JPS61274342A - Ferroelectric element and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable the selection of a directional property of crystallizability of a substrate and a ferroelectric thin film according to the use by making at lest 40% of the plane parallel to a surface of the substrate of the ferroelectric thin film into (101) face of ferroelectric crystal of perovskite structure. CONSTITUTION:The ferroelectric element is formed basically by effecting the first step for vapor depositing a ferroelectric substance on the plane for vapor deposition of the substrate heated to a specified temperature and the second step for subjecting the thin film of ferroelectric substance which was vapor deposited on the plane for vapor deposition during the first step to the heat treatment at a specified temperature. In the second step, the ferroelectric substance vapor deposited on the plane for vapor deposition during the first step is treated by heating at a specified temperature to cause the crystal growth by which at least 40% of the plane parallel to a surface of the substrate of ferroelectric thin film becomes (101) face of ferroelectric crystal of perovskite structure. The heat treatment is made by heating the ferroelectric substance vapor deposited on the plane for vapor deposition of the substrate to temperature 500 deg.C or over. More particularly, the heating temperature in a range 550-700 deg.C is preferable for being preset to effect the heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel ferroelectric element and a method of manufacturing the ferroelectric element.

[Background of the invention] Recently, barium titanate and lead zirconate titanate (PZ
T), materials with ferroelectric properties (ferroelectrics) such as lead lanthanum zirconate titanate (PLZT) have piezoelectric properties,
It is used for applications that utilize properties such as pyroelectricity and ferroelectricity. In particular, ferroelectric materials are increasingly being used as infrared sensors or temperature sensors by taking advantage of their pyroelectric properties.

Although it is known that ferroelectric materials can utilize their excellent pyroelectric properties when used as a single crystal, it is difficult to manufacture single crystals of the above-mentioned ferroelectric materials by methods such as pulling. Because of the difficulty of porcelain, it is usually fired and used as porcelain. However, fired products are difficult to process into thin films. Especially 1
When using a ferroelectric material as a pyroelectric element, such as an infrared sensor, it is necessary that the heat capacity of the ferroelectric material be small in order to increase the temperature rise for a given amount of energy. In order to reduce the heat capacity of the dielectric, it is necessary to make the thickness of the ferroelectric as thin as possible.

[Prior Art and its Problems] In response to these demands, reactive sputter deposition or reactive sputter deposition methods, which can easily epitaxially grow a thin ferroelectric single crystal on a substrate, have been developed in place of the conventionally used porcelain. Methods such as the CVD method are used.

For example, Japanese Patent Application Laid-Open No. 59-35098 describes oxides of lead, titanium, and lanthanum (for example, PLZT).
The main feature of the invention is to epitaxially grow the [1113 crystal plane of a thin film on a sub-147C plane substrate,
JP-A-58-186105 discloses an invention whose main feature is that the [111] crystal plane is epitaxially grown on the [100] plane of magnesium oxide.

The thin films disclosed by these inventions are manufactured by reactive sputter deposition. The thin film obtained by this method has a thin film thickness unlike that of an Al container, and is therefore suitable for a pyroelectric element.

However, when these methods are used, the ferroelectric thin film grows epitaxially on the surface of the substrate to be evaporated.
The crystal orientation of the ferroelectric thin film is limited depending on the type of substrate used. That is, when PLZT is deposited on the sapphire C plane and the magnesium oxide [100] plane, [111]
Epitaxial growth occurs predominantly on the surface. Therefore, there is a problem in that it is not possible to select the direction of crystallinity of the substrate and the ferroelectric thin film depending on the application.

On the other hand, in order to integrate various circuits incorporating a ferroelectric thin film, it is necessary to perform surface treatment on the surface of the substrate on which the ferroelectric thin film is formed to make it suitable for integrated circuits. Since it is not possible to attach an integrated circuit directly onto a sapphire substrate, the integrated circuit must be attached after surface treatment of the sapphire substrate with a substance such as silicon, which complicates the manufacturing process. There's a problem.

[Object of the Invention] An object of the present invention is to provide a novel ferroelectric element and a method for manufacturing the ferroelectric element.

