Parylene Film Research Articles

Ag nanoparticles cladded with parylene for high-stability microfluidic surface-enhanced Raman scattering (SERS) biochemical sensing

A method for fabricating the stable and reusable microfluidic-integrated devices based on the Ag nanoparticles cladded with parylene have been demonstrated, which can be applied for biochemical sensing. The excellent parylene cladding structure acted as a protection layer for the Ag nanoparticles, enhancing the Raman spectrum intensity by forming the hot spot structure between the nanoparticles. By optimizing the parylene film thickness, the surface enhanced Raman spectroscopy sensitivity of the R6G solution could be enhanced by three times, comparing with the initial substrate. The hydrophobic and biocompatible parylene cladding film also increased the repulsive to the molecular probes, enabling hundreds of measurement cycles and greatly increasing the stability and reproducibility. This method was also demonstrated to be reusable by flushing with water and alcohol through the integrated micro-channel.

Integration of Organic Electrochemical and Field-Effect Transistors for Ultraflexible, High Temporal Resolution Electrophysiology Arrays.

Integration of organic electrochemical transistors and organic field-effect transistors is successfully realized on a 600 nm thick parylene film toward an electrophysiology array. A single cell of an integrated device and a 2 × 2 electrophysiology array succeed in detecting electromyogram with local stimulation of the motor nerve bundle of a transgenic rat by a laser pulse.

Dispersion Curve Engineering of TiO₂/Silver Hybrid Substrates for Enhanced Surface Plasmon Resonance Detection.

As surface plasmon resonance (SPR)-based biosensors are well translated into biological, chemical, environmental, and clinical fields, it is critical to further realize stable and sustainable systems, avoiding oxidation susceptibility of metal films—in particular, silver substrates. We report an enhanced SPR detection performance by incorporating a TiO2 layer on top of a thin silver film. A uniform TiO2 film fabricated by electron beam evaporation at room temperature is an effective alternative in bypassing oxidation of a silver film. Based on our finding that the sensor sensitivity is strongly correlated with the slope of dispersion curves, SPR sensing results obtained by parylene film deposition shows that TiO2/silver hybrid substrates provide notable sensitivity improvement compared to a conventional bare silver film, which confirms the possibility of engineering the dispersion characteristic according to the incidence wavelength. The reported SPR structures with TiO2 films enhance the sensitivity significantly in water and air environments and its overall qualitative trend in sensitivity improvement is consistent with numerical simulations. Thus, we expect that our approach can extend the applicability of TiO2-mediated SPR biosensors to highly sensitive detection for biomolecular binding events of low concentrations, while serving a practical and reliable biosensing platform.

Studies of Parylene C Microfibrous Thin Films Electrical Properties

Parylene C is known for its flexibility, transparency, biocompatibility, and dielectric reliability. Parylene C is, hence, researched for use as a gate dielectric in transistors and capacitors for flexible electronics as well as for nano/microelectromechanical system applications [1-3]. In this study, we use metal–insulator–metal (MIM) capacitor structures to examine the electrical characteristics of columnar microfibrous thin films (µFTFs) of Parylene C prepared using oblique-angle physicochemical deposition [4,5], whereby a collimated vapor Parylene C is directed at an angle χv with respect to the exposed face of a planar substrate. The values of χv used were 30°, 60°, and 90°. We found that the low-frequency relative permittivity of the columnar µFTF increases with χv. This is explained in terms of the porosity as a function of χv, the porosity being higher for lower χv. Leakage current and charge deep-level transient spectroscopy (Q-DLTS) measurements at temperatures in the 230–470 K range and at frequencies in the 1–1000 kHz range were used to evaluate the dielectric integrity of the columnar µFTFs. Observed capacitance transients and Q-DLTS peaks in temperature were analyzed to uncover carrier traps located in the Parylene C bulk and at the metal/Parylene C interfaces in the MIM structures. The variations of DC and AC conductivities can be explained in terms of charge transport mechanisms involving thermionic emission and electron hopping. W. T. Wondmagegn, N. T. Satyala, I. Mejia-Silva, D. Mao, S. Gowrisanker, H. N. Alshareef, H. J. Stiegler, M. A. Quevedo–Lopez, and B. E. Gnade, Thin Solid Films, 519(13), 4313–4318 (2011).T. Trantidou, D. J. Payne, V. Tsiligkiridis, Y.-C., Chang, C. Toumazou, and T. Prodromakis, Sensors and Actuators B: Chemical, 186(1), 1–8 (2013).B. Park B., K-J. Im, K. Cho, and S. Kim, Organic Electronics, 9(5), 878–882(2008).C. Chindam, N. M. Wonderling, A. Lakhtakia, O. O. Awadelkarim, and W. Orfali, Applied Surface Science, 345(1), 145–155 (2015).Khawaji, I. H., Chindam, C., Orfali, W., Awadelkarim, O. O., Lakhtakia, A. ECS Transactions, 69(5), 113-119 (2015).

