JPH10270766A - Ferroelectric thin film element, piezoelectric element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for formation of an electrode separate from a substrate by providing a composition oxide thin film containing two or more kinds of metals selected from lead, zircon and titanium, and constituting a substrate of a ferroelectric thin film element, provided with a substrate on one side of front and back thereof, with a kind of zircon and titanium. SOLUTION: A Ti foil 2 is a lower electrode, and a Pt electrode 4 is an upper electrode. In a structure of this element 1, the Ti foil 2 is provided as a structural substrate 2, and a TiO2 layer 5 is provided as a buffer layer on the substrate 2, and a PZT thin films 4 is provided on the upper side the buffer layer 5. This material is provided with a perovskite structure as what is called a crystal structure, showing ferroelectricity. In addition, an upper electrode layer is provided as a Pt thin film electrode 4. Because a kind of lead, zircon and titanium is employed as a substrate, the substrate itself can be used as at least one electrode, thereby formation of an electrode separate from a substrate is necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a composite oxide thin film including two or more metals selected from the group consisting of lead, zircon and titanium, typified by so-called PZT (lead zirconate titanate). The present invention relates to a ferroelectric thin film device having a substrate on either side of the front and back surfaces of a composite oxide thin film, or a method for manufacturing such a device.

[0002]

2. Description of the Related Art A ferroelectric substance has a spontaneous polarization generated by parallel or antiparallel permanent dipoles in a substance itself even in the absence of an electric field, which can be reversed in direction by an external electric field. It is a substance having properties. Utilizing this property, the ferroelectric material can be applied to various electronic components such as a pyroelectric infrared detecting element, a piezoelectric element, an optical modulator utilizing an electro-optical effect, and a nonvolatile memory element.
A typical ferroelectric material is an oxide having a perovskite crystal structure, for example, PbZrTi _1-x O ₃ (PZ
T), Pb _1-X La _X Ti _{1-X / 4} O ₃ (PLT), PbTi
O _{3 and the} like are particularly famous. In the manufacture of such a thin film type, a ferroelectric thin film is conventionally formed on a Si substrate or a sapphire substrate. Such a substrate had no conductivity and was rigid.

[0003]

In order to obtain an electrical output from a ferroelectric thin film, it is necessary to construct an element with an electrode thin film made of, for example, platinum with the ferroelectric thin film interposed therebetween. FIG. 5 shows an element structure (conventional structure) in the case of using Si as a substrate, forming a PZT thin film on the Si substrate, and obtaining output from the PZT thin film. This element 50 is formed by sequentially forming a Ti layer 52, a Pt layer 53, and a TiOx layer 54 on the surface side of a Si substrate 51, forming a PZT layer 55 on the surface side of the TiOx layer 54, and further forming a PtT layer on the surface side. Layer 56
Is provided. Here, Ti layer 52, Pt layer 53, TiOx
The reason for requiring the layer 54 is that when the Pt layer 53 is provided as an electrode, the P
This is because the relationship between the t-layers 53 is made favorable from the viewpoints of conformity, coefficient of thermal expansion, and the like. When Si is used as the substrate material as described above, a new electrode (the Pt layer in the above-described structure) is required because of non-conductivity, and the production is troublesome and the production cost is increased. Furthermore, since the Si material is rigid, for example, when a ferroelectric thin film element is used as a piezoelectric element, the use of the element is limited to a flat surface, and there is a problem that it is difficult to use the ferroelectric thin film element on a curved surface. That is, conventionally, an element having a PZT thin film has been developed, but in such an element, a flexible ferroelectric thin film element has been practically used because the substrate is rigid. Above, not obtained. An object of the present invention is to provide a ferroelectric thin film element which does not require providing an electrode separately from a substrate, thereby simplifying a manufacturing process and reducing cost, and is also suitable for a vibration detection target having a curved surface. An object of the present invention is to provide a ferroelectric thin film element having adaptable flexibility.

[0004]

According to the present invention, there is provided a composite oxide thin film including at least two metals selected from the group consisting of lead, zircon, and titanium. In order to construct a ferroelectric thin-film device having a substrate on either side of the front and back surfaces, the substrate is made of any one of lead, zircon, and titanium. In forming a ferroelectric thin film in a ferroelectric thin film element having this configuration, a thin film layer having a composition close to the material can be formed on a substrate (for example, when Ti is used as a substrate, A ferroelectric thin film layer can be formed by solving the problems of the oxide layer of Ti), the thermal expansion coefficient, etc., which are adapted to the surface side of the oxide layer.
That is, in the case of the above example, it has a perovskite structure,
A PZT layer having ferroelectric properties can be grown, in which respect the present application is advantageous. Further, in the ferroelectric thin film element having this configuration,
Since any one of lead, zircon, and titanium is used as the substrate (element support), the substrate itself can be used as at least one electrode, and the simplification described above can be achieved.

