Chromium Thin Films Research Articles

Direct laser writing of gray-scale microimages with a large dynamic range in chromium films

A method for direct laser thermochemical writing of gray-scale microimages in thin chromium films is developed and studied. The method includes exposing a chromium film with a focused laser beam with variable power intensity and developing it in a selective etchant. The range of variation of the transmission by more than 100 times is obtained. The nonlinearity of the dependence of the chromium film transmission on the power intensity of the exposing beam is eliminated by software correction. The samples of the raster (with a size of 64×64 and a step of 176 μm) of apertures (36 μm) with the gray-scale Gaussian transmission function are manufactured experimentally. This raster is used in the modified Shack — Hartmann sensor.

Spectral characteristics of nanometer-thick chromium films in terahertz frequency range

The spectral characteristics (reflection, transmission, and absorption coefficients) of thin chromium films on silica substrates have been measured using a pulsed source of terahertz radiation. The spectra of optical coefficients were obtained in a frequency range of 0.25–1.1 THz. Dependences of the optical coefficients on the metal film thickness at 1 THz were constructed. The maximum absorption coefficient (43%) was observed at a film thickness of 10 nm.

Improved Electrical Properties of Cr/ITO Ohmic Contact Using RF Sputtering System

In order to obtain a suitable ohmic contact with the lowest resistivity, chromium (Cr) thin films were deposited on a transparent conductive oxide (TCO) Indium Tin Oxide (ITO) by radio frequency (RF) sputtering method in argon atmosphere and its electrical properties were optimized. The deposition of Cr thin film has been performed for the layers with different thicknesses of 150, 300, and 600 nm at constant Ar gas flow of 30 SCCM. Results showed that the lowest contact resistivity belongs to the layer with 600 nm thickness. Furthermore Cr/ITO has been studied for five different RF powers of 100, 150, 200, 250, and 300 W for a 600 nm thickness Cr sample, which showed the lowest contact resistivity. On the other hand Cr/ITO has been studied for different flows of argon gas 10, 30, 50 and 70 SCCM, during the deposition with constant thickness of 600 nm Cr thin films. Our experimental results suggest that the best specific contact resistance was achieved at RF power of 150W, which was 4.7×10−6 Ωm2. The best specific contact for Cr/ITO has been obtained 4.5×10−6 Ωm2 at argon gas flow 10 SCCM with 600 nm thickness.

Combined study on conductive AFM and damascene process to visualize Nano-Scaled defects in Cr thin films on polymer substrate

The evolution of a direct observation technique for small-sized defects in a thin film is important in understanding of a water-vapor barrier layers. An investigation into the availability of direct observation techniques for detecting nano-scaled defects in a chromium thin film on a polymer substrate was performed. The best images of nano-scaled defects in Cr thin films were obtained using conductive atomic force microscopy (C-AFM) in conjunction with a damascene process. When a dielectric Al2O3 layer was filled into the defects, such as voids or grain boundaries, in the Cr coating via this damascene process, a distinctive conductivity image was obtained from C-AFM. The major role of the dielectric material of the Al2O3 layer, when filled into the nano-scaled defects in the Cr coating, was the generation of different values in conductivity during the C-AFM analysis. The results confirmed that the combination of C-AFM and the filling of the dielectric Al2O3 layer into the defects via the damascene process is a useful method for the direct observation of nano-scaled defects comprised of deep and narrow trenches in metallic thin films on a polymer substrate.

B224 凝縮熱伝達に及ぼすMEMS加工面の影響 : MEMS計測技術を利用した濡れ性の検討(OS-01:沸騰・凝縮伝熱および混相流の最近の進展(4))

Dropwise condensation(DWC) has high heat transfer coefficient. However, DWC may no maintain long period. In order to maintain DWC long enough, it is important to understand the effect of the surface condition. In the present paper, wettability of metal-sputtered surfaces was controlled by MEMS technology. The effect of several metal-sputtered surfaces, i.e., Cupper(Cu), Titanium(Ti), Silver(Ag) and Chromium(Cr) respectively, and the on the pattern of the condensation, i.e., DWC or FWC, was examined qualitatively. The surface condensation with sputtered thin Silver(Ag) and Chromium(Cr) films were DWC. On the other hand, the surface condensation with sputtered thin Cupper(Cu) and Titanium(Ti) films were FWC. When equivalence contact angle was over 72 degree, DWC was found. The other hand, when the angle was under 62 degree, FWC was observed.

