Vapor deposition routes to conformal polymer thin films

Wafer Scale Insulation of High Aspect Ratio Through-Silicon Vias by iCVD

In microelectronics, one of the main 3D integration strategies consists of vertically stacking and electrically connecting various functional chips using through-silicon vias (TSVs). For the fabrication of the TSVs, one of the challenges is to conformally deposit a low dielectric constant insulator thin film at the surface of the silicon. To date, there is no universal technique that can address all types of TSV integration schemes, especially in the case requiring a low deposition temperature. In this work, an organosilicate polymer deposited by initiated chemical vapor deposition (iCVD) was developed and integrated as an insulating layer for TSVs. Process studies have shown that poly(1,3,5-trivinyl-1,3,5-trimethyl cyclotrisiloxane) (P(V3D3)) can present good conformality on high aspect ratio features by increasing the substrate temperature up to 100 °C. The trade-off is a moderate deposition rate. The thermal stability of the polymer has been investigated, and we show that a thermal annealing at 400 °C (with or without ultraviolet exposure) allows the stabilization of the dielectric films by removing residual oligomers. Then, P(V3D3) was integrated in high aspect ratio TSV (10 × 100 μm) on 300 mm silicon wafers using a standard integration flow for TSV metallization. Functional devices were successfully fabricated (including daisy chains of 754 TSVs) and electrically characterized. Our work shows that the metallization barrier should be carefully selected to eliminate the appearance of voids at the top corner of the TSV after the Cu annealing step. Moreover, an appropriate integration process should be used to avoid the appearance of cohesive cracks in the liner. This work constitutes a first proof of concept of the use of an iCVD polymer in a quasi-industrial microelectronic environment. It also highlights the benefit of iCVD as a promising technique to deposit conformal dielectric thin films in a microelectronic pilot line environment.

Surface modifications towards superhydrophobic wood-based composites: Construction strategies, functionalization, and perspectives

Amidst the burgeoning interest in multifunctional superhydrophobic wood-based composites (SWBCs) for their varied applications and the need for improved environmental resilience, recent efforts focus on enhancing their utility by integrating features such as mechanical and chemical stability, self-healing capabilities, flame resistance, and antimicrobial properties. Research indicates that various external conditions can influence the wettability and additional characteristics of SWBCs. This comprehensive review outlines three critical factors affecting SWBCs' performance: synthesis methods, wood taxonomy, and chemical agents. It further provides a detailed overview of SWBCs' specific attributes, including essential qualities for diverse applications and the limitations posed by different contexts. Additionally, it elaborates on performance evaluation techniques, offering a foundational framework for SWBCs' practical application. This work aims to serve as an important resource for future research and development in SWBC engineering.

Ultrathin organosiloxane membrane for precision organic solvent nanofiltration

Promising advances in membrane technology can lead to energy-saving and eco-friendly solutions in industrial sectors. This work demonstrates a highly selective membrane with ultrathin and highly interconnected organosiloxane polymer nanolayers by initiated chemical vapor deposition to effectively separate solutes within the molecular weight range of 150-300 g mol-1. We optimize the poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) membrane by adjusting both the thickness of the selective layer and the pore sizes of its support membranes. Notably, the 29 nm selective layer imparts a uniformly narrow molecular sieving property, providing a record-high solute-solute selectivity of 39.88 for different-sized solutes. Furthermore, a solute-solute selectivity of 11.04 was demonstrated using the real-world active pharmaceutical ingredient mixture of Acyclovir and Valacyclovir, key components for Herpes virus treatment, despite their molecular weight difference of less than 100 g mol-1. The highly interconnected membrane is expected to meet rigorous requirements for high-standard active pharmaceutical ingredient separation.