In the present application, a composite oxide thin film containing at least two metals selected from the group consisting of lead, zircon and titanium is provided, and an electrode is provided on each of the front and back surfaces of the composite oxide thin film. The characteristic configuration of the ferroelectric thin-film element that obtains an electrical output between the electrodes is that a substrate (element) in which one of the upper electrode and the lower electrode described above is made of one of lead, zircon, and titanium. Support). The ferroelectric thin film element of this configuration has electrodes on the front and back surfaces of the ferroelectric thin film, and has a structure in which a change in the electrical characteristics of the thin film between these electrodes is captured between the electrodes. . When the substrate is made of a specific material as in the present application, an element output can be obtained by utilizing the electrical conductivity of the substrate, and there is no need to provide a separate Pt layer electrode or the like. Can be obtained.

Here, it is preferable that the substrate made of the specific metal is a flexible thin film (so-called foil). Since the metal of the present invention can be formed as a thin film and a material having flexibility itself can be selected, if such a material having flexibility is adopted as a so-called substrate, it has flexibility and a piezoelectric element. In such a case, it is possible to obtain a ferroelectric element that can be used by being fitted well on a curved surface.

[0007] As described above, it is preferable that an oxide layer of a substrate material is provided between the substrate and the composite oxide thin film as the ferroelectric thin film. This is because conformity between the substrate and the ferroelectric thin film, such as conformity and coefficient of thermal expansion, can be favorably performed.

It is preferable that the composite oxide described so far is lead zirconate titanate, and the substrate is made of a titanium material. Lead zirconate titanate has high dielectric performance as a ferroelectric material. As will be shown later, by using Ti as a substrate, a perovskite-type This is because a thin film can be formed.

It is preferable that the ferroelectric thin-film element described above is subjected to a poling process. This is because the poling process promotes the polarization of the ferroelectric thin film, so that a piezoelectric element having good characteristics can be obtained.

In the case of manufacturing a ferroelectric thin-film element having a composite oxide thin film containing two or more metals selected from lead, zircon and titanium on the substrate surface as described above, As a substrate, a specific material substrate made of any one of lead, zircon and titanium is used, and after forming an oxide layer of a substrate material on the surface of the specific material substrate,
A composite oxide thin film that is a ferroelectric thin film can be formed.

Also in this method, the specific material substrate is
It is preferably a thin film having flexibility (so-called foil). As a result, a flexible ferroelectric thin film element can be obtained.

Further, also in this method, it is preferable that the composite oxide is lead zirconate titanate and the substrate is made of a titanium material. Similarly, it is preferable to perform a poling process on the obtained ferroelectric thin film element from the viewpoint of manufacturing a piezoelectric element.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a ferroelectric thin film element 1 of the present invention will be described with reference to FIG. [Structure of Element] FIG. 1 (a) is a perspective view of the entire structure of the ferroelectric thin film element 1 of the present application, and FIG. 1 (b) is a sectional view of the element 1 in the thickness direction. The element 1 is generally formed by forming a PZT thin film 3 on a Ti foil 2, and the Ti foil 2 and a Pt electrode 4 provided on the surface side of the PZT thin film 3 function as an electrode referred to in the present application. Becomes here,
In effect, the Ti foil 2 is a lower electrode, and the Pt electrode 4 is an upper electrode. Now, the structure of the element 1 will be described in more detail with reference to FIG. 1 (b) in relation to each material layer. The element 1 has a thickness of 2 as a structural substrate (element support).
A Ti foil 2 of about 0 μm is provided. On this substrate, a TiO ₂ layer 5 is provided as a buffer layer. This layer thickness is about 0.09 μm. Next, a PZT thin film layer 3 is provided on the upper side of the buffer layer. This layer thickness is about 2 μm. This material has a so-called perovskite structure as a crystal structure, and exhibits ferroelectricity. Further, as described above, the upper electrode layer is provided as the Pt thin-film electrode 4. This layer thickness is 0.24μ
m.

[Production of Element] In the production of the element 1, the following procedure is adopted. 1) 50 mm × 20 mm × 20 μm (t) Ti foil 2
Is washed with boiling acetone for 15 minutes and further with boiling i-propanol for 15 minutes, and then dried at 100 ° C. for 12 hours. This cleaned Ti foil becomes the structural substrate of the device of the present invention. In forming the element, the element is used with a diameter of about 10 mm. In forming the thin film, a so-called MOCVD method (using a simple MOCVD apparatus without a plasma apparatus) is employed. M
The settings for performing OCVD were as follows. B) The reaction chamber pressure is 300 Pa and the substrate temperature is 450 ° C. b) The source gases are Pb (C ₁₁ H ₁₉ O ₂ ) ₂ and Zr (t−
OC ₄ H ₉ ) ₄ and Ti (i-OC ₃ H ₇ ) ₄ , and the respective cylinder temperatures were set at 135 ° C., 35 ° C., and 46 ° C. in the order described. C) Carrier gas and diluent gas were nitrogen.

