Flexible Plastic Sheet Research Articles

Stacked lightweight metasurfaces for wider stopband in X-K band

Frequency selective surfaces printed on optically transparent, large-area, flexible plastic sheets are studied for their passband and stopband characteristics when present as single-layer, two-layer and three-layer stacks. The unit cell design, its size, spacing and thickness on the substrate enable the single layer metasurface to yield a stopband width of 4.46 GHz (corresponding to 34.80%), when the center frequency is at 12.83 GHz in simulation and 12.86 GHz in measurement. On stacking identical surfaces as two-layer and three-layer configurations with suitable displacements both within the surface plane and perpendicular to the surface plane, the structural geometry of the unit cell gets varied leading to an ultra-wide stopband of 8.96 GHz in the range from 12.16 GHz to 21.11 GHz which covers X to K band. This leads to a wider stopband width of 43.60% for two-layer stack and 48.10% for three-layer stack with no in-plane shift. This is further enhanced to 65.50% with suitable shift within the plane of the stacked design. The three-layer stacked structure is ultra-thin with a thickness of 0.012 λ0. The single layer as well as all the three stacked structures have stopband characteristics that are invariant to incidence angle variation up to 750.

Dry Printing of Ag–Ni Conductive Particles Using Toner-Type Printed Electronics

Printed electronics are a set of additive manufacturing methods for creating future flexible electronics on thin polymeric sheets. We proposed the toner-type, dry, page-printing of Ag–Ni composite conductive particles on flexible plastic sheets without pre-treatment. No chemical solvents are necessary to compose the inks of the electronic materials used for the toner-type printing, and no chemical treatment is required for the plastic film substrate surface. In addition, multilayer printing is simple when using toner printing because previously printed materials do not need to be resolved; furthermore, composing the thick films of the electronic materials is relatively simple. In this study, we fabricated an Ag–Ni composite toner to improve the fluidity of the toner particles compared to bare Ag particles. We successfully printed IC peripheral circuits at a resolution of 0.20 mm and demonstrated that the actual electrical circuit pattern can be formed using our method.

Over 130 cm2/Vs Hall mobility of flexible transparent conductive In2O3 films by excimer-laser solid-phase crystallization

Flexible transparent electrodes on flexible plastic sheets are in significant demand for use in flexible perovskite solar cells (f-PSCs). However, the combination of the broadband high optical transparency and low electrical resistivity required for the tandemization of f-PSCs sets a stringent requirement on flexible transparent electrodes that are based on traditional Sn-doped In2O3 (ITO) films, owing to the high free-carrier concentration needed to reduce the electrical resistivity. Herein, we used excimer laser irradiation to achieve a Ce and H codoped In2O3 (ICO:H) film on flexible polyethylene terephthalate (PET) that had ultrahigh electron mobility of 133 cm2/Vs, which is the highest among those reported for flexible transparent electrodes, and low sheet resistance of 14.2 Ω/□, which is approximately three times lower than the 40 Ω/□ sheet resistance of commercially available ITO/PET. Furthermore, compared to ITO, this ICO:H film had higher infrared transparency. These nontrivial performances were achieved by an optimized excimer-laser solid-phase crystallization process guided by the correlation between laser pulse counts and the volume fractions of the amorphous and crystalline phases in the films. These high performances resolved the problems faced by ITO films, thus facilitating the performance of flexible solar cells and optoelectronic devices.

Direct Printed Silver Nanowire Strain Sensor for Early Extravasation Detection.

In this study, we presented a wearable sensor patch for the early detection of extravasation by using a simple, direct printing process. Silver nanowire (AgNW) ink was first formulated to provide necessary rheological properties to print patterns on flexible plastic sheets. By adjusting printing parameters, alignments of AgNWs in the printed patterns were controlled to enhance the resistance change under stretching conditions. A resistive strain-sensing device was then fabricated by printing patterned electrodes on a stretchable film for skin attachment. The designed sensor pattern was able to detect forces from a specific direction from the resistance change. Moreover, the sensor showed excellent sensitivity (gauge factor (GF) = 100 at 50% strain) and could be printed in small dimensions. Sensors of millimeter size were printed in an array and were used for multiple detection points in a large area to detect extravasation at small volumes (<0.5 mL) at accurate bump location.

