Piezoresistive properties of diamond like carbon films containing copper

In the present study diamond like carbon films containing copper (DLC:Cu) were deposited by reactive magnetron sputtering. Direct current (DC) sputtering and high power pulsed magnetron sputtering (HIPIMS) were used. The influence of the composition and structure on piezoresistive properties of DLC:Cu films was investigated. Structure of DLC:Cu films was investigated by Raman scattering spectroscopy and transmission electron microscopy (TEM). Chemical composition of the films was studied by using energy-dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). Particularly analysis of XPS O1s spectra revealed oxidation of Cu nanoparticles. Piezoresistive gauge factor of DLC:Cu films was in 3–6 range and decreased with the increase of copper atomic concentration. Tendency of the decrease of the gauge factor of DLC:Cu films with the increased D/G peak area ratio (decreased sp³/sp² carbon bond ratio) was observed. It was found that resistance (R) of DLC:Cu films decreased with the increase of Cu atomic concentration by logarithmic law. It is shown that a quasilinear increase of piezoresistive gauge factor with log(R) is in good accordance with percolation theory. Temperature coefficient of resistance (TCR) of DLC:Cu films was negative and decreased with copper amount in Cu atomic concentrations ranging up to ~ 40%. Very low TCR values (zero TCR) were observed only for DLC:Cu films with low gauge factor that was close to the gauge factor of the metallic strain gauges. Role of some possible mechanisms: copper amount as well as Cu cluster size on the value of gauge factor is discussed.     

Structural effects of nanocomposite films of amorphous carbon and metal deposited by pulsed-DC reactive magnetron sputtering

The relationship between metal-induced (W, Mo, Nb and Ti) structures and the surface properties of Me–DLC thin films is discussed. Nanocomposite films were deposited on c–Si wafers by pulsed-DC reactive magnetron sputtering controlling the gas ratio CH₄/Ar. The sputtering process of metals such as Ti, Nb and Mo (unlike the tungsten) in the presence of methane shows a low reactivity at low methane concentration. The deposition rate and the spatial distribution of sputtered material depend of Z-ratio of each metal. The surface contamination of metal targets by carbon, owing to methane dilution, limits the incorporation of metals into DLC films according to an exponential decay. Results of electron probe microanalysis and X-ray photoelectron spectroscopy indicate a C rich Me/C composition ratio for low relative methane flows. According to the depth profile by secondary ion mass spectrometry, the films are systematically homogeneous in depth, whereas at high carbon contents they exhibit a metal-rich interfacial layer on the substrate. Moreover, high resolution transmission electron microscopy has evidenced important structural modifications with respect to DLC standard films, with marked differences for each Me/C combination, providing nanodendritic, nanocrystallized or multilayered structures. These particular nanostructures favour the stress decrease and induce significant changes in the tribological characteristics of the films. This study shows the possibilities of controlling the amorphous carbon films structure and surface properties by introducing metal in the DLC matrix.     

Deposition of Indium Tin Oxide Films on Acrylic Substrates by Radiofrequency Magnetron Sputtering

Indium tin oxide (ITO) films were deposited onto acrylic substrates by rf magnetron sputtering. Low substrate temperature (<80°C) and low rf power (<28 W) were maintained during sputtering to prevent acrylic substrate deformation. The influence of sputtering parameters, such as rf power, target-to-substrate distance, and chamber pressure, on the film deposition rate, the electrical properties, as well as the optical properties of the deposited films was investigated. Both the refractive index and the extinction coefficient were derived. The high reflection at wavelengths greater than 3 μ made these sputtered ITO films applicable to infrared mirrors.     

