JPS6291013A - Piezoelectric filter and its manufacture - Google Patents

Abstract

PURPOSE:To improve the degree of filter design by constituting a part or all of lead electrodes by high resistance electrode film by means of the thick film print and constituting other electrodes except a part or all of the lead electrodes by low resistance electrode film. CONSTITUTION:A part or all of the 3rd lead electrodes 11a, 11b are constituted of high resistor electrode film by the thick print. Other electrode patterns except a part or all of the 3rd lead electrodes 11a, 11b are constituted of the low resistance electrode film. As resistors Ra, Rb of the 3rd lead electrodes 11a, 11b are increased, the group delay time characteristic is made flat, since the insertion loss is increased conversely, the value is set properly for the application. Further, since the 3rd lead electrodes 11a, 11b are formed by the thick film technology, the resistance trimming is applied in the forming process.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a piezoelectric filter, and particularly to a piezoelectric filter having an energy-trapped thickness vibration mode.

<Prior art> In general, this type of piezoelectric filter has two filter sections each having an energy-trapped thickness vibration mode, for example.
It is known that the filters are formed in a stage configuration on the same piezoelectric substrate, and both filter sections are cascade-connected via parallel coupling capacitances.

Conventionally, the electrode film in a piezoelectric filter having such a structure is usually formed by depositing or baking a low resistance electrode material such as silver (Ag) or copper (Cu). Therefore, the direct current resistance of the electrode film was almost a value close to 0Ω.

However, if such a piezoelectric filter is used in an F''M reception system where sound quality is important, the phase linearity will deteriorate.In other words, if each filter section is concentrated by capacitive coupling, its overall characteristics will be There was a problem in that the group delay time characteristics did not become flat, which adversely affected the amplitude and phase characteristics.

So, here are some suggestions for improving this: 1. For example, JP-A-54-8
The one shown in Japanese Patent No. 9460 has been proposed. In this improvement plan, which is the prior art of the present invention, in a piezoelectric filter having the same basic configuration as the conventional example, a resistance value of several ohms to several tens of ohms is created between the ground side vibrating electrode and the external extraction electrode. By damping the symmetric mode resonance and not damping the oblique symmetric mode resonance,
The group delay time characteristics are improved to improve phase linearity.

<Problems to be Solved by the Invention> The piezoelectric filter of the above-mentioned improvement example actually uses a substrate ware, which is the base of the piezoelectric substrate, in order to add resistance between the vibrating electrode and the external lead electrode. - is masked with a pattern mask, and then a high resistance electrode material such as monel metal is sputter-linked to form the entire electrode pattern including the lead electrode.

However, when sputtering is used to form the entire electrode pattern using monel metal or the like, it is inevitable that variations in the resistance value of the electrode film on the substrate wafer will occur. There is also a problem in that variations occur in the characteristics of individual piezoelectric filters.

Furthermore, since it is impossible to individually adjust the resistance value of each piezoelectric filter, the rate of non-defective products is low and the manufacturing yield is poor. Furthermore, the Monel metal mentioned above has poor soldering properties, so if an electrode pattern is constructed using this material, it is difficult to solder the parts of the electrode pattern that require soldering using a material with good soldering properties, such as silver. Due to manufacturing reasons, such as the need to add
There are many problems that need to be resolved.

In view of these conventional problems, the primary purpose of the present invention is to equalize the delay time characteristics and to facilitate the setting of the resistance value adjustment. The second purpose is to enable manufacturing.

Means for Solving the Problems> Therefore, in order to achieve the first object, in the first invention, part or all of the lead electrodes formed on at least one main surface of the piezoelectric substrate is made of a high-resistance electrode film by thick-film printing, and the other electrodes, excluding some or all of the lead electrodes, are made of low-resistance electrode films.

Further, in order to achieve the second object, in the second invention, a high resistance electrode film is thickly printed and baked on the main surface of the piezoelectric ceramic substrate to form part or all of the lead electrodes. After forming the piezoelectric substrate, a low resistance electrode film is deposited on the main surface of the piezoelectric substrate, followed by polarization treatment, and an etching lens nost film is printed on the required portions of the low resistance electrode film. A method in which the low resistance electrode film is removed by etching, and other electrodes excluding part or all of the lead electrode are formed using the remaining portion of the low resistance electrode film covered with the etching resist film. It has characteristics.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is an enlarged perspective view of a piezoelectric filter according to this embodiment, and FIG. 2 is an equivalent circuit diagram thereof.

