JP5115161B2 - Piezoelectric thin film element - Google Patents

Description

  The present invention relates to a piezoelectric thin film comprising a dielectric thin film of alkali niobium oxide having excellent piezoelectric characteristics and a piezoelectric thin film element.

  Piezoelectric materials are processed into various piezoelectric elements according to various purposes, and functions such as an actuator that causes deformation by applying voltage to the element, and a sensor that applies pressure to the element and generates voltage according to the deformation Widely used as a sexual electronic component.

As the piezoelectric material used in the actuator and sensor applications, excellent ferroelectric material lead-based material having piezoelectric _{properties, Pb (Zr 1-x Ti} x) O 3 based perovskite ferroelectric particularly called PZT Body materials have been widely used so far, and such ferroelectric materials are usually produced by sintering oxide powders of materials composed of individual elements.

  On the other hand, in recent years, there has been a demand for further miniaturization of piezoelectric elements such as actuators, which has necessitated the need to fabricate piezoelectric elements using photolithography technology used when fabricating semiconductor integrated circuits. Yes. In this case, the ferroelectric material is also required to be formed into a thin film shape with a thickness of several microns to several tens of microns because of the necessity of fine processing. In such a case, it is not a realistic method from the economical and industrial point of view to process this into a thin film shape from the sintered body produced as described above, and a thin film is formed on an appropriate substrate. Is used.

As a method for forming a thin film on a substrate, for example, a sputtering method as described in Patent Document 1, a PLD (laser ablation method), a sol-gel method, and the like are known.
JP 2002-151754 A

  A piezoelectric thin film made of PZT contains lead oxide (PbO) in an amount of about 60 to 70% by weight, which is not preferable from the viewpoint of ecology and pollution prevention. Therefore, development of a piezoelectric thin film that does not contain lead is desired in consideration of the environment.

Currently, various lead-free piezoelectric materials have been studied, among which general formulas: (Na _x K _y Li _z ) NbO ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z <1) X + y + z = 1), which is represented by lithium potassium sodium niobate. Since this piezoelectric material has piezoelectric characteristics comparable to PZT, it is expected as a promising candidate that can be realized among piezoelectric materials that do not contain lead, and a thin film forming technique for this material has been vigorously developed.

  However, there is no report that a piezoelectric thin film having excellent piezoelectric characteristics of lithium potassium sodium niobate can be stably obtained by a thin film forming method such as sputtering.

  In bulk materials made of sintered oxide powder, it is known that the composition ratio of sodium and potassium needs to be adjusted to around 0.5 as lithium potassium sodium niobate having excellent piezoelectric properties. When this condition is satisfied, the material has a perovskite crystal structure having excellent piezoelectric characteristics. At the same time, it is known that a polycrystalline film whose crystal plane is predominantly oriented in the (001) direction is necessary for having excellent piezoelectric characteristics.

  However, when a thin film having the above composition ratio is formed on the substrate by the thin film formation method, sodium is difficult to enter at the crystal lattice position of potassium, particularly in the initial stage of film formation in which a seed crystal is generated on the substrate. It is difficult to form a film with a composition ratio of around 0.5, and the composition ratio of sodium and potassium in the thin film formed on the substrate deviates from 0.5 even if the film formation conditions slightly deviate from the optimum conditions. Thus, there is a problem that the crystal structure does not become a perovskite structure. Even if a perovskite crystal structure can be realized, the crystal plane often becomes a polycrystalline film oriented in a direction other than the (001) direction, and there is a problem that reproducibility and stability are extremely poor. It was.

  Accordingly, an object of the present invention is to solve the above-mentioned problems, and is composed of a polycrystalline film made of lithium potassium sodium niobate having a perovskite crystal structure and a crystal plane preferentially oriented in the (001) direction, and has excellent piezoelectric characteristics. Another object is to provide a piezoelectric thin film element excellent in reproducibility and stability.

In order to achieve the above object, the present invention provides a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially disposed on a substrate, wherein the piezoelectric thin film has a general formula (Na _x1 K _y1 Li _z1 ). A dielectric thin film of niobate oxide represented by NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1) between the piezoelectric thin film and the lower electrode A niobium oxide represented by the general formula (Na _x2 K _y2 Li _z2 ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1), A base dielectric thin film having a composition ratio of 0 <x2 <x1 is inserted.

  The term “thin film” as used herein refers to a plate-like support (substrate) formed by a physical thin film formation method such as sputtering or a chemical thin film formation method such as CVD (chemical vapor deposition). A thin film of generally several tens of microns or less deposited.

