parylene-C Substrate Research Articles

Parylene-C-based flexible organic thin-film transistors and their reliability improvement using SU-8 passivation

Flexible and biocompatible organic thin-film transistors (OTFTs) can be well-suited for biological applications due to their compatibility with biomaterials. In this study, flexible OTFTs were fabricated with a Parylene-C substrate and gate dielectric, a material known for its flexibility and biocompatibility. We used poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] as organic channel material. To ensure the longevity and protection of the channel, SU-8, known for its biocompatibility and transparency, effectively safeguarded the OTFT and ensured its sustained operation. Flexible OTFTs were affixed to a curved fixture, referred to as a “curved condition.” The device parameters at −20 V of VD in the curved condition shows an Ion/off ratio of 3.5 × 104, threshold voltage (VTH) of −0.42 V, and mobility of 0.003 cm2/V s. The Parylene-C-based OTFT with SU-8 passivation demonstrated reliability by maintaining performance under curved conditions for 40 days. The results show that the proposed device is suitable for flexible electronics and sensor applications.

Analysis of electrical and hysteresis characteristics of flexible OTFT using solution-processable DPP-DTT polymer and Parylene-C

Organic thin-film transistors (OTFTs) fabricated on Parylene-C substrates have the advantages of a simple process, low cost, and flexible characteristics. This study introduces the manufacturing method and electrical characteristics of an OTFT using organic materials as the substrate, gate dielectric, and channel material. PDPP2T-TT-OD(DPP-DTT) is used as the channel material, which is a highly mobile p-type polymer with good air stability. The proposed OTFT device has flexible characteristics because it is fabricated on a Parylene-C substrate and can be used even in a curved state. Furthermore, the manufacturing process was largely achieved via a simple, low-cost solution process using spin-coating and photolithography with a photo-curable material. Under flat conditions, the threshold voltage (VTH) is approximately –3 V, the average ION/IOFF ratio is approximately 105, and the mobility is 0.84 cm2/Vs.

Development of Organic Thin-film Transistors on a Biocompatible Parylene-C Substrate

Organic thin-film transistors (OTFTs) fabricated on a biocompatible Parylene-C substrate can be applied to biosensors using a simple and cost-effective process. In this study, we developed biocompatible OTFTs by using organic materials to fabricate the substrate, gate dielectric, channel, and passivation layer. Poly(3-hexylthiophene) (P3HT) was used to fabricate the OTFTs on a Parylene-C-based platform. As the gate dielectric, Parylene-C showed promising insulation properties. Finally, we generated a cyclic olefin polymer (COP) passivation layer to protect P3HT from oxygen and moisture, and the effect of the COP passivation layer on the P3HT channel was analyzed. The proposed materials and fabrication methods will be useful for various bio-applications of OTFTs.

Flexible Organic Electronic Devices for Pulsed Electric Field Therapy of Glioblastoma

Glioblastoma is difficult to eradicate with standard oncology therapies due to its high degree of invasiveness. Bioelectric treatments based on pulsed electric fields (PEFs) are promising for the improvement of treatment efficiency. However, they rely on rigid electrodes that cause acute and chronic damage, especially in soft tissues such as the brain. In this work, flexible electronics were used to deliver PEFs to tumors and the biological response was evaluated with fluorescent microscopy. Interdigitated gold electrodes on a thin, transparent parylene-C substrate were coated with the conducting polymer PEDOT:PSS, resulting in a conformable and biocompatible device. The effects of PEFs on tumors and their microenvironment were examined using various biological models. First, monolayers of glioblastoma cells were cultured on top of the electrodes to investigate phenomena in vitro. As an intermediate step, an in ovo model was developed where engineered tumor spheroids were grafted in the embryonic membrane of a quail. Due to the absence of an immune system, this led to highly vascularized tumors. At this early stage of development, embryos have no immune system, and tumors are not recognized as foreign bodies. Thus, they can develop fast while developing their own vessels from the existing embryo vascular system, which represents a valuable 3D cancer model. Finally, flexible electrode delivery of PEFs was evaluated in a complete organism with a functional immune system, using a syngenic, orthograft (intracranial) mouse model. Tumor spheroids were grafted into the brain of transgenic multi-fluorescent mice prior to the implantation of flexible organic electrode devices. A sealed cranial window enabled multiphoton imaging of the tumor and its microenvironment during treatment with PEFs over a period of several weeks.