The piezoelectric filter shown in these figures is a two-stage energy trap type thickness vibration mode filter. This filter includes two-stage filter sections L a and 1 b formed on the same piezoelectric substrate 2 . Both filter sections 1a and 1b are cascade-connected via a parallel coupling capacitor C.

The piezoelectric substrate 2 is formed by polarizing a rectangular ceramic plate whose main component is lead zirconate titanate. Each filter section 1 is provided on each of the main surfaces 2a and 2b of the piezoelectric substrate 2.
Electrode patterns 3.4 (indicated by diagonal lines) of a, lb are formed.

One electrode pattern 3 includes a vibrating electrode pair 5a, 5b formed for each filter part 1a, 1b, and one vibrating electrode 5a++ in each vibrating electrode pair 5a, 5b.
L-shaped first lead electrodes 6a each drawn out from 5112.

6b, rectangular external lead electrodes 7a, 7b drawn out to both ends of the piezoelectric substrate 2 via the first lead electrodes 6a, 6b, and each vibrating electrode pair 5a,
It consists of a T-shaped second lead electrode 8 drawn out in common from the other vibrating electrode 5 a2.5 b+ in 5 b, and a capacitor electrode 9 drawn out in common via the second lead electrode 8. There is.

The other electrode pattern 4 is a common ground-side vibrating electrode 10a facing each of the image moving electrode pairs 5a and 5b.

10b, third lead electrodes 11a and llb drawn out from the ground side vibrating electrodes 10a and 10b, respectively, and a ground side capacitor that is commonly drawn out through the third lead electrodes 11a and Ilb and facing the capacitor electrode 9. It is composed of an electrode 12.

The ground side capacitor electrode 12 also serves as an external lead electrode.

In the piezoelectric filter having such a basic configuration, the third lead electrodes 11a, 11b are partially or entirely formed of a high resistance electrode film by thick film printing. As a material for this high resistance electrode film, for example, a thick film resistance material such as silver-palladium (Ag-Pd) is used. Moreover, the third lead electrode 11a.

The other electrode pattern parts except for part or all of 11b are made of a low resistance electrode film. As a material for this low resistance electrode film, for example, a highly conductive material such as silver (Ag) or copper (Cu) is used.

A piezoelectric filter with such a configuration is shown in Fig. 2.
Isometrically, only the resonances of the symmetrical modes are damped, and the obliquely symmetrical modes are not damped.

In this case, each resistance R of the third lead electrodes 11a and llb
As the values of a and Rh become larger, the group delay time characteristics become flatter, but on the other hand, the insertion loss also increases, so they are set appropriately depending on the purpose of use.

Further, since the third lead electrodes 11a and Ilb are formed by thick film printing technology, resistance trimming can be performed during the formation process.

FIGS. 3 to 9 are diagrams illustrating the manufacturing process of the piezoelectric filter having the above structure in order of process.

■First step In FIG. 3, first, a high resistance electrode film (indicated by mesh in the figure) is placed on the back main surface 2b of the substrate wafer 13, which is the mother substrate of the piezoelectric substrate 2. ill... (The code 11 in this case indicates the third lead electrode 11a, llb.
collectively referred to as ) on a part or all of the repeating pattern by a well-known thick film printing method, and then the third lead electrodes 11 . . . are baked onto the substrate wafer 13.

(2) Second step Each of the third lead electrodes 11 thus formed is trimmed, if necessary, using a laser or the like, as shown in FIG.・Adjust the resistance value. In FIG. 4, the symbol T indicates a trimming portion. Therefore, since the resistance value of the third lead electrode 11 can be individually adjusted during the formation process, it is possible to equalize the characteristics of each piezoelectric filter taken out from the substrate wafer 13.

■Third step When the resistance value adjustment of the third lead electrode 11... is completed,
As shown in FIG. 5, a low resistance electrode film (indicated by diagonal lines) 14 is formed by vapor deposition over the entire backside main surface 2b of the substrate wafer 13. As shown in FIG. In this case, the third lead electrode 11 is covered with the low resistance electrode film 14.

■Fourth step After forming the low resistance electrode film 14, polarization treatment is applied to the necessary parts of the substrate wafer 13, and then, as shown in FIGS. 6 and 7, electrodes other than the third lead electrode 11... An etching resist film (indicated by two diagonal lines) 15 is printed on the pattern 4, that is, on the formation position of the ground side vibrating electrode 10 (in this case, the reference numeral 10 collectively refers to 10a and 10b) and the ground side capacitor electrode 12. Form.

