Cyclo-olefin Polymer Substrates Research Articles

Fabrication of highly-oriented β-Ga2O3 thin film on ZnO/AlO x -buffered cyclo-olefin polymer substrate by excimer laser annealing at room temperature

The fabrication of highly-oriented β-Ga2O3 thin films on cyclo-olefin polymer (COP) substrates with oxide-buffer layers of amorphous AlO x and c-axis-oriented crystalline ZnO by excimer laser annealing at RT was investigated. An amorphous GaO x thin film deposited on a COP substrate by pulsed laser deposition at RT was irradiated with a pulsed KrF excimer laser from the film surface at RT in air. X-ray diffraction, reflection-high-energy-electron diffraction, and high-resolution transmission-electron microscopy results revealed solid-state crystallization of the uniaxial-oriented β-Ga2O3 (01) thin film on the ZnO/AlO x -buffered COP substrate. The obtained β-Ga2O3 thin film exhibited green-, blue-, and UV-band cathode-luminescence.

Crystallinity improvement of room-temperature PLD-deposited ZnO thin films on cyclo-olefin polymer substrates subject to surface-pretreatment with vacuum-UV-light irradiation

The effect of the surface-pretreatment of cyclo-olefin polymer (COP) substrates with vacuum-ultraviolet (VUV) light irradiation on the crystal growth of ZnO thin films deposited by room-temperature pulsed laser deposition (PLD) was investigated for development of flexible optical devices. 172-nm-excimer light irradiation with durations of 60 to 600 s in air was found to make the COP surface more hydrophilic and smooth. It was verified from measurements of X-ray diffraction, atomic force microscope and high-resolution transmission electron microscope that the ZnO thin films grown on the VUV-light-pretreated COP substrates exhibited enhanced (0001) orientation growth and increased crystallinity compared with the samples grown on substrates not subject to the pretreatment; the samples on the pretreated substrates also showed a smooth surface and atomically sharp interface between the thin film and the substrate. The electrical resistivity of the ZnO thin film grown on the VUV-light-pretreated COP substrate was estimated to be 2.3 × 10−3 Ωcm, which was 40% lower than that of the film grown on the untreated substrate.

Repeated bending durability evaluation of ZnO and Al-doped ZnO thin films grown on cyclo-olefin polymer for flexible oxide device applications

ZnO and Al-doped ZnO (AZO) thin films were fabricated on cyclo-olefin polymer (COP) substrates with different thicknesses for flexible device applications, and their bending strength was evaluated using surface observations and two-terminal resistance measurements. The fabricated films were subjected to repeated bending endurance tests up to 10 000 cycles. As COP substrate thickness was decreased, surface distortion decreased, two-terminal resistance fluctuations decreased, cracks in SiO2 buffer layer suppressed, and bending strength improved. When COP substrate thickness was 50 μm, variation in two-terminal resistance was negligible, and an oxide thin film device with durability of 10 000 cycles was successfully fabricated. Crystallinity evaluation using X-ray diffraction and mechanical characterization using nanoindentation were performed. This study discusses ZnO and AZO thin films for flexible device applications in relation to their surface conditions, electrical properties, crystallinity, and mechanical properties in cyclic bending tests. The results indicate that these thin films are useful materials for flexible devices.

Combination of Capped Gold Nanoslit Array and Electrochemistry for Sensitive Aqueous Mercuric Ions Detection.

Label-free surface plasmon resonance (SPR) detection of mercuric ions in various aqueous solutions, using capped gold nanoslit arrays combined with electrochemical (EC) sensing technique, is demonstrated. The nanoslit arrays are fabricated on flexible cyclo-olefin polymer substrates by a nanoimprinting lithography method. The EC and SPR signals for the investigation of current responses and transmission SPR spectra are simultaneously measured during metal ions electrodeposition. Glycerol–water solution is studied to evaluate the resonant peak wavelength sensitivity (480.3 nm RIU−1) with a FOM of 40.0 RIU−1 and the obtained intensity sensitivity is 1819.9%. The ferrocyanide/ferricyanide redox couple performs the diffusion controlled electrochemical processes (R2 = 0.99). By investigating the SPR intensity changes and wavelength shifts of various mercuric ion concentrations, the optical properties are evaluated under chronoamperometric conditions. The sensors are evaluated in the detection range between 100 μM and 10 nM with a detection limit of 1 μM. The time dependence of SPR signals and the selectivity of 10 μM Hg2+ in the presence of 10 μM interfering metal ion species from Ca2+, Co2+, Ni2+, Na+, Cu2+, Pb2 + and Mn2+ are determined. The capped gold nanoslit arrays show the selectivity of Hg2+ and the EC sensing method is effectively utilized to aqueous Hg2+ detection. This study provides a label-free detection technique of mercuric ions and this developed system is potentially applicable to detecting chemicals and biomolecules.

