Charles C. Bonham

Organic light-emitting devices with extended operating lifetimes on plastic substrates

We fabricate long-lived organic light-emitting devices using a 175 μm thick polyethylene terephthalate substrate coated with an organic–inorganic multilayered barrier film and compare the rate of degradation to glass-based devices. The observed permeation rate of water vapor through the plastic substrate was estimated to be 2×10−6 g/m2/day. Driven at 2.5 mA/cm2, we measure a device lifetime of 3800 h from an initial luminance of 425 cd/m2.

Ultra barrier flexible substrates for flat panel displays

Abstract We describe a flexible, transparent plastic substrate for flat panel display applications. Using roll-coating techniques, we apply a composite thin film barrier to commercially available polymers, which restricts moisture and oxygen permeation to undetectable levels using conventional permeation test equipment. The barrier film can be capped with a thin film of transparent conductive oxide in the same roll-coater, yielding an engineered substrate (Barix™) for next generation, rugged, lightweight or flexible displays. The substrate is sufficiently impermeable to moisture and oxygen for application to moisture-sensitive display applications, such as organic light emitting displays. This enables, for the first time, lightweight and flexible emissive organic displays.

Gas permeation and lifetime tests on polymer-based barrier coatings

We describe a flexible, transparent plastic substrate for OLED display applications. A flexible, composite thin film barrier is deposited under vacuum onto commercially available polymers, restricting moisture and oxygen permeation rates to undetectable levels using conventional permeation test equipment. The barrier is deposited under vacuum in a process compatible with conventional roll- coating technology. The film is capped with a thin film of transparent conductive oxide yielding an engineered substrate (BarixTM) for next generation, rugged, lightweight or flexible OLED displays. Preliminary tests indicate that the substrate is sufficiently impermeable to moisture and oxygen for application to moisture-sensitive display applications, such as organic light emitting displays, and is stable in pure oxygen to 200 degrees Celsius.

An Approach to Make Macroporous Metal Sheets as Current Collectors for Lithium-Ion Batteries

A new approach and simple method is described to produce macroporous metal sheet as current collector for anode in lithium ion battery. This method, based on slurry blending, tape casting, sintering, and reducing of metal oxides, produces a uniform, macroporous metal sheet. Silicon film sputter-coated on such porous copper substrate shows much higher capacity and longer cycle life than on smooth Cu foil. This methodology produces very limited wastes and is also adaptable to many other materials. It is easy for industrial scale production.

Highly efficient blue organic light emitting device using indium-free transparent anode Ga:ZnO with scalability for large area coating

Organic light emitting devices have been achieved with an indium-free transparent anode, Ga doped ZnO (GZO). A large area coating technique was used (RF magnetron sputtering) to deposit the GZO films onto glass. The respective organic light emitting devices exhibited an operational voltage of 3.7 V, an external quantum efficiency of 17%, and a power efficiency of 39 lm/W at a current density of 1 mA/cm2. These parameters are well within acceptable standards for blue OLEDs to generate a white light with high enough brightness for general lighting applications. It is expected that high-efficiency, long-lifetime, large area, and cost-effective white OLEDs can be made with these indium-free anode materials.

High-pressure hydrogen materials compatibility of piezoelectric films

Hydrogen is well known for materials compatibility issues, including blistering and embrittlement in metals, which are challenges for its use as the next-generation “green” fuel. Beyond metals, hydrogen also degrades piezoelectric materials used as actuators used in direct injection hydrogen internal combustion engines. We present the materials compatibility studies of piezoelectric films in high-pressure hydrogen environments. Absorption of high-pressure hydrogen and composition changes were studied with an elastic recoil detection analysis and Rutherford back-scattering spectrometry in lead zirconate titanate and barium titanate thin films. Hydrogen surface degradation in the form of blistering and Pb mixing was also observed.

Sputtered Coatings for Microfluidic Applications

Magnetron sputter-deposited features and coatings are finding a broad range of uses in microfluidic devices being developed at the Pacific Northwest National Laboratory. Such features are routinely incorporated into multilayer laminated microfluidic components where specific functionality is required, and where other methods for producing these features have been deemed unacceptable. Applications include electrochemical sensors, heaters and temperature probes, electrical leads and insulation layers, piezoelectric actuators and transducers, and chemical modification of surfaces. Small features, such as those required for the production of microsensor electrodes or miniature resistive heaters on microfluidic chips, were patterned using standard lithographic methods, or with masks produced by laser micromachining processes. Thin-film piezoelectric materials such as aluminum nitride have been deposited at low temperatures for use with temperature sensitive materials. Use of the coating technology and its appl...

Microstructure Evolution and Composition Control During the Processing of Thin-Gage Metallic Foil

The manufacture of thin-gage superalloy and gamma-titanium-aluminide foil products via near-conventional thermomechanical processing and two different vapor-deposition methods was investigated. Thermomechanical processing was based on hot-pack rolling of plate and sheet. Foils of the superalloy LSHR and the near-gamma titanium aluminide Ti-45.5Al-2Cr-2Nb made by this approach exhibited excellent gage control and fine two-phase microstructures. The vapor-phase techniques used magnetron sputtering (MS) of a target of the desired product composition or electron-beam physical vapor deposition (EBPVD) of separate targets of the specific alloying elements. Thin deposits of LSHR and Ti-48Al-2Cr-2Nb made by MS showed uniform thickness/composition and an ultrafine microstructure. However, systematic deviations from the specific target composition were found. During subsequent heat treatment, the microstructure of the MS samples showed various degrees of grain growth and coarsening. Foils of Ti-43Al and Ti-51Al-1V fabricated by EBPVD were fully dense. The microstructures developed during EBPVD were interpreted in terms of measured phase equilibria and the dependence of evaporant flux on temperature.

Development of large area transparent conducting oxides from a combinatorial lead for organic solid state lighting

Organic light emitting devices (OLEDs) are projected to provide a low-cost, long-lived, and efficient wide area lighting solution if challenges in reliability, cost, and efficiency can be overcome. Development of new transparent conducting oxides (TCOs) that do not contain indium for use as the anode in bottom-emitting OLEDs can lead to cost savings and provide longer device lifetimes. Indium-free TCOs need to meet or exceed performance targets including high conductivity and visible light transmission, acceptable stability and, for blue or white OLEDs, a high work function to match the deep HOMO of the hole transport material. In this work, we report results from our efforts to scale up sputter deposition on large area substrates (up to hundreds of cm2) of a Ga-doped ZnO TCO having a composition identified using combinatorial methods. We present the results of initial scale-up efforts and evaluate relevant properties for these films. Finally, we have incorporated these materials in the production of OLEDs, and show performance comparisons between devices fabricated on the scaled-up GZO and commercial indium tin oxide (ITO). The results demonstrate that we are able to generate substrates with the appropriate work function to reduce the operating voltage of blue phosphorescent OLEDs compared to commercial ITO. This work function-HOMO energy matching leads to more efficient charge injection into the device hole transport layer.

Recent progress in flexible displays

Organic light emitting diodes (OLEDs) have recently entered the market place as a competitive flat panel display technology. OLED displays are moving rapidly from small passive matrices (i.e. <3 inches diagonal) to full color active matrices based on rigid substrates. This paper is focused on new developments to help enable flexible OLED (FOLED) displays. Presented here will be high efficiency phosphorescent OLED displays that can be used in either passive or active matrix drive configurations. Passive matrix displays incorporating this technology fabricated on flexible substrates are also reported. These early demonstrations of flexible OLED displays illustrate the promise for a whole new generation of display products based on the design dimension of flexibility.