William A. MacDonald

Engineered films for display technologies

Flexible displays and flexible electronics is an area generating considerable interest at present. This article will discuss the requirements of a base substrate for flexible displays and contrast the plastic films that are being developed for this application. The review will cover how the surfaces and properties of the films are being engineered to make them suitable for laying down barrier coatings and for laying down thin film transistor arrays. The barrier technologies that are being developed and the issues facing the development of a “flexible glass” will be discussed.

Latest advances in substrates for flexible electronics

Abstract— Recent advances in both organic- and inorganic-based electronics processed on flexible substrates offer substantial rewards in terms of being able to develop displays that are thinner, lighter, robust, and conformable, and can be rolled away when not required. In addition, plastic-based substrates coupled with the recent developments in solution deposition and ink-jet printing for laying down OLED materials and active-matrix thin-film-transistor (TFT) arrays open up the possibility of cost-effective processing in high volumes using roll to roll (R2R) processing. To replace glass, however, a plastic substrate needs to be able to offer some or all of the properties of glass, i.e., clarity, dimensional stability, thermal stability, barrier, solvent resistance, and low coefficient of thermal expansion (CTE) coupled with a smooth surface. In addition, a conductive layer may be required. No plastic film offers all these properties so any plastic-based substrate will almost certainly be a multilayer composite structure. This paper will discuss the issues associated with selecting plastic materials, contrast the various options, and highlight how to gain optimum performance through process control. This will be illustrated with examples of film in use in flexible electronic applications.

Transesterification in poly(ethylene terephthalate) and poly(ethylene naphthalene 2, 6-dicarboxylate) blends; the influence of hydroxyl end groups

Two samples of a single composition blend of PET and PEN were prepared by solution blending using different solvents such that the hydroxyl end groups in one blend were modified. The rate of transesterification in each blend was studied using proton NMR, an established technique for this system. The results indicate that the rate of transesterification is influenced dramatically by end group modification, providing clear evidence that hydroxyl end groups participate in the reaction mechanism.

Differential scanning calorimetry and optical microscopy investigations of the isothermal crystallization of a poly(ethylene oxide)-poly(methyl methacrylate) block copolymer

The isothermal crystallization of the poly(ethylene oxide) block in a linear diblock copolymer of poly(methyl methacrylate) poly(ethylene oxide) with a poly(ethylene oxide) weight fraction of 0.76, has been evaluated using optical microscopy and differential scanning calorimetry. The copolymer was quenched from the melt to a range of crystallization temperatures between 289 K and 316 K and the crystallization monitored by observation of the increase in radius of spherulites (microscopy) or the enthalpy of fusion (calorimetry) as a function of time. Comparison experiments were also made on physical blends of the two homopolymers where the weight fraction of polyethylene oxide ranged from ∼0.6 to 0.9. The block copolymer has an observed melting point which is 2–3 K lower and the spherulite growth rate was reduced compared with the equivalent blend. The growth rates calculated from optical microscopy have been subjected to crystallization regime analysis. All three regimes are observable in the block copolymer for the supercooling conditions used here, only regimes I and II are evident for the pure poly(ethylene oxide), and for the blends regime I appears to be completely suppressed. From the regime analysis a fold surface free energy in the block copolymer of 16–20 erg cm−2 has been obtained, which is much less than that obtained for the pure poly(ethylene oxide) or the blends. An explanation based on the favourable enthalpy of mixing with poly(methyl methacrylate) is suggested. Enthalpy of fusion data from isothermal crystallization studies on all polymers in the d.s.c. have been analysed using Avrami theory. The Avrami exponent was obtained together with an effective rate constant of crystallization. The exponent suggests that crystallization takes place via homogeneous nucleation with a spherical growth morphology, growth being controlled by the rate of attachment of molecules to the interface. By comparison of the Avrami exponent with values obtained for blends differing only in the molecular weight, the influence of melt viscosity on growth control is evident.

Polymer substrates for flexible electronics: achievements and challenges

Flexible electronics technology can potentially result in many compelling applications not satisfied by the rigid Si-based conventional electronics. Commercially available foils such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) have emerged as the most suitable polymer materials for wide range of flexible electronics applications. Despite the enormous progress which has been recently done on the optimization of physical and mechanical properties of PET and PEN foils, their dimensional stability at the micro-scale is still an issue during patterning of wiring by means of lithography. Consequently, the measurement of in-plane micro-deformation of foil is of great importance for understanding and predicting its thermal, hydroscopic and mechanical behaviour during processing.

Aromatic and heteroaromatic polyesters: 1. The 1,3,4-oxadiazole unit as an angular spacer in polyesters based on phenylene and naphthylene groups☆

Abstract Polyesters synthesized (by a melt-phase transesterification route) from terephthalic acid, hydroquinone diacetate, 6-acetoxy-2-naphthoic acid, 2,5-bis(acetoxyaryl)-1,3,4-oxadiazoles and (1,3,4-oxadiazole-2,5-diyl)dibenzoic acids have been studied by differential scanning calorimetry, hot-stage polarized light microscopy and thermal gravimetric analysis. Their fibre-forming properties have also been explored. Many of these polyesters have high thermal stability (>400°C), a liquid-crystalline melt phase and a light colour. Some also yield strong, stiff fibres.

P-17: Plastic Displays - New Developments in Polyester Film for Plastic Electronics

Polyester films are well-known substrates for a wide range of electronic applications. This contribution will describe new developments in polyester film substrates for OLED displays.

P‐65: Optimising Polyester Films for Flexible Electronic Applications

DuPont Teijin Films™ (DTF) have developed engineered substrates for the flexible electronics market. Teonex ®Q65FA and Melinex® ST506/504 are biaxially oriented semi-crystalline polyesters. for applications requiring high surface smoothness over wide area, planarised Teonex® Q65FA and Melinex® ST506 are emerging as suitable substrate materials for backplanes and frontplanes. The property set requirements for these films can be demanding as they are replacing rigid glass substrates. It is important to understand and control factors that can influence properties to achieve the optimum performance for a given flexible display application. This contribution will discuss the impact of applying a planariser coating to biaxially oriented semi-crystalline polymers.

P‐62: Latest Developments In Polyester Film For Flexible Electronics

DuPont Teijin Films(DTF) have developed engineered substrates specifically for the flexible electronics market. Teonex ®Q65 is a biaxially oriented crystalline polyester with a tailored surface and it is emerging as a competitive material for the base substrate in OLED displays and active matrix backplanes. To meet the demanding requirements of flexible displays the engineered substrates are likely to be multilayer structures. This contribution will discuss the mechanical properties of multilayer structures on flexing and the impact of the processing environment on dimensional reproducibility. Understanding the influence of these factors is critical to achieving the performance required of substrates for flexible electronic applications.

P‐50: The Impact of Thermal Stress, Mechanical Stress and Environment on Dimensional Reproducibility of Polyester Film During Flexible Electronics Processing

DuPont Teijin Films™ (DTF) have developed engineered substrates specifically for the flexible electronics market. Teonex ®Q65 and Melinex ST506/504 are biaxially oriented crystalline polyesters with the option of planarised surfaces are emerging as competitive materials for the base substrate in OLED displays and active matrix backplanes. Given the demanding dimensional reproducibility requirements in the display applications, it is critical to control the several factors that can influence the film distortion to achieve the ultimate performance that can be achieved with the base substrate. This paper will discuss the impact of thermal stress, mechanical stress and the processing environment on dimensional reproducibility of polyester film and give examples of how this impacts on the film in device manufacture.