Properties of Sputter Deposited Cr Thin Film on Polymer Substrate by Glancing Angle Deposition

Glancing angle deposition (GLAD) is a powerful technique to control the morphology and microstructure of thin film prepared by physical vapor deposition. Chromium (Cr) thin films were deposited on a polymer substrate by a sputtering technique using GLAD. The change in thickness and Vickers microhardness for the samples was observed with a change in the glancing angle. The adhesion properties of the critical load (Lc) by a scratch tester for the samples were also measured with varying the glancing angle. The critical load, thickness and Vickers microhardness for the samples decreased with an increase in the glancing angle. However, the thickness of the Cr thin film prepared at a 90o glancing angle showed a relatively large value of 50 % compared to that of the sample prepared at 0o. The results of X-ray diffraction and scanning electron microscopy demonstrated that the effect of GLAD on the microstructure of samples prepared by sputter technique was not as remarkable as the samples prepared by evaporation technique. The relatively small change in thickness and microstructure of the Cr thin film is due to the superior step-coverage properties of the sputter technique.

Microstructure and mechanical properties of chromium thin film implanted with nitrogen ions

Chromium films were deposited on 304 stainless steel using the hollow cathode discharge (HCD) method. The films were implanted with nitrogen ions at fluences of (1-3-5-7-10) × 1017 ions/cm2 and energy of 45 keg. The structure and surface topography of the implanted films were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The mechanical properties of the implanted films were investigated for micro-hardness, friction coefficient, and wear resistance. XRD results showed that fluencies of up to 7 × 1017 ions/cm2 did not cause formation of a CrN phase, but at 10 × 1017 ions/cm2, CrN and Cr2N phases were formed. AFM images indicated that increasing grain size increased roughness. As fluence increased, hardness and Young's modulus increased because of the formation the CrN and Cr2N phases. The friction coefficient results showed that, as fluence increased, the friction coefficient decreased. The results showed that increasing the fluence of nitrogen ion implantation changed the type of wear from abrasion to soft.

Time dependency of the laser-induced nanostructuring process of chromium layers with different thicknesses on fused silica

Nanostructures exhibit a raised importance in manifold application fields like electronics and optics. The laser irradiation of thin metal layers allows the fabrication of metal nanostructures induced by a melting and deformation process where the resultant structures are dependent on the laser and metal layer parameters. However, for an optimization of this process a detailed physical understanding is necessary. Therefore, the dynamics of the metal layer deformation process was measured by time-dependent reflection and transmission as well as shadow graph measurements at different KrF excimer laser parameters (laser fluence and number of laser pulses) and metal layer thicknesses were used. Magnetron-sputtered thin chromium films with a thickness from 10 to 100nm on fused silica substrates were studied. Based on the optical measurements the liquid phase lifetime of the metal was estimated and compared with the calculated lifetime using a simple thermodynamic model.

Impact of capillarity forces on the steady-state self-organization in the thin chromium film on glass under laser irradiation

Metal films on transparent substrates are widely used for mask production in lithography, and lasers are frequently applied for their patterning. Steady self-organization of a chromium thin film on the glass substrate to parallel metal lines under irradiation with partially overlapping highly astigmatic nanosecond laser pulses above the ablation threshold has been observed. Transformations in a chromium film were investigated experimentally and numerically. The theoretical model of the steady self-organization is presented and discussed. It was demonstrated that the capillarity convection force was responsible for the transformation process in the molten metal. It was shown that the thermo-capillarity (Marangoni) shear stress and the stress originating from a variation in the radius of curvature along the structure were equally important in the case of the steady self-organization process.