The film forming procedure was as follows. 1) Only Ti derived from Ti (i-OC ₃ H ₇ ) ₄ was first introduced into a reaction chamber (not shown) in which a substrate was set, by a carrier gas 5C.
CM and a diluent gas of 55 ccm flowed for 2 minutes.
By this treatment, a TiO ₂ layer was formed on the surface of the Ti foil. 2) Next, from all the raw materials mentioned above, P
b, Zr, and Ti were simultaneously supplied under the following conditions.

[0016]

[Table 1] Substance name Supply amount Supply amount Pb: Carrier gas 7 CCM, diluent gas 38 CCM Zr: carrier gas 4 CCM, diluent gas 41 CCM Ti: carrier gas 5 CCM, diluent gas 40 CCM

Under the above conditions, a film is formed for 4 hours.
A PZT thin film 3 was obtained. The physical properties of the formed film are as follows.

[0018]

[Table 2] Film thickness measured by ellipsometer: 202
10Å Film composition measured by EDX: Pb: Zr: Ti =
1: 0.66: 0.81

FIG. 2 shows an x-ray diffraction pattern measured by XRD. As can be seen from the figure, the obtained ones have the perovskite crystal structures (001) and (11).
0) and (002) reflections and higher-order reflections were mainly observed.

The electrical characteristics of the ferroelectric thin film device obtained as described above were as follows.

[0021]

[Table 3] Dielectric constant εr: 726 Dielectric loss tanδat 100 kHz: 135 × 10 ^-4 Remanent polarization: 0.03 × 10 ^-6 C / cm ² At this time, the piezoelectric constant h immediately after film formation is −1.21 × 10
⁸ V / m.

Further, the ferroelectric thin film element 1 thus obtained was subjected to a poling treatment. 20 × 10 ⁶ V
The piezoelectric constant h after poling at / m (a DC voltage of 40 V applied to the film thickness of 2 μm between the upper and lower electrodes at room temperature in the air) was 6.17 × 10 ⁸ V / m.

The method employed for measuring the above piezoelectric constant h will be described with reference to the drawings and the following equations.
In the measurement, a measuring device 30 having a cantilever configuration as shown in FIG. 3A is constructed, a forcible displacement is applied to the element, and the voltage output thereof is monitored. h was calculated. In the measurement, a measurement sample (sample) 31 was cut into a size of 5 mm × 5 mm, and the upper Pt sputtered layer 4 was used as an upper electrode 32. However, in FIG. 3, the upper electrode is drawn small for easy understanding. FIG. 3A is a schematic diagram of the measuring apparatus 1. The apparatus 1 is configured so that an element (measurement sample 31) to be measured can be supported on a fixed base 38 in a cantilevered manner. The element end 31 a on the side is configured to be able to be subjected to periodic bending deformation (bending) by a cam 34 rotated and driven by a motor 33. On the other hand, regarding the output from the element and the deformation of the element, the electric output by the piezoelectric effect from the element is obtained by the upper electrode 32 (Pt sputtered layer) and the lower electrode 35 (this is the Ti foil 2 which is the element substrate in this application) In addition, an optical displacement meter 37 for measuring the bending of the element is installed at a predetermined portion 37b of the element so that the output can be guided to the oscilloscope 36 to display and detect. did. FIG. 4 shows a display screen of the oscilloscope 36. The electric output from the device is indicated by a solid line (shown by V)
In, shows output from the optical displacement meter by broken lines (zeta indicated by _0). It can be seen that mechanical deflection can be well represented.
Next, the derivation of the piezoelectric constant h will be described. FIG. 3B schematically shows the configuration of the measurement system in the above-described measuring apparatus 1. The description of each code is shown in the same figure and the description of the code of the following formula. Here, the input constant is a constant known in advance from the configuration of the system, and the approximate constant is an approximate value of a constant necessary for deriving the piezoelectric constant h. The piezoelectric constant h was determined based on the following equation.

[0024]

(Equation 1)

Further, in the same manner as described above, an experiment was conducted in which the film forming conditions and the poling conditions in forming the PZT thin film 3 on the Ti foil 2 were changed. Table 4 shows the thickness, composition, electrical characteristics, and poling applied electric field of the obtained PZT thin film 3. In the same table, the film forming conditions include the substrate temperature during film formation, the cylinder temperature (° C.), the carrier gas flow rate (CCM), and the developing gas flow rate (CCM). The pressure in the film forming chamber was the same as in the above example. In the flow rate section, “first” indicates a flow rate when an oxide layer of Ti is formed, and “after” indicates a flow rate at the time of forming a PZT thin film. . Electrical characteristics include dielectric constant εr, dielectric loss tanδat 100 kHz, remanent polarization, piezoelectric constant h
(Before the poling process (as-is) and after the poling process).

[0026]

[Table 4]

The elements shown in the table are all formed on a flexible Ti foil, and are thin-film elements having dielectric properties. Further, a Ti foil serving as a substrate plays a role as one electrode. For comparison, the electrical characteristics of a device made of bulk PZT are as follows: dielectric constant εr is about 1000, and piezoelectric constant h is 700 (MV
/ M), which indicates that the present invention is superior to bulk. Further, the effect of the polling process is great. When this element is used as a piezoelectric element, it is preferable to form a film at a substrate temperature of 410 to 490 ° C. Outside this temperature range, the piezoelectric constant e (C ² / m) tends to be low. On the other hand, when this temperature range is set to 435 to 485 ° C., a material having a high piezoelectric constant e (C ² / m) can be obtained, which is more preferable.

[Other Examples] (A) In the above embodiment, PZT was described as a ferroelectric thin film, but the present invention is applied to two or more types selected from lead, zircon, and titanium. The configuration of the present application can be adopted as long as the composite oxide thin film has a perovskite structure containing the above metal. (B) In the above embodiment, the case where the Ti foil is used as the substrate (element support) has been described. However, as the material, lead, zircon, or the like can be used, and the foil is used. Such a material is preferred in terms of imparting flexibility. The thickness of such a foil (thin film) is preferably 0.1 to 50 μm (more preferably 10 to 50 μm). (C) As in the present application, when the substrate is an electrode, the substrate may be one electrode, and the upper electrode, the lower electrode,
It does not matter in which case. (D) In the above embodiment, the MOCVD method is employed as a thin film manufacturing method.
Laser ablation method, plasma spray method and the like can also be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a ferroelectric thin film element of the present application.

FIG. 2 shows an X-ray diffraction pattern of a ferroelectric thin film.

FIG. 3 is a diagram showing an apparatus for testing the characteristics of a ferroelectric thin film element.

FIG. 4 is a diagram showing a relationship between an output voltage of an element and a deflection signal of an optical displacement meter.

FIG. 5 is a diagram showing a cross-sectional configuration of a conventional ferroelectric thin-film element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ferroelectric thin film element 2 Ti foil (substrate) 3 PZT thin film (ferroelectric thin film) 5 TiO ₂ layer (oxide layer of substrate material)

Claims (10)

[Claims] 1. A material selected from the group consisting of lead, zircon and titanium.
A ferroelectric thin-film element comprising a composite oxide thin film containing at least one kind of metal, and a substrate provided on either side of the front and back surfaces of the composite oxide thin film, wherein the substrate is composed of lead, zircon, and titanium. A ferroelectric thin-film element comprising any one of them. 2. A material selected from the group consisting of lead, zircon and titanium.
A ferroelectric thin-film element comprising a composite oxide thin film containing at least one kind of metal, front and back surfaces of the composite oxide thin film, each having an electrode, and obtaining an electric output between an upper electrode and a lower electrode. One of the upper electrode and the lower electrode,
A ferroelectric thin film element which is a substrate made of any one of lead, zircon and titanium. 3. The ferroelectric thin film element according to claim 1, wherein the substrate is a thin film having flexibility. 4. The ferroelectric thin-film element according to claim 1, wherein an oxide layer of a substrate material is provided between said substrate and said composite oxide thin film. 5. The ferroelectric thin-film element according to claim 1, wherein said composite oxide is lead zirconate titanate, and said substrate is made of a titanium material. 6. A piezoelectric element obtained by subjecting the ferroelectric thin-film element according to claim 1 to a poling process. 7. A method of manufacturing a ferroelectric thin film element comprising a composite oxide thin film containing at least two metals selected from lead, zircon and titanium on a surface of a substrate, wherein the substrate comprises lead, A method of manufacturing a ferroelectric thin-film element, comprising using a specific material substrate made of one of zircon and titanium, forming an oxide layer of a substrate material on the surface of the specific material substrate, and then forming the composite oxide thin film. 8. The method according to claim 7, wherein the specific material substrate is a thin film having flexibility. 9. The method according to claim 7, wherein the composite oxide is lead zirconate titanate, and the substrate is made of a titanium material. 10. A method for manufacturing a piezoelectric element, comprising subjecting a ferroelectric thin-film element manufactured by the method for manufacturing a ferroelectric thin-film element according to claim 7 to a poling process.