Parylene Layer Research Articles

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.

Multilayer Flexible Metamaterials With Fano Resonances

A set of multilayer flexible metamaterials (MMs), which consist of three layers of parylene C films and three layers of gold split ring resonators (SRRs), was designed and fabricated. The transmission spectra of these MMs were measured in the terahertz (THz) region. Additionally, the structures of SRRs on each layer were changed from symmetric to asymmetric to investigate Fano resonances shown in these MMs. Meanwhile, by changing the thickness of each layer of parylene C, the coupling between different layers and the corresponding spectra change were explored. The results show that increased layers of MMs support new resonant modes and lead to Fano resonances with narrow linewidths in spectra. Therefore, this kind of multilayer flexible MM has potential applications in the THz biomolecule sensing field.

High voltage insulation properties of DLC-Parylene multilayer films for microsurgery instruments

In minimally invasive surgery, there is a continuous trend towards the miniaturization of instruments in order to keep the incisions as small as possible. In this context, extensive use is made of electrosurgery. In order to optimize and miniaturize electrosurgical instruments, new ultrathin insulation methods with film thicknesses below 50μm need to be developed. These electrical insulation films must comply with the requirements of Standard DIN EN ISO 60601-2-2.For this purpose, a high-voltage insulation layer based on a diamond like carbon (DLC) multilayer in combination with a topping layer of Parylene C has been developed. With a total thickness of less than 50μm, this film withstands an electrical high-voltage treatment of more than 1kV required in Standard DIN EN ISO 60601-2-2. In addition to the film's dielectric strength, its adhesion and suitability for reprocessing were investigated.

Ammonia sensing for enzymatic urea detection using organic field effect transistors and a semipermeable membrane.

Organic Field Effect Transistors (OFETs) are used to measure ammonia in solution via ammonia diffusion into the OFET channel. An increase in ammonia concentrations results in a decrease in transistor currents. The regeneration of the OFET current after ammonia uptake is slow, which allows us to read out the maximum ammonia dose which was applied. A 100 nm parylene-C layer serves as a semipermeable top gate dielectric. The parylene layer is functionalized with the covalently attached enzyme urease. The enzyme catalyses the hydrolysis of urea to ammonia and carbon dioxide, i.e. urea can be detected via its hydrolysis product ammonia. The sensitivity covers a range of physiological concentrations of urea, which are several mM.

Robust surface patterning by parylene-reinforced breath figures: An enabling tool for liquid crystal microcell arrays

We propose a novel fabrication method for realizing robust and solvent resistant honeycomb films by combining parylene deposition with the polymer auto-organization phenomenon leading to breath figures. Parylene CVD process is suitable for producing a conformal protective layer on the honeycomb surface, reinforcing and stabilizing this structure. We demonstrate that the stabilized porous films can be filled with chloroform solution of fluorescent materials, without losing the integrity of their microstructure. In addition, liquid crystals can be encapsulated inside the patterned surface between two layers of parylene, showing interesting organization features dictated by the spatial constrains. This is the first reported application of breath figures with liquid crystals, suggesting a new approach for the development of honeycomb-based liquid crystal cells for flexible displays.

Effect of different initial finishes and Parylene coating thickness on the surface properties of coated PMMA

Statement of the problemThe colonization of microorganisms on acrylic resin dentures may result in denture-induced stomatitis. No efficient coating has yet been proposed to address this issue. PurposeThe purpose of this in vitro study was to assess the effect of various initial surface finishes and different Parylene coating thicknesses on the surface roughness (Ra) and surface free energy (SFE) of Parylene coated polymethyl methacrylate (PMMA). Material and methodsOne hundred and sixty PMMA specimens were produced and divided into 8 groups as follows: group A: uncoated, 1000 grit finish; group Ap1: 10 μm Parylene coated, 1000 grit finish; group B: uncoated, 1200 grit finish; group Bp: 10 μm Parylene coated, 1200 grit finish; group C: uncoated, 2400 grit finish; group Cp: 10 μm Parylene coated, 2400 grit finish; group Ap2: 20 μm Parylene coated, 1000 grit finish; group Ap3: 30 μm Parylene coated, 1000 grit finish. The Ra of all specimens was measured with a noncontact profilometer. To calculate the SFE, the Owens-Wendt approach was applied after measuring the contact angles with a goniometer. The topography of the specimens was observed by scanning electron microscope. ResultsGroups Ap1 and Bp presented significantly lower Ra values compared with their respective uncoated groups A and B (P<.001). No statistical difference was found between the Ra values of groups C and Cp, between A and Ap3, and between Ap2 and Ap3. The SFE values of the coated groups were significantly higher than the SFE values of the uncoated groups with the same initial finish (P<.001). ConclusionsCoating with a 10-μm layer of Parylene C resulted in lower Ra values for the rougher groups and increased SFE values. Increasing the coating thickness resulted in an increase of the Ra.

