Heat-sensitive Substrates Research Articles

Bayesian Optimization of Low-Temperature Nonthermal Plasma Jet Sintering of Nanoinks.

In response to the escalating demand for flexible devices in applications such as wearables, sensors, and touch panels, there is a need for innovative fabrication approaches for devices made from nanomaterial-based inks. Subsequent to ink deposition, a pivotal stage in device manufacturing typically involves high-temperature sintering, posing challenges for heat-sensitive substrates. Nonthermal plasma jet sintering utilizing an atmospheric pressure dielectric barrier discharge (DBD) plasma jet enables sintering at room temperature and standard pressure, facilitating the sintering of printed nanoparticle films without compromising substrate or film surface integrity. However, determining optimal plasma jet sintering conditions can be challenging due to multiple processing variables with intricate interrelationships. This work employed Bayesian optimization (BO) and machine learning (ML) to identify optimal values for seven primary plasma jet sintering variables. Optimization yielded a 99.2% increase in the measured electrical conductivity for plasma jet-sintered indium tin oxide (ITO) films after five rounds of experiments. Moreover, the optimal sintering conditions achieved an electrical conductivity that was 81.4% of conventional furnace sintering at 300 °C, but was three times faster and with a peak substrate temperature below 47 °C. This result demonstrates the prospect of applying BO to optimize processing techniques for emerging low-temperature requirements.

Room temperature compressed air-stable conductive copper films for flexible electronics

The state-of-the-art technology of fabricating printed copper electronics is focussed largely on thermal sintering restricting transition towards heat sensitive flexible substrates. Herein we report a pioneering technology which eliminates the need for conventional sintering. Biopolymer-stabilised copper particles are prepared such that they can be compressed at room temperature to generate air-stable films with very low resistivities (2.05 – 2.33 × 10−8 Ω m at 20 °C). A linear positive correlation of resistivity with temperature verifies excellent metallic character and electron microscopy confirms the formation of films with low porosity (< 4.6%). An aqueous ink formulation is used to fabricate conductive patterns on filter paper, first using a fountain/dip pen and then printing to deposit more defined patterns (R < 2 Ω). The remarkable conductivity and stability of the films, coupled with the sustainability of the approach could precipitate a paradigm-shift in the use of copper inks for printable electronics.

Nanosized curing catalyst via nano-templated plasma PVD for attaining superior low-cure powder coating films

The addition of curing catalysts into powder coating is a key method to fabricate low-temperature curing powder coating for reducing energy consumption and expanding its applications to heat-sensitive substrates. However, the heterogeneous dispersion of the unmodified catalysts in powder coatings results in inconsistent catalysis of resin crosslinking, thus leading to compromised surface smoothness and gloss. Utilizing nanosized catalysts is an efficient solution to such problems. In this paper, we propose a nano-templated dielectric barrier discharge (DBD) plasma-assisted physical vapor deposition (PVD) strategy to fabricate the nanosized catalysts. The curing catalyst, 2-ethylimidazole (2-elm), is successfully vaporized and deposited on nano-carrier SiO2 (SiO2-NPs) in the DBD plasma reactor at atmospheric pressure, producing 2-elm@SiO2-NPs. The mechanical strength and chemical resistance of finishes of powder coating incorporated with the 2-elm@SiO2-NPs remained at low curing temperature (170 °C for 15 min) and fast curing condition (190 °C for 8 min). In addition, their surface qualities are comparable to that of the original powder coating, with up to 100 % gloss retention, successfully eliminating the issue of more than 25 % gloss attenuation of the powder coating with unmodified 2-elm. This study provides an effective, solvent-free strategy for fabricating nanosized curing catalysts and achieving high-quality film finishes.

