JP2955293B2 - Manufacturing method of dielectric thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for producing a dielectric thin film useful for capacitors and the like.

(Prior Art) Composite oxides composed of two or more metal elements, especially Pb (Mg
Perovskite-type oxide ceramics represented by _1/3 Nb _2/3 ) O ₃ (hereinafter referred to as PMN) is known to be useful as a capacitor material. However, this type of composite oxide tends to form a stable pyrochlore phase at low temperatures. Oxide ceramics containing a large amount of pyrochlore phase have a low dielectric constant and are often unsuitable as capacitor materials. In addition, in the PMN composition system, the ceramic raw material powder (calcined powder) or the sintered body obtained by the ordinary solid-phase reaction method has a high perovskite phase with a high dielectric constant due to the non-uniformity of the raw material components. Is difficult to obtain. In particular, in the case of a thin film having a small volume, there is a problem that this phenomenon appears remarkably and a perovskite phase is not generated, and another oxide phase such as a pyrochlore phase is easily generated.

By the way, as a method for producing a ceramic thin film, a technique for thermally decomposing an organometallic compound into a thin film is described in, for example, JP-A-59-213665 and JP-A-61-64112. Although it is an excellent method for forming a thin film in terms of mass production and the like, if it is applied to a composite oxide thin film such as PMN, there is a problem that a pyrochlore phase is easily generated and a perovskite phase cannot be generated.

(Problems to be Solved by the Invention) As described above, a dielectric thin film made of a composite oxide such as Pb (Mg _1/3 Nb _2/3 ) O ₃ is not uniform in the conventional manufacturing method due to the non-uniformity of the raw material components. In addition, there is a problem that a perovskite phase is hardly generated and a thin film having a high dielectric constant cannot be obtained.

An object of the present invention is to provide a method for producing a dielectric thin film having a high perovskite phase generation rate.

[Constitution of the Invention] (Means and Action for Solving the Problems) In the present invention, a mixed solution of two or more metal alkoxides is applied on a substrate, dried, and then fired to form a dielectric composed of a perovskite oxide ceramic. A method for producing a dielectric thin film for obtaining a thin film, characterized in that after drying, the temperature is raised to a firing temperature at a temperature increasing rate of 100 ° C./min or more. In particular, when the dielectric thin film is a PMN-based ceramic, it is preferable to raise the temperature to a firing temperature of 600 ° C. or more by rapid heating at 100 ° C./min or more after drying.

In the present invention, since a homogeneous solution of a metal alkoxide is used as a starting material, a component having a significantly different decomposition temperature, for example, an inorganic salt or an organic acid salt is not contained. Therefore, an oxide having a target composition can be generated without generating another oxide other than the target composition.

Furthermore, in the present invention, after drying, the firing temperature is 100 ° C /
By heating at a rapid rate of temperature rise, a stable pyrochlore phase at a low temperature is hardly generated, and a perovskite phase with good crystallinity can be generated in a short time. In particular, when the dielectric thin film is a PMN-based material, the perovskite phase starts to be generated at a temperature around 500 ° C., but since the pyrochlore phase still tends to be generated at this temperature, the firing temperature is preferably set to 600 ° C. or higher. .

In the present invention, a metal alkoxide serving as a starting material is represented by a general formula of A (OR) _x . Here, as the alkoxy group (OR), those having an ester bond chain such as a methoxyethoxy group or an ethoxyethoxy group are effective in addition to those comprising an alkyl group such as a methoxy group, an ethoxy group, a propoxy group and a butoxy group. is there. A represents a metal element.

These metal alkoxides are dissolved or diluted in an organic solvent to obtain a uniform solution.In this case, each metal alkoxide may be a previously synthesized one, or may be synthesized in an organic solvent and used as it is. good.

In particular, when obtaining a PMN-based composite oxide,
The solution is adjusted to have the composition of (Pb _1-x M _x ) [(Mg _1/3 Nb _2/3 ) _1-y M ′ _y ]. Here, M is 2 of Ba, Sr, Ca, etc.
Synthesis 2 such as a valent metal element or (K _1/2 Bi _1/2 ) system
M ′ is a tetravalent metal element such as Ti, Zr, Hf, or (Zn _1/3 Nb _2/3 ), (Fe _1/2 Nb _1/2 ), (Ni _1/3 Nb _{2 / 3} ),
It is a synthetic tetravalent element system such as (Co _1/3 Ta _2/3 ) system. In addition, it is added to obtain desired characteristics such as temperature dependence of the dielectric constant. In particular, the size of the dielectric constant in a used temperature range and the characteristics as a dielectric thin film such as tan δ (loss) are taken into consideration. As a composition for obtaining well-balanced properties,
It is desirable that the range is ≦ x ≦ 0.35 and 0 ≦ y ≦ 0.65. In addition, if each component has a deviation of up to ± 5 mol%, a dielectric thin film having a desired characteristic can be obtained. In particular, the content of Mg may be increased up to 10 mol%.

