Ultrafine metal oxide particle dispersion liquid and ultrafine metal oxide particle thin film

Abstract

An ultrafine metal oxide particle dispersion liquid is prepared by mixing an ultrafine titanium-based composite metal oxide particle dispersion liquid prepared by hydrolysis in a microemulsion containing a hydrophobic dispersion medium, water, and a surfactant and an organic metal compound solution for the same titanium-based composite metal oxide at a ratio of 1:1 to 1:30 in terms of the composite metal oxide contained.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to ultrafine metal oxide particle dispersion liquids in which ultrafine metal oxide particles are dispersed and ultrafine metal oxide particle thin films composed of metal oxide nanoparticles and having excellent dielectric properties. [0003] 2. Description of the Related Art [0004] In recent years, higher-performance devices have been intensively researched and developed with the increasing need for the miniaturization of devices. For example, composite metal oxides such as barium titanate and lead titanate zirconate are widely used for devices such as monolithic capacitors and actuators since such materials have excellent dielectric and piezoelectric properties. Development of smaller, higher-performance devices demands the establishment of techniques for manufacturing thinner, higher-quality films composed of finer particles. [0005] One of such thin-film manufacturing techniques is t...

AI Technical Summary

Benefits of technology

[0021] The present inventor has found that the above problem can be solved with an ultrafine metal oxide particle dispersion liquid prepared by mixing an ultrafine titanium-based composite metal oxide particle dispersion liquid (A) prepared by the microemulsion method and an organic metal compound solution (B) for the same titanium-based composite metal oxide with high storage stability at a ratio of A:B in the range of 1:1 to 1:30 in terms of the composite metal oxide contained, thus completing the present invention. Using this dispersion liquid, an excellent titanium-based composite metal oxide nanoparticle thin film that has high dielectric properties and causes less leakage current can be produced at a higher rate of deposition for each coating.

[0022] According to this approach, the concentration of the dispersion liquid can be increased with no increase in the proportion of the surfactant in the microemulsion, thus increasing the rate of deposition for each coating. In addition, a dense, smooth thin film that has excellent electrical properties and causes less leakage current can be achieved because voids between the particles are filled with the MOD solution.

[0025] Using the ultrafine metal oxide particle dispersion liquid according to the present invention, an excellent thin film that has high dielectric properties and causes less leakage current can be produced more efficiently at a higher rate of deposition for each coating.

[0026] The concentration of the surfactant in the ultrafine titanium-based composite metal oxide particle dispersion liquid is preferably 10% or less by volume of the hydrophobic dispersion medium. For such a concentration, a smaller amount of surfactant remains, thus reducing the viscosity of the dispersion liquid and preventing the production of porous films due to loss of the surfactant during firing. In addition, the concentration of the ultrafine titanium-based composite metal oxide particles is preferably 0.05 mol / l or less in terms of the composite metal oxide. For such a concentration, the resultant composite metal oxide nanoparticles can be highly dispersed to provide a transparent dispersion liquid.

[0028] The present invention further provides an ultrafine metal oxide particle thin film produced with the above ultrafine metal oxide particle dispersion liquid. This film has excellent dielectric properties, including a high relative dielectric constant.

Problems solved by technology

This is probably because a gradual reaction does not allow the particles to take in excess water.

A coating liquid prepared by a conventional microemulsion method, however, undesirably requires the repetition of coating many times to form a thin film having a desired thickness because the concentration of the coating liquid is low and therefore the rate of deposition is low, namely 10 to 20 nm for each coating.

According to the first approach, the removal of the hydrophobic medium increases the proportion of the residual surfactant, thus undesirably increasing the viscosity of the dispersion liquid and producing porous films due to loss of the surfactant during firing.

In this approach, however, an increased content of water relative to that of metal alkoxide causes aggregation at the beginning of the addition of the metal alkoxide to the microemulsion to produce a cloudy dispersion liquid unless the metal alkoxide is exceptionally rapidly and uniformly added.

Such a cloudy dispersion liquid is extremely difficult to disperse again.

As a result, this dispersion liquid undesirably exhibits low storage stability and repeatability.

MOD, however, has a fundamental problem: this method poses difficulty in providing good electrical properties, though producing an apparently good-quality film that is relatively dense and smooth.

This is probably because the resultant film has insufficient crystallinity.

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