Electrically conductive gold films formed by sintering of gold nanoparticles at room temperature initiated by ozone

Understanding and controlling the sintering behaviour of gold nanoparticles is important in the field of ligand-protected nanoparticles for their use as precursors for thin film fabrication. Lowering the temperature of the sintering event of gold nanoparticles by facilitating desorption of the ligand through oxidation can provide compatibility of sintered gold nanoparticle thin films onto heat-sensitive substrates. Here we examine the processes by which 1-butanethiol-protected gold nanoparticles sinter under an ozone-rich environment. Upon heating, an ozone-rich environment significantly reduces the temperature of the sintering event when compared to sintering under ambient conditions. At room temperature, exposure to an ozone-rich environment induces sintering over a period of 2.5 h. Upon exposure to ozone, the surface-bound butanethiol ligands are oxidised to 1-butanesulfonic acid which facilitates sintering.

Direct Graphene Deposition via a Modified Laser-Assisted Method for Interdigitated Microflexible Supercapacitors.

The transcendence toward smarter technologies and the rapid expansion of the Internet of Things requires miniaturized energy storage systems, which may also be shape-conformable, such as microflexible supercapacitors. Their fabrication must be compatible with emerging manufacturing platforms with regard to scalability and sustainability. Here, we modify a laser-based method we recently developed for simultaneously synthesizing and transferring graphene onto a selected substrate. The modification of the method lies in the tuning of two key parameters, namely, the inclination of the laser beam and the distance between the precursor material and the acceptor substrate. A proper combination of these parameters enables the displacement of the trace of the transmitted laser beam from the deposited graphene film area. This mitigates the negative effects that arise from the laser-induced ablation of graphene on heat-sensitive substrates and significantly improves the electrical conductivity of the graphene films. The optimized graphene exhibits very high C/O (36) and sp2/sp3 (13) ratios. Post-transport irradiation was used to transform the continuous graphene films to interdigitated electrodes. The capacitance of the microflexible supercapacitor was measured to be among the highest reported ones in relation to interdigitated supercapacitors with electrodes based on laser-grown graphene. The device shows good cycling stability, retaining 91% of its capacitance after 10,000 cycles, showing no substantial degradation after applying bending conditions. This promising laser-based approach emerges as a viable alternative for the fabrication of microflexible interdigitated supercapacitors for paper electronics and smart textiles.

Reduced leakage current in atomic-layer-deposited HfO2 thin films deposited at low temperature by in-situ defect passivation

HfO2 films grown via atomic layer deposition (ALD) at low temperature generally exhibit high impurity content, reduced density, and increased oxygen defects, resulting in degraded electrical properties. To overcome this issue, this study applied an in-situ defect passivation technique at low temperature, modifying the ALD oxygen source feeding step to suit heat-sensitive substrates. The electrical properties of the ALD HfO2 film grown at 80 °C are improved when the oxygen source feeding step is repeated twice, and especially the leakage current density is significantly decreased, which is approximately 1/7 smaller at an electric field of 1 MV/cm compared to the film grown via the conventional ALD process at 80 °C. This improvement in the electrical properties can be attributed to decreased carbon impurities and oxygen defects and increased film density. A simple modification of the oxygen source feeding step during the ALD process can effectively reduce defects within the ALD HfO2 films at the atomic layer level, even when grown at low deposition temperatures.

A latened catalytic strategy for low cure thermoset powder coating by post-dry-blending technique

