Piezoelectric Materials

The MEMS (microelectromechanical systems) community, which now includes several major integrated circuit producers, is working toward the development of fully integrated sensor-actuator systems which can exert continuous control over a local environment. Because of their good stability and activity, piezoelectric materials will be the materials of choice for fabricating microactuator elements within these smart systems. EMARC is responding to this need by developing new piezoelectric ceramics with improved responsiveness and durability.

In this area is a cooperative project with AlliedSignal Aerospace for the development of Ultrasonic Traveling Wave Motors  for military and commercial applications. This project has reached the point where motors are being prototyped and the outlook for a successful result looks bright.

Ferroelectric Materialsls

Ferroelectric ceramics are being targeted for use as capacitor elements in nonvolatile memory devices. EMARC has developed a new thin-film coating technology which allows complex metal oxides such as ferroelectrics to be deposited from a polymeric precursor solution. The precursor solution is spin coated onto the substrate and then fired to form a dense, defect-free metal oxide coating. However, unlike sol-gel coatings which are prone to aging and particle formation problems, the new precursor coatings are stable at room temperature and can be prepared from routinely available metal salts; unstable metal alkoxides are not required. EMARC researchers are also involved in the development of new pervoskite ceramics which exhibit higher ferroelectric responses and can be deposited as stable thin films.

The expertise in ferroelectrics has lead to another cooperative project with AlliedSignal Aerospace and Lawrence Livermore National Lab. This project is dedicated towards the development of electroceramic materials for use in several technologies: 1) high energy electron emitters (ferroelectric emission - FE) for use as cathodes in accelerators, and for flat panel displays, 2) controlled permittivity dielectrics for "fast-kicker" transmission lines, 3) high gradient multilayer insulators, and 4) TiO2dielectrics for the dielectric wall accelerator.

Photolithography

EMARC has recently begun the development of a photosensitive metal oxide precursor coating which will allow direct patterning of a ceramic coating by conventional photolithographic means, thus eliminating the need for separate photoresist application and etching processes. This technology should be extendable to most applications where metal oxide coatings must be selectively deposited on device substrates. An ideal extension of the technology, for example, would be the deposition of ferroelectric emitter arrays on emissive display substrates.

The industrial applicability is now being evaluated in a joint project with Brewer Science, Inc. of Rolla, Missouri. The program is dedicated to two primary technical objectives:

1. Showing that a thin coating of a ceramic precursor can be applied onto a color layer and then processed into a plasma etch resistant mask for patterning the color layer
2. Demonstrating that the ceramic precursor can be formulated into a photodefinable composition by the addition of appropriate polymer components and additives.

The progress of this project is very encouraging resulting in product development at Brewer Science, Inc.

Planarizing Dielectric Materials

High performance hybrid circuits are constructed on ceramic substrates such as alumina which often display severe surface roughness. EMARC has developed a series of spin-coatable inorganic sols for planarizing rough ceramic substrates while retaining the electrical integrity of the starting substrate material. A similar dielectric coating technology is now being explored for gap-fill and planarizing of multi-level metallization structures within integrated circuits.

This ability to coat substrates with oxide films has lead EMARC to a project with TDA Research, Inc. This is a program which is sponsored by DARPA in cooperative partnership between Missouri S&T, TDA Research in Denver, Colorado and Rice University in Houston, Texas. This is a high profile program which will be extremely beneficial to the aircraft industry and the military.

A large portion of the U.S. painting industry is directed at providing protective coatings for metals, aluminum in particular. For these coatings, the undercoat or transfer coating has traditionally contained chromates whose use is now banned because of health hazards associated with their use. As a result there is a large effort to develop replacements for the chromates.

Another project related to planarization of alumina substrates is just beginning with early results showing that alumina substrates can be smoothed from a 2 micron roughness to less than 0.5 microns by our coatings technique.

Thin Film Resistor and Conductor Materials

Tin oxide and indium-tin oxide (ITO) coatings are used as thin, transparent electrodes in a variety of electronic applications, most notable in liquid crystal displays and other flat panel devices. Such coatings are typically applied by sputtering and then patterned in a photoresist process which uses a strong chemical etchant. A stable deposition and patterning process is difficult to establish, and U.S. producers of displays and display components have had recurrent problems with obtaining consistently high quality ITO-coated glass panels from domestic suppliers. The photosensitive metal oxide precursor technology developed by EMARC could be applied to simplify the deposition and patterning of ITO electrodes in displays and various sensor devices.

Electrochromic Materials

Electrochromic devices utilize a composite, multi-layer film structure comprised of complex metal oxide coatings such as LixNi1-xO and indium-tin oxide. While sputtering and atmospheric pressure chemical vapor deposition have been the preferred techniques for applying these materials to large-area substrates such as window glazings, there is growing interest in the use of solution coating methods such as sol-gel since the stoichiometries of the complex metal oxides could be controlled more precisely and easily than by using vacuum deposition methods. The solution-stable metal oxide precursor technology developed by EMARC is readily applicable to the deposition of electrochromic films on commercial substrates. Furthermore, it would allow a broad range of new electrochromic metal oxides to be prepared and characterized much more conveniently.

Anti-reflective Coating Materials

The performance of solar cells, flat-panel displays, window glazings, and a host of other large-area substrates can be improved by the application of thin ceramic anti-reflective (dielectric) coatings. Sol-gel and PVD coating methods are now used extensively to apply anti-reflective films. A critical factor in these processes is controlling the film thickness of the coating. In comparison to sol-gel techniques, EMARC's ceramic precursor coating technology offers the advantage of being able to carefully and reliably control the viscosity of the coating solution, and thereby control film thickness with great accuracy.

Solid Oxide Fuel Cell (SOFC) and Oxygen Separation Materials

SOFC's require thin complex metal oxide films such as yttrium-doped zirconia and La1-xSrxMnO3as the operating electrolyte and electrode, respectively. EMARC researchers have been actively involved in the development of SOFC materials and devices for many years. Their metal oxide precursor coating technology originally emerged from this work and has now been expanded to applications in small-scale electronic devices.

Another outcome of this work has been the development of complex perovskite structured oxides which have mixed ionic and electronic conductivity which can be used to separate oxygen from nitrogen in air. EMARC participates in a program which is sponsored by Commerce through the Applied Technology Program involving the companies of Praxair and BP Chemical. This is a $12 million program in which the role at Missouri S&T is to help develop the new ceramic oxygen separation membrane materials which are required to build the oxygen separation reactors. Progress towards commercialization has been such at the Praxair, BP Chemical, AMOCO, Statoil, and Sastech Ltd. have formed a consortium for the commercialization of the process to produce syngas. EMARC plays a role of materials development and characterization in this project.

Related Applications

An exciting area for investigation and development is the fabrication of ceramic-on-polymer multi-layer devices which are analogous to present-day flex circuits. Flexible circuits are used in almost all electronic instrumentation and hardware; a common example is the personal computer. Flex circuitry has been comprised traditionally of thick film copper wiring bonded to a high temperature-stable polymer film such as polymide. EMARC has capabilities for developing low-firing ceramic materials and ceramic-polymer nanocomposites as well as processing methods for depositing and patterning these materials on polymeric substrates to create forms of flexible circuitry with greater functionality and sophisticationn.