JP2005278121A - Piezo-electric element and piezo-electric component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezo-electric element and a piezo-electric component, which are not influenced from a loss caused by conductivity in a real usage temperature range of the piezo-electric part even if they are under high temperature circumstances. <P>SOLUTION: The piezo-electric element includes: a polarized piezo-electric substrate; each electrode formed on positive and negative pole sides in the polarized direction of the piezo-electric substrate; and a temperature sensing semiconductor formed on the piezo-electric substrate and having a negative resistance temperature coefficient for connecting the respective electrodes electrically. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a piezoelectric element used for a piezoelectric buzzer, a piezoelectric sensor, a piezoelectric transformer, a piezoelectric actuator, a bulk wave filter / oscillator, a surface wave filter / oscillator, and a piezoelectric component using the piezoelectric element, and particularly has excellent heat resistance and heat resistance. The present invention relates to a piezoelectric element that requires stability and a piezoelectric component using the same.

  In recent years, there are a wide variety of electronic parts using a piezoelectric body, and a large number of piezoelectric buzzers, piezoelectric sensors, piezoelectric transformers, piezoelectric actuators, filters, oscillators, and the like are used in mobile communication devices, AV devices, OA devices, and the like. . In these devices, since a solder reflow process is used for high-density mounting of electronic components, there is a strong demand for electronic components with small characteristic changes even when the solder reflow process is used. In addition, electronic parts for mobile communication devices may be temporarily placed in a high temperature environment during processing or the like, and therefore there is a strong demand for improved stability of characteristics and reliability against temporary storage at high temperatures and thermal shock. In particular, with the shift to the lead-free solder reflow process, the demand for improving the heat resistance of the piezoelectric element and electronic parts using the piezoelectric element is rapidly increasing.

  In particular, the pyroelectric coefficient of materials with high piezoelectricity increases, so when high-temperature heat treatment such as solder reflow or equivalent high-temperature thermal shock is applied, pyroelectric charges are generated according to the polarization direction of the piezoelectric material. It is known that this changes the polarization state of the piezoelectric material and causes a change in the characteristics of the piezoelectric element and the piezoelectric component using the piezoelectric element and destruction of the element.

In order to reduce the influence of such pyroelectric charges, in Patent Documents 1 to 3, a pyroelectric charge is discharged by forming a conductive material between IDTs (interdigital transducers) for surface acoustic wave elements. Technology has been proposed. Also, using the same effect, Patent Documents 4 and 5 disclose piezoelectric elements and piezoelectric parts in which a conductive material or a resistive material is formed between electrodes for piezoelectric parts and piezoelectric elements. Further, Patent Documents 6 and 7 disclose a high heat-resistant piezoelectric ceramic that reduces the electrical resistivity at room temperature of the piezoelectric ceramic material itself by material design and at the same time achieves desired piezoelectric characteristics.
Japanese Patent Laid-Open No. 09-055574 JP 09-172649 A JP 09-199974 A JP-A-11-298996 JP-A-11-330578 Japanese Patent Laid-Open No. 09-1000015 Japanese Patent Laid-Open No. 10-955666

  However, in order to reduce the effect of pyroelectric charge, the piezoelectric element using the conductive material or the resistance material as described above, or the piezoelectric element using the piezoelectric ceramic having a low electrical resistivity, the actual operating temperature of the piezoelectric element. Since the electrical resistivity within the range is low, there is a problem that the loss of the piezoelectric element increases due to the loss due to the conductivity.

  In particular, it is premised on driving large electric fields such as piezoelectric elements, piezoelectric actuators, and piezoelectric transformers that increase the electric field applied to the piezoelectric elements by reducing the element thickness or reducing the thickness of one layer of the laminate. In such piezoelectric parts, and in piezoelectric parts that require low loss characteristics such as surface acoustic wave filters and low loss ceramic filters, loss due to conductivity has been a major problem.

  In addition, because a high electric field cannot be applied during the polarization process, the conductive material and the resistive material must be formed after the piezoelectric substrate is polarized, and there is a problem that the process design and part design are greatly restricted. In addition, when a low resistivity piezoelectric ceramic is employed, there is a problem that there is a great restriction on material design for achieving both low resistivity characteristics and desired material characteristics.

