Synthesis and Properties of Barium Titanate Thin Films on Copper Substrates
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0902-T02-03.1
Synthesis and Properties of Barium Titanate Thin Films on Copper Substrates Jon F. Ihlefeld1, William Borland2, and Jon-Paul Maria1 1 North Carolina State University, Department of Materials Science and Engineering, Raleigh, NC, USA 27695 2 DuPont Electronic Technologies, Research Triangle Park, NC, USA 27709 ABSTRACT Barium titanate thin films have been deposited on copper foils in the absence of interfacial layers via a chemical solution process. The dielectric – base metal stacks have been processed in reductive atmospheres such that substrate oxidation is avoided while allowing the perovskite film phase to crystallize. This accomplishment has facilitated the pursuit of a new embedded capacitor technology offering compatibility with polymer printed wiring boards and capacitance densities in excess of 2.5 µF/cm2. This represents a distinct improvement beyond conventional foil-based capacitor strategies. Finally, two critical phenomena will be discussed: (1) the effect of grain size on the dielectric properties of barium titanate thin films and (2) the effect of the Bsite substituent Zr on the lattice, microstructure, and dielectric properties. Most importantly, high processing temperatures have allowed for microstructural and dielectric properties similar to well-prepared bulk ceramics, including average grain diameters greater than 0.1 µm, relative permittivities in excess of 2000, and coercive fields below 10 kV/cm. These properties will be discussed in the context of bulk ceramic and thin film reference data and with regard to integration into printed wiring boards. INTRODUCTION Research on the deposition and processing of ferroelectric thin films has generated a great deal of interest over the last three decades. Much of this work has focused on depositing thin films on refractory or noble metal substrates for applications in ferroelectric memory (FeRAM), actuators for MEMS, high capacitance charge storage for random access memory (DRAM), on-chip decoupling capacitors for integrated circuits, and tunable circuits for communications. While these substrate materials are appropriate for the above uses, their cost, rigidity, and potential thermo-physical instabilities under high processing temperatures impose limitations on applications where these factors must be considered. One such embodiment is in the embedded passive field where a cost competitive marketplace requires inexpensive materials and processes and a flexible substrate material that will facilitate lamination into printed wiring boards. Several groups have worked toward the development of a materials set where a ferroelectric material could be deposited on a metallic substrate material that is both inexpensive and flexible [1-8]. Much of this work, however, has utilized traditional oxide thin film processing techniques where oxidizing atmospheres and high temperatures are used to crystallize the film materials. Subsequently, the substrate materials are allowed react with the atmosphere and the thin film materials, resulting in interfac
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