JPH0469826B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric diaphragm used as a piezoelectric sounding body, a piezoelectric actuator, and the like.

[Conventional technology]

Piezoelectric sounding bodies and piezoelectric actuators utilize the deformation of piezoelectric materials that occurs when an electric field is applied, and statically they are in a state where electric charge is accumulated, similar to a capacitor, so the deformation state is No current flows during the holding state. Therefore, it has the characteristics of high electromechanical conversion efficiency and being able to be driven with low power. Therefore, in recent years, they have been used as printing heads for printers, piezoelectric motors, and the like. It has also come to be used as a sounding body for telephone handsets. In order to cause such deformation of a piezoelectric material due to an electric field, it is generally well known that a unimorph material is attached to a metal plate, which is a dissimilar material, and the unimorph is created by applying an electric field to the piezoelectric material. There is a bimorph structure that utilizes the curvature that occurs when two piezoelectric materials are stacked and the electrodes are connected so that they are opposite to each other with respect to polarization, and when an electric field is applied, one expands and the other contracts. The curvature caused by pasting the piezoelectric material is alternately displaced by applying an alternating voltage to the electric field, and by fixing the periphery, the center becomes a vibrating diaphragm, and the alternating voltage applied to this diaphragm changes the frequency of the audible frequency. It becomes possible to use it as a sounding body.

[Problem that the invention seeks to solve]

Piezoelectric diaphragms used in actuators and sounding bodies as described above are used with the periphery or one end fixed, but in the case of a circular diaphragm, it is necessary to increase the fixed diameter or increase the overall thickness of the diaphragm. By making it thinner, the displacement as a diaphragm becomes larger,
When used as a sounding body, the sound pressure characteristics at low frequencies are improved. For this reason, attention has been focused on making the diaphragm thinner, and efforts are being made to establish techniques for making the diaphragm thinner.

7a and 7b show a piezoelectric material 7 on a metal plate 71.
2 is a cross-sectional structure of a commonly used piezoelectric diaphragm with a unimorph structure. For example, by applying an electric field to the piezoelectric material 72 of such a piezoelectric diaphragm in a direction opposite to the polarization direction, the piezoelectric material 72
2 causes elongation in the plane direction, and is deflected and deformed as shown in FIG. 7b. At this time, as shown by the arrows in the figure, the piezoelectric material 72 does not extend uniformly from top to bottom, but this elongation is naturally suppressed at the bonding surface with the metal plate 71, and the bonding surface The closer you get, the smaller the stretch will be. Therefore, piezoelectric material 7
As the thickness of the piezoelectric material 72 becomes thinner, the elongation of the piezoelectric material 72 approaches a state where it is suppressed by the metal plate 71. For this reason, as the thickness of the piezoelectric material 72 becomes thinner, the displacement at the center becomes smaller, resulting in a sounding body with a lower sound pressure level. This is the same for the bimorph structured diaphragm shown in Figures 8a and 8b; as one surface expands, the other side contracts, as shown by the arrows in the figure. However, at this time as well, since the bonding surfaces of the two piezoelectric materials 81 and 82 have expansion and contraction in opposite directions, they press against each other and cannot move at all near this boundary. Therefore, when only the piezoelectric materials 81 and 82 become thinner, the movement of the two piezoelectric materials 81 and 82 becomes smaller as they get closer to this boundary. As a result, the displacement in the center becomes smaller,
As a sounding body, the sound pressure level becomes low.

Figures 9a and 9b show the frequency characteristics of sound pressure obtained through actual measurements when a bimorph-structured diaphragm made by bonding two piezoelectric materials is used as a sounding body. Here, instead of directly changing the thickness of the piezoelectric material, the thickness of the adhesive layer that bonds the piezoelectric materials together is changed.

This is because changing the thickness of the piezoelectric material changes the impedance of the diaphragm, which is thought to add to differences in drive conditions, etc., and changing the thickness of the adhesive layer also changes the impedance of the diaphragm. This is because the positional relationship with respect to the thickness between the two piezoelectric materials is the same. FIG. 9a shows the frequency characteristics of sound pressure when the total thickness of the bimorph is 214 μm, and FIG. 9b shows the frequency characteristics of sound pressure when the thickness of the entire bimorph is 420 μm. As can be seen from both figures, as the thickness decreases, the peak (resonance point) at which the sound pressure is maximum moves to the lower frequency side, but it can be seen that at this time the sound pressure level becomes smaller.

