Transparent conducting oxides (TCO) have been widely used for opto-electronic devices such as light emitting diodes, photo-detectors, touch panels, flat panel displays, and solar cells. Low resistivity, high mobility, and good transparency are the prime requirements for these devices. There is an increasing interest in TCO with high mobility to decrease their electrical resistivity without a significant decrease in the optical transparency. Highly conducting and transparent tungsten doped indium oxide thin films were deposited on quartz substrate by ablating the sintered In2O3 target containing WO3 with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). The effect of growth temperature and oxygen pressure on structural, optical, and electrical properties has been studied. The transparency of the films largely depends on the growth temperature. The electrical properties are found to depend strongly on the growth temperature as well as on oxygen pressure. The temperature dependence resistivity measurement shows the transition from semiconductor to metallic behavior as the growth temperature increases from room temperature to 500 °C. The high mobility (up to 358 cm2V−1s−1), low resistivity (1.1 × 10−4 Ω.cm), and relatively high transmittance of ∼90 % have been observed on the optimized film grown at 500 °C and under oxygen pressure at 1 × 10−6 bar.

Due to the steady increase in substrate sizes for low-temperature poly-Si devices and LSIs, there are strong demands for larger substrate handling, more accurate positioning and shorter tact time for many processes such as laser crystallization scan exposure, [3], and dopant activation [4] and so on. In order to satisfy such demands, we have developed a high-performance scan-type stage for large substrates. In this paper, we describe the outline of the mechanical structure and also the performance of this stage.

The XY moving stage was installed on an air slider of planarized granite. Stroke sizes of the stage were more than 920 mm and 730 mm for scan and step directions, respectively; the stage size was matched to the large glass substrates (4th generation). The stroke in the vertical direction was more than 32 mm, and the stage could rotate for more than ±0.3 degree for alignment.

The stage is driven by a newly introduced shaft-type linear motor, which consists of a fixed stainless-steel pipe shaft and a moving cylindrical coil rounded around the shaft. There are thin annular permanent magnets stacked inside the shaft. Since this coaxially aligned structure of permanent magnets and the coil is a nearly ideal configuration for efficient magnetic coupling, this motor could generate a stronger driving force; this enabled rapid acceleration and deceleration of the stage. Since stacked magnets generate parallel and uniform magnetic field along the shaft surface but slight field for transverse direction, electromagnetic force slightly fluctuated along the shaft, independent of the pitch of the magnet plate. This introduced another important advantage of the shaft-type linear motor that cogging, which has a serious impact on processing, was almost eliminated. This fluctuation was further reduced by introducing a real-time feedback system. The shaft-type motor, however, had been said to have the serious difficulty of elongation since its own weight bends the shaft. This problem was solved by using new magnetic materials and an optimized design of physical dimensions of the motor.

Experiments have been conducted under stabilized temperature conditions. The maximum scan speed of the stage was more than 500 mm/s with a speed stability of 0.03%, about one order of magnitude better than the reported value of about 0.5%. Acceleration and deceleration times from the halt condition to the constant velocity condition and vise versa were 1.0 s; the scan time was as short as 1.8 s for a 920 mm stroke. The “straight extent” was always better than ±0.5 mm Projection optics is commercially available for shaping a 30-mm-long excimer laser light beam on a sample surface. If we combine this stage and such optics, the whole area of a 4th-generation substrate surface can be scanned within a little more than 1 minute; that is, extremely high throughput can be expected. For example, to grow arrays of large Si grains, two-dimensional position control is the most important subject.

Patterning materials over large areas on flexible plastic or metal substrates, and on rigid ones, where multiple layers of different materials are being applied in order to create active devices brings with it the real challenge of accurate materials placement [1]. The additive process of printing expensive functional materials reduces costs associated with the losses of subtractive processing, but focuses the technological necessity on the precision of materials alignments on the target substrates. During the past decade, both materials and their print processing have developed to a near commercial level for optical and electronic devices. Industrial success will be assured when their production enjoys the economies of scale that large area processing can bring. Ink jet technology has developed in the last twenty-five years to a level of sophistication that is now adequate for the challenges of processing large area substrates for optical and electronic devices. Some equipment and processing will be covered in this paper.

It is reported that the global market for flexible electronics will reach 250 billion dollars by 2025, driven by the products on a human scale (the so called “electronics for life”). These devices such as LCDs cannot be made smaller. However, this field is immature and significant research and development is being conducted for the synthesis, manufacture and characterization of these kinds of devices. The manufacturing process has been identified as the bottleneck of the advancement of these products. High throughput, reliable and yet cost effective technologies are greatly needed for the developing of affordable and functional devices. Researchers and engineers at nScrypt have developed enabling tools and processing solutions for patterning components on large areas with great accuracy and repeatability. In this paper, we will present innovative printing/dispensing solutions as well as novel pumping technologies (smart pump) for the manufacturing and packaging on large areas. In addition to the smart pump, we have a mixer head and spray attachment for the developing of new materials and covering large area.

