Encapsulation Layer Research Articles

Scalable Van der Waals Encapsulation by Inorganic Molecular Crystals.

Encapsulation is critical for devices to guarantee their stability and reliability. It becomes an even more essential requirement for devices based on 2D materials with atomic thinness and far inferior stability compared to their bulk counterparts. Here a general van der Waals (vdW) encapsulation method for 2D materials using Sb2 O3 layer of inorganic molecular crystal fabricated via thermal evaporation deposition is reported. It is demonstrated that such a scalable encapsulation method not only maintains the intrinsic properties of typical air-susceptible 2D materials due to their vdW interactions but also remarkably improves their environmental stability. Specifically, the encapsulated black phosphorus (BP) exhibits greatly enhanced structural stability of over 80 days and more sustaining-electrical properties of 19 days, while the bare BP undergoes degradation within hours. Moreover, the encapsulation layer can be facilely removed by sublimation in vacuum without damaging the underlying materials. This scalable encapsulation method shows a promising pathway to effectively enhance the environmental stability of 2D materials, which may further boost their practical application in novel (opto)electronic devices.

Engineering Bilayer AlOx /YAlOx Dielectric Stacks for Hysteresis-Free Switching in Solution-Processed Metal-Oxide Thin-Film Transistors

Solution processing and low-temperature annealing (T < 300°C) of the precursor compounds promise low-cost manufacturing for future applications of flexible oxide electronics. However, thermal budget reduction comes at the expense of increased charge trapping residuals in the dielectric layers, which result in hysteretic switching of transistors. This work reports on a novel bilayer dielectric scheme combining aluminum oxide (AlOx) as a positive charge trapping insulator and yttrium aluminum oxide (YAlOx) as a negative charge trapping dielectric to obtain hysteresis free switching in the solution-processed metal-oxide thin-film transistors. Devices were processed at a thermal budget of 250°C, without an encapsulation layer. The presence of H+ and OH− in the AlOx were found responsible for the hysteresis in the switching, which was suppressed successfully with the thickness optimization of the YAlOx in the dielectric stack. Fabricated devices yield ON/OFF ratios of 106, sub-pA level gate leakage currents, a subthreshold swing of 150 mV/decade, and field-effect mobility of 1.5 cm2/V-sec.

Theoretical analysis of phase change heat transfer and energy storage in a spherical phase change material with encapsulation

Encapsulation of a phase change material (PCM) is a commonly used technique for providing mechanical and chemical stability, and enabling the manufacturing of PCM composites. However, thermal impedance of the encapsulating layer may adversely affect phase change heat transfer in the PCM. Experimental measurement of heat transfer and phase change in an encapsulated PCM is difficult, particularly for the case of micro/nano-encapsulation. As a result, development of robust theoretical phase change heat transfer models in presence of encapsulation is critical. This paper presents theoretical analysis of the problem of phase change heat transfer in a spherical PCM with an encapsulant layer. Temperature distribution in the newly formed phase and the encapsulant layer is determined by solving a spherical two-layer thermal conduction problem in non-dimensional form. The rate of phase change propagation is then determined from the temperature distribution. The effect of thermal contact resistance at the PCM-encapsulant interface is accounted for. Results are shown to be consistent with past work for the special case of no encapsulation. Results are also shown to agree well with numerical simulations. The use of only a few eigenvalues is shown to result in good accuracy. The effect of encapsulant thickness, thermal properties and PCM-encapsulant thermal contact resistance as well as external boundary condition on phase change propagation is analyzed. The non-dimensional model is used to address practical problems in phase change energy storage with typical materials and conditions. This work contributes an important theoretical analysis tool for a problem of much practical importance. Results from this work may help optimize and improve the performance of encapsulated PCMs for energy storage and thermal management.

Charge transfer in the vertical structures formed by two-dimensional layers

Electronic structures of superlattices and encapsulated layers are obtained by Green's function method. The simple scheme for estimation of interlayer charge transfer is proposed. As an example, layers of graphene and graphene-like compounds are considered. Keywords: 2D structure, superlattice encapsulated layer

A highly aligned microgrid structure for wearable nanofibrous sensors with an enhanced sensitivity and detection range

Novel pressure sensing platform that features Ag/Ti3C2Tx (MXene)-modified grid-like polyurethane (PU) nanofibers was prepared sandwiched between the encapsulation layer and interdigital electrodes.

Wearable Pressure Sensors Based on MXene/Tissue Papers for Wireless Human Health Monitoring.