Designing Organic and Hybrid Surfaces and Devices with Initiated Chemical Vapor Deposition (iCVD)

The initiated chemical vapor deposition (iCVD) technique is an all-dry method for designing organic and hybrid polymers. Unlike methods utilizing liquids or line-of-sight arrival, iCVD provides conformal surface modification over intricate geometries. Uniform, high-purity, and pinhole-free iCVD films can be grown with thicknesses ranging from >15 µm to <5 nm. The mild conditions permit damage-free growth directly onto flexible substrates, 2D materials, and liquids. Novel iCVD polymer morphologies include nanostructured surfaces, nanoporosity, and shaped particles. The well-established fundamentals of iCVD facilitate the systematic design and optimization of polymers and copolymers. The functional groups provide fine-tuning of surface energy, surface charge, and responsive behavior. Further reactions of the functional groups in the polymers can yield either surface modification, compositional gradients through the layer thickness, or complete chemical conversion of the bulk film. The iCVD polymers are integrated into multilayer device structures as desired for applications in sensing, electronics, optics, electrochemical energy storage, and biotechnology. For these devices, hybrids offer higher values of refractive index and dielectric constant. Multivinyl monomers typically produce ultrasmooth and pinhole-free and mechanically deformable layers and robust interfaces which are especially promising for electronic skins and wearable optoelectronics.

Breakup-Free and Colorful Liquid Metal Thin Films via Electrochemical Oxidation

Thin-film metal conductors featuring high conductivity and stretchability are basic building blocks for high-performance conformable electronics. Gallium-based liquid metals are attractive candidates for thin-film conductors due to their intrinsic stretchability and ease of processing. Moreover, the phase change nature of liquid metal provides an opportunity to create conformal electronics in a substrate-free manner. However, thin liquid metal films tend to break during the solid-to-liquid transition due to the high surface tension of liquid metal. Here, we created breakup-free liquid metal thin films by the electrochemical oxidation of solid gallium films. We show that electrochemical oxidation can enhance the mechanical strength of the gallium oxide layer and its interfacial adhesion to the gallium core. When heated to the liquid state, the oxidized gallium films can maintain their structural integrity on various solid substrates, hydrogels, and even the water surface. The solid-liquid phase change-induced stiffness decrease allowed the gallium films to be conformably attached to various nonplanar surfaces upon heating or water transfer printing. Moreover, we also found that enhanced electrochemical oxidation can result in the formation of structure color due to nanoporous structures on the film surface. We also demonstrate the applications of oxidized liquid metal films in functional electronics, electrophysiological monitoring, and tattoo art.

Hematite photoanodes for water splitting from directed assembly of Prussian blue onto CuO-Sb2O5-SnO2 ceramics

We report the controlled layer-by-layer growth by the directed assembly of Prussian blue to form (via thermolysis) a functional hematite coating on the grain surfaces of porous CuO-Sb2O5-SnO2 ceramics. The impact of the hematite coating on the physicochemical properties of the ceramics is demonstrated through Raman spectroscopy, and photoelectric and electrochemical impedance measurements. The directed assembly of ionic layers described here is a promising approach for introducing thin film deposits into porous structures and modifying/tuning the photoelectrochemical properties of SnO2-based ceramic materials.

Micropyramid structured photo capacitive interfaces

Optically driven electronic neuromodulation devices are a novel tool in basic research and offer new prospects in medical therapeutic applications. Optimal operation of such devices requires efficient light capture and charge generation, effective electrical communication across the device's bioelectronic interface, conformal adhesion to the target tissue, and mechanical stability of the device during the lifetime of the implant-all of which can be tuned by spatial structuring of the device. We demonstrate a 3D structured opto-bioelectronic device-an organic electrolytic photocapacitor spatially designed by depositing the active device layers on an inverted micropyramid-shaped substrate. Ultrathin, transparent, and flexible micropyramid-shaped foil was fabricated by chemical vapour deposition of parylene C on silicon moulds containing arrays of inverted micropyramids, followed by a peel-off procedure. The capacitive current delivered by the devices showed a strong dependency on the underlying spatial structure. The device performance was evaluated by numerical modelling. We propose that the developed numerical model can be used as a basis for the design of future functional 3D design of opto-bioelectronic devices and electrodes.

