JPH0235492B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a mechanical resonator using a piezoelectric transducer and applied components thereof (hereinafter referred to as a mechanical resonator device using a piezoelectric transducer). A mechanical resonator using a piezoelectric transducer uses a piezoelectric transducer made of a ceramic material that has a piezoelectric effect. Typical materials include barium titanate-based, lead titanate-based, lead zirconate titanate-based ceramics, and the like. Typical examples of mechanical resonators using piezoelectric transducers include piezoelectric tuning forks and electromechanical filters.
They are used as selection elements in remote control systems, pagers, etc., and as oscillators, and in recent years, highly reliable mechanical resonator devices using these various piezoelectric transducers have become increasingly popular. required, external environment,
In particular, properties that are stable against temperature and thermal environments are required. However, when conventional piezoelectric transducers are placed in severe temperature or thermal environments, for example when special tests such as high-temperature storage tests and thermal shock tests are performed, the piezoelectric properties of the piezoelectric transducer deteriorate and insertion loss occurs. The phenomenon of an increase in the resonant frequency or a shift of the resonant frequency often occurs. To this end, various improvement plans have been attempted in the past, but the current situation is that the best solution has not yet been found. Ferroelectric substrates used in piezoelectric transducers of mechanical resonator devices must (1) have insertion loss and resonance frequency that do not change even with temperature changes, (2) have a large electromechanical coupling coefficient, etc. are required as important characteristics. For example, various additives are added to the main component of lead zirconate titanate ceramics in order to improve the properties of the material itself. However, when changing the material itself in this way, it is possible to improve the high temperature storage test and thermal shock test to some extent,
Although the above characteristic (1) may be satisfied, a phenomenon was observed in which the above characteristic (2) conversely deteriorates. In addition, attempts have been made to improve the characteristic (1) above by examining various firing conditions; however, variations in the characteristic (2) described above still occur or the characteristic deteriorates. However, it is not suitable for industrial production because it has the drawbacks of sintering, and it is also difficult to control the firing conditions. Therefore, the main object of the present invention is to provide a mechanical resonator device using a piezoelectric transducer that is stable in severe temperature environments and has good piezoelectric characteristics. Another object of the present invention is to provide a mechanical resonator device using a piezoelectric transducer that can reliably stabilize piezoelectric characteristics in severe temperature and thermal environments using simpler means. Still another object of the present invention is to provide a mechanical resonator device using a piezoelectric transducer that can be produced efficiently and has piezoelectric characteristics that are stable in harsh temperature and thermal environments. The present invention is a mechanical resonator device using a piezoelectric transducer, in which at least a portion of a ferroelectric substrate that has been subjected to a polarization treatment is applied to a surface of the ferroelectric substrate intersecting the polarization direction through the ferroelectric substrate. Opposing 1
A piezoelectric transducer having a structure in which a pair of conductive members is formed, and charge discharging means for discharging positive and negative charges accumulated in the pair of conductive members, the charge discharging means including the ferroelectric The mechanical resonator device is configured to connect the pair of conductive members via a resistance component lower than the resistance value of the conductive substrate, and is built in a mechanical resonator device. The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings. FIGS. 1 and 2 are diagrams showing a piezoelectric tuning fork, which is an example of a mechanical resonator using a piezoelectric transducer in which the present invention can be implemented. The overall structure of such a piezoelectric tuning fork is already well known, and the parts related to the present invention will be briefly explained here. A counter electrode is attached to the piezoelectric tuning fork 1, and the shape is
1.7×7×0.2 ^t mm rectangular piezoelectric substrate 11, 11'
is attached at or near the vibration node of the tuning fork leg. That is, this piezoelectric substrate 11 (piezoelectric substrate 11' is also the same, so the piezoelectric substrate 11' will not be explained again below. Similarly, the one with the dash symbol is the same as the one without the dash symbol, so it will not be explained again. ) is made of ferroelectric ceramic such as lead zirconate titanate, and is polarized in the thickness direction. On this piezoelectric ceramic substrate 11, electrodes 12 and 13 are formed facing each other. The electrode 12 is connected to a lead terminal 15 by a lead 14. Further, a protrusion integrally provided on the base edge of the tuning fork 1a is fixed to the common extraction terminal 16. Pull-out terminal 15,
15', the common extraction terminal 16 is held in a penetrating state by the resin base 17, and the base 17 and the conductor case 18
The inside is sealed. From FIG. 3 onward, different embodiments of the present invention are shown, and only the main parts thereof are shown. It is obvious that the actual piezoelectric tuning fork to be implemented is not limited to the structure shown in FIGS. 1 and 2. The external dimensions of the piezoelectric substrate 11 and the external dimensions of the electrodes 12 and 13 are the same as in FIGS. 1 and 2. In these embodiments, the composition of the piezoelectric substrate 11 is as shown in FIG.