In order to achieve the above object, the present invention provides a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially arranged on a substrate, wherein the piezoelectric thin film has a general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1), and the piezoelectric thin film, the lower electrode, And an alkali niobium oxide represented by the general formula (Na _x2 K _y2 Li _z2 ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1) The base dielectric thin film whose sodium composition ratio is x2 = 0 is inserted.

In order to achieve the above object, the present invention provides a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially arranged on a substrate, wherein the piezoelectric thin film has a general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1), and the piezoelectric thin film, the lower electrode, And an alkali niobium oxide represented by the general formula (Na _x2 K _y2 Li _z2 ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1) The base dielectric thin film in which the sodium composition is increased stepwise or continuously while satisfying the relationship of 0 ≦ x2 ≦ x1 from the lower electrode to the upper electrode is inserted.

  In order to achieve the above object, the present invention provides a piezoelectric thin film element configured by sequentially arranging a lower electrode, a piezoelectric thin film, and an upper electrode on a substrate, wherein the substrate comprises a Si substrate or a glass substrate, The piezoelectric thin film has a crystal structure of a perovskite structure, and the crystal plane is preferentially oriented to any of the (100) plane, (010) plane, or (001) plane.

  The lower electrode and the electrode are composed of a single layer or a stack of Ti, Ru, Ir, Sr, or an oxide thereof, in addition to a single layer of Pt, a stack of Pt / Ti, and a stack of Pt / Ir. Is preferred.

  Here, even if a small amount of an additive is mixed in lithium potassium sodium niobate, the same effect can be expected.

  Moreover, the piezoelectric thin film element of the present invention can be used for an inkjet printer, a scanner, a gyroscope, an ultrasonic generator, an ultrasonic sensor, a pressure sensor, a speed sensor, and an acceleration sensor.

According to the piezoelectric thin film element of the present invention, the alkali represented by the general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1) Between the piezoelectric thin film made of a dielectric thin film of niobium oxide and the lower electrode, the general formula (Na _x2 K _y2 Li _z2 ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1), and a base dielectric thin film having a sodium composition ratio of 0 <x2 <x1 is inserted, whereby the base dielectric thin film has a crystalline structure. Since the composition ratio of sodium that causes disturbance is relatively low, it is possible to easily obtain a polycrystalline film in which the crystal plane is preferentially oriented to any of the (100) plane, (010) plane, or (001) plane. And said Since the piezoelectric thin film is formed by inheriting the crystallinity of the underlying dielectric thin film, the lithium potassium niobate with the crystal plane preferentially oriented to either the (100) plane, the (010) plane, or the (001) plane. A piezoelectric thin film element composed of a polycrystalline film made of sodium and having excellent piezoelectric characteristics and reproducibility and stability can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a piezoelectric thin film element 6 in which a conductive lower electrode 2, a base dielectric thin film 3, a piezoelectric thin film 4, and a conductive upper electrode 5 are integrally formed on a substrate 1. The piezoelectric thin film 4 is a lithium potassium sodium niobate represented by the general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1). The base dielectric thin film 3 has the general formula (Na _x2 K _y2 Li _z2 ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1) Lithium potassium sodium niobate represented by the following formula, and the sodium composition is a dielectric thin film having a relationship of 0 <x2 <x1.

  As the substrate 1, an inexpensive Si substrate or glass substrate is used, but in addition to this, a magnesium oxide substrate, a stainless steel substrate, a copper substrate, or an aluminum substrate can also be used. When the substrate 1 is conductive, an insulating film may be formed on the surface.

  By adopting such a configuration, the piezoelectric thin film element exhibits excellent piezoelectric characteristics as a thin film, and uses a dielectric thin film of lithium potassium sodium niobate that does not contain lead. It is also very useful from the point of view of ecology and pollution prevention.

  As Example 1 of the present invention, a piezoelectric thin film element 6 having the structure shown in FIG. 1 was produced.

  That is, by using a sputtering method as a thin film formation method on a Si substrate 1 with a square surface oxide film having a (001) plane, a thickness of 0.5 mm, and a 20 × 20 mm crystal plane, a Pt / Ti layer having a thickness of 200 nm is used. A lower electrode 2 made of a laminate was produced.

  The Ti film formation conditions are a substrate temperature of 300 ° C., a discharge power of 200 W, an introduction gas Ar atmosphere, a pressure of 1 Pa, and a film formation time of 3 minutes. The Pt film formation conditions are a substrate temperature of 300 ° C., a discharge power of 200 W, and an introduction gas Ar. The atmosphere, the pressure was 1 Pa, and the film formation time was 15 minutes.

An underlying dielectric thin film 3 made of lithium potassium sodium niobate represented by (Na _0.20 K _0.80 Li _0.00 ) NbO ₃ was formed on the lower electrode 2 by sputtering. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 75 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 30 minutes.

