JPH06260018A - Ferroelectric thin film element and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a ferroelectric thin film made of lead titanate, lead zirconate, or barium titanate crystal-oriented on a substrate made of glass, metal, or Si to be used for a pyroelectric infrared sensor, a piezoelectric-applied element, or an electrochemical element. CONSTITUTION:A ferroelectric thin film element is constituted of a substrate 1, a crystalline intermediate layer 2 formed on it, and a crystal-oriented ferroelectric thin film 3. The intermediate layer 2 has the misfit ratio within 15% to the ferroelectric thin film 3, the substrate 1 has the thermal expansion coefficient of 70X10<-7>/ deg.C, and the element has the ferroelectric substance thin film with good crystalline orientation. For example, a NaCl oxide thin film with (100) plane orientation is formed on a substrate by the plasma excited MO-CVD method using organometallic complex vapor as the raw material gas, and a ferroelectric thin film of perovskite type oxide PbTiO with (001) plane orientation is formed on it by sputtering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pyroelectric infrared detecting element,
The present invention relates to a dielectric thin film element used for a piezoelectric element, an electro-optical element, etc. and a method for manufacturing the same.

[0002]

2. Description of the Related Art Ferroelectric materials have a property that spontaneous polarization caused by permanent dipoles arranged in parallel or antiparallel in the substance itself is present even without an electric field, and it can reverse its direction by an external electric field. The substance of. Utilizing this property well, the ferroelectric material can be applied to various electronic parts such as a pyroelectric infrared detecting element, a piezoelectric element, an optical modulator using the electro-optical effect, and a non-volatile memory element.
As a typical ferroelectric material, an oxide having a perovskite crystal structure, for example, PbTiO ₃ , Pb _1-x La _x Ti
_{1-x / 4} O ₃ (PLT), PbZr _x Ti _1-x O ₃ (PZ
T) and BaTiO ₃ are especially famous.

By the way, in applications where changes in the spontaneous polarization P _s of a ferroelectric substance are taken out as an output, for example, in a pyroelectric infrared detecting element or a piezoelectric element, when P _{s of the} ferroelectric material is aligned in one direction. The largest output is obtained. In addition, many ferroelectrics have different physical properties, such as dielectric constant and sound velocity, depending on the direction of the crystal axis, and there is a demand for a technique for aligning the crystal axes in order to significantly improve the characteristics and realize a novel device. At present, most of the ferroelectric materials used for infrared detection elements and piezoelectric elements are polycrystalline porcelains, the crystal axes are not directional, and the spontaneous polarizations P _s are randomly arranged.

With the recent miniaturization of electronic components, it has been required to miniaturize the electronic components to which the above-mentioned ferroelectric material is applied, and the thinning of the ferroelectric is being advanced. In particular,
Research and development of epitaxial thin films and oriented thin films have become active.

The crystal axis of the ferroelectric substance largely depends on the substrate used for manufacturing. For example, PbTiO ₃ and PZT are <001 for the MgO single crystal substrate cleaved at (100).
>, And the <111> direction on the c-plane of sapphire (for example, J. Appl. Phy).
s. , Vol. 60, P. 361 (1986)).

[0006]

Since a single crystal such as MgO or sapphire is used for the underlying substrate, the structure of the ferroelectric thin film element and the electronic component element made using the same become expensive. was there. Further, since the epitaxial thin film and the oriented thin film do not grow directly on the Si substrate, it is not possible to realize integration with the signal processing device which greatly improves the device performance.

[0007]

[Means for Solving the Problems] A substrate, an intermediate layer formed on the substrate, and a ferroelectric thin film formed on the substrate are formed. Coefficient of thermal expansion up to the temperature during production is 70 × 10 ^-7 /
By using a material having a temperature of at least ℃, the misalignment of the lattice constant between the intermediate layer and the ferroelectric thin film within 15% at the temperature during the production of the ferroelectric thin film, thereby making the ferroelectric thin film <001. Orient in the> direction.

The substrate, the intermediate layer formed on the substrate, and the ferroelectric thin film formed on the substrate are formed, and the temperature of the substrate from room temperature to the temperature at the time of manufacturing the ferroelectric thin film is increased. With a coefficient of thermal expansion of 70 × 10 ⁻⁷ / ° C. or less, the misfit of the lattice constant between the intermediate layer and the ferroelectric thin film is 15% at the temperature during the preparation of the ferroelectric thin film.
Within this range, the ferroelectric substance is oriented in the <100> direction.

As a manufacturing method, an oxide thin film having a (100) -oriented NaCl-type crystal structure is formed on a substrate by a sputtering method or a plasma excited MO-CVD method using a vapor of an organic metal complex as a source gas. When a tetragonal perovskite type ferroelectric thin film is further formed thereon by a sputtering method or a plasma excited MO-CVD method, by using a substrate having a different coefficient of thermal expansion, the <001> direction or It is manufactured by forming a ferroelectric thin film oriented in the <100> direction.

[0010]

When the alignment film such as PbTiO ₃ which is a perovskite type oxide is formed by the sputtering method, the substrate temperature needs to be about 600 ° C. This fabrication temperature is PbTi
Since it is higher than the Curie point of O ₃ (490 ° C.), it undergoes a phase transition from a cubic system to a tetragonal system after completion of film formation. Therefore, it is presumed that the crystal orientation at the phase transition depends on the magnitude of the coefficient of thermal expansion of the substrate. As described above, PbTiO ₃ is <001> oriented on the MgO single crystal cleaved at (100). One major factor is considered to large thermal expansion coefficient of MgO (to 120 × 10 ^-7). In the cooling process, P
<001> axis of bTiO ₃ (coefficient of thermal expansion: −900 × 10
^-7 ) increases rapidly, and the <100> axis (coefficient of thermal expansion: 380
This is because × 10 ⁻⁷ ) decreases, and strain energy becomes smaller when the <001> axis is arranged perpendicularly to the substrate as the MgO substrate contracts. The present inventors have found that substrates having different coefficients of thermal expansion can be selected and the orientation of the ferroelectric thin film formed thereon can be controlled. However, for the epitaxial thin film and the oriented thin film, a base substrate having a small lattice misfit with the substrate at the manufacturing temperature is desirable.
<001> for PbTiO ₃ , PZT, BaTiO _3, etc.
The oxygen-oxygen distance in the azimuth shows a value around 4.0 angstrom. For example, one of them is Pb (Z
The oxygen-oxygen distance in the <001> orientation of r _{1 -x} Ti _x ) O ₃ shows a value between approximately 3.90 and 4.15 angstroms, while MgO in the <100> orientation has 4.21.
Angstrom. NiO with the same NaCl structure is 4.19 angstroms and the same NaCl
CoO of the structure is 4.26 angstroms, both of which have less misfit like MgO and are desirable as a base substrate.

Therefore, it is considered that an oriented ferroelectric thin film having good crystallinity can be realized by the magnitude of the coefficient of thermal expansion of the substrate through an intermediate layer having a small misfit with the ferroelectric thin film to be produced. Clarified.

Further, the inventors of the present invention can easily perform the vertical direction with respect to the substrate by the plasma-excited MO-CDV method using an organometallic complex such as metal acetylacetonate as a source gas, regardless of the underlying substrate. 100> N with the axis oriented
It has been found that various oxide thin films having an aCl crystal structure can be obtained. Using this method, nickel acetylacetonate can be used as a source gas to form NiO thin films having <100> axis crystallographic orientation on substrates made of various materials. <100 with cobalt acetyl acetylate
A CoO thin film having a <100> crystallographic orientation can be formed, and a magnesium acetylacetonate can be used to form a <100> crystallographically oriented MgO thin film. Instead of the conventional single crystal MgO substrate, a substrate having these thin films formed on its surface can be used as a base of the above ferroelectric thin film. As a result, it is possible to manufacture a dielectric thin film structure having similar properties without using an expensive MgO single crystal.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

Example 1 FIG. 1 is a schematic sectional view showing the structure of a ferroelectric thin film element of the present invention.

The substrate 1 has a size of 20 mm × 20 m.
m quartz glass with a thickness of 1 mm (coefficient of thermal expansion: 5 x 1
0^{ー 7}), (100) plane cut Si substrate (coefficient of thermal expansion: 2
5 x 10^{ー 7}), Glass substrate (Corning 7059, thermal expansion
Rate: 46 x 10^{ー 7}), Glass substrate (soda lime, thermal expansion
Rate: 90 × 10^{ー 7}), Stainless metal substrate (coefficient of thermal expansion:
180 x 10^{ー 7}) Was used. Bind it to the <100> axis
Formed NaCl-type oxide intermediate layer 2 of MgO thin film with crystal orientation
And then Pb on top of it by sputtering._xLa_1-xTi
_{1-x / 4}O₃ Ferroelectric thin film of composition (0 ≦ x ≦ 0.25)
3 is a thin film structure in which No. 3 is formed.

A method of manufacturing the ferroelectric thin film element 4 having the above structure will be described below.

The formation of the NaCl type oxide intermediate layer 2 of the MgO thin film oriented in the <100> crystal orientation is carried out on the surface of each of the above substrates by the following method by the plasma-enhanced MO-CVD process shown in FIG. It was performed using a membrane device.

The plasma-enhanced MO-CVD film forming apparatus 5 shown in FIG. 2 generates plasma by high frequency between two electrodes, a ground side electrode 7 and an RF side electrode 8, which are arranged in parallel in a vacuum chamber 6. It is an apparatus for forming a thin film by decomposing an organic metal source gas therein and performing chemical vapor deposition on the substrate 1. Here, the substrate 1 was held in a state in which one side was in close contact with the earth side electrode 7 and was previously heated to 400 ° C. by the substrate heater 9.

On the other hand, magnesium acetylacetonate 11 was placed in the raw material vaporization vessel 10 and heated using an oil bath 12 kept at 190 ° C. The vapor of magnesium acetylacetonate vaporized by heating in this manner was introduced into the vacuum chamber 6 using the carrier gas (nitrogen) 13 having a flow rate of 30 ml / min.
Further, oxygen gas 14 as a reaction gas was caused to flow at 2 ml / min, this was mixed in the middle and flowed into the vacuum chamber 6 through the blowout nozzle 15. At this time, the inside of the vacuum chamber 6 is evacuated from the exhaust port 16 to 7.
The vacuum was maintained at 90 Pa. In this state, RF
A high frequency of 400 W at 13.56 MHz is applied to the side electrode 10.
By applying the voltage for a minute, plasma was generated between the ground-side electrode 7 and the MgO thin film 2 crystallized in the <100> orientation on the one-side surface of the substrate 1 to a thickness of 200 nm. During this film formation, the substrate 1 was rotated by the substrate rotation motor 17 at a speed of 120 rpm.

Then, Pb _x La _{1-x is formed} on the intermediate layer 2.
A ferroelectric thin film 3 having a composition of Ti _{1-x / 4} O ₃ (0 ≦ x ≦ 0.25) was formed by a high frequency magnetron sputtering method.
The substrate 1 uses a 0.2 mm thick stainless mask,
A film was formed into a desired pattern. The target is Pb
O. La ₂ O ₃ and TiO ₂ powders were mixed, and the mixture was mixed at 750 ° C for 4
After being calcined for a period of time, they were pulverized, and in order to prevent a shortage of Pb, an excess of 20 mol% PbO powder was further mixed and produced. The film formation conditions for sputtering are: substrate temperature of 600 ° C .; sputtering gas of Ar (90%) and oxygen (1
(0%) mixed gas, the gas pressure was 0.5 Pa, and the high-frequency input power was 90 W (13.56 MHz). The film thickness is about 1
was μm.

In FIGS. 3A to 3D, quartz glass, Si,
A sample in which an x-ray diffraction pattern of a ferroelectric thin film element formed on soda lime glass or stainless steel was formed on a direct substrate 1 (in the case of a stainless steel substrate) without the intermediate layer 2 (Fig. 3).
(E)) is shown in comparison. The sample formed directly on the substrate 1 (in the case of a stainless steel substrate) without the intermediate layer 2 shows a polycrystalline perovskite crystal structure, whereas the ferroelectric thin film element according to the present invention has a perovskite crystal structure (00
Only the 1) and (100) reflections and their higher order reflections were observed. It was also found that as the coefficient of thermal expansion of the substrate 1 increased, the intensity of (001) reflection was significantly higher than that of (100), and the film was a <001> axis oriented film. On the contrary, a <100> axis oriented film was obtained on a substrate having a small coefficient of thermal expansion.

NaC by plasma enhanced MO-CVD method
When forming the l-type oxide intermediate layer 2, as a source gas source,
Instead of the magnesium acetylacetonate mentioned above,
CoA and NiO with cobalt acetylacetonate and nickel acetylacetonate, respectively.
The (100) plane alignment film of was able to be formed on various substrates. Even in the case of forming a Pb _x La 1 _{over x Ti 1-x / 4 O} 3 becomes ferroelectric thin film 3 of the composition to these intermediate layers, on a large substrate 1 in thermal expansion coefficient is <001> axis oriented thin film A <100> oriented thin film was obtained on the substrate 1 having a small coefficient of thermal expansion.

Similar results were obtained with ferroelectric thin films such as PbTiO ₃ , PZT and BaTiO ₃ .

Example 2 Various substrates 1 similar to Example 1
On top, NaC of MgO thin film with crystallographic orientation in <100> axis
This is a thin film structure in which an l-type oxide intermediate layer 2 is formed, and a ferroelectric thin film 3 made of PbTiO ₃ is further formed thereon by a plasma excited MO-CDV method.

A method of manufacturing the ferroelectric thin film element 4 having the above structure will be described below.

After forming the NaCl type oxide intermediate layer 2 of the MgO thin film oriented in the <100> crystal orientation, the ferroelectric thin film 3 of PbTiO ₃ is continuously formed on the intermediate layer 2 as shown in FIG.
It was formed using the plasma-excited MO-CVD film forming apparatus shown in FIG.

The plasma-enhanced MO-CVD film forming apparatus 21 shown in FIG. 4 generates plasma by high frequency between two electrodes, the earth side electrode 23 and the RF side electrode 24, which are arranged in parallel in the vacuum chamber 22. It is an apparatus for forming a thin film by decomposing an organic metal source gas therein and performing chemical vapor deposition on the substrate 1. Here, this substrate 1 was held in a state in which one side face was in close contact with the earth-side electrode 23 and was previously heated to 400 ° C. by the substrate heater 25.

On the other hand, magnesium acetylacetonate was placed in the raw material vaporization vessel (1) 26 and kept at 190 ° C. The vapor of magnesium acetylacetonate vaporized by heating in this way is changed to 30 ml / min.
The carrier gas (nitrogen) 27 having the flow rate of was used to flow into the vacuum chamber 22. Oxygen gas 28 was made to flow as a reaction gas at 2 ml / min, and this was mixed in the middle and flowed into the vacuum chamber 22 from the blowing nozzle. At this time, the inside of the vacuum chamber 22 was maintained at a vacuum degree of 7.90 Pa by the vacuum exhaust system 29. In this state,
By applying a high frequency of 400 W at 13.56 MHz for 10 minutes to the RF-side electrode 24, plasma is generated between the RF-side electrode 24 and the ground-side electrode 23, and <1 on one surface of the substrate 1.
The thickness of the MgO thin film 2 crystallized in the 00> direction is 200n.
m formed.

Then, PbTiO ₃ is formed on the intermediate layer 2.
The ferroelectric thin film 3 is formed. First, the substrate heater 2
5 was heated from 400 ° C to 500 ° C. Next, lead dipivaloylmethanate: Pb was placed in the raw material vaporization container (2) 30.
(C ₁₁ H ₁₉ O ₂ ) was added and the temperature was maintained at 130 ° C. Tetraisopropyl titanate: T was added to the raw material vaporization container (3) 31.
It placed _{i (i-C 3 H 7} O) 4, and held at 50 ° C.. In this way, the vaporized lead dipivaloylmethanate and tetraisopropyl titanate vaporized by heating were poured into the vacuum chamber 22 with a carrier gas 27 at a flow rate of 10 ml / min. Also, 40 ml of oxygen gas 28 as a reaction gas
/ Min, and mix this in the middle to create a vacuum chamber 2
It flowed into 2 through the blowing nozzle. At this time, the vacuum chamber 22 was maintained at a vacuum degree of 3.90 Pa by the vacuum exhaust system 29. In this state, by applying a high frequency of 400 W to the RF electrode 24 for 20 minutes, plasma is generated between the RF electrode 24 and the ground electrode 23, and PbTi is deposited on the <100> -oriented MgO thin film 2 formed on the substrate 1.
O ₃ was grown to 1 μm.

The x-ray diffraction pattern of the ferroelectric thin film element formed on the substrate of the type "A" was similar to that of Example 1.
In the ferroelectric thin film element according to the present invention, only the (001) and (100) reflections of the perovskite crystal structure, and their higher-order reflections were observed. Further, in the case of the substrate 1 having a large thermal expansion coefficient, a <001> axis oriented film was obtained, and conversely, in the substrate having a small thermal expansion coefficient, a <100> axis oriented film was obtained. Compared with the first embodiment, the film formation rate of the ferroelectric thin film 3 was improved three times.

It should be noted that (10
Even when a 0) plane-oriented oxide thin film having a NaCl-type crystal structure is formed and a tetragonal perovskite-type ferroelectric thin film is further formed thereon by the same sputtering method, the thermal expansion coefficient of the substrate 1 causes 001> direction or <100
It was possible to form a ferroelectric thin film oriented in the> direction. However, the crystallinity tended to depend on the substrate.

As described above, the ferroelectric thin film element of the present invention produced by the manufacturing method of the present invention has a conventional single-crystal M substrate as a substrate.
It was found that it is possible to provide a ferroelectric thin film element having a ferroelectric thin film in which crystal orientations are aligned in the direction perpendicular to the substrate, not only the one obtained by cutting out the (100) plane with gO but also using substrates made of various materials. .

[0033]

According to the present invention, the manufactured ferroelectric thin film element has the same performance as that of the base material without the need of using the single crystal MgO substrate as the base substrate at a low cost. Since the dielectric thin film element can be obtained, it can be used in a wider range in the field of electronic parts and is extremely effective in practical use. Further, an epitaxial thin film and an oriented thin film can be grown on the Si substrate, and it is possible to realize the integration of signal processing devices, which greatly improves the device performance.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a film structure of a ferroelectric thin film element according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a plasma-enhanced MO-CVD film forming apparatus used for manufacturing a ferroelectric thin film element according to an example of the present invention.

FIG. 3 is a diagram showing an X-ray diffraction pattern of a ferroelectric thin film element according to an example of the present invention.

FIG. 4 is a schematic cross-sectional view of a plasma-enhanced MO-CVD film forming apparatus used for manufacturing the ferroelectric thin film element shown in another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 NaCl type oxide intermediate layer 3 Ferroelectric thin film 4 Ferroelectric thin film element 5 Plasma excited MO-CVD film forming apparatus 6 Vacuum chamber 7 Earth side electrode 8 RF side electrode 9 Substrate heating heater 10 Raw material vaporization vessel 11 Magnesium Acetylacetonate 12 Oil bath 13 Carrier gas 14 Oxygen gas 15 Blow-out nozzle 16 Exhaust port 17 Substrate rotation motor 23 Earth side electrode 24 RF side electrode 25 Substrate heating heater 26 Raw material vaporization container (1) 30 Raw material vaporization container (2) 31 Raw material Vaporization container (3)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuko Okano 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hideo Torii, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. A substrate, a crystalline intermediate layer formed on the substrate, and a ferroelectric thin film oriented in the <001> direction formed on the substrate. The coefficient of thermal expansion up to the temperature during production of the body thin film is 70 ×
Ferroelectric material having a temperature of 10 ⁻⁷ / ° C. or more, and a misfit of lattice constant between the intermediate layer and the ferroelectric thin film within 15% at a temperature at which the ferroelectric thin film is manufactured. Thin film device. 2. A substrate, a crystalline intermediate layer formed on the substrate, and a ferroelectric thin film oriented in the <100> direction formed on the substrate. The coefficient of thermal expansion up to the temperature during production of the body thin film is 70 ×
Ferroelectric material having a temperature of 10 ⁻⁷ / ° C. or less, and a misfit of lattice constant between the intermediate layer and the ferroelectric thin film within 15% at a temperature at which the ferroelectric thin film is manufactured. Thin film device. 3. The ferroelectric thin film element according to claim 1, wherein the ferroelectric thin film is mainly composed of lead titanate, lead zirconate titanate, and barium titanate. 4. The ferroelectric thin film element according to claim 3, wherein the crystal structure of the ferroelectric thin film is tetragonal. 5. The ferroelectric thin film element according to claim 1, wherein the intermediate layer is an oxide thin film having a NaCl type crystal structure. 6. An oxide thin film having a NaCl-type crystal structure comprises (1
The ferroelectric thin film element according to claim 5, which is oriented in the (00) plane. 7. An oxide thin film having a NaCl type crystal structure is made of Ni.
The ferroelectric thin film element according to claim 5, which is one of O, CoO, and MgO. 8. (100) is formed on a substrate by a sputtering method.
A method for producing a ferroelectric thin film, which is produced by forming an oxide thin film having a plane-oriented NaCl type crystal structure, and further forming a tetragonal perovskite type ferroelectric thin film on the oxide thin film by sputtering. A method of manufacturing a ferroelectric thin film element, characterized by using a substrate having a different coefficient of thermal expansion to orient in a <001> direction or a <100> direction. 9. A (100) plasma-enhanced MO-CVD method using a vapor of an organometallic complex as a source gas on a substrate.
A method for producing a ferroelectric thin film, which is produced by forming an oxide thin film having a plane-oriented NaCl type crystal structure, and further forming a tetragonal perovskite type ferroelectric thin film on the oxide thin film by sputtering. A method of manufacturing a ferroelectric thin film element, characterized by using a substrate having a different coefficient of thermal expansion to orient in a <001> direction or a <100> direction. 10. A plasma-enhanced MO-CVD method using a vapor of an organometallic complex as a source gas on a substrate (10)
(0) Ferroelectric thin film produced by forming an oxide thin film having a NaCl-type crystal structure of plane orientation and further forming a tetragonal perovskite type ferroelectric thin film on it by plasma enhanced MO-CVD method The method for manufacturing a ferroelectric thin film element according to the method of (1) above, wherein the substrates having different coefficients of thermal expansion are oriented in the <001> direction or the <100> direction.