Thin Film Fabrication Techniques Research Articles

Preventing unwanted atomic layer deposition by liquid sealing

Atomic layer deposition (ALD) is an essential thin film fabrication technique widely used in electronic and energy systems, but avoiding ALD in untargeted areas has been a long-standing challenge that excludes the possibility of creating patterns through bottom-up processes. We present a liquid sealing strategy to prevent unwanted ALD by combining shadow masks with viscous perfluoropolyether oil that conformally fulfills all gaps between the mask and substrate down to the molecular level. Due to the anti-adsorption and non-defective nature of the liquid sealant, ALD molecules are forced away from the masking areas, resulting in order-of-magnitude improvements in the patterning resolution compared with conventional shadow masks. The liquid sealant does not change the growth rate and film properties of ALD oxides and can be easily removed by solvents. This liquid sealing strategy applies to a variety of shadow masks (e.g., curved mask and anodic aluminum oxide), substrates (e.g., silicon, plastic, and elastomer), patterning materials (e.g., oxide and metal), and deposition methods (e.g., sputtering and thermal evaporation), providing new insights for bottom-up pattern fabrications.

Magnetron Sputtered Lead Titanates Thin Films for Pyroelectric Applications: Part 1: Epitaxial Growth, Material Characterization.

Pyroelectric materials, are those materials with the property that in the absence of any externally applied electric field, develop a built-in spontaneous polarization in their unit cell structure. They are regarded as ideal detector elements for infrared applications because they can provide fast response time and uniform sensitivity at room temperature over all wavelengths. Crystals of the perovskite Lead Titanate (PbTiO3) family show pyroelectric characteristics and undergo structural phase transitions. They have a high Curie temperature (the temperature at which the material changes from the ferroelectric (polar) to the paraelectric (nonpolar) phase), high pyroelectric coefficient, high spontaneous polarization, low dielectric constant, and constitute important component materials not only useful for infrared detection, but also with vast applications in electronic, optic, and Micro-electromechanical systems (MEMS) devices. However, the preparation of large perfect, and pure single crystals of PbTiO3 is challenging. Additionally, difficulties arise in the application of such bulk crystals in terms of connection to processing circuits, large size, and high voltages required for their operation. A number of thin film fabrication techniques have been proposed to overcome these inadequacies, among which, magnetron sputtering has demonstrated many potentials. By addressing these aspects, the review article aims to contribute to the understanding of the challenges in the field of pyroelectric materials, highlight potential solutions, and showcase the advancements and potentials of pyroelectric perovskite series including PbZrTiO3 (PZT), PbxCa1-x (PZN-PT), etc. for which PbTiO3 is the end member. The review is presented in two parts. Part 1 focuses on material aspects, including preparation methods using magnetron sputtering and material characterization. We take a tutorial approach to discuss the progress made in epitaxial growth of lead titanate-based ceramics prepared by magnetron sputtering and examine how processing conditions may affect the crystalline quality of the growing film by linking to the properties of the substrate/buffer layer, growth substrate temperature, and the oxygen partial pressure in the gas mixture. Careful control and optimization of these parameters are crucial for achieving high-quality thin films with desired structural and morphological characteristics.

Roll-to-Roll Printing of Anomalous Nernst Thermopile for Direct Sensing of Perpendicular Heat Flux.

The anomalous Nernst effect (ANE) converts heat flux perpendicular to the plane into electricity, in sharp contrast with the Seebeck effect (SE), enabling mass production, large area, and flexibility of their devices through ordinary thin-film fabrication techniques. Heat flux sensors, one of the most promising applications of ANE, are powerful devices for evaluating heat flow and could lead to energy savings through efficient thermal management. In reality, however, SE caused by the in-plane heat flux is always superimposed on the measurement signal, making it difficult to evaluate the perpendicular heat flux. Here we fabricate ANE-type heat flux sensors that selectively detect the perpendicular heat flux by adjusting the net Seebeck coefficient in their thermopile circuit with mass-producible Roll-to-Roll sputtering methods. The direct sensing of perpendicular heat flux using ANE-based flexible thermopiles, as well as their simple fabrication process, paves the way for the practical application of thin-film thermoelectric devices. This article is protected by copyright. All rights reserved.