Subsequently, a piezoelectric thin film 4 made of lithium potassium sodium niobate represented by (Na _0.48 K _0.52 Li _0.00 ) NbO ₃ was produced by a sputtering method. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 125 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 3 hours 30 minutes.

  In order to evaluate the quality of the crystal structure of the piezoelectric thin film of this example, X-ray diffraction measurement (2θ-ω scan) was performed on a sample of this structure in which the upper electrode was not manufactured. The X-ray diffraction pattern is shown in FIG. The horizontal axis represents twice the angle (°) between the X-ray irradiation direction and the substrate surface (the surface of the piezoelectric thin film), and the vertical axis represents the number of counts per second (times / times) of X-ray diffraction at that angle. Seconds).

  Further, the upper electrode 5 made of Pt was produced by the same sputtering method. The film formation conditions were a substrate temperature of 200 ° C., a discharge power of 200 W, an introduced gas Ar atmosphere, a pressure of 2.5 Pa, and a film formation time of 1 minute.

  Thereafter, as shown in FIG. 9, a strip-shaped piezoelectric thin film element (sample) 7 having a length of 20 mm and a width of 3 mm is cut out from the multilayer structure including the piezoelectric thin film, and one end in the longitudinal direction is placed on the vibration isolation table 8. A simple unimorph cantilever was prepared by fixing with a clamp 9 provided on the surface.

  In this state, a voltage was applied between the lower electrode 2 and the upper electrode 5, and the piezoelectric thin film element (sample) 7 was expanded and contracted to operate the lever tip. The displacement at the tip at that time was measured with a laser Doppler displacement meter 10.

  As Example 2 of the present invention, a piezoelectric thin film element 13 having the structure shown in FIG. 2 was produced.

The process up to the production of the lower electrode 2 was carried out in exactly the same manner as in Example 1, and the underlying dielectric composed of lithium potassium sodium niobate represented by (Na _0.00 K _0.98 Li _0.02 ) NbO ₃ thereon. The thin film 11 was produced by a sputtering method. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 75 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 28 minutes.

Subsequently, a piezoelectric thin film 12 made of lithium potassium sodium niobate represented by (Na _0.47 K _0.51 Li _0.02 ) NbO ₃ was produced by a sputtering method. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 125 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 3 hours and 20 minutes.

  In order to evaluate the crystal structure of the piezoelectric thin film of this example, X-ray diffraction measurement was performed in exactly the same manner as in Example 1. The X-ray diffraction pattern is shown in FIG.

  Furthermore, after the upper electrode 5 was produced in the same manner as in Example 1, a simple unimorph cantilever was produced and an operation experiment was performed.

  As Example 3 of the present invention, a piezoelectric thin film element 17 having the structure shown in FIG. 3 was produced.

The process up to the production of the lower electrode 2 was performed in exactly the same manner as in Example 1, and (Na _0.10 K _0.90 Li _0.00 ) NbO ₃ and (Na _0.20 K _0.80 Li _{0. A} base dielectric thin film (a) 14 and a base dielectric thin film (b) 15 made of lithium potassium sodium niobate represented by ( ₀₀ ) NbO ₃ were prepared in this order from the substrate side by sputtering. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 75 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and film formation times of 20 minutes and 10 minutes, respectively.

Subsequently, a piezoelectric thin film 16 made of lithium potassium sodium niobate represented by (Na _0.48 K _0.52 Li _0.00 ) NbO ₃ was produced by a sputtering method. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 125 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 3 hours 30 minutes.

  In order to evaluate the crystal structure of the piezoelectric thin film of this example, X-ray diffraction measurement was performed in exactly the same manner as in Example 1. The X-ray diffraction pattern is shown in FIG.

  Furthermore, after the upper electrode 5 was produced in the same manner as in Example 1, a simple unimorph cantilever was produced and an operation experiment was performed.

  As Example 4 of the present invention, a conventional piezoelectric thin film element 19 shown in FIG. 4 was produced.

The process up to the production of the lower electrode 2 was carried out in exactly the same manner as in Example 1, and on this, from the lithium potassium sodium niobate represented by (Na _0.48 K _0.52 Li _0.00 ) NbO ₃ by the direct sputtering method. A piezoelectric thin film 18 was produced. The film formation conditions were a substrate temperature of 650 ° C., a discharge power of 125 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 3 hours 30 minutes.

  In order to evaluate the crystal structure of the piezoelectric thin film of this example, X-ray diffraction measurement was performed in exactly the same manner as in Example 1. The X-ray diffraction pattern is shown in FIG.

  Furthermore, after the upper electrode 5 was produced in the same manner as in Example 1, a simple unimorph cantilever was produced and an operation experiment was performed.

