JP4736315B2 - Piezoelectric element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piezoelectric element incorporated in various electronic devices and a method for manufacturing the same.

  Generally, a piezoelectric element has a piezoelectric plate made of a dielectric, and applies a predetermined voltage to the piezoelectric plate or applies a predetermined stress to generate a distortion or voltage proportional to the voltage or the stress on the piezoelectric plate. It is.

  Currently, there is a bimorph piezoelectric element as a widely used piezoelectric element. This bimorph piezoelectric element has a structure in which an intermediate electrode plate is sandwiched between two piezoelectric plates made of ceramics. By applying a predetermined voltage to the electrode plate, a strain proportional to the voltage is applied to the piezoelectric plate. It is a substantially strip-shaped piezoelectric element to be generated. Thus, the bimorph piezoelectric element is an element having a so-called reverse piezoelectric effect that converts an applied voltage into a stress (displacement) in the element thickness direction, and can obtain a relatively large displacement with low piezoelectricity. The bimorph piezoelectric element is mainly used for microphones, headphones, speakers, and the like.

  In addition, as an element similar to this bimorph piezoelectric element, there is a stacked piezoelectric element that can obtain a large displacement in the element thickness direction by stacking the piezoelectric plates and electrode plates in multiple layers.

Patent Document 1 describes a piezoelectric element in which the surface roughness of the piezoelectric element is 0.1 to 2.3 μm in order to increase the operating life of the piezoelectric element and increase the peeling strength of the electrode.
Patent Document 2 describes a piezoelectric element in which the pressing plate on the side in contact with the piezoelectric element has a surface roughness of 10 μm or less in order to prevent cracking of the piezoelectric element.
JP-A-8-125245 Japanese Patent Laid-Open No. 8-1111012

As described above, the bimorph piezoelectric element is characterized by a relatively large amount of displacement in the element thickness direction at a low voltage, but stress concentrates on the piezoelectric plate with the displacement. For this reason, some piezoelectric elements are cracked as soon as they are driven. When a crack occurs in the piezoelectric element, it is very difficult to continue normal operation. In general, PbZrO ₃ -PbTiO ₃ ceramics, which are widely used as piezoelectric plate materials, exhibit the above-mentioned phenomenon particularly markedly because of their brittle mechanical properties, resulting in reduced cracking and operational stability. Has been a problem.

  In view of the above points, the present invention provides a piezoelectric element that greatly improves the deflection width of a piezoelectric element, particularly a bimorph piezoelectric element, and does not generate cracks, and a method for manufacturing the same.

The piezoelectric element according to the present invention has a piezoelectric plate made of a dielectric, and applies a predetermined piezoelectric force or applies a predetermined stress to the piezoelectric plate, thereby applying a strain or a voltage proportional to the stress to the piezoelectric plate. This is a piezoelectric element to be generated . That is, the present invention includes two piezoelectric plates made of a dielectric, an intermediate electrode plate sandwiched between the two piezoelectric plates, and a counter electrode formed on each outer surface of the piezoelectric plate. The structure is structured, and the arithmetic average roughness Ra of the surface of the piezoelectric plate is 2.5 μm to 3.5 μm. Here, when the Ra of the piezoelectric plate is larger than 3.5 μm, the surface roughness is large, so that the bending strength is lowered and the quality is adversely affected. Further, when Ra is smaller than 2.5 μm, cracks are likely to occur in the piezoelectric plate, and the adhesion strength of the electrode formed on the surface of the piezoelectric plate is reduced, that is, the formed electrode is removed from the surface of the piezoelectric plate. Since it becomes easy to peel, it becomes inconvenient.

In the present invention, as the material of the upper Symbol piezoelectric plate mainly used ceramics, for example, a sintered body of large PbZrO ₃ -PbTiO ₃ system ceramics of the piezoelectric constant, also primarily as the material of the intermediate electrode plate It is preferable to use a shim material.

