Polyethersulfone Substrate Research Articles

Gas Barrier of Plastic Substrate and Performance of White OLED

Flexible white OLED (organic light emitting diode) is a subject of intense research due to its application as versatile lightings for housing and flexible backlight unit for TFT-LCD. In order to make flexible OLED, flexible transparent conductor substrate is required which can replace ITO-glass used in current OLED devices. Another important point is a good gas barrier property of the flexible ITO-film, since the water vapor transmission rate (WVTR) of polymer film is much higher than that of ITO-glass and the life time of OLED device is very sensitive to the transmitted water vapor. In this work, a wet process of forming gas barrier layer on polyethersulfone (PES) film was studied utilizing spin coating of polysilazane solution and thermal conversion to thin SiO2 barrier layer. The flexible white OLED fabricated with this ITO-SiO2 (polysilazane)-PES substrate exhibited about equal power and current efficiencies to the OLED made with ITO-glass.

A flexible organic thin-film transistor with 6,13-bis(triisopropylsilylethynyl)pentacene and a methyl-siloxane-based dielectric

In this paper, we describe our fabrication of a solution-processed organic thin-film transistor (OTFT) with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as the organic semiconductor (OSC) and methyl-siloxane-based spin-on glass (SOG) as the inorganic gate dielectric. Also, we compare these results with OTFTs using different substrates such as a silicon wafer or a polyethersulfone (PES) substrate. From electrical measurements, we observed exemplary I– V characteristics for these TFTs. We calculated the field effect mobility to be 0.007 cm 2/V s for an OTFT fabricated on a wafer and 0.004 cm 2/V s for an OTFT fabricated on a PES substrate.

Fabrication and opto-electric properties of ITO/ZnO bilayer films on polyethersulfone substrates by ion beam-assisted evaporation

Transparent conducting oxides bilayer films stacked by one 130-nm-thick indium tin oxide (ITO) top layer and one 75-nm-thick zinc oxide (ZnO) buffer layer were grown onto polyethersulfone (PES) substrates by ion beam-assisted evaporation. The effects of ion energy and ZnO buffer layers on the structural and opto-electric properties of ITO films were initially investigated. The as-deposited ZnO buffer layers show wurtzite (0 0 2) preferred orientation on the PES substrates with ion beam assistance. The results of X-ray diffraction reveal a marked increase in the crystallinity of the ITO films which use ZnO as a buffer layer material. A drop of ∼60% in electrical resistivity of the ITO film on the PES can be achieved by using ZnO buffer layer. The transmittance of the ITO/ZnO bilayer was not deteriorated due to the insertion of ZnO layer. The lowest electrical resistivity of 6.552×10 −4 Ω-cm associated with the transmittance of ∼80% at the wavelength of 550 nm can be obtained for the ITO film on the ZnO-coated PES at ion energy of 60 eV. The ITO films on the ZnO-buffered PES with moderate control of ion energy have a promising future for the application of the contact layers for flexible solar cells.

Electrical and optical properties of ZnO:Al film prepared on polyethersulfone substrate by RF magnetron sputtering

This study investigates the process parameter effects on the electrical and optical properties of AZO (ZnO:Al) thin film using radio frequency (RF) magnetron sputtering on flexible PES (polyethersulfone) substrates. The process parameters include RF power, working pressure and substrate bias. Results show that RF power was increased to promote the crystalline quality and decrease AZO thin film resistivity. However, when the RF power was increased to 200 W the AZO thin film crystalline quality and conductivity became worse. Along with the working pressure increase, regarding the AZO thin film crystalline quality, conductivity and transmittance has the promotion. Substrate bias added has not help to increases crystalline quality, electrical and optical properties of film. At a 150 W RF power, 670 MPa working pressure and substrate bias 0 V, the AZO thin film with a better electrical resistivity of 1.51 × 10 −2 Ω cm and an average optical transmittance of above 90% in the visible region is obtained.

