JP3714133B2 - Piezoelectric polarization treatment method - Google Patents

Description

【００３４】
図９，図１０は、高温，高電圧で分極中の圧電体のΔｆ挙動を示したものであり、図９は位相０°法で測定したもの、図１０はインピーダンス測定法で測定したものである。
また、表２は、各測定方法の違いによるΔｆ挙動の測定精度を比較したものである。表２では、各測定法毎の近似直線を求め、相関係数および近似直線との相対誤差で測定精度の比較を行ったものである。
図９，図１０および表２から明らかなように、動的状態（分極中）でのΔｆ挙動は、インピーダンス測定法に比べて位相０°法ではリニアに変化していることがわかる。そのため、位相０°法では実測値と近似値との誤差も小さく、Δｆ挙動を高精度に測定できたことを示している。
そのため、本発明における分極中の分極度測定に、位相０°法を用いる方が、より高精度な分極コントロールが可能となる。
【００３５】
【表２】

【００３６】
本発明は上記実施例に限定されるものではない。
上記実施例では、分極とエージングとを共に２００℃で行なった例を示したが、分極温度はエージング温度以上であればよく、２００℃に限るものではない。
圧電セラミックの場合、分極温度およびエージング温度は材料により異なるが、分極ばらつきを小さくするためには、１８０〜２１０℃の温度範囲が望ましい。
【００３７】
【発明の効果】
以上の説明で明らかなように、請求項１に記載の発明によれば、気中であって、かつエージング温度以上の温度雰囲気中で、圧電体に直流電圧を印加して分極処理を行なうようにしたので、液中分極より低い電圧でも分極が進行し、短時間で液中分極と同等の分極度を得ることができる。また、分極中に同時にエージングも進むことから、電圧印加停止後のエージング時間も短縮できる。また、分極中の圧電体の分極度を測定しながら、測定分極度が設定レベルに到達した時に電圧印加を停止し、その後、エージング温度でエージングを行なうようにしたので、分極度のバラツキを小さくでき、目標とする分極度へ精度よく到達できる。
【００３８】
また、請求項２に記載の方法によれば、請求項１に記載の発明と同様に、分極時間およびエージング時間を短縮できるとともに、測定された分極度から分極度の分極時間に対する一次特性式を求め、その特性式から分極終了時刻を予測するようにしたので、分極終了付近における分極時間を測定するだけでよく、測定遅れによる過剰分極を防ぐことができ、高精度に分極コントロールできるという効果を有する。
【図面の簡単な説明】
【図１】分極処理過程における圧電体の分極度の変化を示す図である。
【図２】分極中の分極度と常温戻し後の分極度との相関関係を示す図である。
【図３】本発明にかかる分極処理装置の一例を示す回路図である。
【図４】分極温度と常温戻し後の分極度との関係を示す図である。
【図５】分極中の分極度の挙動を示す図である。
【図６】分極時の電流の挙動を示す図である。
【図７】圧電体の高温気中でのインピーダンス測定法を示す図である。
【図８】圧電体の高温気中での位相０°法を示す図である。
【図９】高温，高電圧で分極中の圧電体のΔｆを位相０°法で測定した図である。
【図１０】高温，高電圧で分極中の圧電体のΔｆをインピーダンス測定法で測定した図である。
【符号の説明】
Ｗ₁ 〜Ｗｎ 圧電体
１ 恒温槽
２ 高電圧直流電源
３₁ 〜３ｎ 高電圧切換スイッチ
４₁ 〜４ｎ 電流制限抵抗
７ 測定器
８₁ 〜８ｎ，９₁ 〜９ｎ 測定用スイッチ
１１ 電流検出回路
１２ 制御装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for polarization treatment of a piezoelectric body used for a ceramic filter, a ceramic oscillator, or the like.
[0002]
[Prior art]
In the case of a PZT or PT-based piezoelectric ceramic substrate (block, unit, etc.), the polarization treatment is performed by firing a piezoelectric ceramic substrate and then providing double-sided electrodes such as silver on the relative surface of the piezoelectric ceramic substrate A plurality of sheets were simultaneously immersed in a polarizing solution at 60 to 100 ° C., and a voltage of 2 to 8 kV / mm was applied for about 10 to 30 minutes to obtain a desired degree of polarization.
