JP2005057243A - Method of inspecting laminated piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of inspecting a laminated piezoelectric element capable of easily and more certainly discovering defects. <P>SOLUTION: In a laminated piezoelectric element 1 constituted by alternately laminating a piezoelectric layer 11 and internal electrode layers 121, 122, defective goods are separated by monitoring a detection current which is generated by impressing a dc voltage to the laminated piezoelectric element 1 so that the internal electrode layers 121, 122 adjoining through the piezoelectric layer 11 may have different potentials. Besides, if an electric field strength at the time of impressing the dc voltage to the laminated piezoelectric element to be inspected is set to E (kV/mm), and if the detection current generated by impressing the dc current to the laminated piezoelectric element is set to X (μA), it is desirable to classify the case as the defective goods when there exist one or more peaks having a distance 0.008E or more between base lines in a wave representing a time variation of the detection current X. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for nondestructively inspecting a laminated piezoelectric element.

In the multilayer piezoelectric element, defects such as delamination (cracking), cracks, pores (pores, cavities), etc. may occur inside the manufacturing process.
As an inspection method for finding these defects, there is a method in which a high voltage is applied to the multilayer piezoelectric element and the insulation resistance of the multilayer piezoelectric element is measured after the defect is deteriorated.
There is also a method of measuring by applying two kinds of voltages to the laminated piezoelectric element.
Furthermore, there is a method of measuring the insulation resistance by applying a voltage several times to several tens of times the rated voltage in a short time to the multilayer piezoelectric element.

JP-A-8-186057 Japanese Patent Laid-Open No. 11-345738 JP-A-9-152455

  However, although there are defects, there are defective products that have high initial insulation resistance and cannot be distinguished by conventional methods. This defective product can be inspected nondestructively by using an ultrasonic flaw detector or the like, but these methods are not suitable for mass inspection.

  The present invention has been made in view of such conventional problems, and is intended to provide a method for inspecting a multilayer piezoelectric element that is nondestructive and can detect defects easily and more reliably. .

A first aspect of the present invention is a multilayer piezoelectric element formed by alternately laminating piezoelectric layers and internal electrode layers.
Defective products are separated by monitoring a detection current generated by applying a DC voltage to the stacked piezoelectric element so that adjacent internal electrode layers alternately have different potentials through the piezoelectric layer. A method for inspecting a multilayer piezoelectric element is provided.

Next, the effects of the present invention will be described.
The stacked piezoelectric elements are stacked so that the internal electrode layers sandwiching the piezoelectric layers have different potentials. The piezoelectric layer is a dielectric material, and the laminated piezoelectric element has the same electrical characteristics as a capacitor.
Therefore, when a DC voltage is applied to a normal multilayer piezoelectric element, a current flows immediately after the application, but as the time passes, the current monotonously decays and eventually becomes a saturated state. Become. A characteristic as shown by the solid line in FIGS. 3 to 8 described later is obtained from an ideal laminated piezoelectric element having no defect.

Here, it is assumed that the laminated piezoelectric element has defects such as delamination, cracks, pores (pores, cavities), and the like. If there is a defect, a minute current flows in the vicinity of the defect, and therefore, as shown by a broken line in FIGS. 3 and 4 to be described later, a disturbance deviating from the base line (a sharp peak or a gentle rise) occurs. Here, when there is a disturbance in the detected current, a base line is formed by eliminating the disturbance and forming a virtual curve in the peak exclusion portion by a chart diagram or a curve function. Alternatively, even if a sufficiently long time elapses, the current does not become saturated and changes with time as shown by a broken line in FIG.
Therefore, by applying a DC voltage to the multilayer piezoelectric element so that adjacent internal electrode layers have different potentials through the piezoelectric layer, and monitoring the detection current generated in the multilayer piezoelectric element, defective products can be detected. Can be separated.