Flexible Organic Electronic Devices for Pulsed Electric Field Therapy of Glioblastoma.

Glioblastoma is difficult to eradicate with standard oncology therapies due to its high degree of invasiveness. Bioelectric treatments based on pulsed electric fields (PEFs) are promising for the improvement of treatment efficiency. However, they rely on rigid electrodes that cause acute and chronic damage, especially in soft tissues such as the brain. In this work, flexible electronics were used to deliver PEFs to tumors and the biological response was evaluated with fluorescent microscopy. Interdigitated gold electrodes on a thin, transparent parylene-C substrate were coated with the conducting polymer PEDOT:PSS, resulting in a conformable and biocompatible device. The effects of PEFs on tumors and their microenvironment were examined using various biological models. First, monolayers of glioblastoma cells were cultured on top of the electrodes to investigate phenomena in vitro. As an intermediate step, an in ovo model was developed where engineered tumor spheroids were grafted in the embryonic membrane of a quail. Due to the absence of an immune system, this led to highly vascularized tumors. At this early stage of development, embryos have no immune system, and tumors are not recognized as foreign bodies. Thus, they can develop fast while developing their own vessels from the existing embryo vascular system, which represents a valuable 3D cancer model. Finally, flexible electrode delivery of PEFs was evaluated in a complete organism with a functional immune system, using a syngenic, orthograft (intracranial) mouse model. Tumor spheroids were grafted into the brain of transgenic multi-fluorescent mice prior to the implantation of flexible organic electrode devices. A sealed cranial window enabled multiphoton imaging of the tumor and its microenvironment during treatment with PEFs over a period of several weeks.

A Dense Conformal Electrode Array for High Spatial Resolution Stimulation of Electrosensory Systems.

Studies of electrosensory systems have led to insights into to a number of general issues in biology. However, investigations of these systems have been limited by the inability to precisely control spatial patterns of electrosensory input. In this paper, an electrode array and a system to selectively stimulate spatially restricted regions of an electroreceptor array is presented. The array has 96 channels consisting of chrome/gold electrodes patterned on a flexible parylene-C substrate and encapsulated with another parylene-C layer. The conformability of the electrode array allows for optimal current driving and surface interface conditions. Recordings of neural activity at the first central processing stage in weakly electric mormyrid fish support the potential of this system for high spatial resolution stimulation and mapping of electrosensory systems.

Flexible terahertz metamaterial biosensor for label-free sensing of serum tumor marker modified on a non-metal area.

Terahertz (THz) metamaterials for rapid label-free sensing show application potential for the detection of cancer biomarkers. A novel flexible THz metamaterial biosensor based on a low refraction index parylene-C substrate is proposed. The biomarkers are modified on non-metal areas by a three-step modification method that simplifies the modification steps and improves the modified effectivity. Simulation results for non-metal modification illustrate that a bulk refractive index sensitivity of 325 GHz/RIU is achieved, which is larger than that obtained for the traditional metal modification (147 GHz/RIU). Meanwhile, several fluorescence experiments proved the uniform modification effect and selective adsorption capacity of the non-metal modification method. The concentration of the carcinoembryonic antigen (CEA) biomarkers for breast cancer patients tested using this THz biosensor is found to be consistent with results obtained from traditional clinical tests. The limit of detection reaches 2.97 ng/mL. These findings demonstrate that the flexible THz metamaterial biosensor can be extensively used for the rapid detection of cancer biomarkers in the future.