Similar to Figure 2 (Pb _0.95 Sr _0.05 ) (Ti _0.48 Zr _0.52 ) O ₃
+0.75Wt%Nb ₂ O ₅ +0.15Wt%Cr ₂ O ₃ +0.5Wt%
Lead zirconate titanate ceramics such as MnO ₂ were used. When this ceramic is used, the resistance value between the electrodes 12 and 13 was 7×10 ¹¹ Ω in the conventional configuration before the present invention was applied. In the embodiment of FIG. 3, a discrete resistor 2 is connected between electrodes 12 and 13. For example, the resistance value is 1KΩ, 100KΩ, 10MΩ
Alternatively, a resistor with a value such as 1000MΩ can be used, but in this example a 100KΩ resistor element was used. The connection point of the resistor 2 is arbitrary as long as it is between 12 and 13 as long as it meets the spirit of the present invention. In the embodiment of FIG. 4, the piezoelectric ceramic substrate 11
A resistive paste 21 was baked over both surfaces of the electrode, thereby connecting the electrodes 12 and 13 with a certain resistance value. As the resistor paste 21, for example, a material in which carbon is dispersed in phenolic resin is used, and its resistance value is 1KΩ, 100KΩ,
It can take a value of 10MΩ, 1000MΩ, etc., but in the experiment, a resistor paste 21 of 1KΩ or 10MΩ was baked. In addition, this resistor paste 2
1 can also be formed, for example, at the position shown at 22 in FIG. 5, thereby connecting the electrodes 12 and 13. In other words, the connection location is arbitrary as long as it meets the spirit of the invention. In the embodiment shown in FIG. 5, the embodiment shown in FIGS. 3 and 4 and the embodiment shown in FIG. In contrast, these electrodes are formed of a resistive metal (eg, tantalum, titanium, etc.) or a resistive metal oxide (eg, tin oxide, etc.) by, for example, a vapor deposition method or a sputtering method. In this embodiment, a silver paste 22 having a resistance value of approximately zero is baked onto both sides of the piezoelectric ceramic substrate 11, thereby directly connecting the electrodes 12 and 13 without using a resistor. Of course, instead of the silver paste 22, lead wires may be used for short-circuiting, and these connection points are arbitrary as long as they meet the spirit of the invention. Furthermore, the silver paste 22 or the short-circuit lead wire may have a resistance component. The combined resistance value of the electrodes, the silver paste 22, and the short-circuit lead wire must be selected to be smaller than the resistance value between the electrodes 12 and 13 of the piezoelectric ceramic substrate 11 itself. In the embodiment shown in FIG. 6, a resistive (or semiconductor) resin is used as the material for forming the base 17. Materials for the base 17 include, for example, epoxy resin, carbon, metal, metal oxide,
A material in which semiconductor oxide powder, semiconductor glass powder, or the like is dispersed can be used. And its resistance value is 1KΩ, 100KΩ, 10MΩ and
The resistance value can be set to 1000MΩ, etc., but in the experiment, the resistance values were 10MΩ and 1000MΩ. In the case where a resistive base 17 is used as in this embodiment, it is desirable that the base 17 is further coated with a highly insulating and/or moisture-resistant resin 23. Note that this insulating resin 23 may be a conventional epoxy resin or the like. In this embodiment, when the electrode 13 is electrically connected to the tuning fork 1a, the extraction terminal 15 and the common extraction terminal 16 are connected to each other by the resistive base 17. Thus, the electrodes 12 and 13 are connected through the resistance value of the resin base 17. The piezoelectric tuning fork thus formed was then subjected to a thermal shock test. The conditions for the thermal shock test are as follows. That is, one cycle consisted of holding the temperature at −55° C. and +100° C. for 60 minutes and shifting from −55° C. to +100° C., and this cycle was repeated 100 times. And the transition from -55℃ to +100℃,
and vice versa, each within a few seconds. The results of this thermal shock test are shown in Table 1. In addition,
In this Table 1, especially Figures 3, 4, or 6
The examples shown in the figure were used as sample numbers 2 to 6, and the conventional example shown in FIG. 1 was used as sample number 1. In any of the embodiments, the point is that the charge generating electrodes should be connected with a resistance value lower than the resistance value of the piezoelectric ceramic substrate between the charge generating electrodes. A thermal shock test was conducted for each of the examples under the conditions described above. Table 1 shows the results.

