Flexible Film Substrate Research Articles

Electrically conducting, transparent, graphene based nanocomposite coatings on flexible film substrate

Transparent, electrically conducting nanocomposite coated polyethylene terephthalate (PET) films are prepared using two types of bulk synthesized few layered graphene; namely reduced graphene oxide (rGO) and liquid exfoliated graphite (EG) dispersed in ultra high molecular weight polyethylene (UHMWPE). This study focuses on application of high concentration of such nanofillers (1: 1 to 2.5: 1 ratios with polymer) in order to develop a highly conducting but ultrathin coating for better transparency. The coated PET films are characterized for their surface morphology, electrical and optical properties. High resolution transmission electron microscopic (HRTEM) images and corresponding selected area electron diffraction (SAED) patterns confirm that the graphite has been exfoliated to few layer graphene using both the synthesis routes. Transmittance values of these coated films are measured in UV visible spectrum. The rGO based samples have high transmittance (~90–95%) compared to EG based samples (~40–50%). From current-voltage (I‒V) graph and surface resistivity studies, it has been observed that rGO based samples are dielectric in nature similar to UHMWPE while EG based samples are electrically conducting and its conductivity increases with its concentration. EG based nanocomposite coated samples show much better electrical conductivities (resistance 338 to 66 kΩ at different concentrations of EG) than rGO based samples.

Development of Transparent Electrodynamic Screens on Ultrathin Flexible Glass Film Substrates for Retrofitting Solar Panels and Mirrors for Self-Cleaning Function

ABSTRACTDevelopment of transparent electrodynamic screens (EDS) printed on ultrathin flexible glass film substrates for retrofitting on solar panels and solar mirrors to perform self cleaning function is reviewed. Large-scale solar plants are generally installed in semi-arid and desert areas where dust layers build up on solar collectors causes major energy-yield loss. Maintaining designed plant capacities requires more than 90% reflectivity for CSP mirrors and 90% transmission efficiency for PV modules; solar collectors must therefore be cleaned at a frequency depending on the rate of dust deposition. Scarcity of water in these regions requires a cleaning method that drastically reduces or eliminates water and the associated labor costs for high efficiency operation of large-scale solar plants. An EDS film consists of rows of interdigitated, transparent conducting parallel electrodes embedded within a flexible ultrathin glass film and an optically clear adhesive film used for retrofitting the film on the surface of solar collectors. When phased voltage pulses activate the electrodes, the dust particles are first electrostatically charged, then repelled and removed from the surface of the solar collectors by Coulomb force, restoring transmission efficiency greater than 90%. The electrodes of EDS are either made from silver nanowire or another conductive transparent material printed on a highly transparent, ultrathin (100-μm thick), flexible borosilicate glass film. Applications of different conducting transparent electrodes and methods of printing are reviewed for optimizing self-cleaning function of solar panels and mirrors.

Organic Phototransistors With All-Polymer Bulk Heterojunction Layers of p-Type and n-Type Sulfur-Containing Conjugated Polymers

All-polymer phototransistors were fabricated using both glass and flexible plastic film substrates by employing bulk heterojunction channel layers of p-type polymer (P3HT) and n-type polymer (THBT-ht). The devices could detect the entire visible light because the n-type polymer could sense photons in the deep red parts (>650 nm). The responsivity of devices was higher at the lower light intensity, while it could be controlled by varying the gate and/or drain voltages. Similar performances were measured for flexible all-polymer phototransistors with a bottom-source/drain and top-gate electrode configuration.

An MRI-readable wireless flexible pressure sensor.

We developed a magnetic resonance imaging (MRI) -detectable wireless flexible pressure sensor with pressure-sensitive LC resonator fabricated on a flexible film substrate. Measuring pressures in the body such as blood vessels and cardiac ventricle are very important in making diagnoses and in postoperative observation. However, conventional wired pressure sensors have difficulty in maintaining their connections to external readout equipment, and they also increase the risk of infection during and after implantation. In this study, to read the pressure wirelessly using an MRI system, an LC resonator consisting of a spiral coil and a pressure-sensitive capacitor was designed resonate at 300 MHz which corresponds to the Larmor frequency in an external magnetic field of 7-T. In order to validate the operating principle of the fabricated device, the frequency-impedance characteristics were measured by changing the pressure. The resonance frequencies of complemented LC circuits were lower by approximately 10% than those of nonpressured conditions. After implanting these devices in a 1% agarose gel, MR images were acquired by inducing pressures close to blood pressures of 20 kPa. As a result, contrast changes in the MR images were observed around the integrated spiral coils. This result indicated that the developed flexible pressure sensor has sufficient sensitivity to measure physiological pressure such as blood pressure of 20 kPa wirelessly in the body. In the future, quantitative pressure sensing will be evaluated by comparing it to the contrast changes in MR images with flip angle mapping.

Diamond micro engraving of gravure roller mould for roll-to-roll printing of fine line electronics

Printing electronics has attracted great attention in recent years due to its various superior performances compared with conventional silicon-based semiconductor industry. Roll-to-Roll gravure printing is able to transfer conductive nanoparticle ink onto the flexible film substrate to form continuous fine metal lines using a gravure roller mould with tens of thousands of tiny gravure cells on its surface. However, it is difficult to scale down the printed line width, which is crucial for the film's circuit density, resolution and transparency, because the market-available rollers fabricated by conventional engraving techniques for graphic printing usually have gravure cells larger than 25μm. Hence, in this study, a novel method based on ultraprecision machining technology, Diamond Micro Engraving (DME), is introduced to miniaturize the gravure cells in order to reduce the ink volume transfer during the printing process. A V-shape sharp diamond tool is used to continuously generate concave inverted micro pyramidal structures on the gravure roller surface using the Slow Slide Servo technology. Geometrical modelling of the engraving process is conducted to help programming the tool path to realize accurate control of the instantaneous position of two linear axes and one rotatory axis. Through applying the DME process, generation of consistent cell structure is achieved. The engraved gravure cell width is successfully miniaturized to 7μm. With the optimized cell spacing value, the DME-machined roller moulds are used in gravure printing of metal mesh film, which works as a potential transparent conductive film to replace the expensive indium-tin-oxide (ITO). The printed line width is reduced from 47μm to 19μm, and the transmittance of the printed metal mesh film for visible light is increased from 65.2% to 80.4% accordingly, which is comparable to the transmittance of ITO film.

A novel OFET-based biosensor for the selective and sensitive detection of lactate levels.

Biosensors based on organic field effect transistors (OFETs) are one of the more promising device applications in organic electronics. However, OFET-based biosensors are still in their early stages of development compared to other electrochemical biosensors. This study is the first to report on an extended-gate type organic field effect transistor (OFET) for lactate detection in aqueous media. Here, the extended-gate electrode of the OFET was modified with layers of a lactate oxidase and a horseradish peroxidase osmium-redox polymer on a flexible plastic film substrate for an enzymatic redox reaction of lactate. The device exhibited both high selectivity and sensitivity. The limit of detection (LOD) and the limit of quantification (LOQ) were estimated to be 66 nM and 220 nM, respectively, which are the sufficient detection limit for practical sensor applications. The obtained results confirm that extended-gate type OFET devices are applicable to enzyme-based biosensors for detecting lactate levels.

Fabrication of nanometer electrodes by electro migration on an embedded metal pattern.

Electrodes with several tens nanometer gap are very important parts in the nano devices such as SETs (Single Electron Transistor), and quantum dots. However, fabricating nanometer electrode with the EBL (Electron Beam Lithography) process is too costly and time consuming to be commercially feasible. To overcome these disadvantages and to enable mass production, nano imprint lithography is applied to a master fabrication technique via EBL. In this paper, several tens nanometer gap electrodes are fabricated by EBL in order to characterize SET. The embedded metal pattern is made by the NIL (Nanoimprint Lithography) process, which is suggested for mass production. In order to fabricate without chemical process, the embedded metal process was executed with nanoimprint lithography. And the nanometer gap was made by electro migration process on flexible film substrate. That is, the electro migration process was executed on the embedded metal pattern to fabricate the nano gapped electrodes.

Fabrication of Multiple Gas Barrier Layers Utilizing Roll-to-Roll Sputter and Performance

Flexible organic light emitting diodes (OLEDs) have been studied actively for the potential application to OLED display and OLED lighting. One of the key materials for flexible OLED is the flexible and transparent film substrate which can substitute ITO glass in flat panel OLEDs.In this work we deposited silicon and aluminium oxide and nitride single layer thin films on different flexible substrates such as poly(polyethylene terephthalate) (PET) and poly(polyethylene naphthalate (PEN) to investigate the gas barrier properties. After selecting the polymer film substrate and thin inorganic layer material, the inorganic/organic/inorganic multiple gas barrier was formed on film substrate by using roll-to-roll sputter and their property was examined from the viewpoint of multilayer structure and gas barrier properties for application to flexible substrate of OLED devices.

Conducting polymer/in-situ generated platinum nanoparticle nanocomposite electrodes for low-cost dye-sensitized solar cells

Here we report new low-cost nanocomposite counter electrodes for dye-sensitized solar cells (DSSCs), which were prepared by in-situ generation of platinum (Pt) nanoparticles inside poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solutions at room temperature. The Pt nanoparticles (Ptnp) were evenly dispersed in the PEDOT:PSS films and their size was 20∼40nm. The PEDOT:PSS-Ptnp films were well coated on substrates, and their optical transmittance was slightly better than conventional thermally-reduced Pt electrode. The short circuit current density of DSSCs with the PEDOT:PSS-Ptnp films was almost comparable to that with the conventional Pt film. The thickness control experiment disclosed that the series resistance of the PEDOT:PSS-Ptnp films is mainly responsible for the low fill factor. We found that the Ptnp was enriched on the surface of the nanocomposite films when the spin-coating speed was high, which has been assigned as an additional reason for the improved device performance. Hence further improvement in device performance is expected by employing high conductivity PEDOT:PSS materials. Finally, we expect that the present method can contribute to the fabrication of low-cost DSSCs using flexible plastic film substrates at low temperatures.

유연성 기판을 이용한 자동차 유리 부착용 다중 대역 안테나

본 논문에서는 대역 저지 U형태의 슬롯이 추가된 다중 대역 모노폴 안테나를 제안하였다. 안테나는 유연성을 가지는 폴리마이드 필름 기판으로 제작하였다. 제안된 안테나는 U-슬롯이 추가된 패치 형태의 모노폴 안테나로 2.7 GHz 대역에서 저지 특성을 갖도록 설계하였으며, 인접한 주파수 대역에서 반사 손실 특성의 개선을 얻을 수 있었다. 실제 자동차 유리에 부착한 실험을 통해 ISM 대역(2.4~2.483 GHz)과 WAVE 대역(5.85~5.925 GHz)에서 10 dB 이상의 반사 손실을 가지는 것을 확인하였다. 방사 패턴은 높은 주파수 대역에서 일부 패턴의 널이 있으나 전반적으로 전방향성의 특성을 나타내었으며, 2.8, 5.7 dBi의 최대 이득을 가졌다. In this paper, we propose a multi-band monopole antenna with a band-notching U-slot, which is fabricated inside the flexible polymide film substrate. The U-shaped slot located on the patch-shaped monopole antenna provides band-notch at 2.7 GHz, but also helps to improve return loss at adjacent frequency bands. The performance of the antenna attached on an automobile-glass has been simulated and measured. The fabricated antenna provides more than 10 dB return loss for ISM band(2.4~2.483 GHz) and WAVE band(5.85~5.925 GHz), 2.8~5.7 dBi maximum gain, and good radiation patterns.

Microfluidic origami: a new device format for in-line reaction monitoring by nanoelectrospray ionization mass spectrometry

Microfluidics is an attractive platform for chemical synthesis because it offers fast reaction times, reduced reagent usage, and the ability to integrate multiple functions on a single device. Digital Microfluidics (DMF) is particularly well-suited for microscale chemical synthesis, as it permits discretized sample handling, allowing for total process control. However, a limitation of DMF-based synthesis is analysis, which is often performed offline. To this end, we have developed "microfluidic origami", a new device format that integrates DMF with in-line analysis by mass spectrometry (MS). This format comprises a DMF platform and a folded nanoelectrospray ionization (nanoESI) emitter formed on a single flexible polyimide film substrate. Additionally, the device contains a two-plate-to-one-plate DMF interface, which allows for straightforward coupling of micro-reaction operations and product delivery to the emitter for analysis. The integrated platform was used to perform the Morita-Baylis-Hillman (MBH) reaction using DMF followed by inline MS analysis for monitoring the reaction progress in real-time. We propose that this platform has potential as a new tool for real-time monitoring of reaction rates and reaction pathways and could be a useful addition to the synthetic organic chemistry laboratory.