Solid-phase crystallization of gallium arsenide thin films on insulators

• The grain size and crystal orientation of polycrystalline GaAs on insulators are discussed for the first time. • The precursor conditions dramatically influence the subsequent solid-phase crystallization of GaAs layers. • The GaAs layer crystallizes at 400 °C, developing polycrystalline GaAs layer on a flexible plastic sheet. • The findings can be key parameters for synthesizing polycrystalline compound semiconductors.

Zn-induced layer exchange of p- and n-type nanocrystalline SiGe layers for flexible thermoelectrics

Fermi-level control in a polycrystalline SiGe layer is challenging, especially under a low thermal budget owing to the low activation rate of impurities and defect-induced acceptors. Here, we demonstrate the low-temperature (120–350 °C) synthesis of nanocrystalline p- and n-type Si1−xGex (x: 0–1) layers using the layer exchange technique with a Zn catalyst. Pure Zn formed p-type SiGe layers (hole concentration: 1020 cm−3 for x ≥ 0.8) due to the shallow acceptor level of Zn in Ge. Conversely, As-doped Zn allowed us to synthesize n-type SiGe layers (electron concentration: 1019 cm−3 for x ≤ 0.3) at the lowest ever temperature of 350 °C, owing to the self-organized As doping to SiGe during layer exchange. The resulting p-type Si0.2Ge0.8 and n-type Si0.85Ge0.15 layers exhibited the largest ever power factors (280 μW/mK2 for the p-type and 15 μW/mK2 for the n-type), for SiGe fabricated on a flexible plastic sheet. The low-temperature synthesis technology, for both p- and n-type SiGe layers, opens up the possibility of developing human-friendly, highly reliable, flexible devices including thermoelectric sheets.

Universal Spray-Deposition Process for Scalable, High-Performance, and Stable Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) with high transconductance and good operating stability in an aqueous environment are receiving substantial attention as promising ion-to-electron transducers for bioelectronics. However, to date, in most of the reported OECTs, the fabrication procedures have been devoted to spin-coating processes that may nullify the advantages of large-area and scalable manufacturing. In addition, conventional microfabrication and photolithography techniques are complicated or incompatible with various nonplanar flexible and curved substrates. Herein, we demonstrate a facile patterning method via spray deposition to fabricate ionic-liquid-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based OECTs, with a high peak transconductance of 12.9 mS and high device stability over 4000 switching cycles. More importantly, this facile technique makes it possible to fabricate high-performance OECTs on versatile substrates with different textures and form factors such as thin permeable membranes, flexible plastic sheets, hydrophobic elastomers, and rough textiles. Overall, the results highlight the spray-deposition technique as a convenient route to prepare high-performing OECTs and will contribute to the translation of OECTs into real-world applications.

E-Information on Wires: A First Step toward Two-Terminal Silicon Nanowires for Electronic Memory Devices

Presently, there is a rapid growth of interest in the area of flexible electronics. Benefits such as light weight, durability, and low cost are among the most appealing aspects. However, the high temperatures throughout the fabrication processes are still the main hurdle. In this study, the deposition of silicon nanowires (SiNWs) at low temperature (300 °C) using tin (Sn) catalyst is studied. Silicon nanostructures have been the center of research for many years for a number of applications in different areas. Chemical vapor deposition (CVD) and other industrial deposition techniques for the growth of crystalline silicon micro- and nanostructures use high temperatures and therefore are not compatible with temperature-sensitive substrates. This work utilizes a low-temperature deposition method for the growth of SiNWs and creates a leeway to use flexible plastic sheets as substrates. The silicon nanowires were deposited by exploiting the vapor–liquid–solid (VLS) material growth mechanism using the plasma-en...

