JP2009170631A - Piezoelectric element, manufacturing method thereof, and piezoelectric application device using the same - Google Patents

Abstract

Disclosed are a piezoelectric element having good dielectric properties by reducing a difference in displacement due to the polarity of an applied voltage, a method of manufacturing the piezoelectric element, and a piezoelectric application device using the piezoelectric element.
A substrate 6, a metal layer 7 disposed on the substrate 6, a dielectric film 8 disposed on the metal layer 7, and an adhesive layer 9 disposed on the dielectric film 8 are provided. The dielectric film 10 and the metal layer 11 disposed on the dielectric film 10 are provided, and the dielectric films 8 and 10 have higher crystal orientation as they approach the bonding surface with the adhesive layer 9. It was. Thereby, as a whole piezoelectric element, the difference of the voltage-displacement characteristic by the polarity of an applied voltage can be reduced.
[Selection] Figure 1

Description

  The present invention relates to a piezoelectric element having good dielectric properties and a method of manufacturing the same, and further to a piezoelectric application device using the same.

  A dielectric is an insulator in which a charge appears on its surface when an external electric field is applied (polarization occurs), and is widely used in general electronic components such as capacitors. Among them, a ferroelectric has electric polarization without applying an external electric field, and can reverse the direction of this polarization (spontaneous polarization) with an electric field applied from the outside. This ferroelectric material is used as an information storage (memory) medium because it can take two states when the electric field is zero. In addition, it is a promising material as a conversion element such as mechanical-electrical, temperature-electrical, and optical-electrical. In particular, ferroelectrics having a perovskite structure exhibit excellent ferroelectricity, piezoelectricity, pyroelectricity, and electro-optical properties, and are attracting attention as effective materials for a wide range of devices such as various sensors and actuators. The range of use is expected to expand rapidly.

  In recent years, devices using such dielectrics have been strongly demanded from the market for miniaturization, low profile, and integration. In order to realize this, it is effective to form a ferroelectric thin film. . Each research and development organization is also researching and developing using various methods and methods to realize high performance dielectric thin films.

As an example of applying a ferroelectric thin film, a Pb (Zr _x Ti _1-x ) O ₃ -based thin film having an ABO ₃ structure has high piezoelectricity, and therefore, a piezoelectric thin film of a piezoelectric element such as a piezoelectric sensor or a piezoelectric actuator. It is used as. The piezoelectric sensor uses a ferroelectric piezoelectric effect. A ferroelectric has spontaneous polarization inside and generates positive and negative charges on its surface. In the steady state in the atmosphere, it is in a neutral state combined with the charge of the molecules in the atmosphere. When an external pressure is applied to the piezoelectric body, an electrical signal corresponding to the amount of pressure can be extracted from the piezoelectric body. The piezoelectric actuator also uses the same principle, and when a voltage is applied to the piezoelectric body, the piezoelectric body expands and contracts according to the voltage, and displacement can be generated in the expansion / contraction direction or a direction orthogonal to the direction.

  Not only such a ferroelectric material but also a dielectric material used as a device is often used in a configuration in which the dielectric material is sandwiched between upper and lower electrode films.

  For example, as shown in FIG. 8, a conventional piezoelectric element includes a substrate 1 made of a silicon single crystal or the like, a metal layer 2 (lower electrode) sequentially formed on the substrate 1 by sputtering or the like, a dielectric film 3, and It consists of a metal layer 4 (upper electrode). In FIG. 9, the arrow in the dielectric film 3 indicates the polarization direction of the crystal.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP 2003-46160 A

  The conventional piezoelectric element has problems such as voltage-displacement characteristics differing depending on the polarity of the applied voltage, and the degree of freedom in device design is reduced.

  The reason is considered that in the conventional dielectric film 3, the initial layer side 5 close to the substrate 1 has low crystal orientation, so that polarization inversion tends to occur when an electric field opposite to the polarization direction is applied. .

  As a result, as a whole, the relationship between the voltage and the amount of displacement differs depending on the polarity of the applied voltage as the entire piezoelectric element.

  Accordingly, an object of the present invention is to reduce the difference in voltage-displacement characteristics depending on the polarity of the applied voltage.

  To achieve the above object, the present invention provides a substrate, a first metal layer disposed on the substrate, a first dielectric film disposed on the first metal layer, and the first metal layer. A second dielectric film disposed on the dielectric film via an adhesive layer, and a second metal layer disposed on the second dielectric film, the first and second dielectric films The body film has a higher crystal orientation as it approaches the bonding surface with the adhesive layer.