In order to prevent deterioration of characteristics due to heat treatment or the like in the subsequent process, the characteristics of the piezoelectric body over time are obtained by allowing the film to stand (aging) in an atmosphere at about 150 ° C. for 20 to 30 minutes and forcibly deteriorating the characteristics. Is stabilizing.
[0003]
As described above, there are two types of polarization treatments in piezoelectric materials: liquid polarization performed in an insulating polarization liquid and air polarization performed in the air or gas atmosphere. In air polarization, the voltage is about 1 kV / Since it discharges at mm or more, a desired electric field strength cannot be obtained. Therefore, in order to obtain a high degree of polarization, it is common to perform polarization in liquid.
[0004]
However, in the case of polarization in liquid, the degree of polarization of the piezoelectric body cannot be measured during polarization. This is because the vibration characteristics of the piezoelectric body arranged in the liquid are damped because of the liquid, and the frequency characteristics cannot be measured. Therefore, in conventional submerged polarization, constant-time polarization is performed in which polarization is performed for a predetermined time. As a result, there is a problem in that the degree of polarization cannot be accurately controlled, and the degree of polarization varies due to the firing variation and composition variation of the piezoelectric body.
[0005]
In Japanese Patent No. 2656041, a piezoelectric constant value during polarization (for example, an electromechanical coupling coefficient K) is measured, and when a set level determined by the correlation between K immediately after stopping polarization and a stable value K after time has elapsed, A polarization method for stopping the application has been proposed. As a result, it is possible to reduce the variation in the degree of polarization caused by the variation in the material, the variation in the firing conditions, and the like, and to obtain a piezoelectric body having a constant quality.
[0006]
[Problems to be solved by the invention]
In the case of the above method, since the piezoelectric constant value during polarization is measured, it is necessary to perform polarization treatment in the air. However, in the air polarization, a voltage is applied at a voltage of about 1 kV / mm or more, so a high voltage is applied. There is a problem that a long-time polarization process is required to obtain a degree of polarization equivalent to that in liquid.
In the above method, the set level is determined by the correlation between the value K immediately after the stop of polarization and the stable value K after the elapse of time. However, if aging is performed after the polarization process, the degree of polarization changes, and K The value of will also change. Therefore, when aging is performed after the polarization process, the set level cannot be obtained from the correlation between the value K immediately after the polarization is stopped and the stable value K after the lapse of time.
[0007]
Therefore, an object of the present invention is to provide a method for polarization processing of a piezoelectric body that can obtain a polarization degree equivalent to polarization in liquid in the air in a short time.
Another object of the present invention is to provide a piezoelectric material polarization processing method that can reduce variations in the degree of polarization of each piezoelectric material and can accurately reach the target degree of polarization.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 includes a step of applying a direct current voltage to the piezoelectric body and performing a polarization treatment in an air atmosphere at a temperature equal to or higher than the aging temperature, and the piezoelectric body. The step of measuring the degree of polarization while performing the polarization treatment, the step of stopping the application of the DC voltage when the measured degree of polarization reaches a set level, and the aging at the aging temperature after the voltage application is stopped. a polarization treatment method of a piezoelectric body and a step of performing, the, the setting level, the polarization degree immediately before stopping the application of the DC voltage, the polarization degree after returning to room temperature aging after stopping the application stability The present invention provides a method for polarization processing of a piezoelectric body characterized in that it is obtained by a correlation between values .
[0009]
When the polarization treatment is performed in the air, a voltage of about 1 kV / mm or more cannot be applied. However, since the polarization treatment can be performed at a higher temperature than in the liquid polarization, the polarization proceeds even at a low voltage, and the time is short. A desired degree of polarization can be obtained. In addition, since aging proceeds simultaneously during polarization, the aging time after the voltage application is stopped can be shortened. For example, in the past, an aging time of about 20 to 30 minutes was required in an atmosphere of about 150 ° C., but in the present invention, it takes only a few minutes and the aging time can be reduced to about 1/10. Thus, since the polarization time and the aging time can be shortened, the entire time required for the polarization process can be shortened.