Studies of Parylene C Microfibrous Thin Films Electrical Properties

We have fabricated and measured the room-temperature capacitance in metal-insulator-metal (MIM) structures utilizing the Parylene C films as the insulators in the frequency range 1 kHz to 1 MHz. The Parylene-C films were of variable thicknesses and were either spin-on dense films or columnar microfibrous thin films (μFTFs) grown using oblique angle physicochemical vapor deposition. The values of the vapor tilt angle, χv, used were 30°, 60°, or 90°. Expectedly, columnar microfibrous thin film of Parylene C is observed to have lower values of k than the dense one. However, it is observed that the dielectric constant of the μFTFs is increased with increasing deposition tilt angle χv. This is explained in terms of film porosity as a function of χv, which is enhanced in films deposited at lower tilt angles. The dependence of k on measurement frequency suggests that molecular dipole effects dominate charge polarization in the films.

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.

Temperature-dependent dynamic moduli of Parylene-C columnar microfibrous thin films

Columnar microfibrous thin films (μFTFs) of the polymer Parylene C with different microfiber inclination angles were fabricated using a physicochemical vapor deposition process whereby a collimated flux of hot monomers is obliquely directed towards a planar substrate. Each μFTF was then subjected to cyclic elastic loading in one of two orthogonal directions lying wholly in the substrate plane: either (i) normal or (ii) parallel to the morphologically significant plane of the μFTF. Dynamic storage and loss moduli were determined in the 1–80 Hz frequency range for temperatures between −40 °C and 125 °C. For all columnar μFTFs, the storage and loss moduli for normal loading did not exceed their counterparts for parallel loading. All columnar μFTFs were found to be softer than a bulk film of Parylene C. In both bulk and columnar forms, Parylene C was found to be rheologically not simple.

Spontaneously Formed Wrinkled Substrates for Stretchable Electronics Using Intrinsically Rigid Materials

The preparation of a stretchable substrate was carried out by blending poly (ethylene glycol)-block-poly (propylene glycol)-block-poly(ethylene glycol) and polydimethylsiloxane (PDMS) to enhance the stretchability and the surface energy of the elastic film. The deposition of a thin parylene film on this modified PDMS led to the formation of a spontaneously wrinkled surface, resulting in a highly stretchable substrate. Rigid Au conductors were deposited on the resultant wrinkles substrates, and could be stretched up to 20% strain. In addition, stretchable pentacene thin-film transistors were successfully fabricated on the wrinkled substrate without the formation of stiff islands.

Surface modification of parylene-N films for the culture of osteoblast-like cells (MG-63)

The influence of microenvironments on the culture of osteoblast-like cells (MG-63) has been investigated using parylene films with different surfaces, such as parylene-N film, UV-modified parylene-N film, functional parylene film with amine groups (parylene-A), and UV-modified parylene-A film. In this work, parylene-N film was found to induce dramatic changes in cell adhesion and cell viability before and after UV-treatment with respect to the culture of osteoblast-like cells (MG-63). The influences of such a chemical environment on cell culture were investigated in relation to the cell proliferation (viability and proliferation rate) and the cell physiology (cell cycle, protein synthesis, and differentiation) of cells grown on parylene-N film, UV-modified parylene-N film, parylene-A film, and UV-modified parylene-A film in comparison with cells grown on a polystyrene surface.

An easy fabrication process of fully-sealed parylene microfluidic channels with a single deposition step

We present a simple fabrication method for microfluidic channels in which all walls consist of parylene. Only one parylene deposition step is required to achieve monolithical integration of fully-sealed parylene structures. Thus, the commonly used polymer-to-polymer bonding procedures are not needed. A pattern of grooves was etched into a silicon substrate, determining the shape and depth of the channels to be fabricated. A polyvinyl chloride (PVC) foil was affixed to the top of the wafer. After a single deposition step, a 15 µm-thick film of parylene C conformally coated all surfaces. The PVC foil was peeled off from the parylene surface leaving fully-sealed parylene channels embedded in the silicon. The channels were characterized optically and by scanning electron microscopy. Their functionality was verified by flow tests with polystyrene microbeads dispersed in deionized water and the robustness of the structures was confirmed by hydrostatic tests. The fabricated channels are shown to be fully sealed and mechanically stable.

