Sputtering Oxidation Research Articles

Damage to passivation contact in silicon heterojunction solar cells by ITO sputtering under various plasma excitation modes

Analysis of damage to passivation contact in heterojunction with intrinsic thin layer (HIT) solar cells by indium tin oxide (ITO) sputtering under various plasma excitation modes such as radio frequency (RF), direct current (DC), RF-superimposed DC, pulsed DC is presented. A significant degradation of effective minority carrier lifetime of the precursor cells at both low and high-level injections after the ITO deposition by sputtering technique was observed regardless of plasma excitation modes. We found that the main reason for this degradation was mainly due to the ion flux in the sputtering plasma rather than the ion kinetic energy. On the basis of the experimental and simulated results, we attributed the degradation of surface passivation quality mainly to the damage of the amorphous-silicon/crystalline-silicon interfaces rather than that of the intrinsic hydrogenated amorphous silicon layers. This degradation could be significantly reduced by the ITO deposition at a high temperature in which a trade-off between degradation and curing step was expected to occur. The cell performance of the HIT solar cells using the ITO films deposited by various plasma excitation modes at 180 °C was subsequently discussed. The ITO films deposited by the RF-superimposed DC mode exhibited a high potential as excellent opto-electrical properties and free sputter-induced damage electrodes for HIT solar cell applications. To our best knowledge, this is the first time that the ITO films deposited by the RF-superimpose DC mode are used as electrodes in the HIT solar cells.

Structure of uniform and high-quality Al-doped ZnO films by magnetron sputter deposition at low temperatures

Spatial distribution of highly energetic negative ions inherent in magnetron sputtering of oxides has long made low temperature deposition unsuitable for high quality films uniform over relatively large areas. Here we examine the distributions of structure as well as physical properties of magnetron sputtered Al-doped ZnO (AZO) films deposited at low temperatures (≤393 K) in which the bombardment from the negative oxygen ions was systematically studied by changing the discharge voltage (i.e., ion energy) and the substrate position (i.e., ion flux). The film structure was characterized by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy; and the electrical and optical properties were obtained by a Hall system and Spectroscopic Ellipsometry. We found (i) that uniform yet high crystallite quality films can be obtained only when the energy of the negative ions was set below a threshold; (ii) that the ion flux exerted an ever-decreasing effect on modifying the film structure as the ion energy was reduced; and (iii) that a set of structural criteria, incorporating crystallite quality (orientations, size, lattice spacing) and point defects, were derived for low resistivity AZO films. The benefit of lowering the ion energy is then explained in terms of the favorable competition between radiation-induced defect generation and the subsequent dynamic annealing. These findings may pave a way for large-area coating of high quality AZO films at low temperatures.

A Thin-Film Platform for Chemical Gas Sensors

In the study, a technique for formation of planar microheaters that make it possible to heat an active zone to a temperature higher than 500°С is proposed and successfully implemented. The developed heating elements are distinguished by low power consumption, short response time, and extremely high resistance to impact loads. The synthetic approaches used in the work (anodic oxidation, photolithography, and magnetron sputtering) feature manufacturability and scaling simplicity. This makes planar heating elements a promising platform based on which semiconductor and thermocatalytic sensors of toxic and explosive gases may be created.

Anomalous effects in the aluminum oxide sputtering yield

The sputtering yield of aluminum oxide during reactive magnetron sputtering has been quantified by a new and fast method. The method is based on the meticulous determination of the reactive gas consumption during reactive DC magnetron sputtering and has been deployed to determine the sputtering yield of aluminum oxide. The accuracy of the proposed method is demonstrated by comparing its results to the common weight loss method excluding secondary effects such as redeposition. Both methods exhibit a decrease in sputtering yield with increasing discharge current. This feature of the aluminum oxide sputtering yield is described for the first time. It resembles the discrepancy between published high sputtering yield values determined by low current ion beams and the low deposition rate in the poisoned mode during reactive magnetron sputtering. Moreover, the usefulness of the new method arises from its time-resolved capabilities. The evolution of the alumina sputtering yield can now be measured up to a resolution of seconds. This reveals the complex dynamical behavior of the sputtering yield. A plausible explanation of the observed anomalies seems to originate from the balance between retention and out-diffusion of implanted gas atoms, while other possible causes are commented.