Broadband complex permittivity and conductivity measurements in the millimeter-wave bands over variable temperatures using a balanced-type circular disk resonator

A broadband measurement system is developed to address the issue of temperature dependence of the complex permittivity and conductivity of low-loss substrates in the millimeter-wave bands for fifth/sixth generation wireless communication applications. The developed system can provide broadband material measurements from less than 20 GHz to over 100 GHz over variable temperatures by utilizing higher order mode resonances of a balanced-type circular disk resonator (BCDR). The broadband measurement capability of the developed system is attributed to the mode-selective behavior of the BCDR over a wideband. To demonstrate the developed system, we measure the complex permittivity of the following three substrate materials over variable temperatures from 25 °C to 100 °C: cyclo-olefin polymer (COP), ceramic-filled polytetrafluoroethylene composites, and fused silica. Furthermore, the temperature dependence of the conductivity of the surface-mounted metal is characterized for the COP substrate. The measurements indicate that the loss tangents and conductivities of the substrates increase and decrease, respectively, with the temperature and frequency in the millimeter-wave bands. The full-wave simulations using the measured complex permittivity and conductivity of the COP substrate reveal that the propagation loss of the microstrip line using the COP substrate increases with the temperature and frequency and that the increase in the loss is primarily attributed to the decrease in the conductivity.

D-Band Perfect Anomalous Reflectors for 6G Applications

We demonstrate anomalous reflectors at 140 GHz for the application of 6G communication coverage expansion. The reflectors are designed on cyclo-olefin polymer (COP) substrates on the basis of measured complex permittivity and conductivity at millimeter frequencies obtained with the balancedtype circular disk resonator method. From full-wave simulations, we confirm that nearly perfect anomalous reflection characteristics are realized with suppressed parasitic reflections in undesired directions. The simulated efficiencies excluding the material losses of the reflectors designed with the reflection angle θR = 30°, 45°, 60°, and 75° are 99.5%, 98.9%, 99.7%, and 99.8%, respectively. In addition, we fabricate the designed reflectors on the COP substrates and experimentally evaluate their anomalous reflection performances. The measured overall efficiencies of the reflectors with θR = 450, 600, and 750 are 88.0%, 83.6%, and 81.6%, respectively. This is the first demonstration of highly efficient anomalous reflectors in the D-band.

Fabrication of ultra-flat c-axis oriented ZnO thin films on atomically stepped cyclo-olefin polymer (COP) substrates by pulsed laser deposition at RT

Highly crystalline c-axis oriented ZnO thin films with ultra-flat surfaces were fabricated by pulsed laser deposition at RT on 0.3 nm high atomically stepped cyclo-olefin polymer (COP) substrates whose surfaces were thermally nanoimprinted using atomically stepped sapphire molds. X-ray diffraction and atomic force microscopy measurements showed that the atomically-controlled surfaces of COP substrates enhanced the c-axis orientation and surface flatness of the crystalline ZnO thin films. The ZnO thin films grown on the atomically stepped COP substrates exhibited atomically stepped surface morphology, and also the optical bandgap of about 3.3 eV and RT resistivity of 5.0 × 10−2 Ω cm.

Subtractive transfer printing process for rapid fabrication of Au nano/micro structures on a polymer substrate

This paper presents a fast stamp method for fabricating Au mico/nano structures based on subtractive cold-welding transfer printing. Cyclo-olefin polymer (COP) was used as the substrate. Polymer materials such as polymethylmethacrylate, polyethylene terephthalate, polycarbonate (PC) can be used to peel off Au films from the COP substrate. Uniform micro/nanodisk patterns of a large area were fabricated by means of a PC stamp fabricated by nanoimprinting. The transfer mechanism was studied. The influence of Au film thickness on the substrate was investigated. Thicker Au film was found more difficult to be broken and peeled-off than thin films. Step-by-step multiple stamping by the same PC stamp was investigated. The damage of the nanodisk pattern was studied. This work demonstrated a rapid fabrication process for nano/micro structures and studied the key factors for the process.

