Thin film superlattice materials can exhibit physical, optical and mechanical properties very
different and superior to those of single layer counterparts. In the past fifteen years, hard coating,
optical and electrical device technologies have advanced beyond the use of single layer coatings
with the development of nanoscale compositionally modulated coatings, or superlattices and
nanocomposites. A typical superlattice consists of hundreds to thousands of nm-scale layers with
alternating compositions and/or crystalline phases. It is possible to engineer the electrical and
mechanical properties by choice of layer thicknesses and compositions. Typical layer thicknesses
are between 2 and 100 nm. We report of three types of superlattice coatings: (1) AlN/Si3N4 optical
superlattice for abrasion protection of ZnS IR windows, (2) Al/Cu structural superlattices and (3)
advanced thermoelectric superlattices. All superlattice coatings were deposited by DC and RF
reactive magnetron sputtering. The AlN/Si3N4 superlattice had layer thicknesses of 2 nm and
exhibited a nanohardness of 35 GPa. The Al/Cu superlattice had layer thicknesses of 1.5 nm and a
hardness near 6.5 GPa and is being developed for lightweight optics for space applications. The
thermoelectric superlattice demonstrated a figure of merit (ZT) ~ 1.5 and is being developed for
power generation from waste heat sources.
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.
Today organic light emitting diodes (OLEDs) are entering the market lace as a competitive flat panel display technology. Rapidly OLED displays are moving from small passive matrices to full color active matrices built on conventional indium tin oxide coated glass. The work in this paper is focused on developing high resolution full color displays on flexible substrates. Presented here will be new developments in high efficiency OLED displays with the application of this technology to flexible substrates thus allowing a whole new generation of display concepts to be realized.
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.
Applications for micro fluidic components continue to expand as the benefits resulting from the small volumes and light weight of such devices are recognized. Such benefits are particularly attractive for man-portable and automotive devices where reduction of weight is critical. As applications expand, so too does the need for the development of methods for producing micro fluidic components from unconventional materials (i.e., materials other than silicon). At the Pacific Northwest National Laboratory, we are currently developing processes for producing laminated multilevel ceramic components containing microchannel features that will find applications in micro fluidic chemical processing and energy management systems. Thin layers of green ceramic tape are patterned with micro fluidic flow features using one of a number of cutting processes. The patterned layers are then stacked and laminated with other layers of green tape, ceramic plate, or other materials using a series of processing steps. The resulting monolithic, leak-tight micro fluidic ceramic components are capable of tolerating high temperature or chemically corrosive environments. Fabrication issues associated with the use of the green ceramic tape for this type of application will be discussed, and examples of test components produced using these processes will be presented.
Microchannel microfluidic components are being developed for heat transfer, chemical reactor, chemical analysis, and biological analytical applications. Specific applications include chemical sensing, DNA replication, blood analysis, capillary electrophoresis, fuel cell reactors, high temperature chemical reactors, heat pumps, combustors, and fuel processors. Two general types of component architectures have been developed and the fabrication processes defined. All involve a lamination scheme using plastic, ceramic, or metal laminates, as opposed to planar components. The first type is a stacked architecture that utilizes functionality built in each layer, with fluid flow interconnects between layers. Each layer of the laminate has specific microchannel geometry, and performs a specific function. Polymeric materials are used primarily. Fabrication processes used are laser micromachining, wet and dry etching, and coating deposition. the laminates can also be micromolded plastics. The second architecture employs laminates to form internal microchannels and interconnects. Materials include ceramic tapes and high temperature metals. Catalysts can be placed in the microchannels. Fabrication processes used are diffusion bonding, ceramic bonding and firing, photochemical etching, and electrochemical micromachining. Bonding, thus sealing, the laminates is an important issue. Process conditions have been develop to reduce distortion of the laminates and to hermetically seal the components.
Excimer lasers have proven to be powerful tools for machining polymeric components used in microanalytical and microchemical separation devices. We report the use of laser machining methods to produce microfluidic channels and liquid/liquid contact membranes for a number of devices fabricated at our laboratory. Microchannels 50- to 100- micrometers -wide have been produced directly in bulk polycarbonate chips using a direct-write laser micromachining system. Wider microchannels have been produced by laser machining paths through sheets of polyimide film, then sandwiching the patterned piece between solid chips of polycarbonate stock. A comparison of direct-write and mask machining processes used to produce some of the microfluidic features is made. Examples of microanalytical devices produced using these methods are presented. Included are microdialysis units used to remove electrolytes from liquid samples and electrophoretic separation devices, both used for extremely low volume samples intended for mass spectrometric analysis. A multilayered microfluidic device designed to analyze low volume groundwater samples for hazardous metals and a fluidics motherboard are also described. Laser machining processes have also been explored for producing polymeric membranes suitable for use in liquid/liquid contactors used for removal of soluble hazardous components from waste streams. A step-and-repeat mask machining process was used to produce 0.5 X 8 cm membranes in 25- and 50-micrometers -thick polyimide. Pore diameters produced using this method were five and ten micrometers. The laser machined membranes were sputter coated with PTFE prior to use to improve fluid breakthrough characteristics.