  As a result of intensive research on the above problem, the above problems can be solved by connecting each electrode formed on the positive and negative sides of the polarization direction of the piezoelectric substrate with a temperature-sensitive semiconductor having a negative resistance temperature coefficient. I found out.

  In other words, by connecting a temperature-sensitive semiconductor having a negative resistance temperature coefficient, the piezoelectric element used for the piezoelectric component maintains a high electrical resistivity within the temperature range of the actual usage condition of the piezoelectric component, and the piezoelectric component By reducing the electrical resistivity of the piezoelectric element on the higher temperature side than the upper limit temperature of the temperature range of the actual use conditions, the above-mentioned problems can be solved.

  That is, when a piezoelectric element or a piezoelectric component using the piezoelectric element is placed in a high temperature environment, the pyroelectric charge is selectively discharged only in a high temperature range that is greatly affected by the pyroelectric charge, and The inventors have found a piezoelectric element that is not affected by the loss due to conductivity within the operating temperature range and a piezoelectric component using the piezoelectric element.

  It is known that piezoelectric materials generally have a lower coercive electric field as the temperature rises, and polarization changes are likely to occur even at a relatively low electric field. It is also known that the pyroelectric charge is proportional to the pyroelectric coefficient p and the temperature change rate ΔT / t per unit time t.

  Here, since the electric field opposite to the polarization direction of the piezoelectric material is applied by pyroelectric charge when the temperature is lowered, paying attention to the temperature lowering process after the heat treatment, the temperature change rate ΔT / t of the piezoelectric element immediately after the heat treatment ΔT / t decreases as the temperature approaches room temperature (since the difference between the room temperature and the heat treatment temperature is large immediately after the heat treatment, the temperature of the piezoelectric element rapidly decreases, but over time, the temperature of the piezoelectric element approaches the room temperature. The temperature change rate of the piezoelectric element is small).

  When the magnitude of ΔT / t and the above-described decrease in coercive electric field at high temperatures are taken into account, it can be seen that the influence of pyroelectric charge is greater in the high temperature range. Therefore, by using a temperature-sensitive semiconductor to form a piezoelectric element whose electrical resistivity decreases only at high temperatures, the effect of pyroelectric charges can be reduced by selectively discharging pyroelectric charges at high temperatures. Piezoelectric elements and piezoelectric parts having excellent properties can be obtained.

  On the other hand, within the actual use temperature range of the piezoelectric component, the piezoelectric element maintains a high electrical resistivity and is not affected by the loss due to conductivity. As a result, the piezoelectric element of the present invention and the low loss characteristic can be maintained within the actual use temperature range, and further, it is possible to apply a high electric field necessary for use and a high electric field during polarization treatment. Furthermore, since the piezoelectric element and the piezoelectric component of the present invention are not restricted by the electrical resistivity of the piezoelectric material itself employed, the degree of freedom in material design is greatly improved.

  As described above, the piezoelectric element of the present invention maintains a high electrical resistivity within the actual use temperature range, and the electrical resistivity decreases at a temperature higher than the upper limit temperature of the actual use temperature range. Therefore, the electrical resistivity of the piezoelectric element of the present invention has a negative temperature coefficient in a temperature range higher than the upper limit temperature of the operating temperature range.

  Furthermore, the temperature coefficient of the electrical resistivity in the temperature range higher than the upper limit temperature of the operating temperature range has a negative value larger than the temperature coefficient of the electrical resistivity in the operating temperature range.

Specifically, the electrical resistivity of the piezoelectric element is 1 × 10 ¹¹ Ω · cm or more within the actual usage temperature range, and the electrical resistance is less than 1 × 10 ¹¹ Ω · cm at a temperature higher than the upper limit temperature of the usage temperature range. It is preferable to decrease to. For example, when the actual use temperature range is less than 150 ° C., it is more desirable that the electrical resistivity of the piezoelectric element at 150 ° C. is smaller by one digit or more than the electrical resistivity at 25 ° C. In the following examples, the upper limit temperature of the actual use temperature range of the piezoelectric element is assumed to be less than 150 ° C., and specifically, the effect is confirmed up to the upper limit temperature of 130 ° C. of the use temperature range.

