Thin Film Deposition Techniques Research Articles

Tailoring 3D structured nanofibrous nickel/gadolinium-doped ceria anodes for high-performance thin-film solid oxide fuel cells

Solid Oxide Fuel cells (SOFCs) operating at low temperature (450–600 °C) have been investigated in order to achieve rapid on/off, improved long-term stability and a wide selection of low cost materials, but decrease in ionic conductivity and slowed electrode kinetics still remain as challenges. Anodized aluminum oxide (AAO)-supported thin-film SOFCs (TF-SOFCs) fabricated by thin film deposition techniques exhibit exceptional performances at low temperature owing to extremely reduced electrolyte thickness and nanostructured electrodes. However, limited electrical conduction in anodes on AAO coerces metallic anodes and studies on cermet anodes are still insufficient. In this work, nickel-gadolinium doped ceria (Ni-GDC) thin-film anodes with different thickness are co-sputtered on AAOs with subsequently sputter-deposited yttria-stabilized zirconia electrolyte and platinum cathode. The TF-SOFCs represent maximum power densities of 223, 281, 353 and 177 mW/cm2 at 500 °C for Ni-GDC thickness of 300, 500, 800, 1000 nm, respectively. 800 nm thickness shows the best performance since porosity is maximized by columnar growth behavior during sputtering and lateral electrical conduction is consistently improved as the anode becomes thicker, which is confirmed by electrochemical impedance spectroscopy, field-emission scanning electron microscopy, and focused ion beam. Transmission electron microscopy/energy-dispersive X-ray spectroscopy are utilized to get structural and chemical information.

An overview of conventional and new advancements in high kappa thin film deposition techniques in metal oxide semiconductor devices

An overview of conventional and new advancements in high kappa thin film deposition techniques in metal oxide semiconductor devices

Automated Instrument for the Deposition of Thin Films Using Successive Ionic Layer Adsorption and Reaction

The development and improvement of thin film deposition techniques is an important research topic to obtain new materials at submicro and nano scale with high homogeneity and thickness control. Here, we designed and built an automated device for the deposition of binary or ternary compound films using Successive Ionic Layer Adsorption and Reaction (SILAR). The instrument is integrated by three different systems. The first system consists of a mobile platform of two degrees of freedom. The second part has an 8-bit microcontroller used to adjust the velocities along the horizontal and vertical axes. The third, the control system, uses a mobile app that can be implemented in smart devices, developed in free code software for programming and monitoring the main deposition parameters of the SILAR device such as the number of cycles, the immersion and emersion velocities, the residence time at each step, and the number of reactors. The performance of our instrument was verified through the deposition of PbS films, varying the number of deposition cycles to study the variations in the film thickness and structure, and assessed by profilometry, Raman spectroscopy, X-ray diffraction and atomic force microscopy. The system demonstrated is useful to obtain crystalline films with controllable thicknesses.

Investigating the variation in the optical properties of TiO2 thin-film utilized in bifacial solar cells using machine learning algorithm

Among various solar cell architectures, dye-sensitized solar cells (DSSCs) and perovskite solar cells have demonstrated the capability of being bifacial as both can be fabricated on conducting glass electrodes. In both cells, TiO2 plays a key role in the optoelectronic properties of the cell. Various studies have reported a range of recipes and deposition techniques for TiO2 thin films. Such variety introduces some uncertainties into the optical properties of the prepared films as well as in the process repeatability. Here, we utilized machine learning methods to correlate the film porosity to the film refractive index, making it capable of studying the impact of varying the fabrication and deposition techniques. Image postprocessing for scanning electron microscope measurements was utilized to estimate the film porosity, and the refractive index was calculated from the T–λ spectra. Four sets of samples with complete bifacial DSSCs were fabricated and characterized. They recorded a maximum current of 23.42 mA. They were fabricated using carboxymethyl cellulose-based suspension and deposited via the spin-coating sol-gel method. The fabricated cells showed an overall conversion efficiency of 7.9% under optical injection of the AM1.5G spectrum from the front side and LED indoor lighting from the counter electrode.