We have already reported AC-drive CdSe/ZnS quantum dot (QD) inorganic electroluminescent (EL) devices from colloidal solution. The EL spectra of the devices reproduced photoluminescent spectra of the source QD solutions. Furthermore, the observation of time resolved luminescent properties in ambient atmosphere at room temperature, are analyzed for improvements and projection of brightness and efficiency. The results suggest that the lifetimes of excited states in quantum dots are affected by the electric field in the electroluminescent devices.

Thin-film transistors (TFT) of poly and nano crystalline silicon have been made at temperature as low as 170°C on flexible PET (polyethylene terephthalate) substrates.The crystallization of the silicon film has been achieved using external mechanical stress assisted by a plasma hydrogenation technique. The formation of TFT is possible by means of a lateral crystallization of amorphous silicon under the channel region. High mobility TFTs with an electron mobility of 25cm2/Vs and an on/off ratio of 2000 have been obtained. Scanning electron microscopy, X-ray diffraction analysis and optical microscopy have been used to examine the crystallinity of the layer. In addition we report the deposition of high quality low-temperature silicon-oxide layers on PET substrates using an RF-plasma enhanced chemical vapor deposition unit with direct introduction of oxygen gas into the chamber and its reaction with Silane. Infrared spectroscopy was used to examine the quality of the oxide layer.

We report on the MOCVD growth of GaAs on patterned Si utilizing the Aspect Ratio Trapping (ART) method to reduce threading dislocations resulting from lattice mismatch. Defect-free GaAs was obtained from growth in sub-micron trenches formed in SiO2 on Si (001) substrates. Material quality has been characterized by cross-sectional and plan-view TEM and XRD. It was found that when growing GaAs above the trenched region, coalescence-induced threading dislocations (TDs) and planar defects were introduced at the coalescence junction interfaces. These defects were found to be unrelated to the misfit defects (MDs) on GaAs/Si interface that originated during initial epitaxial growth. Causes of coalescence defect formation were experimentally investigated by employing a two-step defect reduction scheme. It is concluded that by further optimizing growth conditions during coalesce layer growth, low defect-density GaAs material can be obtained on Si substrate.

We have developed a new silicon nitride (SiNx) multilayer barrier film by a plasma-enhanced chemical vapor deposition (CVD) for a flexible organic light emitting diode (OLED), which consists of SiNx films in two different deposition conditions, that is, a transparent SiNx layer (tr-SiNx) deposited with NH3 gas and an ultra-thin SiNx layer (cap-SiNx) deposited without NH3 gas, which caps over the former layer. This barrier film is expected to exhibit high durability under high temperature and high humidity conditions even at high deposition rate over 100 nm / minute, because the transparent SiNx layer, that is easily oxidized under such conditions, is protected by the cap-SiNx layer and the interface between them, and also show good transparency, because the opaque cap-SiNx layer is enough thin to be almost transparent to visible light. Thus, the multi-layer SiNx barrier film indicates the specific features as a high barrier performance, high transparency, and high productivity, and makes it possible to apply flexible OLED displays to automobile use.

Thin steel foils have been successfully demonstrated as outstanding substrate materials for flexible electronics because of their high mechanical strength, flexibility, light weight and thermal stability. This work investigates mechanical limitations of thin film materials on steel foil substrates. We characterize a three layer structure consisting of 100μgm thick stainless steel foil as the substrate, followed by 1μgm thick spin-on-glass passivation layer and 0.3μgm thick patterned aluminum interconnect layer on top with varying widths between 10- 35μgm by means of a bending experiment. A collapsing radius test method was adopted for the bending experiment and an elliptical curve fit was used to facilitate the strain measurement. The failure strain of aluminum interconnect layer was detected by monitoring the continuity of the test circuit during the experiment. The corresponding results reveal that the passivation layer cracked at a tensile strain of 0.46% and delaminated at a compressive strain of 0.68%. The metal interconnect layer ruptured at a tension strain of 1.26% and delaminated from substrate at a compressive strain of 1.22% due to the delamination of the passivation layer underneath. We determined that the failure of the aluminum interconnect under tension was due to localized elongation caused by cracking of the passivation layer underneath and concluded that a wider interconnect could withstand a larger strain. The stainless steel foil plastically deformed at a relatively small strain of 0.13%; thus, the use of stainless steel with reversible bending capability for flexible electronics is mostly limited by the minimum elastic bending radius of the steel substrate. The flexibility of steel foil based devices can be effectively improved by decreasing the substrate thickness.

Manufacturing transistors on thin flexible polymer foils is challenging and differs from standard Si processing due to the dimensional instability of the substrate influenced by moisture uptake, temperature and handling. A thorough analysis of material properties of the tested foil was performed to understand its behavior during lithography and subsequently to improve the processing. Imaging experiments on 100 µm polyethylene naphthalate (PEN) foils were performed with a PAS 5500/100D ASML step and repeat I-line (365 nm) system equipped with reticles having features of several microns and also sub-micrometer dimensions. A foil lamination process was developed to improve the dimensional stability during processing and to achieve a good surface flatness crucial for sub-micrometer imaging. The optimum process window for sub-micrometer critical dimensions was determined by performing a Focus Exposure Matrix (FEM) experiment in which the energy and focus were increased stepwise. The optimum imaging conditions were derived from SEM analysis. The results indicated a reproducible and good patterning accuracy for making patterns below 1µm size.