Fabrication and spectroscopic characterization of graphene transparent electrodes on flexible cyclo-olefin substrates for terahertz electro-optic applications

We demonstrate graphene on flexible, low-loss, cyclo-olefin polymer films as transparent electrodes for terahertz electro-optic devices and applications. Graphene was grown by chemical vapor deposition and transferred to cyclo-olefin polymer substrates by the thermal release tape method as layers on an approximate area of 4 cm2. The structural and electromagnetic properties of the graphene samples as well as their spatial variation were systematically mapped by means of µRaman, terahertz time-domain and mid-infrared spectroscopy. Thanks to the small thickness and very low intrinsic absorption of the employed substrates, both high transmittance and conductivity were recorded, demonstrating the suitability of the technique for the fabrication of a new class of transparent and flexible electrodes working in the terahertz spectrum.

Effects of irradiation atmosphere on vacuum ultraviolet-induced surface modification of cyclo-olefin polymer substrates

The surface of a cyclo-olefin polymer was modified using vacuum ultraviolet (VUV) light to obtain a wettable surface. We found that the surface hydrophilicity is dependent on both VUV irradiation distance and irradiation time, which affected the concentration of oxygen functional groups. We investigated the effects of the VUV irradiation atmosphere and aging of the treated surfaces. We concluded that VUV treatment in low-humidity air (1% relative humidity) was the most effective condition for introducing oxygen functional groups on the surface; the concentration of these groups decreased over time (a drop of 11% over 5 d).

Terahertz-wave generation devices using electro-optic polymer slab waveguides and cyclo-olefin polymer clads

We fabricated terahertz (THz) wave generation devices using electro-optic (EO) polymer slab waveguides and cyclo-olefin polymer (COP) clads with very small absorption loss of the THz waves based on a novel device fabrication procedure involving bonding of the poled EO polymer layer to the COP substrates. We demonstrated THz wave generation from the EO polymer slab devices using a 1.55 µm-band femtosecond fiber laser and evaluated the THz wave generation properties of the devices. Our results will lead to the development of compact, highly efficient, and ultrabroadband THz devices using EO polymers.

Thin-Film Magnetoimpedance Structures Onto Flexible Substrates as Deformation Sensors

The magnetic and magnetoimpedance (MI) properties of a Permalloy-based thin-film structure, deposited onto a polymeric flexible substrate, are investigated as a function of the applied stress. The selected structure, a sandwich of NiFe/Ti multilayers with a central Cu layer, has been previously shown to produce extraordinary MI performance when deposited onto rigid substrates. Here, grown onto a cyclo olefin polymer substrate, it is evaluated as a deformation sensor and its properties analyzed in terms of the preparation conditions. A specially designed sample holder allows measuring simultaneously the hysteresis loop of the sample using magneto-optical Kerr effect and its MI using a network analyzer, while applying a controlled stress to the sample. The magnetoelastic anisotropy developed in the sample is longitudinal, revealing that the magnetostriction coefficient is positive, and competes with the transverse magnetic anisotropy induced during the sputtering deposition of the multilayer structure. The combined, effective anisotropy determines the shape of the hysteresis loop and the MI curves. We show how the evolution of the maxima of the MI curves with the applied stress allows a precise determination of the magnetostriction coefficient of the sample. The stress impedance is determined as the impedance change, measured at $H =0$ Oe, as function of the applied stress. It displays a linear behavior with a corresponding gauge factor of 60, thirty times larger than the one of conventional metallic strain gauges.

Three-dimensional plasma micro–nanotextured cyclo-olefin-polymer surfaces for biomolecule immobilization and environmentally stable superhydrophobic and superoleophobic behavior

