JPH08167325A - Dielectric layered product having deformed ilmenite structure and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a dielectric compound having new structure used for a nonvolatile memory and the like. CONSTITUTION: (Na1-x Kx )(Nb1-y Tay )O3 , (x and y are zero or more but 1 or less) having deformed ilmenite structure (LiNbO3 ferroelectric structure), and a multilayer dielectric compound formed with the above compound and Li(Nbx Ta1-x )O3 , (x is zero or more but 1 or less) are manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a novel dielectric laminate for use in non-volatile memory devices, SAW devices, capacitors and optical element materials.

[0002]

2. Description of the Related Art A modified ilmenite structure (LiNbO₃strength
The compound of the dielectric structure) is LiNbO ₃And LiTaO₃
Good electrical characteristics (piezoelectricity, ferroelectricity, etc.) and optical characteristics
(Electro-optical effect, nonlinear optical effect, etc.)
It has a high Curie point and is called a frozen ferroelectric.
Many exhibit stable characteristics. However, the deformation
There are few substances showing the lumenite structure, and Li (Nb_xTa
_1-x) O₃Mostly known except (x is 0 or more and 1 or less)
Not not. In addition, it is difficult to reverse the polarization at room temperature.
There is a point.

[0003] On the other hand, NaNbO _3, KTaO ₃ is LiN
Although it has a composition close to that of bO ₃ or LiTaO ₃ , the present situation is that no perovskite structure as a stable structure and a modified ilmenite structure have been obtained in the world. The Curie points of NaNbO ₃ and KTaO _{3 having} a perovskite structure are low, -200 ° C and -271 ° C, respectively.
Is.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to establish a technique for synthesizing a dielectric compound having a modified ilmenite structure, which facilitates polarization reversal at room temperature, and to provide the substance.

[0005]

The present inventors have found that NaNbO
₃, KTaO₃The structure of the material from the perovskite structure
Deformed ilmenite by changing to a modified ilmenite structure
It has a menite structure, has ferroelectricity at room temperature, and
We thought that a substance that could easily invert the polarization could be obtained. Invention
As a result of intensive studies by the researchers, the modified ilmenite structure
Li (Nb _xTa_1-x) O₃And deformation of the ilmenite structure
(Na_1-xK_x) (Nb_1-yTa_y) O₃Form a laminated structure
Found that the above substances can be obtained for the first time
did.

That is, according to the present invention, Li (Nb _x Ta _1-x ) O ₃ (x is 0 or more and 1 with a modified ilmenite structure is formed on the substrate.
(Below) layer and (Na _1-x K _x ) (N of modified ilmenite structure
b _{1- y} Ta _y ) O ₃ and (x, y are 0 or more and 1 or less) layers are alternately laminated, and the composition formula is (Na _1-x K _x ) (Nb _1-y Ta _y ) O ₃ , (x, y
Is 0 or more and 1 or less) and has a modified ilmenite structure, a dielectric laminate of these compounds, and a method for producing the compound.

Having a modified ilmenite structure of the present invention
(Na_1-xK_x) (Nb_1-yTa_y) O ₃To a compound having
In the above, x and y are each 0 or more and 1 or less, and preferably
Is 0 ≦ x ≦ 0.1 and 0 ≦ y ≦ 0.1. This layer is one
Generally, directly on the substrate or Li (Nb_xTa_1-x) O₃
Are stacked through. Example of lamination of the dielectric laminate of the present invention
It is shown in FIG. In FIG. 1, 1 is a modified ilmenite structure
Of (Na_1-xK_x) (Nb_1-yTa_y) O₃Is a compound,
2 is a modified ilmenite structure (Li (Nb_xTa_1-x)
O₃Compound 3 is the substrate. The number of stacks for each is 1 or more
It is essential that it is above, and preferably twice or more. here
There is no limitation on the substrate used in, but for example, sapphire,
Recon, SrTiO₃, MgO, etc. can be used
It

Li (Nb _x Ta) having a modified ilmenite structure
The film thickness of the _1-x ) O ₃ compound per lamination is usually 0.
0006 to 10 μm, more preferably 0.00
012 to 1 μm, more preferably 0.0024
Is about 0.15 μm. The film thickness of (Na _1-x K _x ) (Nb _1-y Ta _y ) O _{3 having} a modified ilmenite structure per lamination is usually 0.0003 to 10 μm, preferably 0.0006 to It is 1 μm, and more preferably 0.0012 to 0.15 μm.

In the present invention, the modified ilmenite structure means a structure possessed by LiNbO ₃ or the like and has ferroelectricity. The fact that the film has a modified ilmenite structure means that
It can be identified by confirming that it has three-fold symmetry in the X-ray pole figure and that it has ferroelectricity by electrical measurement of the film. Hereinafter, the method for producing the dielectric laminate and the compound of the present invention will be described.

The dielectric laminate of the present invention comprises, on a substrate, Li (Nb _1-x Ta _x ) O ₃ having an ilmenite structure and (Na _1-x K _x ) (Nb _1-y Ta _y ) having an ilmenite structure. ) It can be easily obtained by forming a laminated film with O ₃ or a superlattice film and annealing at 550 ° C. or higher. Li (Nb _1-x Ta _x ) O ₃ , (Na _1-x K _x ) (Nb having an ilmenite structure
_1-y Ta y) The synthesis of O _3, for example, Li-Nb-O, N
Although it is possible to use a single target such as a-Nb-O, the synthesis can be easily performed by using a plurality of targets.

Originally (Na _1-x K _x ) (Nb _1-y Ta _y ) O ₃
Has a perovskite structure, and the stable structure of Li (Nb
The stable structure of _1-x Ta _x ) O ₃ is a modified ilmenite structure. However, both have an ilmenite structure as a metastable structure. Li (Nb _1-x Ta _x ) O with ilmenite structure
₃ is irreversibly transformed into LiNbO ₃ having a stable ilmenite structure and a deformed structure by annealing at 550 ° C. or higher.
Due to this phase change, (Na of the ilmenite structure is
_1-x K _x ) (Nb _1-y Ta _y ) O ₃ also has a modified ilmenite structure by changing to a modified ilmenite structure (Na _{1- x} K _x ) (Nb _1-y Ta _y). ) A dielectric laminate containing O ₃ can be obtained.

Further, the deformed ilmenite structure has good reproducibility.
Of (Na_1-xK_x) (Nb_1-yTa_y) O₃To synthesize
Is always Li (Nb_xTa_1-x) O₃To
(Na _1-xK_x) (Nb_1-yTa_y) O₃Thicker than
What is necessary is just to form a film. Deformed ilmenite structure (Na
_1-xK_x) (Nb_1-yTa_y) O₃The reason why
Li (Nb) with ilmenite structure_xTa_1-x) O₃And stack
It is presumed that it is because it is stabilized by doing. As well
Such a laminated structure is not possible if it has a stable stabilizing effect.
At least deformed ilmenite structure (Na_1-xK_x) (Nb
_1-yTa_y) O₃It is believed that the compound can be synthesized.

Having a modified ilmenite structure (Na _1-x
To obtain a ferroelectric compound containing K _x ) (Nb _1-y Ta _y ) O ₃ , a substrate and Li (Nb _x
Ta _1-x ) O ₃ may be removed by any method.

[0014]

Next, the present invention will be described in more detail with reference to examples. First, as an intermediate, Li having an ilmenite structure is used.
NbO ₃ and make a NaNbO ₃ of the membrane of the ilmenite structure, on a sapphire C-plane of the substrate to form a laminated structure of LiNbO ₃ and NaNbO ₃ above, by which the post-deposition annealing, variations ilmenite as a target substance A laminated film of NaNbO ₃ and LiNbO _{3 having} a structure was produced.

Ilmenite NaNbO ₃ , LiNbO ₃
The film was synthesized by using the laser ablation method. First, ilmenite type LiN is formed on a sapphire substrate.
A bO ₃ film is formed, and then ilmenite NaN is formed on it.
A bO ₃ film was formed. The film forming conditions are shown below. (1) Ilmenite LiNbO ₃ film synthesis conditions Substrate temperature 450 ° C. Introduced gas Oxygen + ozone (8% ozone) Oxygen 99.9999 vol% Distance between target and substrate 3.5 cm Reaction pressure 0.5 mTorr Target 1 Sintered body of LiCO ₃ Target Target 2 Nb ₂ O ₅ sintered body target Laser wavelength 193 nm (ArF excimer laser) Laser output 300 mJ Laser frequency 20 Hz Reaction time 0.2 to 600 minutes (2) Ilmenite NaNbO ₃ film synthesis conditions Substrate temperature 450 ° C. Introduced gas oxygen + ozone (8% ozone) oxygen 99.9999Vol% target and sintered target laser wavelength 193n of the sintered body target target 4 Nb ₂ O ₅ of the distance of the substrate 3.5cm reaction pressure 0.5mTorr target 3 NaCO ₃ Thickness at (ArF excimer laser) Laser Output 300mJ laser frequency 20Hz reaction time from 0.1 to 300 minutes 1 stacked, LiNbO ilmenite structure
_{When 3} was 1.44 nm and NaNbO ₃ was an integral multiple of 1.56 nm, the target product was obtained with particularly good reproducibility.

First, the film thickness per lamination is 15.84 nm for LiNbO ₃ having an ilmenite structure, and NaNbO.
₃ was 10.92 nm, the number of times of lamination was 5, and an ilmenite structure multilayer film as an intermediate was synthesized by the above laser ablation method. LiNb with ilmenite structure
Both O ₃ and NaNbO ₃ were epitaxially grown. The LiNbO ₃ film having the ilmenite structure had a c-axis length of 1.44 nm and an a-axis length of 0.52 nm. NaNbO ₃ having an ilmenite structure has a c-axis length of 1.56 nm,
The a-axis length was 0.53 nm.

By annealing this intermediate in air at 550 ° C., NaNbO having a desired modified ilmenite structure is obtained.
_{A 3} and LiNbO ₃ laminated film was obtained. As a result of analyzing the obtained laminated film of NaNbO ₃ and LiNbO ₃ having a modified ilmenite structure by an X-ray pole figure, it was confirmed that each layer was epitaxially grown and had 3-fold symmetry. By ion milling method, scrape the film to form a platinum electrode,
As a result of evaluating the electrical characteristics of NaNbO ₃ , it was confirmed that it exhibits ferroelectricity at room temperature. Therefore, the Curie point is room temperature or higher, and NaNbO ₃ (−20 having a perovskite structure) is used.
It was confirmed that the temperature was significantly improved from 0 ° C. Also,
As a result of evaluation by the 2θ-θ method of X-ray diffraction, the surface spacing was 1
A 5.1 nm peak and a 1.39 nm peak were observed. The peak at 15.1 nm is N with a modified ilmenite structure.
The peak of aNbO ₃ and 1.39 nm is the peak of LiNbO ₃ having a modified ilmenite structure. Therefore, it is considered that NaNbO ₃ having a modified ilmenite structure is generated.

Further, using a platinum electrode, the temperature is 15 kV at room temperature.
It was confirmed that the polarization was easily inverted when a voltage of / mm was applied.

[0019]

[Comparative Example 1] NaNbO having an ilmenite structure was formed on a sapphire substrate by the laser ablation method in the same manner as in the example.
_{Although 3} was deposited and annealed, a NaNbO ₃ film of polycrystalline perovskite structure was obtained at room temperature, but a film of modified ilmenite structure was not obtained. Also, the Curie point was measured, but it was as low as -200 ° C.

[0020]

Comparative Example 2 LiNbO ₃ having a directly deformed ilmenite structure was formed on a sapphire substrate by a laser ablation method. 15 kV / mm was applied at room temperature using a platinum electrode, but polarization reversal was difficult. Also, the Curie point is 10
It was at least 00 ° C.

[0021]

According to the present invention, a modified ilmenite structure is provided.
Of (Na_1-xK_x) (Nb_1-yTa_y) O ₃, (X and y are 0
Provided above (1 or less), (x and y are 0 or more and 1 or less)
For manufacturing dielectric devices such as non-volatile memory.
And exhibits ferroelectricity at room temperature and can easily invert polarization.
Available modified ilmenite dielectric laminates
Was. (It became available.)

[Brief description of drawings]

FIG. 1 shows a modified ilmenite structure (Na _1-x K _x ) (Nb
_{1-y Ta y) O 3} Li compound and deformation ilmenite structure
Example of stacking of (Nb _x Ta _1-x ) O ₃ compound

[Explanation of symbols]

1 (Na _1-x K _x ) (Nb _1-y ) with modified ilmenite structure
Ta _y ) O ₃ compound 2 Li (Nb _x Ta _1-x ) O ₃ having a modified ilmenite structure
Compound 3 substrate

Continuation of the front page (51) Int.Cl. ⁶ Identification code Reference number within the agency FI Technical indication location H01L 27/04 21/822 27/108 21/8242 21/8247 29/788 29/792 7735-4M H01L 27 / 10 651 29/78 371

Claims (3)

[Claims] 1. A Li having a modified ilmenite structure is formed on a substrate.
(Nb _x Ta _1-x ) O ₃ (x is 0 or more and 1 or less) layer and a modified ilmenite structure (Na _1-x K _x ) (Nb _1-y Ta _y ).
A dielectric laminate, wherein O ₃ and (x and y are 0 or more and 1 or less) layers are alternately laminated. 2. The composition formula is (Na _1-x K _x ) (Nb _1-y T
a _y ) O ₃ , (x and y are 0 or more and 1 or less), and
A compound having a modified ilmenite structure. 3. Li having an ilmenite structure as an intermediate
(Nb_xTa_1-x) O₃(X is 0 or more and 1 or less) Layer and ilme
Knight structure (Na_1-xK_x) (Nb_1-yTa_y) O
₃(X, y is 0 or more and 1 or less) and a laminated film is formed.
Then, this intermediate is annealed at 550 ° C or higher and deformed.
A phase change to an ilmenite structure is performed.
1. The method for manufacturing a dielectric laminate according to 1.