The method for manufacturing a piezoelectric element according to the present invention includes a step of forming a sintered body that is a PbZrO ₃ —PbTiO ₃ based material, a step of slicing the sintered body into a required shape, and forming a plate shape, A step of polishing the shaped sintered body to a predetermined thickness to form a piezoelectric plate, a step of etching until the arithmetic average roughness Ra of the surface of the piezoelectric plate is 2.5 μm to 3.5 μm, and a piezoelectric plate Forming a counter current by plating on one main surface of the substrate, and sandwiching and fixing the intermediate electrode plate so that the counter electrode is on the outside by two piezoelectric plates , and formed into a bimorph structure It is characterized by that.

  In the piezoelectric element according to the present invention, when the arithmetic average roughness (Ra) of the surface of the piezoelectric plate made of a dielectric is 2.5 μm or more and 3.5 μm or less, stress is applied to the piezoelectric plate during operation of the piezoelectric element. Even if a large displacement is exhibited, the arithmetic average roughness of the piezoelectric plate is improved, so there is little fatigue, and excellent durability is exhibited even after many uses.

In the piezoelectric element according to the present invention, especially it assumes the server Imorufu piezoelectric element, even if a relatively large stress by low voltage indicates a large amount of displacement depends on the piezoelectric plate, the surface of the as piezoelectric plate Is improved, the fatigue of the piezoelectric plate is extremely small.

  In the method for manufacturing a piezoelectric element according to the present invention, a sintered body made of a piezoelectric material is sliced and polished to a predetermined thickness, and then the surface is etched to remove polishing distortion on the surface of the piezoelectric plate, and at the same time The surface roughness of the plate, that is, the arithmetic average roughness can be optimized, and the deflection width can be improved to produce a piezoelectric element free from cracks.

  According to the piezoelectric element according to the present invention, by optimizing the surface roughness of the piezoelectric material, which is a component of the piezoelectric element, it is possible to provide a piezoelectric element free from cracks by improving the deflection width of the product. .

  According to the method for manufacturing a piezoelectric element according to the present invention, it is possible to optimize the surface roughness of a piezoelectric material that is a component of a piezoelectric element, to improve the deflection width of the product, and to manufacture a piezoelectric element that does not generate cracks. it can.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment in which a piezoelectric element according to the present invention is applied to a bimorph piezoelectric element (hereinafter simply referred to as a piezoelectric element). Here, the bimorph piezoelectric element has a structure in which an intermediate electrode is sandwiched between two piezoelectric plates as described above, and a strain proportional to the voltage is applied to the piezoelectric plate by applying a predetermined voltage to the piezoelectric plate. It is an element to be generated. A piezoelectric element 1 according to the present embodiment includes an intermediate electrode plate 4 made of a shim material sandwiched between two piezoelectric plates 2 and ₃ made of PbZrO ₃ -PbTiO ₃ based ceramics. ing. Electrodes 5 and 6 are formed on the upper and lower surfaces of the piezoelectric element 1, that is, on the upper surface 2 a of the piezoelectric plate 2 and the lower surface 3 b of the piezoelectric plate 3, respectively.

  In the present embodiment, the arithmetic average roughness Ra of the upper surfaces 2a, 3a and the lower surfaces 2b, 3b of the surfaces of the piezoelectric plates 2, 3, that is, the surfaces of the piezoelectric plates 2, 3, is 2.5 μm. It is formed with a thickness of 3.5 μm or less. Here, when the arithmetic average roughness Ra of the upper surfaces 2a and 3a and the lower surfaces 2b and 3b of the piezoelectric plates 2 and 3 is larger than 3.5 μm, the bending strength of the piezoelectric plates is remarkably lowered due to the large surface roughness. In addition, when the arithmetic average roughness Ra is smaller than 2.5 μm, the electrodes 5 and 6 formed on the upper surface 2a and the lower surface 3b of the voltage plates 2 and 3 are likely to be cracked in the piezoelectric plate, and This is inconvenient because the piezoelectric plates 2 and 3 are easily separated from the upper surface 2a and the lower surface 3b.

FIG. 2 shows a manufacturing process of the bimorph piezoelectric element. First, when a piezoelectric element is specifically manufactured, in order to obtain a relatively large displacement even at a low voltage, a sintered body of a PbZrO ₃ —PbTiO ₃ based ceramic having a large piezoelectric constant (hereinafter simply referred to as a PZT sintered body). Is used). Next, this PZT sintered body is sliced to a thickness of about 220 μm.