Iridium Oxide pH Sensor Based on Stainless Steel Wire for pH Mapping on Metal Surface

A simple technique to fabricate the iridium oxide pH sensor is useful in several applications such as medical, food processing and engineering material where it is able to detect the changes of pH. Generally, the fabrication technique can be classified into three types: electro-deposition iridium oxide film (EIrOF), activated iridium oxide film (AIROF) and sputtering iridium oxide film (SIROF). This study focuses on fabricating electrode, calibration and test. Electro-deposition iridium oxide film is a simple and effective method of fabricating this kind of sensor via cyclic voltammetry process. The iridium oxide thick film was successfully electrodeposited on the surface of stainless steel wire with 500 cycles of sweep potential. A further analysis under FESEM shows detailed image of iridium oxide film which has cauliflower-liked microstructure. EDX analysis shows the highest element present are iridium and oxygen which concluded that the process is successful. The iridium oxide based pH sensor has shown a good performance in comparison to conventional glass pH sensor when it is being calibrated in buffer solutions with 2, 4, 7 and 9 pH values. The iridium oxide pH sensor is specifically designed to measure the pH on the surface of metal plate.

Mitigating target degradation in sputtering manganite thin films

In this paper, we address the issue of aging of oxide sputtering targets, using the example of La0.7Ca0.3MnO3 (LCMO), a material which is quite sensitive to the amount of oxygen. After prolonged use we find that the morphology of the films becomes poor: holes appear, the size of the steps between terraces becomes larger, the roughness increases, and electrical conductance in the metallic state at temperatures below the metal-insulator transition becomes smaller. We have performed experiments on reactive sputtering with water vapor in order to reverse their degradation. We discuss the growth and properties of films of LCMO on flat SrTiO3 substrates before and after the target treatment. We study both the morphological and structural changes in these films as well as the transport properties. The results indicate that a correct concentration of oxygen in the targets is important, and that a deficiency can be compensated by the water treatment, thus increasing the usable life time of targets.

Quantitative evaluation of high-energy O− ion particle flux in a DC magnetron sputter plasma with an indium-tin-oxide target

O− ion flux from the indium tin oxide (ITO) sputter target under Ar ion bombardment is quantitatively evaluated using a calorimetry method. Using a mass spectrometer with an energy analyzer, O− energy distribution is measured with spatial dependence. Directional high-energy O− ion ejected from the target surface is observed. Using a calorimetry method, localized heat flux originated from high-energy O− ion is measured. From absolute evaluation of the heat flux from O− ion, O− particle flux in order of 1018 m−2 s−1 is evaluated at a distance of 10 cm from the target. Production yield of O− ion on the ITO target by one Ar+ ion impingement at a kinetic energy of 244 eV is estimated to be 3.3 × 10−3 as the minimum value.

Thin-film encapsulation of organic electronic devices based on vacuum evaporated lithium fluoride as protective buffer layer

Encapsulation is indispensable for organic thin-film electronic devices to ensure reliable operation and long-term stability. For thin-film encapsulating organic electronic devices, insulating polymers and inorganic metal oxides thin films are widely used. However, spin-coating of insulating polymers directly on organic electronic devices may destroy or introduce unwanted impurities in the underlying organic active layers. And also, sputtering of inorganic metal oxides may damage the underlying organic semiconductors. Here, we demonstrated that by utilizing vacuum evaporated lithium fluoride (LiF) as protective buffer layer, spin-coated insulating polymer polyvinyl alcohol (PVA), and sputtered inorganic material Er2O3, can be successfully applied for thin film encapsulation of copper phthalocyanine (CuPc)-based organic diodes. By encapsulating with LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films, the device lifetime improvements of ~10 and 15 times can be achieved. These methods should be applicable for thin-film encapsulation of all kinds of organic electronic devices. Moisture-induced hole trapping, and Al top electrode oxidation are suggest to be the origins of current decay for the LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films encapsulated devices, respectively.