Nanoscale self-assembly: concepts, applications and challenges

Self-assembly offers unique possibilities for fabricating nanostructures, with different morphologies and properties, typically from vapour or liquid phase precursors. Molecular units, nanoparticles, biological molecules and other discrete elements can spontaneously organise or form via interactions at the nanoscale. Currently, nanoscale self-assembly finds applications in a wide variety of areas including carbon nanomaterials and semiconductor nanowires, semiconductor heterojunctions and superlattices, the deposition of quantum dots, drug delivery, such as mRNA-based vaccines, and modern integrated circuits and nanoelectronics, to name a few. Recent advancements in drug delivery, silicon nanoelectronics, lasers and nanotechnology in general, owing to nanoscale self-assembly, coupled with its versatility, simplicity and scalability, have highlighted its importance and potential for fabricating more complex nanostructures with advanced functionalities in the future. This review aims to provide readers with concise information about the basic concepts of nanoscale self-assembly, its applications to date, and future outlook. First, an overview of various self-assembly techniques such as vapour deposition, colloidal growth, molecular self-assembly and directed self-assembly/hybrid approaches are discussed. Applications in diverse fields involving specific examples of nanoscale self-assembly then highlight the state of the art and finally, the future outlook for nanoscale self-assembly and potential for more complex nanomaterial assemblies in the future as technological functionality increases.

Green Nanofabrication Opportunities in the Semiconductor Industry: A Life Cycle Perspective

The turn of the 21st century heralded in the semiconductor age alongside the Anthropocene epoch, characterised by the ever-increasing human impact on the environment. The ecological consequences of semiconductor chip manufacturing are the most predominant within the electronics industry. This is due to current reliance upon large amounts of solvents, acids and gases that have numerous toxicological impacts. Management and assessment of hazardous chemicals is complicated by trade secrets and continual rapid change in the electronic manufacturing process. Of the many subprocesses involved in chip manufacturing, lithographic processes are of particular concern. Current developments in bottom-up lithography, such as directed self-assembly (DSA) of block copolymers (BCPs), are being considered as a next-generation technology for semiconductor chip production. These nanofabrication techniques present a novel opportunity for improving the sustainability of lithography by reducing the number of processing steps, energy and chemical waste products involved. At present, to the extent of our knowledge, there is no published life cycle assessment (LCA) evaluating the environmental impact of new bottom-up lithography versus conventional lithographic techniques. Quantification of this impact is central to verifying whether these new nanofabrication routes can replace conventional deposition techniques in industry as a more environmentally friendly option.

Controlled Release Utilizing Initiated Chemical Vapor Deposited (iCVD) of Polymeric Nanolayers

This review will focus on the controlled release of pharmaceuticals and other organic molecules utilizing polymeric nanolayers grown by initiated chemical vapor deposited (iCVD). The iCVD layers are able conform to the geometry of the underlying substrate, facilitating release from one- and two-dimensional nanostructures with high surface area. The reactors for iCVD film growth can be customized for specific substrate geometries and scaled to large overall dimensions. The absence of surface tension in vapor deposition processes allows the synthesis of pinhole-free layers, even for iCVD layers <10 nm thick. Such ultrathin layers also provide rapid transport of the drug across the polymeric layer. The mild conditions of the iCVD process avoid damage to the drug which is being encapsulated. Smart release is enabled by iCVD hydrogels which are responsive to pH, temperature, or light. Biodegradable iCVD layers have also be demonstrated for drug release.

Vapor-deposited functional polymer thin films in biological applications

Functional polymer coatings have become ubiquitous in biological applications, ranging from biomaterials and drug delivery to manufacturing-scale separation of biomolecules using functional membranes. Recent advances in the technology of chemical vapor deposition (CVD) have enabled precise control of the polymer chemistry, coating thickness, and conformality. That comprehensive control of surface properties has been used to elicit desirable interactions at the interface between synthetic materials and living organisms, making vapor-deposited functional polymers uniquely suitable for biological applications. This review captures the recent technological development in vapor-deposited functional polymer coatings, highlighting their biological applications, including membrane-based bio-separations, biosensing and bio-MEMS, drug delivery, and tissue engineering. The conformal nature of vapor-deposited coatings ensures uniform coverage over micro- and nano-structured surfaces, allowing the independent optimization of surface and bulk properties. The substrate-independence of CVD techniques enables facile transfer of surface characteristics among different applications. The vapor-deposited functional polymer thin films tend to be biocompatible because they are free of remnant toxic solvents and precursor molecules, potentially lowering the barrier to clinical success.

