Polyethylene Naphthalate Substrates Research Articles

Roll-to-roll atomic layer deposition process for flexible electronics encapsulation applications

At present flexible electronic devices are under extensive development and, among them, flexible organic light-emitting diode displays are the closest to a large market deployment. One of the remaining unsolved challenges is high throughput production of impermeable flexible transparent barrier layers that protect sensitive light-emitting materials against ambient moisture. The present studies deal with the adaptation of the atomic layer deposition (ALD) process to high-throughput roll-to-roll production using the spatial ALD concept. We report the development of such a process for the deposition of 20 nm thickness Al2O3 diffusion barrier layers on 500 mm wide polymer webs. The process uses trimethylaluminum and water as precursors at a substrate temperature of 105 °C. The observation of self-limiting film growth behavior and uniformity of thickness confirms the ALD growth mechanism. Water vapor transmission rates for 20 nm Al2O3 films deposited on polyethylene naphthalate (PEN) substrates were measured as a function of substrate residence time, that is, time of exposure of the substrate to one precursor zone. Moisture permeation levels measured at 38 °C/90% relative humidity by coulometric isostatic–isobaric method were below the detection limit of the instrument (<5 × 10−4 g/m2 day) for films coated at web moving speed of 0.25 m/min. Measurements using the Ca test indicated water vapor transmission rates ∼5 × 10−6 g/m2 day. Optical measurements on the coated web showed minimum transmission of 80% in the visible range that is the same as the original PEN substrate.

English

RF-sputtered gallium tin zinc oxide (GSZO) thin fims for application in transparent amorphous oxide semiconductors (TAOSs) have been investigated. Morphological, structural, electrical, optical properties and its mechanical robustness have been studied on polyethylene naphthalate (PEN) substrates using variety of characterization techniques. The fims deposited on PEN substrates retained amorphous structure even after annealing for 12 hours in vacuum at 200°C. The optical band edge is ~ 3.3eV, greater than ZnO fims. Best μHall of 3 cm²V- 1s- 1 have been observed on annealed GSZO fims at 200°C. The critical radii of bending improve from 14.5 mm to 11 mm with decreasing RF power of deposition from 90W to 80W, indicative of its suitability for flxible electronics.

Alumina nanoparticle/polymer nanocomposite dielectric for flexible amorphous indium-gallium-zinc oxide thin film transistors on plastic substrate with superior stability

In this study, the Al2O3 nanoparticles were incorporated into polymer as a nono-composite dielectric for used in a flexible amorphous Indium-Gallium-Zinc Oxide (a-IGZO) thin-film transistor (TFT) on a polyethylene naphthalate substrate by solution process. The process temperature was well below 100 °C. The a-IGZO TFT exhibit a mobility of 5.13 cm2/V s on the flexible substrate. After bending at a radius of 4 mm (strain = 1.56%) for more than 100 times, the performance of this a-IGZO TFT was nearly unchanged. In addition, the electrical characteristics are less altered after positive gate bias stress at 10 V for 1500 s. Thus, this technology is suitable for use in flexible displays.

Characteristics of photoconductive UV photodetector based on ZnO nanorods grown on polyethylene naphthalate substrate by chemical bath deposition method

Vertically aligned ZnO nanorods were synthesized on a polyethylene naphthalate (PEN) substrate using a chemical bath deposition method at a low temperature. The structural and optical investigations revealed the high quality of the fabricated ZnO nanorods on flexible substrate. A metal-semiconductor-metal UV photodetector based on ZnO nanorods was fabricated on the PEN substrate. The optoelectronic characteristics of fabricated UV photodetector were studied in the dark and under 325 nm UV light illumination at −3 V and 3 V bias voltages. The responsivity and photosensitivity of the ZnO nanorod UV photodetector were 2.856 A/W and 1175% at 3 V bias voltage, respectively. Moreover, the response and the recovery times measured during the turn-on and turnoff of UV illumination were 1.2 s and 1.8 s, respectively.

20.4L: Late‐News Paper: A Flexible AMOLED Display on PEN Substrate Driven by Oxide Thin‐Film Transistors

AbstractWe report a flexible AMOLED display driven by oxide thin film transistors (TFTs) on a polyethylene naphthalate (PEN) substrate with process temperature below 160 °C. The TFTs exhibit a field‐effect mobility of 12.9 cm2 V−1 s−1, a subthreshold swing of 0.20 V/decade, and an Ion/Ioff ratio of 109.