  Next, in the lapping step, the oval PZT sintered body is adjusted to a thickness of about 190 μm using # 1000 abrasive grains. By this lapping treatment, the surface of the sliced PZT sintered body is most flattened. Next, in the etching step, the PZT sintered body polished using a hydrofluoric acid aqueous solution is etched for 3 minutes. In this etching step, the surface roughness of the PZT sintered body that will be the upper surfaces 2a and 3a and the lower surfaces 2b and 3b of the piezoelectric plates 2 and 3 later, that is, the arithmetic average roughness Ra is 2.5 μm or more and 3.5 μm or less. Adjust so that

  Thereafter, by plating the one main surface of each PZT sintered body by an electroless plating method, the electrodes 5 and 6 serving as counter electrodes are formed. Next, an epoxy adhesive is applied to both sides of the shim material to be the intermediate electrode plate 4 having a thickness of 150 to 170 μm, and the electrodes 5 and 6 are formed by the PZT sintered bodies in which the electrodes 5 and 6 are plated. The intermediate electrode plate 4 is nipped and fixed so as to be on the outside.

  Each PZT sintered body via the intermediate electrode plate 4 is subjected to polarization treatment while being heated in silicon oil at a temperature of 80 ° C., and then processed into a predetermined strip shape to complete a piezoelectric element. To do.

  According to the method for manufacturing a piezoelectric element according to the present embodiment, a piezoelectric element having an optimal arithmetic mean roughness can be formed.

  Here, some experimental examples will be described. In these experiments, the surface property improvement effect of the piezoelectric element of the embodiment was examined. In Experiment 1, the piezoelectric element was vibrated with 100 values of vibration width. The occurrence rate of cracks at the time was investigated. In Experiment 2, the bending strength of the piezoelectric plates 2 and 3 was examined.

First, FIG. 3 is an explanatory diagram for measuring by vibrating a piezoelectric element. That is, in this experiment 1, the piezoelectric element is fixed to the jig A, a voltage of 380 Vp-p and a frequency of 60 Hz is passed through the piezoelectric element 1 to vibrate the tip B of the piezoelectric element 1. The displacement C was obtained with a laser displacement meter D, and this value was taken as the runout width.
As shown in FIG. 4, the vibration work is performed on 100 piezoelectric elements, the number of cracks generated is examined, and the ratio of the number of cracks F generated in 100 piezoelectric elements is defined as the crack generation rate.

  Next, in Experiment 2, first, samples of the piezoelectric plates 2 and 3 were processed into a shape having a length of 20 mm, a width of 7 mm, and a thickness of 0.19 mm. FIG. 5 shows the measurement of the bending strength when this sample is used. In FIG. 5, sample piezoelectric plates 2 and 3 are horizontally determined at a discretion portion 12 of the weight measuring device 11, and a vertical load is applied to the piezoelectric plates 2 and 3 from above by a pressurizer 13. The bending strength is measured by the load when the plates 2 and 3 are broken.

  The samples having different arithmetic average roughness used in the above-described experiment have different etching times before the plating process for the PZT sintered body. That is, Samples 1 to 9 shown in Table 1 are samples in which the etching time is changed from 0 to 8 minutes every minute, and the arithmetic average roughness is changed by increasing or decreasing the etching time.

  As a result of these treatments, the arithmetic average roughness becomes 1.5 μm in sample 1 (etching time 0 minutes), and the arithmetic average roughness increases with an increase in etching time. The maximum etching time is 8 minutes, and the arithmetic average roughness is 4.3 μm.

In Experiment 1 and Experiment 2, each sample is the piezoelectric element in Experiment 1, and the piezoelectric plate 1 or 2 in Experiment 2. Here, both samples are shown as Samples 1 to 9 for convenience.
The results of Experiment 1 and Experiment 2 are also shown in Table 1 below.