Filling of Nanometric Pores with Polymer by Initiated Chemical Vapor Deposition

The integration of porous thin films using microelectronic compatible processes sometimes requires the protection of the interior of the pores during the critical integration steps. In this paper, the polymerization of neo-pentyl methacrylate (npMA) is performed via initiated chemical vapor deposition (iCVD) on a porous organosilicate (SiOCH) and on a dense SiOCH. The characterizations by Fourier-transform infrared spectroscopy, spectroscopic ellipsometry, and time-of-flight secondary ion mass spectrometry of the different stacks show that iCVD is a powerful technique to polymerize npMA in the nanometric pores and thus totally fill them with a polymer. The study of the pore filling for very short iCVD durations shows that the polymerization in the pores is complete in less than ten seconds and is uniform in depth. Then, the poly(npMA) film growth continues on top of the filled SiOCH layer. These characteristics make iCVD a straightforward and very promising alternative to other infiltration techniques in order to fill the porosity of microporous thin films.

A Comparative Study on the Effects of Au, ZnO and AZO Seed Layers on the Performance of ZnO Nanowire-Based Piezoelectric Nanogenerators

In this study, different seed layers like gold (Au), zinc oxide (ZnO) and aluminum-doped ZnO (AZO) have been associated to ZnO nanowires (NWs) for the development of mechanical energy harvesters. ZnO NWs were grown by using a low temperature hydrothermal method. The morphological properties were investigated using Scanning Electron Microscopy (SEM) and the analysis of crystalline quality and growth orientation was studied using X-ray Diffraction (XRD). The obtained ZnO NWs are found to be highly dense, uniformly distributed and vertically well aligned on the ZnO and AZO seed layers, while ZnO NWs grown on Au possess a low density and follow a non-uniform distribution. Moreover, the NWs exhibited good crystal quality over the seed layers. The piezoelectric nanogenerator (PENG) consists of ZnO NWs grown on the three different seed layers, parylene-C matrix, Ti/Al top electrode and poly(dimethylsiloxane) (PDMS) encapsulated polymer composite. The measurements of the open circuit voltage (V_OC) were around 272 mV, 36 mV for ZnO, AZO seed layers while the PENG including Au seed layer presented a short-circuited state. This study is an important step in order to investigate the effect of different seed layers influencing the magnitude of the generated electrical performances under identical growth and measurement conditions. It will also help identify the most suitable seed layers for energy harvesting devices and their future integration in industrial applications.

Fabrication of a Conjugated Fluoropolymer Film Using One-Step iCVD Process and its Mechanical Durability

Most superhydrophobic surface fabrication techniques involve precise manufacturing process. We suggest initiated chemical vapor deposition (iCVD) as a novel CVD method to fabricate sufficiently durable superhydrophobic coating layers. The proposed method proceeds with the coating process at mild temperature (40 °C) with no need of pretreatment of the substrate surface; the pressure and temperature are optimized as process parameters. To obtain a durable superhydrophobic film, two polymeric layers are conjugated in a sequential deposition process. Specifically, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4D4) monomer is introduced to form an organosilicon layer (pV4D4) followed by fluoropolymer formation by introducing 1H, 1H, 2H, 2H-Perfluorodecyl methacrylate (PFDMA). There is a high probability of covalent bond formation at the interface between the two layers. Accordingly, the mechanical durability of the conjugated fluoropolymer film (pV4D4-PFDMA) is reinforced because of cross-linking. The superhydrophobic coating on soft substrates, such as tissue paper and cotton fabric, was successfully demonstrated, and its durability was assessed against the mechanical stress such as tensile loading and abrasion. The results from both tests confirm the improvement of mechanical durability of the obtained film.

Ultrathin conformal polycyclosiloxane films to improve silicon cycling stability

Electrochemical reduction of lithium ion battery electrolyte on Si anodes was mitigated by synthesizing nanoscale, conformal polymer films as artificial solid electrolyte interface (SEI) layers. Initiated chemical vapor deposition (iCVD) was used to deposit poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (pV4D4) onto silicon thin film electrodes. pV4D4 films (25 nm) on Si electrodes improved initial coulombic efficiency by 12.9% and capacity retention over 100 cycles by 64.9% relative to untreated electrodes. pV4D4 coatings improved rate capabilities, enabling higher lithiation capacity at all current densities. Impedance spectroscopy showed that SEI resistance grew from 50 to 191 ohms in untreated Si and only 34 to 90 ohms in pV4D4-coated Si over 30 cycles. Post-cycling Fourier transform infrared and x-ray photoelectron spectroscopy showed that pV4D4 moderated electrolyte reduction and altered SEI composition, with LiF formation being favored. This work will guide further development of polymeric artificial SEIs to mitigate electrolyte reduction and enhance capacity retention in Si electrodes.

