Low-Temperature Synthesis and Dielectric Properties of Single-Phase Lead Zirconate Titanate Thin Film with a Nano Partic
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Low-Temperature Synthesis and Dielectric Properties of Single-Phase Lead Zirconate Titanate Thin Film with a Nano Particle Seeding Technique Tomokazu Tanase, Yoshio Kobayashi, Takao Miwa1and Mikio Konno Department of Chemical Engineering, Graduate School of Engineering, Tohoku University, Aoba, Aramaki-aza, Aoba-ku, Sendai 980-8579, Japan 1 Hitachi Research Laboratory, Hitachi, Ltd., Omika, Hitachi, Ibaraki 319-1292, Japan
ABSTRACT The low temperature synthetic method, which combines chemical solution deposition and nm-seeding technique, was applied to the fabrication of lead zirconate titanate (PZT) thin films. Nano-crystallines of barium strontium titanate (BST) particles were prepared by the hydrolysis reaction of the complex alkoxides. PZT precursor solutions containing the BST particles were spin-coated on Pt/Ti/SiO2/Si substrates to film thickness of 500 － 800 nm at particle concentrations of 0 – 25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 oC in unseeded PZT films, and crystallized PZT into perovskite structures at 420 oC, which was more than 100 oC below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 o C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10-6 A/cm2 at applied electric field from 0 to 64 kV/cm. INTRODUCTION Reduction in size of high performance electrical devices has lead to downsizing and integration of constituent parts such as dynamic random access memory, non-volatile memory, and micro-actuators. For the case of memory capacitors, stacking of the films to obtain large capacitance areas is usually applied to increase charge capacity. On the other hand, high dielectric constant films are required to achieve large capacitance because the complexities of the integrated circuit have reached a practical limitation in terms of current lithotechnology. Lead zirconate titanate (PZT) and barium strontium titanate (BST) films with dielectric constants greater than 1000 are promising candidates for high dielectric capacitors as opposed to silicon nitride (Si3N4) or tantalum oxide (Ta2O5). In general, this property can be attained by promoting formation of crystal structures that have high dielectric constant. Since the films are deposited on the surface of the electrode with the underlying circuit, high temperature treatment often seriously damages the films/electrode interfaces by the diffusion of the constituent elements. To avoid annealing damage, it is required to develop low temperature annealing in the preparation of the film. To lower the crystallization temperature, extensive work has been done, which has included rapid heating or high pressure annealing of the amorphous films, interlayer deposition between substrate and film, and the use of materials with appropriate lattic
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