Cyclo-olefin polymer (COP) surfaces are micro–nanotextured using O2 plasma chemistry in one-step process. These surfaces subsequently display multiple functionality, (A) they are stable in time (i.e. non ageing), functional, high surface area, substrates suitable for biomolecule binding, after thermal annealing in order to induce accelerated hydrophobic recovery while preserving the chemical functionality created by the plasma. (B) Alternatively, they are robust and environmentally stable superhydrophobic and superoleophobic surfaces, after mechanical stabilization via wetting–drying and gas-phase coating with a perfluoroctyltrichlorosilane monolayer (PFOTS) or plasma deposited Teflon-like polymer layer. The plasma treated, micro–nanotextured surfaces used for biomolecule binding exhibit remarkable retention of the initially immobilized biomolecule compared to untreated COP surfaces (up to 75%), after washing with aggressive washing solutions (sodium dodecyl sulfate), while showing excellent intensity, uniformity and sensitivity. The superoleophobic COP material surfaces exhibit very high static contact angles (SCA >150°) and very low hysteresis (CAH <10°), for a wide range of liquids from water (surface tension: 72.8mN/m) to hexadecane (surface tension: 27mN/m). In addition, these superhydrophobic and superoleophobic surfaces exhibit excellent stability against environmental ageing after 60 continuous cycles of exposure to various harsh environmental conditions (heat, moisture, UV irradiation) in a controlled environment. Finally, the two presented functionalities are combined for the first time on the same COP substrate, creating localized rough hydrophilic and antifouling patterns that exhibit spatially selective biomolecule immobilization inside a microfluidic device.

Surface activation of cyclo olefin polymer by oxygen plasma discharge: a molecular dynamics study

Thermoplastic substrates made of cyclo olefin polymer (COP) are treated with oxygen plasma discharges to introduce polar groups at the surface. This is the first step in the process of surface functionalization of COP substrates used in biosensor devices. A molecular dynamics model of basic COP structure is implemented using the second-generation reactive empirical bond order (REBO) potentials for hydrocarbon–oxygen interactions. The model includes covalent bond and Van der Waals interactions. The bombardment of a COP surface with mono-energetic atomic oxygen ions, energy in the range 1-35 eV, is simulated and reported here. The dynamics of the substrate modification reveals that the substrate top layer is de-hydrogenated and subsequently builds up an oxygen–carbon matrix layer, ∼10 Å thick. Analysis of the modified substrates indicates that surface yield is predominantly peroxide groups.

Wetting Transition from the Cassie–Baxter State to the Wenzel State on Textured Polymer Surfaces

The wetting transition from the Cassie-Baxter state to the Wenzel state on textured surfaces was investigated. Nano- to microscale hexagonal pillared lattices were prepared by nanoimprint lithography on fluorinated cycloolefin polymer substrates. The transition was clearly observed for water and some ionic liquids through contact angle measurements and optical microscopy. A simple model clearly demonstrated that the energy barrier in the wetting transition from the Cassie-Baxter state to the Wenzel state was dominated by the competition between the energy barrier and external forces, particularly the Laplace pressure in the present case.

Ultra-rapid flow-through polymerase chain reaction microfluidics using vapor pressure

A novel flow-through polymerase chain reaction (PCR) microfluidic system using vapor pressure was developed that can achieve ultra-rapid, small-volume DNA amplification on a chip. The 40-cycle amplification can be completed in as little as 120 s, making this device the fastest PCR system in the world. The chip device is made of a pressure-sensitive polyolefin (PSP) film and cyclo-olefin polymer (COP) substrate which was processed by cutting-work to fabricate the microchannel. The enclosed structure of the microchannel was fabricated solely by weighing the PSP film on the COP substrate, resulting in superior practical application. The vapor pressure in the denaturation zone of the destabilizing flow source was applied to the flow force, and ultra-rapid, efficient amplification was accomplished with a minimal amount of PCR reagents for detection. The flowing rhythm created by vapor pressure minimized the residual PCR products, leading to highly efficient amplification. For field test analysis, airborne dust was collected from a public place and tested for the presence of anthrax. The PCR chip had sufficient sensitivity for anthrax identification. The fastest time from aerosol sampling to detection was theoretically estimated as 8 min.

Functionalization of cyclo-olefin polymer substrates by plasma oxidation: Stable film containing carboxylic acid groups for capturing biorecognition elements

Many current designs in biomedical diagnostics devices are based on the use of low cost, disposable, easy-to-fabricate chips made of plastic material, typically a cyclo-olefin polymer (COP). Low autofluorescence properties of such material, among others, make it ideal substrate for fluorescence-based applications. Functionalization of this plastic substrate for biomolecule attachment is therefore of great importance and the quality of films produced on such surface have often a significant influence on the performance of the device. In this communication we discuss the surface chemistry and some other characteristics of hydrophilic films, containing carboxylic acid functional groups, formed by plasma oxidation of COP and also films containing cross-linked, polymerized acryclic acid produced by sequential deposition of tetraorthosilicate and acrylic acid by plasma enhanced chemical vapor deposition (PECVD). Immobilization of labeled, single stranded DNA revealed high binding capacity for both coatings. To our best knowledge, this is the first example of direct immobilization of biomolecules on just plasma oxidized COP. Furthermore, more sophisticated treatment of the oxidized plastic substrate by PECVD with other organic precursors increased the binding capacity by some 40% than that of just plasma oxidized COP. The carboxy functionalized surfaces, due to the negative charge of the carboxy groups, showed very positive trends towards increasing the signal to noise ratio when charged biomolecules such as DNA, are used.