Vapor-printed polymer electrodes for long-term, on-demand health monitoring

We vapor print conformal conjugated polymer electrodes directly onto living plants and use these electrodes to probe the health of actively growing specimens using bioimpedance spectroscopy. Vapor-printed polymer electrodes, unlike their adhesive thin-film counterparts, do not delaminate from microtextured living surfaces as the organism matures and do not observably attenuate the natural growth pattern and self-sustenance of the plants investigated here. On-demand, noninvasive bioimpedance spectroscopy performed with long-lasting vapor-printed polymer electrodes can reliably detect deep tissue damage caused by dehydration and ultraviolet A exposure throughout the life cycle of a plant.

Synthesis of rare-earth metal and rare-earth metal-fluoride nanoparticles in ionic liquids and propylene carbonate

Decomposition of rare-earth tris(N,N'-diisopropyl-2-methylamidinato)metal(III) complexes [RE{MeC(N(iPr)2)}3] (RE(amd)3; RE = Pr(III), Gd(III), Er(III)) and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium(III) (Eu(dpm)3) induced by microwave heating in the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm][NTf2]) and in propylene carbonate (PC) yield oxide-free rare-earth metal nanoparticles (RE-NPs) in [BMIm][NTf2] and PC for RE = Pr, Gd and Er or rare-earth metal-fluoride nanoparticles (REF3-NPs) in the fluoride-donating IL [BMIm][BF4] for RE = Pr, Eu, Gd and Er. The crystalline phases and the absence of significant oxide impurities in RE-NPs and REF3-NPs were verified by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED) and high-resolution X-ray photoelectron spectroscopy (XPS). The size distributions of the nanoparticles were determined by transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to an average diameter of (11 ± 6) to (38 ± 17) nm for the REF3-NPs from [BMIm][BF4]. The RE-NPs from [BMIm][NTf2] or PC showed diameters of (1.5 ± 0.5) to (5 ± 1) nm. The characterization was completed by energy-dispersive X-ray spectroscopy (EDX).

Ultrathin and Conformal Initiated Chemical-Vapor-Deposited Layers of Systematically Varied Surface Energy for Controlling the Directed Self-Assembly of Block CoPolymers

Directed self-assembly (DSA) of block copolymer (BCP) thin films is a promising approach to enable next-generation patterning at increasingly smaller length scales. DSA utilizes interfacial wetting layers to force the BCP domains to self-assemble with the desired orientation with respect to the substrate. Here, we demonstrate that initiated chemical-vapor-deposited (iCVD) polydivinylbenzene (pDVB) ultrathin films can direct the self-assembly of poly(styrene- block-methylmethacrylate). We found that the methyl radicals formed at increased filament temperatures during the iCVD process result in the backbone methylation of pDVB. By tuning the degree of backbone methylation, we systematically changed the wetting properties of the iCVD pDVB from a slight poly(methylmethacrylate) preference to complete poly(styrene) preference. Additionally, we utilize the conformal nature of the iCVD to form a wetting layer over a topographical line and space pattern, which is subsequently used to produce self-assembled BCP films with both perpendicular orientation and long-range alignment.

Strategies for Drug Encapsulation and Controlled Delivery Based on Vapor‐Phase Deposited Thin Films

Vapor‐phase deposition methods allow the synthesis and engineering of organic and inorganic thin films, with high control on the chemical composition, physical properties, and conformality. In this review, the recent applications of vapor‐phase deposition methods such as initiated chemical vapor deposition (iCVD), plasma enhanced chemical vapor deposition (PE‐CVD), and atomic layer deposition (ALD), for the encapsulation of active pharmaceutical drugs are reported. The strategies and emergent routes for the application of vapor‐deposited thin films on the drug controlled release and for the engineering of advanced release nanostructured devices are presented.