JPH08253324A - Ferroelectric thin film constitution body - Google Patents

Abstract

PURPOSE: To obtain a ferroelectric thin-film constitution body having a ferroelrctric thin film having the properly arranged c-axis direction perpendicular to the surface of a substrate regardless of the kind thereof even without using a conventional expensive MgO single crystal substrate in relation to a ferroelectric thin-film constitution body used in, e.g. a pyroelectric type infrared detecting element, an actuator or a nonvolatile and nondestructive memory. CONSTITUTION: This ferroelectric thin-film constitution body is obtained by forming an oxide thin film of a Bi-based layer perovskite type crystal structure on a substrate so as to properly arrange the (c)-axis of the crystal axis in the direction perpendicular to the substrate surface and further forming a ferroelectric thin film having the perovskite type crystal structure represented by the general formula ABO3 (A denotes one or more of Bi, Pb, Ba, Sr, Ca, Na, K and rare earth elements; B denotes one or more of Ti, Nb, Ta, W, Mo, Fe, Co, Cr and Zr) on the resultant oxide thin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric thin film structure for use in, for example, a pyroelectric infrared detecting element, an actuator, a non-volatile and non-destructive memory.

[0002]

BACKGROUND ART Generally Ferroelectrics electric field also exists spontaneous polarization P _S without a substance capable of reversing its direction by an external electric field, a pyroelectric type infrared detection element, an actuator, a non-volatile Moreover, it is widely applied to non-destructive memory devices and the like.

For example, a pyroelectric infrared device utilizes a change in spontaneous polarization with temperature, and can maximize the output when the spontaneous polarization in a substance is aligned in one direction. However, most of the infrared detectors currently in practical use are made of polycrystalline ceramics, and the directions of the crystal axes are not aligned, so even if polarization treatment is performed, the direction of spontaneous polarization must be perfectly aligned. I can't.

In recent years, there has been an increasing demand for miniaturization of electronic parts, and in order to achieve this, the use of a ferroelectric material in the form of a thin film is drawing attention. Also in that case, the spontaneous polarization P
_A ferroelectric thin film in which the _S directions are aligned in one direction is considered effective. For example, PbTiO ₃ whose crystal system is tetragonal,
A typical ferroelectric substance such as Pb (Zr, Ti) O ₃ or (Pb, La) TiO ₃ has a spontaneous polarization direction in the c-axis direction of the crystal, and therefore has a crystal orientation perpendicular to the substrate surface. The maximum output can be obtained by aligning the c-axes of.

As a conventional example for producing the ferroelectric thin film as described above, for example, as described in JP-A-58-186105, M cleaved along the {100} plane is disclosed.
An example of the ferroelectric thin film having the chemical composition as described above is manufactured by epitaxially growing the surface of a base substrate of a gO single crystal substrate. The lattice on the {100} plane of the MgO single crystal as described above is {10} of the ferroelectric substance having the above composition.
The substrate is 550-6 because it has a good match with the lattice on the 0} plane.
An epitaxial film can be formed by sputtering or CVD film formation while heating at 50 ° C. The ferroelectric thin film having the above composition produced in this manner is a thin film in which the c-axis is aligned in the direction perpendicular to the substrate surface, and has excellent characteristics.

[0006]

However, since the MgO single crystal substrate as described above is expensive, a ferroelectric thin film structure manufactured by using the above substrate and further manufactured from the structure. There has been a problem that the electronic components and electronic devices to be used become expensive.

The present invention has been proposed in view of the above problems, and the c-axis is perpendicular to the substrate surface without using the above MgO single crystal substrate and regardless of the type of the substrate. It is an object of the present invention to provide a ferroelectric thin film structure having a ferroelectric thin film having the same direction.

[0008]

In order to achieve the above object, the ferroelectric thin film structure according to the present invention has the following structure.

That is, an oxide thin film having a Bi-based layered perovskite crystal structure is formed on a substrate so that the c-axes of its crystal axes are aligned in the direction perpendicular to the substrate surface, and further on the oxide thin film. A ferroelectric thin film having a perovskite type crystal structure represented by the general formula of ABO ₃ is formed. However, in the above general formula, A = Bi, Pb, Ba, Sr, Ca, Na, K, one or more kinds of rare earth elements B = Ti, Nb, Ta, W, Mo, Fe, Co, Cr,
One or more of Zr

As the Bi-based layered perovskite type crystal structure oxide, for example, one represented by the following chemical formula is used. (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ^2- However, A = Bi, Pb, Ba, Sr, Ca, Na, K, one or more of rare earth elements B = Ti, Nb, Ta, W, Mo, Fe, Co, Cr One or more kinds m = 1, 2, 3, 4, 5

[0011]

As described above, as the ferroelectric thin film, for example, PbTiO ₃ , Pb (Zr, Ti) O ₃ , (Pb,
When a thin film of La) TiO ₃ is used, if the crystal orientation is aligned with the c-axis, the directions of spontaneous polarization are aligned, and if it is used for a pyroelectric infrared detection element that utilizes the temperature change of spontaneous polarization, the maximum It is convenient because it produces output.

The compound having a Bi-based layered perovskite structure has a low symmetric structure and is characterized in that crystals easily grow in the a-axis and b-axis directions of the crystal axis. When the compound having the Bi-based layered perovskite structure is formed on the substrate, the a-axis or the b-axis is easily formed in the substrate surface direction without forming the lattice matching with the substrate, and the c-axis is formed in the direction perpendicular to the substrate surface. It is easy to take a film structure like that.

On the other hand, the lattice on the ab plane of the Bi-based layered perovskite structure compound and PbTiO ₃ , Pb (Zr, Ti) O ₃ , (Pb, L of the perovskite type ABO ₃ structure).
a) Since it has good compatibility with the lattice on the ab plane of TiO ₃ ,
If a thin film of these compositions is formed on the c-axis oriented film of the Bi-based layered perovskite structure compound while having such a lattice matching property, the c-axis oriented state is likely to occur.

Therefore, PbTiO ₃ , which has c-axis orientation and excellent characteristics, without using an expensive MgO single crystal substrate,
It is possible to produce a ferroelectric thin film structure having a film of Pb (Zr, Ti) O ₃ , (Pb, La) TiO _3, or the like.

[0015]

EXAMPLE A ferroelectric thin film structure according to the present invention will be described below.
A specific description will be given based on examples.

[Example] In the following examples, a ferroelectric thin film structure was produced by a high frequency sputtering method. First, in Example 1, a Bi ₄ Ti ₃ O ₁₂ thin film was formed on a substrate by sputtering as an oxide thin film having a Bi-based layered perovskite type crystal structure. B as the target material
i ₄ Ti ₃ O ₁₂ powder and 20 mol% B based on this powder
A powder mixed with i ₂ O ₃ was used, and the powder was spread on a target dish made of oxygen-free copper and pressed while flattening the surface to obtain a target. Atmosphere gas for sputtering is Ar
90% and O ₂ 10% mixed gas, total pressure 1P
a.

Corning 7059 glass was used as the substrate, and this was fixed to a substrate holder, the distance from the target was set to 10 cm, and a thin film having a thickness of 0.5 μm was formed while heating the substrate to 650 ° C. Structural analysis of this thin film by X-ray diffractometry and composition analysis by ICP emission spectrometry confirmed that the resulting film was Bi ₄ Ti ₃ O ₁₂ strongly oriented in the c-axis. .

Next, a 0.1 μm platinum film was formed as a lower electrode on the Bi ₄ Ti ₃ O ₁₂ film by a high frequency sputtering method. A platinum plate target was used for the sputtering, the distance between the target and the substrate was 10 cm, and the substrate was 60
The heating was performed at 0 ° C. and the total pressure was 0.5 Pa in an Ar gas atmosphere.

Further, a PbTiO ₃ thin film was formed on the above lower electrode under the following conditions by sputtering. A powder of PbTiO ₃ mixed with 20 mol% of PbO was used as the target material, and the powder was spread on a target dish made of oxygen-free copper and the surface was flatly pressed to form a target. The sputtering atmosphere was a mixed gas of 90% Ar and 10% O _{2 at} a total pressure of 1 Pa, and the substrate was heated to 620 ° C. to form a PbTiO ₃ thin film having a thickness of 1.0 μm.

When the crystal structure and composition of the thin film obtained as described above were examined by X-ray diffraction measurement and ICP emission spectrometry, it was found that a PbTiO ₃ film having a strong c-axis orientation was produced. all right. The c-axis orientation rate α (%) was calculated from the X-ray diffraction peak intensity using the following formula, and was found to be 95%. α = {I ₀₀₁ / (I ₀₀₁ + I ₁₀₀ + I ₁₀₁ + I ₁₁₀ + I
₁₁₁ )} × 100

Next, as Examples 2 to 9, ferroelectric films having various compositions were prepared by changing the compositions of the substrate and the Bi-based layered perovskite type crystal structure oxide in the same manner as in Example 1 above. Then, their c-axis orientation rates were investigated. The above results are summarized in Table 1 below.

[0022]

[Comparative Example] As a comparative example to the above example, a ferroelectric thin film was formed on a Corning 7059 glass without forming a Bi-based layered perovskite oxide as a base film, and a conventional {100}. Table 2 below shows the c-axis orientation ratio when a ferroelectric thin film is formed on a MgO single crystal substrate cleaved at the plane.

[0024]

As shown in Comparative Example 1 in Table 2 above, Corning 7059 glass was used as a substrate, and a ferroelectric thin film was formed on the substrate without forming a Bi-based layered perovskite oxide as an underlayer. The c-axis orientation ratio in the case of forming a film is very low. A ferroelectric thin film having a high orientation rate can be formed. Moreover, the c-axis orientation rate α of each Example is equal to or higher than that when the conventional expensive MgO single crystal substrate shown in Comparative Example 2 of Table 2 above is used, and the orientation rate is extremely high. It is possible to form a good ferroelectric thin film.

As a result, the ferroelectric thin film structure according to the present invention can be used as a ferroelectric element having good characteristics which is useful for a pyroelectric infrared detecting element, an actuator and the like.
In this case, the electrodes are provided on both sides of the ferroelectric thin film,
After the lower electrode and the ferroelectric thin film are sequentially formed on the oxide thin film having the Bi-based layered perovskite type crystal structure as in the above embodiment, the upper electrode is formed on the ferroelectric thin film.
Alternatively, the upper electrode may be formed on the ferroelectric thin film and the substrate may be used as the lower electrode. In that case, the ferroelectric thin film is formed on the above-mentioned oxide thin film without forming the lower electrode as in the embodiment, and even in such a case, the ferroelectric thin film having a high orientation rate is used. Of course, a body thin film can be formed.

[0027]

As described in detail above, in the ferroelectric thin film structure according to the present invention, the oxide thin film of the Bi-based layered perovskite type crystal structure has its crystal axis c-axis aligned in the direction perpendicular to the substrate. Since a ferroelectric thin film having a perovskite type crystal structure represented by the general formula ABO ₃ is further arranged on the substrate, a MgO single crystal substrate which is expensive as a base substrate is conventionally used. , A structure having a ferroelectric thin film having a c-axis orientation which is equal to or better than the case of using the MgO single crystal substrate can be obtained by using another inexpensive substrate. As a result, there is an effect that an electronic component such as a pyroelectric infrared detecting element, an actuator, or a nonvolatile and nondestructive memory can be manufactured at low cost.

Claims (4)

[Claims] 1. An oxide thin film having a Bi-based layered perovskite crystal structure is formed on a substrate such that the c-axes of its crystal axes are aligned in the direction perpendicular to the substrate surface, and further on the oxide thin film. A ferroelectric thin film structure characterized in that a ferroelectric thin film having a perovskite crystal structure represented by the general formula of ABO ₃ is formed. However, in the above general formula, A = Bi, Pb, Ba, Sr, Ca, Na, K, one or more kinds of rare earth elements B = Ti, Nb, Ta, W, Mo, Fe, Co, Cr,
One or more of Zr 2. The ferroelectric thin film structure according to claim 1, wherein the oxide of the Bi-based layered perovskite type crystal structure has the following chemical formula. (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ^2- However, A = Bi, Pb, Ba, Sr, Ca, Na, K, one or more of rare earth elements B = Ti, Nb, Ta, W, Mo, Fe, Co, Cr One or more kinds m = 1, 2, 3, 4, 5 3. The ferroelectric thin film structure according to claim 1, wherein an upper electrode is formed on the ferroelectric thin film and a substrate serves as a lower electrode. 4. A lower electrode is formed between the oxide thin film having the Bi-based layered perovskite crystal structure and the ferroelectric thin film, and an upper electrode is formed on the ferroelectric thin film. 2. The ferroelectric thin film structure described in 2.