JP2017117998A - Piezoelectric element and method of manufacturing the same, foreign matter removal unit and ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element capable of ensuring connection of an electrode with a sufficient thickness, by dispersing the surface tension of a routing section when baking the electrode paste, and to provide a method of manufacturing the same, a foreign matter removal unit and an ultrasonic sensor.SOLUTION: A single layer piezoelectric element 100 formed into a rectangular body, where one principal surface is bonded to a plate member, includes a piezoelectric 110 polarized in the thickness direction, and a pair of electrodes 121, 122 printed on the opposite principal surfaces. A routing part 122a for taking out the connection to the other side principal surface is formed on one 122 of the pair of electrodes, and the average surface roughness (Ra) of a region where the routing part 122a of one electrode is formed, out of the surface of the piezoelectric 110, is 1-7 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a single-layer piezoelectric element formed in a rectangular shape and having one main surface bonded to a plate member, a method for manufacturing the same, a foreign matter removing unit, and an ultrasonic sensor.

  In recent years, a piezoelectric element has been used as a mechanism for removing foreign substances adhering to a cover glass or a filter of a digital camera (Patent Document 1). In the vibration wave driving device described in Patent Document 1, an electrode is formed on the bonding surface of the piezoelectric element bonded to the lower surface on the short side of the vibration plate, and the end surface of the piezoelectric element and the vibration plate are formed on the electrode exposed from the notch. Via the end face, a lead electrode is provided by conductive paste.

  Further, as described in Patent Document 1, in the conventional piezoelectric element, in order to form electrodes facing both surfaces of the piezoelectric body and to arrange one electrode and the other electrode on one surface side, A routing electrode is provided that allows conduction from a part of the electrode to the other electrode side through the end face of the piezoelectric body.

  When arranging such routing electrodes, use a dicing saw, cut the fired piezoelectric body to the required dimensions, and then apply the necessary Ag electrodes to the front and back surfaces and side surfaces of the element by screen printing Or, it is generally formed by drawing with a brush.

JP 2007-264095 A

  When the Ag electrode is screen-printed after the piezoelectric body is processed with a dicing saw, the Ag paste becomes thin at the edge of the end face of the piezoelectric body due to the surface tension of the Ag paste during baking, and the conduction resistance increases or the connection cannot be made. In order to avoid such a problem, a chamfering process for cutting the piezoelectric body at the edge of the end face may be included. However, if the piezoelectric body is thin, the amount of cutting is difficult to control and the number of manufacturing steps increases.

  The present invention has been made in view of such circumstances, and a piezoelectric element capable of ensuring the connection of the electrode with sufficient thickness by dispersing the surface tension when the electrode paste is baked in the lead-out portion, the manufacturing method thereof, and the foreign matter An object is to provide a removal unit and an ultrasonic sensor.

  (1) In order to achieve the above object, the piezoelectric element of the present invention is a single-layer piezoelectric element formed in a rectangular body and having one main surface bonded to a plate member, and is polarized in the thickness direction. A piezoelectric body and a pair of electrodes printed on both main surfaces, and one of the pair of electrodes is formed with a lead-out portion for taking out a connection on the other main surface; Of these, the average surface roughness (Ra) of the region in which the routing portion of the one electrode is formed is 1 to 7 μm. Thereby, the surface tension at the time of baking the electrode paste is dispersed in the drawn portion, and the connection of the electrode can be ensured with a sufficient thickness.

  (2) Moreover, the piezoelectric element of the present invention is characterized in that the piezoelectric body is not chamfered at the edge of the end surface on which the lead portion of the one electrode is formed. Thereby, the chamfering process can be omitted from the manufacturing process of the piezoelectric element, and the productivity is improved.

  (3) The foreign matter removing unit of the present invention is a foreign matter removing unit that removes foreign matter in the camera, and the piezoelectric element according to (1) or (2) and one main surface of the piezoelectric element are bonded. And a plate-like optical member, and when the voltage is applied to the piezoelectric element, the optical member is vibrated to remove foreign matters on the optical member. Thereby, the electrical connection to a piezoelectric element is ensured and the foreign material removal unit which can maintain sufficient drive with high reliability can be comprised.