Moreover, since polarization can be performed at a relatively low voltage, the load on the piezoelectric body can be reduced, and problems such as cracking and chipping due to polarization can be solved.
Since polarization is performed in the air, the frequency characteristics of the piezoelectric body being polarized can be measured, and the degree of polarization can be easily measured. While measuring the degree of polarization, the voltage application is stopped when the measured degree of polarization reaches the set level, and after the voltage application is stopped, aging is performed at the aging temperature, thereby reducing the variation in the degree of polarization. Extremely accurate. The set level may be a value determined in advance according to the piezoelectric material, or may be a value determined according to a polarization condition such as a polarization temperature or a polarization voltage.
[0010]
FIG. 1 shows changes in the degree of polarization of a piezoelectric body in a process from polarization to aging to returning to room temperature.
As is apparent from FIG. 1, the degree of polarization rises to the maximum during polarization, and after the degree of polarization decreases due to aging, a part of the degree of polarization is restored and stabilized by returning to room temperature. There is a high correlation between the maximum degree of polarization Δf ₁ during this polarization and the stable degree of polarization Δf ₂ after returning to room temperature.
Here, the degree of polarization is obtained from the frequency difference Δf between the resonance frequency fr and the antiresonance frequency fa, but may be obtained from an electromechanical coupling coefficient K, a center frequency, or other piezoelectric constants.
[0011]
FIG. 2 shows the correlation between the maximum degree of polarization Δf ₁ during polarization and the stable degree of polarization Δf ₂ after returning to room temperature. This correlation was obtained under the following conditions.
Piezoelectric body: PZT block (thickness 8 mm)
Polarization voltage (voltage between electrodes): 8.7 kV
Polarization temperature: 200 ° C
Aging temperature: 200 ° C
As can be seen from FIG. 2, there is a high correlation between Δf ₁ and Δf ₂ . In this example, Δf ₁ and Δf ₂ are in a proportional relationship.
[0012]
Therefore, the setting level for stopping the application of the DC voltage can be determined by the method of the present invention . That is, the set level is obtained from the correlation between the degree of polarization just before the application of the DC voltage is stopped and the stable value of the degree of polarization after aging after the application is stopped and returning to room temperature. Since there is a high correlation between the degree of polarization during polarization and the degree of polarization after aging and returning to room temperature (referred to as the residual polarization degree), as shown in FIG. The degree of polarization during polarization is calculated backward, and voltage application is stopped when this degree of polarization is reached.
By this method, the target degree of polarization can be controlled with high accuracy, and polarization variation can be further reduced.
[0013]
The method according to claim 2 measures the degree of polarization while performing the polarization treatment of the piezoelectric body, obtains a primary characteristic equation for the polarization time of the degree of polarization from the measured value, and the degree of polarization becomes a set level by this characteristic equation. The reaching time is calculated, and when the calculated time is reached, the application of the DC voltage is stopped. That is, when the composition of the piezoelectric body is constant, the behavior of the polarization degree after the polarization has progressed to some extent is almost constant, and the time until the polarization degree reaches the set level can be predicted from this behavior. When the predicted time is reached, the voltage application is stopped.
In this method, the measurement of the degree of polarization, the formulation of the characteristic, the calculation of the time to reach the set level, etc. are performed during the polarization of each piezoelectric body. In the method of claim 2 , unlike the method of claim 1 in which the degree of polarization at the end of polarization is measured, it is only necessary to measure the polarization time in the vicinity of the end of polarization. There is an advantage that polarization can be controlled accurately.
