JP2001044792A - Surface acoustic wave device and band frequency adjustment method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cancel the band frequency deviation within a wafer or a batch by arranging a surface acoustic wave resonator and a comb-shaped conductor pattern, which has one end part connected to a terminal of the surface acoustic wave resonator and has an electrostatic capacity, on a piezoelectric substrate. SOLUTION: The surface acoustic wave resonator and a comb-shaped conductor pattern 2 which has one end part connected to a terminal of the surface acoustic wave resonator and has an electrostatic capacity are arranged on the piezoelectric substrate, and the comb-shaped conductor pattern 2 has a structure to have the other end bent. By this constitution, the number of teeth of the comb-shaped conductor pattern 2 is reduced to adjust the electrostatic capacity to a prescribed value. Concretely, electrodes of an input terminal 3 and an output terminal 4 are arranged on a piezoelectric substrate 9, and surface acoustic wave resonators 1a are connected in series between them, and parallel surface acoustic wave resonators 1b are connected from respective connection points to the side of a ground terminal 5. The comb-shaped conductor pattern 2 is connected between series surface acoustic wave resonators 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device frequently used as a high-frequency element in a mobile communication device such as a cellular phone or a cellular phone in the field of telecommunications, and a method of adjusting the band frequency thereof.

[0002]

2. Description of the Related Art FIG. 9 shows an electric equivalent circuit of a conventional general surface acoustic wave device J, and FIG. 10 shows a specific plan configuration of the surface acoustic wave device.

The surface acoustic wave device J has a ladder-type structure in which surface acoustic wave resonators are alternately connected in series and in parallel on a piezoelectric substrate. Here, between the input / output terminals 3 and 4 provided on the piezoelectric substrate 9, two series surface acoustic wave resonators 1 a are provided.
2.5 connected three parallel surface acoustic wave resonators 1b
3 shows an example of a ladder-type structure of steps. In the figure, reference numeral 5 denotes a ground terminal. Further, the surface acoustic wave resonator includes electrodes that excite opposed comb-like surface acoustic waves, and electrodes that reflect the excited surface acoustic waves and confine energy.

FIG. 11 shows the attenuation characteristic 106 of the surface acoustic wave device J constructed as described above, and FIG. 12 shows the impedance characteristics 107a and 107b of the surface acoustic wave resonator constituting the surface acoustic wave device J.

[0005] The impedance characteristic 107a of the series surface acoustic wave resonator 1a depends on the pass band 13 to be filtered.
, And the impedance characteristic 107 b of the parallel surface acoustic wave resonator 1 b is designed to be maximum in the pass band 13. That is, in the passband 13, the series surface acoustic wave resonator 1a is short-circuited, and conversely, the parallel surface acoustic wave resonator 1b is open, and the signal coming from the input terminal 3 is not degraded to the output terminal 4 as much as possible. Designed to output in

In such a surface acoustic wave device (filter) for mobile communication, the allocated frequency bandwidth becomes insufficient due to the intensification of the frequency and the increase in the density, and as a result, contrary to the increase of the carrier frequency. There is a problem that the interval between the transmission and reception bands does not increase.

Factors controlling the attenuation characteristics of the surface acoustic wave filter include the film thickness of the electrodes constituting the surface acoustic wave resonator and the pitch between the electrodes. There are electrode line width and duty ratio between lines, etc., such as a method of trimming the electrode by etching or the like, a method of etching the groove on the piezoelectric substrate using the electrode that constitutes the surface acoustic wave resonator as a mask, etc. Has been adopted.

However, in the method of etching the surface acoustic wave resonator electrode, both the electrode thickness and the duty are changed at the same time, so that not only the attenuation characteristic but also the pass band characteristic is changed. For this reason,
The band frequency adjustment method has a large characteristic deviation.

On the other hand, in the groove processing by etching the piezoelectric substrate using the surface acoustic wave resonator electrode as a mask, the electrode material mainly used is made of aluminum or an aluminum alloy. It requires a combination of etching gases capable of obtaining a sufficient ratio, and is applied exclusively to a quartz single crystal substrate. In a useful piezoelectric substrate having a high electromechanical coupling coefficient such as LiTaO ₃ or LiNbO ₃ single crystal,
An etching gas that has a sufficient selectivity with respect to a surface acoustic wave resonator electrode made of aluminum or an aluminum alloy has not been found, and has not been applicable up to now.

[0010] When such a high electromechanical coupling coefficient substrate is used, a method of adjusting the band frequency for each wafer by using a method of etching a surface acoustic wave excitation electrode has been mainly adopted. In this case, there is a problem that the frequency deviation in the wafer or the batch cannot be eliminated.

Accordingly, an object of the present invention is to provide a surface acoustic wave device capable of eliminating a band frequency deviation in a wafer or a batch, and a method of adjusting the band frequency.