Thin film charged particle detectors

Silicon tracking detectors have grown to cover larger surface areas up to hundreds of square meters, and are even taking over other sub-detectors, such as calorimeters. However, further improvements in tracking detector performance are more likely to arise from the ability to make a low mass detector comprised of a high ratio of active sensor to inactive materials, where dead materials include electrical services, cooling, mechanical supports, etc. In addition, the cost and time to build these detectors is currently large. Therefore, advancements in the fundamental technology of tracking detectors may need to look at a more transformative approach that enables extremely large area coverage with minimal dead material and is easier and faster to build. The advancement of thin film fabrication techniques has the potential to revolutionize the next-to-next generation of particle detector experiments. Some thin film deposition techniques have already been developed and widely used in the industry to make LED screens for TVs and monitors. If large area thin film detectors on the order of several square meters can be fabricated with similar performance as current silicon technologies, they could be used in future particle physics experiments. This paper aims to review the key fundamental performance criteria of existing silicon detectors and past research to use thin films and other semi-conductor materials as particle detectors in order to explore the important considerations and challenges to pursue thin film detectors.

Recent Advances and Challenges in Thin-Film Fabrication Techniques for Low-Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are amongst the most widely used renewable alternative energy systems with near-zero carbon emission, high efficiency, and environment-friendly features. However, the high operating temperature of SOFCs is still considered a major challenge due to several issues regarding the materials’ corrosion, unwanted reactions between layers, etc. Thus, low-temperature SOFCs (LT-SOFCs) have gained significant interest during the past decades. Despite the numerous advantages of LT-SOFCs, material selection for each layer is of great importance as the common materials have not shown a desirable performance so far. In addition to the selection of the materials, fabrication techniques have a great influence on the properties of the SOFCs. As SOFCs with thinner layers showed lower polarisation resistance, especially in the electrolyte layer, different thin-film fabrication methods have been employed, and their effect on the overall performance of SOFCs has been evaluated. In this review, we aim to discuss the past and recent progress on the materials and thin-film fabrication techniques used in LT-SOFCs.

The Effect of Thin Film Fabrication Techniques on the Performance of rGO Based NO2 Gas Sensors at Room Temperature

Reduced graphene oxide (rGO) has attracted enormous interest as a promising candidate material for gas detection due to its large specific surface areas. In our work, rGO films were fabricated on a large scale using dip-coating and spin-coating methods for the detection of nitrogen dioxide (NO2) gas at room temperature. The influence of different test environments on the sensing performance, including the test atmosphere, gas flow and gas pressure was evaluated. The response time of the dip-coating method was 573 s with a long recovery period of 639 s and for the spin-coating method, the response time and recovery time was 386 s and 577 s, respectively. In addition, the spin-coated sensor exhibited high selectivity to NO2, with the response increasing by more than 20% (for 15 ppm NO2) as compared with that for HCHO, NH3, and CH4. Our results indicated that the spin coating method was more suitable for rGO-based gas sensors with higher performance.

Synthesis of bismuth sulphoiodide thin films from single precursor solution

Bismuth sulphoiodide (BiSI) is considered as an excellent absorber material for toxicity-free photovoltaics (PV). Nevertheless, its applications in thin-film PV are often limited by the lack of pure phase thin-film fabrication techniques. Here, we design a novel precursor composition to fabricate pure phase thin-films by conventional spin-coating route. The as-prepared thin-films are characterized by X-ray diffraction studies, optical absorption spectroscopy, X-ray photoelectron spectroscopy, and transmission electron spectroscopy to confirm the phase purity. The thin-films also exhibit decent photoconductivity which demonstrate its potential as a non-toxic, air-stable absorber materials for PV.