Furthermore, the present invention provides a ferroelectric element with an excellent pyroelectric effect and a method for manufacturing a ferroelectric element with an excellent pyroelectric effect, in which the material of the substrate on which the ferroelectric crystal is deposited or the crystallinity of the surface, etc. Regardless, the object of the present invention is to provide a ferroelectric element in which the [101] plane of the ferroelectric crystal grows predominantly parallel to the surface to be vapor-deposited on the substrate, and a method for manufacturing the ferroelectric element.

[Summary of the Invention] The present invention provides a ferroelectric element comprising a substrate and a ferroelectric thin film including a ferroelectric crystal with a perovskite structure provided on the surface of the substrate, the substrate surface of the ferroelectric thin film at least 40 planes parallel to
% is a [101] plane of a ferroelectric crystal having a perovskite structure.

The above ferroelectric element is produced by: (I) depositing a ferroelectric material on the deposition target surface of a substrate heated to a temperature of less than 500°C; and (n) heating the deposited ferroelectric material to a temperature of 500°C or more. A manufacturing method comprising the step of heating the ferroelectric thin film at a high temperature and growing the ferroelectric thin film so that at least 40% of the planes parallel to the plane to be vaporized become the [1011 planes of the ferroelectric crystal having a perovskite structure. It can be easily manufactured by

Furthermore, ferroelectric crystals with perovskite structure.

It is preferable that the crystal is at least one type of ferroelectric crystal selected from the group consisting of lead titanate, lead lanthanum titanate, lead zirconate titanate, and lead lanthanum zirconate titanate.

[Detailed Description of the Invention] The ferroelectric element of the present invention basically comprises a substrate and a ferroelectric thin film including a ferroelectric crystal with a perovskite structure provided on the surface of the substrate to be vapor-deposited.

At least 40% of the plane parallel to the substrate surface of this ferroelectric thin film is a ferroelectric crystal with a perovskite structure [
101] surface.

Conventionally, the [001] plane of a ferroelectric crystal has been mainly used as a ferroelectric material, but according to the study of the present inventor, the [101] plane of a ferroelectric material such as PLZT also has good properties. have.

The ferroelectric element of the present invention can be manufactured in a first-order manner.

The ferroelectric element of the present invention basically consists of a step (first step) of evaporating a ferroelectric material onto the surface to be vapor-deposited of a substrate heated to a specific temperature; The process of heat-treating the ferroelectric thin film at a specific temperature (second process)
It can be manufactured by carrying out a process including.

The first step is a step of vapor-depositing a ferroelectric material on the surface of the substrate heated to a specific temperature to be vapor-deposited.

Various substrates can be used as the substrate. Examples of materials that can be used as the substrate include conductors such as metals, A I We can list semiconductors such as
Further mention may be made of insulators such as sapphire.

Incidentally, examples of A Jl z G a l + x As single crystals include AmiO, aGao, n AS single crystals and GaeAs single crystals.

In particular, it is directly deposited on the metal part of the gate part of the integrated circuit, or directly on the semiconductor used as the substrate of the integrated circuit, such as A 41 x Ga 1-X As single crystal and silicon single crystal. Using the method it is possible to manufacture compact two-dimensional sensors.

Unlike conventional methods, the surface to be vapor-deposited on the substrate on which the ferroelectric material is vapor-deposited does not need to be a specific crystal plane of the substrate.
, When using an As single crystal, its [100] plane,
Specifically, when using a Ga*As single crystal substrate, its [100] plane, the [100] plane of a GaeAs single crystal (7
) A lo, n Ga o, g A S single crystal [100] plane, etc. can be used as the vapor deposition target surface.
Further, when a metal surface is to be used as a surface to be vapor-deposited, it is desirable to perform vapor deposition on a metal surface that has been subjected to a mirror treatment to have a smooth surface.

The thickness of the substrate can be appropriately selected depending on the intended use, but for example, when used as an infrared sensor, a substrate having a thickness of about 0.02 to 1 mm is usually used.

Ferroelectric crystals include lead titanate, lanthanum lead titanate,
Since lead zirconate titanate (PZT) and lanthanum lead zirconate titanate (PLZT) exhibit good physical properties,
It is preferable to use the above-mentioned ferroelectric materials, which may be used alone or in combination. Lead titanate and lanthanum lead zirconate titanate are particularly preferable.

The above-mentioned ferroelectric substance does not need to be a pure substance, and may contain small amounts of other components in addition to the above-mentioned components. Generally, when vapor deposition is performed using a high-frequency sputtering device, In this method, the ferroelectric material described above is sintered into a certain shape and loaded into the device. However, since the ferroelectric sintered body described above is very brittle, it may collapse during cooling after sintering. Therefore, it may be preferable to add a small amount of other components to supplement the strength of the sintered body. Examples of other ingredients to add include zirconium, niobium, manganese,
Mention may be made of magnesium, yttrium and cobalt and their oxides. Furthermore, it may contain trace amounts of alkali metal elements, alkaline earth elements, iron elements, etc. However, the ferroelectric composition of each component forming the ferroelectric thin film and the amount of other components added It is necessary that the amount is within a range that can maintain the perovskite structure.The amount usually used is 10% by weight or less.

When evaporating the ferroelectric material onto the surface of the substrate to be evaporated, it is necessary that the substrate be heated to a temperature of less than 500°C. In particular, it is preferable to perform vapor deposition by heating the substrate to a temperature within the range of about room temperature (approximately 20°C) to 450°C.
If the temperature of the substrate is 500°C or higher, the ferroelectric material is deposited and grows epitaxially while being influenced by the surface to be deposited, and the [101] surface cannot be grown dominantly even by subsequent heat treatment. Although it is possible to deposit a ferroelectric material even at a low temperature of less than 20° C., the subsequent heat treatment requires a long time.

Vapor deposition can be performed using a vacuum deposition method such as a reactive sputter deposition method or a CVD method.

The reactive sputter deposition method and the CVD method can basically be performed according to known methods.

That is, when manufacturing a dielectric element using, for example, a reactive sputter deposition method, a substrate is mounted on a reactive sputter deposition apparatus such as a high frequency magnetron sputter deposition apparatus, and titanium oxide and titanium oxide are used as targets. Set a sintered body of ferroelectric material such as lead oxide. Replace the air in the device with a mixture of inert gas (e.g., argon, helium) and oxygen to reduce the pressure to within the range of 2 to 20 Pa (Pascals).Usually, a mixture of inert gas and oxygen is used. Set the capacity ratio within the range of 2:1 to 1:2.

The thickness of the i-film varies depending on the use of the device, but for example, in the case of a pyroelectric device having a thin film of lead titanate, it is generally 0.1
−10 μm, preferably 0.2 to 5 gm. The thickness of the thin film can be controlled, for example, by adjusting the deposition time.

In the second step, the ferroelectric material deposited on the surface to be vapor-deposited in the first step is heat-treated at a specific temperature, so that at least 40% of the surfaces parallel to the substrate surface of the ferroelectric thin film have a perovskite structure. This is a step of growing a ferroelectric crystal so that it becomes a [101] plane.

The heat treatment is performed by heating the ferroelectric material deposited on the surface of the substrate to be vapor-deposited.
The heat treatment is preferably carried out by heating to a temperature of 0°C or higher, particularly by setting the heat treatment temperature within the range of 550 to 700°C. Normally, the heat treatment is performed using the equipment used in the first step, Perform in an inert gas (e.g. nitrogen, argon) atmosphere.

In the ferroelectric material deposited in the first step, since the temperature of the substrate is low, a very small amount of very fine crystals are generated, and other deposits do not show crystallinity. It has a constant directionality regardless of the crystal plane of the surface to be evaporated. Then, by the heat treatment in the second step, the ferroelectric substance 1 grows using these fine crystals as nuclei. During this crystal growth, the influence of the fine crystals generated during vapor deposition in the first step is greater than the influence of the surface to be vaporized, and at least 40% of the crystal planes parallel to the surface to be vaporized are [101
]It is a surface. Especially as a substrate A lo, n Ga
o, as A11. such as A S single crystal or Ga@As single crystal. Ga□-xAs single crystal is used, and its [
When the 1001 plane is the plane to be vapor-deposited, 60% or more of the crystal planes parallel to the plane to be vapor-deposited are [101] planes, and sometimes 70% or more are [101] planes.

Therefore, if the heat treatment temperature is less than 500°C, crystallization will not proceed sufficiently;
If the temperature exceeds °C, long-term heat treatment may vaporize lead, which has a low boiling point, and change the composition of the ferroelectric thin film. Therefore, the heat treatment time must be shortened, and the crystal growth may be insufficient. Incidentally, the heat treatment time is usually set within a range of 10 minutes to 5 hours, and is generally shortened as the heat treatment temperature increases.

After the heat treatment as described above, at least 4 of the planes parallel to the substrate surface of the ferroelectric thin film are usually
[101] ferroelectric crystal with 0% perovskite structure
The ferroelectric element of the present invention, which is characterized in that it is a plane, has an excellent pyroelectric effect. Particularly suitable for use as an infrared sensor.

Furthermore, unlike conventional ferroelectric thin films in which the entire ferroelectric thin film is formed of a single crystal, the thin film of the ferroelectric element of the present invention is an aggregate of ferroelectric crystals having a perovskite structure with a relatively small particle size. be. Note that [1
The planes other than the [01] plane are mainly the [110] plane.

[Effects of the Invention] The ferroelectric element of the present invention exhibits an excellent pyroelectric effect and is particularly suitable for use as a pyroelectric element.

For example, a conventional pyroelectric sensor incorporates a detection section having a ferroelectric thin film in a package and an FET (field effect transistor) for impedance adjustment connected to the ferroelectric thin film. The ferroelectric element uses a semiconductor such as A single crystal as a substrate, and a thin film FET is integrally attached to this substrate, resulting in a small and lightweight two-dimensional sensor. It can be done. In addition, by using metal as the substrate, F
It is also possible to form a sensor by attaching a ferroelectric thin film directly to the gate portion of the ET.

This kind of integration of a ferroelectric thin film and an electronic circuit part is
It can be advantageously implemented not only in pyroelectric elements but also in fields that utilize ferroelectricity or other characteristics.

Furthermore, the ferroelectric element of the present invention has excellent electro-optical properties and ferroelectricity.

Next, Examples and Comparative Examples of the present invention will be shown.

[Example 1] A stainless steel plate (substrate) with a mirror-finished surface was attached to a high-frequency magnetron sputter deposition apparatus.

Further, a lead and titanium oxide sintered body (target) having a P b /Ti atomic ratio of 1.15/1 and a diameter of 80 mm was loaded so that the distance from the stainless steel substrate was 50 mm. Note that since pure lead titanate is easily disintegrated during cooling after sintering, 5% by weight of zirconium oxide was added during sintering.

The inside of the above high frequency magnetron sputter deposition equipment is
After reducing the pressure to 0-'Pa or less, the substrate temperature was set to 400° C., and the pressure inside the apparatus was adjusted to 5 Pa while introducing a mixed gas of argon and oxygen at a ratio of 1:1 (volume ratio).

Input too much high frequency power into the above device.

Reactive sputter deposition was performed for 8 hours.

The thickness of the thin film formed on the stainless steel substrate by reactive sputter deposition was about 1.5 JLm.

The substrate on which the thin film was formed was heat treated at 600° C. for 2 hours, and then slowly cooled at a cooling rate of 100° C./hour. In addition, heat treatment and slow cooling.

The test was carried out in a nitrogen gas stream.

Figure 1 shows the diffraction diagram of the crystal structure of this thin film measured using an X-ray diffractometer.55% of the surfaces parallel to the surface to be vaporized on the stainless steel substrate are the [101] planes of the lead titanate crystal, which has a perovskite structure. It turned out to be.

[Example 2J In Example 1, Ga*As was used instead of the stainless steel substrate.
A ferroelectric element was manufactured in the same manner except that a single crystal was used and the vapor deposition was performed on the [100] plane. The Ga fist As single crystal used was a Ga fist As single crystal produced by a pulling method.
It is cut out from an As single crystal.

FIG. 2 shows a diffraction diagram of the crystal structure of the thin film of the obtained ferroelectric element measured using an X-ray diffraction apparatus.

70 of the planes parallel to the [1003 plane of the Ga-clouded As single crystal
% of lead titanate crystal with perovskite structure [101
] surface.

[Example 3] In Example 1, instead of the stainless steel substrate, an A pattern of 0.3
1i G & O, using As single crystal, its [10
A ferroelectric element was manufactured in the same manner except that the evaporation was performed on the 01 side.

FIG. 3 shows a diffraction diagram of the crystal structure of the thin film of the obtained ferroelectric element measured using an X-ray diffraction apparatus.

It was found that 80% of the planes parallel to the [1001 planes of Alo, gGao, and 5sAs single crystals are the [1013 planes of the lead titanate crystal with a perovskite structure.

[Brief explanation of drawings]

FIG. 1 is an example of an X-ray diffraction diagram of lead titanate formed on the surface of a stainless steel substrate. FIG. 2 is an example of an X-ray diffraction diagram of lead titanate formed on the [100] crystal plane of a GaFist As single crystal. Figure 3 shows A l 6.3 @ G a @, g A S
X of lead titanate formed on the [100] crystal plane of a single crystal
This is an example of a line diffraction diagram. Patent applicant Ube Industries Co., Ltd. Representative Patent attorney Yasuo Yanagawa (lol) Diffraction angle (2e) Figure 2 Diffraction angle t2e)

Claims (1)

[Claims] 1. A ferroelectric element comprising a substrate and a ferroelectric thin film including a ferroelectric crystal with a perovskite structure provided on the surface of the substrate, the substrate surface of the ferroelectric thin film and at least 40 parallel planes
% is a [101] plane of a ferroelectric crystal having a perovskite structure. 2. The ferroelectric element according to claim 1, wherein the ferroelectric thin film is provided on a metal substrate with a smooth surface. 3. The ferroelectric element according to claim 1, wherein the ferroelectric thin film is provided on the [100] plane of a single crystal. 4. The ferroelectric element according to claim 3, wherein the single crystal is an Al_xGa_1_-_xA_s single crystal; (provided that 0≦x≦0.35). 5. Ferroelectric crystal with perovskite structure is lead titanate,
The ferroelectric crystal according to claim 1, wherein the ferroelectric crystal is at least one type of ferroelectric crystal selected from the group consisting of lanthanum lead titanate, lead zirconate titanate, and lanthanum lead zirconate titanate. dielectric element. 6. A method for manufacturing a ferroelectric element comprising a substrate and a ferroelectric thin film including a perovskite-structured ferroelectric crystal provided on the surface of the substrate, the method comprising: (I) heating to a temperature of less than 500°C; (II) heating the deposited ferroelectric material at a temperature of 500° C. or higher to form a ferroelectric thin film parallel to the surface to be deposited; 1. A method for manufacturing a ferroelectric element, comprising the step of growing a ferroelectric crystal having a perovskite structure so that at least 40% of its faces become [101] planes. 7. The method of manufacturing a ferroelectric element according to claim 6, wherein the surface of the substrate to be vapor-deposited is a smooth metal surface. 8. The method for manufacturing a ferroelectric element according to claim 6, wherein the surface to be vapor-deposited on the substrate is a [100] plane of a single crystal. 9. A method for manufacturing a ferroelectric element according to claim 8, characterized in that the single crystal is an Al_xGa_1_-_xA_s single crystal (provided that 0≦x≦0.35). 10. The method for manufacturing a ferroelectric element according to claim 6, wherein the heating temperature of the substrate in the first step is within the range of 20 to 450°C. 11. The method for manufacturing a ferroelectric element according to claim 6, wherein the heat treatment temperature in the second step is within the range of 550 to 700°C.