Crystallinity and mechanical effects from annealing Parylene thin films

Parylene is commonly used as thin film polymer for MEMS devices and smart materials. This paper investigates the impact on bulk properties due to annealing various types of Parylene films. A thin film of Parylene N, C and a hybrid material consisting of Parylene N and C were deposited using a standard Gorham process. The thin film samples were annealed at varying temperatures from room temperature up to 300°C. The films were analyzed to determine the mechanical and crystallinity effects due to different annealing temperatures. The results demonstrate that the percentage of crystallinity and the full-width-half-maximum value on the 2θ X-ray diffraction scan increases as the annealing temperature increases until the melting temperature of the Parylene films was achieved. Highly crystalline films of 85% and 92% crystallinity were achieved for Parylene C and N respectively. Investigation of the hybrid film showed that the individual Parylene films behave independently to each other, and the crystallinity of one film had no significant impact to the other film. Mechanical testing showed that the elastic modulus and yield strength increase as a function of annealing, whereas the elongation-to-break parameter decreases. The change in elastic modulus was more significant for Parylene C than Parylene N and this is attributed to the larger change in crystallinity that was observed. Parylene C had a 112% increase in crystallinity compared to a 61% increase for Parylene N, because the original Parylene N material was more crystalline than Parylene C so the change of crystallinity was greater for Parylene C.

Adjustable Tilt Angle of Liquid Microlens With Four Coplanar Electrodes

We present a novel method to adjust the beam tilt angle and tune the axial focus of an electrowetting on dielectric liquid microlens encapsulated by parylene film. The lens system consists of four control electrodes with two immiscible spherical liquid lenses of different refractive indexes encapsulated by a flexible polymer. To tilt the incident beam, the lateral position and curvature of the inner lens were modulated by ac voltage applied to the electrodes. The measured lateral position and curvature of the inner lens allowed us to estimate the position of the focal point. The tunability of the tilt angle was increased by ±2.13° at an applied voltage of $45.3~V_{\mathrm {rms}}$ when using thin dielectric layers. The resolvable image was 80% and 68% of the aperture diameter for 20 and 50 L&S/mm, respectively, assuming that the critical modulation transfer function value was 50% for quality imaging.

Review of Surface Modification of Nanoporous Polyethersulfone Membrane as a Dialysis Membrane

Nanoporous polyethersulfone (PES) membrane is widely used as a filtration membrane in hemodialysis systems. Unfortunately, it has low blood compatibility, and induces blood clots that adhere to the membrane’s surface during dialysis treatment. This paper reports on a review of surface modification that is used to improve the PES membrane’s blood compatibility. The method consists of applying two coating materials, in the form of parylene and fluorinated diamond-like carbon (F-DLC) films, onto the membrane’s surface. The parylene film is deposited on the diffusion layer of the membrane surface using glycerin liquid, while the FDLC film is specially coated on the supporting layer of the membrane. The unique property of parylene, which has the characteristics of conformal coating, prevents the parylene from being coated on the supporting layer of the membrane. Conversely, F-DLC film, which is hard, fragile and has a less conformal coating than parylene, is only meant to be coated on the supporting layer. Finally, the coated membranes, along with the bare PES membrane, are compared and investigated under a long-term diffusion test to assess their permeability and blood compatibility. The experiment results show that both coating materials have the capacity to improve the membrane’s blood compatibility in different ways.

Co-Design Method and Wafer-Level Packaging Technique of Thin-Film Flexible Antenna and Silicon CMOS Rectifier Chips for Wireless-Powered Neural Interface Systems.

In this paper, a co-design method and a wafer-level packaging technique of a flexible antenna and a CMOS rectifier chip for use in a small-sized implantable system on the brain surface are proposed. The proposed co-design method optimizes the system architecture, and can help avoid the use of external matching components, resulting in the realization of a small-size system. In addition, the technique employed to assemble a silicon large-scale integration (LSI) chip on the very thin parylene film (5 μm) enables the integration of the rectifier circuits and the flexible antenna (rectenna). In the demonstration of wireless power transmission (WPT), the fabricated flexible rectenna achieved a maximum efficiency of 0.497% with a distance of 3 cm between antennas. In addition, WPT with radio waves allows a misalignment of 185% against antenna size, implying that the misalignment has a less effect on the WPT characteristics compared with electromagnetic induction.