Plastic components have many advantages, including ease of fabrication, low cost, chemical inertness, lightweight, and disposability. We report on the fabrication of three plastics-based microfluidic components: a motherboard, a dialysis unit, and a metal sensor. Microchannels, headers, and interconnects were produced in thin sheets (≥50 microns) of polyimide, PMMA, polyethylene, and polycarbonate using a direct-write excimer laser micromachining system. Machined sheets were laminated by thermal and adhesive bonding to form leak-tight microfluidic components. The microfluidic motherboard borrowed the `functionality on a chip' concept from the electronics industry and was the heart of a complex microfluidic analytical device. The motherboard platform was designed to be tightly integrated and self-contained (i.e., liquid flows are all confined within machined microchannels), reducing the need for tubing with fluid distribution and connectivity. This concept greatly facilitated system integration and miniaturization. As fabricated, the motherboard consisted of three fluid reservoirs connected to micropumps by microchannels. The fluids could either be pumped independently or mixed in microchannels prior to being directed to exterior analytical components via outlet ports. The microdialysis device was intended to separate electrolytic solutes from low volume samples prior to mass spectrometric analysis. The device consisted of a dialysis membrane laminated between opposed serpentine microchannels containing the sample fluid and a buffer solution. The laminated metal sensor consisted of fluid reservoirs, micro-flow channels, micropumps, mixing channels, reaction channels, and detector circuitry.
Microscale chemical devices have potential application as fuel processors to produce high purity hydrogen for PEM fuel cells from hydrocarbon fuels such as methane, methanol, ethanol, or gasoline. The fabrication of a novel stainless steel catalytic microcombustor/reactor suitable for use to high temperatures is described. The device consisted of three parts to accommodate catalyst loading: a laminated reactor body, a laminated combustor, and a solid cover plate. The laminated components were produced using stacks of photochemically machined stainless steel shims. When formed into solid leak-tight components using a diffusion bonding process, the laminated parts were designed to contain a complex series of internal gas-flow microchannels that could not be produced in a solid metal block by other fabrication methods. Included within the reactor body was an array of heat exchanger microchannels 250 microns wide and 5000 microns deep that were designed to extract heat from the catalytic reaction region and pre-heat the reactant gases. Catalytic combustion of hydrogen or hydrocarbon fuel occurred in a separate laminated combustor plate. The laminated combustor/reactor design has potential for use in a variety of chemical processing and heat exchanger applications.
The fabrication of microchannel chemical sensors with seven laminated individual functional modules is described. The sensors, used to detect chromium in nuclear and chemical waste streams, were fabricated using laser micromachining, bulk silicon micromachining, photolithographic techniques, sputter coating deposition, and anodic and adhesive bonding processes. The size of the sensor was 2 cm by 2.2 cm, with a total thickness of 2.2 cm. It consisted of two or more reservoir modules to hold the liquids being evaluate, two or more micropump modules to pump the liquids through the sensor, a chemical mixing module, a reaction module, and a sensor module with electrical circuitry for connection to external measurement equipment. The fluids were directed through the layers by interconnecting flow channels. The reservoir modules were fabricated by machining Pyrex and anodic bonding to silicon. The chemical mixing module was fabricated by wet etching Pyrex and anodic bonding to silicon. The reaction module contained a serpentine 200- micrometers -wide channel, and was formed by laser micromachining polyimide. The first prototype of this sensor employed external micropumps, while the second prototype will use off-the-shelf piezoelectric micropumps. The detector layer consisted of iridium, silver, and platinum sensor pads connected to gold contact strips. The modules were joined using adhesive bonding, and an electrostatic technique was used for silicon-Pyrex bonding.
The fabrication of components for a microchannel chemical solvent separation unit is described. The performance of this unit is intended to employ enhanced kinetic effects due to short contact times encountered in to facilitate extraction of one dissolved species from one solvent into another. Components for the device are fabricated by laser micromachining, photochemical machining, and photolithographic patterning. The separation unit consists of a series of parallel flow and counterflow microchannels separated by micromachined membranes and assembled into a single unit by a lamination process. In a sample design, channel width, membrane width and length are 100 micrometer, 1 cm, and 8 cm respectively. Test membranes were fabricated from stainless steel using photochemical machining and from polyimide by using two distinct laser micromachining processes. Use of the lamination fabrication method allows flexibility in the design of the microchannels within the unit. Preliminary results of membrane tests and a brief discussion of future efforts are included.
This paper presents details of fabrication and performance testing of prototype microchannel heat exchangers. The microchannel heat exchangers are being developed for advanced cooling and climate control applications, and are designed for heat loads of 100 W/cm2. Bulk and surface micromachining techniques are used to fabricate the test devices. Each heat exchanger section consists of over 150 microchannels etched in silicon substrates by either chemical etching or ion milling processes. The channels are 100-micrometers deep, 100-micrometers wide, and spaced 50- to 100-micrometers apart and connected with headers. Other heat exchangers have also been fabricated in copper and aluminum using machining and ion milling processes. Process steps involved photolithographic patterning, deposition of etch masks, ion or chemical etching, electrostatic bonding of the silicon to glass, insulator deposition, lamination of silicon to metals, application of thin heater coatings with busbars, and installation of the inlet/outlet hardware and valves. Recent hear exchangers have the silicon laminated to copper substrates. Performance testing focuses on determining the performance characteristics of the microchannel heat exchangers over a wide range of flow and heat transfer conditions. The working fluid for heat transfer is restricted to water or SUVA refrigerant HCFC-124 (R-124). Testing with water is run under single-phase conditions. The tests with R-124 are run under single-and two-phase flow conditions.
Large-optics coating facilities and processes at Pacific Northwest Laboratory (PNL) that were used to develop large-area high-performance laser mirrors for SDIO are now being used to fabricate a variety of optical components for commercial clients, and for novel applications for other DoD clients. Emphasis of this work is on technology transfer of low-cost coating processes and equipment to private clients. Much of the technology transfer is being accomplished through the CRADA (Cooperative Research and Development Agreement) process funded by the Department of Energy (DOE).
Weatherable, low cost, front surface, solar reflectors on flexible substrates would be highly desirable for lamination to solar concentrator panels. The method to be described in this paper may permit such reflector material to be fabricated for less the 50$CNT per square foot. Vacuum deposited Polymer/Silver/Polymer reflectors and Fabry-Perot interference filters were fabricated in a vacuum web coating operation on polyester substrates. Reflectivities were measured in the wavelength range from .4 micrometers to .8 micrometers . It is hoped that a low cost substrate can be used with the substrate laminated to the concentrator and the weatherable acrylic polymer coating facing the sun. This technique should be capable of deposition line speeds approaching 1500 linear feet/minute2. Central to this technique is a new vacuum deposition process for the high rate deposition of polymer films. This polymer process involves the flash evaporation of an acrylic monomer onto a moving substrate. The monomer is subsequently cured by an electron beam or ultraviolet light. This high speed polymer film deposition process has been named the PML process- for Polymer Multi- Layer.
Ion beam figuring has been demonstrated to be a deterministic efficient flexible technique for removing material from optical surfaces. Recent interest in using this process to produce high quality optical components has driven the need to fully characterize the resulting surfaces. We have performed a polishing parameter matrix investigation to optimize fused silica (Corning 7957) surfaces for subsequent ion milling. Samples were characterized for surface scatter surface absorption surface roughness subsurface damage and laser damage as a function of mill depth. Small defects (pits) were evident on surfaces after milling a few microns with pit density dependent to some degree upon the surface preparation technique. The defects were often in lines apparently following a surface or subsurface scratch in the materiaL Surface scatter decreased significantly (up to lOX) and laser damage threshold increased in some cases by 400. Laser damage was not correlated with defects in the material. Key words: ion beam milling laser damage scatter fused silica absorption. 1.
Thin-film silicon carbide (SiCi) and germanium carbon (Ge,Ci) alloy coatings with low Üifrared optical absorption
have been fabricated by DC- and RF-reactive magnetron sputtering. The optical and mechanical properties of the coatings
depend on composition determined by deposition conditions. The refractive index and optical absorption coefficient of
SiCi. alloys were varied from those of amorphous Si to those near diamond-like carbon (DLC) by increasing C
content. The band edge shifted below 1.2 eV with C content as high as 0.8. The useful range of the SiCi coatings
was extended to wavelengths as low as 1 jim. The useful transparency range of GeCi coatings is from 3 to 12 jim.
The refractive index of GeCi coatings was varied from 4.2 of amorphous Ge to near 3.4 by increasing x from 0 to 0.5.
The optical absorption coefficient was a complex function of composition and C-H, Ge-H, and Ge-C bonding. Mechanical
stress in both materials was generally moderate, and increased with increasing C content for the GeC alloys and
decreased with increasing C for the SiC alloys.
The wide range of optical properties obtainable for both coating types makes them useful in many types of multilayer
designs. Abrasion-resistant infrared (IR) multispectral antireflection coatings on zinc sulfide (ZnS) were demonstrated
using Geij•9C and DLC layers.