Thin Parylene Layer Research Articles

Tunneling Dielectric Thickness‐Dependent Behaviors in Transistors Based on Sandwiched Small Molecule and Insulating Layer Structures

AbstractThis work demonstrates the floating gate devices featuring a small molecule‐insulator‐small molecule‐insulator sandwiched structure, where the versatile electrical characteristics can be achieved depending on the thickness of the intermediate parylene tunneling dielectric layer (TDL). For the thin parylene layer of 15 nm (parallel DNTT channel transistor), channel also forms in the lower DNTT layer, allowing hole carriers to tunnel through the parylene TDL. The parallel DNTT channel transistor exhibits electrical characteristics similar to a conventional DNTT transistor with the increased contact resistance due to the presence of the intermediate parylene layer. When the parylene TDL is slightly thicker to be 45 nm, negative differential transconductance followed by current saturation behavior is observed, due to tunneling through the parylene TDL. Finally, photomemory is demonstrated with the sufficiently thick parylene layer (≈80 nm), where hole carriers injected from the electrode cannot tunnel through the parylene TDL, allowing the lower DNTT layer to act as a floating gate for the photogenerated charge carriers. This photomemory shows programmability under the light illumination with the specific wavelength as well as the robust retention and endurance characteristics. Furthermore, the photomemory has been successfully implemented on flexible paper substrates.

Easy-To-Wear Auxetic SMA Knot-Architecture for Spatiotemporal and Multimodal Haptic Feedbacks.

Wearable haptic interfaces prioritize user comfort, but also value the ability to provide diverse feedback patterns for immersive interactions with the virtual or augmented reality. Here, to provide both comfort and diverse tactile feedback, an easy-to-wear and multimodal wearable haptic auxetic fabric (WHAF) is prepared by knotting shape-memory alloy wires into an auxetic-structured fabric. This unique meta-design allows the WHAF to completely expand and contract in 3D, providing superior size-fitting and shape-fitting capabilities. Additionally, a microscale thin layer of Parylene is coated on the surface to create electrically separated zones within the WHAF, featuring zone-specified actuation for conveying diverse spatiotemporal information to users with using the WHAF alone. Depending on the body part it is worn on, the WHAF conveys either cutaneous or kinesthetic feedback, thus, working as a multimodal wearable haptic interface. As a result, when worn on the forearm, the WHAF intuitively provides spatiotemporal information to users during hands-free navigation and teleoperation in virtual reality, and when worn on the elbow, the WHAF guides users to reach the desired elbow flexion, like a personal exercise advisor.

Assessment of transfer of morphological characteristics of Anomalous Aortic Origin of a Coronary Artery from imaging to patient specific 3D Printed models: A feasibility study

Background and ObjectiveThis study aims to determine the accuracy of patient specific 3D printed models in capturing pathological anatomical characteristics derived from CT angiography (CTA) in children with anomalous aortic origin of a coronary artery (AAOCA). Methods & MaterialsFollowing institutional regulatory approval, a standardized protocol for CTA of AAOCA was utilized for imaging. Blood volume of the aorta and coronaries were segmented from the DICOM images. A total of 10 models from 8 AAOCA patients were created, including 2 post-operative models. Mechanical properties of Agilus30 a flexible photopolymer coated with a thin layer of parylene, polyurethane (PU) and silicone and native aortic tissue from a postmortem specimen were compared. AAOCA models with wall thicknesses of 2mm aorta and 1.5mm coronaries were 3D printed in Agilus30 and coated with PU. CT of the printed models was performed, and 3D virtual models were generated. Transfer of anatomical characteristics and geometric accuracy were compared between the patient model virtual models. ResultsDynamic modulus of Agilus30 at 2mm thickness was found to be close to native aortic tissue. Structured reporting of anatomical characteristics by imaging experts showed good concordance between patient and model CTA Comparative patient and virtual model measurements showed Pearson's correlation (r) of 0.9959 for aorta (n=70) and 0.9538 for coronaries (n=60) linear, and 0.9949 for aorta (n=30) and 0.9538 for coronaries (n=30) cross-sectional, dimensions. Surface contour map mean difference was 0.08 ± 0.29mm. ConclusionsGeometrically accurate AAOCA models preserving morphological characteristics, essential for risk stratification and decision-making, can be 3D printed from a patient's CTA.

