JP2008127244A - Piezoelectric ceramics and piezoelectric ceramics element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramics which is composed of a thin film of an alkali niobate having a lead-free specified composition and has excellent piezoelectric characteristics, and to provide a piezoelectric ceramics element. <P>SOLUTION: The piezoelectric ceramics comprises a thin film of an alkali niobate, expressed by general formula: (Na<SB>x</SB>K<SB>1-x</SB>)<SB>1-y</SB>Nb<SB>y</SB>O<SB>3</SB>, wherein 0.40≤x≤0.48 and 0.48≤y≤0.55. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to piezoelectric ceramics and piezoelectric ceramic elements made of alkali niobium oxide having excellent piezoelectric characteristics.

  Piezoelectric ceramics are processed into various piezoelectric elements for various purposes, and actuators that cause deformation by applying voltage to the elements, and deformation by applying pressure to the element, and voltage is applied according to the deformation. Widely used as functional electronic components such as sensors to be generated.

As the piezoelectric ceramics to be used for an actuator or 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, and it has become necessary to fabricate elements using a photolithography technique used when fabricating a semiconductor integrated circuit. In this case, the piezoelectric ceramic is required to have a thin film shape with a film 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 viewpoints 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

  Piezoelectric ceramics made of PZT contain about 60 to 70% by weight of lead oxide (PbO), which is not preferable from the viewpoint of ecology and pollution prevention. Therefore, development of piezoelectric ceramics that do not contain lead is desired in consideration of the environment.

Currently, various lead-free piezoelectric ceramics have been studied. Among them, lithium potassium sodium niobate (general formula: (Na _x K _y Li _z ) NbO ₃ (0 <x <1, 0 <y <1) , 0 <z <1, x + y + z = 1)). Since this lithium potassium sodium niobate has piezoelectric characteristics comparable to PZT, it is expected as a promising candidate for lead-free piezoelectric ceramics.

Sodium-based piezoelectric ceramic lithium potassium niobate is generally prepared by sintering _{method, Nb 2 0 5, K 2} CO 3, NaCO 3, LiCO 3 each powder is used as the starting material at that time. The target piezoelectric ceramic sintered body is manufactured by solid-phase reaction of these powder materials, but it is difficult to completely solid-phase react all of the starting materials, and a part of the starting materials is sintered. It remains in the body. Among these, since K ₂ CO ₃ has deliquescence properties, there is a problem that the sintered body is decomposed by reacting with moisture in the atmosphere, which makes it difficult to obtain a stable sintered body.

On the other hand, when a thin film forming method such as a sputtering method is used, it is possible to avoid decomposition due to deliquescence of the residual K ₂ CO ₃ , which was a problem in the sintering method. However, in the thin film formation method, there has been no report that a crystalline piezoelectric ceramic having excellent piezoelectric characteristics has been obtained so far, and the cause thereof has not been clarified.

  In view of the above problems, an object of the present invention is to provide a piezoelectric ceramic made of a niobium oxide having a specific composition having excellent piezoelectric characteristics, and a piezoelectric ceramic element using the thin film.

In order to achieve the above object, the piezoelectric ceramic of the present invention is composed of an alkali niobium oxide represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ , and the composition is 0.40 ≦ x ≦ 0.48 and 0.48 ≦ y ≦ 0.55.

In order to achieve the above object, the piezoelectric ceramic of the present invention comprises an alkali niobium oxide thin film represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ , and the composition is 0.40 ≦ x ≦ 0.48 and 0.48 ≦ y ≦ 0.55.

  The piezoelectric ceramics are preferably made of a polycrystalline body having a perovskite crystal structure and having piezoelectricity.

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

In order to achieve the above object, the piezoelectric ceramic element of the present invention comprises an alkali niobium oxide thin film represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ , and its composition is A piezoelectric ceramic in which 0.40 ≦ x ≦ 0.48 and 0.48 ≦ y ≦ 0.55 is arranged between a conductive lower electrode and a conductive upper electrode. It is.

  The conductive lower electrode is preferably any one of a Pt single layer, a Pt / Ti laminate, and a Pt / Ir laminate.

  In the piezoelectric ceramic of the present invention, a small amount of additive may be mixed in the alkali niobium oxide, and the same effect can be obtained.

According to the present invention, with respect to the alkali niobium oxide represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ , excellent piezoelectric characteristics can be obtained by adopting such a specific composition. The piezoelectric ceramic can be obtained, and with such a specific composition, the thin film can be stably obtained by the thin film forming method.

  The same effect can be obtained when a small amount of additive is mixed in the piezoelectric ceramic.

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

FIG. 1 shows a piezoelectric ceramic element 5 in which a piezoelectric ceramic 1 according to the present invention is disposed between a conductive lower electrode 2 and a conductive upper electrode 3 and is integrally formed on a substrate 4. The piezoelectric ceramic is made of an alkali niobium oxide represented by a general formula of (Na _x K _1-x ) _1-y Nb _y O ₃ and has a composition of 0.40 ≦ x ≦ 0.48 and 0.48. ≦ y ≦ 0.55 is satisfied.

  The piezoelectric ceramics 1 is formed as a thin film on a substrate 4 through a lower electrode 2 by a thin film forming method.

  As the substrate 4, 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 4 is conductive, an insulating film may be formed on the surface.

  By adopting such a configuration, the piezoelectric ceramic element 5 is a thin film that exhibits excellent piezoelectric characteristics and is made of an alkali niobium oxide ceramic that does not contain lead. It is very useful from the point of view of science and pollution prevention.

  As an example of the present invention, a piezoelectric ceramic element 5 having a structure shown in FIG. 1 is manufactured.

  A lower electrode 2 made of a Pt / Ti layer having a thickness of 200 nm is formed on a Si substrate 4 with an oxide film having a (001) plane, a thickness of 0.5 mm, and a thickness of 20 × 20 mm by using a sputtering method as a thin film forming method. did.

  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.

On this lower electrode 2, a piezoelectric ceramic 1 made of a thin film of alkali niobium oxide represented by (Na _0.45 K _0.55 ) _0.48 Nb _0.52 O ₃ was produced by a sputtering method. The film formation conditions were a substrate temperature of 700 ° C., a discharge power of 75 W, an introduced gas Ar atmosphere, a pressure of 0.4 Pa, and a film formation time of 3 hours 30 minutes.

  Further, the upper electrode 3 made of Pt was formed 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, a strip-shaped piezoelectric ceramic element (sample) 6 having a length of 20 mm and a width of 3 mm is cut out from the multilayer structure including the piezoelectric ceramic, and one end in the longitudinal direction is cut off from the base 7 of the vibration isolation table 7 as shown in FIG. A simple unimorph cantilever was prepared by fixing with the clamp 8 provided above.

  In this state, a voltage was applied between the electrodes 2 and 3, and the piezoelectric ceramic element (sample) 6 was expanded and contracted to operate the tip of the lever. The tip displacement at that time was measured with a laser Doppler displacement meter 9.

  Further, among the piezoelectric ceramic elements (samples) 6, those in which only the piezoelectric ceramic composition was changed were produced in the same manner as described above.

That is, the composition of sodium and potassium is changed (Na _0.00 K _1.00 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.15 K _0.85 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.19 K _0.81 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.25 K _0.75 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.32 K _0.68 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.39 K _0.61 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.41 K _0.59 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.43 K _0.57 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.47 K _0.53 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.49 K _0.51 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.58 K _0.42 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.62 K _0.38 ) _0.48 Nb _0.52 O ₃ ,
(Na _0.75 K _0.25 ) _0.48 Nb _0.52 O ₃ ,
13 types were produced.

  FIG. 3 shows the relationship between the sodium composition of the piezoelectric ceramic element (sample) 6 manufactured using the above 14 kinds of sodium and potassium compositions different from each other and the piezoelectric constant obtained from the measurement result of FIG. . It can be seen that when the sodium composition x is in the range of 0.40 ≦ x ≦ 0.48, the piezoelectric constant is rapidly improved and the piezoelectric characteristics are improved.

On the other hand, assuming that the composition of niobium relative to sodium and potassium is changed,
(Na _0.45 K _0.55 ) _0.54 Nb _0.46 O ₃ ,
(Na _0.45 K _0.55 ) _0.53 Nb _0.47 O ₃ ,
(Na _0.45 K _0.55 ) _0.52 Nb _0.48 O ₃ ,
(Na _0.45 K _0.55 ) _0.50 Nb _0.50 O ₃ ,
(Na _0.45 K _0.55 ) _0.47 Nb _0.53 O ₃ ,
(Na _0.45 K _0.55 ) _0.46 Nb _0.54 O ₃ ,
(Na _0.45 K _0.55 ) _0.45 Nb _0.55 O ₃ ,
(Na _0.45 K _0.55 ) _0.44 Nb _0.56 O ₃ ,
(Na _0.45 K _0.55 ) _0.43 Nb _0.57 O ₃ ,
(Na _0.45 K _0.55 ) _0.42 Nb _0.58 O ₃ ,
10 types were produced.

  FIG. 4 shows the relationship between the niobium composition of a piezoelectric ceramic element manufactured using the above-described eleven types of piezoelectric ceramic elements (samples) 6 having different niobium compositions with respect to sodium and potassium, and the piezoelectric constant obtained from the measurement results of FIG. Shown in It can be seen that when the niobium composition y is in the range of 0.48 ≦ y ≦ 0.55, the piezoelectric constant is rapidly improved and the piezoelectric characteristics are improved.

From this example, the composition of the thin film of alkali niobium oxide represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ is 0.40 ≦ x ≦ 0.48 and 0 It is apparent that piezoelectric ceramics and piezoelectric ceramic elements having excellent piezoelectric characteristics can be obtained by setting .48 ≦ y ≦ 0.55.

It is a schematic diagram which shows the cross-sectional structure of the piezoelectric ceramic element which concerns on one embodiment of this invention. It is a schematic diagram which shows the shape and measurement state of a unimorph cantilever. It is a graph which shows the relationship between the sodium composition with respect to potassium and a piezoelectric constant of an alkali niobium oxide thin film. It is a graph which shows the relationship between the niobium composition with respect to sodium and potassium of an alkali niobium oxide thin film, and a piezoelectric constant.

Explanation of symbols

1 Piezoelectric Ceramics 2 Lower Electrode 3 Upper Electrode 4 Substrate 5 Piezoelectric Ceramic Element 6 Piezoelectric Ceramic Element (Sample)
7 Isolation table 8 Clamp 9 Laser Doppler displacement meter

Claims (5)

It consists of an alkali niobium oxide represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ , and its composition is 0.40 ≦ x ≦ 0.48 and 0.48 ≦ y ≦ 0.55. Piezoelectric ceramics characterized by the above. It consists of a thin film of an alkali niobium oxide represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ and has a composition of 0.40 ≦ x ≦ 0.48 and 0.48 ≦ y ≦ 0. .55, which is a piezoelectric ceramic.   3. The piezoelectric ceramic according to claim 1, wherein the piezoelectric ceramic is made of a polycrystal having a perovskite crystal structure and has piezoelectricity. It consists of a thin film of an alkali niobium oxide represented by the general formula (Na _x K _1-x ) _1-y Nb _y O ₃ and has a composition of 0.40 ≦ x ≦ 0.48 and 0.48 ≦ y ≦ 0. A piezoelectric ceramic element comprising: a piezoelectric ceramic of .55, disposed between a conductive lower electrode and a conductive upper electrode.   5. The piezoelectric ceramic element according to claim 4, wherein the conductive lower electrode is any one of a Pt single layer, a Pt / Ti laminate, and a Pt / Ir laminate.

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