  When the piezoelectric element of the present invention or a piezoelectric component using the piezoelectric element is placed in a high-temperature environment of 150 ° C. or higher depending on the processing step or being left standing, the heat resistance effect of the piezoelectric element of the present invention or the piezoelectric component using the piezoelectric element. Works effectively, and is particularly effective when the high temperature environment is a high temperature condition of 200 ° C. or higher such as a solder reflow process.

  In the piezoelectric element according to the present invention, since the electrical resistivity of the piezoelectric element decreases at a temperature higher than the upper limit temperature of the actual usage condition of the piezoelectric element, the piezoelectric element is subjected to heat treatment such as a solder reflow process or an equivalent high temperature environment. Even when placed underneath, the pyroelectric charge is selectively discharged only in a high temperature range that is greatly affected by the pyroelectric charge, and thus exhibits excellent heat resistance.

  Furthermore, the piezoelectric element of the present invention exhibits excellent characteristics without being affected by loss due to conductivity because the piezoelectric element maintains high electrical resistivity within the temperature range of the actual usage conditions of the piezoelectric element. To do.

  Therefore, in the piezoelectric element of the present invention, it is possible to obtain a piezoelectric element having both excellent heat resistance that can cope with high-temperature heat treatment such as a solder reflow process and excellent characteristics within the operating temperature range.

  In addition, it is possible to apply a high electric field that is necessary for use and a high electric field during polarization processing, and it is not subject to restrictions on the material design of the piezoelectric ceramic itself that is used. The degree is improved.

  Furthermore, even with a piezoelectric component using this piezoelectric element, it is possible to achieve both excellent heat resistance and excellent characteristics within the operating temperature range. For example, a piezoelectric component that can be subjected to high-temperature heat treatment such as a solder reflow process and has excellent characteristics. can get.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an embodiment of the present invention. Electrodes are formed on both main surfaces of the piezoelectric substrate, and a temperature-sensitive semiconductor is arranged so as to short-circuit the electrodes. The polarization direction in this case is the thickness direction. In this embodiment, a lead zirconate titanate (PZT) piezoelectric ceramic material is used as the piezoelectric material, and a metal / silica glass composite material is used as the temperature-sensitive semiconductor material.

Next, a manufacturing process of the sample of this example will be described. Two types of piezoelectric materials, soft and hard, were used as the piezoelectric ceramic material. Piezoelectric material A represented by the composition formula Pb (Zr _0.52 Ti _0.46 Nb _0.02 ) O ₃ is used for the soft system, and composition formula Pb {(Mn _1/3 Nb _2/3 ) _0.10 Zr _0.43 Ti for the _{hard system.} Piezoelectric material B represented by _0.47 } O ₃ was used. These piezoelectric materials use Pb ₃ O ₄ , ZrO ₂ , TiO ₂ , MnCO ₃ , and Nb ₂ O ₅ as raw materials, and are weighed so that the composition formulas of the piezoelectric materials A and B are obtained. The solid phase method (ball mill mixing and calcination) was synthesized. A binder was added to the obtained powder, and after press molding and firing, the obtained sintered body was subjected to surface polishing and cutting steps to produce a piezoelectric ceramic rectangular plate. Ag electrodes were baked on both main surfaces of the rectangular plate to obtain a piezoelectric element A using the soft piezoelectric material A and a piezoelectric element B using the hard piezoelectric material B.

  In this example, a Zn-silica glass composite material was used for the temperature-sensitive semiconductor. For this composite material, a silica glass composite material containing about 35 vol% Zn was prepared according to the production method described in Journal of Ceramic Society of Japan 109 [2] p.122-126 (2001). In the above document, this composite material is reported as a material exhibiting CTR (critical temperature thermally) characteristics. The reason why we used this material in this example is that the temperature characteristic of the electrical resistivity of this material is piezoelectric. This is because it has a large negative temperature coefficient in a temperature range higher than the operating temperature range assumed by the device.

  Next, piezoelectric element samples shown in Tables 1 and 2 were constructed using the piezoelectric elements A and B.

  FIG. 1 is a schematic configuration diagram of A-1 and B-1 which are piezoelectric element samples of the present invention, and A-2 and B-2 and A-3, B-3 and B which are piezoelectric element samples of comparative examples. Schematic diagrams of the configuration of −4 are shown in FIGS. 10 and 11, respectively.