[0012]

In order to achieve the above object, a surface acoustic wave device according to the present invention comprises a surface acoustic wave resonator on a piezoelectric substrate and one end connected to a terminal of the surface acoustic wave resonator. A comb-shaped conductor pattern having a connected capacitance is provided.

In particular, the comb-shaped conductor pattern is characterized in that the other end is bent.

In the band frequency adjusting method according to the present invention, a part of the comb-shaped conductor pattern is divided and the number of comb teeth of the comb-shaped conductor pattern connected to the surface acoustic wave resonator is reduced. It is characterized in that the capacitance is adjusted to a predetermined value.

[0015]

Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a top view of a surface acoustic wave device according to the present invention. As shown in FIG. 1, the surface acoustic wave device S is a comb-shaped conductor having a surface acoustic wave resonator on a piezoelectric substrate 9 and one end connected to a terminal of the surface acoustic wave resonator and having a capacitance. The comb-shaped conductor pattern 2 is characterized in that the other end is bent. With such a configuration, a part of the comb-shaped conductor pattern 2 is divided, and the capacitance is adjusted to a predetermined value by reducing the number of comb teeth of the comb-shaped conductor pattern 2. .

More specifically, for example, an input terminal made of aluminum or an alloy thereof is placed on a piezoelectric substrate 9 made of, for example, lithium tantalate single crystal, lithium tetraborate single crystal, or a single crystal having a langasite type crystal structure. 3 and an electrode of the output terminal 4 are arranged, a surface acoustic wave resonator 1a made of the same material is connected in series between the electrodes, and a parallel surface acoustic wave resonator 1b is connected from each connection point to the ground terminal 5 side. Is connected.

A comb-shaped conductor pattern 2 is connected between the terminals of the series surface acoustic wave resonator 1a. The comb-shaped conductor pattern 2 has two base electrodes 10a and 10b, and cross electrodes 11a, 11b and 11c protruding from each of the base electrodes 10a and 10b form a counter electrode capacitance. A non-intersecting portion 12 is provided between the intersecting electrodes, and one end of each of the base electrodes 10a and 10b is bent to reduce the size of the entire device. Then, the band frequency is adjusted by dicing or laser cutting the pattern near the non-intersecting portion 12.

FIG. 2 shows an electric equivalent circuit of the surface acoustic wave device S according to the present invention. The surface acoustic wave device S is configured as a ladder type filter in which the surface acoustic wave resonators 1 are alternately connected in series and in parallel. Although an example of a configuration in which two series surface acoustic wave resonators 1a and three parallel surface acoustic wave resonators 1b are shown, the number of stages is not a limitation of the present invention.

FIG. 3 shows the adjustment of the band frequency of the attenuation characteristic of the surface acoustic wave device S. FIG.
7 shows how the frequency characteristic of the impedance characteristic of the series surface acoustic wave resonator 1a to which is connected is adjusted. The state of the impedance characteristics 7a and 7b in FIG.
3 is appropriately cut and adjusted as in the impedance characteristic 7c, so that the attenuation characteristics 6a and 6b in FIG.
Can be adjusted like the attenuation characteristic 6c.

As can be seen from FIG.
By changing the anti-resonance frequency without changing the impedance characteristics near the resonance frequency, and adjusting the impedance gradient between resonance and anti-resonance frequency, the attenuation characteristics of the filter can be adjusted without affecting the pass band as much as possible. It is possible to

The length of the cut portion of the comb-shaped conductor pattern 2 to be adjusted is preferably 20 μm or more, and if it is less than this, dicing or laser cutting becomes impossible. It is needless to say that the use of the bent pattern as described above facilitates adjustment by dicing or laser cutting.

[0023]

An embodiment of the surface acoustic wave device according to the present invention will be described below.

As shown in the top view of the surface acoustic wave device shown in FIG. 1, a 42 ° YX cut lithium tantalate single crystal is used for the piezoelectric substrate 9, and the surface acoustic wave resonator 1 a is provided on the piezoelectric substrate 9. , 1b, the capacitor 2, the input / output terminals 3, 4, and the fine electrode of the ground terminal 5 were patterned by photolithography. Here, the electrode material is Al-Cu 1% by weight.
And the thickness was 2100 °. The surface acoustic wave resonator 1 was constituted by comb-shaped excitation electrodes having a period length of about 2 μm.

FIG. 5 shows how the frequency characteristics are adjusted by the surface acoustic wave device according to the present invention. The surface acoustic wave device performs film formation of electrodes and patterning of surface acoustic wave resonator electrodes, selects non-defective products in the wafer state, performs dicing, performs assembly, and then processes in the order of characteristic inspection Is done.

The selection in the wafer state can be determined by the correlation with the finished product. The defective surface acoustic wave element is potted with a resin paste as a discrimination mark, and is not put into the assembly process. Therefore, with the configuration of the present invention, it is possible to adjust the band frequency of a wafer having many elements that are expected to be correlated when the attenuation amount of the attenuation band in the wafer state does not satisfy the standards 13 and 14.