Indium tin oxide sputtering damage to catalytic chemical vapor deposited amorphous silicon passivation films and its recovery

We investigated the influence of indium tin oxide (ITO) sputtering damage to various types of amorphous silicon (a-Si) passivation films deposited by catalytic chemical vapor deposition. Intrinsic (i-) a-Si, n-type (n-) a-Si/i-a-Si, and p-type (p-) a-Si/i-a-Si stacked films were prepared on crystalline Si, and ITO was sputtered at various temperatures and RF powers, followed by post-annealing at 200°C. Effective minority carrier lifetime (τeff) of almost all the samples decreases drastically after sputtering, while τeff of the samples with ITO sputtered at room temperature recovers significantly by post-annealing. Annealing before sputtering and sputtering at lower RF power leads to more effective recovery of τeff. The samples with ITO sputtered to an n-a-Si/i-a-Si stack show large τeff recovery, while the samples with ITO sputtered to a p-a-Si/i-a-Si stack show much smaller τeff recovery. τeff recovery after ITO sputtering thus depends on the types of a-Si passivation films, which may be related to the modification of band alignment by the existence of ITO.

Analysis of Sputtering Damage on I–V Curves for Perovskite Solar Cells and Simulation with Reversed Diode Model

Tin-doped indium oxide (ITO) sputtering is known as a damaging cause on organic hole transporting material in solar cells. In order to gain more insights into the reasons for poor device performance of perovskite solar cells by the ITO sputtering on Spiro-OMeTAD, here we present an in-depth study by I–V simulation analysis using corresponding equivalent circuit models. First, experimental I–V data were obtained for the perovskite solar cells with ⟨FTO/TiO2(dense)/TiO2(mesoporous)/CH3NH3PbI3/Spiro-OMeTAD/ITO/Au⟩ configuration. An Au layer (t = 50 nm) was deposited on the ITO as a contact layer. The simulation studies indicated that sputtering of ITO onto Spiro-OMeTAD introduced a reverse Schottky diode and an additional diode to the device that could be relating the sputtering damage of the Spiro-OMeTAD layer. By considering the parameter of the reverse diode element as a function of sputtering time, it was found that the barrier height of the reverse Schottky diode was enhanced by the sputtering damage ag...

Square-inch 2D-arrays of Au nanodisks fabricated by sputtering Au onto anodic aluminum oxide templates for SERS applications

Two-dimensional (2D) arrays of gold nanodisks (Au NDs) with different sizes of 75, 95 and 115 nm, with the distances between NDs of 10, 30 and 50 nm were fabricated on square-inch substrates. The optimal conditions regarding the thickness of anodic aluminum oxide (AAO) template, sputtering time and annealing temperature for Au, lift-off the walls of AAO template for getting the highest quality 2D arrays of Au NDs have been determined. Morphology and surface plasmon resonance (SPR) absorption of the 2D arrays of Au NDs were examined by using appropriate techniques. The 2D arrays of fabricated Au NDs show different SPRs peaking in the spectral range of 600–1600 nm, which are very promising for surface-enhanced Raman scattering (SERS)-based sensor applications. As an example for the potential use of fabricated SERS substrates, we have demonstrated the detection of methamidophos at various concentrations ranging from 1 ppb to 103 ppm. Moreover, the method we have used to fabricate the 2D arrays of Au NDs can be applied to other kinds of metals or alloys just by varying the targets in the sputtering process.

Science and technology of cuprate-based high temperature superconductor thin films, heterostructures and superlattices—the first 30 years (Review Article)

During the three decades after the discovery of superconductivity at high temperatures in copper oxides, intense research activities generated a tremendous progress in both, mastering the scientific challenges underpinning the understanding of the properties of these chemically and structurally complex materials as well as achieving a mature technology in preparing single phase bulk specimens—including single crystals—and epitaxially grown single crystalline thin films. This review covers in addition to more basic physics oriented developments mainly technological aspects of complex oxide thin film deposition as an enabling technology to explore the physics of these materials. It consists of two parts: after a brief introduction to the materials development prior to the discovery of superconducting copper oxides, a description of the relevant properties of copper oxide superconductors with focus on YBa2Cu3O7−δ is given, followed by the coverage of essentials of complex oxide thin film deposition technology with the copper oxides at its core. Here, the major physical vapor deposition technologies (evaporation and oxide molecular beam technology, sputtering and pulsed laser deposition) are described followed by an overview of substrate requirements to deposit high quality thin films. Opportunities by choosing special substrates with unique properties far beyond the usual mechanical support for a film are introduced with examples aside from usual lattice mismatch induced strain effects. One is the continuous modification of the strain state by poling ferroelectric oxide substrates linked to a piezoelectric effect, the other is the nanoscale tailoring of substrate step-and-terrace structures resulting in a controllable generation of planar defects in complex oxides, thus contributing to the physics of flux-line pinning in cuprate superconductors. In the second part of this review, first some highlights of single layer thin film research are given such as to tailor thin film orientation, generating well defined antiphase boundaries in YBa2Cu3O7−δ thin films as flux-line pinning centers as well as contributions to understand fluctuation conductivity in relation to the pseudogap state. In the last section new developments in high Tc cuprate based heterostructures and superlattices are reviewed with a special focus on the opportunities offered by interface-induced electronic interactions.