Flexible high gain complementary inverter using n-ZnO and p-pentacene channels on polyethersulfone substrate

We report on the fabrication of complementary inverters that have ZnO and pentacene as n-type and p-type channels on a polyethersulfone substrate operating under 7V. Patterned Al and AlOx thin film were deposited at room temperature on the plastic as a common gate electrode and dielectric, respectively. After initial gate instability between ZnO channel and AlOx dielectric was controlled, our n-type thin-film transistors (TFTs) displayed quite a similar drain current level to that of p-type TFTs. Our flexible complementary device showed much high voltage gain of ∼100 even under a bent condition (56mm radius of curvature). Our complementary inverter also demonstrates a promising dynamic behavior of ∼20ms.

Electrical characteristics of HgTe nanocrystal-based thin film transistors fabricated on flexible plastic substrates

HgTe nanocrystal-based thin film transistors were fabricated on flexible polyethersulfone substrates and their electrical properties were characterized. Hydrophilic Al 2O 3 buffer layers were first deposited on the flexible substrates and HgTe nanocrystal films were then formed on top of the buffer layers. A representative top-gate flexible thin film transistor with a channel composed of a HgTe nanocrystal film functioned as a p-channel transistor and exhibited a mobility of ~ 1.20 cm 2/V∙s and an on/off current ratio of ~ 1 × 10 3.

Electrical and optical study of ITO films on glass and polymer substrates prepared by DC magnetron sputtering type negative metal ion beam deposition

Transparent, conducting indium tin oxide (ITO) films were deposited without intentional substrate heating on glass and polyethersulfone (PES) substrates by a magnetron sputter type negative metal ion source (MSNIS). The effect of substrate type on optical transmittance, electrical resistivity, surface morphology and roughness of the ITO film was analyzed. ITO/glass substrates show a higher optical transmittance (89%) and lower resistivity (4 × 10 −4 Ω cm) than ITO/PES (78%, 6 × 10 −4 Ω cm). X-ray diffraction (XRD) spectra indicate polycrystalline ITO films deposited on glass and amorphous ITO films on PES. Atomic force microscopy (AFM) images also indicate that ITO/glass has a lower surface roughness than ITO/PES. The values of figure of merit ( T 10/ R sh) for ITO/glass ( ϕ TC = 7.7 × 10 −3 Ω −1) are higher than ITO/PES ( ϕ TC = 1.3 × 10 −3 Ω −1), indicating that ITO/glass achieved the best performance in this study.

Characteristics of ITO Thin Films for Organic Light Emitting Diode by using a Low-Frequency Magnetron Sputtering Method

In this study, we have tried the growth of indium tin oxide (ITO) thin films by using low-frequency magnetron sputtering method (LFMSM). Characteristics of ITO thin films deposited on polyethersulfone (PES) and polyetyleneterephthalate (PET) substrates are investigated. Experiments were carried out as a function of deposition time. With increasing the deposition time of the ITO thin films on PES substrate, the sheet resistance is decreased. ITO thin films on polymer substrates were amorphous structure.

Properties of Indium Zinc Oxide Films on Various Polymer Substrates Deposited by Low-Frequency 60 Hz Magnetron Sputtering Method

We introduce indium zinc oxide (IZO) thin films grown at room temperature by using a low-frequency (LF) 60 Hz magnetron sputtering system. The flexible substrates are PES, PET and PC. The optical, electrical and structural properties of IZO films on flexible substrates were investigated. The alloy target was In2O3:ZnO (90:10 wt%) with a diameter of 3 inch and thickness of 5 mm. The vacuum chamber was evacuated down to pressure 5 × 10−6 torr prior to deposition. The flow rates of argon gas (99.999 %) were kept at a constant value of 30 sccm by a mass flow controller(MFC). The discharges were performed by power of 300 V, 310 V, 320 V. They have low sheet resistance of about 30 Ω/sq., high transmittance of over 85 % in the range of 400–700 nm. Also they showed good band gap of about 3.43 eV on polyethersulfone (PES) substrates, 3.50 eV on polyethylene terephthalate (PET) and 3.30 eV on polycarbonate (PC). The experimental results imply that the films with good qualities in surface morphology, transmittance and electrical conduction can be grown by a low-frequency magnetron sputtering method an PES is the most recommendable substrate.

