A parylene/graphene UV photodetector with ultrahigh responsivity and long term stability.

Long term stability, high responsivity, and fast response speed are essential for the commercialization of graphene photodetectors (GPDs). In this work, a parylene/graphene UV photodetector with long term stability, ultrahigh responsivity and fast response speed, is demonstrated. Parylene as a stable physical and chemical insulating layer reduces the environmental sensitivity of graphene, and enhances the performances of GPDs. In addition, utilizing bilayer electrodes reduces the buckling and damage of graphene after transferring. The parylene/graphene UV photodetector exhibits an ultrahigh responsivity of 5.82 × 105AW-1under 325 nm light irradiation at 1 V bias. Additionally, it shows a fast response speed with a rise time of 80µs and a fall time of 17µs, and a long term stability at 405 nm wavelength which is absent in the device without parylene. The parylene/graphene UV photodetector possesses superior performances. This paves the way for the commercial application of the high-performance graphene hybrid photodetectors, and provides a practical method for maintaining the long term stability of two dimensional (2D) materials.

Nationwide multicenter study on adverse events associated with a patency capsule: Additional survey of appropriate use of patency capsule study.

BACKGROUND AND AIM: The PillCam patency capsule (PC) without a radio frequency identification tag was released to preclude retention of the small bowel capsule endoscope (CE) in Japan in 2012. We conducted a multicenter study to determine tag-less PC-related adverse events (AEs). METHODS: We first conducted a retrospective survey using a standardized data collection sheet for the clinical characteristics of PC-related AEs among 1096 patients collected in a prospective survey conducted between January 2013 and May 2014 (Cohort 1). Next, we retrospectively investigated additional AEs that occurred before and after Cohort 1 within the period June 2012 and December 2014 among 1482 patients (Cohort 2). RESULTS: Of the 2578 patients who underwent PC examinations from both cohorts, 74 AEs occurred among 61 patients (2.37%). The main AEs were residual parylene coating in 25 events (0.97%), PC-induced small bowel obstruction, suspicious of impaction, in 23 events (0.89%), and CE retention even after patency confirmation in 10 events (0.39%). Residual parylene coating was significantly associated with Crohn's disease (P < 0.01). Small bowel obstruction was significantly associated with physicians with less than 1 year of experience handling the PC and previous history of postprandial abdominal pain (P < 0.01 and P < 0.03, respectively). CE retention was ascribed to erroneous judgment of PC localization in all cases. CONCLUSIONS: This large-scale multicenter study provides evidence supporting the safety and efficiency of a PC to preclude CE retention. Accurate PC localization in patients without excretion and confirmation of previous history of postprandial abdominal pain before PC examinations is warranted (UMIN000010513).

Significantly Improved Dielectric Performance of All-Organic Parylene/Polyimide/Parylene Composite Films with Sandwich Structure.

The development of novel polymer dielectrics with enhanced dielectric performance is a great challenge for application of film capacitors in modern electronics and electrical systems. Herein, an innovative approach of chemical vapor deposition polymerization technology is proposed to prepare the all-organic sandwich structured parylene/polyimide/parylene (Py/PI/Py) composite films by employing poly(chloro-para-xylylene) (parylene C) as the outer layers and polyimide (PI) as the inner layer. The Py/PI/Py composites exhibit superior thermal resistance and outstanding mechanical properties. Moreover, thanks to the interfacial effect which contributes to reinforcing the dielectric response and the thickness effect which facilitates improving the breakdown strength, the dielectric performance of Py/PI/Py composites has been enhanced significantly. Accordingly, dielectric constant of 4.52-5.09, dissipation factor of 0.21-1.01%, and breakdown strength of 307-460 MV m-1 are achieved. Besides, notable energy storage performance is also obtained in Py/PI/Py composite dielectrics. Consequently, this novel application of chemical vapor deposition polymerization method in preparing all-organic multilayered polymer composite films with sandwich structure shows promising potential in film capacitor applications in harsh conditions.

Characterization of thin film Parylene C device curvature and the formation of helices via thermoforming.

In microfabricated biomedical devices, flexible, polymer substrates are becoming increasingly preferred over rigid, silicon substrates because of their ability to conform to biological tissue. Such devices, however, are fabricated in a planar configuration, which results in planar devices that do not closely match the shape of most tissues. Thermoforming, a process which can reshape thermoplastic polymers, can be used to transform flat, thin film, polymer devices with patterned metal features into complex three-dimensional (3D) geometries. This process extends the use of planar microfabrication to achieve 3D shapes which can more closely interface with the body. Common shapes include spheres, which can conform to the shape of the retina; cones, which can be used as a sheath to interface with an insertion stylet; and helices, which can be wrapped around nerves, blood vessels, muscle fibers, or be used as strain relief feature. This work characterizes the curvature of thin film Parylene C devices with patterned metal features built with varying Parylene thicknesses and processing conditions. Device curvature is caused by film stress in each Parylene and metal layer, which is characterized experimentally and by a mathematical model which estimates the effects of device geometry and processing on curvature. Using this characterization, an optimized process to thermoform thin film Parylene C devices with patterned metal features into 0.25 mm diameter helices while preventing cracking in the polymer and metal was developed.

Wearable System Based on Ultra-Thin Parylene C Tattoo Electrodes for EEG Recording.

In an increasingly interconnected world, where electronic devices permeate every aspect of our lives, wearable systems aimed at monitoring physiological signals are rapidly taking over the sport and fitness domain, as well as biomedical fields such as rehabilitation and prosthetics. With the intent of providing a novel approach to the field, in this paper we discuss the development of a wearable system for the acquisition of EEG signals based on a portable, low-power custom PCB specifically designed to be used in combination with non-conventional ultra-conformable and imperceptible Parylene-C tattoo electrodes. The proposed system has been tested in a standard rest-state experiment, and its performance in terms of discrimination of two different states has been compared to that of a commercial wearable device for EEG signal acquisition (i.e., the Muse headset), showing comparable results. This first preliminary validation demonstrates the possibility of conveniently employing ultra-conformable tattoo-electrodes integrated portable systems for the unobtrusive acquisition of brain activity.

Parylene-based memristive crossbar structures with multilevel resistive switching for neuromorphic computing.

Currently, there is growing interest in wearable and biocompatible smart computing and information processing systems that are safe for the human body. Memristive devices are promising for solving such problems due to a number of their attractive properties, such as low power consumption, scalability, and the multilevel nature of resistive switching (plasticity). The multilevel plasticity allows memristors to emulate synapses in hardware neuromorphic computing systems (NCSs). The aim of this work was to study Cu/poly-p-xylylene(PPX)/Au memristive elements fabricated in the crossbar geometry. In developing the technology for manufacturing such samples, we took into account their characteristics, in particular stable and multilevel resistive switching (at least 10 different states) and low operating voltage (<2 V), suitable for NCSs. Experiments on cycle to cycle (C2C) switching of a single memristor and device to device (D2D) switching of several memristors have shown high reproducibility of resistive switching (RS) voltages. Based on the obtained memristors, a formal hardware neuromorphic network was created that can be trained to classify simple patterns.

A versatile technology for colloidal crystal transfer using parylene coatings and hydrosoluble polymers.

We propose a novel versatile colloidal crystal transfer technique compatible with a wide range of water-insoluble substrates regardless of their size, material, and wettability. There are no inherent limitations on colloidal particles material and size. The method possibilities are demonstrated via the colloidal transfer on quartz, glass substrates with a flat and curved surface, and via the fabrication of 3D colloidal structure with 5 overlaid colloidal monolayers. The process occurs at a room temperature in water and is independent from the illumination conditions, which makes it ideal for experimental manipulations with sensitive functional substrates. We performed the nanosphere photolithography process on a photosensitive substrate with a transferred colloidal monolayer. The metallized hexagonal arrays of nanopores demonstrated a clear resonant plasmonic behavior. We believe that due to its high integration possibilities the proposed transfer technique will find applications in a large-area surface nanotexturing, plasmonics, and will speed up a device fabrication process.

An Inkjet Printed Flexible Electrocorticography (ECoG) Microelectrode Array on a Thin Parylene-C Film.

Electrocorticography (ECoG) is a conventional, invasive technique for recording brain signals from the cortical surface using an array of electrodes. In this study, we developed a highly flexible 22-channel ECoG microelectrode array on a thin Parylene film using novel fabrication techniques. Narrow (<40 µm) and thin (<500 nm) microelectrode patterns were first printed on PDMS, then the patterns were transferred onto Parylene films via vapor deposition and peeling. A custom-designed, 3D-printed connector was built and assembled with the Parylene-based flexible ECoG microelectrode array without soldering. The impedance of the assembled ECoG electrode array was measured in vitro by electrochemical impedance spectroscopy, and the result was consistent. In addition, we conducted in vivo studies by implanting the flexible ECoG sensor in a rat and successfully recording brain signals.

Cell viability and cytotoxicity of inkjet-printed flexible organic electrodes on parylene C.

This study reports on the fabrication of biocompatible organic devices by means of inkjet printing with a novel combination of materials. The devices were fabricated on Parylene C (PaC), a biocompatible and flexible polymer substrate. The contact tracks were inkjet-printed using a silver nanoparticle ink, while the active sites were inkjet-printed using a poly (3,4ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) solution. To insulate the final device, a polyimide ink was used to print a thick film, leaving small open windows upon the active sites. Electrical characterization of the final device revealed conductivities in the order of 103 and 102 S.cm-1 for Ag and PEDOT based inks, respectively. Cell adhesion assays performed with PC-12 cells after 96 h of culture, and B16F10 cells after 24 h of culture, demonstrated that the cells adhered on top of the inks and cell differentiation occurred, which indicates Polyimide and PEDOT:PSS inks are non-toxic to these cells. The results indicate that PaC, along with its surface-treated variants, is a potentially useful material for fabricating cell-based microdevices.

A portable multi-sensor module for monitoring external ventricular drains.

External ventricular drains (EVDs) are used clinically to relieve excess fluid pressure in the brain. However, EVD outflow rate is highly variable and typical clinical flow tracking methods are manual and low resolution. To address this problem, we present an integrated multi-sensor module (IMSM) containing flow, temperature, and electrode/substrate integrity sensors to monitor the flow dynamics of cerebrospinal fluid (CSF) drainage through an EVD. The impedimetric sensors were microfabricated out of biocompatible polymer thin films, enabling seamless integration with the fluid drainage path due to their low profile. A custom measurement circuit enabled automated and portable sensor operation and data collection in the clinic. System performance was verified using real human CSF in a benchtop EVD model. Impedimetric flow sensors tracked flow rate through ambient temperature variation and biomimetic pulsatile flow, reducing error compared with previous work by a factor of 6.6. Detection of sensor breakdown using novel substrate and electrode integrity sensors was verified through soak testing and immersion in bovine serum albumin (BSA). Finally, the IMSM and measurement circuit were tested for 53 days with an RMS error of 61.4 µL/min.

Fabrication of a Multilayer Implantable Cortical Microelectrode Probe to Improve Recording Potential.

Intracortical neural probes are a key enabling technology for acquiring high fidelity neural signals within the cortex. They are viewed as a crucial component of brain-computer interfaces (BCIs) in order to record electrical activities from neurons within the brain. Smaller, more flexible, polymer-based probes have been investigated for their potential to limit the acute and chronic neural tissue response. Conventional methods of patterning electrodes and connecting traces on a single supporting layer can limit the number of recording sites which can be defined, particularly when designing narrower probes. We present a novel strategy of increasing the number of recording sites without proportionally increasing the size of the probe by using a multilayer fabrication process to vertically layer recording traces on multiple Parylene support layers, allowing more recording traces to be defined on a smaller probe width. Using this approach, we are able to define 16 electrodes on 4 supporting layers (4 electrodes per layer), each with a 30 µm diameter recording window and 5 µm wide connecting trace defined by conventional LWUV lithography, on an 80 µm wide by 9 µm thick microprobe. Prior to in vitro and in vivo validation, the multilayer probes are electrically characterized via impedance spectroscopy and evaluating crosstalk between adjacent layers. Demonstration of acute in vitro recordings in a cerebral organoid model and in vivo recordings in a murine model indicate the probe's capability for single unit recordings. This work demonstrates the ability to fabricate smaller, more compliant neural probes without sacrificing electrode density.

Surface Modification of Parylene C Film via Buchwald-Hartwig Amination for Organic Solvent-Compatible and Flexible Microfluidic Channel Bonding.

Surface modification offers an efficient and economical route to installing functional groups on a polymer surface. This work demonstrates that primary amine groups can be introduced onto a polymer surface via Buchwald-Hartwig amination, and the functionalized substrates can be chemically bonded to produce functional microfluidic devices. By activating the CCl bond in commercially used poly(chloro-p-xylylene) (parylene C) by Pd catalyst and substituting Cl with the amine source, the amine groups are successfully installed in a facile and recyclable manner. The substrates can be covalently bonded with each other via amine-isocyanate chemistry, providing much higher bonding strength compared to previous methods based on noncovalent adhesive coatings. As a result, transparent and flexible microfluidic channels can be fabricated that are compatible with organic solvents and high pressure. Retention of amine group reactivity in the channel suggests the potential of this methodology for the surface immobilization of functional molecules for microfluidic reactors and biosensors.

Bonding methods for chip integration with Parylene devices.

Flexible electronics require more compact interconnects for next-generation devices. Polymer devices can be bonded to integrated circuit chips, but combining flexible and rigid substrates poses unique technical challenges. Existing technologies either cannot achieve the density required for modern chips or employ specialized equipment and complex processes to do so. Here, we adapt several approaches to achieve fine-pitch bonding between rigid and flexible substrates including epoxy, ultrasonic wire, and anisotropic conductive film bonding and also introduce a novel technique called polymer ultrasonic on bump (PUB) bonding. Using Parylene C devices and various rigid substrates as our model testbed systems, we investigate these four methods across a range of bond pad size and pitch by measuring yield and resistance and by subjecting devices to thermomechanical reliability tests. We demonstrate that all methods are capable of bonding fine pitch interconnects (100 µm) at low temperature (<100 °C). Additionally, we focus on PUB bonding and join a packaged chip and a bare die to Parylene devices.

Defect Filling Method of Sensor Encapsulation Based on Micro-Nano Composite Structure with Parylene Coating.

The demand for waterproofing of polymer (parylene) coating encapsulation has increased in a wide variety of applications, especially in the waterproof protection of electronic devices. However, parylene coatings often produce pinholes and cracks, which will reduce the waterproof effect as a protective barrier. This characteristic has a more significant influence on sensors and actuators with movable parts. Thus, a defect filling method of micro-nano composite structure is proposed to improve the waterproof ability of parylene coatings. The defect filling method is composed of a nano layer of Al2O3 molecules and a micro layer of parylene polymer. Based on the diffusion mechanism of water molecules in the polymer membrane, defects on the surface of polymer encapsulation will be filled and decomposed into smaller areas by Al2O3 nanoparticles to delay or hinder the penetration of water molecules. Accordingly, the dense Al2O3 nanoparticles are utilized to fill and repair the surface of the organic polymer by low-rate atomic layer deposition. This paper takes the pressure sensor as an example to carry out the corresponding research. Experimental results show that the proposed method is very effective and the encapsulated sensors work properly in a saline solution after a period of time equivalent to 153.9 days in body temperature, maintaining their accuracy and precision of 2 mmHg. Moreover, the sensors could improve accuracy by about 43% after the proposed encapsulation. Therefore, the water molecule anti-permeability encapsulation would have broad application prospects in micro/nano-device protection.

Reduced bacterial adhesion with parylene coating: Potential implications for Micra transcatheter pacemakers.

INTRODUCTION: Infections of cardiac implantable electronic devices remain a prevalent health concern necessitating the advent of novel preventative strategies. Based on the observation that bacterial infections of the Micra transcatheter pacemaker device are extremely rare, we examine the effect of parylene coating on bacterial adhesion and growth. METHODS: Bacterial growth was compared on polyurethane coated, bare, or parylene coated titanium surfaces. Eight test samples per bacterial species and material combination were incubated with Staphylococcus Aureus or Pseudomonas aeruginosa for 24 hours and then assayed for bacterial growth. The surface contact angle was also characterized by measuring the angle between the tangent to the surface of a liquid droplet made with the surface of the solid sample. RESULTS: The mean bacterial colony counts were significantly reduced for both parylene coated titanium versus bare samples (3.69 ± 0.27 and 4.80 ± 0.48 log[CFU/mL] respectively for S. aureus [P < .001] and 5.51 ± 0.27 and 6.08 ± 0.11 log[CFU/mL] respectively for P. aeruginosa [P < .001]), and for parylene coated titanium versus polyurethane samples (4.27 ± 0.42 and 5.40 ± 0.49 log[CFU/mL] respectively for S. aureus [P < .001] and 4.23 ± 0.42 and 4.84 ± 0.32 log[CFU/mL] respectively for P. aeruginosa [P = .006]). Parylene coated titanium samples had a higher contact angle compared with bare titanium, but lower compared with polyurethane (mean contact angle 87.5 ± 3.1 degrees parylene, 73.3 ± 3.7 degrees titanium [P < .001 vs parylene], and 94.8 ± 3.7 degrees polyurethane [P = .002 vs parylene]). CONCLUSIONS: Parylene coating significantly reduced the ability of bacteria to grow in colony count assays suggesting that this could contribute to the reduction of bacterial infections of Micra transcatheter pacemakers.

Rapid lipid bilayer membrane formation on Parylene coated apertures to perform ion channel analyses.