Fabrication of iridium oxide neural electrodes at the wafer level

Electro-deposition, electrical activation, thermal oxidation, and reactive ion sputtering are the four primary methods to fabricate iridium oxide film. Among these methods, reactive ion sputtering is a commonly used method in standard micro-fabrication processes. In different sputtering conditions, the component, texture, and electrochemistry character of iridium oxide varies considerably. To fabricate the iridium oxide film compatible with the wafer-level processing of neural electrodes, the quality of iridium oxide film must be able to withstand the mechanical and chemical impact of post-processing, and simultaneously achieve good performance as a neural electrode. In this study, parameters of sputtering were researched and developed to achieve a balance between mechanical stability and good electrochemical characteristics of iridium oxide film on electrode. Iridium oxide fabricating process combined with fabrication flow of silicon electrodes, at wafer-level, is introduced to produce silicon based planar iridium oxide neural electrodes. Compared with bare gold electrodes, iridium oxide electrodes fabricated with this method exhibit particularly good electrochemical stability, low impedance of 386 kΩ at 1 kHz, high safe charge storage capacity of 3.2 mC/cm2, and good impedance consistency of less than 25% fluctuation.

Preparation and Blood Compatibility of Multilayers on the Surface of Medical NiTi Alloy

In this paper, the TiO2 film and Ti/TiN/TiO2 multilayers were prepared by anodic oxidation and RF magnetron sputtering technology on surface of NiTi shape memory alloy, respectively. The structure and surface morphology of films were systematically studied by X ray diffracmeter (XRD) and scanning electron microscope (SEM); blood compatibility was researched by kinetic clotting time and platelets adsorption experiment. The result showed that, blood compatibility was improved in varying degrees after surface treatment. And the multilayer which was deposited on NiTi alloy by RF reactive magnetron sputtering after the method of constant voltage anodization had optimal Anti-clotting properties.

Comparing Microstructures of ITO Sputtering Targets Prepared by Tin Doped Indium Oxide Powders and In2O3-SnO2 Mixed Powders

Abstract Indium Tin Oxide sputtering target (ITO) is widely used in the formation of electrically transparent thin films, which adopt direct current magnetron sputtering process for electrodes in flat panel displays, solar cells, gas sensors and so on. In order to improve ITO thin film property, ITO sputtering target requires high purity, homogeneous microstructure, high density and high electrical conductivity. In the present paper, ITO sputtering targets were fabricated using In2O3-SnO2 mixed powders and tin doped indium oxide powders. Meanwhile, their discrepancies in microstructure and sintering mechanism, especially grain size distribution, grain morphology, major element distribution and sintering rate, were studied. The results show that the sintering rate of the mixed powders is faster than that of the doped powders, but it is difficult to obtain homogeneous microstructure for the mixed powders. In contrast, it is easy to obtain the ITO sputtering target with homogeneous microstructure using the doped powders, under the condition that the decomposition of indium oxide is inhibited in process of sintering. These results are helpful to fabricate ITO sputtering target with good microstructure, while decrease nodulation and improve production efficiency.

Correlation between dry etching resistance of Ta masks and the oxidation states of the surface oxide layers

Mechanisms of dry etching resistance of Ta masks, which are widely used for magnetic random access memory etching processes, have been investigated for a better understanding of their faceting characteristics. In magnetic-material etching processes by CO/NH3 or CH3OH plasmas, CO+ ion is considered as one of the most dominant ion species irradiating the substrate surface. An earlier study by Li et al. [J. Vac. Sci. Technol. A 33, 040602 (2015)] has shown that the Ta sputtering yield by CO+ ion irradiation depends strongly on the ion irradiation angle and the level of the surface oxidation. In this study, the primary focus is placed on the effects of surface oxidation and physical sputtering only (without possible chemical effects of carbon) on the etching rate of Ta, and the etching characteristics of Ta and Ta2O5 have been examined with Ar+ and/or oxygen ion beams. It has been found that there is a strong negative correlation between the etching rate of Ta and the oxidation states of the surface oxide layer formed during the etching process; the higher the oxidation states are, the lower the etching rate becomes. The results indicate that a strong propensity of a Ta mask to taper by irradiation of oxidizing ions (i.e., strong ion-irradiation-angle dependence of the Ta etching rate) arises from less efficient oxidation of a tapered surface by incident oxidizing ions, which enter the surface with an oblique angle.