Y-doped HfO2 deposited by atomic layer deposition using a cocktail precursor for DRAM capacitor dielectric application

A Y-doped HfO 2 thin film deposited using a cocktail precursor for a DRAM capacitor dielectric application was investigated. It has been difficult to adapt HfO 2 , a potential high-dielectric-constant material, deposited by a typical thin-film deposition technique to actual devices owing to its low dielectric constant of approximately 20, resulting from its monoclinic-phase crystal structure. Although several methods have been investigated to increase the dielectric constant by crystal structure transformation to the tetragonal phase, which has a dielectric constant as high as approximately 40, the formation of the monoclinic phase was not successfully suppressed. In this study, the tetragonal-phase formation of HfO 2 thin films was investigated using a cocktail precursor consisting of Y and Hf precursors. The monoclinic formation suppression mechanism in the Y-doped HfO 2 thin film was determined from the physical and chemical analyses results. Moreover, the leakage current change caused by the introduced oxygen vacancy with respect to the Y dopant concentration was investigated. Improved electrical properties of the dielectric constant and leakage current were achieved with Y-doped HfO 2 .

Nanometer-thin L1-MnAl film with B2-CoAl underlayer for high-speed and high-density STT-MRAM: Structure and magnetic properties

The material development of magnetic tunnel junction with a perpendicular easy axis is in great demand to advance spin-transfer torque magnetoresistive random access memory (STT-MRAM) technologies. To realize high-speed and high-density STT-MRAM, a thin-film magnetic material with large perpendicular anisotropy and small spontaneous magnetization has great potential. Here, we develop a thin-film deposition technique for a-few-nanometer-thin L10-MnAl by sputtering and investigate its structure and magnetic properties. Utilization of the B2-CoAl buffer layer allows us to grow L10-MnAl with a large crystalline anisotropy of 8.5 × 105 J/m3, the small spontaneous magnetization of 0.62 T, and the tolerance for 400 °C annealing even at the MnAl thickness of 2 nm. We calculate the device properties based on the obtained material parameters and find that high retention properties, high-speed switching, and low write-error rate can be obtained at the single-digit-nm region, which are not readily achieved by conventional material systems. The results show the potential of L10-MnAl for high-density and high-speed STT-MRAM.

Enhanced thin film analysis via High Resolution RBS using the NEC CARBS system

Advancements in thin film deposition techniques can now produce films of only a few monolayers in thicknesses, with multiple applications emerging in the nano technology field. This maturing manufacturing technique is driving the need for diagnostics tools able to accurately measure depth profiles. To meet this need, the Compact Automated Rutherford Back-Scattering (CARBS) system is under development at National Electrostatics Corp. (NEC) for nanometer thin film analysis using High-resolution RBS (HRBS) within a 4 x 4meter footprint. We present the recent development of the system and demonstrate a study of HRBS applied to a 30nm CoAl alloy film. We compare the performance of the CARBS system with the conventional NEC HRBS end station and discuss the advantages of HRBS over SIMS method.

Machine learning-based analysis of the physio-chemical properties for the predictive thickness control of atomic layer deposition

Atomic layer deposition (ALD) is an outstanding thin film deposition technique based on the surface chemical reaction. As the conventional device fabrication method is reported to be ineffective under the 5nm process, ALD drew attention to its ability to control the film growth. To develop an efficient ALD process, controlling film thickness is one of the most important factors. The key requirement for the film thickness control is to understand their chemical reactivity upon adsorption on different substrate surfaces. However, the current research on viable ALD development have remained inefficient because of the expensive and time-consuming experiments. In this study, we aim to analyze and suggest a strategy for identifying the contribution of ALD process features on the device film thickness based on principal component analysis (PCA) method. First, the features of ALD experiment (Precursor properties, reactant type, substrate properties, operating conditions) are compiled to define the chemical dimension of ALD process. Then, the contributions of ALD experiment features on the thickness growth are analyzed by projecting ALD chemical dimension into the information space using PCA technique. As a result, we could identify highly sensitive features for ALD film growth and suggest the strategy for controlling film thickness. From providing the analysis for the film growth, we elucidate the importance of high dimension analysis of ALD process and improve the understanding on film growth control.