Thermal stability of metal-doped diamond-like carbon fabricated by dual plasma deposition

Metal incorporation into amorphous diamond-like carbon films can provide superior properties as metal nano-clusters or nanocrystalline metallic carbides can be embedded in the carbon network. In this work, a filtered metal plasma cathodic arc technique is used to generate a metal plasma and acetylene is introduced to the metal plasma plume to deposit metal-containing DLC (Me-DLC) films and form nanocrystalline carbide phases in the amorphous carbon matrix. The films exhibit high thermal stability up to annealing temperatures of 500 °C as revealed by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. At treatment temperature over 500 °C, a large amount of hydrogen is lost from the Me-DLC films as shown by elastic recoil detection. Breakdown and structural collapse of the film at high temperature can be attributed to the breaking of C–H bonds. Consequently, the C–C networks become more graphite-like to facilitate the formation of volatile C–O and metal oxides phases.     

Strain sensitivity of nickel-containing amorphous hydrogenated carbon (Ni:a-C:H) thin films prepared by r.f. sputtering using substrate bias conditions

Thin films of nickel-containing amorphous hydrogenated carbon Ni:a-C:H were deposited by means of a reactive r.f. powered sputter process with different argon/ethene gas mixtures. The amount of incorporated nickel, measured by energy dispersive X-ray analysis (EDX) and the electrical conductivity of the films were obtained as a function of the ethene concentration in the processes, showing that the conductivity is strongly dependent on the nickel concentration in the films and may be varied over 8 orders of magnitude.The temperature coefficient of resistivity (TCR) and the strain sensitivity in terms of the gauge factor were measured for films under various process conditions. It turned out that low TCR values (300 ppm/K) and higher gauge factors of approx. 8 could be produced simultaneously, yet only with the help of an additional substrate r.f. bias power. In addition the long term stability of the produced resistors was improved by means of substrate bias sputtering. Therefore these films proved to be very promising candidates as strain gauge devices for sensors able to measure mechanical quantities such as pressure, force, weight and torque.     

Preparation and properties of sputtered “glassy” carbon films

Some remarkable “glassy” carbon films with densities from 0.5 to 1.79 have been prepared by sputtering from carbon targets. Conditions for the preparation of various carbon films by rf sputtering and data on the density, mechanical properties, microhardness, microstructure and crystal structure of the films formed are presented. Optimum sputtering conditions for obtaining mechanically stable films up to 40μ thick are described. It is shown that density and microhardness of the carbon can be controlled within wide limits, and both increase with decreasing deposition rate. The higher density carbon films adhere poorly to glass, while the low density carbon films on glass are stable. All sputtered carbon films are non-crystalline and have a grainy microstructure. Potential applications exclude corrosion protection but include novel catalyst supports.     

Controllable fabrication and temperature-resistance characteristics of ordered nanoporous Au and Pt films

In this work, the ordered nanoporous arrays of Au and Pt films are fabricated using anodized aluminum oxide (AAO) template based on the sputtering method. The presented synthetic strategy is scalable to large area by incorporating the deposition of a thin layer of Au or Pt. In addition, the grain size of Au and Pt nanoporous films is controlled with sputtering time. The thorough study of electrical transport properties for these metal films enables us to infer the nanoporous film morphology, and the evolution of the grain size with the change of sputtering time. In fact, the different physical behaviors are observed to occur in these metal films. The negative temperature coefficient of resistance (TCR) is visible for Pt nanoporous films, while Au nanoporous films show the positive TCR. With the increasing of sputtering time, the Pt grain size gradually becomes bigger, and the negative TCR properties weaken because the interface scattering of the electrons reduces. Therefore, the fabrication of metal nanoporous films with well-controlled physical properties might open new pathways for the growth of metal electrodes on AAO substrates for nanoelectronic devices.     

A DLC/W-DLC multilayered structure for strain sensing applications

The strain dependence in tungsten-containing diamond-like carbon (W-DLC) film was investigated. The W-DLC film was deposited onto Si substrate by plasma enhanced chemical vapor deposition and DC magnetron co-sputtering of tungsten metal target. The strain dependence of resistance was measured by four-point bending test under well controlled temperature condition. The observed dependence was linear one and calculated gauge factor is 6.1. The high value of the gauge factor is originated from the piezoresistive effect. In addition, double layered structure of DLC/W-DLC film was fabricated. The double layerness and interface structure were investigated by transmission electron microscope. No clear boundary between DLC and W-DLC was observed. This was because of the continuous carbon matrix from the bottom layer of W-DLC to top DLC layer.     

Low‐Temperature Co‐Fired Ceramic Substrates for High‐Performance Strain Gauges

Recent advances in the development of high gauge factor thin films for strain gauges prompt the research on advanced substrate materials. A glass ceramic composite has been developed in consideration of a high coefficient of thermal expansion (9.4 ppm/K) and a low modulus of elasticity (82 GPa) for the application as support material for thin‐film sensors. In the first part, constantan foil strain gauges were fabricated from this material by tape casting, pressure‐assisted sintering, and subsequent lamination of the metal foil on the planar ceramic substrates. The accuracy of the assembled load cells corresponds to accuracy class C6. That qualifies the load cells for the use in automatic packaging units and confirms the applicability of the low‐temperature co‐fired ceramic (LTCC) substrates for fabrication of accurate strain gauges. In the second part, to facilitate the deposition of thin‐film sensor structures to the LTCC substrates, pressure‐assisted sintering step is modified using smooth setters instead of release tapes, which resulted in fabrication of substrates with low average surface roughness of 50 nm. Titanium thin films deposited on these substrates as test coatings exhibited low surface resistances of 850 Ω comparable to thin films on commercial alumina thin‐film substrates with 920 Ω. The presented material design and advances in manufacturing technology are important to promote the development of high‐performance thin‐film strain gauges.     

DLC coating for video head

The effect of the thickness of DLCs sputtered on video heads upon the value of the playback signal and visibility of the gap in the ferrite surface was examined. It was found that DLCs improve the wear resistance of the heads, whereas the playback quality depends on the probability of the DLC peeling off during friction on the video tape. Technological regimes involving vacuum-pulsed arc sputtering of graphite in combination with ionic bombardment of the ferrite surface and the DLC were worked out. These regimes provide a good adhesion and smoothness of the film surface. Tests of video heads covered with DLCs showed that the wear resistance and the ‘still frame’ time of these heads are several times larger than those of standard video heads. A reliable and highly efficient commercial technology for the production of DLC video heads has been developed.     

Growth and Characterization of Tungsten Oxide Thin Films using the Reactive Magnetron Sputtering System

WO₃ thin film is one of the most important and applied metal oxide semiconductors that have attracted the scientist’s attention in recent decades. WO₃ thin films by two different methods: reactive and non-reactive RF magnetron sputtering deposited on soda lime glass. The effect of presence and absence of oxygen gas in system and RF power on structural, morphological and optical properties of thin films were investigated. The XRD analysis of the films shows the amorphous structure. Spectrophotometer analysis and calculation show that the optical properties of reactive sputtered layers were better than the non-reactive sputtered thin films. By changing deposition parameters, over 70 % transmission achieved for WO₃ films. The results showed that reactive sputtering method improved the optical properties of layers and increased band gap up to 3.49 eV and on the other hand reduced roughness of thin films. On the whole, presence of oxygen in the chamber during sputtering improved properties of WO₃ thin films.     

Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH₄/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp² carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.     

The optical properties of Ti-doped TiO2 nanoceramic films deposited by simultaneous rf and dc magnetron sputtering

The Ti-doped TiO₂ (TiO₂:Ti) nanoceramic films were deposited by simultaneous rf magnetron sputtering of TiO₂ and dc magnetron sputtering of Ti. When dc power increased, TiO preferentially formed and the deposited films had lower O/Ti atomic ratio, especially at low substrate temperature. With the decrease of substrate temperature, the TiO₂:Ti film had relatively high optical energy gap, therefore the absorption edge showed the blue shift. The nonlinear refractive indices of TiO₂:Ti films prepared at different dc powers and substrate temperatures were measured by Moiré deflectometry, and were of the order of 10^?8 cm² W^?1. By decreasing dc power and increasing substrate temperature, TiO₂:Ti film exhibited lower surface roughness, higher linear refractive index and lower stress-optical coefficient.     