Effect of Mg on structural, morphological and optical properties of Mg-doped V2O5 nanostructures

The spray pyrolysis is the simple and most promising thin-film fabrication technique in the deposition of Vanadium pentoxide (V2O5) thin film. Thin films of pure V2O5 and Magnesium (Mg) doped V2O5 were fabricated by spraying precursor solution on a glass substrate by spray pyrolysis at 350 °C. The doping concentrations of 1, 3, 5, & 10 wt% of Mg deposited followed by the heat treatment process at 350 °C. Field emission scanning microscopy (FESEM) and atomic force microscope (AFM) images have been used to study the morphology of the film showed the presence of white nanoparticles and surface roughness thereby effect of doping have been noticed. The XRD study shows the increase in the growth of film in (200) direction and enhancement in crystallite size with increase in doping. EDAX study confirms the presence of vanadium and doped Magnesium. Optical property study using UV–visible spectroscopy shows a rapid decrease in absorbance whereas transmittance increases with an increase in wavelength and also observed varying optical bandgap (Eg) from 3.55 eV to 3.75 eV for pure and Mg-doped V2O5 thin films. Compared to other transition metals, V2O5 exhibits properties appropriate for lithium-ion batteries and sensor applications at very low Mg-doping concentrations.

Preparation and Characterization of NbxOy Thin Films: A Review

Niobium oxides (NbO, NbO2, Nb2O5), being a versatile material has achieved tremendous popularity to be used in a number of applications because of its outstanding electrical, mechanical, chemical, and magnetic properties. NbxOy films possess a direct band gap within the ranges of 3.2–4.0 eV, with these films having utility in different applications which include; optical systems, stainless steel, ceramics, solar cells, electrochromic devices, capacitor dielectrics, catalysts, sensors, and architectural requirements. With the purpose of fulfilling the requirements of a vast variety of the named applications, thin films having comprehensive properties span described by film composition, morphology, structural properties, and thickness are needed. The theory, alongside the research status of the different fabrication techniques of NbxOy thin films are reported in this work. The impact of fabrication procedures on the thin film characteristics which include; film thickness, surface quality, optical properties, interface properties, film growth, and crystal phase is explored with emphases on the distinct deposition process applied, are also described and discussed.

Synthesis of MoS2 Thin Film by Ionized Jet Deposition: Role of Substrate and Working Parameters

The lack of scalable synthesis of transition metal dichalcogenides, such as molybdenum disulfide (MoS2), has proved to be a significant bottleneck in realization of fundamental devices and has hindered the commercialization of these materials in technologically relevant applications. In this study, a cost-efficient and versatile thin-film fabrication technique based on ionized jet deposition (IJD), i.e., a technique potentially providing high processing efficiency and scalability, is used to grow MoS2 thin films on silicon substrates. The operating conditions of IJD were found to influence mainly the ablation efficiency of the target and only slightly the quality of the deposited MoS2 thin film. All as-deposited films show chemical properties typical of MoS2 with an excess of free, elemental sulfur that can be removed by post-deposition annealing at 300–400 °C, which also promotes MoS2 crystallization. The formation of an interface comprised of several silicon oxide species was observed between MoS2 and the silicon substrate, which is suggested to originate from etching and oxidizing processes of dissociated water molecules in the vacuum chamber during growth. The present study paves the way to further design and improve the IJD approach for TMDC-based devices and other relevant technological applications.

Spin coating method improved the performance characteristics of films obtained from poly(lactic acid) and cellulose nanocrystals

For the last few decades, the application of biopolymers such as poly(lactic acid, PLA) as an alternative to synthetic polymers in the packaging industry is in great demand. However, to rival the traditional polymers, the barrier properties and antimicrobial activities of PLA need to be adapted to the food packaging requirements. The purpose of this research was to compare the impact of thin-film fabrication techniques in combination with different contents of cellulose nanocrystals (CNCs) (1–5 wt%) on the barrier and antimicrobial properties of PLA films. The nanocomposite thin films were manufactured via solvent casting and spin-coating techniques. The spin-coating method has been employed for the first time in this work to prepare nanocomposite thin films with a thickness of ˂ 0.2 mm. The nanocomposite films were tested for surface morphology, degree of crystallinity, water vapor permeability, contact angle, and antimicrobial properties. Scanning electron microscopy (SEM) micrographs revealed the strong tendency of CNCs to establish microscale aggregates, however, a high drying rate in the spin-coating method decreases the self-assembly in CNCs. Thus, a significantly higher degree of crystallinity and glass transition temperature were observed in spin-coated films due to a more uniform dispersion of CNCs in PLA. Higher contact angle and lower water vapor transfer rate in spin-coated samples confirmed the lower hydrophilicity character of spin-coated thin films. Two separate assays were employed for evaluating the anti-microbial activity of PLA on the foodborne pathogens. The results showed that the film manufacturing technique and CNC concentration have a strong influence on microbial reduction.