Efficient, Flexible, and Ultra‐Lightweight Inverted PbS Quantum Dots Solar Cells on All‐CVD‐Growth of Parylene/Graphene/oCVD PEDOT Substrate with High Power‐per‐Weight

AbstractUltra‐lightweight and flexible solar cells are desired for many potential applications, such as self‐powered aviation, wearable electronics, and the Internet of things. PbS quantum dots (QDs) are good candidates for this purpose due to their low‐cost and low‐temperature processing. In this work, a thin layer of parylene (1 µm) is deposited on a poly(ethylene teraphthalate) (PET) substrate using chemical vapor deposition (CVD) and is employed as a flexible substrate for PbS QDs solar cell. Here, the commonly used ITO electrode in the QDs photovoltaics (PVs) is replaced by CVD‐graphene and its wettability issue is addressed using a thin layer of oxidative CVD poly(3,4‐ethylene dioxythiophene) (oCVD PEDOT), which also works as second hole transporting layer in the device. Inverted PbS QDs device is fabricated on PET/parylene/graphene/oCVD PEDOT stack and finally by removing the PET substrate, an ultra‐lightweight PbS QDs solar cell is achieved. Using this architecture, a power conversion efficiency (PCE) of 7.1% and a power‐per‐weight of 12.3 W g−1 are achieved. Additionally, the QDs device on graphene shows good flexibility as compared to the device on PET/ITO. This work highlights the advantages of oCVD PEDOT and CVD‐graphene for the fabrication of flexible and ultralight weight photostatics.

A Microfluidic MEMS-Microbalance Platform With Minimized Acoustic Radiation in Liquid.

In this article, the microfluidic channels that deliver liquid to a microscale thin-film piezoelectric-on-silicon (TPoS) gravimetric resonant sensor are incorporated into the backside of the silicon-on-insulator (SOI) wafer on which the resonator is fabricated. Specifically, a microwell is embedded at the bottom of the disk -shaped TPoS resonator, while a very thin layer of parylene covering the backside of the resonator and the microwell forms an isolation layer between the liquid and the top device-layer features. In this way, the liquid is in contact with the backside of the resonator, while the device-defining trenches and the electrical connections to the resonator stay clear, thus mitigating the acoustic energy loss and undesirable feedthroughs. The impact of the parylene layer thickness on a few symmetric ( S ) and antisymmetric ( A ) Lamb wave modes of the resonator is experimentally studied, and the performance of such modes in the liquid is characterized by filling the microwells through a PDMS-based microfluidic channel. The parylene layer, while marginally affecting the resonator in the air, is found to substantially enhance its performance in the liquid media. Strong resonance peaks with high quality factors ( Q ) are observed for the S modes, among which Q values above 400 are recorded for a specific mode named S (4, 2) (among the highest ever reported). This article can potentially facilitate the realization of highly stable and sensitive resonant mass sensors (i.e., microbalance) for real-time applications. Additionally, the effect of the acoustic energy radiation in the form of evanescent shear and longitudinal waves in liquid on the Q and resonance frequency of the disk resonators is experimentally validated.

Ultra-broadband terahertz absorption using bi-metasurfaces based multiplexed resonances.

In this paper, we demonstrate an ultra-broadband terahertz (THz) bi-metasurfaces absorber composed of two stacking metasurfaces backed by a metallic ground plane. The bottom metasurface consists of four multiplexed cross resonators with different geometries on a thin parylene layer, achieving a bandwidth of 3.80 THz with the absorption higher than 50% at high frequency. Meanwhile, the top metasurface, including two multiplexed cross resonators with different sizes on a relatively thicker parylene layer, provides a low frequency absorption band with an additional Salisbury screen absorption peak that connects the two absorption bands of the two metasurfaces, therefore enabling an ultra-broadband absorption. The experimental absorption spectrum of the bi-metasurfaces shows a bandwidth of 4.46 THz while the absorption exceeding 50% and a full width at half maxima (FWHM) of 97.7%. The ultra-broadband absorber will be a promising candidate for THz broadband detection.