Principal challenges to direct fabrication of high performance a-Si:H transistor arrays on flexible substrates include automated handling through bonding-debonding processes, substrate-compatible low temperature fabrication processes, management of dimensional instability of plastic substrates, and planarization and management of CTE mismatch for stainless steel foils. In collaboration with our industrial and academic partners, we have developed viable solutions to address these challenges, as described in this paper.

A novel, cost effective technology to manufacture high density embedded electronic circuitry is demonstrated. The process consists of laser photoablation of the circuitry into a substrate through a mask and subsequent filling using a polymer thick film paste. Because the volume of the substrate is used it is possible to make thick and thereby highly conductive lines using low cost materials and processes. The process is demonstrated for a fan out circuitry in 100 µm thick polyethylene naphthalate (PEN). The fan out circuitry has linewidths of 50 µm and line spacings of 100 µm. The usability of the circuitry is demonstrated by the successful flipchip bonding of a thinned Si daisy chain dummy chip with 176 IO's.

Thin films of polyaniline (PANI) deposited onto different substrates were nano-structured using direct laser interference patterning (DLIP) at room temperature and pressure in air atmosphere. Regular line-like arrays with thicknesses up to 600 nm were fabricated by means of this technique in only one single step. The activity of the remained polyaniline was determined by monitoring its doping level using Energy Dispersive X-Ray Analysis (EDX), while its chemical structure was confirmed by Fourier Transform Infrared Spectroscopy using Attenuated Transmission Reflectance (FTIR-ATR). The structuring mechanisms of PANI supported in both polycarbonate (PC) and polyimide (PI) films were demonstrated using cross-sectional analyses performed with a dual-beam workstation (FIB/SEM Tomography). Moreover, by varying the fluence of the laser beam, it is possible to control the width of the PANI arrays, and large areas (mm2 - cm2) could be patterned. Additionally, electrical resistance measurements of the individual PANI strips demonstrated that electrical properties of unmodified regions remain unchanged.

Traditional plasma based dielectric films are conformal and cost-prohibitive for large displays. Solution based dielectrics are planarizing in nature and provide a flat surface for indium tin oxide (ITO) layer with the resultant uniform liquid crystal response throughout the pixel. In this paper, we present the display-related material properties and integration results obtained by using a solution-based organosilsesquioxane material. The material exhibits extremely high transmittance and planarization, low outgassing, high resistance to moisture absorption and diffusion, good adhesion to other layers integrated with it and ease of integration.

Carbon nanotube films can be used in a wide range of applications, from fuel cells, storage batteries, and super-capacitors, electron field emitters for displays, x-ray and beam sources, heat sinks and heat spreaders, and chemically robust filtering membranes, to name a few. Present approaches to carbon nanotube film production rely on filtration of a suspension, but creating this suspension requires the use of toxic and hazardous reagents and lengthy processing times. We describe an approach of uniaxial die pressing that incorporates a sacrificial layer to prevent binding of the carbon nanotube film to the compression surfaces. Water, or other solvents, acts as a release agent. No binder is used. The process is scalable in terms of film thickness and area. Development of an extrusion process employing these principles is described.

A novel electro-fragmentation method was developed as a fast alternative to the time consuming fragmentation test carried out in situ in a microscope, to investigate the failure of dielectric coatings on polymer substrates using an ultrathin conductive layer. Focus was put on SiNx coatings on polyimide substrates. A careful selection of the conductive layer was carried out to avoid artifacts resulting for instance from a change of the residual stress state of the investigated coating. Au layers were found to be too ductile and Al-Ti layers altered the stress state of the nitride, which invalidated their use to probe the failure of the nitride coatings. In contrast, a 20 nm thick graphite layer was found to accurately reproduce the failure of the nitride, which was analyzed in terms of residual strain and cohesive properties of the graphite layer. An electro-fatigue device was built and preliminary results suggest that damage already develops in ultrathin coatings at relatively low strain levels under long-term fatigue loading.

There is a growing need for optical fiber coatings that can sustain higher temperatures than present materials permit. To date, polyimides are used predominantly but they generally are difficult to process and usually require multiple depositions to achieve the desired film thickness. Perfluorocyclobutyl (PFCB) aryl ether polymers have demonstrated much success as processable and amorphous fluoropolymers,[1] with particular emphasis on high performance optical applications.[2] This work discusses recent efforts into perfluorocyclobutyl aryl ether polymer-based optical fiber coatings.[3] A series of silica-based optical fibers were drawn with differing PFCB polymer coatings compositions and molecular weights on a Heathway draw tower. Results include a more than doubled usage temperature of coating (decomposition temperatures (Td) in nitrogen and air were above 450 °C) without affecting fiber mechanical properties and comparable isothermal stability to conventional coatings, except with a >150 °C higher temperature. Preliminary results of the first successful coating of optical fibers by PFCB polymers will be presented herein, as well as future endeavors.