[0014]
When a thick piezoelectric ceramic substrate such as a block is polarized in a high temperature atmosphere, the current flowing through the piezoelectric body may increase with time. This increase in current is due to the fact that the internal orientation of the crystal is aligned in the direction of the electric field as polarization progresses, so that the insulation resistance of the piezoelectric body decreases with time, and the current value increases as this insulation resistance decreases. It is believed that there is. This increase in current during polarization appears more markedly at higher temperatures. As the current increases, a voltage drop occurs in the current limiting resistor for preventing overcurrent connected in series with the piezoelectric body, and the voltage applied to the piezoelectric body decreases. This decrease in voltage causes problems such as a decrease in the polarization rate of each of the piezoelectric bodies W _{1 to} Wn and a desired degree of polarization cannot be obtained.
[0015]
Therefore, in the third aspect of the present invention , in the case where the current flowing through the piezoelectric body increases during polarization, the DC voltage is applied, and the voltage drop at the current limiting resistor is calculated from the current value flowing through the piezoelectric body. This is done by adding the drop to the initial applied voltage.
That is, the applied voltage is determined based on the following calculation formula.
Applied voltage = initial voltage + current value x current limiting resistance In this way, the voltage applied to each piezoelectric body is always maintained at a constant voltage, thereby eliminating the variation in the degree of polarization between the piezoelectric bodies due to variations in the applied voltage. it can. In this method, in addition to controlling the degree of polarization, the polarization condition (voltage) can be made constant, so that the variation in the degree of polarization can be further reduced.
[0016]
When measuring the degree of polarization while performing polarization processing of a piezoelectric body, it is common to measure the impedance waveform and obtain the degree of polarization Δf based on the difference between the maximum frequency fa and the minimum frequency fr. It is.
However, when polarization is performed by applying a high voltage in a high-temperature atmosphere, the impedance waveform during polarization becomes broad in the vicinity of fr and fa, and the peak value varies due to noise. Therefore, there is a problem that variation in measurement of Δf occurs.
Accordingly, in claim 4 , the phase of the piezoelectric body being polarized is measured, the frequency (fa, fr) when the phase becomes 0 ° is calculated, and the frequency difference Δf (= fa−) of the frequency (fa, fr) is calculated. The method of obtaining the degree of polarization from fr) is used. In the phase 0 ° method, the phase characteristics in the vicinity of fr and fa change linearly including the phase 0 °, so that the values of fr and fa are stable even in polarization in a high temperature atmosphere and a high voltage. This is because the variation in measurement of Δf can be reduced.
In particular, an oxide film is easily formed on an electrode or the like in high-temperature air, and the contact resistance of the contact terminal varies. For this reason, the impedance fluctuates and Δf also varies. In contrast, in the phase 0 ° method, the slope of the phase changes depending on the contact resistance, but the position of the phase waveform passing through the phase 0 °, that is, the values of fa and fr do not change. High-accuracy Δf measurement that is not received is possible.
Since Δf can be measured with high accuracy by using the phase 0 ° method in this way, the degree of polarization control during polarization according to the present invention can be performed with high accuracy.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 shows an example of a polarization processing apparatus for performing the piezoelectric material polarization processing method according to the present invention.
W _{1 to} Wn are a plurality of piezoelectric bodies for performing polarization treatment, 1 is a thermostatic chamber that houses the piezoelectric bodies W _{1 to} Wn and controls them to a predetermined temperature atmosphere, 2 is a high-voltage DC power supply for polarization, 3 _{1 to} 3n Is a high voltage changeover switch for applying a voltage to a plurality of piezoelectric bodies W _{1 to} Wn, 4 _{1 to} 4 n are current limiting resistors for preventing overcurrent, and 5 _{1 to} 5 n are discharges for discharging the charges of the piezoelectric bodies W _{1 to} Wn. changeover switch, 6 ₁ ~6n discharge resistor, 7 measuring device for measuring the polarization degree of the piezoelectric bodies W ₁ wn in the middle polarization, 8 ₁ ~8n and 9 ₁ ~9n measurement switch, 10 during polarization An AC / DC separation circuit for blocking the direct current high voltage, 11 is a current detection circuit for detecting a current flowing through the piezoelectric body, and 12 is a control device for controlling applied voltage and polarization degree.