A Self-Wetting Paper Electrode for Ubiquitous Bio-Potential Monitoring

This paper aims to develop a flexible and cost-effective dry electrode with low and stable contact impedance. With these benefits, the electrode can be practically used in ubiquitous bio-potential monitoring with similar signal-to-noise ratio as commercial wet electrode. A self-wetting electrode is developed by the aid of moisture naturally created by skin under the electrode. It consists of a layer of ethylcellulose fiber paper coated with PEDOT/PSS (PCwPEDOT) and a thin layer of parylene. PCwPEOT, which has a large contact area composed of micro-scale fibers, is a 30-μm flexible membrane that acts as the electrode material. A 3-μm parylene bonding at the backside of PCwPEOT, as a high-performance vacuum membrane, can collect moisture or sweat naturally evaporating from the skin and store it in the PCwPEDOT layer. This design increases the humidity of skin, especially the water content in the corneum, acting as electrolyte containing ions, increases effective contact area between electrode and skin, and decreases the impedance of the electrode. With an environmentally friendly and cost-effective fabrication process, the 33-μm thickness of electrode is light and flexible. It can be tailored to proper size according to the application. It achieves lower contact impedance compared with dry electrodes with a similar structure. Its recording performance is comparable to commercial patch electrode. The proposed electrode provides high-quality signals, and comfortable user experience in bio-potential recording. It is feasible for developing a long-term wearable system for bio-potential monitoring.

Topography-guided buckling of swollen polymer bilayer films into three-dimensional structures.

Thin films that exhibit spatially heterogeneous swelling often buckle into the third dimension to minimize stress. These effects, in turn, offer a promising strategy to fabricate complex three-dimensional structures from two-dimensional sheets. Here we employ surface topography as a new means to guide buckling of swollen polymer bilayer films and thereby control the morphology of resulting three-dimensional objects. Topographic patterns are created on poly(dimethylsiloxane) (PDMS) films selectively coated with a thin layer of non-swelling parylene on different sides of the patterned films. After swelling in an organic solvent, various structures are formed, including half-pipes, helical tubules, and ribbons. We demonstrate these effects and introduce a simple geometric model that qualitatively captures the relationship between surface topography and the resulting swollen film morphologies. The model's limitations are also examined.

Statistical analysis of dielectric breakdown of liquid insulated printed circuit boards

For introducing power converters at ambient pressure at large sea depths, dielectric liquids are proposed as insulation for power electronic converters. This paper presents statistical analysis of short time tests of partial discharge and breakdown voltage on the trench between metallized edges of printed circuit boards (PCBs) embedded in in different dielectric liquids. Performance of Nytro 10XN, Midel 7131 and Galden HT230 were investigated. Investigations were done both for sinusoidal voltages and for positive fast transient square voltages. Galden as insulating liquid has the highest withstand voltage with higher breakdown voltage at low probability of failure. The overall evaluation shows that all the liquid samples possessed high dielectric strength that has the potential of providing sufficient insulation for subsea power converters. Coating the metal surfaces with thin layer of parylene increases the system reliability by reducing the effect of contaminations.

A novel fabrication method of Parylene-based microelectrodes utilizing inkjet printing

We report a novel fabrication method of creating thin flexible Parylene-based microelectrodes. The fabrication technique described here is based on inkjet printing and thus does not require conventional photolithography and thin-film deposition processes. First, silver microelectrodes are printed on poly-dimethylsiloxane (PDMS) spin-coated on a silicon wafer. Then a thin Parylene layer is deposited on top of the PDMS layer followed by peeling-off. The silver microelectrode patterns are flawlessly transferred to the Parylene film during this process. Finally, sintering of the silver pattern is achieved in vacuum oven. Narrow (40–100μm) silver microelectrodes were perfectly transferred from PDMS onto Parylene film without structural damages or significant drop in electrical resistance (Note that direct printing of silver microelectrode patterns on Parylene is very challenging due to the surface property of Parylene.). In fact, the silver microelectrodes transferred onto Parylene showed lower electrical resistance and better adhesion than the original silver microelectrodes printed on PDMS. In order to demonstrate the utility of thin flexible Parylene-based silver microelectrodes, we fabricated diverse microelectrodes and conducted dielectrophoretic (DEP) manipulation of microbeads with them. We believe that this rapid and low-cost fabrication method of creating thin flexible Parylene-based microelectrodes can be used in a variety of applications in flexible electronics, neural engineering, medical implants as well as MEMS and lab on a chip.

Silver ions eluted from partially protected silver nanoparticles.

The most prominent character of a new type of antibacterial urological catheters is the zebra-stripe pattern of a silver film, which is plated electroless on their interior wall and capped by a very thin semipermeable layer of parylene. This design effectively controls the release rate of Ag(+) ions in artificial urine, which has been measured as function of time with optical emission spectroscopy. By evaluating the minimum inhibitory concentration against certain strains of bacteria with solutions of AgNO3 of known concentration with the method of optical density and applying this analysis to the silver-eluting catheters, it was shown that this moderation prolongs the period of their application significantly. But to act as antibacterial agent in chlorine-containing solutions, as in urine, the presence of urea is required to avoid precipitation of AgCl and to meet or even exceed the minimum inhibitory concentration of Ag(+). The quality of the silver depot layer was further determined by the deposition rate and its morphology, which revealed that the film consisted of grains with a mean size of 150 nm.

