effects of the Ge content and substrate bias voltage on the films’ structure, internal stress, hardness and oxidation resistance were investigated. Substrate bias strongly influenced the chemical composition of the films being observed by means of a steep decrease in the Ge content for negative bias voltages higher than � 80 V. In these cases, a significant hardness improvement was registered. For � 100 V biased films, in the Ge concentrations range tested in this study, only ZrN grains were evidenced by X-ray diffraction. The film compressive stresses increased with the germanium concentration. An unexpected effect of the Ge content on the films’ hardness was observed. In spite of the increase in the compressive stresses of the films with increasing Ge content, the hardness monotonously dropped from 38 GPa for pure ZrN down to 21.5 GPa for 4.6 at.% Ge. Addition of Ge into ZrN-based coatings induced an improvement of the oxidation resistance and it favoured the tetragonal form of zirconia in oxidised Zr–Ge–N coatings. D 2005 Elsevier B.V. All rights reserved.