Characteristics of indium–tin oxide thin films grown on flexible plastic substrates at room temperature

Transparent and conductive indium–tin oxide (ITO) thin films were deposited on polyethersulfone (PES) flexible plastic substrates by DC magnetron sputtering. The crystalline structure and optical–electric characteristics were investigated to achieve the optimum room-temperature growth conditions. The crystalline orientation and the surface morphology were characterized by X-ray diffraction (XRD) and the atomic force microscopy (AFM), respectively. The ITO/substrate interfaces were observed by scanning electron microscopy (SEM). In addition, the resistivity, the Hall effect, and the optical transmittance were measured to characterize the photo-electric properties of as grown films. It is found that the ITO films are epitaxially grown with the orientations 〈2 2 2〉, 〈4 0 0〉, and 〈4 4 0〉 perpendicular to the film plane. Moreover, the resistivity of thin film decreases with an increase in the (2 2 2) diffraction intensity. The obtained optimum growth conditions for the room-temperature deposition are: DC power=300 W, deposition pressure=2.0 mTorr, and the gas of Ar:O 2=100:1. With the optimum conditions, the resistivity of 6.42×10 −3 Ω cm, carrier concentration of 1.13×10 19 cm −3, and transmittance of 85% for films grown on PES substrates are obtained. Comparing the results with those reported by other workers, we conclude that improved photo-electric properties of ITO films can be obtained by using the DC magnetron sputtering technique at room temperature.

Effects of oxygen gas flow rate and ion beam plasma conditions on the opto-electronic properties of indium molybdenum oxide films fabricated by ion beam-assisted evaporation

The purpose of the present work is to experimentally study the effects of the oxygen gas flow rate and ion beam plasma conditions on the properties of indium molybdenum oxide (IMO) films deposited onto the polyethersulfone (PES) substrate. Crystal structure, surface morphology, and optoelectronic properties of IMO films are examined as a function of oxygen gas flow rate and ion beam discharge voltage. Experimental results show that the IMO films consist of a cubic bixbyite B-In 2O 3 single phase with its crystal preferred orientation alone B(222). Mo 6+ ions are therefore considered to partially substitute In 3+ sites in the deposit. Under-controlled ion bombardment during deposition enhances the reaction among those arriving oxygen and metal ion species to condense into IMO film and facilitates a decreased surface roughness of IMO film. The film with ultimate crystallinity and the lowest surface roughness is obtained when the oxygen flow rate of 3 sccm and the discharge voltage of 110 V are employed. This results in the lowest electrical resistivity due mainly to the increased Hall mobility and irrelevant to carrier concentration. The lowest electrical resistivity of 8.63 × 10 − 4 ohm-cm with a 84.63% transmittance at a wavelength of 550 nm can be obtained, which satisfies the requirement of a flexible transparent conductive polymer substrate.

Evaluation of gas permeation barrier properties using electrical measurements of calcium degradation

In this work, we developed a thin calcium degradation method introducing sensitive electrical resistance monitoring. We have demonstrated structural models of the inorganic/organic thin films to evaluate barrier properties against water and oxygen permeation. The time-dependent transmission curve of a multibarrier coated on both sides of the polyethersulfone substrate had a linear slope which was measured as 5.17 x 10(-3) gm(2) day at 20 degrees C and 60% relative humidity. This system can measure an accurate permeation rate with a high sensitivity in the measurable range of 10(1)-10(-6) gm(2) day. In addition, the test structure devised is applicable to various fabrication techniques for passivation layers with durability and ultralow permeability for flexible organic light emitting diodes.