Manganese Precursor Selection and the Thermal Atomic Layer Deposition of Copper/Manganese Alloy Films

Our laboratory seeks to develop the growth of metallic first row transition metal thin films using atomic layer deposition (ALD). The microelectronics industry is calling for the growth of metallic first row transition metal films by the ALD method for a variety of applications, including copper metallization, seed layers for copper metallization, copper/manganese alloys for self-forming copper diffusion barriers, and magnetic alloys. The ALD growth of noble metal thin films has been explored extensively in the past ten years, due to the positive electrochemical potentials of these metal ions and relative ease of reduction to the metallic state. The low temperature ALD of high purity, low resistivity Cu films has been described, but ALD routes to the other metallic first row transition metal films remain poorly developed, largely because of the negative electrochemical potentials of most of the ions and a corresponding lack of powerful reducing co-reagents that can convert precursors in positive oxidation states to the metals. We will describe the synthesis, structure, and properties of a large series of new first row transition metal ALD precursors that combine high volatilities, high thermal stabilities, and high reactivities toward reducing agents. We will also report borane and other reducing agents that can react with the metal precursors to afford metallic films. Additionally, we will overview the thermal growth of metallic copper, nickel, cobalt, iron, manganese, and chromium thin films from these new precursors. Key advances include development of optimized ALD precursors with very similar ligands and chemistry, and identification of new reducing co-reagents that can rapidly reduce the positive oxidation state precursors to the metals.

Single-shot ablation threshold of chromium using UV femtosecond laser pulses

Single-shot ablation threshold for thin chromium film was studied using 266 nm, femtosecond laser pulses. Chromium is a useful material in the nanotechnology industry and information on ablation threshold using UV femtosecond pulses would help in precise micromachining of the material. The ablation threshold was determined by measuring the ablation crater diameters as a function of incident laser pulse energy. Absorption of 266 nm light on the chromium film was also measured under our experimental conditions, and the absorbed energy single-shot ablation threshold fluence was $$46 \pm 5$$ mJ/cm2. The experimental ablation threshold fluence value was compared to time-dependent heat flow calculations based on the two temperature model for ultrafast laser pulses. The model predicts a value of 31.6 mJ/cm2 which is qualitatively consistent with the experimentally obtained value, given the simplicity of the model.

Chromium thin film deposition on ITO substrate by RF sputtering

To obtain a suitable ohmic contact with the lowest resistivity, chromium (Cr) thin films were deposited on transparent conductive oxide indium tin oxide (ITO) by RF sputtering method in argon atmosphere and its electrical properties were optimized. The deposition of Cr thin film has been performed for the layers with thickness of 150, 300 and 600 nm in constant Ar gas flow of 30 SCCM. Results show that the lowest contact resistivity belongs to the layer with 600 nm thickness. Furthermore, Cr/ITO has been studied for five different RF powers of 100, 150, 200, 250 and 300 W. Experimental results show that specific contact resistance of Cr/ITO contact decreases in condition of depositing chromium thin films on ITO at higher RF powers. Analysis of SEM has been performed on the samples. The SEM micrographs show Cr thin films have smaller grains at RF power of 150 W, in comparison with other RF powers. The lowest specific contact resistivity for Cr/ITO has been obtained 4.7 × 10−2 Ω cm2 at RF power of 150 W with 600 nm thickness of chromium thin films.

Mechanisms of formation of sub- and micrometre-scale holes in thin metal films by single nano- and femtosecond laser pulses

Mechanisms of formation of sub- and micrometre-scale holes in thin silver and chromium films of variable thickness by tightly-focused single nanosecond IR laser pulses with fluences in the range of are studied by means of optical and scanning electron microscopy. At the minimal fluences above , the micrometre ( in radius) holes are produced in these films, accompanying the lateral heat conduction in the film during the pump laser pulse, cavitation at the metallic/glass interface and subsequent explosive removal of the molten film. At the fluences of much larger ( in radius) holes are formed in the film as a result of its heating by the erosive surface microplasma through the lateral heat conduction in the film during the plasma lifetime of the order of a few microseconds. Finally, at the maximal fluences (well above ), the sub-millimetre holes were produced in these films by intense shock waves, generated in the erosive microplasmas. The comparative analysis of the formation mechanisms for sub- and micrometre-scale holes in the same thin metal films by the single nano- and femtosecond laser pulses is provided.

Optical and electrical properties of very thin chromium films for optoelectronic devices

Establishing the optimal experimental conditions for the development of transparent metal contacts to be used in optoelectronic devices, such as organic light-emitting diodes and solar cells, is an important task. In this paper we present an overview of the development of very thin e-beam-deposited chromium films with high optical transparency. The surface morphology is investigated by scanning electron microscopy. The variation is examined of the films' electrical and optical properties (transmittance and complex refractive index) with the variation of the thickness and deposition rate. We observed that, for a given thickness of the chromium films, the absorption coefficient increases when the deposition rate is decreased. We also found that the thin films with a thickness of less than 10 nm show an average transmittance exceeding 60 % in the spectral range 400 – 1500 nm. The films' resistivity, ρ, is determined by the four-point probe method. The value of ρ varies in the range of 10−3 -10−4 Ω cm for chromium coatings in the thickness interval 5 – 100 nm. The results obtained show that very thin metal films could be an alternative to the transparent conductive oxides.