Though the widely available, low-cost, and disposable papers have been explored in flexible paper-based pressure sensors, it is still difficult for them to simultaneously achieve ultrahigh sensitivity, low limit and broad range of detection, and high-pressure resolution. Herein, we demonstrate a novel flexible paper-based pressure sensing platform that features the MXene-coated tissue paper (MTP) sandwiched between a polyimide encapsulation layer and a printing paper with interdigital electrodes. After replacing the polyimide with weighing paper in the MTP pressure sensor, the silver interdigital electrodes can be recycled through incineration. The resulting pressure sensor with polyimide or paper encapsulation exhibits a high sensitivity of 509.5 or 344.0 kPa-1, a low limit (∼1 Pa) and a broad range (100 kPa) of detection, and outstanding stability over 10 000 loading/unloading cycles. With ultrahigh sensitivity over a wide pressure range, the flexible pressure sensor can monitor various physiological signals and human movements. Configuring the pressure sensors into an array layout results in a smart artificial electronic skin to recognize the spatial pressure distribution. The flexible pressure sensor can also be integrated with signal processing and wireless communication modules on a face mask as a remote respiration monitoring system to wirelessly detect various respiration conditions and respiratory abnormalities for early self-identification of opioid overdose, pulmonary fibrosis, and other cardiopulmonary diseases.

Colorimetric Phosphate Detection Using Organic DFB Laser Based Absorption Spectroscopy.

A novel compact laser absorption spectrometer is developed for colorimetric detection. We demonstrate the realization of the system as well as example measurements of phosphate in water samples based on the malachite green (MG) method. A phosphate concentration range of to (which corresponds to a molar concentration range of to ) is investigated. This photometer demonstrates the ease of integration of organic distributed feedback (DFB) lasers and their miniaturizability, leading the way toward optofluidic on-chip absorption spectrometers. We constructed an optically pumped organic second-order DFB laser on a transparent substrate, including a transparent encapsulation layer, to have access to both emission directions of the surface-emitting laser. Using the two different surface emission directions of the laser resonator allows monitoring of the emitted light intensity without using additional optical elements. Based on these advances, it is possible to miniaturize the measurement setup of a laser absorption spectrometer and to measure analytes, such as phosphate.

Effect of Bulky Atom Substitution on Backbone Coplanarity and Electrical Properties of Cyclopentadithiophene-Based Semiconducting Polymers.

The effect of atomic substitution on the optoelectronic properties of a coplanar donor-acceptor (D-A) semiconducting polymer (SPs), prepared using cyclopentadithiophene (CDT) and 2,1,3-benzothiadiazole (BT) moieties, is investigated. By substituting a carbon atom in the BT unit with CF or C-Cl, two random D-A SPs are prepared, and their optoelectronic properties are thoroughly investigated. Density functional theory calculations demonstrate that the fluorinated polymer has a slightly smaller dihedral angle (ϴ = 0.6°) than the pristine polymer (ϴ = 1.9°) in its lowest-energy conformation, implying efficient charge transport through the coplanar backbone of the fluorinated polymer. However, the chlorinated polymer shows the lowest energy at a relatively larger dihedral angle (ϴ = 139°) due to the steric hindrance induced by bulky chlorine atoms in the backbone, thereby leading to thin-film morphology, which is unfavorable for charge transport. Consequently, the fluorinated polymer yields the highest field-effect mobility (μ) of 0.57 cm2 V-1 s-1 , slightly higher than that of the pristine polymer (μ = 0.33 cm2 V-1 s-1 ), and the extended device lifetime of organic field-effect transistors over 12 d without any encapsulation layers. The results of this study provide design guidelines for air-stable D-A SPs.

Influence of electric field, temperature, humidity, elastomer material, and encapsulation on the lifetime of dielectric elastomer actuators (DEAs) under DC actuation