Electrostatic MEMS vibration energy harvester for HVAC applications

This paper reports on an electrostatic MEMS vibration energy harvester with gapclosing interdigitated electrodes, designed for and tested on HVAC air ducts. The device is fabricated on SOI wafers using a custom microfabrication process. A dual-level physical stopper system is implemented in order to control the minimum gap between the electrodes and maximize the power output. It utilizes cantilever beams to absorb a portion of the impact energy as the electrodes approach the impact point, and a film of parylene with nanometer thickness deposited on the electrode sidewalls, which defines the absolute minimum gap and provides electrical insulation. The fabricated device was first tested on a vibration shaker to characterize its resonant behavior. The device exhibits spring hardening behavior due to impacts with the stoppers and spring softening behavior with increasing voltage bias. Testing was carried out on HVAC air duct vibrating with an RMS acceleration of 155 mgRMS and a primary frequency of 60 Hz with a PSD of 7.15·10-2 g2/Hz. The peak power measured is 12nW (0.6 nW RMS) with a PSD of 6.9·10-11 W/Hz at 240 Hz (four times of the primary frequency of 60 Hz), which is the highest output reported for similar vibration conditions and biasing voltages.

Electrical Studies on Parylene-C Columnar Microfibrous Thin Films

Columnar microfibrous thin films (μFTFs) of Parylene C are deposited on top of p-type Si substrate using physicochemical vapor deposition to form metal-insulator-semiconductor and metal-insulator-metal structures utilizing the Parylene-C μFTFs as the gate dielectric. The columnar μFTFs were characterized for their electrical properties and dielectric integrity using leakage-current and capacitance measurements at temperatures in the 200K - 500 K range and at frequencies in the range 1 kHz to 1 MHz. Observed variations in leakage current and capacitance were found to be consistent with transport mechanisms involving the Poole–Frenkel and Schottky emission mechanisms as well as carrier trapping/detrapping at interfacial traps.

Applications of parylene films in the manufacture of organic field-effect transistors

Abstract Along with the technology of microscopic electromechanical systems and that of brain–machine interface, the area of organic electronics presents a major development direction of high-tech applications of parylene coatings. Within this area, a fabrication of organic field-effect transistors (OFETs), where parylene C is applied as a gate dielectric, makes the most common use of these materials. The main advantage of parylene coatings in the OFET technology is their very high purity. Depending on a transistor design, films of parylene C may play a role of the gate dielectric material, that of a protective insulator coating, and/or that of a device substrate. The work presents a number of applications of parylene C in different OFET devices, namely in organic thin film transistors (OTFTs) and organic single-crystal transistors developed by the authors. A combination of zone-cast films of active materials, both n-type and p-type, with parylene C gate dielectric makes a principal design of the OTFTs. In this group, the best performance parameters and namely μFE = 0.18 cm2/Vs, Ion/off = 104 and turn-on voltage

Chemical Vapor Jet Deposition of Parylene Polymer Films in Air

Parylene films are commonly used as transparent, flexible coatings in electronic devices and biomedical applications, exhibiting barrier properties against corrosion, low dielectric constant, and moisture resistance. Reactive vapor deposition of parylene results in conformal coverage of features at room temperature, which is advantageous for passivating, for example, organic optoelectronic devices. Conventional parylene deposition methods, however, coat surfaces virtually indiscriminately and utilize separate chambers for vaporization, pyrolysis, and polymerization, resulting in a large footprint and limited processing integration ability, especially at a laboratory scale. Here, we demonstrate the vaporization and pyrolysis of the di-p-xylylene (parylene dimer) in a single compact nozzle, producing a jet of monomer that polymerizes into a film upon contact with the substrate at room temperature. A guard flow jet is employed to shield the reactive monomer molecules en route to the substrate, thereby enabli...

Highly sensitive photosensor based on in situ synthesized CdS nanowires

In this work, CdS nanowires were synthesized in situ on the finger electrodes of interdigitated Au-electrodes via pulsed-laser deposition (PLD, KrF excimer laser excited at 248nm) using a sintered CdS target at the center of a quartz tube in a hot-wall furnace. The photo-response characteristics of the in situ synthesized CdS nanowires such as sensitivity, reproducibility, and response according to the wavelength of the incident light were analyzed and compared to those of a CdS thin-film electrode. Photosensitivity enhancement was investigated following the deposition of a parylene film with anti-reflecting properties on the CdS nanowires.

Focus-tunable low-power electrowetting lenses with thin parylene films.

Electrowetting lenses with record low power consumption (microwatts) have been demonstrated using high-quality parylene AF-4 dielectric layers and large dodecyl sulfate ions. Water and propylene glycol are interchanged as the polar liquid to enable diverging and converging lens operation achievable with the application of 15V. The optical quality of the lenses is comparable to conventional microlenses and the tuning exhibits very little (<0.5°) contact angle hysteresis.