Fabrication of Spin Coater Device using Hematocrit Centrifuge with Vacuum Substrate Holder for Thin Film Deposition

One of the most important thin film deposition techniques on a silicon, quartz or sapphire substrate in the world is the spin coating method. Hematocrit centrifuge was used to elaborately manufacture the spin coating machine from affordable materials without vibrations. The vacuum holder substrate in this system is used for substrate adhesion. This method provides a dimensionally free substrate with appropriate adhesion for sedimentation upon high-speed spinning. A platinum thin film was deposited on a fluorine-doped tin oxide glass (FTO) substrate with a specific concentration of hexa-chloro-platinic acid. Platinum thin films were investigated by Field Emission Scanning Electron Microscope (FESEM) and UV-Vis spectroscopy. FESEM displays successfully produced platinum thin films. The results showed a platinum film transmittance decrement with increasing of hexachloro-platinic acid content. Therefore, the suggested spin coater in this work can deposit platinum thin films with high transmittance up to (98 a.u.).

Effect of nanostructured grains in co-sputtered Ni-GDC thin-film anode on methane conversion kinetics for low temperature solid oxide fuel cells operating on nearly dry methane

Direct-methane solid oxide fuel cells (DMSOFCs) have recently attracted substantial attention due to their simplified system, reduced cost, and the direct availability of methane fuel obtained from natural gas. Among oxygen-ion conductive materials, doped-ceria such as gadolinium-doped ceria (GDC) or samarium-doped ceria can be incorporated into Ni-based anodes to reinforce their coking resistance, enlarge their electrochemical reaction area, and improve the kinetics of the internal reforming/electrochemical oxidation of methane. To reduce the range of operating temperatures of DMSOFCs while maintaining their performance, the thin film deposition technique of magnetron sputtering was adopted in this work. An Ni-GDC thin-film anode and a Pt thin-film cathode were deposited on scandia-stabilized zirconia (ScSZ) electrolyte supports. This fuel cell was tested with directly supplied methane fuel (3% H2O) at 500 °C. The results demonstrated the effects of the GDC volume fraction in the anode—which was controlled by co-sputtering power—on open circuit voltage and electrochemical performance. The co-sputtered Ni-GDC anode was able to survive through 36-h operation, although there was some performance degradation. Field-emission scanning electron microscopy results revealed no formation of filamentous carbon on the Ni catalysts, despite the fact that both X-ray photoelectron spectroscopy and Raman spectroscopy analyses detected carbon coking. The relatively high performance and resistance to carbon coking of co-sputtered thin-film anode were attributed to its intrinsic small grain size.

Design of Hybrid Waveguide Structures for High-Efficiency Integrated Optical Superconducting Single Photon Detectors On Ti:LiNbO3Waveguides

A configuration of integrated optical superconducting single photon detectors on lithium niobate substrates based on conventional titanium in-diffused waveguides with hybrid waveguide structures for enhancing the detector efficiency is proposed and analyzed. The sensing element in the form of a meander-like superconducting nanowire from niobium nitride is covered with an additional hybrid waveguide from a dielectric material with a higher refractive index than the LiNbO3 substrate to increase the light absorption. A special mode converter in the region free from a superconducting nanostructure is used to excite a localized mode with the maximum absorption coefficient that strongly interacts with the superconductive nanostructure. Silicon and titanium dioxide are considered and compared as suitable materials for the hybrid waveguide structures. Silicon based structures give a higher light concentration and, hence, a higher absorption coefficient. However, they are very demanding to the technological accuracy. Titanium dioxide structures potentially can be produced by the standard thin-film deposition technique and contact photolithography. The estimated absorption coefficient of 1.31 dB/μm is four orders of magnitude higher than that for the detectors with a standard titanium in-diffused waveguide, and a high transformation mode efficiency opens a way for fabrication of integrated optical superconducting single photon detectors with the efficiency comparable with other competing material platforms.