【table】

[Table] This Table 1 shows the measurement results of the characteristics (insertion loss and resonance frequency) of the piezoelectric resonator according to the number of test cycles through a thermal shock test. As can be seen from Table 1, in the conventional case shown in Figures 1 and 2, that is, in the case where there is no insertion resistance, the insertion loss change and resonance frequency change increase as the number of thermal shock cycles increases. I can see that On the other hand, in the embodiment shown in FIG. 4, for example, the resistor paste 21 is
In the case of 1KΩ, that is, the data of sample number 2, the insertion loss hardly changes and the change in the resonance frequency is also within the allowable limit. Similarly, in the example of FIG. 3, the case where the solid resistance element 2 is 100KΩ is shown as sample number 3. In the example row shown in FIG. 6, the case where the resistance value of the resistive resin base 17 is 10 MΩ is shown as sample number 4. Furthermore, the example in Figure 4 with a resistance value of 10MΩ is shown as sample number 5, and the example in Figure 6 with a resistance value of 10MΩ.
The sample with a resistance of 1000MΩ is shown as sample number 6. The changes in insertion loss and changes in resonant frequency of samples No. 2 to 6 in Table 1 are shown in Figure 1.
It can be seen that this is clearly and reliably improved compared to the conventional one as shown in FIG. 2, that is, the one of sample number 1. Figure 7 shows sample number 6, the example shown in Figure 6, with the resistance value of the resin base 17 being 1000 MΩ, and sample number 1, the conventional example shown in Figure 1. This is a graph showing the amount of change and created based on the data shown in Table 1. Note that the solid resistance element 2 in the embodiment shown in FIG.
, the resistance value of the resistor paste 21 in the embodiment shown in FIG. 4, and the resistance value of the resin base 17 in the embodiment shown in FIG. The condition is that it is smaller than the value. In addition, in the embodiment shown in FIG. 5, each electrode 1 formed of resistor paste
The sum of the resistance values of electrodes 2 and 13 and the resistance value of silver paste 22 is the sum of the resistance values of electrodes 11 and 12 of piezoelectric ceramic substrate 11.
The condition is that the resistance value is selected to be smaller than the resistance value between the two. In other words, when we determined the relationship between the resistance value of ceramic substrates made of various materials and the amount of change in electrical characteristics during thermal shock tests, we found that when the resistance value of ceramic substrates becomes lower than a certain value, It has become clear that the amount of change in characteristics becomes smaller. This is because due to the pyroelectric effect, charges in the opposite electric field to the direction of the electric field during polarization are not accumulated on the opposing electrode side of the ferroelectric ceramic substrate, but are spontaneously discharged through the inside of the ceramic substrate. it is conceivable that. However, as mentioned above, it has become clear that as the resistance of the piezoelectric ceramic substrate decreases, the piezoelectricity decreases and the variation in electrical characteristics increases. Without reducing the value, other forms of spontaneous discharge must be considered. In other words,
Instead of discharging through the inside of the ceramic substrate,
All you have to do is discharge it through an external circuit,
Therefore, it is sufficient to connect the electrodes where charges are generated using a resistor (including the case where no resistor is used) having a lower resistance value than that inside the ceramic substrate. However, in a structure where the electrode surface and the polarization direction intersect, it is necessary to ensure that the original operation of the piezoelectric transducer is not hindered.