[0018]
The thermostat 1 is used to perform the processes of polarization of the piezoelectric bodies W _{1 to} Wn, aging, and return to room temperature, and is controlled by the control device 12 to a temperature suitable for each process. The polarization temperature is set to a temperature at which the polarization degree is equal to or higher than the aging temperature and the same degree of polarization as in the conventional liquid polarization. FIG. 4 shows the relationship between the polarization temperature in air polarization and the maximum degree of polarization Δf after returning to room temperature. The conditions were the same as in FIG. In this example, the temperature that is as high as possible within the range where no significant difference in the maximum degree of polarization Δf after returning to room temperature in air polarization is observed was taken as the polarization temperature.
[0019]
The measuring device 7 is composed of, for example, a network analyzer or the like, applies an AC signal to each of the piezoelectric bodies W _{1 to} Wn from a built-in AC signal source, detects a resonance frequency fr and an anti-resonance frequency fa from its impedance characteristics, and detects the frequency. The degree of polarization is measured by the difference Δf. As will be described later, a method of obtaining Δf not from the impedance characteristic but from the phase characteristic may be used. Further, the degree of polarization may be measured by an electromechanical coupling coefficient K in addition to Δf.
[0020]
Current detection circuit 11, a detection resistor 11a, is constituted by an amplifier 11b, such as OP amplifier for detecting a potential difference between both ends of the resistor 11a, the current flowing from the voltage across the resistor 11a to the respective piezoelectric bodies W ₁ wn Are detected individually. Detecting resistor 11a and the amplifier 11b are connected individually to each of the piezoelectric bodies W ₁ wn.
[0021]
The polarization degree signal of the measuring instrument 7 and the current detection signal of the amplifier 11 b are input to the control device 12. The control device 12 controls the thermostatic chamber 1, the high voltage DC power source 2, the high voltage changeover switches 3 _{1 to} 3n, the discharge changeover switches 5 _{1 to} 5n, the measurement switches 8 _{1 to} 8n, 9 _{1 to} 9n, and the like. . Note that after ON of the high-voltage changeover switch 3 ₁ 3n, measurement switch 8 ₁ ~8n and 9 ₁ ~9n is continuously switched drive each piezoelectric body. Switching among the measurement switch 8 ₁ ～8N and 9 ₁ ～9N, switches that are connected to each other (8 ₁ and 9 _1), (8 ₂ and 9 ₂₎ · · · (8n and 9n) is to be turned ON at the same time It is done. The high voltage changeover switches 3 _{1 to} 3n and the discharge changeover switches 5 _{1 to} 5n are alternatively turned on, the high voltage changeover switches 3 _{1 to} 3n are turned on during polarization, and the discharge changeover switch 5 ₁ after polarization. ˜5n is turned on.
[0022]
Next, a polarization method of the polarization processing apparatus having the above configuration will be described.
First, the piezoelectric bodies W _{1 to} Wn are accommodated in the thermostatic chamber 1, and the temperature is controlled so that all the piezoelectric bodies have a predetermined temperature equal to or higher than the aging temperature (for example, 200 ° C.). Next, the high voltage changeover switches 3 _{1 to} 3n are turned on, and a DC voltage for polarization is simultaneously applied to all the piezoelectric bodies W _{1 to} Wn. After the voltage application is started, the measurement switches 8 _{1 to} 8n and 9 _{1 to} 9n are switched to supply AC signals for measuring the degree of polarization from the measuring device 7 to the piezoelectric bodies W _{1 to} Wn in order.
[0023]
As the polarization of the piezoelectric bodies W _{1 to} Wn proceeds, the degree of polarization Δf increases as shown in FIG. That is, the measuring device 7 measures the resonance frequency fr and the antiresonance frequency fa of the piezoelectric bodies W _{1 to} Wn, and individually calculates the degree of polarization based on the frequency difference Δf. The control device 12 is preset with a polarization degree Δf ₁ during polarization having a high correlation with the stable polarization degree Δf ₂ after returning to room temperature, and the polarization degree during polarization is set to the set value Δf ₁ . At that time, the control device 12 individually turns off the high voltage changeover switches 3 _{1 to} 3n, and stops the application of the DC voltage to the piezoelectric bodies W _{1 to} Wn. For example, referring to FIG. 2, in order to obtain the target degree of polarization Δf ₂ = 2.97 kHz, voltage application may be stopped when the degree of polarization Δf during polarization reaches 4.13 kHz. When there is piezoelectric polarization degree it does not reach the set value Delta] f _1, until the polarization degree of the piezoelectric body becomes the set value Delta] f _1, to continue the voltage application to the piezoelectric body. When the voltage application is stopped, the control device 12 turns on the discharge changeover switches 5 ₁ to 5 n to discharge the charges accumulated in the piezoelectric bodies W _{1 to} Wn. This is because if the discharge is not performed, a reverse electric field is applied by the electric charges accumulated in the piezoelectric bodies W _{1 to} Wn, and the polarization may be returned. This terminates the polarization.