Advanced Development of Sustainable PECVD Semitransparent Photovoltaics: A Review

Energy is the driving force behind the upcoming industrial revolution, characterized by connected devices and objects that will be perpetually supplied with energy. Moreover, the global massive energy consumption increase requires appropriate measures, such as the development of novel and improved renewable energy technologies for connecting remote areas to the grid. Considering the current prominent market share of unsustainable energy generation sources, inexhaustible and clean solar energy resources offer tremendous opportunities that, if optimally exploited, might considerably help to lessen the ever-growing pressure experienced on the grid nowadays. The R&D drive to develop and produce socio-economically viable solar cell technologies is currently realigning itself to manufacture advanced thin films deposition techniques for Photovoltaic solar cells. Typically, the quest for the wide space needed to deploy PV systems has driven scientists to design multifunctional nanostructured materials for semitransparent solar cells (STSCs) technologies that can fit in available household environmental and architectural spaces. Specifically, Plasma Enhanced Chemical Vapor Deposition (PECVD) technique demonstrated the ability to produce highly transparent coatings with the desired charge carrier mobility. The aim of the present article is to review the latest semi-transparent PV technologies that were impactful during the past decade with special emphasis on PECVD-related technologies. We finally draw some key recommendations for further technological improvements and sustainability.

Solution ALD: A Versatility Process for Various Material Growth

We have proposed and demonstrated a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. The technique can also be considered as a generalization of already established methods such as the ‘layer by layer’ growth or the ‘successive ion layer adsorption and reaction’ (SILAR). 'Solution ALD' (sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), specially the self-limiting growth and the ability to coat conformally deep pores. It has been already shown that it is possible to transfer standard reactions from gALD to sALD such as TiO2 deposition . However, sALD also offers novel opportunities such as overcoming the need for volatile and thermally robust precursors.To illustrate this, we establish sALD procedures for depositing films of non oxides layers such as Pb-compound deposition, MOF, selenides and sulfides. Those examples highlight how ionic, polar, or high-molecular weight precursors that only exist in the condensed phase are now rendered amenable to being utilized in surface-controlled thin film formation by sALD for depositing materials that would otherwise be more difficult or more expensive to achieve by gALD or hazardous. The deposition was achieved on small (2 cm*1 cm) and large samples (up to 10 cm*10 cm). The ALD behavior has been shown. The influence of the deposition parameters on the morphology, the crystalline structure and the chemical composition has been investigated by scanning electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. Additionally, the nucleation is studied in function of chemical pretreatment to control the gowth and allow selective deposition of CuS, ZnS and SnS.This particular ALD process offer the growth of high quality and crystalline layers in middle conditions with the use of low cost and environmental friendly precursors. Y. Wu, D. Döhler, M. Barr, E Oks,M. Wolf, L. Santinacci and J. Bachmann, Nano Lett. 2015, 15, 6379 J. Fichtner, Y. Wu, J. Hitzenberger, T. Drewello and J. Bachmann, ECS J. Solid State Sci. Technol. 2017, 6, N171 Figure 1

A Mechanistic Study of the HF Pulse in the Thermal Atomic Layer Etch of Crystalline and Amorphous HfO2