(Invited) Advanced Crystallization Using Blue Laser-Diode Annealing for Low Temperature Poly Si TFTs

Laser Crystallizations using Blue Laser-Diodes Annealing (BLDA) as well as conventional Excimer Laser Annealing (ELA) are discussed for mounting the TFTs on flexible panels. On glass, high crystallinity of Si films can be obtained by using multi-shots ELA as well as CW laser scanning [1, 2]. There are some issues for Si film after ELA, such as rough Si surface or shots MURA including the fabrication cost. As a result of scanning BLDA for thin Si films, remarkable crystallization occurs with keeping the surface smooth not only for CVD film but also for sputtered Si film [3]. By changing the laser power of 445 nm beam, the grain size can be controlled from micro-grains to large grains as well as to anisotropic long crystal grains [4]. For the Si films of heavily phosphorus doped condition, the resistivity decreased drastically due to the increase in the carrier mobility with high carrier concentration after BLDA of single beam scanning as well as after multi-shots ELA [5]. To realize high performance poly Si films directly not only on flexible glass [6] but also on flexible plastic sheet, effective laser annealing for high quality Si film by low temperature deposition is expected and a design for the thermal buffer layers on flexible sheet is effective [7]. To perform ultra-low temperature TFT process, metal source/drain structure without using ion implantation is also proposed. High performance poly Si TFTs with low fabrication cost on flexible panel should be possible not only for n-channel but also for p-channel [8, 9]. References M. Tai, M. Hatano, S. Yamaguchi, S. K. Park, T. Noda, M. Hongo, T. Shiba and M. Ohkura, Proc. of AM-LCD, TFT3-3, p.231 (2002)T. Noguchi, Mat. Res. Soc. Symp. Proc., 557, p.213 (1993),T. Okada, K, Sugihara, S. Chinen and T. Noguchi, J. Korean Phys. Soc., 66, No.8, pp.1266-1269 (2015). .T. Noguchi, J. Inf. Display, 11, No.1, p.12 (2010).T. Noguchi and T. Okada, J. of Inf. Display, 15, No.1, p.47 (2014).T. Harada, F. Gakiya, Y. Ishiki, T. Okada, T. Noguchi, K. Noda, A. Suwa and H. Ikenoue, Proc. of IDW, AMDp2-11L, p.444 (2016).T. Okada, J.D. Mugiraneza, K. Shirai, T. Suzuki, T. Noguchi, H. Matsushima, T. Hashimoto, Y. Ogino and E. Sahota, Jap. J. Appl. Phys. 51, 03CA02 (2012).K. Sugihara, K. Shimoda, T. Okada and T. Noguchi, J. Inf. Display, 18, No.4, 173-176 (2017).T. Ashitomi, T. Harada, T. Okada, T. Noguchi, O. Nishikata and A. Ota, J. Inf. Display, 18, No.4, 185-189 (2017).

High‐Mobility Transparent p‐Type CuI Semiconducting Layers Fabricated on Flexible Plastic Sheets: Toward Flexible Transparent Electronics

AbstractTransparent p‐type CuI layers with high hole mobility can be fabricated on flexible plastic sheets, a system which has been unattainable with p‐type transparent oxide semiconductors. Mildly heat‐treated CuI layers have mobilities of ≈20 cm2 V−1 s−1, which are comparable to those of p‐type GaN epilayers. Highly transparent p–n diodes with sufficient rectification ratio (106) can be manufactured by employing a heterojunction of p‐type CuI and amorphous n‐type In‐Ga‐Zn‐O layers on plastic sheets. Thus, CuI can be regarded as an excellent transparent p‐type semiconductor for flexible transparent electronics.

High-Speed Plastic Integrated Circuits: Process Integration, Design, and Test

In this paper we propose the design and measurement of functional analog and digital circuits with a response time below 1 ms, based on organic thin film transistors (OTFTs) fabricated by means of contact photolithography and self-alignment procedures. An adapted amorphous Silicon TFT compact model is used both in analytic equations and in DC Spice simulations for the design of simple organic circuits. Digital circuits such as inverters and logic gates are demonstrated with DC gains of almost 19 dB. Two analog circuits are also shown: first a differential amplifier with an open loop DC gain of 10 dB and a gain-bandwidth of 3 kHz, and second, a source coupled latch comparator tested with an input frequency of 1 kHz and a clock frequency of 10 kHz. These simple circuits comprised of only a few OTFTs are fabricated directly on flexible plastic sheets and therefore are ideal front-end interfaces for the control and fast read-out of flexible sensors.