Nanoimprint lithography with a soft roller and focused UV light for flexible substrates

This paper presents a nanoimprint lithography system for flexible substrates. With this system, a flexible substrate is pressed on a stamp with a low pressing load, a narrow contact area, and a focused ultraviolet (UV) light. The system efficiently transfers a pattern from the stamp to the substrate. A pressing roller is made of a hard material wrapped with silicone rubber. The roller ensures the flexible substrate is in contact with the patterned surface of the stamp. A heavy pressing load widens the contact area of the substrate and the stamp. The focused line beam of UV light, which is smaller than the contact area, cures the resist between the substrate and stamp. The contact length and pressure can be calculated in simulations on the basis of the pressing load and the thickness of the silicone rubber. The simulation results show the stress and strain of all components, such as the pressing roller, the silicone rubber, the substrate, and the stamp. Some of the experiments confirm that the nanoimprint lithography system can be used to transfer nanopatterns and micropatterns from a hard stamp to a flexible film substrate. The system can be applied to the fabrication of flexible electronic devices for applications pertaining to energy, biology, and the environment.

Fabrication of a nano-scale embedded metal electrode in flexible films by UV/thermal nanoimprint lithography tools

Nanoimprint lithography (NIL) which is well-known as a type of next-generation lithography, is a promising technology to produce sub-50 nm half-pitch features on several types of substrates. Particularly, ultraviolet (UV) nano-imprint lithography technology has the advantages of a simple process with low pressure of less than room temperature, a low cost, high replication fidelity, and relatively high throughput [1,2]. Recently, many researchers have applied the NIL technique to fabricate metal patterns on a flexible film substrate. Although a flexible film as a substrate has many advantages, most types of flexible polymer film incur weakness caused by the chemicals during the metal lift-off and/or metal etching processes. In this paper, a fabrication method is proposed to create nanoscale metal electrode patterns on a UV-curable polyurethane resist using a UV/thermal nanoimprint lithography processes. A replica fabrication process using the fabricated polyurethane stamp is also proposed. Second- and the third-generation replicas with 30 and 100 nm dot patterns are fabricated using UV and thermal nanoimprint lithography tools.

Laser microperforated biodegradable microbial polyhydroxyalkanoate substrates for tissue repair strategies: an infrared microspectroscopy study

Flexible and biodegradable film substrates prepared by solvent casting from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) solutions in chloroform were microperforated by ultraviolet laser ablation and subsequently characterized using infrared (IR) microspectroscopy and imaging techniques and scanning electron microscopy (SEM). Both transmission synchrotron IR microspectroscopy and attenuated total reflectance microspectroscopy measurements demonstrate variations in the polymer at the ablated pore rims, including evidence for changes in chemical structure and crystallinity. SEM results on microperforated PHBHV substrates after cell culture demonstrated that the physical and chemical changes observed in the biomaterial did not hinder cell migration through the pores.

Fabrication of 100nm Sized Patterns on Flexible Polyethylene-Terephthalate Substrate Using Monomer Based Thermal Curing Nanoimprint Lithography

In order to build a nano-device on polymer substrate, nano-size patterning must be done. However, conventional photolithography cannot be used to fabricate nano-sized patterns on polymer film due to the flexibility of polymer film and its potential interaction with developer solution and organic solvent. In this study, 100nm sized dense line and space patterns were made on flexible PET (polyethylene-terephthalate) substrate using newly developed monomer based imprinting lithography. Compared to hot embossing lithography, thermal curing imprint lithography uses monomer based imprint resin which consists of base monomer and thermal initiator. Since it is liquid phase and polymerization temperature is much lower than glass temperature of polymer, the nano-sized patterns can be transfer at much lower temperature and pressure. Hence, patterns as small as 100nm were successfully fabricated on flexible PET film substrate by monomer based thermal curing imprinting lithography at 85°C and 5atm.

有機電界発光デバイス用フィルム保護膜の開発

This review paper describes the present status of passivation films with organic/Inorganic multilayer structure on flexible organic film substrate designed for electronic devices such as organic light emitting diode (OLED). Passivation film of SiNx/CN:H multilayer showed an excellent barrier properties for water and oxygen and strongly suppressed an appearance of dark spots on OLED surface during operation. The luminous efficiency of flexible OLED thus formed with passivation films revealed to be equivalent to that on glass substrate encapsulated by can. substrate.

Fabrication of nano-sized resist patterns on flexible plastic film using thermal curing nano-imprint lithography

Due to polymer’s excellent flexibility, transparency, reliability and light weight, it is a good candidate material for substrate of devices including organic electronic devices, biomedical devices, and flexible displays (LCD and OLED). In order to build such devices on polymer, nano- to micron-sized patterning must be accomplished. Since polymer materials reacts with organic solvents or developer solutions which are inevitably used in photolithography and cannot bear high temperature (∼140 °C) process for photoresist baking, conventional photolithography cannot be used to polymer substrate. In this research, monomer based thermal curing imprinting lithography was used to make as small as 100 nm dense line and space patterns on flexible PET (polyethylene-terephthalate) film. Compared to hot embossing lithography, monomer based thermal curing imprint lithography uses monomer based imprint resin which consists of base monomer and thermal initiator. Since it is liquid phase at room temperature and polymerization can be initiated at 85 °C, which is much lower than glass temperature of polymer resin, the pattern transfer can be done at much lower temperature and pressure. Hence, patterns as small as 100 nm were successfully fabricated on flexible PET film substrate by monomer based thermal curing imprinting lithography at 85 °C and 5 atm without any noticeable degradation of PET substrate.

Study and design of a capacitively coupled polymeric internal antenna

A capacitively coupled polymeric internal antenna is introduced for Bluetooth or GPS applications. Such an antenna can be easily fabricated on a flexible film substrate and attached to the inside surface of the plastic housing of a portable wireless device, such as a PDA. The proposed antenna saves critical space on the printed circuit board (PCB) and eliminates the need for a vertical contact feed. Thus manufacturing is also simplified and cost is reduced. Practical examples of utilizing such a concept for Bluetooth (2.45 GHz) and GPS (1.575 GHz) applications are provided. The antenna system requires a small coupling plate (as small as 4 by 4 mm/sup 2/) that can be easily surface mounted on a PCB. The solution proposed provides wideband operation satisfying Bluetooth functionality with good radiation pattern and gain.

II–VI compounds as the top absorbers in tandem solar cell structures

Efficiencies of 19% have been achieved with copper indium gallium diselenide (CIGS) solar cells with a band gap of about 1.1 eV. Simulations indicate that if these are combined with a transparent top cell of band gap in the range 1.6–2.0 eV and with comparable efficiency, tandem efficiencies in the 25–30% range can be attained. We are developing II–VI based top cells for this application on both glass as well as lightweight substrates for space applications. To achieve these objectives, short circuit currents ( J scs) in the range 18–19 mA/cm 2 are needed. We have attained internal J scs in this range for 1.7 eV CdSe absorbers, and external J scs are rapidly approaching these values. Single-phase Cd 1− X Zn X Te (CZT; E G = 1.6–1.8 eV) films have been deposited by co-deposition on glass and flexible polyimide film substrates from the binary compounds using two deposition technologies. CZT absorber performance is presently limited by poor transport properties and influence from the contact layers. To develop open circuit voltages ( V ocs) in the range of 1 V, a nearly degenerate, transparent p-type contact is needed. We have focused our efforts on ZnSe and ZnTe for this contact and thus far have attained V ocs approaching 500 mV for ZnSe/CdSe and 800 mV for ZnTe/CZT. Transmission of 80% of the low energy light to be utilized by the CIGS bottom cell has also been demonstrated.

Thermal characterization of micro heater arrays on a polyimide film substrate for fingerprint sensing applications

A new type of micro fingerprint sensor was proposed and the sensing principle was demonstrated using micro heaters as the sensing elements. The arrayed sensing elements were micro resistors made of sputtered 200 nm thick platinum film on a 50 µm thick flexible polyimide film substrate. The temperature coefficient of resistance was 0.0029 (K−1) and showed good linearity. Because of the small thermal capacity and effective thermal isolation, the resistance of the heater showed high sensitivity and short response time to the applied power. By applying a pulsed voltage of 5.4 V at ambient air, the heater temperature could be increased from room temperature to 300 °C in 0.1 µs. When a fingerprint model (line and space: 100 µm; pattern height: 50 µm) made of silicone rubber was in contact with the sensor surface, contacting patterns of the fingerprint model were clearly recognized as the difference in resistance, i.e. in temperature. Micro through-holes with a diameter of 90 µm were wet etched vertically on the polyimide film substrate. The sensor array on the front surface and the wiring on the rear surface of the substrate were interconnected by depositing 1 µm thick copper film inside the through-holes using the electroless plating technique. The whole fabrication processes were simple and achieved in a low temperature range (<130 °C) on the non-silicon, low-cost and flexible substrate.