A ‘T’ shaped flexible multiband ultra-thin terahertz metamaterial with consistent curved transmission spectra

In this paper, we designed a flexible multiband ultra-thin terahertz metamaterial with four ‘T’ shaped beams deposited on parylene-C substrate to achieve sensing. The simulated and experimental investigations of transmission spectra showed two resonant peaks, respectively, which demonstrated a good numerical and experimental agreement. Due to this special ‘T’ shaped structure, the transmission spectra were nearly unchanged in the first resonant peak and slightly fluctuant in the second resonant peak after bending with a constant step, which successfully confirmed a pretty consistent curved transmission performance. A further study about the effect of polarization and incident angle direction of terahertz wave on transmission spectra indicated that the transmission of the sample did not vary with the change of polarization angles but would be influenced by incident angles. In order to explore the performance of the structure in terms of sensing phenomenon, a final contrast simulation on different surface analytes and without analyte was carried out, consequently suggesting a promising and remarkable function in sensing applications especially in detecting biomolecules.

Large-scale, all polycrystalline diamond structures transferred onto flexible Parylene-C films for neurotransmitter sensing.

Boron-doped diamond (BDD) has superior electrochemical properties for bioelectronic systems. However, due to its high synthesis temperature, traditional microfabrication methods have limits to integrating BDD with emerging classes of flexible, polymer-based bioelectronic systems. This paper introduces a novel fabrication solution to this challenge, which features (i) a wafer-scale substrate transfer process with all diamond structures transferred onto a flexible Parylene-C substrate and (ii) Parylene anchors introduced to strengthen the bonding between BDD and Parylene substrates, as demonstrated by a peeling test. The electrochemical properties of the transferred BDD-polymer electrodes are evaluated using (i) an outer sphere redox couple Ru(NH3)62+/3+ to study the electron transfer process and (ii) quantitative and qualitative studies of the neurotransmitter redox couple dopamine/dopamine-o-quinone. A linear response of the BDD sensor to dopamine concentrations of 0.5 μM to 100 μM is observed (R2 = 0.999) with a sensitivity of 0.21 μA cm-2 μM-1. These examples of fabricated diamond-polymer devices suggest a broad application in advanced bioelectronics and optoelectronics.

Super multi-channel recording systems with UWB wireless transmitter for BMI.

In order to realize a low-invasive and high accuracy Brain-Machine Interface (BMI) system for clinical applications, a super multi-channel recording system was developed in which 4096 channels of Electrocorticogram (ECoG) signal can be amplified and transmitted to outside the body by using an Ultra Wide Band (UWB) wireless system. Also, a high density, flexible electrode array made by using a Parylene-C substrate was developed that is composed of units of 32-ch recording arrays. We have succeeded in an evaluation test of UWB wireless transmitting using a body phantom system.

Correction to Mobility Improvement and Temperature Dependence in MoSe2 Field-Effect Transistors on Parylene-C Substrate

Correction to Mobility Improvement and Temperature Dependence in MoSe₂ Field-Effect Transistors on Parylene-C Substrate

Mobility improvement and temperature dependence in MoSe2 field-effect transistors on parylene-C substrate.