P‐93: Highly Conductive and Uniform Graphene hybrid Electrode with Chemical Reduction for Flexible Organic Light‐Emitting Diodes

AbstractHighly conductive, uniform, transparent and flexible films were produced by mixing graphene oxide (GO) with poly (3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and then chemically reduced by HI‐AcOH. Using the optimized graphene hybrid film as anode, a fascinating flexible organic light‐emitting diode (FOLED) has been demonstrated on polyethylene naphthalate (PEN) substrate.

Moisture barrier properties of thin organic-inorganic multilayers prepared by plasma-enhanced ALD and CVD in one reactor.

A widely used application of the atomic layer deposition (ALD) and chemical vapour deposition (CVD) methods is the preparation of permeation barrier layers against water vapour. Especially in the field of organic electronics, these films are highly demanded as such devices are very sensitive to moisture and oxygen. In this work, multilayers of aluminium oxide (AlO x ) and plasma polymer (PP) were coated on polyethylene naphthalate substrates by plasma-enhanced ALD and plasma-enhanced CVD at 80℃ in the same reactor, respectively. As precursor, trimethylaluminium was used together with oxygen radicals in order to prepare AlO x , and benzene served as precursor to deposit the PP. This hybrid structure allows the decoupling of defects between the single AlO x layers and extends the permeation path for water molecules towards the entire barrier film. Furthermore, the combination of two plasma techniques in a single reactor system enables short process times without vacuum breaks. Single aluminium oxide films by plasma-enhanced ALD were compared to thermally grown layers and showed a significantly better barrier performance. The water vapour transmission rate (WVTR) was determined by means of electrical calcium tests. For a multilayer with 3.5 dyads of 25-nm AlO x and 125-nm PP, a WVTR of 1.2 × 10 −3 gm−2d−1 at 60℃ and 90% relative humidity could be observed.

Growth of Aligned ZnO Nanorods Grown on Polyethylene Naphthalate Substrates: Effect of the Growth Duration

Aligned ZnO nanorods were synthesized on a polyethylene naphthalate (PEN) substrates using a chemical bath deposition method. The growth temperature and precursor concentration were 95 °C and 0.025 M, respectively. The effects of growth duration (2 h to 8 h) on the optical and structural properties of the obtained ZnO nanorods on seed layer ZnO/PEN substrate were then investigated using X-ray diffraction, field-emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectroscopy at room temperature. The high intensity of (002) peak compared with (100) and (101) in the X-ray diffraction (XRD) pattern demonstrated that the ZnO nanorods grown for 6.5 h had more vertical higher crystal quality than the samples grown for other durations. The average diameter of ZnO nanorods grown on PEN substrates increased from 19 nm to 45 nm with increased growth duration from 2 h to 8 h, respectively.

Effect of Reflective Platinum Film on the Performance of Flexible Dye Solar Cell (DSC)

Robust and flexible dye solar cell (DSC) made up of nanocrystalline TiO2 encapsulated in polyethylene naphthalate (PEN) substrate will be able to fulfill the demand for indoor power applications as it has lower energy and manufacturing cost, produces electricity in low light conditions even under artificial light. The fabrication using PEN substrate has the advantage of scalability and compatible with the roll to roll manufacturing method. This paper reports the study on the effect of platinum film reflectance on the counter electrode to the DSC performance and efficiency. The reflective counter electrode uses the commercially available Pt/Ti PEN film with 100% reflectance properties. The transparent counter electrode with 20.9% reflectance is prepared using pre-treated indium doped tin oxide (ITO). The platinum film is sintered at 170°C followed by direct heat of 150°C to achieve a good bonding between the ITO and the deposited platinum film. Both cells uses TiO2 coated ITO PEN as the working electrode. The DSC test cell with reflective counter electrode increases the cell efficiency compared to the non-reflective counter electrode as there is a higher light spectrum response on the reflective DSC cell.

Hydrophobicity enhancement of Al2O3 thin films deposited on polymeric substrates by atomic layer deposition with perfluoropropane plasma treatment

Abstract The optoelectronics devices such as organic light emitting diodes are greatly vulnerable to moisture, which reduces their functionality and life cycle. The Al 2 O 3 thin films are mostly used as barrier coatings in such electronic devices to protect them from water vapors. The performance of the Al 2 O 3 barrier films can be improved by enhancing their hydrophobicity. Greater the hydrophobicity of the barrier films, greater will be their protection against water vapors. This paper reports on the enhancement of hydrophobicity of Al 2 O 3 thin films through perfluoropropane (C 3 F 8 ) plasma treatment. Firstly, good quality Al 2 O 3 films have been fabricated through atomic layer deposition (ALD) on polyethylene naphthalate (PEN) substrates at different temperatures. The fabricated films are then plasma treated with C 3 F 8 to enhance their hydrophobicity. Hydrophobic Al 2 O 3 thin films have shown good morphological and optical properties. Low average arithmetic roughness (Ra) of 1.90 nm, 0.93 nm and 0.88 nm have been recorded for the C 3 F 8 plasma treated films deposited at room temperature (RT), 50 °C and 150 °C, respectively. Optical transmittance of more than 90% has been achieved for the C 3 F 8 plasma treated films grown at 50 °C and 150 °C. The contact angle has been increased from 48° ± 3 to 158° ± 3 for the films deposited at RT and increased from 41° ± 3 to 148° ± 3 for the films deposited at 150 °C.