  Thereby, this invention can reduce the difference of the voltage-displacement characteristic by the polarity of an applied voltage.

  In other words, according to the present invention, since the first dielectric film and the second dielectric film have a plane of crystal orientation, the relationship between these voltages and the amount of displacement depends on the polarity of the applied voltage. The relationship is opposite to each other.

  As a result, the piezoelectric element as a whole can reduce the difference in voltage-displacement characteristics due to the polarity of the applied voltage.

(Embodiment 1)
As shown in FIG. 1, the piezoelectric element according to one embodiment of the present invention includes a substrate 6, a metal layer 7 disposed on the substrate 6, and a dielectric film 8 disposed on the metal layer 7. A dielectric film 10 disposed on the dielectric film 8 via an adhesive layer 9 and a metal layer 11 disposed on the dielectric film 10 are provided. The thicknesses of the substrate 6 were 400 μm to 600 μm, the metal layers 7 and 11 were 100 nm to 500 nm, the dielectric films 8 and 10 were 1 μm to 5 μm, and the adhesive layer 9 was 10 nm to 500 nm.

  By setting the film thickness of the metal layers 7 and 11 within the above-described range, high conductivity can be maintained when these are used as electrodes, and the crystal orientation of the dielectric films 8 and 10 is improved. I can do it.

  Moreover, the film thickness of the dielectric films 8 and 10 can be formed by the sputtering method, the CVD method, the sol-gel method, etc. by setting it as the above-mentioned range.

  Furthermore, the adhesive strength with the dielectric films 8 and 10 can be increased by setting the film thickness of the adhesive layer 9 within the above-mentioned range.

In this embodiment, single crystal silicon having SiO ₂ formed on the surface is used as the substrate 6, and the metal layers 7 and 11 are mainly composed of Pt. The adhesive layer 9 includes various materials such as metal and resin, but metal is preferable to suppress a decrease in dielectric constant, and Au is used in the present embodiment.

  In the case where a resin is used as the adhesive layer 9, it is possible to reduce the decrease in the dielectric constant in the adhesive layer 9 and to weaken the electric field applied to the dielectric films 8 and 10 by applying thinly (thickness 2 nm or less). It is necessary to prevent.

Furthermore, the dielectric films 8 and 10 are compound dielectrics each having a perovskite structure crystal structure exhibiting high piezoelectric characteristics. In the present embodiment, lead zirconate titanate Pb (Zr _x Ti _1-x ) O _{3 is used.} It was. The dielectric film 8 and the dielectric film 10 are preferentially oriented in the rhombohedral or tetragonal (001) plane.

  The dielectric films 8 and 10 have crystal orientation that is plane-symmetric with respect to the adhesive layer 9, and the crystal orientation is gradually improved as it approaches the joint surface with the adhesive layer 9 in the thickness direction. . As shown in the schematic diagram of FIG. 2, in this embodiment, the composition ratios of the dielectric films 8 and 10 change symmetrically with respect to the adhesive layer 9. In this embodiment, the adhesive layer 9 A structure in which the relative composition ratio of Pb to (Ti + Zr) decreases with increasing distance from the distance.

  Next, a method for manufacturing a piezoelectric element using the sputtering method in the present embodiment will be described.

First, as shown in FIGS. 3B and 3C, a metal layer 7 and a dielectric film 8 are sequentially formed on the SiO ₂ film (not shown) of the substrate 6 shown in FIG. To do.

  On the other hand, as shown in FIGS. 3B and 3C, the metal layer 11 and the dielectric film 10 are sequentially formed on the substrate 12 shown in FIG.

  At this time, it is desirable to form the dielectric film 8 and the dielectric film 10 under the same conditions. Then, as shown particularly in the sputtering apparatus of FIG. 4, the substrates (6 and 12 in FIG. 3C) are arranged side by side on the same substrate holder 13, and simultaneously the same target 14A is sputtered to form a metal layer (FIG. 7) and 11) of c) are laminated, and then the same target 14B is simultaneously sputtered to deposit a dielectric film (8, 10 in FIG. 3C). Thereby, the crystal orientation of the dielectric film 8 and the dielectric film 10 can be made equal. Therefore, when these are bonded together, the dielectric film 8 and the dielectric film 10 are crystallized in a very symmetrical manner via the adhesive layer 9.

  Next, as shown in FIG. 3D, gold is vapor-deposited on the surfaces of the dielectric films 8 and 10 to form adhesive layers 16 and 17.

  Thereafter, a series strong electric field is applied to the dielectric films 8 and 10 to align the polarization axis direction in the crystal in one direction. At this time, as indicated by an arrow 15 in the dielectric films 8 and 10 of FIG. 3D, the dielectric films 8 and 10 have variations in the polarization axis direction from the upper layer side to the initial layer side. This is because the lattice constants at the interfaces between the metal layer 7 and the dielectric film 8 and between the metal layer 11 and the dielectric film 10 do not completely coincide with each other, so that defects and distortions occur in the crystal. Such crystal orientation is improved as the film thickness increases.

  After that, as shown in FIG. 3E, the adhesive layer 16 and the adhesive layer 17 are joined by ultrasonic bonding or the like, and then the substrate 12 is wet-etched or dry-etched as shown in FIG. 3F. To remove. In the present embodiment, the adhesive layer 9 in FIG. 1 shows a state where the adhesive layer 16 and the adhesive layer 17 are joined.

  In this embodiment, the dielectric film is formed by the sputtering method as described above. However, a chemical vapor deposition method, a sol-gel method, or the like may be used.

  In the above embodiment, the metal layers 7 and 11 and the dielectric films 8 and 10 are laminated on the substrates 6 and 12 respectively divided in advance. However, the metal layer, the dielectric film, and the adhesive layer are formed on the wafer-like common substrate. May be formed sequentially and then cut to a desired size. In this case, especially when the adhesive layers of adjacent substrates after cutting are joined together, the crystallinity of each dielectric film approximates. Therefore, these dielectric films are crystallized very symmetrically via the adhesive layer. Will be oriented.

  The effects of the piezoelectric element in the present embodiment will be described below.

  In the present embodiment, the difference in voltage-displacement characteristics due to the polarity of the voltage applied to the metal layer 7 as the lower electrode or the metal layer 11 as the upper electrode can be reduced. In other words, the piezoelectric element exhibits substantially the same drive regardless of the polarity of the voltage applied to either of the metal layers 7 and 11 or whichever is used as the reference electrode.

  Conventionally, as shown in FIG. 8, the initial layer side 5 of the dielectric film 3 is more disturbed in the crystal orientation and the polarization is smaller.

  For example, when the lower electrode (metal layer 2) is connected to the ground and a negative voltage is applied to the upper electrode (metal layer 4), the dielectric film is displaced so as to extend in the film thickness direction. On the other hand, when a positive voltage is applied to the upper electrode (metal layer 4), it is displaced so as to shrink in the film thickness direction.

  Here, in the piezoelectric element of FIG. 8, as shown in FIG. 9, it was found that the displacement in the contracting direction when a positive voltage is applied is smaller than the displacement in the extending direction when a negative voltage is applied.

  The reason for this is not clear yet, but the initial layer side 5 of the dielectric film 3 has a low crystal orientation, and therefore, when an electric field opposite to the polarization direction is applied, polarization inversion easily occurs. Conceivable. Accordingly, in the piezoelectric element of FIG. 8, as shown in FIG. 9, when a positive voltage is applied, the amount of displacement of the entire dielectric film is smaller than when a negative voltage is applied, or between the voltage and the amount of displacement. There is a problem that the relationship does not show linearity.

  If there is a difference in the relationship between the voltage and the amount of displacement depending on the polarity of the voltage in this way, the device depends on whether the metal layer 2 or the metal layer 4 is the upper electrode, the lower electrode, or which is the reference electrode. When the positive and negative voltages are alternately applied between the metal layer 2 and the metal layer 4, the amount of displacement proportional to the applied voltage cannot be obtained, and the degree of freedom in device design is narrowed. .

  In contrast, in the present embodiment, as shown in FIG. 1, the dielectric film 8 and the dielectric film 10 are configured such that the crystal orientation becomes higher as they approach the bonding surface with the adhesive layer 9. In other words, since the dielectric film 8 and the dielectric film 10 are arranged so that the crystal orientation is plane-symmetric, in the initial state of zero potential, for example, as shown in FIG. The dielectric film 10 indicates the polarization direction upward and downward. The initial layer side of each of the dielectric films 8 and 10 has a small polarization.

  For example, when the metal layer 7 is a ground electrode and a negative voltage is applied to the metal layer 11, the dielectric film 10 has a different electric field and polarization direction. Therefore, polarization inversion easily occurs from the initial layer side, and the displacement is reduced. . Further, the dielectric film 8 is displaced (shrinks) relatively large because the electric field and the polarization direction are the same.

  On the other hand, when a positive voltage is applied to the metal layer 11, the dielectric film 10 has a large displacement and the dielectric film 8 has a small displacement.

  That is, in the present embodiment, the dielectric film 8 and the dielectric film 10 are bonded to each other in a plane symmetry, so that the piezoelectric element as a whole shows the same relationship between the voltage and the displacement even if the polarity of the applied voltage is changed. It is.

  Further, in this embodiment, in addition to the crystal orientation being symmetric as described above, the composition ratio of Pb: (Ti + Zr) between the dielectric film 8 and the dielectric film 10 is set as shown in FIG. By making the plane symmetry via the adhesive layer 9, the difference in voltage-displacement characteristics due to the polarity of the applied voltage can be further reduced. And thereby, the freedom degree of the design of the device using this piezoelectric element can be raised.

  In this embodiment, since the metal layers 7 and 11 are made of the same material, the crystal orientation is approximated if the dielectric films 8 and 10 are formed under the same conditions. Therefore, even if the polarity of the applied voltage is changed, the relationship between the voltage and the displacement amount is almost the same proportional relationship.

Further, in this embodiment, since the metal layers 7 and 11 are made of Pt, the lattice constants with the dielectric films 8 and 10 made of Pb (Zr _x Ti _{1 -x} ) O ₃ are approximated, and the crystal disorder of the initial layer is disturbed. Can be relatively reduced. Therefore, a dielectric element having excellent piezoelectric characteristics can be formed.

  In the present embodiment, since the adhesive layer 9 is made of gold, it can be easily formed on the dielectric films 8 and 10, and the bonding strength thereof can be increased.

  Note that the piezoelectric element of the present embodiment can achieve good piezoelectric characteristics regardless of the polarity of the applied voltage. For example, as shown in FIG. 5, a mirror unit 18 is disposed on the substrate 6 of the piezoelectric element. A mirror device (piezoelectric actuator) that reflects and scans the light from the light source 19 can be formed.

  In addition, it is used for piezoelectric sensors such as angular velocity sensors, acceleration sensors, pressure sensors, flow sensors, piezoelectric actuators such as microswitches, micropumps, component separation devices, inkjet heads, or piezoelectric acoustic devices such as microspeakers and microphones. Thus, the degree of freedom in designing these devices is increased, and various drive modes can be realized.

  In the above embodiment, the dielectric film has two layers. However, as shown in FIG. 6, the dielectric film 20 and the metal layer 7, and the dielectric film 20 and the metal layer 11 are respectively provided with the dielectric film 20. Alternatively, a laminate in which the same number of the metal layers 21 and the metal layers 21 are laminated may be disposed. In FIG. 6, the dielectric film 20 and the metal layer 21 are laminated one by one. By further laminating the dielectric film 20 in this way, the displacement of the entire piezoelectric element can be increased.

  6 includes a dielectric film 20 disposed between the metal layer 7 and the dielectric film 8, and a dielectric film 20 disposed between the metal layer 11 and the dielectric film 10. The crystal orientation is symmetrical with respect to the adhesive layer 9. Thereby, the difference of the voltage-displacement characteristic by the positive / negative of the voltage applied to the metal layer 11 which is an upper electrode, and the metal layer 7 which is a lower electrode can be reduced.

  As shown in FIG. 6, a method of laminating a dielectric film is to form a thin film on the substrate 6 in the order of the metal layer 7, the dielectric film 8, the metal layer 21, the dielectric film 20, and the adhesive layer 9 by sputtering or the like. It can be formed by laminating and similarly laminating the metal layer 11, the dielectric film 10, the metal layer 21, the dielectric film 20 and the adhesive layer 9 in this order on another substrate, and bonding the adhesive layers 9 together.

(Embodiment 2)
In the present embodiment, as shown in FIG. 7, four layers of dielectric films 8, 10, 22, and 23 are laminated on the substrate 6. The lower electrode is a metal layer 7 between the substrate 6 and the dielectric film 8, and the upper electrode is a metal layer 24 formed on the dielectric film 23.

  The dielectric film 8 to the dielectric film 23 are joined to each other by an adhesive layer 25 made of metal. That is, in this embodiment, there are an even number of dielectric films, and the number of dielectric films having the same polarization direction in the initial state is the same. The dielectric film 8 and the dielectric film 10, the dielectric film 10 and the dielectric film 22, and the dielectric film 22 and the dielectric film 23 have crystal orientations that are plane-symmetric with respect to the adhesive layers 25. Yes.

  Accordingly, in the present embodiment, as in the first embodiment, the difference in the relationship between the voltage and the displacement amount due to the polarity of the applied voltage can be reduced in the entire piezoelectric element.