(5) Fifth step After forming the etching resist film I5 in this manner, the low resistance electrode film 14 is removed by etching, and then the etching resist film 15 is further removed. As a result, the remaining portion of the low resistance electrode film 14 that was covered with the etching resist film 15 causes one vibration pole 10 on the ground side.
And a ground side capacitor electrode 12 is formed.

Further, the electrode pattern 3 formed on the front main surface 2a of the substrate wafer 13 can be formed by vapor deposition or the like as in the conventional method.

After forming the electrode patterns 3.4 on both main surfaces of the substrate wafer 13 in the manner described above, the substrate wafer 13 is divided into each piezoelectric substrate 2, and individual filters are taken out. After soldering the lead wire to the external lead electrode 7 (in this case, 7a and 7b are collectively referred to as 7a and 7b) and the ground side capacitor electrode 12 of each filter, each piezoelectric substrate 2 is attached to the resin. A three-terminal piezoelectric filter is obtained by encasing with a mold.

It should be noted that the number of stages of the filter section of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that the present invention can also be applied to a multimode filter having three or more stages.

<Effects of the Invention> As described above, according to the first invention, part or all of the lead electrodes formed on at least one main surface of the piezoelectric substrate are coated with a high resistance electrode film by thick film printing il+. At the same time, the other electrodes, excluding part or all of this lead electrode, are made of a low resistance electrode film, so when forming the lead electrode, it is possible to eliminate unevenness in the electrode film, and it can be applied over a wide range. In a piezoelectric filter having flat group delay time characteristics over a wide range, the resistance value of the lead electrode can be freely adjusted, and the degree of freedom in designing the filter is improved.

Further, according to the second aspect of the present invention, after forming part or all of the lead electrodes by thickly printing and baking a high resistance electrode film on the main surface of the piezoelectric ceramic substrate, the piezoelectric ceramic substrate After depositing a low-resistance electrode film on the main surface of the electrode, polarization treatment is performed, and an etching resist film is printed on the required portions of the low-resistance electrode film, and then the low-resistance electrode film is removed by etching. Since the remaining portion of the low-resistance electrode film covered with the etching resist film forms other electrodes excluding part or all of the lead electrode, for example, each piezoelectric filter formed on the substrate wafer The resistance values of the lead electrodes can be individually adjusted during their formation. therefore,
It is possible to equalize the group delay time characteristics of piezoelectric filters with a single-crystal number, and the manufacturing yield is significantly improved compared to the conventional method.

[Brief explanation of drawings]

1 to 9 show an embodiment of the present invention, FIG. 1 is an enlarged perspective view of this embodiment, FIG. 2 is an equivalent circuit diagram thereof, and FIG. 3 is a partially taken out perspective view showing the first step. Figure 4 is the second
FIG. 5 is a partially taken-out perspective view showing the third step. FIG. 6 is a partially taken-out perspective view showing the fourth step. FIG. 7 is a partially taken-out perspective view showing the fourth step. FIG. 8 is an enlarged sectional view taken along section line IX-IX in FIG. 2 piezoelectric substrate, 5 a, 5 b... vibrating electrode pair, 1 1 (11a, I 1b)... lead electrode-1
2 External extraction electrode, I5... Etching resist film. Applicant Murata Manufacturing Co., Ltd. Representative Patent Attorney Oka 1) Kazu
Hide 1st figure 5: Son Tp electric food 11: Hayabusa 3 leet electric b 2nd figure 12-n-Tsubokai-con Y〉angle [
3rd ward, 4th figure, 5th figure, 7th figure, 8th figure, 9th figure

Claims (2)

[Claims] (1) In a piezoelectric filter including a vibrating electrode and an external extraction electrode on both main surfaces of a piezoelectric substrate, and a lead electrode connecting between the two electrodes, one of the lead electrodes formed on at least one main surface of the piezoelectric substrate is provided. What is claimed is: 1. A piezoelectric filter characterized in that part or all of the piezoelectric filter is made of a high resistance electrode film by thick film printing, and the other electrodes, excluding part or all of the lead electrode, are made of a low resistance electrode film. (2) After forming part or all of the lead electrodes by thickly printing and baking a high resistance electrode film on the main surface of the piezoelectric ceramic substrate, a low resistance electrode film is applied to the main surface of the piezoelectric substrate. After depositing
After performing polarization treatment and further printing and forming an etching resist film on the required portions on this low resistance electrode material film, the low resistance electrode material film is removed by etching, and the low resistance electrode covered with the etching resist film is removed. A method for manufacturing a piezoelectric filter, characterized in that other electrodes excluding part or all of the lead electrodes are formed using the remaining portion of the material film.