  Here, A-1 and B-1 of the present invention are piezoelectric elements in which the main surface electrodes of the piezoelectric elements A and B are short-circuited using the above-described temperature-sensitive semiconductor. Comparative examples A-2 and B-2 are piezoelectric elements in which the main surface electrodes of the piezoelectric elements A and B are short-circuited using a conductive adhesive, respectively. It is the same as the element. Moreover, A-3 and B-3 of the comparative example are those in which both principal surface electrodes of the piezoelectric elements A and B are in an open state. Furthermore, B-4 of the comparative example is a piezoelectric element in which the electrical resistivity is reduced by using the piezoelectric material B in the same manner as in Patent Document 6.

  The temperature dependence of the electrical resistivity of A-1 to A-3 and B-1 to B-4 is shown in FIGS. 2 and 3, respectively. Tables 3 and 4 show the electrical resistivity at each measurement temperature of A-1 to A-3 and B-1 to B-4.

2 and 3 and Tables 3 and 4, the piezoelectric elements A-1 and B-1 of the present invention show a low electrical resistivity of 1 × 10 ¹¹ Ω · cm or less at 150 ° C., whereas 0 to 130 ° C. It can be seen that a high resistivity of 1 × 10 ^{1 1} Ω · cm or more is maintained in between. On the other hand, A-2 and B-2 show low resistivity of 1 × 10 ¹¹ Ω · cm or less even near room temperature.

On the other hand, A-3 and B-3 show a resistivity of 1 × 10 ¹¹ Ω · cm or higher at 130 ° C. or lower, but still show a high resistivity of 1 × 10 ¹¹ Ω · cm or higher at 150 ° C. ing.

Furthermore, although B-4 shows a resistivity of 1 × 10 ¹¹ Ω · cm or more near room temperature, it can be seen that the electrical resistivity decreases rapidly with increasing temperature.

  This difference in temperature dependence of the electrical resistivity is the greatest difference between the piezoelectric element of the present invention and the piezoelectric element of the prior art.

  That is, when the upper limit temperature of the actual use temperature range of the piezoelectric element is, for example, 130 ° C., the piezoelectric element of the present invention maintains high electrical resistivity within the actual use temperature range, and the upper limit of the temperature range of the actual use condition. On the higher temperature side than the temperature, the electrical resistivity is remarkably lowered.

  In this case, the influence can be selectively reduced only in a high temperature range that is greatly affected by the pyroelectric charge. In addition, at least when the upper limit temperature of the actual use temperature range is 130 ° C. or lower, the electrical resistivity is kept high within the actual use temperature range, so that it is not affected by the loss due to conductivity, and therefore has excellent characteristics. Can be expressed.

  Hereinafter, the effect of the temperature dependency of the electrical resistivity will be described based on specific measurement results.

  Table 3 summarizes the electrical resistivity at each temperature of A-1 to A-3, the rate of change of the electromechanical coupling coefficient k before and after the heat treatment, and the piezoelectric strain constant when a high electric field is applied at room temperature.

  From Table 3, it can be seen that the change rate of k before and after the heat treatment is small and good in A-1 and A-2, whereas the change rate is large in A-3. On the other hand, the d constants during high electric field driving at room temperature are large for A-1 and A-3, whereas the decrease is significant for A-2. In order to suppress the characteristic change before and after the heat treatment, it is preferable that the electrical resistivity is low in order to discharge the pyroelectric charge as described above.

  However, when the electrical resistivity at the operating temperature is low as in A-2, when a constant high voltage is applied to the piezoelectric element, the voltage actually applied to the piezoelectric element drops, It is not preferable.

  Therefore, in order to make all the above characteristics compatible in a preferable direction, a piezoelectric element that maintains a high electrical resistivity under actual use conditions and has a low electrical resistivity at higher temperatures is effective, as in A-1. is there.

  Next, Table 4 summarizes the electrical resistivity at each temperature of B-1 to B-4, the change rate of the resonance frequency Fr before and after the heat treatment, and the mechanical quality factor Qm at room temperature. Moreover, the temperature characteristic of the mechanical quality factor Qm of B-1 to B-4 is shown in FIG.

