JPH1117491A - Chip type piezoelectric filter and manufacturing method thereof - Google Patents

Abstract

(57) Abstract: Provided is a highly reliable chip-type piezoelectric filter having excellent filter waveforms, excellent sealing properties, and high reliability without generating unnecessary vibration in a relay capacitor section, and a method of manufacturing the same. A double-mode piezoelectric filter is formed on a single piezoelectric element plate via a relay capacitor, and a sealing plate provided with a concave portion for securing a vibration space is provided from above and below. In a chip-type piezoelectric filter bonded so as to sandwich the same, two relay capacitor electrodes 4a, 4a and 4
b, at least a portion of one or both of them, a weight adding portion 5 is formed, and a concave portion 10 for receiving the weight adding portion 5 is provided in a portion of the sealing plate 8 facing the weight adding portion 5.
Is provided. The weight adding section 5 is formed by printing and heat-treating a paste made of solder or resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip-type piezoelectric filter using thickness longitudinal vibration, which is used for channel selection of FM broadcasting and portable telephones.

[0002]

2. Description of the Related Art Conventionally, a double mode piezoelectric filter utilizing thickness vibration of a piezoelectric vibrator has been used as a filter for channel selection for FM broadcasting or the like, since sharp characteristics can be obtained.

FIG. 6 shows an example. (A) As shown in the figure, on one main surface of a flat piezoelectric element plate 1 polarized in the thickness direction, a portion for forming a dual mode piezoelectric filter composed of two resonance electrodes 2a and 2b ( Hereinafter, the filter unit 2), a filter unit 3 composed of two resonance electrodes 3a and 3b, and a relay capacitance unit 4 having a relay capacitance electrode 4a in the middle thereof are provided. Here, the relay capacitance is provided between the output terminal of the previous stage and the input terminal of the next stage in the multi-stage filter. One electrode is connected to the signal line, and the other electrode is grounded. Further, one resonance electrode 2a, 3a of each of the two filter units 2, 3 and the relay capacitor electrode 4a are electrically connected. The other resonance electrodes 2b and 3b of the filter sections 2 and 3 are connected to the extraction electrodes 6a and 6b, respectively. The extraction electrodes 6a and 6b are used as input electrodes or output electrodes of the piezoelectric filter, respectively.

On the other hand, as shown in FIG. 1B, on the other main surface (the back surface of the piezoelectric element plate 1 in FIG.
Two sets of ground electrodes 2c, 3c are provided opposite the resonance electrodes 2a, 2b, 3a, 3b, and a relay capacitor electrode 4b is provided opposite the relay capacitor electrode 4a. The filter unit 2 includes the resonance electrodes 2a and 2b and the ground electrode 2c, and the filter unit 3 includes the resonance electrodes 3a and 3b and the ground electrode 3c.
However, the relay capacitance portion 4 is formed by the relay capacitance electrodes 4a and 4b. The two sets of ground electrodes 2c, 3c and the relay capacitance electrode 4b are electrically connected.

When a signal is input from one of the extraction electrodes 6a, the signal is input from one of the pair of resonance electrodes 2b, and a filtered signal is output from the other 2a. Such a three-terminal type piezoelectric filter is called a dual mode piezoelectric filter.

In the example shown in FIG. 6, two double mode piezoelectric filters are formed on the same piezoelectric element plate 1, and are connected in series via a relay capacitor 4. This is to increase the amount of attenuation by connecting in series and obtain steep characteristics. The reason why the relay capacitor section 4 is provided between the two filter sections 2 and 3 is that the filter characteristics can be changed by inserting the relay capacitor. This is for obtaining a filter having steep characteristics.

Japanese Patent Laid-Open Publication No. Hei 8-237068 discloses such a dual mode piezoelectric filter. FIG.
As shown in FIG. 3, the piezoelectric element plate 1 in which the two filter sections 2 and 3 and the relay capacitor section 4 are formed therebetween is sealed from above and below with a sealing plate 8.
The chip-type piezoelectric filter is configured so as to sandwich the filter.
The sealing plate 8 is provided with concave portions 9a and 9b in a portion facing the two sets of filter portions 2 and 3 for securing a vibration space.