Deposition of chemically reactive and repellent sites on biosensor chips for reduced non-specific binding

The performances of new polymeric materials with excellent optical properties and good machinability have led the biomedical diagnostics industry to develop cheap disposable biosensor platforms appropriate for point of care applications. Zeonor, a type of cycloolefin polymer (COP), is one such polymer that presents an excellent platform for biosensor chips. These polymer substrates have to be modified to have suitable physico-chemical properties for immobilizing proteins. In this work, we have demonstrated the amine functionalization of COP substrates, by plasma enhanced chemical vapour deposition (PECVD), through codeposition of ethylene diamine and 3-aminopropyltriethoxysilane precursors, for building chemistries on the plastic chip. The elemental composition, adhesion, ageing and reactivity of the plasma polymerized film were examined. The Si–O functionality present in amino silane contributed for a good interfacial adhesion of the coating to COP substrates and also acted as a network building layer for plasma polymerization. Wet chemical modification was then carried out on the amine functionalized chips to create chemically reactive isothiocyanate sites and protein repellent fluorinated sites on the same chip. The density of the reactive and repellent sites was altered by choosing appropriate mixtures of homofunctional phenyldiisothiocyanate (PDITC), pentafluoroisothiocyanate (5FITC) and phenylisothiocyanate (PITC) compounds. By tailoring the density of reactive binding sites and protein repellent sites, the non-specific binding of ssDNA has been decreased to a significant extent.

Properties of Highly Transparent Conductive Ga-Doped ZnO Films prepared on Polymer Substrates by Reactive Plasma Deposition with DC Arc Discharge

Highly transparent conductive polycrystalline Ga-doped ZnO (GZO) films with a thickness of about 100nm prepared on cyclo-olefin polymer (COP) or glass substrates at various temperatures below 90(C by ion plating with DC-arc discharge were investigated. A systematic study has been made of the influence of substrate temperature Ts on the structural, electrical, optical and residual stress properties of GZO films. An increase in Ts resulted in a beneficial effect on the crystallinity, electrical conductivity and transmission in the visible (VIS) range regardless of the type of substrate. The minimum resisitivity for GZO on glass and COP substrates was as low as 5.0μΩm and 5.8μΩm, respectively. For all the GZO films with average optical transmission above 90% in the VIS region, with increasing Ts, the optical absorption loss in the visible range decreased according in order of increasing Hall mobility. All the GZO films were found to be compressively stressed. The residual stresses, evaluated from the XRD spectrum, in GZO films on glass substrates are a decreasing function of Ts, whereas they are an increasing function of Ts for GZO films on COP substrates. This finding indicates that for the GZO films on COP substrates deposited at higher temperature, thermal stress is dominant.

Properties of Transparent Conductive Zinc Oxide Films Deposited on COP Substrates by PLD Method

The Al-doped ZnO (AZO) films and ZnO buffer layer were deposited on cyclo-olefin polymer (COP) substrates by pulsed laser deposition (PLD) method using ArF excimer laser (λ = 193 nm) with an energy densities of 1.0 ∼ 2.5 J/cm2. Film structure was composed of a 150 nm-thick AZO film, a 100 nm-thick ZnO buffer layer, and a 188 μm-thick COP substrate. As a result, in the range of 1.0 ∼ 2.5 J/cm2, Hall mobility and carrier concentration were found to decrease linerly. Therefore, the lowest resistivity of 2.77×10-4 Ω-cm was obtained at laser energy density of 1.0 J/cm2. By the results of FE-SEM photograph and AFM image of a AZO / ZnO / COP structure deposited at a laser energy density of 1.0 J/cm2, it was found that smooth-surface-films with average roughness of 4.26 nm and AZO / ZnO films of good quality without cracked or flaked conditions were obtained. This will enables us to realize low-cost, lightweight, and flexible devices.