[0024]
Next, aging is performed while holding the piezoelectric bodies W _{1 to} Wn in the thermostatic chamber 1 at the same temperature (for example, 200 ° C.) or lower than that at the time of polarization. The aging time may be about 2 to 3 minutes. During the aging period, the discharge changeover switches 5 _{1 to} 5n are maintained in the ON state, and the discharge is continued. Thereafter, the piezoelectric bodies W _{1 to} Wn are taken out from the thermostat 1 and returned to room temperature over time, thereby terminating the polarization treatment.
The piezoelectric bodies W _{1 to} Wn that have finished the polarization treatment can obtain a target polarization degree Δf ₂ .
[0025]
In the above embodiment, the degree of polarization Δf ₁ during polarization having a high correlation with the stable degree of polarization Δf ₂ after returning to room temperature is set in advance, and the degree of polarization Δf during polarization is the set value Δf ₁ . At that time, the voltage application to the piezoelectric bodies W _{1 to} Wn was stopped, but the behavior of the degree of polarization was characterized from the measured degree of polarization during polarization, and the time to reach the set level was calculated. Alternatively, a method of stopping the voltage application when the calculated time is reached may be used.
[0026]
That is, as shown in FIG. 5, the behavior of the degree of polarization (Δf) during polarization shows a linear change from the middle of polarization. When the data during polarization is y _{t ,} y _t-1 ... Y _tm (m is arbitrary), the approximate expression y = at + b (y: degree of polarization, t: polarization) is obtained by linear regression calculation from the data during polarization. time)
And the correlation coefficient r ²
And discriminant r ² > c (for example, c = 0.92)
A and b when satisfying the above are obtained.
[0027]
While the discriminant is not satisfied, the data is updated sequentially (however, the number of data is n). The time t ₀ until reaching the set level (polarization degree) y ₀ from a and b when the above discriminant is satisfied is calculated by the following equation.
t ₀ = (y ₀ −b) / a
When the polarization time t reaches the calculated time t ₀ , the application of the DC voltage is stopped. In the case of a plurality of piezoelectric bodies, the prediction calculation is performed for each piezoelectric body, and the application may be stopped individually.
In the case of the above method, it is only necessary to measure the polarization time in the vicinity of the end of polarization, so there is no need to measure the degree of polarization at the end of polarization, and it is possible to prevent excessive polarization due to measurement delay and to control polarization with high accuracy. There are advantages.
[0028]
When a thick piezoelectric body such as a block-shaped ceramic substrate is polarized, the current flowing through the piezoelectric body during polarization tends to increase with time as shown in FIG. This increase in current becomes more pronounced as the polarization is increased at higher temperatures. When the current flowing through the piezoelectric body increases during polarization, a voltage drop occurs in the current limiting resistors 4 _{1 to} 4n, and the voltage between the both end electrodes of the piezoelectric bodies W _{1 to} Wn decreases. This decrease in voltage causes problems such as a decrease in the polarization rate of each of the piezoelectric bodies W _{1 to} Wn and the inability to obtain a desired degree of polarization.
[0029]
Therefore, the control device 12 calculates a voltage drop at the current limiting resistors 4 _{1 to} 4 n from the current value detected by the current detection circuit 11, and adds this voltage drop to the initial applied voltage, thereby providing an electrode of the piezoelectric body. The voltage is controlled so as to be always constant.