However, as described above, the piezoelectric element plate 1
When the relay capacitance is formed on the upper part, the relay capacitance part 4 itself also causes the thickness longitudinal vibration. In addition, the filter units 2, 3
Are formed on the same piezoelectric element plate 1, so that the frequency at which the thickness longitudinal vibration occurs is almost the same, so that the relay capacitance changes near the frequency used as a filter,
There is a problem that stable filter characteristics cannot be obtained.
In the case of the filter disclosed in JP-A-8-237068, since the piezoelectric element plate 1 is sandwiched between the sealing plates 8 shown in FIG. 7, the sealing plate 8 also plays a role of damping excess vibration. However, this alone is not enough to achieve a sufficient damping effect.

As one of the solutions, there is no polarization applied to the portion corresponding to the relay capacitor 4 when the piezoelectric element plate 1 is manufactured. However, in the case of this method, there is a drawback that, in addition to the need for forming a special electrode at the time of polarization, the productivity is reduced, and the piezoelectric element plate 1 is easily broken at the time of polarization.
This is because the piezoelectric element plate 1 expands in the thickness direction at the location where a voltage is applied during polarization, but does not expand at the location where no voltage is applied, and thus a large internal stress is generated in the piezoelectric element plate 1.

As another solution, a relay capacitor electrode 4 is provided.
A method of suppressing vibration by adding some weight to a is disclosed in, for example, JP-A-53-51943.
According to this method, by adding solder or the like to the relay capacitor electrode 4a to such an extent that the relay capacitor unit 4 does not operate as a resonator, vibration is suppressed by its weight. However, since the weighted portion (hereinafter, referred to as a "weight adding portion") protrudes from the surroundings, for example, as shown in Japanese Patent Application Laid-Open No. 8-237068, the piezoelectric element 8
The chip-type piezoelectric filter that is sandwiched between the two has a problem that the sealing property is deteriorated and the reliability is lowered, so that it cannot be adopted.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem. Even though the relay capacitor is provided on the same piezoelectric element plate as the filter, the relay capacitor is provided. It is an object of the present invention to provide a chip-type piezoelectric filter that has a good filter waveform without unnecessary vibration in a portion, has excellent sealing properties, and is highly reliable, and a method of manufacturing the same.

[0012]

The gist of the present invention is shown in FIGS.
3, a chip type piezoelectric filter of the following (1),
And (2) a method for manufacturing a chip-type piezoelectric filter.

(1) Two double-mode piezoelectric filters are formed on one piezoelectric element plate 1 so as to be connected in series via a relay capacitor 4, and a portion facing the double-mode piezoelectric filter is formed. In the chip type piezoelectric filter in which the sealing plate 8 provided with the concave portions 9a, 9b for securing the vibration space is bonded so as to sandwich the piezoelectric element plate 1 from above and below, the relay capacitance portion 4 is formed. A weight adding portion 5 is formed on at least a part of one or both of the relay capacitance electrodes 4a and 4b, and the weight adding portion 5 is placed in a portion of the sealing plate 8 facing the weight adding portion 5. Chip type piezoelectric filter, characterized in that a concave portion 10 is provided.

(2) Front and back 2 provided on piezoelectric element plate 1
Printing a paste made of solder or resin on at least a part of one or both of the relay capacitance electrodes 4a and 4b;
Forming a weight adding portion 5 by heat treatment;
Forming recesses 10 and 9a and 9b in a portion of the sealing plate 8 facing the weight adding portion 5 and a portion facing the dual mode piezoelectric filter; A method of manufacturing the chip-type piezoelectric filter according to the above (1), comprising a step of bonding in a sandwiching mode.