HfO2 is a high-k material that is crucial in semiconductor devices. Atomic-level control of material processing is required for the fabrication of thin films of this material at nanoscale device sizes. Atomic layer deposition (ALD) and thermal atomic layer etching (ALE) allow the fabrication of ultra-thin films for semiconductor device processing. ALD is a well-known metal oxide thin film deposition technique that enables a high level of control over film thickness. Thermal ALE, which is growing in importance, uses self-limiting halogenation (e.g. HF exposure) producing a non-volatile modified layer. Subsequent ligand exchange reactions remove up to a monolayer of the metal oxide. This modern approach for controlled etching is the reverse of ALD. In gate oxides, the use of amorphous materials is better than crystalline films as the lack of grain boundaries allow for a high breakdown voltage. Amorphous materials have a lower density than crystalline materials.Experimental studies have shown that HfO2 amorphous films have higher etch rates per cycle than crystalline HfO2 films regardless of the fluorination reactant. Given that it is difficult to investigate ALE reactions directly using experimental techniques, first-principles-based atomic-level simulations using density functional theory (DFT) can give deep insights into the precursor chemistry and the reactions that drive the etch of different materials. This contribution presents first-principles density functional theory modelling to examine the etch chemistry of crystalline and amorphous films of HfO2. HF molecules adsorb on the surface of HfO2 by forming hydrogen bonds and may remain intact or dissociate to form Hf-F and O-H bonds. The adsorption of one HF molecule at the bare surface of both the crystalline and amorphous models results in dissociative adsorption at all binding sites. For multiple HF adsorption, we find mixed molecular and dissociative adsorption of HF molecules at the bare surfaces of the crystalline and amorphous models of HfO2. We also present a thermodynamic analysis approach to compare reaction models representing the self-limiting (SL) and continuous spontaneous etch (SE) processes taking place during an ALE pulse.

Effect of Substrate-Thickness on Voltage Responsivity of MEMS-Based ZnO Pyroelectric Infrared Sensors

Pyroelectric infrared sensors incorporating suspended zinc oxide (ZnO) pyroelectric films and thermally insulated silicon substrates are fabricated using conventional MEMS-based thin-film deposition, photolithography, and etching techniques. The responsivity of the pyroelectric films is improved through annealing at a temperature of 500 °C for 4 h. The temperature variation and voltage responsivity of the fabricated sensors are evaluated numerically and experimentally for substrate thickness in the range of 1 to 500 μm. The results show that the temperature variation and voltage responsivity both increase with a reducing substrate thickness. For the lowest film thickness of 1 μm, the sensor achieves a voltage sensitivity of 3880 mV/mW at a cutoff frequency of 400 Hz. In general, the results presented in this study provide a useful source of reference for the further development of MEMS-based pyroelectric infrared sensors.

Transmissive nonlocal multilayer thin film optical filter for image differentiation

AbstractIt is well-known that a Fourier optical system can be used to perform specific computing tasks, such as image differentiation, with a superior speed and power consumption in comparison with digital computers, despite bulky optical components that are often required. Recently, there has been a surge in the interest to design much more compact nanophotonic structures, such as dielectric and metallic thin films, photonic crystals, and metasurfaces with a tailored angle-dependent (nonlocal) optical response, to directly perform image differentiation without additional lenses for Fourier transformation. Here, we present a straightforward platform, a multilayer dielectric thin film optical filter, fabricated using mature wafer-scale thin film deposition technique, with an optimized nonlocal optical response, for isotropic image differentiation in transmission mode for arbitrary input polarization. The proposed thin film filter may be conveniently coated at various transparent surfaces and inserted in machine vision or microscopy systems for enhanced, real-time image processing.

Local Inflammatory Response after Intramuscularly Implantation of Anti-Adhesive Plasma-Fluorocarbon-Polymer Coated Ti6AI4V Discs in Rats.