We present the effect of electric field, temperature, humidity, type of elastomer material, and encapsulation on the lifetime of silicone-based dielectric elastomer actuators (DEAs) under DC electric fields. DEAs are promising soft actuators, but little has been reported on their reliability under static electric fields. We report that humidity and electric field are the dominant accelerating factors for device failure, and that a thin encapsulation layer can increase lifetime by more than an order of magnitude with negligible reduction in actuation strain. Our samples are expanding circle, single layer, prestretched films with 5 mm diameter compliant electrodes, operated at electric fields from 80 V µm−1 to 110 V µm−1, with actuation strains from 2% to 6%. We compare four different silicone elastomers, finding highest lifetime with Momentive Electro 242-1, five times higher than Elastosil 2030. Typical mean time to failure (MTTF) for Elastosil 2030 based DEAs at 100 V μm−1, 85 °C and 85% RH are 1.6 h, but this value increases to over 200 h at 20% RH. At 85 °C and 85% RH, the MTTF decreases by a factor of 62 when increasing the electric field from 80 V μm−1 (2.1% actuation strain) to 100 V μm−1 (4.6% actuation strain). Adding a thin, soft silicone encapsulation layer is an effective yet simple strategy to increase DEA lifetime, increasing the MTTF by factors from 2.2 to 75 under humid conditions. Extrapolating from our data, we predict that DC lifetimes above 1000 h can be achieved at fields below 70 V μm−1 (i.e. ≈1.5% strain) for Elastosil 2030/20 DEAs, and below 85 V μm−1 (i.e. ≈2.5% strain) for encapsulated DEAs at 85 °C—85% RH.

N‐Type Conjugated Polymer as Multi‐Functional Interfacial Layer for High‐Performance and Ultra‐Stable Self‐Powered Photodetectors Based on Perovskite Nanowires

AbstractHigh‐performance and long‐term stable self‐powered photodetectors (PDs) based on methylammonium lead iodide nanowires (NWs) are demonstrated by incorporating n‐type conjugated polymer poly{2,5‐bis(2‐dodecylhexadecyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo‐[3,4‐c]pyrrole‐1,4(2H,5H)‐dione‐alt‐(E)‐1,2‐bis(3‐cyanothiophen‐2‐yl)ethene} (DPP‐CNTVT) as multi‐functional interfacial layer. Incorporating DPP‐CNTVT with abundant Lewis base functional groups can effectively passivate under‐coordinated Pb2+ defects, enabling perovskite NWs to exhibit remarkable stability and optoelectronic properties. Meanwhile, high electron mobility, together with the proper energy level of DPP‐CNTVT, makes it ideal for use as an electron transport layer. Particularly, by taking advantage of the low bandgap of DPP‐CNTVT, the utilization of low energy photons can be improved. The resulting PDs exhibit responsivity up to 0.50 A W−1, specific detectivity approaching 1014 Jones, and a wide linear dynamic range of nearly 265 dB under zero bias operation, which represent the best results ever reported for self‐powered perovskite PDs. More encouragingly, with the incorporation of an appropriate encapsulation layer, nearly 90% of the initial detectivity of PDs can be secured after 15 300 h of continuous operation in ambient conditions. The application of NWs PDs for solution‐processed reflective‐mode pulse oximetry is also demonstrated. This study provides valuable insights into developing efficient and ultra‐stable self‐powered perovskite PDs through interfacial engineering, which can accelerate the practical applications of this emerging technology.

Thermoset Shape Memory Polymer Variable Stiffness 4D Robotic Catheters.

Variable stiffness catheters are typically composed of an encapsulated core. The core is usually composed of a low melting point alloy (LMPA) or a thermoplastic polymer (TP). In both cases, there is a need to encapsulate the core with an elastic material. This imposes a limit to the volume of variable stiffness (VS) material and limits miniaturization. This paper proposes a new approach that relies on the use of thermosetting materials. The variable stiffness catheter (VSC) proposed in this work eliminates the necessity for an encapsulation layer and is made of a unique biocompatible thermoset polymer with an embedded heating system. This significantly reduces the final diameter, improves manufacturability, and increases safety in the event of complications. The device can be scaled to sub‐millimeter dimensions, while maintaining a high stiffness change. In addition, integration into a magnetic actuation system allows for precise actuation of one or multiple tools.

Encapsulation of interdigitated electrodes by PTFE coatings via closed batch initiated chemical vapor deposition

Encapsulation of sensor electrodes is critical for stability and optimum performance of the device. Encapsulation method to be employed should be compatible with the device architecture, provide conformal coatings and be cost effective. In this study, closed batch initiated chemical vapor deposition (CB-iCVD) method is used to deposit Polytetrafluoroethylene (PTFE) encapsulation layers on interdigitated electrodes (IDE). The CB-iCVD method enables deposition of conformal, ultra thin PTFE coatings on patterned surfaces with high precursor consumption efficiencies. The electron microscopy analysis confirms the conformality of the smooth coatings on the IDEs. The encapsulation performance of the coatings in the presence of standard pH solution is demonstrated by the frequency dependent electrochemical impedance spectroscopy (EIS) analysis, which confirms that the PTFE layer can successfully isolate the electrodes from the reactive environment.