Conventional thermoset powder coatings typically require curing at a high temperature of 190 °C for a minimum duration of 15 min, which poses challenges when applying them to heat-sensitive substrates and results in elevated energy costs. A solution known as low-temperature-curing powder coating (LCPC) has been developed to address this issue. By normally incorporating the curing catalyst into the coating system via hot extrusion, LCPC can achieve either a reduced curing temperature or a shortened curing period. However, the current extrusion method used for catalyst incorporation leads to undesirable side effects, such as compromised surface quality, shorter shelf-life and a narrower operational window for the hot-extrusion process involved in producing powder coatings. To overcome these challenges, a new strategy is proposed in this study, in which the tailor-made nano-catalyst is post-dry-blended into the powder coating instead of subjecting it to hot treatment with coating ingredients. This dry-blending catalyst (DBC), encapsulating nanosized fumed silica with catalysts by impregnation method, is introduced to the powder coating system before spraying, eliminating the need for hot-kneading into the powder coating system at the beginning. The DBC is attached to the surface of the particle realizing the interparticle contact mode and latening the catalysis. The dry-blended low-temperature-curing powder coating (DB-LCPC), containing a 0.03 % dosage of onium salt and 0.035 % of 2-methylimidazole, is identified as the optimum formulation due to its excellent surface quality, prominent chemical and mechanical characteristics. The sample successfully achieved low-temperature curing or a shortened curing time while maintaining excellent mechanical properties and chemical resistance. Furthermore, it exhibited superior coating appearances and a longer shelf-life compared to the hot-extruded sample. This novel DBC method has the potential to greatly enhance the adoption of low-temperature-curing powder coatings.

Intense Pulsed Light Thermal Treatment of Pb(Zr,Ti)O3 /Metglas Heterostructured Films Resulting in Extreme Magnetoelectric Coupling of over 20Vcm-1 Oe-1.

Magnetoelectric (ME) film composites consisting of piezoelectric and magnetostrictive materials are promising candidates for application in magnetic field sensors, energy harvesters, and ME antennas. Conventionally, high-temperature annealing is required to crystallize piezoelectric films, restricting the use of heat-sensitive magnetostrictive substrates that enhance ME coupling. Herein, a synergetic approach is demonstrated for fabricating ME film composites that combines aerosol deposition and instantaneous thermal treatment based on intense pulsed light (IPL) radiation to form piezoelectric Pb(Zr,Ti)O3 (PZT) thick films on an amorphous Metglas substrate. IPL rapidly anneals PZT films within a few milliseconds without damaging the underlying Metglas. To optimize the IPL irradiation conditions, the temperature distribution inside the PZT/Metglas film is determined using transient photothermal computational simulation. The PZT/Metglas films are annealed using different IPL pulse durations to determine the structure-property relationship. IPL treatment results in an enhanced crystallinity of the PZT, thus improving the dielectric, piezoelectric, and ME properties of the composite films. An ultrahigh off-resonance ME coupling (≈20Vcm-1 Oe-1 ) is obtained for the PZT/Metglas film that is IPL annealed at a pulse width of 0.75ms (an order of magnitude higher than that reported for other ME films), confirming the potential for next-generation, miniaturized, and high-performance ME devices.

Structural evolution and thermoelectric properties of Mg3SbxBi2−x thin films deposited by magnetron sputtering

Mg3Bi2-based compounds are of great interest for thermoelectric applications near room temperature. Here, undoped p-type Mg3SbxBi2−x thin films were synthesized using magnetron sputtering (three elemental targets in Ar atmosphere) with a growth temperature of 200 °C on three different substrates, namely, Si as well as c- and r-sapphire. The elemental composition was measured with energy-dispersive x-ray spectroscopy and the structure by x-ray diffraction. The electrical resistivity and the Seebeck coefficient were determined under He atmosphere from room temperature to the growth temperature. All samples are crystalline exhibiting the La2O3-type crystal structure (space group P-3m1). The observed thermoelectric response is consistent with a semiconductive behavior. With increasing x, the samples become more electrically resistive due to the increasing bandgap. High Bi content (x &amp;lt; 1) is thus beneficial due to lower resistivity and a higher power factor near room temperature. Thermoelectric thin films synthesized at low temperatures may provide novel pathways to enable flexible devices on polymeric and other heat-sensitive substrates.

An innovative method to achieve large-scale high-quality VO2 thin films: Oxidation of vanadium nitride material deposited by sputtering

Depositing high-quality VO2 thin films on a large area has been challenging till date. While magnetron sputtering is widely used for this type of deposition, it faces serious reproducibility issues for VO2 films due to target poisoning. In this work, we present an improved technique called sputtering oxidation coupling (SOC) using VN as intermediate material. VN films are first deposited on quartz by magnetron sputtering. In a second step, a post-annealing process in oxygen is carried out to obtain VO2. For an annealing temperature of 470 °C, 0.5 h of oxidation under an oxygen pressure of 70 mTorr yields VO2 films with the best performance in terms of transition properties. While the resistivity contrast has a magnitude of 2.9, the transmittance contrast is 69.3%. This is comparable to VO2 films produced by Pulsed Laser Deposition (PLD), which is well recognized for its capability to provide high-quality VO2 thin films. Furthermore, the lowest possible temperature for achieving VO2 from VN with an acceptable electrical transition contrast (2.5) is found to be 400 °C, which makes the proposed method promising for growing VO2 films directly on heat-sensitive polymer substrates.

레이저 유도 전사를 이용한 유연기판의 액체금속 미세 패터닝

We have developed a direct conductive patterning method with micro-scale line widths using the laser-induced-forward transfer (LIFT) and liquid metal. As this method does not need post-thermal processing, there is no thermal damage even on heat-sensitive polymer substrates by low-power laser irradiation on the dynamic release layer (DRL). Unlike other liquid metal patterning processes, this procedure can easily achieve fine line widths of a few tens of micrometers corresponding to laser spot size. The solid-state UV pulse laser with 266 nm wavelength and 20 ns pulse duration was used to transfer Eutectic Gallium Indium (EGaIn) liquid metal and the results for the single and multi-pulse laser irradiation were investigated to determine the effective process conditions. The applicability of flexible circuit fabrication and selective circuit repair was successfully tested on Polyimide (PI) substrate. After the LIFT process, the electrical properties of liquid metal on the pattern were measured to be approximately 5~8 x 10SUP-3/SUP Ω/m of resistance.

Multifunctional Nanostructures with Controllable Band Gap Giving Highly Stable Infrared Emissivity for Smart Thermal Management.

Thermal control is essential to guarantee the optimal performance of most advanced electronic devices or systems. In space, orbital satellites face the issues of high thermal gradients, heating, and different thermal loads mediated by differential illumination from the Sun. Todaýs state-of-the-art thermal control systems provide protection; however, they are bulky and restrict the mass and power budgets for payloads. Here, we develop a lightweight optical superlattice nanobarrier structure to provide a smart thermal control solution. The structure consists of a moisture and outgassing physical barrier (MOB) coupled with atomic oxygen (AO)-UV protection functionality. The nanobarrier exhibits transmission and reflection of light by controlling the optical gap of individual layers to enable high infrared emissivity and variable solar absorptivity (minimum ΔαS = 0.30) across other wavelengths. The multifunctional coating can be applied to heat-sensitive substrates by means of a bespoke room-temperature process. We demonstrate enhanced stability, energy-harvesting capability, and power savings by facilitating the radiation cooling and facility for active self-reconfiguration in orbit. In this way, the reduction of the operating temperature from ∼120 to ∼60 °C on space-qualified and nonmechanically controlled composite structures is also demonstrated.

선택적 레이저 소결을 이용한 유연인쇄전자소자 제작

It is necessary to develop a low temperature process that can deposit and pattern metal on a heat sensitive substrate because most flexible printed electronics use high temperature sensitive materials such as plastic. The most commonly used photolithography process is not suitable for flexible printed electronics because the high temperature thermal treatment process and chemicals are not compatible with plastic. Recently research has been actively conducted on a method of minimizing thermal damage to plastic and high-resolution metal patterning by using selective laser sintering after forming a liquid metal nanoparticle thin film without using existing photolithography and vacuum deposition. In this review paper, we explore flexible printed electronics such as flexible thin film transistors and flexible transparent conductors using selective laser sintering of nanomaterials and discuss future development directions.

