Duncan Henry Mackerron

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.

Characterization of strain-induced crystallization of poly(ethylene terephthalate) at fast draw rates using synchrotron radiation

Abstract Structural changes during fast drawing of poly(ethylene terephthalate) were studied by wide-angle X-ray scattering using synchrotron radiation. Drawing was studied at 80, 90, 100 and 110°C to a final draw ratio of ∼4:1 at a draw rate of ∼ 10s−1. Simultaneous video recording of the sample enabled variation in the X-ray pattern to be correlated with local extension. Essentially all oriented crystallization occurred after final extension. Primary crystallization fits a first-order transformation with little change in the rate of crystallization observed over the 30°C range of temperature. These results show that it can be misleading to rely on crystallinity information obtained when samples from interrupted draw experiments are quenched.

Characterisation of biaxial orientation gradients in poly(ethylene terephthalate) films and bottles using polarised attenuated total reflection FTIR spectroscopy

Polarised attenuated total reflection (ATR) infrared spectroscopy has been used to quantify biaxial orientation in commercially manufactured poly(ethylene terephthalate) (PET) films and stretch-blow moulded bottles. Using a single-bounce accessory with a high refractive index element, and applying appropriate data normalisation prior to measuring band intensities, measurement of the average square direction cosines that describe the orientation is simple. Using this technique it was shown that uniaxially drawn PET films were actually biaxially oriented, and there were significant gradients in orientation through the film thickness. Bulk measurements, or methods that assume uniaxial orientation, would give incorrect results from these materials. The bottles exhibited complex orientation patterns that depended on preform and mould design, and again there were strong orientation gradients through the bottle walls. Kratkys model (pseudo-affine) was used in an attempt to predict the biaxial orientation gradients as a function of preform and bottle dimensions.

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.

Microfocus X-ray Diffraction of Spherulites of Poly-3-hydroxybutyrate

The microfocus X-ray beamline at the European Synchrotron Radiation Facility has been used to investigate the variation in molecular orientation and crystallinity in spherulites of the organic polymer poly-3-hydroxybutyrate (PHB). This is the first report of the correlation of optical and X-ray measurements on spherulitic polymer films where X-ray diffraction patterns have been recorded and displayed continuously in real time while the specimen was tracked in steps of 10 mum across an incident X-ray beam with a diameter as small as 10 mum.

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.

Time-resolved X-ray wide angle scattering studies of the effect of draw rate and temperature on the development of orientation and crystallinity in PET

Abstract A purpose-designed X-ray fibre diffraction camera has been used to record the variation in the wide angle X-ray scattering during the drawing and annealing of the organic polymer polyethylene terephthalate. Data were recorded at the Daresbury Laboratory Synchrotron Radiation Source using a Photonics Science electronic area detector interfaced to a Synoptics framegrabber as a series of frames with an exposure time of 40 ms for each frame. Frames could be displayed while the diffraction pattern was being accumulated allowing the experiment to be conducted in a genuinely real-time mode. The draw rate was varied from 20% per min to 72 000% per min and the draw temperature from 80°C to 140°C. The draw ratio in these experiments was designed to be 3.6:1. For the highest draw rates essentially all the change in the diffraction pattern was complete in less than 1 s. The degree of crystallinity and orientation observed in drawn samples depends on both the draw temperature and the draw rate. In particular for draw rates of 72 000% per min the high degree of orientation and crystallinity observed at a draw temperature of 80°C diminishes with increasing draw temperature until for draw temperatures of 140°C the pattern is essentially unoriented and non-crystalline.

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.

P‐56: The Impact of 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 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. Given the demanding dimensional reproducibility requirements in the more demanding display applications, uncontrolled moisture absorption during the processing cycle could potentially be far more significant than the inherent shrinkage of the base substrate. Understanding the impact of this effect and optimising the processing steps involved in device manufacture will be critical to achieving the ultimate performance that can be achieved with the base substrate. This contribution will discuss the impact of the processing environment on dimensional reproducibility of polyethylene naphthalate film (Teonex® Q65) and give examples of the film in use.