We report low-temperature scanning tunneling microscopy characterization of MoSe2 crystals and the fabrication and electrical characterization of MoSe2 field-effect transistors on both SiO2 and parylene-C substrates. We find that the multilayer MoSe2 devices on parylene-C show a room-temperature mobility close to the mobility of bulk MoSe2 (100-160 cm(2) V(-1) s(-1)), which is significantly higher than that on SiO2 substrates (≈50 cm(2) V(-1) s(-1)). The room-temperature mobility on both types of substrates are nearly thickness-independent. Our variable-temperature transport measurements reveal a metal-insulator transition at a characteristic conductivity of e(2)/h. The mobility of MoSe2 devices extracted from the metallic region on both SiO2 and parylene-C increases up to ≈500 cm(2) V(-1) s(-1) as the temperature decreases to ≈100 K, with the mobility of MoSe2 on SiO2 increasing more rapidly. In spite of the notable variation of charged impurities as indicated by the strongly sample-dependent low-temperature mobility, the mobility of all MoSe2 devices on SiO2 converges above 200 K, indicating that the high temperature (>200 K) mobility in these devices is nearly independent of the charged impurities. Our atomic force microscopy study of SiO2 and parylene-C substrates further rules out the surface roughness scattering as a major cause of the substrate-dependent mobility. We attribute the observed substrate dependence of MoSe2 mobility primarily to the surface polar optical phonon scattering originating from the SiO2 substrate, which is nearly absent in MoSe2 devices on parylene-C substrate.

Robust mechanical property measurements of fibrous parylene-C thin-film substrate via moiré contouring technology

Parylene-C is a bio-inert, bio-compatible and relatively inexpensive material with many bio-medical applications from coatings for implantable devices to bio-scaffolds. The main objective of this research was to demonstrate a novel approach to accurately measure the mechanical properties of free-standing fibrous thin-film substrates (TFS) of parylene-C. For that purpose, a two-stage experimental protocol based on the use of moiré contouring technology was developed. In this protocol, local measurements employing an advanced moiré setup that uses non-conventional illumination (i.e. evanescent field) are first performed to gather high-resolution information on a small region of the specimen; then, global measurements based on shadow moiré are performed to monitor the overall behavior of the membrane. The protocol was first calibrated for an aluminum foil and then partially applied to the fibrous parylene-C TFS. Material properties extracted from experiments are f0ully consistent with the data reported in literature and the results of a hybrid identification procedure based on the combination of finite element analysis and nonlinear optimization. The results will help lay the foundation for developing a comprehensive understanding of the influence that morphology and stresses play in the ability to enhance and sustain cell growth and tissue development, for biomedical applications.

Directed assembly of high density single-walled carbon nanotube patterns on flexiblepolymer substrates

We report an effective technique for the controlled assembly of single-walledcarbon nanotubes (SWNTs) and demonstrate organized high density networkarchitectures on soft polymeric substrates. We utilize the surface energy differentialbetween a plasma treated (hydrophilic) parylene-C surface and a photoresist(hydrophobic) surface to create microscale patterns of SWNT networks on a 10 µm thick parylene-C substrate. The large scale fabrication of patterned SWNTstructures presented is achieved by performing site-selective fluidic assembly ofSWNTs. Electrically continuous nanotube network micro-arrays as small as 4 µm wide that areup to 1500 µm long with controlled separation have been fabricated by dissolving the photoresist afterassembly. Electrical and mechanical characterization of nanotube networks on the flexiblesubstrate in both static and dynamic modes indicates that the structure can handle bothcompressive and tensile deformations with no hysteresis. The technology presented hasimmediate applications in making thin film transistors, interconnects and sensors onflexible substrates.

Microstructure and Adhesion of Au Deposited on Parylene-c Substrate With Surface Modification for Potential Immunoassay Application

Improvement of recrystallization and adhesion of gold (Au) deposited on parylene-c (Pa-c) substrate with heat treatment and surface modification using physical and chemical treatment was investigated. Annealing of Au on Pa-c was performed to observe microstructure enhancement due to heat treatment from 100 to 250/spl deg/C. From the peak intensity and full-width at half-maximum of Au(111), its crystallinity appeared to improve as the annealing temperature increased, which can provide the surface with proper creation of monolayers. Several physical and chemical methods of surface modifications were employed to analyze surface energy and adhesion promotion, such as oxygen plasma, atmospheric plasma, ion beam, and Bovine serum albumin. These results exhibit excellent adhesion properties by exploiting oxygen plasma and ion-beam treatment, which induce carbonyl groups via the mechanical interlocking.