Domestic Cooking Affects the Prebiotic Performances of Chinese Yam

The appropriate domestic cooking methods can retain and protect the biological properties of foods well. Thus, the objective of this study was to unravel the effect of different cooking methods on the microbiota modulatory properties of yam and their non-starch polysaccharides by an in vitro simulated digestion and fermentation model. The results showed that different cooking processes led to different changes in polysaccharide content. The polysaccharide content of yam increased by 21.3~108.2% or decreased by 12.0% compared with that of raw yam. Additionally, the soluble polysaccharides contents in all cooked yam samples significantly increased by 16.85~119.97% after in vitro digestion. The regulation of whole-yam digesta on gut microbiota was partly related with yam polysaccharides. Both yam and yam polysaccharide fermentation appeared to promote beneficial bacteria, such as Bifidobacteria, Bacteroides spp. and Megasphaera and suppressed bacterial pathogens such as Ruminococcusforques and Escherichia-Shigella. Household cooking significantly influenced the prebiotic performances of yam and yam polysaccharides by changing the heat-sensitive microbial substrates and their physiology properties. According to our results, normal-pressure steaming and normal-pressure boiling processes can retain the microbiota modulatory effects of Chinese yam.

Multifactorial investigations of the deposition process – Material property relationships of ZnO:Al thin films deposited by magnetron sputtering in pulsed DC, DC and RF modes using different targets for low resistance highly transparent films on unheated substrates

We present a comprehensive study of the many parameters available in magnetron sputtering (including sputtering modes and target choice) to obtain low-resistivity ZnO:Al (AZO) films. The material is widely studied by many groups, however most of the reports focus on the optimization of one parameter, making the translation to another system cumbersome. We aimed to provide a general blueprint for a quick optimization of the process parameters for low resistivity, high crystalline quality AZO films. We found that it was the total argon pressure that controlled the outcomes most and that it is very important to have it the lowest possible. We show that the deposition power and other parameters do not influence the films in such a way. We tested two different (black and white) AZO targets and also did not found many differences, which may also be relevant for the researchers starting their work and wondering if the target they ordered would work well. We obtained very low film resistivities, at 1.2 mΩcm while depositing at room temperature, which is comparable with state-of-the-art results for deposition on heated substrates. We argue, that the sputtering configuration with a short target to substrate distance is responsible for this, opening up the way for low resistivity AZO deposition on heat-sensitive substrates.

The role of fluence in determining the response of thin molybdenum films to ultrashort laser irradiation; from laser-induced crystallization to ablation via photomechanical ablation and nanostructure formation

The selective processing of Mo at low temperatures is challenging, especially in advanced manufacturing on flexible and heat-sensitive substrate due to its higher melting temperature. The key role of fluence in determining the response of thin Mo films to ultrashort laser irradiation is considered in this study. At low fluences, the electrical properties of Mo are enhanced by a localized laser-induced crystallization mechanism; the electrical mobility of Mo is increased and the contact resistance between Mo-Si interface is reduced. At higher fluences, selective patterning of Mo proceeds without impacting the Si layer and the threshold fluence for ablation increases with the film thickness of Mo. Two fluence dependent ablation mechanisms are observed depending on the Mo film thickness. For thin films of thicknesses 20 nm and 40 nm, selective ablation proceeds only by a photothermal interaction. For 60 nm and 80 nm thick films, selective ablation proceeds by both photomechanical and photothermal interactions at two-separate higher fluence regimes, respectively. Interestingly, between these two ablation regimes, a non-ablative nanostructuring regime occurs. The study provides a concise overview of the process window for implementing the laser-induced modifications to Mo layers with minimal impact to the substrate using single wavelength ultrashort pulse laser.

IFS Coatings Appoints Manager for Heat Sensitive Substrates

IFS Coatings Appoints Manager for Heat Sensitive Substrates

Growth of hard nanostructured ZrN surface induced by copper nanoparticles

Surfaces with defined nanoroughness and topography are appreciated in many applications. However, such surfaces, often built from deposited nanoparticles, suffer from low hardness and overall mechanical stability. This paper reports the research of ZrN surfaces with defined nanoroughness attained by seed-like growth evoked by Cu nanoparticles. The two-step process consists of (i) deposition of Cu nanoparticles by gas aggregation forming seeds (ii) growth of ZrN with surface nanoarchitecture. Our study faces the challenge to stabilize soft Cu nanoparticles by coating them with a hard, crystalline ZrN film deposited by High Power Impulse Magnetron Sputtering (HiPIMS) without any post thermal annealing which can be useful for coating heat-sensitive substrates. It is shown that by tailoring the HiPIMS process we were able to deposit hard Cu/ZrN nanocomposite with roughness and morphology predetermined by the Cu nanoparticles. Nano-indentation carried out with a resolution below 1 nm, confirmed sufficient nanohardness of CuNPs/ZrN nanocomposite.

Amorphous thin-film oxide power devices operating beyond bulk single-crystal silicon limit

Power devices (PD) are ubiquitous elements of the modern electronics industry that must satisfy the rigorous and diverse demands for robust power conversion systems that are essential for emerging technologies including Internet of Things (IoT), mobile electronics, and wearable devices. However, conventional PDs based on “bulk” and “single-crystal” semiconductors require high temperature (> 1000 °C) fabrication processing and a thick (typically a few tens to 100 μm) drift layer, thereby preventing their applications to compact devices, where PDs must be fabricated on a heat sensitive and flexible substrate. Here we report next-generation PDs based on “thin-films” of “amorphous” oxide semiconductors with the performance exceeding the silicon limit (a theoretical limit for a PD based on bulk single-crystal silicon). The breakthrough was achieved by the creation of an ideal Schottky interface without Fermi-level pinning at the interface, resulting in low specific on-resistance Ron,sp (< 1 × 10–4 Ω cm2) and high breakdown voltage VBD (~ 100 V). To demonstrate the unprecedented capability of the amorphous thin-film oxide power devices (ATOPs), we successfully fabricated a prototype on a flexible polyimide film, which is not compatible with the fabrication process of bulk single-crystal devices. The ATOP will play a central role in the development of next generation advanced technologies where devices require large area fabrication on flexible substrates and three-dimensional integration.

Research progress in laser direct writing of flexible circuit

<p indent="0mm">At present, the flexible electronics industry is in an important transitional period, and various flexible electronic devices with novel properties and enhanced functions are constantly emerging, from limited flexibility to flexible electronic devices with shape adaptability and ductility. This has greatly stimulated demand for flexible electronic devices. The development of manufacturing technologies for flexible circuits with smaller feature sizes and better performance on larger-format substrates at lower costs has attracted increasing attention. Among various technologies, laser direct writing has proven to be an efficient and flexible manufacturing method that can produce large-area flexible electronic circuits. As a nonlithographic, nonvacuum, and online processing technology, laser direct writing has received considerable attention. It can be employed in the production of circuit electrodes of various substrates, including heat-sensitive flexible substrates, and it has huge application prospects in the production of flexible electronic and energy storage devices, sensors, and wearable electronic devices. On this basis, this article summarizes the latest development in the laser direct writing of flexible circuit (LDWFC) technology for manufacturing flexible circuits. It focuses on the material types and characteristics of the conductive inks suitable for LDWFC in the production of flexible circuits. The LDWFC processing technology is introduced in detail from four aspects: laser sintering technology, laser reduction technology, laser-induced modification technology, and laser auxiliary circuit manufacturing technology. In addition, the application of LDWFC in flexible energy storage devices, tenderness sensors, and flexible displays is introduced, and the development prospects of LDWFC technology in flexible circuit manufacturing are highlighted.