In the present invention, since the weight adding portion 5 is formed on at least a part of one or both of the front and back two relay capacitance electrodes 4a and 4b forming the relay capacitance portion 4, the relay capacitance portion is formed. 4, a good filter waveform can be obtained without generating unnecessary vibration. In addition, the sealing plate 8 sandwiching the piezoelectric element plate 1 from above and below is provided with a concave portion 10 for accommodating the weight adding portion 5 in a portion facing the weight adding portion 5, so that the sealing property is excellent. A highly reliable chip-type piezoelectric filter can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.

FIG. 1 relates to a chip type piezoelectric filter according to the present invention, and shows an electrode arrangement on both main surfaces of a piezoelectric element plate. In the figure, 1 is a piezoelectric element plate, 2a, 2b and 3a, 3b are resonance electrodes, 2c, 3c are ground electrodes,
2a to 2c and 3a to 3c constitute a dual mode piezoelectric filter, respectively. Reference numerals 4a and 4b denote relay capacitance electrodes, which constitute the relay capacitance unit 4. Reference numeral 5 denotes a weight adding portion, and reference numerals 6a and 6b denote extraction electrodes. Two double mode piezoelectric filters are formed on the same piezoelectric element substrate 1 with the relay capacitance section 4 interposed therebetween,
They are connected in series with the relay capacitance section 4 interposed therebetween. The extraction electrodes 6a and 6b are connected to the mounting electrodes 7a and 7c, respectively, and are used as input electrodes or output electrodes of the piezoelectric filter. FIG. 4 shows an equivalent circuit. As shown in the figure, the circuit is a circuit in which a double mode piezoelectric filter is connected in two stages with a relay capacitor interposed therebetween.

As shown in FIG. 1, a weight adding portion 5 is provided on the relay capacitance electrode 4. This portion is thicker than the surrounding relay capacitance electrode 4, and the weight effect damps the relay capacitance portion 4 from vibrating in the thickness longitudinal direction. At the same time, the resonance frequency can be reduced by the weight effect. Even if the thickness longitudinal vibration occurs, the change of the relay capacity occurs on the low frequency side, and the change of the relay capacity in the filter region does not occur. Therefore, stable filter characteristics can be obtained.

The area of the weight adding portion 5 depends on the material to be added, and may be a part or may be necessary over the entire surface. As a material for forming the weight adding portion 5, a material having a relatively large specific gravity and a high adhesion to the material for forming the relay capacitance electrodes 4a and 4b is desirable. Solder, an adhesive made of resin containing metal powder, and the like are preferable. These materials can be added to the relay capacitor electrodes 4a and 4b by soldering or printing.

It is to be noted that, if the weight adding portion 5 is formed on one of the relay capacitor electrodes, a sufficient effect for practical use can be obtained. .

FIG. 2 is an external view of a chip type piezoelectric filter of the present invention, in which the above-mentioned piezoelectric element plate 1 is sandwiched between sealing plates 8 from above and below. FIG. 3 is a sectional view taken along line AA of FIG. Here, 7a, 7b and 7c are mounting electrodes, 8 is a sealing plate, 9a and 9b are concave portions for securing a vibration space facing the filter portions 2 and 3, and 10 is formed to accommodate a weight adding portion. Recess.

In the present invention, the filter portions 2, 3 of the sealing plate 8 are provided.
A concave portion 9 for securing a vibration space
a, 9b as well as a recess 10 for receiving the weight-adding portion 5 in a portion facing the weight-adding portion 5.
Is provided. Thereby, even if the piezoelectric element substrate 1 is sandwiched between the sealing plates 8 from above and below, the sealing plate 8 hits the weight adding portion 5 and no gap is generated between the piezoelectric element substrate 1 and the sealing plate 8. Therefore, a highly reliable chip-type piezoelectric filter having excellent sealing properties can be obtained.

As shown in FIG. 3, the resonance electrodes 2b,
Filter part 2 having ground electrode 2c and resonance electrode 3
b, Filter section 3 having ground electrode 3c and relay capacitor section 4
It is desirable to provide a bonding portion 11 between the piezoelectric element plate 1 and the sealing plate 8 between each of them. That is, the filter portions 2 and 3 that use vibration and the relay capacitance portion 4 that may cause unnecessary vibration are separated by the sealing plate 8, so that unnecessary vibration is more reliably damped and a stable filter characteristic is obtained. is there.