Influence of deposition parameters on the dielectric properties of rf magnetron sputtered Ba(ZrxTi1−x)O3 thin films

Ba(Zr_xTi_1−x)O₃ (BZ_xT_1−x in short) thin films have been deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering and their dielectric properties have been characterized as a function of sputtering parameters. The BZ_xT_1−x thin films are amorphous when sputtered at rf power (R_p)=100 W and substrate temperature (S_T)=300 °C. The crystalline phase of the BZ_xT_1−x thin films appears when the substrate temperature increases from 300 to 400 and 500 °C, respectively, and the films have a high degree of (100) preferred orientation. The dielectric constant decreases with increasing measurement temperature, irrespective of the rf power and Zr content of the BZ_xT_1−x thin films. The BZ_0.3T_0.7 thin films have a low dielectric loss tangent irrespective of the sputtering parameters. The dielectric constant of the BZ_0.3T_0.7 thin film increases with increasing Zr·(Zr+Ti)⁻¹ ratio and deposition temperature but decreases with increasing working pressure. Besides, the dielectric constant suddenly increases from 244.0 to 284.1 when the rf power increases from 100 to 130 W, then it decreases from 284.1 to 270.0 when the rf power increases from 130 to 160 W. The dielectric constant also suddenly increases from 164.1 to 281.5 when the sputtering gas contains O₂ from 0 to 10%, but its variation is insignificant when the sputtering gas contains O₂ from 10 to 20%.     

Amorphous Ge‐Sb‐Se thin films fabricated by co‐sputtering: Properties and photosensitivity

Amorphous Ge–Sb–Se thin films were fabricated by a rf‐magnetron co‐sputtering technique employing the following cathodes: GeSe₂, Sb₂Se₃, and Ge₂₈Sb₁₂Se₆₀. The influence of the composition, determined by energy‐dispersive X‐ray spectroscopy, on the optical properties was studied. Optical properties were analyzed based on variable angle spectroscopic ellipsometry and UV‐Vis‐NIR spectrophotometry. The results show that the optical bandgap range 1.35‐2.08 eV with corresponding refractive index ranging from 3.33 to 2.36 can be reliably covered. Furthermore, morphological and topographical properties of selenide‐sputtered films studied by scanning electron microscopy and atomic force microscopy showed a good quality of fabricated films. In addition, structure of the films was controlled using Raman scattering spectroscopy. Finally, irreversible photoinduced changes by means of change in optical bandgap energy and refractive index of co‐sputtered films were studied revealing the photobleaching effect in Ge‐rich films when irradiated by near‐bandgap light under Ar atmosphere. The photobleaching effect tends to decrease with increasing antimony content.     

A diamond-like carbon film as a self-alignment layer for LCDs

Diamond-like carbon (DLC) films without H deposited with a DC magnetron in-line sputtering system have shown sufficient self-alignment properties towards liquid crystals (LC). The DLC film was successfully used as an alignment layer for LC without any alignment processes such as rubbing or atomic beam bombardment or UV irradiation. From the observations of the test cells, the LC director was aligning parallel to the substrate movement direction of the in-line sputtering system. The alignment property of the DLC films has been demonstrated by a contrast ratio value of close to 200. It appears that DLC film may have anisotropic structure that is interacting with LC to align.     