A Low‐Voltage Microfluidic Valve Based upon a Reversible Hydrophobicity Effect

A microfluidic valve is reported based on a reversible hydrophobicity effect via the growth and retraction of nanotextured metal filaments on the surface of a solid electrolyte. The valve is integrated onto the bottom of the channel and actuated by a DC voltage. The dendritic silver filaments are tens to hundreds of nanometers in height and can be isolated from the channel fluid by a thin Parylene layer. An applied bias of 6 V or less grows or dissolves the filaments, depending on the polarity, and the roughness so created alters the fluid‐surface interface, manipulating hydrophobicity of the interface, transitioning from the lotus effect to the petal effect. To demonstrate this valve, the fluid flow in a poly(dimethylsiloxane)‐enclosed microfluidic channel of up to 30 μm in depth and up to 250 μm in width is stopped and restarted within ≈25 s of actuation. The effect is nonvolatile, thus no static power is required to retain the on/off states of the valve.

A High Fill-Factor Annular Array of High Frequency Piezoelectric Micromachined Ultrasonic Transducers

This paper presents a 1.2-mm diameter high fill-factor array of 1261 piezoelectric micromachined ultrasonic transducers (PMUTs) operating at 18.6 MHz in fluid for intravascular ultrasound imaging. At 1061 transducers/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the PMUT array has a 10-20 times higher density than previous PMUT arrays realized to date. Aluminum nitride (AlN)-based PMUTs described in this paper are fabricated using a process compatible with the fabrication of inertial sensors, radio frequency (RF) resonators, and CMOS integrated circuits. The PMUTs are released using a front-side sacrificial etch through etching holes that are subsequently sealed by a thin layer of parylene. Finite element method and analytical results, including resonant frequency, pressure sensitivity, output acoustic pressure, and directivity are given to guide the PMUT design effectively, and are shown to match well with measurement results. Due to the PMUTs thin membrane (750-nm AlN/800-nm SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and small diameter, a single 25-μm PMUT has approximately omnidirectional directivity and no near-field zone with irregular pressure pattern. PMUTs are characterized in both the frequency and time domains. Measurement results show a large displacement response of 2.5 nm/V at resonance and good frequency matching in air, high center frequency of 18.6 MHz and wide bandwidth of 4.9 MHz, when immersed in fluid. Phased array simulations based on measured PMUT parameters show a tightly focused high-output pressure acoustic beam.

Fine control of drug delivery for cochlear implant applications

Cochlear implants are neuroprostheses that are inserted into the inner ear to directly electrically stimulate the auditory nerve, thus replacing lost cochlear receptors, the hair cells. The reduction of the gap between electrodes and nerve cells will contribute to technological solutions simultaneously increasing the frequency resolution, the sound quality and the amplification of the signal. Recent findings indicate that neurotrophins (NTs) such as brain derived neurotrophic factor (BDNF) stimulate the neurite outgrowth of auditory nerve cells by activating Trk receptors on the cellular surface (1–3). Furthermore, small-size TrkB receptor agonists such as di-hydroxyflavone (DHF) are now available, which activate the TrkB receptor with similar efficiency as BDNF, but are much more stable (4). Experimentally, such molecules are currently used to attract nerve cells towards, for example, the electrodes of cochlear implants. This paper analyses the scenarios of low dose aspects of controlled release of small-size Trk receptor agonists from the coated CI electrode array into the inner ear. The control must first ensure a sufficient dose for the onset of neurite growth. Secondly, a gradient in concentration needs to be maintained to allow directive growth of neurites through the perilymph-filled gap towards the electrodes of the implant. We used fluorescein as a test molecule for its molecular size similarity to DHF and investigated two different transport mechanisms of drug dispensing, which both have the potential to fulfil controlled low-throughput drug-deliverable requirements. The first is based on the release of aqueous fluorescein into water through well-defined 60-μm size holes arrays in a membrane by pure osmosis. The release was both simulated using the software COMSOL and observed experimentally. In the second approach, solid fluorescein crystals were encapsulated in a thin layer of parylene (PPX), hence creating random nanometer-sized pinholes. In this approach, the release occurred due to subsequent water diffusion through the pinholes, dissolution of the fluorescein and then release by out-diffusion. Surprisingly, the release rate of solid fluorescein through the nanoscopic scale holes was found to be in the same order of magnitude as for liquid fluorescein release through microscopic holes.

