Electrical Characteristics of Doped and Undoped High Dielectric Constant BCTZ Thin Films
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Electrical Characteristics of Doped and Undoped High Dielectric Constant BCTZ Thin Films Woo-Chul Yi, T. S. Kalkur, Elliott Philofsky1, and Lee Kammerdiner1 Microelectronics Research Laboratories, Department of Electrical and Computer Engineering, University of Colorado, Colorado Springs, CO 80933-7150 1 Applied Ceramics Research Company, Colorado Springs, 80919
ABSTRACT Ba1-xCaxTi1-yZryO3 materials have very high dielectric constant (up to 30,000) in the bulk form. In this paper, we are presenting the electrical and structural characteristics of undoped and 0.4% Mg-doped Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) thin films on Pt/Ti/SiO2/Si substrates. The BCTZ films were deposited by spin on metal-organic decomposition method and annealed at a temperature 600-900 oC in oxygen environment. The annealed thin films were characterized by X-ray diffraction. The electrical characteristics of the annealed thin films were analyzed by capacitance–voltage and current–voltage measurements. The as-annealed thin films were postannealed in nitrogen and oxygen environments and the effect of post-annealing on their electrical characteristics were also presented in conjunction with 0.4% Mg doping effect of BCTZ thin films for possible high dielectric constant material applications.
INTRODUCTION
Thin films of barium strontium titanate Ba1-xSrxTiO3 (BST) are under consideration as a replacement for silicon dioxide (SiO2) as the dielectric in advanced memory devices. The major attraction of BST is its high dielectric constant compared with SiO2. The high dielectric constant value combined with low dissipation factor makes BST one of the promising candidates for dynamic random access memory (DRAM) applications. The solid solution of barium titanate BaTiO3 and barium zirconate BaZrO3, BaTi1-yZryO3 (BTZ), shows a lot of analogies to BST solid solution [1]. The nature of the ferroelectric phase transition at the Curie temperature (Tc) of BTZ bulk ceramics is known to change strongly with Zr content. At higher Zr contents (y > 0.08), BTZ bulk ceramics show a broad dielectric constant–temperature (ε–T) curve near Tc, which is caused by inhomogeneous distribution of Zr ions on Ti-sites and mechanical stress in the grain. In the related system Ba1-xCaxTi1-yZryO3, Ba1xCaxTi1-yZryO3 bulk ceramics when prepared in oxidizing atmosphere exhibit a broad ε–T curve near Tc, in which peak values up to ε ≈ 30,000 and maximum ε value of doped Ba1-xCaxTi1yZryO3 bulk ceramics is higher compared to undoped one [2]. Mg was selected as an acceptor dopant. Mg2+ ion is thought to be substituted for Ti4+ ion of the BST perovskite because effective ionic radii of Mg2+ and Ti4+ with a coordination number of 6 are 0.072 and 0.0605 nm, respectively [3]. Despite high ε values of Ba1-xCaxTi1-yZryO3 bulk ceramics, any descriptions on fabrication and on dielectric properties of Ba1-xCaxTi1-yZryO3 thin films have not been found in
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the literature. In this work, Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) thin films with 0.4% Mg dopant were proposed as a high dielectric materi
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