We present a chip design allowing rapid and robust lipid bilayer (LBL) membrane formation using a Parylene coated thin silicon nitride aperture. After bilayer formation, single membrane channels can be reconstituted and characterized by electrophysiology. The ability for robust reconstitution will allow parallelization and enhanced screening of small molecule drugs acting on or permeating across the membrane channel. The aperture was realized on a microfabricated silicon nitride membrane by using standard clean-room fabrication processes. To ensure the lipid bilayer formation, the nitride membrane was coated with a hydrophobic and biocompatible Parylene layer. We tested both Parylene-C and Parylene-AF4. The contact angle measurements on both Parylene types showed very good hydrophobic properties and affinity to lipids. No precoating of the Parylene with an organic solvent is needed to make the aperture lipophilic, in contradiction to Teflon membranes. The chips can be easily placed in an array utilizing a 3D printed platform. Experiments show repetitive LBL formation and destruction (more than 6 times) within a very short time (few seconds). Through measurements we have established that the LBL layers are very thin. This allows the investigation of the fusion process of membrane proteins i.e. outer membrane protein (OmpF) in the LBL within a few minutes.

A Parylene Neural Probe Array for Multi-Region Deep Brain Recordings.

A Parylene C polymer neural probe array with 64 electrodes purposefully positioned across 8 individual shanks to anatomically match specific regions of the hippocampus was designed, fabricated, characterized, and implemented in vivo for enabling recording in deep brain regions in freely moving rats. Thin film polymer arrays were fabricated using surface micromachining techniques and mechanically braced to prevent buckling during surgical implantation. Importantly, the mechanical bracing technique developed in this work involves a novel biodegradable polymer brace that temporarily reduces shank length and consequently, increases its stiffness during implantation, therefore enabling access to deeper brain regions while preserving a low original cross-sectional area of the shanks. The resulting mechanical properties of braced shanks were evaluated at the benchtop. Arrays were then implemented in vivo in freely moving rats, achieving both acute and chronic recordings from the pyramidal cells in the cornu ammonis (CA) 1 and CA3 regions of the hippocampus which are responsible for memory encoding. This work demonstrated the potential for minimally invasive polymer-based neural probe arrays for multi-region recording in deep brain structures.

A 512-Channel Multi-Layer Polymer-Based Neural Probe Array.

We present for the first time the design, fabrication, and preliminary bench-top characterization of a high-density, polymer-based penetrating microelectrode array, developed for chronic, large-scale recording in the cortices and hippocampi of behaving rats. We present two architectures for these targeted brain regions, both featuring 512 Pt recording electrodes patterned front-and-back on micromachined eight-shank arrays of thin-film Parylene C. These devices represent an order of magnitude improvement in both number and density of recording electrodes compared with prior work on polymer-based microelectrode arrays. We present enabling advances in polymer micro-machining related to lithographic resolution and a new method for back-side patterning of electrodes. In vitro electrochemical data verifies suitable electrode function and surface properties. Finally, we describe next steps toward the implementation of these arrays in chronic, large-scale recording studies in free-moving animal models.

Fabrication of Parylene-Coated Microneedle Array Electrode for Wearable ECG Device.

Microneedle array electrodes (MNE) showed immense potential for the sensitive monitoring of the bioelectric signals by penetrating the stratum corneum with high electrical impedance. In this paper, we introduce a rigid parylene coated microneedle electrode array and portable electrocardiography (ECG) circuit for monitoring of ECG reducing the motion artifacts. The developed MNE showed stability and durability for dynamic and long-term ECG monitoring in comparison to the typical silver-silver chloride (Ag/AgCl) wet electrodes. The microneedles showed no mechanical failure under the compression force up-to 16 N, but successful penetration of skin tissue with a low insertion force of 5 N. The electrical characteristics of the fabricated MNE were characterized by impedance spectroscopy with equivalent circuit model. The designed wearable wireless ECG monitoring device with MNE proved feasibility of the ECG recording which reduces the noise of movement artifacts during dynamic behaviors.

Self-Folded Three-Dimensional Graphene with a Tunable Shape and Conductivity.

Three-dimensional (3D) graphene architectures are of great interest as applications in flexible electronics and biointerfaces. In this study, we demonstrate the facile formation of predetermined 3D polymeric microstructures simply by transferring monolayer graphene. The graphene adheres to the surface of polymeric films via noncovalent π-π stacking bonding and induces a sloped internal strain, leading to the self-rolling of 3D microscale architectures. Micropatterns and varied thicknesses of the 2D films prior to the self-rolling allows for control over the resulting 3D geometries. The strain then present on the hexagonal unit cell of the graphene produces a nonlinear electrical conductivity across the device. The driving force behind the self-folding process arises from the reconfiguration of the molecules within the crystalline materials. We believe that this effective and versatile way of realizing a 3D graphene structure is potentially applicable to alternative 2D layered materials as well as other flexible polymeric templates.