That is, the applied voltage is determined based on the following calculation formula.
Applied voltage = initial voltage + current value × current limiting resistance In this way, by maintaining the voltage applied to each piezoelectric body at a constant voltage, it is possible to eliminate variations in the degree of polarization between the piezoelectric bodies due to variations in applied voltage. .
[0030]
As for the current value necessary for the above calculation, if there is one applied power supply 2 as shown in FIG. 3, the power supply voltage may be controlled using the minimum value of the current value flowing through each piezoelectric body. This is to prevent destruction of the piezoelectric body due to overvoltage application. On the other hand, when a plurality of applied power sources 2 are provided, the applied voltage is calculated based on the current value of each piezoelectric body, and voltage control of the applied power source is performed for each piezoelectric body. This voltage control may be always performed by feedback as the current value increases.
[0031]
Next, how to obtain fr and fa for calculating the degree of polarization Δf will be described.
7 and 8 show the impedance and phase characteristics of the piezoelectric body in high-temperature air (200 ° C.).
As shown in the figure, the impedance waveform of the piezoelectric body in the high-temperature air tends to be broad in the vicinity of fr and fa, and further, ripples tend to occur in the impedance waveform in the vicinity of fr and fa when a high voltage is applied. Variation is likely to occur. Therefore, as shown in FIG. 7, the possible range of the values of fr and fa obtained from the impedance waveform is widened, and the measurement variation of the degree of polarization Δf increases.
On the other hand, in the case of a phase waveform, even when high voltage is applied and a high voltage is being applied, the values fr and fa are stabilized as shown in FIG. The measurement variation of the degree of polarization Δf can be reduced. Note that the values of fr and fa at a phase of 0 ° and the values of minimum and maximum impedances of fr and fa are not the same, but are approximately approximate.
[0032]
Table 1 compares the variation when Δf is measured by the impedance measurement method (Z measurement method) and the phase 0 ° method after leaving the polarized piezoelectric body in the atmosphere at 200 ° C. for 30 minutes. .
As is apparent from Table 1, when the Δf measurement variation in the static state (polarized state) is compared, it can be seen that the phase 0 ° method has less variation than the impedance measurement method.
[0033]
[Table 1]

[0034]
FIGS. 9 and 10 show the Δf behavior of a piezoelectric body polarized at a high temperature and a high voltage. FIG. 9 shows the measurement by the phase 0 ° method, and FIG. 10 shows the measurement by the impedance measurement method. is there.
Table 2 compares the measurement accuracy of the Δf behavior due to the difference in each measurement method. In Table 2, approximate straight lines are obtained for each measurement method, and the measurement accuracy is compared with the relative error from the correlation coefficient and the approximate straight line.
As is clear from FIGS. 9 and 10 and Table 2, it can be seen that the Δf behavior in the dynamic state (during polarization) changes more linearly in the phase 0 ° method than in the impedance measurement method. Therefore, in the phase 0 ° method, the error between the actually measured value and the approximate value is small, indicating that the Δf behavior can be measured with high accuracy.
Therefore, using the phase 0 ° method for measuring the degree of polarization during polarization in the present invention enables more accurate polarization control.
[0035]
[Table 2]

[0036]
The present invention is not limited to the above embodiments.
In the above embodiment, an example is shown in which both polarization and aging are performed at 200 ° C. However, the polarization temperature may be equal to or higher than the aging temperature, and is not limited to 200 ° C.
In the case of a piezoelectric ceramic, the polarization temperature and the aging temperature vary depending on the material, but a temperature range of 180 to 210 ° C. is desirable in order to reduce the polarization variation.
[0037]
【The invention's effect】
As is apparent from the above description, according to the first aspect of the invention, the polarization treatment is performed by applying a DC voltage to the piezoelectric body in an air atmosphere at a temperature higher than the aging temperature. Therefore, the polarization proceeds even at a voltage lower than the polarization in the liquid, and the degree of polarization equivalent to the polarization in the liquid can be obtained in a short time. In addition, since aging proceeds simultaneously during polarization, the aging time after the voltage application is stopped can be shortened. In addition, while measuring the degree of polarization of the piezoelectric body during polarization, voltage application was stopped when the measured degree of polarization reached the set level, and then aging was performed at the aging temperature. And can reach the target degree of polarization with high accuracy.
[0038]
In addition, according to the method of claim 2 , as in the invention of claim 1, the polarization time and the aging time can be shortened, and a primary characteristic equation for the polarization degree of the polarization degree from the measured polarization degree is obtained. Since the polarization end time is predicted from the characteristic equation, it is only necessary to measure the polarization time in the vicinity of the end of polarization, and it is possible to prevent excessive polarization due to measurement delay and to control polarization with high accuracy. Have.
[Brief description of the drawings]
FIG. 1 is a diagram showing a change in the degree of polarization of a piezoelectric body during a polarization process.
FIG. 2 is a diagram showing the correlation between the degree of polarization during polarization and the degree of polarization after returning to room temperature.
FIG. 3 is a circuit diagram showing an example of a polarization processing apparatus according to the present invention.
FIG. 4 is a graph showing the relationship between the polarization temperature and the degree of polarization after returning to room temperature.
FIG. 5 is a diagram showing the behavior of the degree of polarization during polarization.
FIG. 6 is a diagram showing the behavior of current during polarization.
FIG. 7 is a diagram illustrating a method for measuring impedance of a piezoelectric body in high-temperature air.
FIG. 8 is a diagram illustrating a phase 0 ° method in a high-temperature atmosphere of a piezoelectric body.
FIG. 9 is a diagram in which Δf of a piezoelectric body being polarized at high temperature and high voltage is measured by a phase 0 ° method.
FIG. 10 is a diagram in which Δf of a piezoelectric body being polarized at high temperature and high voltage is measured by an impedance measurement method.
[Explanation of symbols]
W ₁ wn piezoelectric body 1 thermostatic chamber 2 high-voltage direct-current power supply 3 ₁ 3n high-voltage changeover switch 4 ₁ to 4n current limiting resistor 7 meter 8 ₁ ~8n, 9 ₁ ~9n measuring switch 11 current detecting circuit 12 control apparatus

Claims (4)

A step of applying a direct current voltage to the piezoelectric body and performing a polarization treatment in an atmosphere and at a temperature equal to or higher than the aging temperature;
A step of measuring the degree of polarization while performing polarization treatment of the piezoelectric body;
Stopping the application of the DC voltage when the measured degree of polarization reaches a set level;
A step of performing aging at the aging temperature after the voltage application is stopped, and a polarization treatment method of the piezoelectric body ,
The set level is obtained by a correlation between a degree of polarization immediately before the application of the DC voltage is stopped and a stable value of the degree of polarization after aging after the application is stopped and returning to room temperature. Body polarization treatment method. A step of applying a direct current voltage to the piezoelectric body and performing a polarization treatment in an atmosphere and at a temperature equal to or higher than the aging temperature;
A step of measuring the degree of polarization while performing polarization treatment of the piezoelectric body;
From the measured degree of polarization, obtaining a primary characteristic equation for the polarization time of the degree of polarization ;
Calculating the time required for the degree of polarization to reach a set level according to the above characteristic equation ;
Stopping the application of DC voltage when the calculated time is reached;
And a step of performing aging at the aging temperature after the voltage application is stopped. In what has the characteristic that the current flowing through the piezoelectric body increases during polarization,
Application of the DC voltage, calculates the voltage drop at the current limiting resistor from the current value flowing through the piezoelectric element, wherein the voltage drop in claim 1 or 2, characterized in that go in addition to the initial applied voltage The piezoelectric body polarization treatment method. The step of measuring the degree of polarization while performing the polarization treatment of the piezoelectric body,
Measuring the phase of the piezoelectric body during polarization;
Calculating a frequency (fa, fr) when the phase is 0 °;
The method for polarizing a piezoelectric body according to any one of claims 1 to 3 , further comprising a step of obtaining a degree of polarization from a frequency difference Δf (= fa-fr) of the frequencies (fa, fr).

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