  The laminated piezoelectric element is provided with side electrodes so that the internal electrode layers have different potentials when driven. Therefore, a DC voltage is applied from the side electrodes, and the internal electrode layer and side electrode layers of the laminated piezoelectric element are applied. The operation of monitoring the detected current flowing through the switch is easy and inexpensive. Furthermore, the detected current of an ideal laminated piezoelectric element having no defects attenuates exponentially with time due to the characteristics of the capacitor. Therefore, it is easy to detect a slight disturbance in the detection current, and therefore it is possible to detect defects more reliably.

  As described above, according to the present invention, it is possible to provide a method for inspecting a laminated piezoelectric element that is nondestructive and can detect defects easily and more reliably.

The inspection method according to the present invention can be used for various types of laminated piezoelectric elements.
Multilayer piezoelectric elements are generally known to have a full-surface electrode configuration and a partial electrode configuration. The full-surface electrode configuration has a cross-sectional shape of a piezoelectric layer and an internal electrode layer (a shape when cut in a direction perpendicular to the stacking direction). The internal electrode layer is exposed to the side surface of the multilayer piezoelectric element.
Further, in the partial electrode configuration, the cross-sectional shape of the internal electrode layer is smaller than the cross-sectional shape of the piezoelectric layer, and only the internal electrode layer to be electrically connected to the side electrode (see later) is exposed on the side surface.

In addition, there is an integrated type in which a desired number of internal electrode layers and piezoelectric layers are alternately stacked together, and a desired number of piezoelectric units configured by alternately stacking internal electrode layers and piezoelectric layers are stacked. Unit type elements.
The inspection method according to the present invention can find a defective product having a defect without selecting such a kind or configuration of the element.

In addition, it is a time change of the detection current generated by applying a DC voltage to a defect-free multilayer piezoelectric element, and a waveform that decays exponentially with the passage of time is used as a baseline, and the multilayer When the electric field strength when applying a DC voltage to the piezoelectric element is E (kV / mm) and the detection current generated by applying the DC voltage is X (μA),
It is preferable that one or more peak portions having a distance of 0.008E or more between the base line and the waveform representing the time change of X are classified as defective products (claim 2).

When a DC voltage is applied to an ideal laminated piezoelectric element having no defect, the current decays exponentially with time as shown by the solid line in FIGS. Become.
Thus, an exponentially decaying current obtained from a defect-free multilayer piezoelectric element is used as a base line, and there is a peak portion that deviates from the base line. As shown in FIGS. When the distance from the substrate is 0.008E or more, this is evidence that there is a defect somewhere in the laminated piezoelectric element and a minute current flows in the vicinity of the defect.

  Further, when the electric field strength when applying a DC voltage to the multilayer piezoelectric element to be inspected is E (kV / mm) and the detection current generated by applying the DC current is X (μA), 120 It is preferable that after X seconds, X is 0.024E or more to be separated from defective products.

As described above, the multilayer piezoelectric element has electric characteristics similar to those of a capacitor. Therefore, when a DC voltage is applied, the current hardly finally flows.
If the detection current X generated by applying a direct current is 0.024E or more after 120 seconds, there is a defect somewhere in the laminated piezoelectric element, and evidence that a minute current flows in the vicinity of the defect It is.

  Next, the DC voltage is preferably higher than the coercive electric field of the piezoelectric layer and lower than the withstand voltage of the piezoelectric layer.

Thereby, it is possible to eliminate the influence due to the rotation of the electric dipole or the like, and it is possible to prevent the self-destruction due to the dielectric breakdown of the multilayer piezoelectric element.
Here, the coercive electric field is the absolute value of the voltage at which the polarization decreases when the voltage in the direction opposite to the polarization direction is increased in a sufficiently polarized ferroelectric. Yes, it refers to the voltage value at which the polarization reversal current is observed. The withstand voltage is the highest voltage that the sample under test can withstand without breaking.

  Next, the DC voltage is preferably in the range of 1.5E0 to 0.9E1, where E0 is the coercive electric field of the piezoelectric layer and E1 is the withstand voltage.

  By applying a DC voltage in the above range, it is possible to more reliably eliminate the influence of rotation of the electric dipole or the like, and to more reliably prevent self-destruction of the laminated piezoelectric element.