  (4) Moreover, the ultrasonic sensor of the present invention is an ultrasonic sensor that emits or receives ultrasonic waves, and the piezoelectric element according to (1) or (2) and one main surface of the piezoelectric element are A diaphragm to be bonded, and a voltage is applied to the piezoelectric element to vibrate the diaphragm and emit an ultrasonic wave, while receiving the ultrasonic wave by the diaphragm, the piezoelectric element It is characterized by outputting voltage. Thereby, the electrical connection to a piezoelectric element is ensured and the ultrasonic sensor which can maintain sufficient drive with high reliability can be comprised.

  (5) A method for manufacturing a piezoelectric element according to the present invention is a method for manufacturing a single-layer piezoelectric element that is formed in a rectangular body and has one main surface bonded to a plate member. Punching the green sheet with a mold, firing the punched green sheet to produce a fired body, and processing the fired body while leaving the surface punched with the mold as one end face A step of generating a piezoelectric body, a step of printing a pair of electrodes on both principal surfaces of the generated piezoelectric body, and a step of polarizing the piezoelectric body, wherein one of the pair of electrodes is on the other side The one end face is formed with a routing portion so as to go around the main surface. As a result, a piezoelectric element having a sufficiently thick electrode lead-out portion can be manufactured. Moreover, since one end face made by die punching is used, a piezoelectric element can be manufactured efficiently.

  According to the present invention, it is possible to disperse the surface tension at the time of baking the electrode paste for the drawn portion, and to secure the connection of the electrode with a sufficient thickness.

(A), (b) is the top view and sectional side view which show the piezoelectric element of this invention, respectively. It is sectional drawing which shows an element edge part, respectively (a)-(c). (A)-(d) is a figure which shows the manufacturing process of the piezoelectric element of this invention, respectively. It is a front view which shows the structure of a foreign material removal unit. (A), (b) is a figure which shows the measurement data of each surface, and the summary of measurement data, respectively.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Configuration of piezoelectric element)
FIGS. 1A and 1B are a plan view and a side sectional view showing a piezoelectric element, respectively. The piezoelectric element 100 is a single-layer piezoelectric element that is formed in a rectangular body of 4 × 30 × 0.3 mm, for example, and has one main surface bonded to a plate member. The piezoelectric element 110 and the pair of electrodes 121 and 122 I have. The piezoelectric body 110 is made of a piezoelectric material such as PZT or barium titanate and is polarized in the thickness direction. Since the piezoelectric body 110 is a single-layer piezoelectric layer and is not a laminated type, an electrode can be printed and printed on the outer shape after the piezoelectric body 110 is formed. Therefore, the electrode does not need to be fired together with the piezoelectric material, and it is sufficient to use a low-cost material that is limited to baking at a low temperature such as Ag, but an Ag / Pd (silver palladium) material may be used. . The main surface refers to the largest surface.

  The pair of electrodes 121 and 122 is made of, for example, Ag and printed on both main surfaces. On one main surface of the piezoelectric body 110 having a rectangular shape, an electrode 121 is provided over almost the entire surface, and a portion for taking out the electrode 122 is provided in a region other than the electrode 121. This is because the piezoelectric element 100 vibrates the plate member, and when one main surface thereof is in close contact with the plate member, the electrode cannot be taken out from the surface.

  In addition, the other main surface of the piezoelectric body 110 is provided with an electrode 122 as a whole, and the electrode 122 has a routing portion 122a that goes around the end surface to the main surface on the electrode 121 side and takes out the connection. . With such an electrode structure, electrical connection can be established only from one main surface of the piezoelectric element 100.

  The surface of the piezoelectric body 110 is basically processed after firing, is smooth, and has an average surface roughness (Ra) of less than 1 μm. However, the average surface roughness (Ra) of one end surface (end surface in contact with the electrode 122) on which the extraction portion 122a of the electrode 122 is formed among the surfaces of the piezoelectric body 110 is equal to the thickness of the electrode 122. 1-7 μm. Thereby, the routing part 122a of the electrode 122 is sufficiently fixed to the piezoelectric body 110, and disconnection of the electrode can be prevented. The average surface roughness (Ra) of the end face of the piezoelectric body 110 is preferably 2 μm or more.

  The piezoelectric body 110 is preferably not chamfered at the edge of the end surface on which the routing portion 122a of the electrode 122 is formed. Thereby, the chamfering process can be omitted from the manufacturing process of the piezoelectric element 100, and the productivity is improved.