Orthopaedic implants and temporary osteosynthesis devices are commonly based on Titanium (Ti). For short-term devices, cell-material contact should be restricted for easy removal after bone healing. This could be achieved with anti-adhesive plasma-fluorocarbon-polymer (PFP) films created by low-temperature plasma processes. Two different PFP thin film deposition techniques, microwave (MW) and radiofrequency (RF) discharge plasma, were applied to receive smooth, hydrophobic surfaces with octafluoropropane (C3F8) or hexafluorohexane (C6F6) as precursors. This study aimed at examining the immunological local tissue reactions after simultaneous intramuscular implantation of four different Ti samples, designated as MW-C3F8, MW-C6F6, RF-C3F8 and Ti-controls, in rats. A differentiated morphometric evaluation of the inflammatory reaction was conducted by immunohistochemical staining of CD68+ macrophages, CD163+ macrophages, MHC class II-positive cells, T lymphocytes, CD25+ regulatory T lymphocytes, NK cells and nestin-positive cells in cryosections of surrounding peri-implant tissue. Tissue samples were obtained on days 7, 14 and 56 for investigating the acute and chronical inflammation (n = 8 rats/group). Implants with a radiofrequency discharge plasma (RF-C3F8) coating exhibited a favorable short- and long-term immune/inflammatory response comparable to Ti-controls. This was also demonstrated by the significant decrease in pro-inflammatory CD68+ macrophages, possibly downregulated by significantly increasing regulatory T lymphocytes.

Tuning Hybrid Nano-semiconductor-glass Via High Intensity Laser

Conceptually, the high intensity laser represents the simplest thin film deposition techniques that consists of both a target and a substrate holders housed in a vacuum chamber with a high powered pulsed laser as the external energy source for evaporation of target material (Semiconductor Glass). Using deposit thin laser films three ranges of frequencies were produced: (0-15,000 mJ/cm2) as a result tuning of semiconductor was satisfying condition, while the second, 0-33,000 mJ/cm2 as a result tuning of semiconductor had a stable condition and the last 0-100,000 mJ/cm2 as a result tuning of semiconductor was unstable condition. The results demonstrate a decrease in resistance due to charging the semiconductor glass by high intensity laser as well as a superior charge efficiency and lifetime of semiconductor glass coated cells compared to high intensity laser. The current increase in the charge appeared proportional with extra energy stored of the semiconductor glass coated electrodes at 2Co (>23%) in comparison with control. It is concluded that an increase in the capacity of semiconductor glass may address the main difficulty for utilizing the high intensity laser chemistry for future demands.

Enhanced thermal sensitivity in single metal thermocouple: significance of thickness-engineering of the metal layers

Single metal thermocouples (SMTs) have recently been developed with a new design concept of width-engineering of metal segments. In such designs, two segments of different micro-width are formed to obtain different levels of Seebeck effects. The variations in the Seebeck effect achieved from dissimilar segment width are small. In addition, the fabrication of such micro-width patterns requires special fabrication facilities such as photolithography or electron-beam lithography. In this paper, an alternative method is presented that has the potential to give high thermal sensing SMTs and requires no sophisticated facilities to fabricate. The method is based on thickness-engineering instead of width-engineering, and thus devices can be obtained from commonly available thin film deposition techniques. Constructing better thermal sensing SMTs is possible with this approach as thickness can be easily and conveniently varied down to nanoscale range which is necessary to achieve significant changes in the Seebeck effects from effectively utilizing size effects. As a result, a high thermal sensing bismuth based-SMT has been fabricated with a sensitivity of as high as 31 μV K−1, one of the highest values reported for SMTs. It is straightforward, more convenient over width-engineering approach and thus SMTs can be easily developed.

Critical processing temperature for high-performance protected silver mirrors

Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, in this work, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60 {\deg}C to 300 {\deg}C, and then the mirror samples underwent an environmental stress test at 80 {\deg}C and 80% humidity for 10 days. While all the mirror samples annealed below 200 {\deg}C showed negligible corrosion after undergoing the stress testing, those annealed below 160 {\deg}C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200 {\deg}C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation.