Electric Field Assisted Solution Processing for Thick Films and Constrained Sintering of Functional Materials
The use of thick films is becoming more and more important in particular for microelectronic applications.
Major trends in the communication industry are towards increased integration, higher frequencies, smaller size, and reduced cost. These trends have reached the point that one can consider the replacement for example of dielectric components currently utilized in bulk ceramic form, by dielectrics processed as thick films. This approach has the potential advantage of reduced processing costs, and may be applied to resonators, filters, baluns, and antennas. Furthermore, the ability to process thick films conformably on substrates, and also directly on metal foils, opens up the possibility of innovative structures and designs. Thick films are required for most of these applications, rather than thin films, as these are volume devices that store electromagnetic energy within the dielectric volume.
Thick films are normally fabricated by low-cost processes such as tape casting (doctor blading), screen-printing, ink-jetting (or printing) or electrophoretic deposition (EPD). EPD Electrophoretic deposition (EPD) is a simple, fast and inexpensive deposition technique for obtaining thick films. One of the advantages of EPD over other thick film deposition techniques is the ability to coat complex geometries, which allows easy deposition of the materials onto substrates of various shapes.
In EPD charged particles suspended in a solution media will be moved to a counter electrode under the effect of the electric field. The fabrication process by EPD includes three stages: i) the formation of a charged suspension; ii) the deposition of charged particles onto an electrode under the action of a DC voltage and iii) the final sintering.
In this research area we are exploiting EPD to fabricate dielectric thick films for high frequency applications. The materials under study belong to the families: i) BaO-Ln2O3-TiO2 (Ln = La or Nd) characterized by high to intermediate dielectric permittivities and low losses (high Q) and ii) Te based compounds, including TiTe3O8, Cu3TeO6, Al2TeO6. Our research includes the optimization and understanding of the EPD deposition conditions, the characterization of the structural, microstructural and physical properties of these thick films and comparison with bulk and single crystal responses and studies of the constrained sintering of the thick films on different substrates.