FIG. 6 is a graph plotted based on the sample data in Table 1. The horizontal axis represents the arithmetic average roughness, and the vertical axis represents the bending strength (N / mm ² ), the crack occurrence rate (%), and the deflection width (μm).
Thus, cracks occurred in samples 1 to 4 in Experiment 1 of FIG. When the arithmetic average roughness (Ra) is in the range of 1.5 μm to 2.3 μm, cracks due to piezoelectric element vibration occur. In Samples 1 to 4, it is considered that the strain generated in the lapping process remains and cracks are likely to occur. In Samples 5 to 9, no crack was observed. In Samples 5 to 9, it is considered that cracks are less likely to occur because the distortion generated in the etching process is removed. In Experiment 2, the bending strength of Sample 1 to Sample 7 tended to deteriorate as the arithmetic average roughness (Ra) increased. When the surface roughness of the sample 8 became 3.9 μm, it was confirmed that the powder was rapidly deteriorated and powdered fragments etched on the surface adhered.

  According to the piezoelectric element according to the present embodiment, the arithmetic average roughness (Ra) of the piezoelectric plate 2 or 3 is processed in the range of 2.5 μm to 3.5 μm, so that the piezoelectric plate 2 is in operation during the operation of the piezoelectric element. Even if a large displacement is shown in FIG. 3, the stress on the surface with respect to vibration is effectively relieved and the generation of cracks is reduced if it is within the range of the arithmetic average roughness (Ra) of the piezoelectric plates 2 and 3. Therefore, the quality when the piezoelectric element is vibrated is improved, and a swing width of 940 μm or more is obtained, thereby improving the performance.

  Although one embodiment to which the present invention is applied has been described, the present invention is not limited to these one embodiment, and the shape, material, dimensions, manufacturing method, etc., without departing from the scope of the present invention, It is possible to change arbitrarily.

  The piezoelectric element according to the present invention is suitable not only for a microphone, a headphone, and a speaker but also for a magnetic recording / reproducing apparatus such as a dynamic tracking type VTR. In this VTR, a video head is attached to the tip of a bimorph piezoelectric element so that the head follows the track.

1 is a perspective view showing an embodiment of a piezoelectric element according to the present invention. It is a manufacturing process which shows one Embodiment of the piezoelectric element which concerns on this invention. It is a schematic diagram which measures the deflection width of the piezoelectric element which concerns on this invention. It is explanatory drawing which shows the generation | occurrence | production position of the crack when vibrating the piezoelectric element which concerns on this invention. It is a schematic diagram which measures the bending strength of the piezoelectric element which concerns on this invention. It is a graph of arithmetic mean roughness, crack occurrence rate, bending strength, and deflection width showing one embodiment of a piezoelectric element according to the present invention.

Explanation of symbols

  1 .... Piezoelectric element 2,3 ... Piezoelectric plate 4 .... Intermediate electrode plate 5,6 .... Electrode 11 .... Weight measuring device 12 .... Determining part 13 .... Pressurizer

Claims (5)

Two piezoelectric plates made of a dielectric;
An intermediate electrode plate sandwiched between the two piezoelectric plates;
A counter electrode formed on each outer surface of the piezoelectric plate;
Having a bimorph structure,
An arithmetic average roughness Ra of the surface of the piezoelectric plate is 2.5 μm to 3.5 μm. The piezoelectric element according to claim 1, wherein said piezoelectric plate is formed of a material PbZrO ₃ -PbTiO ₃ system. The piezoelectric element according to claim 1 or 2, wherein said intermediate electrode plate is a shim. Forming a sintered body that is a PbZrO ₃ —PbTiO ₃ based material;
Slicing the sintered body into a required shape to form a plate,
Polishing the plate-like sintered body to a predetermined thickness to form a piezoelectric plate;
Etching until the arithmetic average roughness Ra of the surface of the piezoelectric plate is 2.5 μm to 3.5 μm;
Forming a counter current by plating on one principal surface of the piezoelectric plate;
Sandwiching and fixing the intermediate electrode plate with the two piezoelectric plates so that the counter electrode is on the outside; and
A method for manufacturing a piezoelectric element, characterized by comprising a bimorph structure . The intermediate electrode plate is formed of a shim plate
The method for manufacturing a piezoelectric element according to claim 4.

Images