We report recent advances in the development of low power consumption, emissive, flexible active matrix displays through integration of top emitting phosphorescent OLED (T-PHOLED) and poly-Si TFT backplane technologies. The displays are fabricated on flexible stainless steel foil. The T-PHOLEDs are based on UDC phosphorescent OLED technology, and the backplane is based on PARC's Excimer Laser Annealed (ELA) poly-Si TFT process. We also present progress in operational lifetime of encapsulated T-PHOLED pixels on planarized metal foil and discuss PHOLED encapsulation strategy.
OLED display foils fitted conformally to goggles or cockpit canopies are of considerable interest. As films integrated onto pre-existing lenses or canopies they could provide visual information while adding little weight.
However, the conformal shaping of a displays to its mechanical support causes large deformation strain, in contrast to flexible displays whose bending to cylindrical shape can be managed with little strain. The deformation strain may easily exceed the critical strain of OLED materials, which then rupture and damage or destroy the OLED function. New fabrication techniques and OLED circuit architectures are required to prevent such rupture.
We report an experimental phosphorescent OLED array made on a dome shaped transparent plastic substrate. The pixellated array of OLEDs was fabricated and interconnected while flat. Late in the process sequence the array was shaped to a dome. The OLEDs are protected from rupture by their placement on ITO islands. These ITO islands are sized such that the shear strain developed along them does not reach the critical value. Most of the deformation strain is taken up by the plastic substrate that is exposed between the rigid islands. The metal interconnects do undergo this large deformation and must be designed to withstand it. The substrate was shaped to a dome of 6-cm diameter at its base, with a 10-cm radius of curvature. The radial strain at the apex of the dome is 1.5%.
The process produces bottom emitting phosphorescent OLEDs radiating into the hollow of the dome. OLED yields above 95% were achieved for up to 120-μm islands at area fill factors ranging from 4% to 44%.
Two blue-shifted iridium phenyl-pyridine dopants are compared in identical device structures. While the dopants have very similar optical behavior, it is found that the device efficiencies are very different and dependent on the host material. Upon comparison of molecular energy levels it is proposed that the electronic properties of the dopant influence the device efficiency through an electron trapping mechanism. It is believed that the relative energetics between the host and dopant play an integral role in the operation of the device.
In this paper we describe the applications and status of OLED technology to produce displays ideally suited for mobile applications. In particular, we focus on phosphorescent OLED (PHOLED) technology to reduce display power consumption and flexible OLED (FOLED) technology to reduce the display thickness and weight. We show that PHOLED displays can consume less power than an equivalent backlit AMLCD, and have excellent visual performance characteristics which make these displays highly desirable for portable communication devices. We will then describe an example of a unique communication device, a Universal Communication Device (UCD), based on flexible PHOLED technology, to produce a powerful communication device with a low power consumption and a light weight and very portable form factor. This device, enabled by a roll-out phosphorescent active-matrix display fabricated on a metallic or plastic substrate, is of great interest for a range of both consumer and military products.
Organic light emitting devices (OLEDs) are viewed as a potential next generation lighting source. Phosphorescent OLED (PHOLED) technology, with its inherently high efficiencies, represents the best opportunity to meet the challenging requirements of lighting. We discuss the requirements of OLEDs for lighting applications and present the state-of-the-art of white PHOLEDs, which have demonstrated the luminous efficiencies exceeding 30 cd/A at CIE coordinates of (0.35, 0.33).
In this paper we will outline the technical challenges and progress towards enabling a novel communication device based on a roll-out, low power consumption, OLED display. Advanced mobile communication devices require a bright, high information content display in a small, light-weight, low power consumption package. We believe that phosphorescent OLED (PHOLED) technology fabricated on a truly flexible substrate, enables a mobile Universal Communication Device (UCD) to offer a high information content display in an extendable form, while rolling up into a small form factor when not in use. This communication device is of great interest for a range of both consumer and military applications. From the display perspective, the key component is achieving a long-lived, low power consumption display. We believe the OLEDs are the preferred display media, and in this talk we will outline our flexible phosphorescent OLED technology. The key to reliable operation is to ensure that the organic materials are fully encapsulated in a package designed for repetitive flexing. UDC has been developing long-lived flexible OLED (FOLED) displays based on plastic substrates and multi-layer monolithic encapsulation. Recent progress in this area will also be reported. Finally, we will outline the backplane requirements for flexible OLED displays and compare the various technology options that can be used to fabricate the UCD.
High-efficiency electrophosphorescent organic light emitting devices (OLEDs), based on triplet emission, is an enabling technology for low power full-color OLED displays. In addition, top emission OLED architectures can be used to maximize display aperture ratio and pixel current densities. In this paper we report on recent results in red, green and blue phosphorescent and top emission OLEDs and discuss the benefits that these attributes have on both active and passive matrix display performance.
The burgeoning number of mobile consumer electronics has created a demand for lightweight, low-cost, portable displays. The development of a polycrystalline-silicon thin film transistor (TFT) technology compatible with plastic substrates will enable displays and large-area electronics that are low power, rugged and flexible. Significant challenges exist in the development of a polysilicon TFT fabrication process that is compatible with plastic substrates, since plastic has a much lower thermal budget than glass substrates. In general, superior polysilicon TFT performance is achieved with higher temperature fabrication processes because the quality of the polysilicon and gate- dielectric films are very sensitive to process temperature. In this work, an ultra-low-temperature process for fabricating high-quality self-aligned polysilicon TFTs on flexible plastic substrates is described. All fabrication steps are performed at or below 100 degrees C. Polysilicon is formed by crystallizing sputtered amorphous Si films using a XeCl excimer laser with a pulse duration of approximately 35 ns. Gate oxide deposition is formed using high-density plasma CVD, and metal films are deposited by sputtering.