As is clear from the above explanation, by reducing the thickness of the piezoelectric material, the resonance point moves to a lower frequency range, but the movement of the piezoelectric material approaches the bonded plate or moves in the opposite direction. Due to this relationship, the displacement of the center of the curved piezoelectric material becomes small, resulting in a sounding body with a low sound pressure level. Furthermore, in the case of an actuator that simply uses displacement rather than as a sounding body, the displacement will be small, and this application aspect will also be determined.

Furthermore, if the drive voltage is increased to obtain a large displacement, such as with an actuator, stress will cause strain between the pasting member and the piezoelectric material, and between the piezoelectric material and the other piezoelectric material, resulting in the bonding. It may also be destroyed due to cracks on the surface.

[Means for solving problems]

The piezoelectric diaphragm of the present invention includes a piezoelectric material sandwiched between a first electrode and a second electrode facing each other, and a partial space provided at a position corresponding to either the first electrode or the second electrode sandwiching the piezoelectric material. and a member that is coupled to the piezoelectric material. Further, the member is characterized in that it is either a piezoelectric material or a pasting member sandwiched between opposing first and second electrodes.
Furthermore, the partial space is set by forming a groove in the attachment member. Furthermore, the partial space is set by laminating a pore-forming material and a piezoelectric ceramic green sheet.

[Effect]

The piezoelectric diaphragm of the present invention has either a unimorph structure in which one piezoelectric material is attached to a flat plate made of different materials such as a metal plate, or a bimorph structure obtained by bonding or laminating two piezoelectric materials. It can also be applied in cases where the piezoelectric material and the bonded member or the piezoelectric material and the piezoelectric material are not bonded or laminated over the entire surface, but have a partial spatial area on the bonded or laminated surface. . At this time, electrodes are formed on the piezoelectric material only in this space. Further, in the case of a circular diaphragm, the electrodes and spaces are formed in a ring shape concentric with the center, and in the case of a rectangular diaphragm, they are formed in a strip shape in the longitudinal direction of the displacement. By doing this, when an electric field is applied to the piezoelectric material, expansion and contraction in the plane direction occurs only in the portion where the electrode is formed. This electrode forming portion is not in direct contact with the surface to which the pasting member or the other piezoelectric material is pasted, and since there is a space in this portion, expansion and contraction in the surface direction is not suppressed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

1a and 1b are configuration diagrams of a piezoelectric diaphragm with a circular unimorph structure showing an embodiment of the present invention, and FIG. 1a is a partially cutaway internal configuration diagram seen from above; FIG. 1b is a cross-sectional view of the center viewed from the side. First, on one surface of the piezoelectric material 11, the same full-surface electrode 12 as usual is formed, but on the opposite surface, there are a plurality of ring-shaped electrodes 13 that are concentric circles from the center of the piezoelectric material 11. A piezoelectric material 11 having such an electrode 13 is pasted on a bonding member 14, and a plurality of ring-shaped grooves 15 corresponding to the ring-shaped electrodes 13 are formed in this bonding member 14. . Pasting member 14 and piezoelectric material 11
The areas where there is no electrode 13 are bonded with an adhesive layer 16.

2a to 2c are cross-sectional views of the electrode 22 formed on the piezoelectric material 21, the groove 24 of the attachment member 23, and the state of adhesion. 2a shows a state in which no electric field is applied to the piezoelectric material 21, and FIGS. 2b and 2c show states in which an electric field is applied in a direction opposite to the polarization direction of the piezoelectric material 21. In the figure,
The direction indicated by the arrow is the piezoelectric material 2 generated by the electric field.
1 shows the direction of elongation and contraction. Piezoelectric material 2
1 naturally expands and contracts only in the portion where the electrode 22 is formed, and does not occur in the portion of the adhesive layer 25 where the electrode 22 is not present. Since the groove 24 is formed in the attachment member 23, the electrode forming portion is not in contact with the attachment member 23, and the expansion and contraction of the piezoelectric material 21 is not suppressed. Moreover, the piezoelectric material 21 and the pasting member 23
Since there is no expansion or contraction at the adhesive layer 25, no unreasonable stress is applied to this joint surface. For these reasons, even if the thickness of the piezoelectric material 21 is made thinner, there is no difference in expansion and contraction in the direction of the thickness of the piezoelectric material 21, and the displacement of the curved central portion will not become smaller by making the piezoelectric material 21 thinner. Therefore, both the piezoelectric material 21 and the attachment member 23 can be made thinner, and when used as a sounding body, the characteristics in the low frequency region are improved.