In order to manufacture the above-described chip type piezoelectric filter, first, a piezoelectric material such as PZT (lead zirconate titanate) is molded into a block shape and fired. Then, it is sliced into a flat plate shape and polished to a predetermined thickness with a lap plate. Next, silver electrodes are formed by vapor deposition on both surfaces of the polished piezoelectric plate, and polarization treatment is performed. Thereafter, unnecessary electrode portions are removed by resist printing and etching, and a predetermined electrode pattern as shown in FIG. 1 is formed. Next, two relay capacitance electrodes 4a, 4b forming the relay capacitance portion 4
A weight-added portion 5 is formed by applying solder or an adhesive made of resin containing metal powder to at least a part of one or both of them by screen printing and performing a heat treatment.

On the other hand, a sealing plate 8 is manufactured by molding an insulating material such as alumina into a plate shape and firing it. The concave portions 9a and 9b facing the filter portions 2 and 3 and the concave portion 10 for accommodating the additional weight portion 5 are provided in a molding die in advance. The material of the sealing plate 8 is preferably a ceramic such as alumina which is excellent in weather resistance and mechanical strength, but may be an epoxy resin or the like. Further, the concave portion may be formed in the sealing plate 8 by using sandblasting or the like.

Further, the surface of the sealing plate 8 on which the concave portion is formed is polished in order to enhance the adhesion when the piezoelectric element plate 1 is adhered. The three mounting electrodes 7a, 7b, 7 for input, output, and ground are provided on the surface of the sealing plate on which the concave portion is not formed.
Form c. For formation, printing and baking are performed using a paste containing silver-palladium or the like.

Next, an adhesive is applied to the surfaces of the two sealing plates 8 where the recesses are formed, and the piezoelectric element plates 1 are bonded while being pressed and heated so as to sandwich them from above and below. At this time, the positioning is performed such that the filter portions 2, 3 and the weight adding portion 5 of the piezoelectric element plate 1 and the concave portions 9a, 9b, and 10 of the sealing plate 8 face each other.

A method in which a plurality of piezoelectric element plates 1 and a plurality of sealing plates 8 are integrally formed and bonded with an adhesive, and then cut by a dicing machine or the like for each element is used. Is also good. In this case, it is possible to reduce the number of operations such as assembly requiring high accuracy, which is effective for reducing the manufacturing cost.

Finally, the electrodes on the piezoelectric element plate 1 and the mounting electrodes 7a to 7c are connected by a conductive paste, and thereafter, barrel plating is performed to deposit a solder or tin layer.
At this time, Ni base plating is performed as necessary. Also,
Instead of connection with a conductive paste, vapor deposition, sputtering, or the like may be used.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a chip type piezoelectric filter according to an embodiment of the present invention will be described.

Example 1 A PZT-based piezoelectric material was molded into a block and fired. Then, slice into a plate,
Furthermore, it is polished with a lap plate, and 30mm x 40mm x
A 0.22 mmt piezoelectric plate was produced. Next, silver electrodes were formed on the entire surfaces of both surfaces of the piezoelectric plate by vapor deposition, and polarization treatment was performed. Then, unnecessary electrode portions were removed by resist printing and etching, and 40 predetermined electrode patterns as shown in FIG. 1 were formed per sheet to obtain a piezoelectric element plate. Next, in the center of the relay capacitor electrode 4a on one side, a diameter of 1 mm and a thickness of 0.1
A weight addition portion 5 was formed by applying a solder paste in a size of mm by screen printing and performing a heat treatment.

On the other hand, a sealing plate was prepared by molding alumina powder into a plate shape and firing it. The dimensions of the sealing plate were the same as those of the piezoelectric element plate. In the molding die of the sealing plate, concave portions 9a and 9b facing the filter portions 2 and 3 and a concave portion 10 for accommodating the additional weight portion 5 were previously provided. The depth of each recess was set to be 0.15 mm after sintering. Further, the surface of the sealing plate on which the concave portions were formed was polished with a lap plate in order to enhance the adhesion when the sealing plate was bonded to the piezoelectric element plate. On the side of the sealing plate where the recess is not formed,
Three mounting electrodes for input, output and ground were formed. For the formation, printing and baking were performed using a paste containing silver-palladium.