Characterization of Al2O3 thin films fabricated through atomic layer deposition on polymeric substrates

This paper reports on the fabrication of good quality Al2O3 thin films on flexible substrates including polyethylene naphthalate (PEN), polyethylene terephthalate (PET) and Polyamide at different temperatures down to 50 °C under very short water purging steps of 10 s. Al2O3 films with appreciable growth rates having good morphological, chemical, electrical and optical characteristics have been produced. Growth rates of 1.16, 1.14 and 1.15 A/cycle have been observed at 50 °C for PET, PEN and polyamide substrates respectively. The surface morphology has been improved with the increase in deposition temperature. Low average arithmetic roughness of 0.88 and 0.78 nm have been recorded for the Al2O3 films deposited at 150 °C on PEN and polyamide respectively. The XPS analysis confirmed the fabrication of Al2O3 films without any carbon contamination and Al 2p, Al 2s and O 1s peaks were appeared at binding energies of 74, 119 and 531 eV, respectively. Excellent insulating properties were observed for the Al2O3 films and optical transmittance of more than 85 % was recorded in the visible region. The experimental results suggest that polymeric materials are excellent candidates to be used as substrates in the fabrication of Al2O3 thin films through atomic layer deposition.

Selective deposition of graphene sheets on a flexible substrate by a nonuniform electric field

This study reports on the precise positioning of high-quality graphene sheets on a flexible polyethylene naphthalate substrate using a dielectrophoretic (DEP) force. Positive DEP assembly is carried out using a 100 kHz frequency AC signal with a peak-to-peak voltage of 10 V. The presence and quality of the graphene flakes aligned around the prepatterned electrodes are characterized by scanning electron microscopy, optical microscopy, and micro-Raman spectroscopy. Current–voltage measurements were also used to evaluate the electrical properties of these flexible devices under varying compressive (−) and tensile (+) strain conditions up to ±0.6%, where the currents decreased with increasing strains.

Characterization of Al2O3 Thin Films Fabricated at Low Temperature via Atomic Layer Deposition on PEN Substrates

Good quality Al2O3 thin films are deposited on polyethylene naphthalate (PEN) substrates through atomic layer deposition (ALD) at temperatures as low as 35 °C. Trimethylaluminum [TMA, Al(CH3)3] and water are used as precursors in the present study. Growth rates of 1.14 Å per cycle are observed at 35 °C, while the average arithmetic roughness (Ra) of the film is 0.86 nm. X‐ray photoelectron spectroscopy (XPS) analysis confirms the high purity of the grown films with no carbon contamination. Good insulating properties are observed for the films and optical transmittance of more than 90% is recorded in the visible region.

A flexible AMOLED display on the PEN substrate driven by oxide thin-film transistors using anodized aluminium oxide as dielectric

We report a flexible AMOLED display driven by oxide thin film transistors (TFTs) with anodic AlOx gate dielectric on a polyethylene naphthalate (PEN) substrate with a process temperature below 150 °C. The TFTs exhibit a field-effect mobility of 12.87 cm2 V−1 s−1, a subthreshold swing of 0.20 V dec−1, and an Ion/Ioff ratio of 109.

Flexible Reflective Color Displays using Thermochromic Pigments

This research presents a flexible reflective thermochromic display (TCD) comprised of thermochromic pigments and a patterned indium tin oxide (ITO) film coated on a polyethylene naphthalate (PEN) substrate, and the display's thermo-optical characteristics. The display showed maximum red, green, and blue reflectances of 30%, 38%, and 29%, respectively. Furthermore, the display exhibited a continuous grey color when the temperature was changed continuously. As a flexible display, the display showed reliable thermo-optical performance without image damage even when highly bent. We expect the proposed TCD will be used in outdoor information display applications where low cost is a key factor.

Atomic Layer Deposition of Highly Transparent Platinum Counter Electrodes for Metal/Polymer Flexible Dye‐Sensitized Solar Cells

Atomic layer deposition (ALD) is used to deposit Pt nanoparticles at low temperature (25–150 °C) to fabricate highly transparent counter electrodes (CEs) for flexible dye‐sensitized solar cells (DSCs). The Pt nanoparticles (NPs) are deposited for different number of ALD cycles on indium tin oxide (ITO)/polyethylene naphthalate (PEN) substrates. Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM) are used to assess the Pt NP loading, density, and size. There is a trade‐off between transparency and catalytic activity of the CE, and the best cell performances of back‐side‐illuminated DSCs (≈3.7% efficiency) are achieved for Pt ALD at temperatures in the range of 100–150 °C, even though deposition at 25 °C is also viable. The best cell produced with ALD platinized CE (100 cycles at 100 °C) outperforms the reference cells fabricated with electrodeposited and sputtered Pt CEs, with relative improvements in efficiency of 19% and 29%, respectively. In addition, these parameters are used to fabricate a large area CE for a sub‐module (active area of 17.6 cm2), resulting in an efficiency of 3.1%, which demonstrates the scalability of the process.

Highly Flexible Magnetoelectronic Device Integrated With Embedded Ag Nanoparticle Electrode

A flexible magnetoresistance (MR) device is fabricated through the hybrid process of embedding an Ag nanoparticle electrode by thermal imprinting and magnetic multilayer sensor element by sputtering on a polyethylene naphthalate (PEN) substrate. The MR signal profiles for a ring type sensor deposited on the PEN substrate show typical anti-symmetric curves centered for the field H=0, and the maximum signal and its field sensitivity are nearly the same as those of sensors deposited on Si and glass substrates. The root mean square (rms) roughnesses and magnetic properties of magnetic thin film deposited on the different substrates show that Hex was decreased with increasing roughness. Further, MR change with temperature had no significant effect on the sensor performance. The stability of Au electrode and Ag paste electrode were compared during the bending of MR sensor, revealing the cracking of Au electrode above 45°. However, Ag paste electrode was stable up to 90°. The field sensitivity of the MR signal for the full range of fields is inversely proportional to the effective anisotropy field, which is the sum of exchange-bias and stress-induced anisotropy fields. As a whole, the field sensitivity of MR signal depends on bending stress at the sensor position.

Fabrication of Nanostructured Zinc Oxide Films on Plastic Substrates by Pyrolysis Method and their Application to Dye-Sensitized Solar Cells

t has been attempted to utilize plastic substrates for electrodes, instead of conventional glass substrates, to fabricate flexible, lightweight, and low-cost dye-sensitized solar cells (DSSCs). We examined a pyrolysis method by which preformed layered hydroxide zinc acetate (LHZA: Zn5(OH)8(CH3COO)2·2H2O) films were converted into ZnO films at temperatures below 120 oC. Since the pyrolyzed films still contained zinc acetate compounds, they were immersed in hot water aiming at removing such the impurities. This hot water treatment influenced the film morphology to a large extent. The energy conversion efficiency of 3.41% was obtained for the cell using an N719/ZnO electrode fabricated on an indium tin oxide-coated polyethylene naphthalate (ITO-PEN) substrate through the present pyrolysis method.

Quantum Hall effect in multilayered massless Dirac fermion systems with tilted cones

We report the first observation of Shubnikov-de Haas (SdH) oscillations and quantized Hall resistance in the multilayered massless Dirac fermion system $\alpha$-(BEDT-TTF)$_2$I$_3$ with tilted cones. Holes were injected into the thin crystal fixed on a polyethylene naphthalate (PEN) substrate by contact electrification. The detection of SdH oscillations whose phase was modified by Berry's phase $\pi$ strongly suggested that the carrier doping was successful in this system. We succeeded in detecting the quantum Hall effect (QHE) with the steps which is the essence of two dimensional Dirac fermion systems. The number of effectively doped layers was examined to be two in this device. We reveal that the correlation between effective layers plays an important role in QHE.

Interfacial Structure and Electrical Properties of Transparent Conducting ZnO Thin Films on Polymer Substrates

The effects of polymer substrates on the interfacial structure and the thermal stability of Ga-doped ZnO (GZO) thin films were investigated. The GZO thin films were deposited on polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates by rf-magnetron sputtering at room temperature, and thermal stability tests of the GZO thin films on the polymer substrates were performed at 150°C up to 8 h in air. Electrical and structural characterizations of the GZO thin films on the PET and the PEN substrates were carried out, and the origins of the stable interfacial structure and the improved thermal stability of the GZO thin film on the PEN substrate were discussed.