Shock reliability analysis and improvement of MEMS electret-based vibration energy harvesters

Vibration energy harvesters can serve as a replacement solution to batteries for powering tire pressure monitoring systems (TPMS). Autonomous wireless TPMS powered by microelectromechanical system (MEMS) electret-based vibration energy harvester have been demonstrated. The mechanical reliability of the MEMS harvester still has to be assessed in order to bring the harvester to the requirements of the consumer market. It should survive the mechanical shocks occurring in the tire environment. A testing procedure to quantify the shock resilience of harvesters is described in this article. Our first generation of harvesters has a shock resilience of 400 g, which is far from being sufficient for the targeted application. In order to improve this aspect, the first important aspect is to understand the failure mechanism. Failure is found to occur in the form of fracture of the device’s springs. It results from impacts between the anchors of the springs when the harvester undergoes a shock. The shock resilience of the harvesters can be improved by redirecting these impacts to nonvital parts of the device. With this philosophy in mind, we design three types of shock absorbing structures and test their effect on the shock resilience of our MEMS harvesters. The solution leading to the best results consists of rigid silicon stoppers covered by a layer of Parylene. The shock resilience of the harvesters is brought above 2500 g. Results in the same range are also obtained with flexible silicon bumpers, which are simpler to manufacture.

Manufacturing miniature Langmuir probes by fusing platinum bond wires

This paper reports on a novel method for manufacturing microscopic Langmuir probes with spherical tips from platinum bond wires by fusing for plasma characterization in microplasma sources. Here, the resulting endpoints, formed by droplets on the ends of a fused wire, are intended to act as spherical Langmuir probes. For studying the fusing behavior, bond wires were wedge bonded over a 2 mm wide slit, to emulate the final application, and fused with different voltages and currents. For electrical isolation, a set of wires were coated with a 4 μm thick layer of Parylene before they were fused. After fusing, the gap size, as well as the shape and area of the ends of the remaining stubs were measured. The yield of the process was also investigated, and the fusing event was studied using a high-speed camera for analyzing its dynamics. Four characteristic tip shapes were observed: spherical, folded, serpentine shaped and semi-spherical. The stub length leveled out at ∼400 μm as the fusing power increased. The fusing of the coated wires required a higher power to yield a spherical shape. Finally, a Parylene coated bond wire was integrated into a stripline split-ring resonator (SSRR) microplasma source, and was fused to form two Langmuir probes with spherical endpoints. These probes were used for measuring the I–V characteristics of a plasma generated by the SSRR. In a voltage range between −60 V and 60 V, the fused stubs exhibited the expected behavior of spherical Langmuir probes, and will be considered for further integration.

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.

Micromachined Energy-Harvester Stack With Enhanced Electromagnetic Induction Through Vertical Integration of Magnets

This paper presents a stacked microfabricated power generator that vertically integrates multiple magnets on silicon wafers in a batch process to enhance electromagnetic induction multiple times. The power output is increased by increasing the magnetic flux change for each power-generator unit in the stack, in addition to the increase due to increased number of units. A stack consisting of two arrays of four power-generator units is fabricated and characterized. Wax-bonded Nd-Fe-B powders are embedded in the silicon wafer and magnetized as an integrated micromagnet, which serves as a proof mass suspended by a parylene diaphragm. Dual-layer coils are isolated by a parylene layer, connected via a hole and fabricated with electroplating copper on the same wafer. Experimental results show an improvement by about a factor of four on the power output from the same coils when two power-generator arrays are stacked vertically. In particular, an array of four microfabricated power generators occupying a volume of 51 × 11 × 0.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in the stack produces an induced electromotive force of 1.02 mV with 0.55 nW power output when it is vibrated at 400 Hz with vibration amplitude of 10 μm.

Laser Shock-Induced Conformal Transferring of Functional Devices on 3-D Stretchable Substrates

This paper discussed a top-down integration method to achieve the three-dimensional (3-D) microscale conformal transferring of functional devices on flexible elastomeric substrates at ambient conditions. By the tunable laser-induced pressure, the functional device inherits the microscale wrinkle-like patterns, without compromising functions. The functional materials are encapsulated in the biocompatible parylene layers to avoid the drastic plastic deformations in functional layers. The electrical resistivity of functional device increases marginally with the applied laser intensity, aspect ratios of microscale features, and overall tensile strain applied to the whole flexible assembly. The stretchability of the transferred functional devices was studied by measuring the electrical property as function of bending and tensile strains. It shows that the device can sustain more than 40% strain in the stretchable substrate. It is demonstrated that the process can achieve the flexible and stretchable functional integration conformal to 3-D micrometer-patterns in a fast and scalable way.

Self-Closed Parylene Cuff Electrode for Peripheral Nerve Recording

We have designed, fabricated, and characterized a self-closed parylene cuff electrode for peripheral nerve recording, whose curliness and closeness is realized by the difference in self-stress of different parylene layers due to the heat treatments. Compared with the conventional cuff electrodes, the self-closed structure without any additional mechanical locking structure minimizes the mechanical structure of the cuff electrode. Moreover, the self-closed structure made of thin and flexible parylene film minimizes mechanical damage to the nerve and the surrounding tissues. The zero insertion force interface facilitates the connection of 16 channels with external circuits through the integrated parylene bonding pads. To reduce the impedance and increase the charge storage capacity of the electrode, the electrodeposited iridium oxide film is electrodeposited on the electrode sites. Using the fabricated self-closed parylene cuff electrode, acute neural recoding of 16 channels was performed on the rat sciatic nerve to verify the capability of recording the neural activities. The present self-closed parylene cuff electrode is promising to be used as an neural interface for peripheral nerve recording.

A flexible and implantable microelectrode arrays using high-temperature grown vertical carbon nanotubes and a biocompatible polymer substrate

This paper presents a novel microelectrode arrays using high-temperature grown vertically aligned carbon nanotubes (CNTs) integrated on a flexible and biocompatible parylene substrate. A simple microfabrication process is proposed to unite the high quality vertical CNTs grown at high temperature with the heat sensitive parylene substrate in a highly controllable manner. Briefly, the CNTs electrode is encapsulated by two layers of parylene and the device is released using xenon difluoride (XeF2). The process is compatible with wafer-scale post complementary metal oxide semiconductor integration. Lower impedance and larger interfacial capacitance have been demonstrated using CNTs compared to a Pt electrode. The flexible CNT electrodes have been utilized for extracellular neuronal recording and stimulation in rats. The signal-to-noise ratio of the device is about 12.5. The threshold voltage for initiating action potential is about 0.5 V.

Fiber optic Fabry–Perot pressure sensor based on lensed fiber and polymeric diaphragm

A novel optical fiber-based Fabry–Perot pressure sensor fabricated with a lensed fiber and a polymeric diaphragm is proposed for application in the medical field. The lensed fiber was constructed at the tip of a single mode fiber, for use with a deformable flexible polymeric diaphragm. The sensor can reduce the loss of optical power of the back-reflected light, and the flexible diaphragm can increase deformation sensitivity. The lensed fiber was fabricated from a coreless silica fiber attached to a single mode fiber by splicing using a fusion splicing method, and arc discharge. The polymeric diaphragm consists of layered PDMS, parylene and gold mirror. The intermediate parylene layer is helpful to prevent cracking of the mirror when the diaphragm is deformed by external pressure. The polymeric diaphragm was fabricated by MEMS processing including spin-coating, vaporization, and sputtering. The deformation of the polymeric diaphragm was evaluated through numerical simulation. The change in cavity length between the lensed fiber and the polymeric diaphragm with external pressure was estimated using the interference generated from two reflected lights. Experimental results showed that the proposed pressure sensor has a sensitivity of 1.41μm/kPa over a pressure range from 0kPa to 4kPa with good linearity, and its minimum detection resolution is less than 0.03kPa. The proposed sensor could be used for reliable low-pressure measurement, especially in medical applications.

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.

Validation of Parylene Coating to Suppress Alpha Contamination on the Copper Surface in CUORE Bolometers

Backgroundrate reduction is of utmost importance for neutrinoless double beta decay experiments like CUORE (Cryogenic Underground Observatory for Rare Events). A major source of background for CUORE comes from surface contamination from inert materials, mainly degraded alphas from the supporting copper structure of the bolometer modules. We investigated a novel alpha background suppression technique using conformal polymer coating with Parylene in a bolometric validation run. A 50 micron thick layer of Parylene coating on the copper structure surface was chosen to effectively range out degraded alphas. The measured alpha background rate and its implications will be discussed.

A novel method to fabricate parylene-based flexible microfluidic platforms with commercial adhesive tape

We developed a new method to fabricate parylene-based flexible microfluidic platforms using commercial adhesive tape. Most of the previous methods required the preparation of parylene channels via a parylene–to–parylene bonding, which could only be achieved at high pressure and temperature. Instead, our method exploits the adherent property of commercial tape as a substrate for the parylene peel-off process. Once the parylene thin film is deposited by chemical vapour deposition (CVD) on top of the polydimethylsiloxane (PDMS) replica, prepared by conventional lithography process, an adhesive tape peels off the deposited parylene layer with the micro-scale structures from the PDMS replica. We found that the minimum size of the circle posts successfully fabricated by this process is about 10 μm in diameter and 10 μm in height; the maximum value in aspect ratio is about 2.5. In our experimental investigation, pressure in the parylene channels with different wall thicknesses, was measured to estimate the hydraulic resistance of the channel. Our results are comparable with calculated data, with a normalized deviation smaller than 5%. In addition, the hydraulic resistance of the channels on the curved surface obtained with a similar approach showed an increase when the radius of curvature was reduced. Finally, this contribution shows that our method enables a simple and relatively inexpensive fabrication of flexible microfluidic platforms.

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.

Silicon-based wire electrode array for neural interfaces

Objectives. Metal-wire electrode arrays are widely used to record and stimulate neurons. Commonly, these devices are fabricated from a long insulated metal wire by cutting it into the proper length and using the cross-section as the electrode site. The assembly of a micro-wire electrode array with regular spacing is difficult. With the help of micro-machine technology, a silicon-based wire electrode array (SWEA) is proposed to simplify the assembling process and provide a wire-type electrode with tapered tips.Approach. Silicon wires with regular spacing coated with metal are generated from a silicon wafer through micro-fabrication and are ordered into a 3D array. A silicon wafer is cut into a comb-like structure with hexagonal teeth on both sides by anisotropic etching. To establish an array of silicon-based linear needles through isotropic wet etching, the diameters of these hexagonal teeth are reduced; their sharp edges are smoothed out and their tips are sharpened. The needle array is coated with a layer of parylene after metallization. The tips of the needles are then exposed to form an array of linear neural electrodes. With these linear electrode arrays, an array of area electrodes can be fabricated.Main results. A 6 × 6 array of wire-type electrodes based on silicon is developed using this method. The time required to manually assemble the 3D array decreases significantly with the introduction of micro-fabricated 2D array. Meanwhile, the tip intervals in the 2D array are accurate and are controlled at no more than 1%. The SWEA is effective both in vitro and in vivo.Significance. Using this method, the SWEA can be batch-prepared in advance along with its parameters, such as spacing, length, and diameter. Thus, neural scientists can assemble proper electrode arrays in a short time.