JPH09260516A - Ferroelectric thin film coated substrate and capacitor structure element using the same - Google Patents

Abstract

The present invention relates to a ferroelectric thin film coated substrate having a dense and flat thin film surface, excellent leak current characteristics, and a sufficiently large residual spontaneous polarization, and a capacitor structure element using the same. Is intended to provide. Bi ₄ T is formed on a substrate 1 made of silicon or the like.
In a ferroelectric thin film coated substrate formed by forming a ferroelectric thin film 5 made of i ₃ O ₁₂ etc., an overcoat layer 6 made of TiO ₂ etc. for covering the ferroelectric thin film 5 is arranged on the ferroelectric thin film 5. And configure.

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 used for a ferroelectric memory element, a pyroelectric sensor element, a piezoelectric element, a ferroelectric thin film coated substrate, a capacitor structure element, and a ferroelectric thin film. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art Ferroelectric materials have many functions such as spontaneous polarization, high permittivity, electro-optical effect, piezoelectric effect and pyroelectric effect, so that they are widely used in capacitors, oscillators, optical modulators or infrared sensors. Applied to the development of various devices. However, in the past, these applications have been done in the form of single crystals or ceramics.

On the other hand, with the progress of thin film forming technology, high quality ferroelectric thin films can now be obtained, and there are expectations for applications that were not available in the past. Especially recently
By combining with a semiconductor memory device such as RAM,
Ferroelectric non-volatile memory (FRAM) that operates at high density and at high speed has been actively developed. A ferroelectric memory is a non-volatile memory that does not require a backup power supply and uses a ferroelectric characteristic (spontaneous polarization effect) of a ferroelectric. For the development of such a device, a material having properties such as a large residual spontaneous polarization (Pr), a small coercive electric field (Ec), a low leak current, and excellent resistance to repeated polarization inversion is required. Furthermore, in order to reduce the operating voltage and adapt to the semiconductor fine processing process, it is desired to realize the above characteristics with a thin film having a film thickness of 200 nm or less.

Currently, for the purpose of application to FRAM and the like,
PbTiO ₃ , Pb (Zr _1-x Ti _x ) O ₃ (PZT), P
Thin film formation of an oxide ferroelectric having a perovskite structure such as LZT is performed by a sputtering method, a vapor deposition method, a sol-gel method,
Attempts have been made by thin film forming methods such as MOD and MOCVD.

Of the above-mentioned ferroelectric materials, PZT is currently the most intensively studied, and for example, the residual spontaneous polarization Pr is 10 μC / cm ² to 26 μC / cm ^2.
The one with a large value is also obtained. However,
Since Pb having a high vapor pressure is included, the film composition is likely to change during film formation or heat treatment, pinholes are generated, and the low dielectric constant layer is generated due to the reaction between the base electrode Pt and Pb. As the film thickness is reduced, there is a problem in that leakage current and deterioration of polarization inversion repetition resistance occur. Therefore, development of another material having excellent ferroelectric characteristics and polarization reversal resistance is desired. Further, when considering application to an integrated device, it is necessary to have a dense and surface smooth surface of a thin film that can be applied to fine processing.

On the other hand, bismuth titanate (Bi ₄₎ having a layered perovskite structure is used as an oxide ferroelectric containing no Pb which adversely affects the leak current and the resistance to polarization inversion.
Ti ₃ O ₁₂ ). The ferroelectric property of the single crystal is a
Residual spontaneous polarization Pr = 50 μC / cm ^{2 in} the axial direction, coercive electric field Ec = 50 kV / cm, residual spontaneous polarization Pr = in the c-axis direction
It has excellent characteristics of 4 μC / cm ² and coercive electric field Ec = 4 kV / cm. Therefore, this Bi ₄ Ti ₃ O
_In order to apply the large spontaneous polarization of _{12 to} a ferroelectric non-volatile memory, it is desirable to have many a-axis components of the crystal in the direction perpendicular to the substrate.

Bi ₄ Ti ₃ O ₁₂ has been attempted to be a thin film by MOCVD method or sol-gel method, but most of them are c-axis oriented films with small spontaneous polarization. Further, in forming a ferroelectric thin film using a conventional sol-gel method, heat treatment at 650 ° C. or higher is required to obtain good ferroelectric properties, and further, a crystal grain having a film surface morphology of about 0.5 μm. Therefore, it is difficult to apply it to a highly integrated device that requires fine processing. On the other hand, in forming a ferroelectric thin film by the MOCVD method, a c-axis oriented Bi ₄ Ti ₃ O ₁₂ thin film is used at a substrate temperature of 600 ° C. or higher,
Although it is formed on the t electrode layer / SiO ₂ insulating film / Si substrate or Pt substrate, these substrates cannot be applied to the actual device structure as they are. That is, Pt / Ti /
Like the SiO ₂ / Si substrate, the Pt electrode layer and the S below it
An adhesive layer such as a Ti film is necessary to secure the adhesive strength with the iO ₂ film. However, when a Bi ₄ Ti ₃ O ₁₂ thin film is formed on the Pt electrode substrate provided with such an adhesive layer by the MOCVD method, the film surface morphology is 0.
It has been reported that a coarse crystal grain of about 5 μm and a paraelectric pyrochlore phase (Bi ₂ Ti ₂ O ₇ ) are easily generated (Jpn.J.Appl.Phys., 32, 1993, pp. .408
6 and J. Ceramic Soc. Japan, 102, 1994, pp. 512).

If the film surface morphology is composed of coarse crystal grains, it cannot be applied to a highly integrated device that requires fine processing, and a thin film thickness causes pinholes.
This will cause the generation of leakage current. Therefore, with such a conventional technique, it is difficult to realize a ferroelectric thin film having a good ferroelectric property with a thin film thickness of 200 nm or less.

[0009]

As described above, according to the above-mentioned prior art, in order to apply the ferroelectric thin film to the highly integrated device, the fineness of the thin film surface required for fine processing and low leakage current, However, there is a problem in that none of those satisfying various conditions such as flatness, large remanent polarization and low temperature film forming process has been obtained.

The present invention has been made to solve the above-mentioned problems, and the thin film surface is dense and flat,
It is an object of the present invention to provide a ferroelectric thin film-coated substrate which is excellent in leak current characteristics and which can exhibit a sufficiently large residual spontaneous polarization by a low temperature process, and a capacitor structure element using the same.

[0011]

In order to solve the above problems, according to the present invention, in a ferroelectric thin film coated substrate having a ferroelectric thin film formed on a substrate, the ferroelectric thin film is formed on the ferroelectric thin film. An overcoat layer is provided to cover the thin film.

Further, in the present invention, in the above-mentioned ferroelectric thin film coated substrate, the overcoat layer is made of a metal oxide.

Further, according to the present invention, in the above-mentioned ferroelectric thin film coated substrate, the overcoat layer is made of titanium oxide.

Further, in the present invention, in the above-mentioned ferroelectric thin film coated substrate, the ferroelectric thin film is made of bismuth titanate and the overcoat layer is made of titanium oxide.

Further, according to the present invention, in the above-mentioned ferroelectric thin film coated substrate, a buffer layer is provided between the substrate and the ferroelectric thin film.

Further, in the present invention, in the above-mentioned ferroelectric thin film coated substrate, the overcoat layer and the buffer layer are made of metal oxide.

Further, in the present invention, in the above-mentioned ferroelectric thin film coated substrate, the overcoat layer and the buffer layer are made of titanium oxide.

Further, in the present invention, in the above-mentioned ferroelectric thin film coated substrate, the ferroelectric thin film is made of bismuth titanate, and the overcoat layer and the buffer layer are made of titanium oxide.

Further, in the present invention, using the above-mentioned ferroelectric thin film-coated substrate, the first conductive electrode is disposed between the substrate and the ferroelectric thin film, and the second conductive electrode is provided on the overcoat layer. A capacitor structure element is formed by disposing conductive electrodes.

In the ferroelectric thin film coated substrate of the present invention, in the ferroelectric thin film coated substrate in which the ferroelectric thin film is formed on the substrate, an overcoat layer covering the ferroelectric thin film on the ferroelectric thin film. Since the ferroelectric thin film is composed of coarse particles and the surface is rough, the irregularities on the ferroelectric thin film surface are filled with the overcoat layer on the ferroelectric thin film, resulting in a dense and smooth surface. A thin film can be obtained.
That is, conventionally, with the improvement of crystallinity, there has been a problem of coarsening of crystal grains and increase of leak current due to roughness of the film surface. However, according to the ferroelectric thin film-coated substrate of the present invention, the crystallinity is improved. That is, it is possible to obtain a thin film that is excellent in terms of density and has a smooth surface.

Further, in the ferroelectric thin film-coated substrate of the present invention, a buffer layer is further provided between the substrate and the ferroelectric thin film, and the ferroelectric thin film is sandwiched between metal oxide layers of the same kind. Therefore, the occurrence of asymmetry of the ferroelectric hysteresis loop due to the multilayer structure of the film can be prevented, and a hysteresis loop with good symmetry can be obtained. That is, by adopting a structure in which a ferroelectric thin film is sandwiched between two layers of the same material, a structure of a film with good vertical symmetry is realized, and the asymmetry of the hysteresis loop due to the asymmetry of the film structure is eliminated. It can be prevented.

[0022]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.
FIG. 3 is a diagram showing a structure of a capacitor structure element composed of a ferroelectric thin film coated substrate which is the embodiment of FIG. As shown in FIG. 1, this capacitor structure element is made of silicon (Si).
A silicon oxide (SiO ₂ ) layer 2, an adhesive layer 3, a lower electrode 4, a ferroelectric thin film 5, an overcoat layer 6, and an upper electrode 7 are sequentially formed on a substrate 1.

In the first embodiment, a silicon single crystal wafer is used as the silicon substrate 1, and a silicon oxide thin film obtained by thermally oxidizing the surface of the silicon single crystal wafer is used as the SiO ₂ layer 2. Further, a tantalum (Ta) thin film as the adhesive layer 3, a platinum (Pt) thin film as the lower electrode 4, and a bismuth titanate thin film (Bi ₄ Ti ₃ O ₁₂ thin film) as the ferroelectric thin film 5 are overcoated. A titanium oxide (TiO ₂ ) thin film was used as the layer 6, and a platinum (Pt) thin film was used as the upper electrode 7.

Next, a method of manufacturing the ferroelectric thin film coated substrate of the first embodiment shown in FIG. 1 will be described. First,
Fabrication of a Pt / Ta / SiO ₂ / Si substrate will be described. A silicon single crystal wafer (10
The film thickness of 200 nm is obtained by thermally oxidizing the surface of (0) plane.
Forming a SiO ₂ layer 2. Then, the adhesive layer 3 T
The thin film a was formed with a thickness of 30 nm, and the Pt thin film as the lower electrode layer 4 was formed with a thickness of 200 nm by sputtering.

Here, these materials and film thicknesses are not limited to those in this embodiment, and a polycrystalline silicon substrate, a GaAs substrate or the like may be used instead of the silicon single crystal substrate. The adhesive layer prevents peeling of the film due to the difference in thermal expansion coefficient between the substrate and the lower electrode layer during film formation, and the film thickness may be such that peeling of the film can be prevented. As the material, titanium (Ti) or the like can be used in addition to Ta. In the present embodiment, Ti and Pt are used.
It is preferable to use Ta because it forms an alloy with.
The SiO ₂ layer used for the insulating layer does not have to be formed by thermal oxidation, and may be formed by sputtering, vacuum deposition,
A SiO ₂ film, a silicon nitride film, or the like formed by the MOCVD method or the like can be used as long as the material and the film thickness have sufficient insulating properties.

Also for the lower electrode, the film thickness is sufficient as long as it can sufficiently function as an electrode layer, and the material is not limited to Pt, and a conductive material used for a normal electrode material may be used. It can be appropriately selected in relation to other thin films. Further, the film forming method is not limited to the silicon thermal oxidation or the sputtering method, and may be performed by using a normal thin film forming technique such as a vacuum vapor deposition method. Further, the substrate structure is not limited to the above.

Next, the Pt / T thus produced
On the a / SiO ₂ / Si substrate, the ferroelectric thin film Bi ₄ Ti ₃ O ₁₂ ferroelectric thin film and the overcoat layer 6 are formed.
TiO ₂ thin film was sequentially formed by MOCVD. Table 1 shows the film forming conditions for the Bi ₄ Ti ₃ O ₁₂ ferroelectric thin film.

[0028]

[Table 1]

The Bi ₄ Ti ₃ O ₁₂ thin film was formed by using triorthotolylbilyl bismuth (Bi (o-C ₇ H ₇ ) ₃ ) as the Bi raw material and titanium isopropoxide as the Ti raw material, as shown in Table 1. (Ti (i-OC ₃ H ₇ ) ₄ ) is used to heat and vaporize these raw materials to the raw material temperatures shown in Table 1 (Bi raw material 160 ° C., Ti raw material 50).
C.) and an argon (Ar) gas as a carrier gas and an oxygen (O ₂ ) gas as a reaction gas were supplied into the film forming chamber. Here, the flow rate at the time of supplying Ar gas was 200 sccm for the Bi raw material and 100 sccm for the Ti raw material, and the flow rate at the time of supplying O ₂ gas was 1000 sccm. Note that, in this film formation step, if the degree of vacuum in the film formation chamber is 10 Torr or more, a gas phase reaction easily occurs. Under these conditions, the substrate temperature was set to 600 ° C., and a Bi ₄ Ti ₃ O ₁₂ thin film having a film thickness of 100 nm was formed for a film forming time of about 30 minutes.

Subsequently, the substrate temperature is set to 400 ° C.,
Titanium isopropoxide (Ti (i-
OC ₃ H ₇ ) ₄ ), this raw material was heated and vaporized to 50 ° C., and supplied with Ar carrier gas (flow rate 50 sccm),
A titanium oxide overcoat layer having a film thickness of 5 nm was formed in a film forming time of about 2 minutes. Also in this film forming process, the degree of vacuum in the film forming chamber was set to 5 Torr. In addition, Bi ₄ T
The total film thickness of the i ₃ O ₁₂ thin film and the TiO ₂ overcoat layer is 105 nm.

Here, the thickness of the overcoat layer is set so that a sufficient voltage is applied to the ferroelectric thin film.
It is desirable to be as thin as possible, and a certain thickness is required to cover the surface irregularities of the ferroelectric thin film. When this point was examined, good results were obtained when the film thickness of the overcoat layer was 2 to 7 nm.

The surface morphology of the Bi ₄ Ti ₃ O ₁₂ ferroelectric thin film with an overcoat layer formed as described above was observed by SEM (scanning electron microscope), and the result is shown in FIG. According to FIG. 2, it is understood that the surface of the thin film obtained by this embodiment is composed of fine crystal grains, and a dense and smooth thin film is obtained.

The results of evaluating the crystallinity of this thin film by X-ray diffraction are shown in FIG. In FIG. 3, (00
l) (l is an integer) represents a diffraction peak due to the c-axis orientation component of Bi ₄ Ti ₃ O ₁₂ (layered perovskite phase), and (11
7) is a diffraction peak due to the (117) orientation component containing the a-axis component of Bi ₄ Ti ₃ O ₁₂ (layered perovskite phase), and the obtained thin film has a strong c-axis orientation Bi ₄ Ti ₃ O ₁₂
It can be seen that it is.

As a comparative example, the same P as in the first embodiment is used.
Using a t / Ta / SiO ₂ / Si substrate, a Bi ₄ Ti ₃ O ₁₂ thin film (film thickness 105 nm) without an overcoat layer was formed by MOCVD under the same conditions as in the first embodiment. As a result of SEM observation of the surface morphology of the Bi ₄ Ti ₃ O ₁₂ thin film of this comparative example, as shown in FIG. 4, this thin film was composed of coarse particles, and the surface unevenness was severe. From this, it was found that the overcoat layer of the first embodiment fills the gaps of the irregularities on the surface of the Bi ₄ Ti ₃ O ₁₂ thin film, and thus a thin film having a precise surface shape and a flat surface can be manufactured.

On the TiO ₂ overcoat layer of the first embodiment, a Pt electrode (100 μmφ) was formed as an upper electrode by a vacuum evaporation method, and the fabrication of the capacitor structure element as shown in FIG. 1 was completed. .

Next, FIG. 5 shows the result of measuring the leak current characteristics (the applied voltage dependence of the leak current density) of the capacitor structure element of the first embodiment. From FIG. 5, in this capacitor structure element, for example, a value of leak current density Il = 8 × 10 ⁻⁷ A / cm ² was obtained at an applied voltage of 3V. Further, as a result of measuring the ferroelectric characteristics of this capacitor structure element, a clear hysteresis loop as shown in FIG. 6 was obtained, and at the time of applying 3 V, the residual spontaneous polarization Pr = 5 μC / cm ² , the coercive electric field Ec. = 70 kV / c
A value of m was obtained.

Next, as a second embodiment, as shown in FIG. 7, a ferroelectric thin film in which a buffer layer 8 is provided between the lower electrode 4 and the ferroelectric thin film 5 of the first embodiment. A capacitor structure element composed of a coated substrate will be described.

Regarding the fabrication of the second embodiment, a Pt / Ta / SiO ₂ / Si substrate similar to that of the first embodiment is used, and a titanium oxide (TiO ₂ ) buffer layer is formed thereon by MOCVD. Was formed. The film forming conditions at this time were such that the substrate temperature was set to 400 ° C., titanium isopropoxide (Ti (i-OC ₃ H ₇ ) ₄ ) was used as a Ti raw material, and this raw material was heated and vaporized to 50 ° C. Supplying with a carrier gas (flow rate 50 sccm), a titanium oxide buffer layer having a film thickness of 5 nm was formed in a film forming time of about 2 minutes. In this film forming process, the degree of vacuum in the film forming chamber is 10 Tor.
If it is more than r, the gas phase reaction is likely to occur, so 5T
orr.

The thickness of the buffer layer is preferably as thin as possible in order to apply a sufficient voltage to the ferroelectric thin film, like the overcoat layer described in the first embodiment. It was confirmed that good results can be obtained in the range of 1 to 10 nm in order to fulfill the function as the buffer layer.

This TiO_TwoAbove the buffer layer, the first
Similar to the embodiment of_FourTi_ThreeO_{1 Two}Ferroelectric thin film and
TiO_TwoOvercoat layers are sequentially formed by MOCVD method.
Formed. Note that Bi_FourTi_ThreeO₁₂Thin film and TiO_TwoOh
The film thickness of each bar coat layer is the same as in the first embodiment.
Is the same as_TwoBuffer layer, Bi_FourTi_ThreeO
₁₂, And TiO_TwoThe total film thickness of the overcoat layer is
It is 110 nm.

FIG. 8 shows the results of SEM observation of the surface morphology of the thin film thus produced. According to FIG. 8, Bi ₄ with an overcoat layer of the present embodiment is
It can be seen that the Ti ₃ O ₁₂ thin film is a dense and smooth surface composed of grains having a grain size of 0.1 μm. Further, it can be seen that the crystal grains forming the thin film are smaller in the second embodiment than in the first embodiment. In other words, by forming a structure in which the buffer layer and the overcoat layer are sandwiched between the upper and lower sides of the Bi ₄ Ti ₃ O ₁₂ thin film, it is possible to obtain a dense film with smaller crystal grains.

FIG. 9 shows the result of evaluation by X-ray diffraction of the crystallinity of the Bi ₄ Ti ₃ O ₁₂ thin film with an overcoat layer according to the second embodiment. It can be seen from FIG. 9 that the obtained thin film has a larger (117) reflection intensity including the a-axis component than that of the first embodiment.

Next, a Pt upper electrode is formed on the Bi ₄ Ti ₃ O ₁₂ thin film with an overcoat layer of the second embodiment in the same manner as in the first embodiment, and the leakage current characteristic (leak current FIG. 10 shows the result of measurement of the dependency of the density on the applied voltage).
Shown in From FIG. 10, in this capacitor structure element, for example, when the applied voltage is 3 V, the leakage current density Il = 6 × 10 ⁻⁸
A small good value of A / cm ² was obtained. further,
As a result of measuring the ferroelectric characteristics of this capacitor structure element, a clear hysteresis loop as shown in FIG. 11 was obtained, and the residual spontaneous polarization Pr = 7.
Values of 5 μC / cm ² and coercive electric field Ec = 130 kV / cm were obtained. Comparing the hysteresis loop of FIG. 11 with that of the first embodiment of FIG. 6, it can be seen that not only the Pr value is increased, but also the symmetry is improved. This is because the ferroelectric thin film has a structure in which the upper and lower sides of the ferroelectric thin film are sandwiched between the buffer layer and the overcoat layer, so that the film structure with good symmetry can be realized.
This is because it was possible to prevent the asymmetry of the hysteresis loop due to the asymmetry of the film structure.

In the above embodiment, Pt is used as the substrate.
Although the capacitor structure element using the / Ta / SiO ₂ / Si substrate is used, the invention is not limited to this. For example,
An integrated circuit is formed on a Si or GaAs substrate, the surface of the integrated circuit is covered with an interlayer insulating film such as silicon oxide or silicon nitride, and the integrated circuit is formed through a contact hole formed in a part of the interlayer insulating film. An electrode layer electrically connected to the above element may be formed on the interlayer insulating film, and the ferroelectric thin film of the present invention may be formed on the electrode layer. That is, the present invention is an integrated circuit element electrically connected to the elements of the integrated circuit including the capacitor structure and the transistor structure of the above embodiments, other ferroelectric memory elements, pyroelectric sensor elements, piezoelectric elements, etc. It is applicable to various highly integrated devices.

In the above embodiment, titanium oxide was used as the material for the overcoat layer, but the material is not limited to this, and metal oxide is preferable.
Specific examples thereof include tantalum oxide, niobium oxide, strontium titanate, barium titanate, zircon oxide, aluminum oxide, bismuth oxide, yttrium oxide and hafnium oxide. Further, as the material of the buffer layer, titanium oxide was used in the above embodiment, but the material is not limited to this, and metal oxide is preferable, and specifically, tantalum oxide, niobium oxide, and titanium are used. Examples thereof include strontium acid salt, barium titanate, zircon oxide, aluminum oxide, bismuth oxide, yttrium oxide, and hafnium oxide.

[0046]

As described above, according to the present invention, the film structure of the ferroelectric thin film coated with the overcoat layer allows the smoothness and the denseness to be achieved even at an extremely thin film thickness of about 100 μm. Since it is possible to obtain an excellent ferroelectric thin film coated with an overcoat layer, it is possible to significantly improve the leakage current characteristics and realize excellent ferroelectric characteristics.

Furthermore, according to the present invention, by providing the buffer layer, the asymmetry of the hysteresis loop can be improved, and it is possible to provide a high-quality ferroelectric thin film coated substrate and various electronic devices. Becomes

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a capacitor structure element including a ferroelectric thin film-coated substrate according to a first embodiment.

FIG. 2 is a Bi ₄ with an overcoat layer according to the first embodiment.
₃ is a micrograph showing the result of SEM observation of the surface of a Ti ₃ O ₁₂ ferroelectric thin film.

FIG. 3 is a Bi ₄ with an overcoat layer according to the first embodiment.
It is a diagram showing the observation result by X-ray diffraction of the Ti ₃ O ₁₂ ferroelectric thin film.

FIG. 4 Bi ₄ Ti ₃ O without overcoat layer of Comparative Example
₁₂ is a micrograph showing the result of SEM observation of the thin film surface.

FIG. 5 is a diagram showing an applied voltage dependency of a leak current density Il of the capacitor structure element of the first embodiment.

FIG. 6 is a diagram showing a ferroelectric hysteresis loop of the capacitor structure element according to the first embodiment.

FIG. 7 is a schematic cross-sectional view showing the structure of a capacitor structure element including a ferroelectric thin film-coated substrate of the second embodiment.

FIG. 8 is a Bi ₄ with overcoat layer according to the second embodiment.
₃ is a micrograph showing the result of SEM observation of the surface of a Ti ₃ O ₁₂ ferroelectric thin film.

FIG. 9 is a Bi ₄ with overcoat layer according to the second embodiment.
It is a diagram showing the observation result by X-ray diffraction of the Ti ₃ O ₁₂ ferroelectric thin film.

FIG. 10 is a diagram showing an applied voltage dependency of a leak current density Il of the capacitor structure element of the second embodiment.

FIG. 11 is a diagram showing a ferroelectric hysteresis loop of the capacitor structure element according to the second embodiment.

[Explanation of symbols]

 1 Silicon Substrate 2 Silicon Oxide Layer 3 Adhesion Layer 4 Lower Electrode 5 Ferroelectric Thin Film 6 Overcoat Layer 7 Upper Electrode 8 Buffer Layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 27/04 H01L 21/314 A 21/822 27/04 C 27/108 27/10 651 21 / 8242 41/08 C 37/02 41/18 101D 41/09 101Z 41/187 41/18 49/02 // H01L 21/314

Claims (9)

[Claims] 1. A ferroelectric thin film coated substrate comprising a ferroelectric thin film formed on a substrate, wherein an overcoat layer covering the ferroelectric thin film is arranged on the ferroelectric thin film. Ferroelectric thin film coated substrate. 2. The ferroelectric thin film-coated substrate according to claim 1, wherein the overcoat layer is made of a metal oxide. 3. The ferroelectric thin film-coated substrate according to claim 2, wherein the overcoat layer is made of titanium oxide. 4. The ferroelectric thin film coated substrate according to claim 3, wherein the ferroelectric thin film is made of bismuth titanate, and the overcoat layer is made of titanium oxide. 5. The ferroelectric thin film coated substrate according to claim 1, wherein a buffer layer is interposed between the substrate and the ferroelectric thin film. 6. The ferroelectric thin film-coated substrate according to claim 5, wherein the overcoat layer and the buffer layer are made of a metal oxide. 7. The ferroelectric thin film coated substrate according to claim 6, wherein the overcoat layer and the buffer layer are made of titanium oxide. 8. The ferroelectric thin film-coated substrate according to claim 7, wherein the ferroelectric thin film is made of bismuth titanate, and the overcoat layer and the buffer layer are made of titanium oxide. 9. A capacitor structure element using the ferroelectric thin film-coated substrate according to claim 1, wherein a first conductive film is provided between the substrate and the ferroelectric thin film. A conductive electrode is disposed, and a second conductive electrode is disposed on the overcoat layer.