Figures 3a to 3c show other embodiments of the invention. FIG. 3a is a cross-sectional view when no electric field is applied. Grooves 32 are formed on both sides of the pasting member 31, and electrodes 33 with the same pattern as the grooves 32 are formed on both sides.
The piezoelectric material 34 is attached with the side on which it is formed as both sides.
is pasted. By doing this, a bimorph diaphragm can be formed, but also in this case, the electrode 3
The piezoelectric part where 3 is formed is the pasting member 31
Not in contact with By applying electric fields opposite to each other in the polarization direction to the piezoelectric material 34 on both sides, the third
It is curved and deformed as shown in Figure b and Figure 3c. As a result, the piezoelectric material 34 generated by applying an electric field
The expansion and contraction of will not be suppressed. In addition, piezoelectric material 3
Since there is no expansion or contraction in the adhesive layer 35 between the adhesive layer 4 and the attachment member 31, no unreasonable stress is applied to this joint surface. For these reasons, even if the thickness of the piezoelectric material 34 is made thinner, there is no difference in the expansion and contraction in the plane direction when viewed in the thickness direction of the piezoelectric material 34, and by making the piezoelectric material 34 thinner, the displacement of the curved center portion will become smaller. do not have. In this case as well, both the piezoelectric material 34 and the attachment member 31 can be made thin as in the above embodiment, resulting in a diaphragm that is good as a sounding body.

Although each of the above embodiments has been described as a circular diaphragm, the diaphragm is not limited to a circular shape.
When supporting one end and utilizing displacement in the longitudinal direction, as shown in FIGS. 4a and 4b, the electrode 41
By making the groove 43 of the attachment member 42 into a strip shape perpendicular to the longitudinal direction in which the displacement is to be made, the portion of the piezoelectric material 44 sandwiched between the electrodes 41 has the groove 43 on the attachment member 42 side. Therefore, in this case as well, there is no need to suppress the expansion and contraction of the piezoelectric material 44.
The displacement of the end opposite to the side fixed by the support part 45 becomes larger than in the conventional case. As a result,
Its use as an actuator is expanding.

Above, we have explained the case where grooves are formed in the pasting member to which the piezoelectric material is pasted, but when a metal plate is used as the pasting member in this groove formation, it is made using means such as etching, but this groove is formed using epoxy, etc. In order to use an insulating material as a pasting member, a photocuring resin is applied to a base film such as epoxy, and this is cured using a patterned mask, etc., and unnecessary parts are removed to make the insulating material into a pasting member. A plate with grooves formed therein may be obtained, and a piezoelectric material having electrodes in a pattern matching the grooves may be attached. Furthermore, the structure can be obtained not by forming grooves on the pasting member and pasting, but also by a completely different method and structure by laminating a piezoelectric ceramic green sheet, a hole-forming material, and these.

FIG. 5a is a structural sectional view of a piezoelectric diaphragm having a bimorph structure obtained by laminating and sintering a piezoelectric ceramic green sheet and a pore-forming material. There are electrodes 51 on the top and bottom of the stack, and electrodes 51 inside.
Electrodes 52 are formed with the piezoelectric material 53 sandwiched between them, and there are holes 54 for separating the piezoelectric material 53 sandwiched between the electrodes 51 and 52.
This structure, as shown in FIG. 5b, involves making two green sheets 56 with electrode patterns 55 printed on both sides, placing a patterned pore-forming material 57 between them, stacking them, and sintering them. Get it. The pore-forming material 57 burns and gasifies during the firing process, forming cavities. For example, a photosensitive resin is exposed to light and a patterned film is bonded to a piezoelectric green sheet on which electrodes are formed. Reference may be made to Japanese Patent Application No. 60-243218 and Japanese Patent Application No. 60-243219. Also, make a paste of carbon powder and binder in the area corresponding to this hole pattern, and use this to print as a hole formation pattern with a screen printer, or pattern green sheets of carbon etc. and laminate them. You may do so. In the piezoelectric diaphragm with the bimorph structure obtained by lamination in this way, as in the above embodiment, the piezoelectric material in the portion sandwiched between the upper electrodes is not in direct contact with the other piezoelectric material due to the holes. First, for this reason, expansion and contraction in the plane direction that occurs when a voltage is applied to the piezoelectric material is not suppressed.
Further, since no electrode is formed on the joint surface between the upper and lower layers that form the bimorph, the piezoelectric material does not expand or contract at this portion, and no unreasonable stress is applied to this joint surface. In this case as well, as in the above embodiment, there is no difference in expansion and contraction in the surface direction when viewed in the thickness direction of the piezoelectric material, and the displacement of the curved center portion does not become smaller by making it thinner. Therefore, a diaphragm used as a sounding body has good low frequency characteristics, and a piezoelectric element with a large displacement can be used as an actuator.

Note that even in configurations other than those shown in the above embodiments, holes or spaces may not be formed between the piezoelectric material and the bonding member, or between the piezoelectric material and the bonding surface of the piezoelectric material on the other side. It is sufficient that electrodes are formed to sandwich the piezoelectric material in the part where this space is formed.
A cross-sectional structure as shown in FIGS. 6a and 6b may also be used. In short, the same effects as in the above embodiments can be obtained by providing holes or spaces so that the expansion and contraction portions caused by applying an electric field to the piezoelectric material do not come into contact with the attachment member or other surfaces. Furthermore, in the embodiments shown in FIGS. 1 to 4, the electrodes formed on the piezoelectric material were formed on the entire surface of the surface opposite to the bonding surface. Even as a pattern, the locations to which the electric field is applied can be restricted and the characteristics do not change in any way.

〔Effect of the invention〕

As explained above, according to the present invention, holes or spaces are formed between the piezoelectric material and the pasting member or between the piezoelectric material and the piezoelectric material on the other side, and the portion where the holes or spaces are formed is By forming electrodes facing the piezoelectric material, the expansion and contraction in the plane direction of the piezoelectric material that occurs when an electric field is applied to the piezoelectric material is not suppressed, and there is no difference in expansion and contraction in the plane direction when viewed in the thickness direction of the piezoelectric material. Therefore, even if the thickness of the piezoelectric material is reduced, the displacement of the curved central portion or the displacement of the other end when one end is supported will not become smaller. Furthermore, since the expanding and contracting surface is not in contact with the attachment member or other members, unnecessary stress is not generated in this portion, and even if a high electric field is applied, no breakage will occur at the bonded surface.

As a result, the thickness of the piezoelectric material can be reduced, and this thinning allows the diaphragm to have flexibility, resulting in excellent low frequency characteristics when used as a sounding body, for example. Furthermore, even when used as an actuator, the displacement does not decrease even if it is made thinner, so it is possible to drive at a low voltage.

Applications of such diaphragms include not only sounding bodies and actuators, but because they are thin and can be driven at low voltage, they are often used as diaphragms for piezoelectric motors, relay switches, piezoelectric pumps, inkjet heads, etc. You can expect it. In addition, these structures utilize deformation and vibration caused by applying an electric field to the piezoelectric material, but on the other hand, there are microphones, pressure sensors, and acceleration sensors that utilize electronic signals obtained by applying external pressure and vibration to the diaphragm. It can also be used for sensors, etc.

[Brief explanation of the drawing]

Figures 1a and 1b are block diagrams showing one embodiment of the present invention, and Figures 2a, 2b, and 2c show the deformation state of the piezoelectric diaphragm in response to an electric field in the same embodiment. 3a, 3b, and 3c are configuration diagrams showing other embodiments of the present invention, and FIGS. 4a and 4b are configuration diagrams showing still other embodiments of the present invention. 5a and 5b are block diagrams showing another embodiment of the present invention, FIGS. 6a and 6b are block diagrams showing still another embodiment of the present invention, and FIG. 7a and 7b are block diagrams showing an example of a piezoelectric diaphragm with a conventional unimorph structure, FIGS. 8a and 8b are block diagrams showing an example of a piezoelectric diaphragm with a conventional bimorph structure, and FIG. 9a and 9b are diagrams showing the characteristics of a conventional piezoelectric diaphragm. DESCRIPTION OF SYMBOLS 11... Piezoelectric material, 12... Electrode, 13... Electrode, 14... Pasting member, 15... Groove, 16...
... Adhesive layer, 21 ... Piezoelectric material, 22 ... Electrode, 23
...Passing member, 24...Groove, 25...Adhesive layer, 31...Pastement member, 32...Groove, 33...
...Electrode, 34...Piezoelectric material, 41...Electrode, 42...
...Pasting member, 43...Groove, 44...Piezoelectric material,
45... Support part, 51... Electrode, 52... Electrode,
53... Piezoelectric material, 54... Hole, 55... Electrode pattern, 56... Piezoelectric green sheet, 57...
…Vacancy.

Claims (1)

[Scope of Claims] 1. A piezoelectric material sandwiched between a first electrode and a second electrode facing each other, and a partial space provided at a position corresponding to either the first electrode or the second electrode sandwiching the piezoelectric material. A piezoelectric diaphragm comprising: a member having the following properties and coupled to the piezoelectric material. 2. The piezoelectric diaphragm according to claim 1, wherein the member is either a piezoelectric material sandwiched between opposing first and second electrodes or a bonding member. 3. The piezoelectric diaphragm according to claim 2, wherein the partial space is set by forming a groove in the attachment member. 4. The piezoelectric diaphragm according to claim 2, wherein the partial space is defined by laminating a hole-forming material and a piezoelectric ceramic green sheet.