Nanoscale Film Thickness Gradients Printed in Open Air by Spatially Varying Chemical Vapor Deposition

Nanoscale films are integral to all modern electronics. To optimize device performance, researchers vary the film thickness by making batches of devices, which is time-consuming and produces experimental artifacts. We present thin films with nanoscale thickness gradients that are rapidly deposited in open air for combinatorial and high-throughput (CHT) studies. Atmospheric pressure spatial atomic layer deposition reactor heads are used to produce spatially varying chemical vapor deposition rates on the order of angstroms per second. We printed ZnO and Al2O3 films with nm-scale thickness gradients in as little as 45 seconds and performed CHT analysis of a MIM diode and perovskite solar cell. By testing 360 Pt/Al2O3/Al diodes with 18 different Al2O3 thicknesses on a single substrate, we identified a thicker insulator layer (6.5 to 7.0 nm) for optimal diode performance than has been reported previously. An Al2O3 thin film encapsulation layer was deposited by atmospheric pressure chemical vapor deposition (AP-CVD) on a perovskite solar cell stack for the first time and a convolutional neural network was developed to analyze the perovskite stability. The rapid nature of AP-CVD enables thicker films to be deposited at a higher temperature than is practical with conventional atomic layer deposition. The CHT analysis showed enhanced stability for 70 nm encapsulation films.

(Invited) Immobilization of Nanobodies with Vapor-Deposited Polymer Encapsulation for Robust Biosensors

To produce next-generation, shelf-stable biosensors for point-of-care diagnostics, it is imperative to achieve rugged biomolecular recognition elements as well as innocuous deposition approaches for efficient encapsulants. Moreover, to maintain the sensitivity and specificity that is inherent to biological recognition elements in solid-state biosensing systems, site-specific immobilization chemistries must be invoked such that the function of the biomolecule remains unperturbed. In this work, we present a universally applicable strategy to establish robust solid-state biosensors using emergent nanobody (Nb) recognition elements with a vapor-deposited polymer encapsulation layer. As compared to conventional immunoglobulin G (IgG) antibodies, Nbs have multiple advantages, including higher thermal stability and pH tolerance, greater ease of recombinant production, and capable of binding antigens with high affinity and specificity. Photoinitiated chemical vapor deposition (piCVD) provides thin, protective polymer barrier layers over immobilized Nb arrays that allow for retention of biosensing activity and specificity after both storage under ambient conditions and complete desiccation. Most importantly, we also demonstrate that vapor-deposited polymer encapsulation of Nb arrays enables specific detection of target proteins, while suppressing nonspecific binding interactions in complex heterogeneous samples, such as unpurified cell lysate, which is otherwise challenging to achieve with bare Nb arrays. Figure 1

Lithographically patterned stretchable metallic microwiring on electrospun nanofiber mats

Stretchable and flexible electronic applications require mechanically suitable electrical wiring. This article presents, for the first time, the microfabrication of photolithographically patterned microwiring on an electrospun nanofiber mat. The use of a photoresist-based technology allows for better than 10 μm pattern resolution on a good quality nanofiber mat, providing an order of magnitude smaller feature sizes than what has been published before. We demonstrate metallic wiring patterned from a 75 nm thick coating on top of the nanofiber mat. A silicone elastomer was incorporated to serve as a matrix material and form a composite substrate and an encapsulation layer on top of the microwiring. We demonstrate clean and anisotropic dry etching of the elastomer to open electrode sites that can be smaller than 10 μm in size. We speculate that these structures will be mechanically robust while being soft at the same time and provide the properties necessary for potential use in stretchable and flexible electronics.

Development of a Screen-Printable Carbon Paste to Achieve Washable Conductive Textiles

Conductive tracks are key constituents of wearable electronics and e-textiles, as they form the interconnective links between wearable electrical devices/systems. They are made by coating or printing conductive patterns or tracks on textiles or by weaving, knitting, or embroidering conductive yarns into textiles. Screen printing is a mature and cost-effective fabrication method that is used in the textile industry. It allows a high degree of geometric freedom for the design of conductive patterns or tracks. Current screen-printed conductive textiles have the limitations of low durability when washed or when placed under bending, and they typically require encapsulation layers to protect the printed conductor. This paper presents a printable paste formulation and fabrication process based on screen printing for achieving a flexible and durable conductive polyester-cotton textile using an inexpensive carbon as the conductor. The process does not require an interface, the smoothing of the textile, or an encapsulation layer to protect the conductor on the textile. A resistivity of 4 × 10−2 Ω·m was achieved. The textile remains conductive after 20 standard washes, resulting in the conductor’s resistance increasing by 140%. The conductive textile demonstrated less than ±10% resistance variation after bending for 2000 cycles.