(Leading part)
Next, the routing part 122a of the piezoelectric element 100 will be described. FIG. 2A is a cross-sectional view showing an end portion of a conventional piezoelectric element 800. As shown in FIG. 2A, in the piezoelectric element 800, the average surface roughness (Ra) is less than 1 μm for any surface of the piezoelectric body 810 and is smooth. Therefore, the printed film thickness at the edge of the end face is reduced due to the surface tension of the Ag paste at the time of electrode formation, and the electrode 822 of the drawn portion 822a after firing becomes thin at that portion, and the connection is interrupted.

  FIG. 2B is a cross-sectional view showing an element end portion of the piezoelectric element 900 in which a C surface is formed on the edge of the end surface. Even in the piezoelectric element 900, the average surface roughness (Ra) of any piezoelectric body 910 is smooth, being less than 1 μm. However, as shown in FIG. 2B, in the piezoelectric element 900, the corner of the edge of the piezoelectric body 910 is chamfered to form a C surface. As a result, the edge corner of the piezoelectric body 910 becomes dull, and the connection of the routing portion 922a of the electrode 922 is secured. However, in this case, it is necessary to add a precise chamfering process of about C0.1 mm.

  FIG. 2C is a cross-sectional view showing an element end of the piezoelectric element 100. In contrast to the above-described piezoelectric elements 800 and 900, in the piezoelectric element 100, the average surface roughness (Ra) of the end face of the piezoelectric body 110 is 1 to 7 μm, and the end face surface is rough. Therefore, the surface tension of the Ag paste is dispersed at the time of electrode formation, and even if the edge of the piezoelectric body 110 is not chamfered in particular, the thickness of the routing portion 122a of the electrode 122 can be maintained and electrical connection can be ensured.

(Piezoelectric element manufacturing method)
FIGS. 3A to 3D are diagrams showing the manufacturing process of the piezoelectric element 100. First, a piezoelectric material, a solvent, a binder, and the like are mixed in a predetermined composition, a green sheet is formed by extrusion molding, and the green sheet is punched with a mold. As shown in FIGS. 3A and 3B, the punched green sheet can be fired to produce a fired body 50.

  Next, the fired body 50 is cut out and processed. At this time, one end face of the fired body 50 is left as the die punched surface, and the other end face and both side faces of the piezoelectric body 110 are cut out along the broken line 60. The average surface roughness (Ra) of the die punching surface is 1 to 7 μm, whereas the average surface roughness of the cut surface is less than 1 μm. Since the dimensional accuracy of the piezoelectric element 100 affects the characteristics of the element, in order to obtain the required dimensional accuracy of the finished product, the other surface is processed by dicing cutting based on the die punching surface. After forming the lead-out portion 122a of the electrode 122, dicing cutting may be performed with reference to the end face.

  Then, a pair of electrodes is formed on both main surfaces of the piezoelectric body 110 obtained by processing by printing and baking. As an electrode material, for example, Ag paste is used. The film thickness of the Ag paste is about 5 μm in normal printing. If the average surface roughness (Ra) of the piezoelectric body is approximately the same as the thickness of the Ag paste, it is conceivable that the Ag paste is less likely to shrink due to the surface tension during baking of the Ag paste at the corners.

  One of the electrodes thus formed is provided with a lead-out portion at one end so as to go around the other main surface. As a result, a piezoelectric element in which the lead-out portion of the electrode formed to wrap around is sufficiently fixed to the piezoelectric body can be manufactured. As a result, it is possible to efficiently manufacture a piezoelectric element in which a sufficiently thick electrode lead-out portion is formed by using a surface formed by die punching.

(Application 1)
A foreign matter removing unit for removing foreign matter on the dustproof filter in the camera to which the piezoelectric element 100 is applied will be described. FIG. 4 is a front view showing the configuration of the foreign matter removal unit 200. The foreign substance removal unit 200 includes the piezoelectric element 100 and the optical member 210, and is disposed in the vicinity of the front surface of the imaging element, for example.

  Since the foreign matter adhering to the surface of the optical member becomes a shadow and appears in the subject image on the image sensor, it is necessary to remove the foreign matter. The foreign matter removing unit 200 can remove the foreign matter attached to the optical member 210 by vibrating the optical member 210 when an AC voltage is applied to the piezoelectric element 100.

  In the piezoelectric element 100, since the end face surface of the piezoelectric body 110 is rough, the routing portion 122a of the electrode 122 is firmly adhered to the end face of the piezoelectric body 110, and conduction is maintained, so that the foreign matter removing unit 200 can be sufficiently driven. One main surface of the piezoelectric element 100 is bonded to the plate-like optical member 210. The optical member 210 is a low-pass filter or a cover filter, and also functions as a dustproof filter that prevents foreign matter from adhering to the image sensor.

(Application example 2)
The above piezoelectric element 100 can also be applied to an ultrasonic sensor. The ultrasonic sensor emits or receives ultrasonic waves, and includes a piezoelectric element and a diaphragm. One main surface of the piezoelectric element is bonded to the diaphragm.

  The ultrasonic sensor vibrates the diaphragm by applying a voltage to the piezoelectric element and emits an ultrasonic wave, while the piezoelectric element outputs a voltage by receiving the ultrasonic wave by the diaphragm. By using the piezoelectric element 100 as the piezoelectric element of the ultrasonic sensor, it is possible to configure an ultrasonic sensor that can secure electrical connection and maintain sufficient driving with high reliability.

(Example)
FIGS. 5A and 5B are diagrams showing measurement data of each surface and a summary of the measurement data, respectively. According to the manufacturing process of the piezoelectric element 100, the piezoelectric body was fired. Then, the cut surface and the lapping surface were provided while leaving the die-cut surface and the unfired surface of the green sheet in the surface of the piezoelectric body. And the average surface roughness (Ra) was measured about each surface.

  FIG. 5A shows the result of measurement data on each surface. As shown in FIG. 5 (a), Ra was 0.444 μm, 0.380 μm, and 0.052 μm on the burn-in surface, the lap surface, and the cut surface, whereas Ra was 4 on the die-cut surface. .6 μm.

  Similar to the above, the surfaces of a plurality of samples were measured. FIG. 5B shows a summary of measurement data. As shown in FIG. 5 (b), the average surface roughness of the burned surface, the lapping surface, and the cut surface was less than 0.5 μm. On the other hand, it was found that the surface roughness of the die removal surface was in the range of 1 to 7 μm.

50 Firing body 60 Broken line 100 Piezoelectric element 110 Piezoelectric body 121, 122 Electrode 122a Leading part 200 Foreign matter removing unit 210 Optical member

Claims (5)

A single-layer piezoelectric element formed in a rectangular body and having one main surface bonded to a plate member,
A piezoelectric body polarized in the thickness direction;
A pair of electrodes printed on both main surfaces,
One of the pair of electrodes is formed with a lead-out portion for taking out the connection on the main surface on the other side,
The piezoelectric element according to claim 1, wherein an average surface roughness (Ra) of a region where the lead portion of the one electrode is formed in the surface of the piezoelectric body is 1 to 7 μm.   2. The piezoelectric element according to claim 1, wherein an edge of an end surface on which the lead portion of the one electrode is formed is not chamfered. A foreign matter removal unit for removing foreign matter in the camera,
The piezoelectric element according to claim 1 or 2,
A plate-like optical member to which one main surface of the piezoelectric element is bonded,
A foreign matter removing unit that vibrates the optical member when a voltage is applied to the piezoelectric element to remove foreign matter on the optical member. An ultrasonic sensor that emits or receives ultrasonic waves,
The piezoelectric element according to claim 1 or 2,
A diaphragm to which one main surface of the piezoelectric element is bonded;
The piezoelectric element vibrates the diaphragm by applying a voltage to the piezoelectric element and emits an ultrasonic wave, while the piezoelectric element outputs a voltage by receiving the ultrasonic wave by the diaphragm. Sonic sensor. A method of manufacturing a single-layer piezoelectric element formed in a rectangular body and having one main surface bonded to a plate member,
A process of punching out a green sheet of piezoelectric material with a mold with a predetermined dimension;
Firing the punched green sheet to produce a fired body;
Processing the fired body while leaving the surface punched by the mold as one end face, and generating a piezoelectric body;
Printing a pair of electrodes on both principal surfaces of the generated piezoelectric body;
Polarizing the piezoelectric body, and
A method for manufacturing a piezoelectric element, wherein a lead portion is formed on the one end face so that one of the pair of electrodes wraps around the main surface on the other side.

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