Application of diamond-like carbon films to the integrated circuit fabrication process

On account of their attractive properties, amorphous diamond-like carbon (DLC) films have been developed as resist materials for lithography and as hard coatings. In this paper, we investigate the etching properties of DLC films and the electrical properties of a pn junction fabricated using DLC films.Using a parallel-plate radio frequency plasma glow discharge, methane gas was decomposed for the deposition of the DLC films on a silicon substrate. Then oxygen was used to etch the films. Properties, such as the etching rate and the cross-sectional profile, were evaluated by atomic force microscopy (AFM). In order to produce the diode, DLC films were applied to resist materials as a part of the fabrication process.The etching rate of DLC films increases with decreasing oxygen pressure. We suspect that the high etching rate at low pressure from the negative bias voltage originates from the sputtering of accelerated ionic species. The bias voltage also increases with decreasing oxygen pressure. In order to estimate the shape of the etched edge, AFM images and cross-sectional profiles of etched DLC films were investigated as a function of oxygen pressure. At high pressure, isotropic etching by neutral radicals occurred, as the shape of the etched edge was not vertical. The top and bottom edges coincided vertically at low pressure because of the high bias voltage. The yield of excellent pn junctions fabricated using DLC films as resist materials was investigated as a function of deposition and etching pressure. From the results of the characteristics of the pn junction and the yield, for the integrated circuit fabrication process the optimum condition for both deposition and etching is at low pressure.     

Effect of sputtering power on piezoresistivity and interfacial strength of SiCN thin films prepared by magnetic sputtering

SiCN ceramics show large potential in high temperature pressure sensors with excellent stability up to 1000 °C, as it is changeling for the most of the existing pressure sensors to work stably at a temperature above 600 °C. However, bulk SiCN ceramics are not compatible to microelectronic processing and exhibit slow response due to viscoelasticity, it is necessary to propose alternative method to prepare SiCN functional structures. In this work, SiCN piezoresistive thin films are prepared by magnetron sputtering, and the influence of sputtering power on their piezoresistive properties and interfacial strengths are studied. The gauge factors of SiCN films range from 2786 to 4714 at various sputtering powers, which are significantly higher than the range from 46 to 1105 for existing piezoresistive thin films. Upon an optimal sputtering power of 75 W for silicon nitride target, the obtained SiCN sample show the largest gauge factors in a large range from 0.5 to 3.4 MPa. Furthermore, the SiCN thin films present high critical loads up to 36.5 N in scratch tests and indicate strong interfacial adhesion with substrate. This work provides an important reference for developing SiCN-based MEMS pressure sensors.     

Electrochemical characterization of diamond like carbon thin films

Diamond-like carbon (DLC) thin films were deposited from pure graphite target by DC magnetron sputtering method. Experimental parameters, i.e., substrate temperature and negative bias voltage, have been changed to finely tune the chemical bonding property (sp²/sp³) of the as-deposited DLC films. The as-deposited DLC films were characterized as anode materials for Li–ion batteries and special attentions were paid to the effects of sp²/sp³ ratio on the electrochemical properties of the DLC films. The results indicated that a high fraction of sp² bonding in the DLC films is preferred for high lithium storage capacity, flat and low charge voltage plateau, and long cycling retention.     

Structural characterization and properties enhancement of diamond-like carbon films synthesized under low energy Ne bombardment

Diamond-like carbon (DLC) films were synthesized by Ar⁺ sputtering graphite with concurrent Ne⁺ bombardment. Transmission electron microscopy diffraction revealed that some diamond crystals were distributed in the amorphous matrix of DLC films synthesized under Ne⁺ bombardment at an energy of 200 eV and ion current density of 0.19 mA cm⁻². X-ray photo electron spectra showed that the valence band of the DLC films was similar to that of diamond, and the binding energy of electrons was 284.9 eV. The DLC films possessed a high hardness of 42.14 GPa and excellent wear resistance. It was confirmed that the wide atomic intermixed film-substrate interface meant that the DLC films would improve greatly the wear-resistant properties of AISI 52100 steel if the DLC films were coated on its surface.