Bor-Jiunn Wen

Transparent electrodes based on conducting polymers for display applications

The materials science and engineering related to the fabrication of conducting polymer thin films and the progress in the development of devices integrated with organic transparent electrodes based on conducting polymers for display applications are reviewed. Transparent electrodes are essential components for many display modules. With the evolution of display technologies, conducting polymers are recently emerging as important alternative materials for the fabrication of transparent electrodes. Conducting polymers offer some advantages, such as light weight, low cost, mechanical flexibility and excellent compatibility with plastic substrates for the development of next-generation display technologies and, in particular, are expected to play an important role in the development of flexible display technologies.

Flexible-characteristics inspection system for flexible substrates by using image feedback control

The objective of this study is to present a new flexible-characteristic inspection system (FCIS) for measuring bending characteristics of flexible substrates under different bending conditions. In order to quantize bending conditions, charge-coupled device image feedback control is utilized to control radii of curvature of the flexible substrates. As a result, the new technique successfully measures electrical characteristics of flexible polyethylene terephthalate (PET)/indium tin oxide substrates up to 11,000 bending times by using FCIS. In addition, optical-transmittance characteristic measurement of PET/hexamethyldisiloxane substrates up to 5000 bending times under the same radius of curvature is implemented by using FCIS in this study. Inspection results of bending characteristics depicted on flexible displays help a designer or maker of flexible displays design useful and comfortable flexible electronic products.

An alternative bend-testing technique for a flexible indium tin oxide film

The two-dimensional refractive index distribution of a flexible indium tin oxide film deposited on a PET layer is measured before/after the bend-testing with an alternative technique based on Fresnel equations and the heterodyne interferometry. Their standard deviations are derived and they vary more obviously than the resistance variations measured in the conventional method. Hence the standard deviation of the refractive index can be used as the indicator to justify the durability of a flexible indium tin oxide film. The validity is demonstrated.

Experimental and Simulated Investigations of Thin Polymer Substrates with an Indium Tin Oxide Coating under Fatigue Bending Loadings

Stress-induced failure is a critical concern that influences the mechanical reliability of an indium tin oxide (ITO) film deposited on a transparently flexible polyethylene terephthalate (PET) substrate. In this study, a cycling bending mechanism was proposed and used to experimentally investigate the influences of compressive and tensile stresses on the mechanical stability of an ITO film deposited on PET substrates. The sheet resistance of the ITO film, optical transmittance of the ITO-coated PET substrates, and failure scheme within the ITO film were measured to evaluate the mechanical stability of the concerned thin films. The results indicated that compressive and tensile stresses generated distinct failure schemes within an ITO film and both led to increased sheet resistance and optical transmittance. In addition, tensile stress increased the sheet resistance of an ITO film more easily than compressive stress did. However, the influences of both compressive and tensile stress on increased optical transmittance were demonstrated to be highly similar. Increasing the thickness of a PET substrate resulted in increased sheet resistance and optical transmittance regardless of the presence of compressive or tensile stress. Moreover, J-Integral, a method based on strain energy, was used to estimate the interfacial adhesion strength of the ITO-PET film through the simulation approach enabled by a finite element analysis.

Non-contact resistance measurement of transparent electrodes deposited on flexible display substrates under repetitive bending test by terahertz time domain spectroscopy

Abstract The objective of this study is to put forward a new non-contact resistance measurement method for repeating bending tests of transparent electrodes deposited on flexible display substrates. The study utilizes a terahertz time domain spectroscopy (THz-TDS) method to measure electrical properties of flexible polyethylene terephthalate/indium tin oxide samples up to 20,000 bending times. In addition, this study utilizes THz-TDS method to measure electrical characteristics of flexible substrates with hard-coat films. Accordingly, the percentage errors of measured sheet resistances based on THz-TDS method are less than or equal to 5.5% for comparison with a contact type four-point probe method or our previously reported flexible characteristic inspection system method. The values show a reasonable agreement with contact-mode sheet resistance measurements. Therefore, the electrical properties of thin films are measured offline or online easily by using this method.