Hydrogen-assisted low-temperature plasma-enhanced chemical vapor deposition of thin film encapsulation layers for top-emission organic light-emitting diodes

In this work, we developed a single high-performance SiNx encapsulation layer that can be directly integrated into organic devices by low-temperature plasma-enhanced chemical vapor deposition (PECVD). We investigated a hydrogen-assisted low-temperature PECVD process at a temperature of 80 °C. The thin film density improved with an increased hydrogen gas ratio, and the moisture permeability was less than 5 × 10−5 g/m2·day. To verify the stability of the PECVD process, we applied the SiNx encapsulation layer directly to top-emitting organic light-emitting diodes. The results showed minor changes in the current-density–voltage characteristics after the PECVD process, as well as high reliability after a water dipping test.

Using SiO<sub>2</sub> nano-particles for better color uniformity and lumen output in 8500 K conformal and in-cup white LEDs

<span>In the effort of improving the performance of white light LEDs devices (WLEDs), the SiO<sub>2</sub> nano-particles were applied and have shown a significant impact on the optical properties. Specifically, the light output of the lighting devices is enhanced when a mixture of SiO<sub>2</sub> particles and silicone gel is diffused on the encapsulation layer surface. This enhancement is the result of light scattering from SiO<sub>2</sub> that strengthens the emitted blue light at further angles and reduces the color discrepancy. The evidence is that CCT deviation in SiO<sub>2</sub>-doped structure decline from 1000 K to 420 K in -70° to 70°. In addition, the SiO<sub>2</sub> with refractive index in between the phosphor material and outside environment allows light to be emitted outward more effectively. This lighting enhancement of SiO<sub>2</sub>-doped structure increases the lumen output by 2.25% at 120 mA power source in comparison to structure without SiO<sub>2</sub>. These experimental outcomes suggest that SiO<sub>2</sub> is an effective material to add in WLEDs structure for better lighting efficiency.</span>

Waterproof, flexible field-effect transistors with submicron monocrystalline Si nanomembrane derived encapsulation for continuous pH sensing

To understand the physio-pathological state of patients suffering from chronic diseases, scientists and clinicians need sensors to track chemical signals in real-time. However, the lack of stable, safe, and scalable biochemical sensing platforms capable of continuous operation in liquid environments imposes significant challenges in the timely diagnosis, intervention, and treatment of chronic conditions. This work reports a novel strategy for fabricating waterproof and flexible biochemical sensors with active electronic components, which feature a submicron encapsulation layer derived from monocrystalline Si nanomembranes with a high structural integrity due to the high formation temperature (>1000 °C). The ultrathin, yet dense and low-defect encapsulation enables continuous operation of field-effect transistors in biofluids for chemical sensing. The excellent stability in liquid environment and pH sensing performance of such transistors suggest their great potential as the foundation of waterproof and scalable biochemical sensors with active functionalities in the future. The understandings, knowledge base, and demonstrations for pH sensing reported here set the stage for the next generation long-term biosensing with a broad applicability in biomedical research, food science, and advanced healthcare.

Stress-matched laminated thin film of SiOxNy/SiO2/ SiOxNy for enhanced encapsulation of organic light-emitting devices.

The laminated structure of thin-film encapsulation (TFE) plays an important role for the reliability of organic light-emitting devices (OLEDs). In previous studies of TFE-structures, only the density of the films and the gas-barrier properties were taken into account, while a potential internal stress in the film was largely neglected. Internal stress issues can lead to cracks, warping, and delamination, which affect the performance of the encapsulation layer significantly. Finding ways to eliminate or perhaps utilize potential internal stresses of these films could have substantial benefits for future OLEDs. This study is at the forefront of the stress-related properties of TFE in conjunction with optoelectronic devices. We perform a moisture-barrier test of a fabricated encapsulated laminated structure (Si/50 nm SiOxNy/50nmSiO2/900 nm SiOxNy). The 50 nm SiOxNy buffer-layer was deposited (via chemical vapor deposition) to prevent the delamination and peeling between the SiO2 film and the OLEDs because of the high stress acting on the SiO2 layer. The water-vapor transmission rate of the laminated structure is below 5×10-5 g/m2·d at 38°C and 100% relative humidity. The concept of a laminated TFE-structure has a great application potential for future flexible and bendable organic optoelectronics.