Role of polyvinylpyrrolidone bound on silver nanowire surface: Balancing among electrical conductance, sulfuration resistance, and flexibility

The electrical conductivity of silver nanowires (AgNWs) deposited on two types of flexible plastic sheets was traced while being bent at 1 mm radius of curvature, which led to a suggestion of a possible role of surface‐bound PVP as a “glue”, but also to a suggestion of weak “glue” to bind AgNWs to a sheet as preferred for bending durability. Ar plasma bombardment successfully partially removed the surface‐bound insulator PVP, leading to better electrical conductivity. It also suppressed the Rayleigh–Plateau instability of AgNWs well above 300 °C, which has the practical importance of enabling thermal treatment above 300 °C in the atmosphere. PVP proved to endow AgNWs with the antisulfuration and ‐oxidation resistance against two weeks’ exposure to ambient conditions, even after partial removal of PVP by Ar plasma bombardment.

Visual H2 sensor for monitoring biodegradation of magnesium implants in vivo.

Biodegradable Mg implants offer advantages over permanent implants such as stainless steel that are used for broken bone repair. Mg alloys gradually dissolve, avoiding the need for removal by a later surgery if complications arise. Here we report a visual H2 sensor that can be used in the research laboratory to monitor the corrosion process in vivo during animal testing of different Mg alloys. The sensor consists of a plastic sheet with a thin coating that changes color in the presence of H2 gas. The sensor is easily used by taping it on the skin over the Mg implant. The color change gives a map of the H2 level permeating from the degrading Mg through the skin above it. This low cost, simple method of monitoring the dissolution of biodegradable implants would greatly facilitate the development of the biodegradable materials, especially in animal studies where in vivo biodegradation is tested.

Design of a Soft Robotic Glove for Hand Rehabilitation of Stroke Patients With Clenched Fist Deformity Using Inflatable Plastic Actuators

In this paper, we present a soft robotic glove designed to augment hand rehabilitation for stroke patients with clenched fist deformity. The robotic glove provides active finger extension for hand rehabilitative training, through its embedded inflatable actuators that are fabricated by heat bonding of flexible plastic sheets. Upon pressurization, the actuators inflate, stiffen, and extend the fingers. The actuators were embedded in the finger pockets of a glove. In this work, the device was evaluated in terms of its extension torque generated on the metacarpophalangeal (MCP) joint of a dummy finger model and a healthy subject. A stroke patient with finger spasticity was recruited to demonstrate the feasibility of the device to assist in finger extension. Preliminary results showed that the device was able to generate significant extension torques to provide assistance in finger extension for both healthy and stroke participants.

Calcination-free micropatterning of upconversion luminescent layers consisting of rare-earth-doped ceramic nanoparticles on wettability-patterned flexible plastic sheets by soft-liquid phase adsorption

We demonstrate a soft liquid-phase adsorption technique for the fabrication of upconversion luminescent layers consisting of rare-earth-doped ceramic nanoparticle films on wettability-patterned flexible plastic sheets. Visible upconversion luminescence and near-infrared fluorescence were observed under excitation at 980nm in the Ho3+- and Yb3+-codoped-NaYF4 nanoparticles prepared by hydrothermal technique. Wettability-patterned substrates partly covered with self-assembled monolayers of silane-coupling agents were immersed in methanol/hexane emulsions prepared with water-containing methanol dispersion of the Ho3+- and Yb3+-codoped-NaYF4 nanoparticles. The Ho3+- and Yb3+-codoped-NaYF4 nanoparticle films were formed selectively on the hydrophilic regions of the wettability-patterned templates by adjusting the fabrication conditions of the concentration of the Ho3+- and Yb3+-codoped-NaYF4 nanoparticles, the mixing ratio of methanol to hexane, the immersion temperature, and the immersion time. Upconversion luminescence and fluorescence microscopy showed green, red and near-infrared luminescence on the Ho3+- and Yb3+-codoped-NaYF4 nanoparticle films on the wettability-patterned templates. These results demonstrate that the soft liquid-phase adsorption technique enables the fabrication of upconversion luminescent layers on flexible and non-flexible substrates with minimized material consumption.

Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films.

Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

Quasi-single crystal SiGe on insulator by Au-induced crystallization for flexible electronics

Orientation-controlled large-grain (≥10 µm) crystal, i.e., quasi-single crystal, Ge-rich (≥50%) SiGe on insulator grown at low temperatures (≤300 °C) are desired for realization of high-performance flexible electronics. To achieve this, the Au-induced crystallization technique using a-SiGe/Au stacked structures has been developed. This enables formation of (111)-oriented large-grain (≥10 µm) Si1−xGex (x ≥ 0.5) crystals on insulating substrates at low temperatures (300 °C). The surface layers of the grown SiGe crystals have uniform lateral composition profiles. By using this technique, formation of quasi-single crystal Ge on flexible plastic sheets is demonstrated. This technique will be useful to realize high-performance flexible electronics.

The Innovated Flexible Surface Acoustic Wave Devices on Fully InkJet Printing Technology

An innovated fabricated process of the flexible surface acoustic wave (SAW) device is proposed in this study. Fully inkjet printing and sol-gel technology are used in this fabricated process. The flexible SAW device is composed of a ZnO layer sandwiched in between a flexible polyimide plastic sheet and two sets of interdigital transducers layer. The material of the top interdigital transducer layer is nano silver. The ZnO solution is prepared by sol-gel technology. Both the ZnO and top interdigital transducer layers are deposited by inkjet printing. The fully inkjet printing process possesses the advantages of direct patterning and low-cost. It does not require photolithography and etching processes since the pattern is directly printed on the flexible sheet. The center frequency of this prototype is matched with the design frequency. The prototype demonstrates that the presented flexible SAW device is available for the possible application in future. It may be applied to the sensing on curve surface.

(Invited) Gold-Induced Low-Temperature (

A low-temperature (¡Ü300¡ãC) growth technique of quasi-single crystal, i.e., orientation-controlled large-grain (¡Ý10 ¦Ìm), Ge-related semiconductors, on insulator is desired for realization of advanced flexible electronics. To achieve this, we have developed the gold-induced layer-exchange crystallization technique using a-SiGe/Au stacked structures. By introduction of diffusion barrier with appropriate thickness into the a-SiGe/Au interface, (111)-oriented quasi-single crystal SiGe is achieved on insulating substrates at low temperatures (~300¡ãC). Based on these results, this technique is developed to formation of quasi-single crystal Ge on flexible plastic sheets. The grown layers have high carrier mobility, because residual Au hardly deteriorates the electrical properties of grown layers due to low solubility of Au in Ge. This technique will facilitate realization of advanced flexible electronics.

Transparent Nanowire Electrodes As a Tool for Electrochemical Detection

The development of new nanomaterial like carbon nanotubes, graphene and nanowires brings new possibilities to existing technologies. With the emergence of transparent electrode based on these materials, we could imagine new type of sensors, which combines transparency and flexibility. Silver nanowire transparent electrodes are currently transforming this industry. Touch screen sensors, OLED and solar panel can now be fabricated on flexible plastic sheets with low cost printing techniques. In the same way, this new type of electrode could bring electrochemical sensor toward new transparent and flexible sensing application for life science. In our study, we fabricate and characterize transparent electrode based in metal nanowires for electrochemical detection. By changing the length, diameter and amount of deposited nanowires, we can vary their transparency (up to 90% transparent), sheet resistance (up to 0.1 ohm/square) and effective surface area. Compared to conventional evaporated plain electrodes, printed nanowire electrodes can achieve more than 80% transparency (in visible range) with the same electrochemical effective surface area. Using these electrodes, we can fabricate new sensors with high transparency (> 90%), flexibility and high sensitivity to oxygen and hydrogen peroxide. The detection of these two components is predominant in healthcare and environmental monitoring. The combination of those properties could allow us to use this type of sensors as opto-electrochemical sensors for monitoring living cells and also for glucose detection on humans. Transparent nanowire electrodes can also be a real alternative to existing indium tin oxide (ITO) transparent electrodes for other applications. Figure 1.Pictures of electrochemical sensors based on metal nanowires on PET transparent substrate. WE and REF electrodes are made from metal nanowire have 80% transparency, CE electrode are made from gold. Figure 2. SEM image of silver nanowire electrode and the size distribution of nanowires. Figure 3. Voltammetry response of the nanowire based electrochemical sensor to hydrogen peroxide in phosphate buffer (pH=7) Figure 4. Dose-response curve to hydrogen peroxide using the nanowire-based sensor in phosphate buffer (pH=7) Figure 1