Advances in Materials Design for All-Solid-state Batteries: From Bulk to Thin Films

All-solid-state batteries (SSBs) are one of the most fascinating next-generation energy storage systems that can provide improved energy density and safety for a wide range of applications from portable electronics to electric vehicles. The development of SSBs was accelerated by the discovery of new materials and the design of nanostructures. In particular, advances in the growth of thin-film battery materials facilitated the development of all solid-state thin-film batteries (SSTFBs)—expanding their applications to microelectronics such as flexible devices and implantable medical devices. However, critical challenges still remain, such as low ionic conductivity of solid electrolytes, interfacial instability and difficulty in controlling thin-film growth. In this review, we discuss the evolution of electrode and electrolyte materials for lithium-based batteries and their adoption in SSBs and SSTFBs. We highlight novel design strategies of bulk and thin-film materials to solve the issues in lithium-based batteries. We also focus on the important advances in thin-film electrodes, electrolytes and interfacial layers with the aim of providing insight into the future design of batteries. Furthermore, various thin-film fabrication techniques are also covered in this review.

Synthesis of thin isotopic samarium targets for elastic cross-section measurements

Various fabrication techniques of thin films of lanthanides are very well known. Two major techniques, electron gun deposition and thermal resistivity method have been employed here to know their validity in using the fabricated thin films of Samarium (Sm) for elastic cross-section measurements. The purity and thickness of these prepared targets have been verified and confirmed by using several advanced techniques. These targets have also been irradiated during one of the recent nuclear physics experiment involving measurement of the quasi-elastic cross-section. Detailed fabrication methods as well as characterization techniques have been reported.

Methanol and Humidity Capacitive Sensors Based on Thin Films of MOF Nanoparticles.

The successful development of modern gas sensing technologies requires high sensitivity and selectivity coupled to cost effectiveness, which implies the necessity to miniaturize devices while reducing the amount of sensing material. The appealing alternative of integrating nanoparticles of a porous metal-organic framework (MOF) onto capacitive sensors based on interdigitated electrode (IDE) chips is presented. We report the deposition of MIL-96(Al) MOF thin films via the Langmuir-Blodgett (LB) method on the IDE chips, which allowed the study of their gas/vapor sensing properties. First, sorption studies of several organic vapors like methanol, toluene, chloroform, etc. were conducted on bulk MOF. The sorption data revealed that MIL-96(Al) presents high affinity toward water and methanol. Later on, ordered LB monolayer films of MIL-96(Al) particles of ∼200 nm were successfully deposited onto IDE chips with homogeneous coverage of the surface in comparison to conventional thin film fabrication techniques such as drop-casting. The sensing tests showed that MOF LB films were selective for water and methanol, and short response/recovery times were achieved. Finally, chemical vapor deposition (CVD) of a porous thin film of Parylene C (thickness ∼250-300 nm) was performed on top of the MOF LB films to fabricate a thin selective layer. The sensing results showed an increase in the water selectivity and sensitivity, while those of methanol showed a huge decrease. These results prove the feasibility of the LB technique for the fabrication of ordered MOF thin films onto IDE chips using very small MOF quantities.

Electrophoretic deposition of iron oxide nanoparticles to achieve thick nickel/iron oxide magnetic nanocomposite films

For modern switching power supplies, current bulk magnetic materials, such as ferrites or magnetic metal alloys, cannot provide both low loss and high magnetic saturation to function with both high power density and high efficiency at high frequencies (10-100 MHz). Magnetic nanocomposites comprised of a ferrite and magnetic metal alloy provide the opportunity to achieve these desired magnetic properties, but previously investigated thin-film fabrication techniques have difficulty achieving multi-micrometer film thicknesses which are necessary to provide practical magnetic energy storage and power handling. Here, we present a versatile technique to fabricate thick magnetic nanocomposites via a two-step process, consisting of the electrophoretic deposition of an iron oxide nanoparticle phase into a mold on a substrate, followed by electro-infiltration of a nickel matrix. The deposited films are imaged via scanning electron microscopy and energy dispersive X-ray spectroscopy to identify the presence of iron and nickel, confirming the infiltration of the nickel between the iron oxide nanoparticles. A film thickness of ∼7 μm was measured via stylus profilometry. Further confirmation of successful composite formation is obtained with vibrating sample magnetometry, showing the saturation magnetization value of the composite (473 kA/m) falls between that of the iron oxide nanoparticles (280 kA/m) and the nickel matrix (555 kA/m). These results demonstrate the potential of electrophoretic deposition coupled with electro-infiltration to fabricate magnetic nanocomposite films.