  In addition, the manufacturing method of the piezoelectric element in this Embodiment is demonstrated below.

  First, the dielectric film 8 and the dielectric film 10 are formed on separate substrates, and the substrate on which the dielectric film 10 is formed by bonding is removed. Further, the dielectric film 22 and the dielectric film 23 are formed on separate substrates and bonded together, and the substrate on which the dielectric film 22 is formed is removed.

  Thereafter, the dielectric film 10 and the dielectric film 22 are bonded together, and the substrate on which the dielectric film 23 is formed is removed, whereby the piezoelectric element of the present embodiment is formed.

  Description of other configurations and effects similar to those of the first embodiment will be omitted.

  The present invention can reduce the difference in the relationship between the voltage and the amount of displacement depending on the polarity of the applied voltage, and can increase the degree of freedom in designing a piezoelectric device using this piezoelectric element.

Sectional drawing of the piezoelectric element in Embodiment 1 of this invention A diagram schematically showing the composition ratio of the piezoelectric element (A)-(f) The figure which shows the manufacturing method of the same piezoelectric element Schematic diagram of sputtering equipment for manufacturing the same piezoelectric element Schematic cross-sectional view of a mirror device using the same piezoelectric element Sectional drawing of the piezoelectric element of another example in Embodiment 1 of this invention Sectional drawing of the piezoelectric element in Embodiment 2 of this invention Cross-sectional view of a conventional piezoelectric element The figure which shows the relationship between the applied voltage and the amount of displacement in the conventional dielectric element

Explanation of symbols

6 Substrate 7 Metal layer 8 Dielectric film 9 Adhesive layer 10 Dielectric film 11 Metal layer 12 Substrate 13 Substrate holder 14A, 14B Target 15 Arrow 16 Adhesive layer 17 Adhesive layer 18 Mirror part 19 Light source 20 Dielectric film 21 Metal layer 22 Dielectric Body film 23 Dielectric film 24 Metal layer 25 Adhesive layer

Claims (10)

A substrate,
A first metal layer disposed on the substrate;
A first dielectric film disposed on the first metal layer;
A second dielectric film disposed on the first dielectric film via an adhesive layer;
A second metal layer disposed on the second dielectric film,
The first and second dielectric films are
A piezoelectric element in which crystal orientation becomes higher as it approaches a bonding surface with the adhesive layer. The first and second dielectric films are
The piezoelectric element according to claim 1, wherein a composition ratio is plane-symmetric with respect to the adhesive layer. The piezoelectric element according to claim 1, wherein the first and second metal layers are mainly composed of Pt. 2. The piezoelectric element according to claim 1, wherein the first and second dielectric films have a crystal structure of a perovskite structure. Between the first metal layer and the first dielectric film and between the second metal layer and the second dielectric film,
A laminate in which the same number of dielectric films and metal layers are alternately laminated is disposed,
A laminate dielectric film disposed between the first metal layer and the first dielectric film;
The dielectric film of the laminate disposed between the second metal layer and the second dielectric film,
The piezoelectric element according to claim 1, wherein the piezoelectric element has a crystal orientation that is plane-symmetric with respect to the adhesive layer between the first dielectric film and the second dielectric film. Between the second dielectric film and the second metal layer,
A third dielectric film disposed on the second dielectric film via an adhesive layer;
A fourth dielectric film disposed on the third dielectric film via an adhesive layer;
The second dielectric film and the third dielectric film and the third dielectric film and the fourth dielectric film are:
The piezoelectric element according to claim 1, having crystal orientation that is plane-symmetric with respect to each bonding surface. On the other hand, a metal layer, a dielectric film, and an adhesive layer are sequentially formed on the first substrate.
On the other hand, a metal layer, a dielectric film, and an adhesive layer are sequentially formed on the second substrate,
Next, bonding the respective adhesive layers on the first substrate and the second substrate,
A method for manufacturing a piezoelectric element, after which the second substrate is removed. A metal layer, a dielectric film, and an adhesive layer are sequentially formed on the substrate surface,
Next, the substrate is cut to a desired size, and the adhesive layers on the cut first substrate and the second substrate are joined together,
A method for manufacturing a piezoelectric element, after which the second substrate is removed. The method for manufacturing a piezoelectric element according to claim 7 or 8, wherein the dielectric film is formed by any one of a sputtering method, a CVD method, and a sol-gel method. The piezoelectric actuator using the piezoelectric element as described in any one of Claims 1-6, a piezoelectric sensor, or a piezoelectric acoustic device.

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