Characterization and properties of duplex a-C:H/MAO coatings on magnesium alloy using combined microarc oxidation and hybrid magnetron sputtering

The combined microarc oxidation (MAO) and magnetron sputtering deposition process was used to deposit duplex a-C:H/MAO and Ti-a-C:H/MAO coatings on AM80 magnesium alloy. The microstructure, mechanical properties and tribological behavior of the two duplex coatings were investigated. The experimental results showed that the a-C:H and Ti-a-C:H top films on Si substrates were dense and had a low G peak position and ID/IG ratio, compared with the hydrogen-free amorphous carbon films. Numerous micropores were found on the duplex a-C:H/MAO and Ti-a-C:H/MAO coatings together with low values of hardness (H) and elastic modulus (E), which also showed good binding strength with the Mg alloy substrates. Compared to MAO treated substrate used for the protection of the Mg alloy, the duplex a-C:H/MAO and Ti-a-C:H/MAO coatings still had stable and low value of friction coefficient, even though the surface of the duplex coatings was rough and porous. Furthermore, the mechanism of friction reduction of the two duplex coatings on the Mg alloy substrates was discussed.

Structural evolution of cobalt oxide–tungsten oxide nanowire heterostructures for photocatalysis

Tungsten oxide (WO3) and cobalt tungstate (CoWO4) decorated one-dimensional cobalt oxide (Co3O4) nanowire heterostructures were fabricated through a facile and cost-effective approach. The process includes vapor–solid growth of cobalt oxide nanowires via a thermal oxidation method and sputtering coating of tungsten oxide on the standing Co3O4 nanowires. To further modulate the structure and/or morphology and improve the crystallization of tungsten oxide, the product was subjected to a post-annealing process, which resulted in free-standing Co3O4–WO3/CoWO4 multi-component nanowire heterostructures. The crystal structures, morphologies, and chemical composition at each fabrication stage were studied in detail using microscopy and spectroscopy. The investigation for the first time showed the dry processing route for formation of such novel nanowire heterostructures. The photocatalytic performance and behavior of such nanowire heterostructures were further demonstrated for the degradation of water-contaminating organics (via a phenol photodegradation process). The photocatalytic efficiency of the final nanowire heterostructures was estimated to be increased by ∼30% for both visible and UV illumination as compared with the as-produced Co3O4 nanowires.

Growing LaAlO3/SrTiO3 interfaces by sputter deposition

Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showed the same high degree of epitaxy and atomic order as is made by pulsed laser deposition. However, the high pressure sputtering of oxides is not trivial and number of parameters are needed to be optimized for epitaxial growth. Here we elaborate on the earlier work to show that only a relatively small parameter window exists with respect to oxygen pressure, growth temperature, radiofrequency power supply and target to substrate distance. In particular the sensitivity to oxygen pressure makes it more difficult to vary the oxygen stoichiometry at the interface, yielding it insulating rather than conducting.

Switching Behavior of Titania-Zinc Oxide Composites Thin Films

Single layer of titanium dioxide (TiO2) is common metal oxide in fabricating memristor device. In this study, two types of memristor with composite metal oxide thin films will be demonstrated. The two types of memristor are titanium dioxide (TiO2) thin film coated on zinc oxide (ZnO) thin film and ZnO coated on TiO2 thin film. Sol-gel spin coating method was to coat metal oxide thin film and sputtering method for depositing the metal contact. Platinum (Pt) was selected as the top electrode and indium tin oxide (ITO) as the bottom electrode. The electrical characteristics were defined by performing I-V measurement using two point probe equipment. I-V characteristics showed shape of pinched hysteresis loop for both samples. Sample with TiO2 coated on ZnO has slightly higher Roff/Ron ratio than sample ZnO coated on TiO2 which means it more memristive than another one. The cross-section of sample with TiO2 coated on ZnO had been performed as well by using Field-Emission Scanning Electron Microscopy (FESEM).