  From Table 4, B-1, B-2, and B-4, which have low electrical resistivity in the high temperature range or in the entire temperature range, are good because the Fr change rate before and after the heat treatment is small. On the other hand, B-3, which has a high electrical resistivity in the entire temperature range, is not preferable because the Fr change rate before and after the heat treatment is large.

  Also, B-1, B-2, and B-4, which have a high electrical resistivity at room temperature, have a large Qm at room temperature and low loss, whereas B-2, which has a low electrical resistivity at room temperature, has a small Qm. (Loss is large).

  Furthermore, FIG. 4 shows that B-1, B-2, and B-3, which have high resistivity in the range of 0 to 130 ° C., have a small Qm temperature dependency in the same temperature range, but are good. In B-4 in which the resistivity rapidly decreases at ° C., Qm rapidly decreases on the high temperature side, which is not preferable. It can be said that the behavior of these Qm depends on the loss due to conductivity.

  Therefore, in order to make all the above characteristics compatible in a preferable direction, a piezoelectric element that maintains a high electric resistivity within the actual use temperature range and has a low electric resistivity on the higher temperature side, as in B-1. It is very effective.

  In the above-described embodiment, the piezoelectric element having a structure in which both main surface electrodes of the rectangular plate-shaped piezoelectric element are short-circuited with a temperature-sensitive semiconductor is described, but the piezoelectric element of the present invention is not limited to this.

  For example, when the electrodes of the piezoelectric laminate are short-circuited with a temperature-sensitive semiconductor as shown in FIG. 5, or between IDTs of piezoelectric elements having an IDT such as a surface acoustic wave element are short-circuited with a temperature-sensitive semiconductor as shown in FIG. Thus, the same effect can be obtained.

  In addition, when the piezoelectric element of the present invention is applied to a piezoelectric transformer as shown in FIG. 7, the primary and secondary electrodes of the piezoelectric transformer are short-circuited with a temperature-sensitive semiconductor, so that low loss is maintained within the operating temperature range. A piezoelectric transformer having excellent characteristics (high efficiency) and almost no characteristic deterioration can be obtained even through the solder reflow process.

  Furthermore, a through hole or the like is formed between the electrodes of the piezoelectric element as shown in FIG. 8, and a temperature sensitive semiconductor is formed there, or a temperature sensitive semiconductor thin film is used as shown in FIG. It is clear that the same effect can be obtained even if the electrodes of the wave element are short-circuited.

  In the above-described embodiments, a PZT piezoelectric ceramic material is used as the piezoelectric material and a Zn-silica glass composite material is used as the temperature-sensitive semiconductor. However, the present invention is not limited to these materials.

  The essence of the piezoelectric element of the present invention is that the electrical resistivity is lower in the high temperature range than the operating temperature range, so that the pyroelectric charge in the high temperature range can be selectively discharged, thereby improving the heat resistance and the operating temperature. In order to maintain a high electric resistivity within the range, it is not affected by the loss due to the conductivity, and thus exhibits excellent characteristics. The piezoelectric element of the present invention is composed of at least a piezoelectric substrate and a temperature sensitive semiconductor.

  Therefore, even when a piezoelectric ceramic material other than PZT such as lead titanate or Bi layered compound or a single crystal material such as lithium niobate or lithium tantalate is used as the piezoelectric substrate, the same effect can be obtained. Is obvious.

  Furthermore, in this example, a Zn-silica glass composite material was used as the temperature-sensitive semiconductor, but other composite materials using, for example, Ag and Ni and glass, and semiconductors having a negative temperature coefficient such as vanadium oxide are used. It is clear that the same effect can be obtained even if it is used.

  However, for example, when vanadium oxide is used, the temperature at which the resistivity changes abruptly is about 70 to 80 ° C. Therefore, in the case of the piezoelectric element of the present invention using this, the upper limit temperature of its use temperature is 70 to 80 ° C. 80 ° C.

  As described above, it is necessary to select a material and design an element so that a piezoelectric element can obtain a desired resistivity in a desired temperature range by combining a piezoelectric body and a temperature-sensitive semiconductor. The present invention is not limited to the above-described design, and the piezoelectric element design method of the present invention, all piezoelectric elements conforming to the design concept, and piezoelectric parts using the same are brought about in common.

It is a figure which shows an example of the piezoelectric element of this invention, and is a figure which shows the Example which short-circuited between the electrodes formed in both the main surfaces of a piezoelectric material with the temperature sensitive semiconductor. It is a figure which shows an example of the temperature characteristic of the electrical resistivity of a piezoelectric element at the time of comprising the piezoelectric element of this invention using a soft type | system | group PZT piezoelectric material, and is a figure which shows a comparison with the piezoelectric element of a prior art. It is a figure which shows an example of the temperature characteristic of the electrical resistivity of a piezoelectric element at the time of comprising the piezoelectric element of this invention using a hard type PZT piezoelectric material, and is a figure which shows a comparison with the piezoelectric element of a prior art. It is a figure which shows an example of the temperature characteristic of the mechanical quality factor of a piezoelectric element at the time of comprising the piezoelectric element of this invention using a hard type PZT piezoelectric material, and is a figure which shows a comparison with the piezoelectric element of a prior art. It is a figure which shows an example of the piezoelectric element of this invention, and is a figure which shows the Example at the time of using a laminated piezoelectric element. It is a figure which shows an example of the piezoelectric element of this invention, and is a figure which shows the Example at the time of using the piezoelectric element which has IDT. It is a figure which shows an example of the electronic component using the piezoelectric element of this invention, and is a figure which shows the Example at the time of applying to a piezoelectric transformer. It is a figure which shows an example of the piezoelectric element of this invention, and is a figure which shows an example which short-circuited between the electrodes of the piezoelectric element with the temperature-sensitive semiconductor formed in the through hole. The element structure other than the method of forming the temperature-sensitive semiconductor is the same as that of the piezoelectric element shown in FIGS. It is a figure which shows an example of the piezoelectric element of this invention, and is a figure which shows an example which short-circuited between the electrodes of the piezoelectric element using the temperature-sensitive semiconductor film. The element structure other than the method for forming the temperature-sensitive semiconductor is the same as that of the piezoelectric element shown in FIGS. However, the laminated piezoelectric element shows an application example in a laminated actuator in which the number of layers is increased as compared with FIG. It is a figure which shows the outline of the piezoelectric element of a prior art, and is a figure which shows the piezoelectric element which short-circuited between the electrodes formed in the both main surfaces of a piezoelectric material with the electroconductive material or the resistor. It is a figure which shows the outline of the piezoelectric element of a prior art, and is a figure which shows the piezoelectric element which has not short-circuited between the electrodes formed in both the main surfaces of a piezoelectric material.

Explanation of symbols

11, 51, 71, 81 electrodes 12.52, 62, 72, 82 Piezoelectric material (plate)
13, 53.63, 73, 83 Temperature-sensitive semiconductor IDT

Claims (6)

Polarized piezoelectric substrate, electrodes formed on the positive and negative sides of the piezoelectric substrate in the polarization direction, and a temperature-sensitive semiconductor formed on the piezoelectric substrate and having a negative resistance temperature coefficient that electrically connects the electrodes. And a piezoelectric element. A laminated body in which a plurality of polarized piezoelectric substrates are stacked with their polarization directions different from each other, electrodes arranged and formed with the piezoelectric substrate of the laminated body interposed therebetween, and formed in the laminated body And a temperature-sensitive semiconductor having a negative resistance temperature coefficient that electrically connects the electrodes. 3. A piezoelectric component comprising the piezoelectric element according to claim 1, wherein the temperature coefficient of resistance of the temperature-sensitive semiconductor is in a temperature range higher than the upper limit temperature of the operating temperature range of the piezoelectric component. A piezoelectric component having a large negative value as compared with a temperature range within the operating temperature range of the component. 3. A piezoelectric component configured using the piezoelectric element according to claim 1, wherein a resistance temperature coefficient of the piezoelectric element is a negative value in a temperature range higher than an upper limit temperature of a use temperature range of the piezoelectric component. A piezoelectric component characterized by comprising: 5. The piezoelectric component according to claim 3, wherein the piezoelectric component is placed in a high-temperature environment of 150 ° C. or higher in a processing step of the piezoelectric component or in a standing state. 5. The piezoelectric component according to claim 3, wherein the high temperature environment is a solder reflow process.

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