The DC voltage is preferably in the range of 1.8E0 to 0.6E1.
In this case, it is possible to further enhance the effect of eliminating the influence due to the rotation of the electric dipole or the like and preventing the self-destruction of the multilayer piezoelectric element.

Embodiments of the present invention will be described below with reference to the drawings.
(Example 1)
In this example, as shown in FIGS. 1 and 2, in the stacked piezoelectric element 1 in which the piezoelectric layers 11 and the internal electrode layers 121 and 122 are alternately stacked, the internal electrode layers adjacent to each other via the piezoelectric layer 11. A method for separating defective products by monitoring a detection current generated by applying a DC voltage to the multilayer piezoelectric element 1 so that 121 and 122 have different potentials will be described.

As shown in FIGS. 1 and 2, the multilayer piezoelectric element 1 to be inspected in this example is formed by alternately stacking piezoelectric layers 11 and internal electrode layers 121 and 122, and adjacent internal electrode layers with the piezoelectric layer 11 interposed therebetween. One of 121 is exposed on the side surface 101 so as to be electrically connected to the side electrode 131 on the right side of the drawing, and the other is exposed on the side surface 102 so as to be electrically connected to the side electrode 132 on the left side of the drawing. Further, both ends in the stacking direction are dummy layers 151 and 152 that do not expand when the stacked piezoelectric element 1 is driven.
At the time of inspection, as shown in FIG. 1, the inspection circuit 2 is connected to the side electrodes 131 and 132 of the multilayer piezoelectric element 1 and a DC voltage is applied. This DC voltage is a constant voltage.
The inspection circuit 2 includes a protection circuit 21, a DC power supply 22, a resistor 231, a voltmeter 232 connected in parallel to the resistor 231, and a current monitor device 24.

The inspection circuit 2 inspected several laminated piezoelectric elements 1.
First, in the multilayer piezoelectric element 1, the piezoelectric layer 11 is made of PZT (lead zirconate titanate), the internal electrode layers 121 and 122 are made of Ag—Pd, and the side electrodes 131 and 132 are made of baked silver.
The DC power supply 22 is a normal DC power supply with an output of 200 V, the protection circuit 21 uses a 188 kΩ resistor, the resistor 231 uses a 10 kΩ resistor, the voltmeter 232 uses a digital multimeter, and the current monitoring device 24 uses a dedicated PC.

Then, a DC voltage is applied for 120 seconds between the internal electrode layers 121-122 so that the electric field strength becomes 2.0 kV / mm. The shape of the detected current flowing through the current monitoring device 24 is monitored. At this time, a rectangular voltage is applied so that the required electric field strength is obtained within 2 seconds.
An example of the monitored detection current is shown in FIGS. In each drawing, the curve indicated by the thick solid line is the base line, that is, the current that is supposed to be observed when the multilayer piezoelectric element 1 according to this example is in a state without defects. The curve indicated by the broken line is the actually measured detected current.
In this example, it was determined that FIGS. 3 to 5 were defective and FIGS. 6 to 8 were non-defective.

That is, the detected current according to FIG. 3 had a peak in the middle of the waveform, and the deviation of the peak from the baseline was 0.016 (= 2.0 × 0.008) μA or more.
In FIG. 4, the waveform gently swelled, and the deviation of the swell from the baseline was 0.02 μA or more.
Further, in FIG. 5, the detected current did not become 0.048 (= 2.0 × 0.024) μA or less even after 120 seconds had passed since the waveform was partially raised.
Note that the deviation amount of the baseline is the maximum value of the distance in the Y-axis direction between the disturbance (broken line) and the baseline (thick solid line).

6 has the same peak as that in FIG. 3, but the peak height is small and there is a defect in the multilayer piezoelectric element 1, but the defect is very small, and there is no practical problem. Therefore, it was judged as a good product.
The detected current according to FIG. 7 has the same rise as in FIG. 4, but the height of the rise is small, and there is a defect in the multilayer piezoelectric element 1, but the defect is very small and no problem in practical use. It was judged.

  Unlike the case of FIG. 5, the detected current according to FIG. 8 is 0.048 (= 2.0 × 0.024) μA or less after 120 seconds from the start of energization. Accordingly, the multilayer piezoelectric element 1 was judged to be a good product because there was no defect in the multilayer piezoelectric element 1 or the defect was very small and there was no practical problem.

The laminated piezoelectric element 1 according to this example is provided with side electrodes 131 and 132 so that the internal electrode layers 121 and 122 have different potentials when driven.
The operation of applying a DC voltage from the side electrodes 131 and 132 and monitoring the detection current flowing in the internal electrode layers 121 and 122 and the side electrode layers 131 and 132 of the multilayer piezoelectric element 1 should be realized easily and inexpensively. Can do.

  Furthermore, the current that flows when a DC voltage is applied to a multilayer piezoelectric element having no defects is exponentially attenuated with time and becomes a steady state, similar to the characteristics of the capacitor. Therefore, it is easy to detect a slight disturbance in the detection current, and according to this example, the presence or absence of a defect in the multilayer piezoelectric element can be detected more reliably.

  As described above, according to this example, it is possible to provide a method for inspecting a multilayer piezoelectric element that is non-destructive and capable of easily and reliably finding defects.

In this example, the multilayered piezoelectric element having the partial electrode configuration is inspected, but the present invention can also be applied to an element having a full-surface electrode configuration.
Moreover, although the detection current concerning FIG.3, FIG.4, FIG.6 and FIG. 7 has only one peak, a some peak may appear. In such a case, each peak can be examined for deviation from the baseline, and defective products can be sorted.

2 is an explanatory diagram of a multilayer piezoelectric element and an inspection circuit in Embodiment 1. FIG. FIG. 3 is an explanatory diagram according to a stacked state of a piezoelectric layer and an internal electrode layer in a stacked piezoelectric element in Example 1. FIG. 3 is a diagram illustrating a change in detection current with time in Example 1; FIG. 3 is a diagram illustrating a change in detection current with time in Example 1; FIG. 3 is a diagram illustrating a change in detection current with time in Example 1; FIG. 3 is a diagram illustrating a change in detection current with time in Example 1; FIG. 3 is a diagram illustrating a change in detection current with time in Example 1; FIG. 3 is a diagram illustrating a change in detection current with time in Example 1;

Explanation of symbols

1 Stacked Piezoelectric Element 11 Piezoelectric Layer 121, 122 Internal Electrode Layer

Claims (6)

In a laminated piezoelectric element formed by alternately laminating piezoelectric layers and internal electrode layers,
Defective products are separated by monitoring a detection current generated by applying a DC voltage to the stacked piezoelectric element so that adjacent internal electrode layers alternately have different potentials through the piezoelectric layer. Inspection method for multilayer piezoelectric element. 2. The detection current according to claim 1, which is a time change of a detection current generated by applying a DC voltage to a multilayer piezoelectric element having no defect, and has a waveform that decays exponentially with the passage of time as a baseline, When the electric field strength when applying a DC voltage to a certain laminated piezoelectric element is E (kV / mm) and the detection current generated by applying the DC voltage is X (μA),
A multilayer piezoelectric element characterized in that one or more peak portions having a distance of 0.008E or more between the base line and the waveform indicating the time variation of X are classified as defective products. Inspection method.   3. The electric field intensity at the time of applying a DC voltage to the multilayer piezoelectric element to be inspected is E (kV / mm), and a detection current generated by applying the DC current is X (μA). ), A method for inspecting a laminated piezoelectric element characterized in that, after 120 seconds, X is 0.024E or more and is classified as a defective product.   4. The method for inspecting a laminated piezoelectric element according to claim 1, wherein the DC voltage is higher than a coercive electric field of the piezoelectric layer and lower than a withstand voltage of the piezoelectric layer.   4. The laminate according to claim 1, wherein the DC voltage is in a range of 1.5E0 to 0.9E1 where E0 is a coercive electric field of the piezoelectric layer and E1 is a withstand voltage. Inspection method for a piezoelectric element.   6. The method for inspecting a laminated piezoelectric element according to claim 5, wherein the DC voltage is in a range of 1.8E0 to 0.6E1.

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