There is naturally a limit to reducing these resistance values. This lower limit value cannot be determined unconditionally and must be determined for each individual case. In the case of a thermal shock test, when moving from a low temperature (-55℃) to a high temperature (+100℃), the pyroelectric effect causes the substrate 1 to
An electric field is generated between the electrodes on both sides of 1 in the forward direction of the polarization direction, while an electric field is generated in the opposite direction when moving from high temperature to low temperature. Due to such an alternating electric field, the substrate 1
It is thought that the polarization of 1 is removed, resulting in a decrease in the piezoelectric properties. Therefore, in this invention, in order to immediately alleviate such an alternating electric field, the substrate 1
The electrodes on both surfaces intersecting the polarization direction of one were electrically connected to each other with a substantially certain resistance value. In addition, in the above-mentioned embodiment, an example was shown in which a seizure resistor, a discrete solid resistance element, or the like was used as the resistor. An example was also shown in which a resin that also served as a resistor was used. However, in this invention, other semiconductor glass pastes, semiconductor oxide powder pastes, semiconductor resins, etc. may be used, and the point is that it is sufficient to create a state in which a resistor is inserted when viewed from the circuit. be. In the above embodiments, the conductive members on which charges are accumulated are electrodes, and the polarization axis direction is perpendicular to the surface of the piezoelectric ceramic substrate on which these electrodes are provided. Other examples include: FIG. 8 shows another example of the structure of the piezoelectric transducer, in which a ferroelectric ceramic substrate 201
The polarization direction of is parallel to the substrate surface. In this case, the ceramic substrate 201 is 0.2 mm thick and 1.7×
Consists of a 7mm rectangular plate, with two planes perpendicular to the polarization direction.
The resistance between 02 and 203 was 5×10 ¹³ Ω.
Electrodes 12 and 13, which are conductive members, are formed on opposing main surfaces of ceramic substrate 201. Furthermore, side surfaces 202 and 203 of the ceramic substrate 201
In this case, the electrodes 204, 2 are also conductive members.
05 is formed by a conventionally known method. According to this configuration, the conductive members on the side where charges are accumulated due to temperature changes are mainly the electrodes 204 and 205.
, but not the electrodes 12 and 13. Therefore, if you try to apply this invention,
For example, the electrodes 204 and 205 are connected by a short lead wire 206 as shown. Electrode 204,2
05 may be electrically connected through a resistor. In this case, electrodes 204, 205 may be formed from a material that is itself resistive, such as a resistive metal oxide. The present invention can be applied not only to the piezoelectric tuning fork as in the embodiments described above, but also to any other mechanical filter in which a piezoelectric transducer is combined with a mechanical resonator. Typical mechanical filters that can be applied will be described below. What is shown in FIG. 9 is a vibrating element filter in which piezoelectric transducers 32 and 33 are attached to resonators 30 and 31 to cause transverse vibration, and these are connected by torsion connectors 34 and 35. In the device shown in FIG. 10, piezoelectric transducers 41 and 42 are attached to an H-shaped resonator 40 to vibrate vertically. The filter shown in FIG. 11 is an example of a mechanical filter that utilizes multiple vibration modes, and includes piezoelectric transducers 51 and 52 attached to two adjacent sides of a substantially quadrangular prism-shaped resonator 50, respectively. Of course, the present invention is not limited to the structure described above, but can be applied to any structure in which a piezoelectric transducer is combined with a mechanical resonator. In addition, when the polarization axis direction is oblique to the substrate surface, the example in which the polarization axis direction is perpendicular to the substrate surface and the example in which the polarization axis direction is parallel to the substrate surface are changed depending on the temperature change. They may be combined as appropriate depending on the amount of charge generated. As described above, according to the present invention, the pyroelectric effect can be prevented by electrically connecting the electrode on the side where positive charges are accumulated and the electrode on the side where negative charges are accumulated on the piezoelectric substrate. The alternating charges caused by the base charges can be quickly relaxed, and therefore there is no deterioration of piezoelectric properties such as loss of polarization. In addition, a mechanical resonator device using a piezoelectric transducer without such deterioration of piezoelectric characteristics can be obtained with a simple configuration or method, and when manufactured industrially, it can be easily mass-produced and its yield rate is also low. can be improved. Furthermore, since the characteristics are stable even under different temperature and thermal environments, a mechanical resonator device using a piezoelectric transducer with very high reliability can be obtained.