A New Technology of Ultrathin AlN Piezoelectric Sensor for Pulse Wave Measurement

In this study the design and characterization of a new technology of ultrathin AlN piezoelectric sensors able to measure micro-deformations is reported. The sensors are fabricated using a CMOS compatible clean room process in which the sensitive part is embedded into a thin bio-compatible and conformal layer of parylene (total thickness below 10μm). That makes the sensors very flexible and sensitive to micro-deformation measurements. In this study, this technology is applied to monitor heart activity: heart rate, blood pulse wave, pulse wave velocity. Blood pulse wave could be measured with a very good accuracy; this technology could thus be used for the prediction of cardiovascular diseases by analyzing the pulse wave shape.

Catalytic and thermal characterisations of nanosized PdPt / Al&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; for hydrogen detection

Abstract. Palladium platinum (PdPt) has been intensively studied these last decades due to high conversion rate in hydrogen oxidation at room temperature with significant exothermic effects. These remarkable properties have been studied by measuring the temperature variations of alumina (Al2O3) supported nanosized PdPt nanoparticles exposed to different hydrogen concentrations in dry air. This catalyst is expected to be used as a sensing material for stable and reversible ultrasensitive hydrogen sensors working at room temperature (low power consumption). Structural and gas sensing characterisations and catalytic activity of PdPt / Al2O3 systems synthesised by co-impregnation will be presented. Catalytic characterisations show that the system is already active at room temperature and that this activity sharply increases with rise in temperature. Moreover, the increase of the PdPt proportion in the co-impregnation process improves the activity, and very high conversion can be reached even at room temperature. The thermal response (about 3 °C) of only 1 mg of PdPt / Al2O3 is reversible, and the time response is about 5 s. The integration of PdPt / Al2O3 powder on a flat substrate has been realised by the deposition onto the powder of a thin porous hydrophobic layer of parylene. The possibility of using PdPt in gas sensors will be discussed.

Migration issues in sintered-silver die attaches operating at high temperature

Silver sintering is a promising alternative to high melting point (HMP) solders which contain lead. Indeed, it offers better thermal and electrical properties and can operate at higher temperature. However, silver tends to migrate in presence of electric field, oxygen (or moisture) and high temperature, causing short circuits. In this paper, we assess the extent of this issue, and we evaluate the protective effect of a thin layer of parylene. It is shown that silver migration occurs rapidly (tens to hundreds of hours at 300°C), but that parylene offers a good mitigation of this issue.

Control over the interface properties of carbon nanotube-based optoelectronic memory devices

Optoelectronic nonvolatile memory elements based on polymer-coated carbon nanotube devices can serve as building blocks in programmable circuits. Although essential for improving the circuit performances, the details of the charge trapping mechanism in these mixed organic/inorganic optoelectronic devices are not fully elucidated. The detailed mechanism was investigated by intercalating layers of a hydrophobic organic dielectric (parylene) at different interfaces in the device structure. A thin parylene layer separating the SiO2/nanotube interface from the photosensitive polymer coating is presented as an optimized solution in terms of charging, stability, and robustness.

Parylene Insulated Probes for Scanning Electrochemical-Atomic Force Microscopy

Scanning electrochemical-atomic force microscopy (SECM-AFM) is a powerful technique that can be used to obtain in situ information related to electrochemical phenomena at interfaces. Fabrication of probes to perform SECM-AFM experiments remains a challenge. Herein, we describe a method for formation of microelectrodes at the tip of commercial conductive AFM probes and demonstrate application of these probes to SECM-AFM. Probes were first insulated with a thin parylene layer, followed by subsequent exposure of active electrodes at the probe tips by mechanical abrasion of the insulating layer. Characterization of probes was performed by electron microscopy and cyclic voltammetry. In situ measurement of localized electrochemical activity with parylene-coated probes was demonstrated through measurement of the diffusion of Ru(NH)(6)(3+) across a porous membrane.

Quality Factor Enhancement of Lateral Microresonators in Liquid Media by Hydrophobic Coating

In this letter, a new method of improving the quality factor of microresonators inside liquids is presented. By utilizing a conformally coated thin layer of parylene, which is highly hydrophobic, we trap air between the narrow gaps of a lateral resonator and prevent liquids from entering the gaps, thus preventing the viscous damping increase on the side surfaces. Initial tests with capacitive comb drives show that the quality factor decreases only threefold (from 157 to 55) when the device is operated in water after parylene coating. This method is very promising for in-liquid resonator applications, particularly real-time bioagent detection where high quality factor is essential for high mass resolution.