Dynamics of GDOES-induced surface roughening in metal interfaces

The roughness induced during glow-discharge optical-emission spectroscopy (GDOES) measurements has been reported to cause a loss of resolution during GDOES depth-profiling analysis. In this paper, we undertake for the first time a study of the dynamics of the surface morphology of chromium and titanium thin films (designed in mono and multilayer structures) under the impinging of GDOES incoming ions. We performed this study under the theoretical framework of the dynamic scaling theory, by analysing surface morphology changes, as measured ex-situ by AFM, with irradiation time. For single metal layers it was found that, after an initial surface smoothening, the surface undergoes a rapid steep roughening for both systems, with quite similar quantitative dynamics. Once this roughening ends a second temporal scaling regime arises, operating for long length scales with dynamics depending on the sputtering rate of the material. For the chromium layer, with a very high sputtering rate of 5.5 μm min(-1), this regime is consistent with the KPZ model, whereas for the titanium layer an EW scaling regime is indicated. These different scaling regimes are consistent with the development of larger surface slopes for the Cr system. In the multilayer systems, the initial roughness induced on the top Cr layer by GDOES has similar dynamics to that for single-layer Cr. However, a clear decrease in the roughness was observed once the underlying Ti layer, with a lower sputtering rate, was reached. This decrease in the induced roughness is maintained while the Ti layer is eroded. Therefore, choice of appropriate material (i.e. sputtering yield values) combinations and of their depth of location can enable tuning of GDOES-induced roughness and achieve substantial control over the depth profiling process.

Influence of Energy Nitrogen Ion Implantation on Structural and Mechanical Properties of Chromium Thin Film

Chromium thin films were deposited on 304 stainless steel using the hollow cathode discharge (HCD) method. Chromium films were implanted with nitrogen ions at different energies ((15-25-35-45) keV) and at a dose of 5×10 17 ions/cm 2 . The implanted films were characterized using x-ray diffraction (XRD), atomic force microscopy (AFM), microhardness testing, friction coefficient measurements, and wear mechanism study. The XRD results confirmed that increasing energy does not effect the formation of the CrN phase. AFM images showed that surface roughness changed proportionally to grain size after implantation. It was found that hardness increased as energy increased. From the friction coefficient measurement, it could be inferred that the friction coefficient decreased as energy increased. The wear mechanism for the un-implanted sample was abrasion, but it shifted to delamination and adhesive as energy increased.

Fabrication and Characterization of Thin-Film Nickel Hydroxide Electrodes for Micro-Power Applications

INTRODUCTION Micro power sources are very attractive for nano- and micro-scale devices, such as Point-of-Care medical diagnostics and Micro Electro Mechanical Systems, where only low power densities and capacities are required. In the present work, we report on the micro-fabrication of patterned α-Ni(OH)2 films which are suitable for rechargeable nickel metal hydride (Ni-MH) and nickel-zinc (Ni-Zn) micro-batteries as well as for micro-capacitors. The main objective of the current research is to investigate the influence of three-dimensional (3D) patterned structures on the mechanical stability as well as on the electrochemical performance of the electrode. ELECTRODE FABRICATION The patterned electrode is fabricated through multi-layered films which are deposited by employing e-beam evaporation, UV photolithography (using a negative KMPR photoresist), and electro-deposition techniques. In detail, thin films of chromium and nickel with a thickness of 40nm are deposited on glass and used as adhesion (seed) and current collector layers, respectively. NiOx/Ni(OH)2 is electro-deposited from NiCl2 solution followed by electro-precipitation of Ni(OH)2 films from Ni(NO3)2.6H2O aqueous solution to form a grid-like patterned layer. Figure 1 schematically depicts the fabrication process. MATERIALS & ELECTROCHEMICAL CHARACTERIZATION The chemical composition of the micro fabricated electrodes is characterized by employing X-Ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS). The feature size of the grid-like pattern is determined to be roughly 20 microns in height by using a mechanical profilometry technique. Figure 2 illustrates the XPS spectrum of the Ni(OH)2 electrode material based on the Ni2p3/2 spectrum. The electrochemical characteristics are studied using cyclic voltammetry (CV) in a 1M KOH electrolyte. Measurements are performed for unpatterned as well as patterned electrodes to investigate the influence of the 3D structure as shown in Figure 3. CONCLUSIONS We observe that electrode patterning considerably improves the adhesion of the α-Ni(OH)2 film to the nickel current collector layer. It is also found that the micro fabricated α-Ni(OH)2 electrode is reversible and diffusion limited according to the Randles-Sevcik linearity. Furthermore, the electrolyte concentration dependency is studied via CV which shows minimum concentration of around 0.2M required for good electrode REDOX reactions.

Correlation between mass-spectrometer measurements and thin film characteristics using dcMS and HiPIMS discharges

In this work, chromium thin films were deposited using dcMS and HiPIMS technologies. To compare these technologies, we analyzed the ion flux and the Cr coating microstructure in the same plasma conditions. Ion flux was measured with a mass spectrometer in time-averaged for both discharge and time-resolved for HiPIMS discharge. Time-averaged measurements provided important information. First, the low energetic part of the ion energy distribution function (IEDF) was similar in dcMS and HiPIMS and second the high energetic component was more prominent in the HiPIMS discharge. Time-resolved measurements showed that the high energetic part of the ion flux reached the mass spectrometer faster than the lowest part. It is only after the pulse end that most of the thermalized ions arrived and then cooled the flux. The correlation of these results with microstructure analysis shows that energetic particles induced a higher film density and a smoother surface in HiPIMS compared to dcMS discharge.

Reducing the incubation effects for rear side laser etching of fused silica

Laser-induced back side wet and dry etching (LIBWE and LIBDE) were developed for precise etching of transparent materials. However, LIBWE and LIBDE feature characteristics such as incubation effects and etching depth saturation, respectively, that can be unfavourable for applications in ultra-precision machining. Therefore, the techniques of LIBDE and LIBWE were combined in such a manner that the dielectric material was supplied with a thin-film-modified surface before etching by LIBWE.With this goal fused silica samples were covered with a thin chromium film for surface modification before LIBWE etching in acetone with 25ns KrF excimer laser pulses. Etching with the first pulse was observed. At laser fluences adequate for hydrocarbon LIBWE (1J/cm2) the etching rate for LIBDE is much higher than for LIBWE. In consequence, the etching rate decreases with increasing pulse number up to ten. The surface morphology depends very strong on the laser fluence and the pulse number. Smooth etchings were achieved at high fluences and low pulse numbers. However, uneven, wavy etched surfaces and micron pattern formation were observed for moderate and low laser fluences.

Platinum metallization for MEMS application

The adherence of Platinum thin film on Si/SiO2 wafer was studies using Chromium, Titanium or Alumina (Cr, Ti, Al2O3) as interlayer. The adhesion of Pt is a fundamental property in different areas, for example in MEMS devices, which operate at high temperature conditions, as well as in biomedical applications, where the problem of adhesion of a Pt film to the substrate is known as a major challenge in several industrial applications health and in biomedical devices, such as for example in the stents.1-4 We investigated the properties of Chromium, Titanium, and Alumina (Cr, Ti, and Al2O3) used as adhesion layers of Platinum (Pt) electrode. Thin films of Chromium, Titanium and Alumina were deposited on Silicon/Silicon dioxide (Si/SiO2) wafer by electron beam. We introduced Al2O3 as a new adhesion layer to test the behavior of the Pt film at higher temperature using a ceramic adhesion thin film. Electric behaviors were measured for different annealing temperatures to know the performance for Cr/Pt, Ti/Pt, and Al2O3/Pt metallic film in the gas sensor application. All these metal layers showed a good adhesion onto Si/SiO2 and also good Au wire bondability at room temperature, but for higher temperature than 400 °C the thin Cr/Pt and Ti/Pt films showed poor adhesion due to the atomic inter-diffusion between Platinum and the metal adhesion layers.5 The proposed Al2O3/Pt ceramic-metal layers confirmed a better adherence for the higher temperatures tested.