Properties of ITO on PES film in dependence on the coatingconditions and vacuum annealing temperatures

【Transparent conducting indium tin oxide (ITO) films were deposited onto the Polyethersulfone (PES) substrate by using a magnetron sputter type negative metal ion source. In order to investigate the influence of cesium (Cs) partial pressure during deposition and annealing temperature on the optoelectrical properties of ITO/PES film the films were deposited under different Cs partial pressures and post deposition annealed under different annealing temperature from $100^{\circ}C$ to $170^{\circ}C$ for 20 min at $3\;{\times}\;10^{-1}$ Pa. Optoeleetrical properties of ITO films deposited without intentional substrate heating was influenced strongly by the Cs partial pressure and the Cs partial pressure of $1.5\;{\times}\;10^{-3}$ Pa was characterized as an optimal Cs flow condition. By increasing post-deposition vacuum annealing temperature both optical transmission in visible light region and electrical conductivity of ITO films were increased. Atomic force microscopy (AFM) micrographs showed that the surface roughness also varied with post-deposition vacuum annealing temperature.】

Transparent, Low Resistance, and Flexible Amorphous ZnO-Doped In2O3 Anode Grown on a PES Substrate

Transparent and low resistance amorphous ZnO-doped (IZO) anode films were grown by radio-frequency (rf) sputtering on an organic passivated polyethersulfone (PES) substrate for use in flexible organic light-emitting diodes (OLEDs). Under optimized growth conditions, a sheet resistance of , average transmittance above 89% in the green range, and a root mean square roughness of were obtained, even for the IZO anode film grown in a pure Ar ambient without the addition of oxygen as a reactive gas. All of the IZO anode films had an amorphous structure regardless of the rf power and the working pressure due to the low substrate temperature of and the structural stability of the amorphous IZO films. In addition, an X-ray photoelectron spectroscopy depth profile obtained for the IZO/PES showed no obvious evidence of interfacial reactions between the IZO anode and the PES substrate, except for some indiffusion of oxygen atoms from the IZO anode. Furthermore, the current-voltage-luminance of the flexible OLEDs fabricated on IZO anode was found to be critically dependent on the sheet resistance of the IZO anode.

Characteristics of Pentacene Thin Film Transistor with Al[sub 2]O[sub 3] Gate Dielectrics on Plastic Substrate

Pentacene organic thin-film transistors (OTFTs) were fabricated on a polyethersulfone (PES) substrate with an Al 2 O 3 gate dielectric grown at 150°C by plasma enhanced atomic layer deposition. Due to the roughness of the Al 2 O 3 surfaces, the OTFTs with Al 2 O 3 of 150 nm showed better performance compared to that with Al 2 O 3 of 120 nm. When OTFTs with a 150 nm thick Al 2 O 3 layer were fabricated on PES substrate, excellent electrical characteristics were obtained, including carrier mobility as large as 0.62 cm 2 /V s, a subthreshold slope as low as 0.4 V/dec, and on-off current ratio as large as 10 7 .

Properties of Indium Tin Oxide on Polymer Films Deposited by Low-Frequency Magnetron Sputtering Method

In this study, we introduce indium tin oxide (ITO) thin films grown by using low-frequency (60 Hz) magnetron sputtering method. Characteristics of the ITO thin films deposited on polyethersulfone (PES) substrates are investigated. Experiments were carried out as a function of deposition time and substrate temperature. ITO thin films on PES substrate revealed amorphous structure. The optical transmittance, the sheet resistance and the resistivity of the films decreased with the increasing deposition time. The sheet resistance and the roughness of the films increased with the increasing substrate temperature. Roughness values of ITO films on PES substrate deposited at various substrate temperatures are Ra (<2 nm), Rms (<3 nm) and Rp-v (<10 nm). The experimental results confirm that the films with good qualities in surface morphology, transmittance and electrical conduction can be grown by a low-frequency magnetron sputtering method.

Characteristics of SiO xN y films deposited by inductively coupled plasma enhanced chemical vapor deposition using HMDS/NH 3/O 2/Ar for water vapor diffusion barrier

SiO x N y thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) using hexamethyldisilazane (HMDS, 99.9%)/NH 3/O 2/Ar at a low temperature, and examined for use as a water vapor diffusion barrier. The film characteristics were investigated as a function of the O 2:NH 3 ratio. An increase in the O 2:NH 3 ratio decreased the level of impurities such as –CH x , N–H in the film through a reaction with oxygen. Thereby, a more transparent and harder film was obtained. In addition, an increase in the O 2:NH 3 ratio decreased the nitrogen content in the film resulting in a more SiO 2-like SiO x N y film. Using SiO x N y fabricated with an O 2:NH 3 ratio of 1:1, a multilayer thin film consisting of multiple layers of SiO x N y /parylene layers was formed on a polyethersulfone (PES, 200 μm) substrate, and its water vapor transmittance rate (WVTR) was investigated. A WVTR < 0.005 g/(m 2 day) applicable to organic thin film transistors or organic light emitting diodes was obtained using a multilayer composed of SiO x N y (260 nm)/parylene (< 1.2 μm) on the PES.

Ion Shower Doping of Polysilicon Films on Polyethersulfone Substrates for Flexible TFT Arrays

A technique of ion shower doping was performed to form source-drain contacts for polysilicon thin-film transistors (TFTs) on polyethersulfone (PES) substrates. The doped layer was subsequently annealed with an excimer laser to electrically activate the dopant atoms. The doped polysilicon films on the PES substrate showed much higher sheet resistances than those on the glass substrate with the identical doping and activation conditions. Moreover, the plastic substrates is easily heated up and caused a film failure for the prolonged exposure of the ion shower doping. The effective doping time and the resulting ion dose could be increased remarkably by reducing the radio-frequency power as well as by inserting interval pulses for dopants relaxation during the ion doping. As a result, a sheet resistance value as low as 300 ohms/sq. was obtained, which is low enough for a good ohmic contact.

Organic thin-film transistors on plastic substrates

In this paper, organic thin-film transistors (OTFTs) were fabricated on polyethersulfone (PES) and silicon (Si) substrates with top-contact geometry. Several kinds of metals with different work functions were used for source and drain electrodes, and optimum fabrication conditions were found. Photo cross-linkable polymeric gate dielectrics and thermal silicone oxide (SiO 2) were used for the plastic and Si OTFTs, respectively. From the electrical measurements, typical I– V characteristics of the thin-film transistor (TFT) were observed. The field-effect mobility, μ, was obtained to be 2.59 cm 2/(V s) from the flexible OTFT with polymeric gate dielectrics. Moreover, a possible critical work function of 4.3 eV for the electrode of pentacene OTFT with top-contact geometry.

Low-temperature processable inherently photosensitive polyimide gate dielectric for organic thin-film transistors: Synthesis, characterization, and application to transistors

Low-temperature processable inherently photosensitive polyimide was prepared from a dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and aromatic diamines, 4,4′-diamino-3,3′dimethyl-diphenylmethane, through a polycondensation reaction, followed by a chemical imidization method. The photosensitive polyimide cured at 180 °C is used as a gate dielectric to fabricate flexible organic thin-film transistors with pentacene as an active semiconductor on polyethersulfone substrate. With the inherently photosensitive polyimide, the access to the gate electrode could be created easily without complicated and expensive lithographic techniques. A field effect carrier mobility of 0.007 cm2/V s was obtained for the pentacene organic thin-film transistors (OTFTs) with the photo-patterned polyimide as a gate dielectric. More detailed analysis for the pentacene OTFTs will be given with electrical properties of the thin polyimide film. Low-temperature processability and patternability of the polyimide give us more freedom to choose plastic substrates in OTFTs and facilitate the realization of low-cost organic electronics.