Progress in Nickel‐Coordinated Polymers as Intrinsically Conducting n‐Type Thermoelectric Materials

AbstractOrganic thermoelectrics have witnessed rapid development in the past decade for low temperature energy harvesting applications. While high‐performance p‐type polymers have been demonstrated, n‐type materials have lagged behind due to the limited number of stable n‐dopants and low doping efficiencies. Nickel‐coordination polymers are a promising class of n‐type polymers as they are conducting without extrinsic doping, thus overcoming a major challenge. However, advantages in thermoelectric properties are outweighed by a complicated synthesis and a poorly understood reaction mechanism that has resulted in a large variation in literature for the same material. This progress report provides a comprehensive and critical overview of syntheses and thermoelectric property optimization approaches for two coordination polymers, namely Ni‐ethenetetrathiolate (NiETT) and Ni‐tetrathiooxalate (NiTTO). In particular, material characterization and thin film fabrication techniques are discussed, and the importance of reporting statistically relevant thermoelectric properties is highlighted to ensure reproducibility among different groups. A short discussion on prototype devices based on NiETT is presented, and finally, directions for future development of these and other n‐type metal‐coordinated polymers are suggested.

Increasing the Electron Mobility of ZnO-Based Transparent Conductive Films Deposited by Open-Air Methods for Enhanced Sensing Performance

The development of open-air, high-throughput, low-cost thin film fabrication techniques has immense potential and interest in optoelectronics. However, the oxygen-rich atmosphere associated with su...

Organic-Inorganic Hybrid Halide Perovskites for Memories, Transistors, and Artificial Synapses.

Fascinating characteristics of halide perovskites (HPs), which cannot be seen in conventional semiconductors and metal oxides, have boosted the application of HPs in electronic devices beyond optoelectronics such as solar cells, photodetectors, and light-emitting diodes. Here, recent advances in HP-based memory and logic devices such as resistive-switching memories (i.e., resistive random access memory (RRAM) or memristors), transistors, and artificial synapses are reviewed, focusing on inherently exotic properties of HPs: i) tunable bandgap, ii) facile majority carrier control, iii) fast ion migration, and iv) superflexibility. Various fabrication techniques of HP thin films from solution-based methods to vacuum processes are introduced. Up-to-date work in the field, emphasizing the compositional flexibility of HPs, suggest that HPs are promising candidates for next-generation electronic devices. Taking advantages of their unique electrical properties, low-cost and low-temperature synthesis, and compositional and mechanical flexibility, HPs have enormous potential to provide a new platform for future electronic devices and explosively intensive studies will pave the way in finding new HP materials beyond conventional silicon-based semiconductors to keep up with "More-than-Moore" times.

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics.

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high- k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum dot arrays, carbon nanotubes, graphene, and other 2D semiconductors. Since thin-film transistors (TFTs) are the key enablers of FSE devices, we discuss TFT structures and operation mechanisms after a discussion on the needs and general requirements of gate dielectrics. Also, the advantages of high- k dielectrics over low- k ones in TFT applications were elaborated. Next, after presenting the design and properties of high- k polymers and inorganic, electrolyte, and hybrid dielectric families, we focus on the most important fabrication methodologies for their deposition as TFT gate dielectric thin films. Furthermore, we provide a detailed summary of recent progress in performance of FSE TFTs based on these high- k dielectrics, focusing primarily on emerging semiconductor types. Finally, we conclude with an outlook and challenges section.

Development of “Mist CVD”, Functional Thin Film Fabrication Techniques Utilizing Mist Flow

Development of “Mist CVD”, Functional Thin Film Fabrication Techniques Utilizing Mist Flow