Investigation of Optical and Flexible Characteristics for Organic-Based Cholesteric Liquid Crystal Display by Utilizing Bending and Torsion Loadings

Given that the induced stress resulting from fatigue bending or torsional loads increases with increasing display thickness, the long-term mechanical reliability of display modules in soft electronics has attracted considerable attention. Therefore, understanding the related failure mechanism and stress contour distribution in the display structure is important and necessary, particularly in torsional load application. This study introduces two important types of testing loads (i.e., entire reverse of bend and torsion with several cycles) to investigate the optical and flexible characteristics of film-type cholesteric liquid crystal displays (ChLCDs). The bending radius and the torsion angle used are 20 mm and ±10°, respectively. The stress contour and possible failure location of the testing specimens are obtained by using non-linear finite element analysis (FEA). Results indicate that a significant optical characteristic decay occurs beyond 1000 testing times. In 11,000 cycles of fatigue bending and torsion tests, 45% and 55% decay change rates, respectively, are obtained for the National Television System Committee. Accordingly, a worse situation occurs at the torsion test. This phenomenon is attributed to a two-direction bend torsion exerted on the tested ChLCD. The foregoing behavior is validated by using FEA.

P-72: Optical-Characteristic Measurement of Flexible Display for Reliability Test

The purpose of this study is to put forward a new reliability-test method for measuring optical characteristics of flexible display under different radii of curvature by using a flexible-characteristic inspection system. In addition, for reliability test this study also researches about the optical measurement of flexible display after being bended several times. According to inspection results of the bending characteristics depicted on flexible display, a designer or maker of flexible display can design useful and comfortable flexible display product for human being to obtain more comfortable lifestyle in ubiquitous environment.

Edge Contrast Failure Analysis on Vision Angle of Human Eyes for Curve Displays

For curve displays, the purpose of this study is to present edge contrast failure analysis (ECFA) method on the vision angle of human eyes. In order to analyze edge contrast of curve display images, a flexible cholesteric liquid crystal display is bent for different radii of curvature by using a flexible-characteristic inspection system. To simulate the human eye factors, a charge-coupled device colorimeter is utilized based on ECFA to analyze a maximum vision angle of human eyes with respect to curve displays under different radii of curvature. According to analysis results, a designer or maker of curve displays can design large-vision-angle and comfortable curve-display products for human being.

Numerical and experimental analysis of the effect of metal tie layers on improving electrical properties of gold coated poly (dimethylsiloxane) flexible multi-layered films during folding

To improve folding electrical properties of flexible electronics, this study presents a new adhesive stress analysis of depositing an adhesion layer between the conductive film electrode and the flexible substrate during folding test by a folding test platform. The folding test platform controls folding curvature of the flexible conductive substrates, folding times, and velocities in this study. Moreover, the electrical properties of flexible conductive substrates are measured during folding testing by the folding test platform. Eventually, this study successfully analyzes residual strain, adhesive stress, and electrical properties of flexible gold coated on polydimethylsiloxane substrates with chromium, nickel, and titanium adhesion layers up to 0.5/cm folding curvature during folding testing. The chromium adhesion layer had the best performance based on the largest adhesive stress, only 3.74 Ω resistance increase and 4.53 Ω maximum resistance up to 0.5/cm folding curvature during folding test by a folding test platform. The experimental result with chromium adhesion layer is consistent with adhesive stress analysis and provides a better adhesive strength between gold and polydimethylsiloxane than nickel and titanium materials for folding test. Therefore, adhesive stress analysis is adapted to evaluate the foldable electronics performance for improving folding characteristics easier.

Investigation of electrical characteristics of multi-thin-film metal electrodes deposited on flexible polydimethylsiloxane substrates by using an automatic folding test system

This study presents an electrical characterization of multi-thin-film metal electrodes deposited on flexible substrates by using an automatic folding test system (AFTS). To quantize folding conditions, AFTS for folding function is utilized to control radii of curvature of the flexible substrates, folding times, and velocities. Additionally, AFTS measures the electrical characteristics of flexible substrates during folding test. As a result, the new technique successfully measures electrical characteristics of flexible polydimethylsiloxane (PDMS)/gold electrodes for analysis during the 0/cm to 0.5/cm curvature folding cycles. Inspection results of folding characteristics depicted on flexible displays help a designer or maker of flexible displays design useful and comfortable flexible electronic products.