The quality of the crystal structure of the piezoelectric thin film according to the present invention will be compared. As shown in FIG. 8, the X-ray diffraction pattern of the piezoelectric thin film of the conventional example has a very small diffraction peak due to the perovskite structure of lithium potassium sodium niobate, and a crystal film having a good perovskite structure has not been produced. I understand. On the other hand, in the three examples according to the present invention shown in FIG. 1 to FIG. 3, in all the 2θ-ω measurement in the X-ray diffraction analysis, diffraction peaks are clearly observed in the vicinity of 2θ of 21 ° and 45 °, It is clear that a thin film having a good crystal structure has been produced.
In 2θ-ω measurement in X-ray diffraction analysis, the diffraction peak at 2θ of around 21 ° indicates that the crystal film of the perovskite structure is oriented in the (100) plane, (010) plane, or (001) plane. The peak near 45 ° indicates that the crystal film of the perovskite structure is oriented in the (200) plane, the (020) plane, or the (002) plane.

  Furthermore, FIG. 10 shows the result of an operation experiment using an easy unimorph cantilever. The horizontal axis represents the voltage applied to the piezoelectric element, and the vertical axis represents the amount of displacement measured with a laser Doppler displacement meter. Compared to the conventional example, in the three types of embodiments according to the present invention, it was confirmed that the displacement amount was large and the piezoelectric property was excellent.

It is a schematic diagram which shows the cross-sectional structure of the piezoelectric thin film element which concerns on Example 1 of this invention. It is a schematic diagram which shows the cross-section of the piezoelectric thin film element which concerns on Example 2 of this invention. It is a schematic diagram which shows the cross-section of the piezoelectric thin film element which concerns on Example 3 of this invention. It is a schematic diagram which shows the cross-sectional structure of the piezoelectric thin film element which concerns on a prior art example. It is a characteristic view which shows the X-ray-diffraction pattern by the piezoelectric thin film which concerns on Example 1 of this invention. It is a characteristic view which shows the X-ray-diffraction pattern by the piezoelectric thin film which concerns on Example 2 of this invention. It is a characteristic view which shows the X-ray-diffraction pattern by the piezoelectric thin film which concerns on Example 3 of this invention. It is a characteristic view which shows the X-ray diffraction pattern by the piezoelectric thin film which concerns on a prior art example. It is a schematic diagram which shows the shape and measurement state of a unimorph cantilever. It is a characteristic view which shows the relationship between the applied voltage of a piezoelectric thin film element, and a piezoelectric displacement amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower electrode 3, 11 Base dielectric thin film 4, 12, 16, 18 Piezoelectric thin film 5 Upper electrode 6, 13, 17, 19 Piezoelectric thin film element 7 Piezoelectric thin film element (sample)
8 Isolation table 9 Clamp 10 Laser Doppler displacement meter 14 Base dielectric thin film (a)
15 Base dielectric thin film (b)

Claims (4)

In a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially arranged on a substrate, the piezoelectric thin film has a general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1), and a dielectric thin film of an alkali niobium oxide. A general formula (Na _x2 K _y2 Li _z2) is provided between the piezoelectric thin film and the lower electrode. ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1), wherein the sodium composition ratio is 0 <x2 <x1 A piezoelectric thin film element, comprising: a base dielectric thin film having: In a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially arranged on a substrate, the piezoelectric thin film has a general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1), and a dielectric thin film of an alkali niobium oxide. A general formula (Na _x2 K _y2 Li _z2) is provided between the piezoelectric thin film and the lower electrode. ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1), an underlying niobium oxide whose sodium composition ratio is x2 = 0 A piezoelectric thin film element having a body thin film inserted therein. In a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially arranged on a substrate, the piezoelectric thin film has a general formula (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 <1, x1 + y1 + z1 = 1), and a dielectric thin film of an alkali niobium oxide. A general formula (Na _x2 K _y2 Li _z2) is provided between the piezoelectric thin film and the lower electrode. ) NbO ₃ (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 <1, x2 + y2 + z2 = 1), and its sodium composition is from the lower electrode toward the upper electrode 1. A piezoelectric thin film element comprising a base dielectric thin film inserted so as to increase stepwise or continuously while satisfying a relationship of 0 ≦ x2 ≦ x1.   In a piezoelectric thin film element configured by sequentially arranging a lower electrode, a piezoelectric thin film, and an upper electrode on a substrate, the substrate is made of a Si substrate or a glass substrate, and the piezoelectric thin film has a crystal structure of a perovskite structure, 4. The piezoelectric thin film element according to claim 1, wherein the crystal plane is preferentially oriented to any one of a (100) plane, a (010) plane, and a (001) plane.

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