In the present invention, the above solution is applied on a substrate by dipping, spray coating, spin coating, or the like, and the applied film is heated from room temperature to the boiling point of the solvent, at most 200 ° C.
Dry in the range up to. By repeating the coating and drying steps as needed, a coating film having a predetermined thickness can be obtained. After the coating film is dried, the temperature is rapidly increased to a firing temperature at a temperature increase rate of 100 ° C./min or more, and firing is performed for 30 seconds to 2 hours. In the case of PMN-based composite oxides,
Firing at a temperature of at least ° C. is effective in increasing the production rate of the perovskite phase.

The firing may be performed in the air, but may be performed in an atmosphere having a high oxygen concentration. By repeating these coating and firing steps, the film thickness can be increased.

The substrate used in the present invention may be any of heat-resistant glass, various ceramics, various metals, and the like. In particular, by using a substrate in which a conductive layer as an electrode is formed on an insulating substrate made of a highly conductive metal or an oxide, etc.
A ceramic capacitor or a multilayer capacitor can be formed.

According to the present invention, the sintering temperature is 900 ° C. ~ 1200 ° C
A dielectric thin film made of a complex oxide such as PMN consisting of a perovskite phase having good crystallinity can be easily obtained in a short time at a firing temperature lower than or equal to ° C. Further, the present invention can have a large area and is suitable for mass production of capacitors and the like.

(Example) Hereinafter, an example of the present invention will be described.

Example 1 Lead butoxide, magnesium methoxy ethoxide, and niobium butoxide were used in a molar ratio of 1: 1/3: 2/3 2-
Methoxyethanol (methyl cellosolve) solution (10 ^-1 mo
l /) was adjusted. This solution was dip-coated on a magnesium substrate, and the applied film was dried at 120 ° C.
Thereafter, the coating film was heated together with the substrate at a temperature rise rate of 1500 ° C./minute to a firing temperature of 700 ° C., and further fired at this firing temperature for about 10 minutes to obtain a dielectric thin film.

The X-ray diffraction pattern of the obtained dielectric thin film is shown in the drawing. It can be seen from this X-ray diffraction pattern that a (100) -oriented PMN thin film was formed. In this figure,
(100) and (200) indicate diffraction lines from the Pb (Mg _1/3 Nb _2/3 ) O ₃ thin film, and Δ marks indicate diffraction lines from the magnesium substrate.

In addition, as a comparative example, the coating film was fired under the same conditions as in the above example, with the firing temperatures of 500 ° C. and 600 ° C., respectively. Most of the dielectric thin films obtained by firing at 500 ° C consisted of the pyrochlore phase.However, the dielectric thin films obtained by firing at 600 ° C formed a perovskite phase with a low diffraction line intensity. Was confirmed.

If the rate of temperature rise up to the firing temperature is 3000 ° C./min, X
The line diffraction strength was increased, and a dielectric thin film having better crystallinity was obtained.

(Example 2) A PMN thin film was formed under the same conditions as in Example 1 using a magnesium substrate and a substrate obtained by sputtering platinum on a silicon wafer. When the temperature was raised at a rate of 1000 ° C./min, a PMN film having good crystallinity was formed by firing at 700 ° C. for 30 minutes. At 550 ° C./min, formation of a PMN film was confirmed although the crystallinity was reduced. However, when the rate of temperature rise was less than 100 ° C./min, most were in the pyrochlore phase.

(Example 3) A PMN thin film was formed under the same conditions as in Example 1 using a substrate obtained by sputtering platinum on a magnesium substrate. Further, a chromium electrode was formed on the dielectric thin film by vapor deposition to form a ceramic capacitor. The dielectric constant of this dielectric thin film was 2000. Also, its tanδ
Was 0.01-0.05.

Further, a multilayer capacitor was manufactured by alternately laminating the dielectric thin film and the chromium electrode.

Example 4 A 2-ethoxyethanol solution was prepared in which lead proxy, barium ethoxy ethoxide, magnesium ethoxy ethoxide, niobium propoxide, and titanium propoxide were used at a molar ratio of 0.9: 0.10: 0.30: 0.60: 0.1. This solution was spin-coated on a platinum plate to form a coating film. When this coating film was heated and fired under the same conditions as in Example 1, a dielectric thin film composed of a perovskite phase was obtained.
This thin film could be formed to a thickness of about 1000 ° by one coating.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a method for manufacturing a dielectric thin film having a high perovskite phase generation rate.

[Brief description of the drawings]

The drawing is a characteristic diagram showing an X-ray diffraction pattern of a Pb (Mg _1/3 Nb _2/3 ) O ₃ thin film formed on a magnesium single crystal substrate according to an example of the present invention.

Claims (2)

(57) [Claims] 1. A method for producing a dielectric thin film comprising a mixed solution of two or more metal alkoxides on a substrate, followed by drying and baking to obtain a dielectric thin film made of perovskite oxide ceramics. A method for producing a dielectric thin film, wherein the temperature is increased to a firing temperature at a temperature increase rate of not less than / minute. 2. The method for producing a dielectric thin film according to claim 1, wherein the firing temperature is 600 ° C. or higher.