Next, an epoxy-based adhesive was applied to the surfaces of the two sealing plates on which the recesses were formed, and were bonded while pressing and heating the piezoelectric element plates from above and below. At this time, the positioning was performed so that the filter portions 2, 3 and the weight adding portion 5 of the piezoelectric element plate corresponded to the concave portions 9a, 9b, and 10 of the sealing plate. Further, by a dicing machine, every one element having a predetermined electrode pattern as shown in FIG.
It was divided into a size of 3.0 mm × 7.0 mm.

Thereafter, the electrodes on the piezoelectric element plate 1 and the mounting electrodes 7a to 7c were electrically connected by applying a silver-containing epoxy-based paste by screen printing and performing a heat treatment. Furthermore, barrel plating was applied to deposit a layer of solder on the electrode portion to obtain a finished product. 50 finished products are made,
The bandwidth ratio, the rate of change in capacity, and the sealing property were evaluated by the following methods.

First, the completed chip-type piezoelectric filter was tested for 8 MHz to 12 MHz using a network analyzer.
Hz transmission characteristics were measured. FIG. 5 shows an example. In the figure, reference numeral 12 denotes a passband bandwidth, and the insertion loss is 3 from the peak top.
It refers to the bandwidth in dB. Further, in the figure, reference numeral 13 denotes a stopband bandwidth, which indicates a bandwidth where the insertion loss becomes 20 dB across the passband. If the passband bandwidth / stopband bandwidth is defined as the bandwidth ratio, the bandwidth ratio is one of the indexes for judging the filter characteristics, and the filter becomes steeper as it approaches 1 and the selectivity as it approaches 0. A bad filter. The results of measuring the bandwidth ratio are shown in Table 1.

Next, in order to investigate the change in the relay capacity, n
= 10 pieces were polished until the electrodes on the piezoelectric element plate 1 were exposed, and then the relay capacitance electrodes 4a and 4b were separated from the other electrodes. In this state, the terminals are applied to the relay capacitance electrodes 4a and 4b, and the frequency is
The change in capacitance when the frequency was changed to １２12 MHz was measured. Based on the measured data, the capacity change rate was calculated from the following equation, and the results are shown in Table 1. In addition, the larger one of the values calculated from the following equations (1) and (2) was used for the capacity change rate in Table 1. [(C _{10 MHz−} C _min ) / C _{10 MHz} ] × 100 (%) (1) [(C _max− C _{10 MHz} ) / C _{10 MHz} ] × 100 (%) (2) where C _10MHz is the capacity at 10MHz, C _min is 8
The minimum capacity when the frequency is changed from MHz to 12 MHz, _Cmax, is also the maximum capacity.

Further, in order to confirm the sealing property, the following evaluation was performed for n = 40 pieces. First, it was exposed to water vapor at 130 ° C. and 2 atm for 24 hours.
The insulation between the input electrode 7a and the output electrode 7c among a to 7c was measured by a tester. Those with continuity were determined to be defective in sealing. This is because if there is a pinhole or the like and the sealing property is low, water vapor invades and condenses, so that the resonance electrodes are short-circuited, and the input electrode 7a and the output electrode 7c, which are not supposed to be conductive, are conductive. is there. Table 1 shows the defective sealing rate in the test sample.

Example 2 In the same manner as in Example 1, a piezoelectric plate was formed in which 40 predetermined electrode patterns were formed per sheet. Next, a silver-containing epoxy-based paste was applied to a thickness of 0.1 mm over the entire surface of the relay capacitor electrode 4a on one side, and was heated and cured to form the weight adding portion 5. Hereinafter, 50 completed products were manufactured in the same process as in Example 1, and the same evaluation was performed. Table 1 shows the results.

Comparative Example 1 A test sample was prepared and evaluated in exactly the same manner as in Example 1 except that the weight addition portion 5 was not formed on the relay capacitor electrode 4a. Table 1 shows the results.

Comparative Example 2 In the same manner as in Example 2, the weight-added portion 5 was formed by applying a silver-containing epoxy paste to the relay capacitor electrode 4a and curing by heating. A test sample in which the concave portion 10 was not provided in a portion facing 5 was manufactured and evaluated. Table 1 also shows the results.

[0041]

[Table 1]

In Examples 1 and 2, the bandwidth ratio is 0.5 or more, and it can be seen that the filter waveform is relatively steep. Further, since the rate of change in capacitance is low and no sealing failure occurs, it is clear that a highly reliable chip-type piezoelectric filter has been obtained. On the other hand, in Comparative Example 1, the bandwidth ratio was as low as 0.4, and the capacity change rate was significantly large. This is because the weight addition portion 5 was not formed in the relay capacitor electrode 4a, so that vibration occurred in the relay capacitor portion 4 and the change in capacitance became large. Further, in Comparative Example 2, the sealing failure rate is extremely poor. This is because the recess 10 is formed in a portion of the sealing plate 8 facing the weight adding portion 5.
Is not provided, voids are formed around the weight-added portion 5 due to the thickness thereof, and water vapor enters from outside through the voids.

[0043]

As described above, according to the present invention, even though the relay capacitor is provided on the same piezoelectric element plate as the filter, unnecessary vibration does not occur in the relay capacitor and the filter waveform can be obtained. And a chip-type piezoelectric filter having excellent sealing performance and high reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electrode arrangement of a piezoelectric element plate in a chip-type piezoelectric filter of the present invention, wherein FIG.
(B) is the ground electrode side.

FIG. 2 is an external view of a chip-type piezoelectric filter of the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an equivalent circuit of the chip-type piezoelectric filter of the present invention.

FIG. 5 is a diagram schematically showing a frequency change of an insertion loss, which represents a filter characteristic.

FIG. 6 is a perspective view for explaining a conventional dual mode piezoelectric filter, in which (a) shows an electrode arrangement on a resonance electrode side,
(B) is a diagram showing the electrode arrangement on the ground electrode side.

FIG. 7 is a perspective view for explaining a conventional chip type piezoelectric filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric element board 2 Filter part 2a, 2b Resonant electrode 2c Ground electrode 3 Filter part 3a, 3b Resonant electrode 3c Ground electrode 4 Relay capacitance part 4a, 4b Relay capacitance electrode 5 Weight addition part 6a, 6b Extraction electrode 7a-7c Mounting Electrode 8 Sealing plate 9a, 9b Concave portion opposed to vibrating portion 10 Concave portion opposed to weight adding portion 11 Adhesive portion separating filter portion and relay capacitor portion 12 Passband bandwidth 13 Stopband bandwidth

Claims (2)

[Claims] 1. A single piezoelectric element plate is formed such that two double mode piezoelectric filters are connected in series via a relay capacitor, and a vibration space is provided at a portion facing the double mode piezoelectric filter. In a chip type piezoelectric filter in which a sealing plate provided with a concave portion for securing the piezoelectric element plate is sandwiched from above and below, the front and back surfaces 2 forming the relay capacitance portion are provided.
A weight-adding portion is formed in at least a part of one or both of the relay capacitance electrodes, and a concave portion for receiving the weight-adding portion is provided in a portion of the sealing plate facing the weight-adding portion. A chip type piezoelectric filter characterized by the above-mentioned. 2. A weight-added portion is formed by printing a paste made of solder or resin on at least a part of one or both of the two relay capacitor electrodes provided on the piezoelectric element plate and heat-treating the paste. Forming a recess in a portion of the sealing plate facing the weight-adding portion and a portion facing the dual-mode piezoelectric filter, and bonding the piezoelectric element plate from above and below in a manner sandwiching the sealing plate from above and below. The method for manufacturing a chip-type piezoelectric filter according to claim 1, comprising: