JP2008175639A - Piezoelectric element inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method which enables the inspection of a defect such as a microcrack existing inside a piezoelectric element with high precision. <P>SOLUTION: This piezoelectric element inspection method includes: the first characteristic value measuring step for measuring the electric characteristic value of the piezoelectric element as a first characteristic value; the first inspection signal application step for applying a first inspection signal having a first predetermined voltage waveform after the first characteristic value measuring step; the second inspection signal application step for applying a second inspection signal having a second predetermined voltage waveform different in voltage polarity from the first predetermined voltage waveform to the piezoelectric element after the first inspection signal application step; the second characteristic value measuring step for measuring the electric characteristic value of the piezoelectric element after the second inspection signal application as a second characteristic value; and the malfunction judging step for judging whether the piezoelectric element malfunctions according to the value based on the difference between the measured second characteristic value and the measured first characteristic value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for inspecting whether or not a piezoelectric element (including an apparatus using a piezoelectric element) is abnormal.

  A piezoelectric element (including an electrostrictive element in this specification) is an element that contracts or expands when a voltage is applied, and generates a voltage when contracted or expanded. For this reason, the piezoelectric element is used in various types of devices, for example, as a drive actuator such as a liquid ejection device or as a sensor for measuring the viscosity of a fluid.

  When an abnormality such as a microcrack occurs in such a piezoelectric element, the piezoelectric element cannot exhibit its intended function. Further, in a device using a piezoelectric element, if a microcrack or the like occurs in the piezoelectric element, the device cannot obtain the expected ability. Therefore, in the manufacturing process of the piezoelectric element, whether or not an abnormality such as a microcrack has occurred in the manufactured piezoelectric element, or whether or not the manufactured piezoelectric element is likely to generate such an abnormality. An inspection is carried out.

Conventionally, such an inspection is performed, for example, by measuring the frequency characteristic of the impedance of the manufactured piezoelectric element, and a curve pattern indicating the frequency characteristic of the measured impedance and a normal piezoelectric piezoelectric element (hereinafter referred to as a reference). This is performed by comparing the curve pattern indicating the frequency characteristic of the impedance of “reference piezoelectric element” (see, for example, Patent Document 1).
JP-A-6-3305

  However, individual differences exist between manufactured piezoelectric elements. Therefore, according to the above-described conventional inspection method, the manufactured piezoelectric element itself is not abnormal, but if the characteristics of the element deviate from those of the reference piezoelectric element, the error is “the manufactured element is abnormal”. There is a risk of judging. On the other hand, in order to avoid such misjudgment based on the characteristic deviation, if the judgment criteria are relaxed so that “the manufactured piezoelectric element is normal” even if the two curve patterns differ to some extent. Actually, the abnormal piezoelectric element is erroneously determined to be normal.

  Therefore, an object of the present invention is to provide a method for inspecting a piezoelectric element (including an apparatus using a piezoelectric element) that can easily determine whether a piezoelectric element is abnormal or not as much as possible. One.

In order to achieve the above object, a piezoelectric element inspection method according to the present invention comprises:
A method for inspecting a piezoelectric element for determining whether or not the piezoelectric element is abnormal, wherein a first characteristic value measuring step of measuring an electric characteristic value of the piezoelectric element as a first characteristic value, and the first characteristic value A first inspection signal application step for applying a first inspection signal having the first predetermined voltage waveform after the measurement step, and a voltage polarity different from the first predetermined voltage waveform to the piezoelectric element after the first inspection signal application step. (2) a second inspection signal applying step for applying a second inspection signal having a predetermined voltage waveform, and a second characteristic value measurement for measuring, as a second characteristic value, an electrical characteristic value of the piezoelectric element after the second inspection signal is applied. And an abnormality determination step of determining whether or not the piezoelectric element is abnormal based on a value corresponding to a difference between the measured second characteristic value and the measured first characteristic value. .

  In this case, it is preferable that the electrical characteristic value is at least one of, for example, an electric capacity (capacitance), a loss, and a resonance frequency of the piezoelectric element. In order to determine whether or not the piezoelectric element is abnormal based on a value corresponding to a difference between the measured second characteristic value and the measured first characteristic value, the second characteristic value is used. And determining whether or not the piezoelectric element is abnormal based on a result of a magnitude comparison between the first characteristic value and the first characteristic value.

  According to this, first, the electrical characteristic value of the piezoelectric element (for example, the capacitance, loss, resonance frequency, etc. of the piezoelectric element) is measured as the first characteristic value, and then the first inspection having the first predetermined voltage waveform. A signal is applied to the piezoelectric element to be inspected, and then a second inspection signal having a second predetermined voltage waveform is applied to the piezoelectric element to be inspected, and then the electrical characteristic value of the piezoelectric element (for example, the piezoelectric element's The capacitance, loss, resonance frequency, etc.) are measured as the second characteristic value. The first characteristic value and the second characteristic value are values unique to the piezoelectric element to be inspected (values reflecting “characteristics of the piezoelectric element to be inspected” caused by individual differences between manufactured piezoelectric elements). However, the value corresponding to the difference between the second characteristic value and the first characteristic value is a value from which the influence of the individual difference is excluded.

  The resonance frequency may be measured by electrical measurement, or may be measured using a sensor that detects mechanical displacement, speed, acceleration, and the like.

  By the way, the polarity of the voltage of the second inspection signal applied to the piezoelectric element is different from that of the first inspection signal. Therefore, the stress applied to the piezoelectric element by the second inspection signal is a stress in the opposite direction to the stress applied to the piezoelectric element by the first inspection signal. As a result, a stricter test can be performed for the piezoelectric element, and if there is a microcrack inherent in the piezoelectric element, the piezoelectric element can be reliably advanced.

  Here, when the electrical characteristic value is, for example, the resonance frequency, the value corresponding to the difference between the second characteristic value and the first characteristic value is when the microcrack is generated and the microcrack is not generated. Bigger than.

  Furthermore, when the first inspection signal and the second inspection signal are alternately applied a plurality of times, if there is a microcrack inherent in the piezoelectric element, the microcrack can be more reliably developed. That is, the second characteristic value measuring step is performed after the first inspection signal applying step and the second inspection signal applying step are alternately applied a plurality of times, so that a more accurate abnormality determination can be performed. It is suitable.

  In addition, a voltage peak (a voltage waveform voltage of the first inspection signal and the second inspection signal) of at least one of the first predetermined voltage waveform and the second predetermined voltage waveform is a voltage higher than the coercive electric field of the piezoelectric element. It is preferable that According to this, when the microcrack is inherent in the piezoelectric element, the microcrack can be more reliably developed. Here, the coercive electric field is an electric field at which the residual polarization of the piezoelectric element becomes 0 (zero). The direction of the electric field applied to the piezoelectric element when the first inspection signal is applied and the electric field applied to the piezoelectric element when the second inspection signal is applied. Each of the directions has an independent value.

  In addition, if the polarity of the voltage waveform of the second inspection signal is the same as the predetermined polarization direction of the piezoelectric element, if there is a microcrack inherent in the piezoelectric element, it can be more reliably developed and polarization processing can be performed. Can be performed simultaneously.

  In addition, after the second characteristic value measuring step, when a third inspection signal having a larger absolute value than the voltage of the second inspection signal is applied, if there is a microcrack inherent in the piezoelectric element, the microcrack is removed. Since the progress can be made more reliably and the polarization state can be further changed to a better state, the polarization process can be performed without impairing the characteristics of the piezoelectric element.

  Thus, according to the method for inspecting a piezoelectric element of the present invention, if a microcrack is inherent in the piezoelectric element, the microcrack can be surely developed and manifested. There is provided an inspection method capable of determining whether or not there is high accuracy. Further, the present invention can be suitably applied not only to the manufacturing process of the piezoelectric element but also to an apparatus using the piezoelectric element.

  The piezoelectric element to be inspected by such an inspection method may be a piezoelectric element fixed to a diaphragm separate from the piezoelectric element, or a piezoelectric element integrated with a diaphragm made of zirconia by firing. There may be. The present invention can also be applied to a piezoelectric element used alone. Furthermore, the present invention can be applied to an apparatus in which such a piezoelectric element is incorporated. That is, the inspection method of the present invention efficiently reveals microcracks and the like inherent in a piezoelectric element using an electrode formed on the piezoelectric element used in the form incorporated in the apparatus. Therefore, the presence or absence of abnormality of the piezoelectric element can be determined with high accuracy.

<Inspection device>
FIG. 1 is a diagram schematically showing an inspection apparatus 10 for carrying out an inspection method according to the present invention. This inspection apparatus 10 determines whether or not each of k (k is a natural number) piezoelectric elements S (1) to S (k) are abnormal elements having microcracks (or have microcracks). This is a device for determining / inspecting whether or not the element is abnormal. The piezoelectric element S (i) (i is a natural number up to k) includes an upper electrode and a lower electrode as will be described later. The inspection apparatus 10 includes switches A1 to A4, switches SW (1) to SW (k), a measurement control circuit 11, a power supply 12, an LCR meter 13, a network analyzer (NA) 14, and a discharge resistor 15. .

  The upper electrode of the piezoelectric element S (i) to be inspected is connected to the voltage application line LIN via the switch SW (i). The lower electrode of the piezoelectric element S (i) is connected to the common line COM. Each of the switches A1 to A4 includes two switching contacts. The two switching contacts of each of the switches A1 to A4 are simultaneously turned on (closed, connected) and turned off (opened, shut off) based on an instruction signal from the measurement control circuit 11. Note that turning on each of the switches A1 to A4 means simultaneously turning on the two switching contacts of each switch, and turning each switch off means simultaneously turning off the two switching contacts of each switch. It is to be.

  The measurement control circuit 11 is an electric circuit including a computer. The measurement control circuit 11 is connected to the switches A1 to A4 and the switches SW (1) to SW (k), and gives an instruction signal for switching the state (on / off state) of these switches to each switch. ing. Further, the measurement control circuit 11 is connected to a power source 12, an LCR meter 13 and a network analyzer 14. The measurement control circuit 11 sends instruction signals to the power supply 12, the LCR meter 13 and the network analyzer 14, and inputs measurement results from the LCR meter 13 and network analyzer 14.

  The power supply 12 generates a predetermined inspection voltage (first inspection signal, second inspection signal, etc.) to be described later in response to an instruction signal from the measurement control circuit 11. One terminal of the power supply 12 is connected to the voltage application line LIN via one switching contact of the switch A1. The other terminal of the power supply 12 is connected to the common line COM via another switching contact of the switch A1. When the inspection signal is applied to the piezoelectric element, the switch A1 is closed and the other switches A2 to A4 are opened.

  The LCR meter 13 is well known, and the electric capacitance (capacitance) C (i) and loss D (i) of the connected piezoelectric element S (i) are determined according to an instruction signal from the measurement control circuit 11. The measurement result is sent to the measurement control circuit 11. One terminal of the LCR meter 13 is connected to the voltage application line LIN via one switching contact of the switch A2. The other terminal of the LCR meter 13 is connected to the common line COM via another switching contact of the switch A2. When performing measurement by the LCR meter 13, the switch A2 is closed and the other switches A1, A3 and A4 are opened.

  The network analyzer 14 is well-known and measures the resonance frequency fc (i) of the connected piezoelectric element S (i) in response to an instruction signal from the measurement control circuit 11, and the measurement result is measured by the measurement control circuit 11. To send to. One terminal of the network analyzer 14 is connected to the voltage application line LIN via one switching contact of the switch A3. The other terminal of the network analyzer 14 is connected to the common line COM via another switching contact of the switch A3. When performing measurement by the network analyzer 14, the switch A3 is closed and the other switches A1, A2 and A4 are opened. The network analyzer 14 applies a drive signal having a predetermined frequency to the connected piezoelectric element S (i) to vibrate the piezoelectric element S (i) and measures a signal output from the piezoelectric element S (i). It is supposed to be. At this time, the network analyzer 14 sequentially changes the frequency of the drive signal applied to the piezoelectric element S (i) from the lower limit frequency to the upper limit frequency in the range including the expected resonance frequency for the piezoelectric element S (i). That is, frequency sweep (sweep) is performed. Note that a known impedance analyzer may be used instead of the network analyzer 14. It is also possible to calculate the resonance frequency by performing FFT analysis on the signal from the piezoelectric element when the drive voltage is applied by a dedicated circuit, or from the time waveform itself of the signal from the piezoelectric element.

  The discharge resistor 15 is a resistor for discharging the electric charge accumulated in the connected piezoelectric element S (i). One terminal of the discharge resistor 15 is connected to the voltage application line LIN via the switch A4. The other terminal of the discharge resistor 15 is connected to the common line COM via another switching contact of the switch A4. The discharge resistor 15 can be usefully used for preventing a current from suddenly flowing into the circuit, and may be installed according to the application. When discharging by the discharge resistor 15, the switch A4 is closed and the other switches A1 to A3 are opened.

<Devices using piezoelectric elements>
The device 20 according to the first example shown in a sectional view in FIG. 2 is a device used as a sensor for measuring the viscosity of a fluid, and a sensor for measuring the presence or absence of fluid, the concentration of fluid, and the like. It is. The device 20 includes a base plate 21, a frame 22, a diaphragm 23, and a piezoelectric element 24.

  The base plate 21 includes a through hole 21a and a through hole 21b. The frame 22 is disposed on the base plate 21. The diaphragm 23 is disposed on the frame 22. The base plate 21, the frame 22, and the diaphragm 23 are made of a zirconia material, and are joined by firing integrally. A cavity SP is formed in the integrally fired fired product. The cavity SP communicates with the outside through the through hole 21a and the through hole 21b.

  The piezoelectric element 24 includes a piezoelectric body 24a, a lower electrode 24b, and an upper electrode 24c. The lower electrode 24b and the upper electrode 24c are opposed to each other with a thin portion formed in the central portion of the piezoelectric body 24a interposed therebetween. Actually, the lower electrode 24b is formed by screen-printing a platinum paste on the upper surface (the upper surface of the vibration plate 23) of the integrally fired fired material, followed by firing. Next, a paste-like piezoelectric ceramic material is screen-printed so as to cover the lower electrode 24b and the diaphragm 23, and then fired to form the piezoelectric body 24a. Examples of the piezoelectric ceramic material include lead zirconate, lead titanate, and lead magnesium niobate. Finally, a platinum paste is screen-printed on the upper surface of the piezoelectric body 24a and then baked to form the upper electrode 24c. Thus, the lower surface of the piezoelectric element 24 is integrally fired with the diaphragm 23 and is not exposed to the outside.

  In the device 20, the lower electrode 24b and the upper electrode 24c of the piezoelectric element 24 are connected to an electric measurement device such as an oscillator and an LCR meter (not shown). Further, a fluid to be measured for viscosity or the like is introduced into the cavity SP through the through holes 21a and 21b. Then, the piezoelectric element 24 is driven by a signal from the oscillator, and the diaphragm 23 is vibrated. The viscosity of the fluid to be measured affects the vibration of the diaphragm 23, and therefore the resonance frequency of the piezoelectric element 24 changes. The device 20 measures fluid viscosity, concentration, and the like based on this resonance frequency.

A specific example of the piezoelectric element inspection method using the inspection apparatus will be described below.

<Inspection method>
(1) Step 1: The switch SW (i) of the piezoelectric element S (i) to be measured is turned on, and the electrical characteristic value of the piezoelectric element to be measured is measured. In this example, the electrical characteristic values are an electric capacity (electrostatic capacity) C, a loss D, and a resonance frequency fc, and the measurement result is a first characteristic value Ch (1): C (1), D (1), Store as fc (1). The electric capacity C and the loss D are measured by the LCR meter 13. The resonance frequency fc is measured by the network analyzer (or impedance analyzer) 14. The measurement is performed in the order of resonance frequency fc, loss D, and capacitance C.

  (2) Step 2: The first inspection signal and the second inspection signal are applied to the piezoelectric element by the power supply 12. The inspection signals (first inspection signal and second inspection signal) used in this example are shown in FIG. The first inspection signal 31a has a sinusoidal negative voltage having a peak voltage V1 (maximum absolute value of voltage = | V1 |) and a period T1a (a waveform only on the negative side of a sine wave oscillating with reference to 0). Voltage). The voltage waveform of the first inspection signal 31a is also referred to as a first predetermined voltage waveform. The second inspection signal 32a has a peak voltage V2 (maximum absolute value of voltage = | V2 |) and a sinusoidal positive voltage having a period T2a (a waveform only on the positive side of a sine wave that vibrates with reference to 0). Voltage). The voltage waveform of the second inspection signal 32a is also referred to as a second predetermined voltage waveform. After the first inspection signal 31a is applied to the piezoelectric element, the second inspection signal 32a is applied. Further, a first 'inspection signal 31b identical to the first inspection signal 31a and a second' inspection signal 32b identical to the second inspection signal 32a are applied. Here, the time from the application end time of the first inspection signal 31a to the application start time of the second inspection signal 32a, and the time from the application end time of the second inspection signal 32a to the application start time of the first 'inspection signal 31b. The time from the application end time of the first ′ inspection signal 31b to the application start time of the second ′ inspection signal 32b can be arbitrarily set. The first 'inspection signal 31b and the second' inspection signal 32b are set in order to make the micro cracks inherent in the piezoelectric element appear more reliably, and are not necessarily required. Moreover, although it is a sine wave in this example, arbitrary waveforms, such as a pulse wave, a square wave, a triangular wave, and a waveform in which a harmonic wave is included in a pulse wave, can be applied.

  (3) Step 3: The upper electrode and the lower electrode of the piezoelectric element are connected for a predetermined discharge time via the discharge resistor 15 to discharge the charge accumulated in the piezoelectric element.

  (4) Step 4: Further, the electrical characteristic value of the piezoelectric element is measured. The electrical characteristic values to be measured are the capacitance (capacitance) C, the loss D, and the resonance frequency fc, as in Step 1, and the measurement results are the second characteristic values Ch (2): C (2), D (2), stored as fc (2). The electric capacity C and the loss D are measured by the LCR meter 13. The resonance frequency fc is measured by the network analyzer (or impedance analyzer) 14. The measurement is performed in the order of resonance frequency fc, loss D, and capacitance C.

  (5) Step 5: Difference ΔCh (= Ch (2) −Ch (1)) between the second characteristic value Ch (2) measured this time and the first characteristic value Ch (1) memorized and stored last time. ) To determine whether or not the piezoelectric element is abnormal.

For example, if the piezoelectric element is a piezoelectric element mainly composed of (Bi _0.5 Na _0.5 ) TiO ₃ , the loss D, resonance frequency fc, and electric capacity are different depending on the piezoelectric element to be inspected. C shows the following behavior. This example is an example of a piezoelectric element mainly composed of (Bi _0.5 Na _0.5 ) TiO ₃ , and its behavior may change depending on stress applied to the element, delicate composition, inclusion of impurities, and the like. Yes, the determination value may be changed as appropriate under each condition.

<Behavior of loss D>
If there is no microcrack in the piezoelectric element, the loss D decreases and the difference ΔD (= D (2) −D) between the loss D (2) of the second characteristic value and the loss D (1) of the first characteristic value. (1)) is a negative value.

  On the other hand, when the micro crack is generated in the piezoelectric element, the loss D increases, and the difference ΔD (= D () between the loss D (2) of the second characteristic value and the loss D (1) of the first characteristic value. 2) -D (1)) is a positive value. Although this is not certain due to the occurrence of microcracks, the path for electrically coupling the upper and lower electrodes of the piezoelectric element increases, the resistance between the electrodes decreases, and the resistance of the electrodes themselves is small. It can be assumed that it will only increase. However, in this example, it is estimated that the resistance is small.

<Behavior of resonance frequency fc>
If the micro crack does not occur in the piezoelectric element, the resonance frequency fc increases, and the difference Δfc (= fc (2) between the resonance frequency fc (2) of the second characteristic value and the resonance frequency fc (1) of the first characteristic value. ) -Fc (1)) is a positive value.

  On the other hand, when the micro crack is generated in the piezoelectric element, the resonance frequency fc decreases, and the difference Δfc () between the resonance frequency fc (2) of the second characteristic value and the resonance frequency fc (1) of the first characteristic value. = Fc (2) -fc (1)) is a negative value. This is because the rigidity of the piezoelectric element decreases due to the occurrence of microcracks.

<Behavior of capacitance C>
If the micro crack is not generated in the piezoelectric element, the electric capacity C decreases, and the difference ΔC (= C (2) between the electric capacity C (2) of the second characteristic value and the electric capacity C (1) of the first characteristic value. ) -C (1)) is a negative value.

  On the other hand, when the micro crack is generated in the piezoelectric element, the electric capacity C increases, and the difference ΔC () between the electric capacity C (2) having the second characteristic value and the electric capacity C (1) having the first characteristic value. = C (2) -C (1)) is a positive value. This is presumably because the stress state inside the piezoelectric element changes due to the occurrence of microcracks (stress is released).

  Thus, when a microcrack occurs in the piezoelectric element to be inspected (that is, when the piezoelectric element to be inspected is not a normal piezoelectric element), the change tendency regarding the magnitude from the first characteristic value to the second characteristic value is: This is opposite to the change tendency related to the magnitude from the first characteristic value to the second characteristic value when the piezoelectric element to be inspected is a normal piezoelectric element.

<Example>
An inspection example of a piezoelectric element using the inspection apparatus shown in FIG. 1 will be described below. The inspection method was as described in Step 1 to Step 5 of the inspection method described above.

The time from the application end time of the first inspection signal 31a described in step 2 to the application start time of the second inspection signal 32a, and the application start time of the first 'inspection signal 31b from the application end time of the second inspection signal 32a. And the time from the application end time of the first ′ inspection signal 31b to the application start time of the second ′ inspection signal 32b are all 0 seconds. In the inspection signal shown in FIG. 3, the conditions used in this example are as follows. The absolute value of the coercive voltage of the piezoelectric element to be inspected is 100 V in both positive and negative polarities, and the absolute value of V1 and the absolute value of V2 are both values higher than the coercive voltage.
V1 = -110V, V2 = 110V
T1a = T1b = T2a = T2b = 0.1 second

Regarding the determination condition of whether or not the piezoelectric element described in Step 5 is abnormal, it is determined that the piezoelectric element is abnormal when at least one of the following conditions 1) to 3) is satisfied. .
Condition 1) The difference ΔD (= D (2) −D (1)) between the loss D (2) of the second characteristic value and the loss D (1) of the first characteristic value becomes a positive value.
Condition 2) The difference Δfc (= fc (2) −fc (1)) between the resonance frequency fc (2) of the second characteristic value and the resonance frequency fc (1) of the first characteristic value is a negative value.
Condition 3) The difference ΔC (= C (2) −C (1)) between the electric capacity C (2) of the second characteristic value and the electric capacity C (1) of the first characteristic value becomes a positive value.

  A plurality of piezoelectric elements determined to be normal were prepared by the method described above. Hereinafter, the test up to this point is referred to as “Test 1”.

  On the other hand, in Test 1, a plurality of piezoelectric elements determined to be normal were prepared by using only the second inspection signal 32a and the second ′ inspection signal 32b as the inspection signals described in Step 2. Hereinafter, this test is referred to as “Test 2”. In other words, the inspection method of Test 2 includes a first characteristic value measuring step for measuring the electric characteristic value of the piezoelectric element as the first characteristic value, a second inspection signal 32a after the first characteristic value measuring step, 2 'inspection signal 32b, and then a second characteristic value measuring step of measuring the electric characteristic value of the piezoelectric element as a second characteristic value; the measured second characteristic value; and the measured second characteristic value It can be said that the piezoelectric element inspection method includes an abnormality determination step of determining whether or not the piezoelectric element is abnormal based on a value corresponding to a difference from one characteristic value.

  Thereafter, the piezoelectric element determined to be normal in Test 1 and the piezoelectric element determined to be normal in Test 2 were driven for 48 hours in a high humidity environment at a temperature of 40 ° C. and a humidity of 80%. Thereafter, the insulation resistance between the electrodes of the piezoelectric element was measured. As a result, about 5% of the piezoelectric elements determined to be normal in Test 2 were defective in insulation, whereas all of the piezoelectric elements determined to be normal in Test 1 were secured. From these, it was found that the inspection method of Test 1 can determine whether or not the piezoelectric element is abnormal more accurately than the inspection method of Test 2.

  That is, by applying a second inspection signal having a voltage polarity different from that of the first inspection signal after the first inspection signal application step, if there is a microcrack inherent in the piezoelectric element, the piezoelectric element can be reliably developed. It is possible to determine with high accuracy whether or not there is an abnormality.

  As described above, according to the measuring method according to the present invention and the inspection apparatus according to the present invention that implements the measuring method, it is possible to accurately determine whether or not the piezoelectric element is abnormal within a short time. . In addition, this invention is not limited to said each embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, as described above, the measured electrical characteristic value is a characteristic value other than the capacitance (capacitance) C, loss D, and resonance frequency fc, and the value tends to change depending on the presence or absence of microcracks. Any characteristic value may be used if it is reversed.

  The polarity of the second inspection signal 32a (the polarity of the second predetermined voltage waveform) is preferably the same as the predetermined polarization direction of the piezoelectric element. Furthermore, after the second characteristic value measurement step (after the step 2), a third inspection signal having a third predetermined voltage waveform whose absolute value is larger than the voltage of the second inspection signal may be applied. More preferably, the polarity of the voltage waveform of the third inspection signal is the same as the predetermined polarization direction of the piezoelectric element (the polarity of the second inspection signal).

It is a circuit diagram of the inspection device for enforcing the inspection method concerning the embodiment of the present invention. It is sectional drawing of one example of the piezoelectric element used as the test object of the test | inspection method of this invention. It is a voltage waveform of the inspection signal for enforcing the inspection method concerning the embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inspection apparatus, 11 ... Measurement control circuit, 12 ... Power supply, 13 ... LCR meter, 14 ... Network analyzer, 15 ... Discharge resistance, 20 ... Device, 23 ... Diaphragm, 24 ... Piezoelectric element, 24a ... Piezoelectric body, 24b ... lower electrode, 24c ... upper electrode.

Claims (5)

A method for inspecting a piezoelectric element to determine whether or not the piezoelectric element is abnormal,
A first characteristic value measuring step of measuring an electric characteristic value of the piezoelectric element as a first characteristic value;
A first inspection signal applying step of applying a first inspection signal having the first predetermined voltage waveform after the first characteristic value measuring step;
A second inspection signal applying step of applying a second inspection signal having a second predetermined voltage waveform having a voltage polarity different from that of the first predetermined voltage waveform to the piezoelectric element after the first inspection signal applying step;
A second characteristic value measuring step of measuring the electric characteristic value of the piezoelectric element after application of the second inspection signal as a second characteristic value;
An abnormality determination step of determining whether or not the piezoelectric element is abnormal based on a value corresponding to a difference between the measured second characteristic value and the measured first characteristic value;
A method for inspecting a piezoelectric element including: The inspection method according to claim 1,
The method for inspecting a piezoelectric element, wherein the second characteristic value measuring step is executed after alternately applying the first inspection signal applying step and the second inspection signal applying step a plurality of times. In the inspection method according to claim 1 or claim 2,
A method for inspecting a piezoelectric element, wherein a voltage peak of at least one of the first predetermined voltage waveform and the second predetermined voltage waveform is a voltage exceeding a coercive electric field of the piezoelectric element. In the inspection method according to any one of claims 1 to 3,
The method for inspecting a piezoelectric element, wherein a polarity of the second predetermined voltage waveform is the same as a predetermined polarization direction of the piezoelectric element. The inspection method according to claim 4,
A third inspection signal applying step of applying a third inspection signal having a third predetermined voltage waveform having a voltage whose absolute value is larger than the voltage of the second inspection signal after the second characteristic value measuring step;
A method for inspecting a piezoelectric element including:

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