[Brief explanation of drawings]

1 and 2 are diagrams showing an example of a conventional piezoelectric tuning fork in which the present invention can be implemented. FIG. 1 is a plan view with the case removed, and FIG. 2 is a front view with the case removed. 3 to 6 are side views showing different embodiments of the present invention, respectively. FIG. 7 is a graph showing the amount of change in insertion loss between the conventional device and the embodiment shown in FIG. FIG. 8 is a schematic side view showing another configuration example of a piezoelectric transducer using the present invention. FIGS. 9 to 11 each further show other embodiments of the present invention,
FIG. 9 is a schematic perspective view of a vibrating bar filter, FIG. 10 is a schematic perspective view of an H-type filter, and FIG. 11 is a schematic perspective view of a multimode filter. 1 is a piezoelectric tuning fork, 11, 11' is a piezoelectric substrate, 12,
12', 13, 13' are electrodes, 14, 14' are leads, 15, 15' are lead terminals, 1a is a tuning fork, 16
is a common extraction terminal, 17 is a resin base, 18 is a conductor case, 2 is a resistor, 21 is a resistive paste, 22
2 is a silver paste, 23 is an insulating resin, 201 is a ferroelectric ceramic substrate, 204 and 205 are electrodes, 2
06 is a rectangular lead wire.

Claims (1)

[Scope of Claims] 1. A mechanical resonator device using a piezoelectric transducer, wherein at least the surface of a polarized ferroelectric substrate intersecting the polarization direction is injected via the ferroelectric substrate. A piezoelectric transducer having a structure in which a pair of electrically conductive members are partially opposed to each other, and a charge discharge means for discharging positive and negative charges accumulated in the pair of electrically conductive members, the charge discharger comprising: The means is configured to connect the pair of conductive members via a resistance component lower than the resistance value of the ferroelectric substrate, and is built in the mechanical resonator device. do,
A mechanical resonator device using a piezoelectric transducer. 2. A mechanical resonator device using a piezoelectric transducer according to claim 1, wherein the conductive member includes a vibrating electrode. 3. A mechanical resonator device using a piezoelectric transducer according to claim 1, wherein the conductive member includes a conductive material other than a vibrating electrode. 4. Claims 1 to 4, wherein the crystal orientation axis of the polarized ferroelectric substrate is oriented perpendicularly to the conductive member between the conductive members on the side where charges are accumulated due to temperature changes. A mechanical resonator device using the piezoelectric transducer according to any one of Item 3. 5. Claims 1 to 3, wherein the crystal orientation axis of the ferroelectric substrate polarized between the conductive members on the side where charges are accumulated due to temperature change is oriented obliquely with respect to the conductive members. A mechanical resonator device using the piezoelectric transducer according to any one of paragraphs. 6. The charge discharging means includes forming at least one of the conductive member on the side where positive charges are accumulated or the conductive member on the side where negative charges are accumulated to have a predetermined resistance value, and electrically connecting both conductive members. A mechanical resonator device using the piezoelectric transducer according to claim 1, which is configured by directly connecting the piezoelectric transducer to the piezoelectric transducer according to claim 1. 7. A resistor is electrically connected in series between the conductive member on the side where the positive charges are accumulated and the conductive member on the side where the negative charges are accumulated, and the resistance value of each of the conductive members and the resistance of the resistor are 7. A mechanical resonator device using a piezoelectric transducer according to claim 6, wherein the sum of the resistance value and the resistance value of the ferroelectric substrate itself is smaller than the resistance value of the ferroelectric substrate itself. 8. Claim 1, wherein the charge discharging means is configured using a case of a mechanical resonator device.
A mechanical resonator device using the piezoelectric transducer described in . 9. A mechanical resonator device using a piezoelectric transducer according to claim 8, wherein the charge discharging means is constructed using a conductor portion of a case of the mechanical resonator device. 10. A mechanical resonator device using a piezoelectric transducer according to claim 8, wherein the charge discharging means is constructed using a resin molded part of a case of the mechanical resonator device.