In the inspection of the surface acoustic wave element in a wafer state, FIG. 5 shows an element which does not satisfy the element standards 13 and 14, for example, an elastic surface having an attenuation characteristic 51 having a large loss on the high frequency side within the pass band standard 13. The wave element was formed by cutting the comb-shaped conductor pattern so that the loss on the high frequency side within the passband standard 13 had good attenuation characteristics 52.

FIG. 6 shows details of the comb-shaped conductor pattern 2. The comb-shaped conductor pattern 2 has two base electrodes 10a and 10b having a width of about 10 μm, and a pair of comb-shaped widths of 60 μm with a pitch of 4 μm protruding from the base electrodes.
m crossed electrode 11a, 30 pairs of 10 μm wide crossed electrodes 11b and crossed electrodes 11 in a comb-like shape with a pitch of 4 μm
The counter electrode capacitance is formed by the same cross electrode 11c as that of FIG.

In addition, there are 20 non-intersecting portions 12 between the intersecting electrodes.
.mu.m, and the base electrodes 10a, 10b
Is bent at one end. The cross electrodes projecting from the comb-shaped conductor pattern 2 were formed such that the ratio of the opposing capacitances was 2: 1: 1 (may be changed as appropriate). When the base electrodes 10a and 10b of the comb-shaped conductor pattern 2 are cut off at the dicing position 15a, the capacitance between the opposing electrodes at the intersection electrode 11c does not contribute to the capacitance between the base electrodes.

When the cutting is performed at the dicing position 15b, the capacitance between the opposing electrodes of the cross electrodes 11b and 11c does not contribute to the capacitance between the base electrodes. That is, it is possible to adjust the value of the capacitance entering in parallel with the series surface acoustic wave resonator.

FIG. 7 shows the impedance characteristic of only the comb-shaped conductor pattern. Since a comb-shaped conductor pattern is formed on the piezoelectric substrate 9, surface acoustic waves can be excited. Therefore,
As described with reference to FIG. 6, by widening the interval between the electrode fingers, the excitation (resonance, anti-resonance) frequency of the surface acoustic wave generated in this portion is shifted sufficiently from the pass band 13 to the lower frequency side, and the pass band is changed. In the vicinity of 13, it was set so as to act as a simple capacity.

FIG. 8 shows the layout of the surface acoustic wave element on which the frequency has been adjusted by dicing on the wafer (only four elements are indicated by dashed lines for convenience on the paper) and the element outer shape 16 after dicing. The appearance when the electrode base is cut off at the dicing position indicated by 15a in FIG. 6 is shown. As described above, in the present embodiment, the band frequency can be adjusted by controlling the dicing position without changing the outer shape of the chip after dicing.

[0033]

As described above, according to the surface acoustic wave device of the present invention, the cutting position of the comb-shaped conductor pattern is changed according to the average frequency of the elements in the wafer and the frequency characteristics of each element. By adjusting the capacitance value of the pattern, it is possible to easily adjust the filtering characteristics of the surface acoustic wave device, and to provide an excellent surface acoustic wave device capable of eliminating a band frequency deviation in a wafer or a batch. Can be provided.

[Brief description of the drawings]

FIG. 1 is a top view of a surface acoustic wave device according to the present invention.

FIG. 2 is an equivalent circuit diagram of the surface acoustic wave device according to the present invention.

FIG. 3 is a characteristic diagram before and after adjustment of the surface acoustic wave device according to the present invention. .

FIG. 4 is a characteristic diagram of the surface acoustic wave resonator according to the present invention.

FIG. 5 is a characteristic diagram illustrating adjustment of electrical characteristics of the surface acoustic wave device according to the present invention.

FIG. 6 is a plan view showing an example of a comb-shaped conductor pattern according to the present invention.

FIG. 7 is a characteristic diagram showing impedance characteristics of a comb-shaped conductor pattern according to the present invention.

FIG. 8 is a plan view showing a pattern layout and a dicing position of a surface acoustic wave element formed on a wafer.

FIG. 9 is an equivalent circuit diagram of a conventional surface acoustic wave device.

FIG. 10 is a top view of a conventional surface acoustic wave device.

FIG. 11 is a characteristic diagram showing electric characteristics of a conventional surface acoustic wave device.

FIG. 12 is a characteristic diagram showing a resonator characteristic of a conventional surface acoustic wave device.

[Explanation of symbols]

 1a, 1b: surface acoustic wave resonator 2: comb-shaped conductor pattern 3: input terminal 4: output terminal 5: ground terminal 6, 106: electrical characteristics of surface acoustic wave device 7, 107: impedance of surface acoustic wave resonator Characteristic 8: Surface acoustic wave element 9: Piezoelectric substrate 10: Base electrode 11: Crossing electrode 12: Non-crossing part 13: Pass band standard 14: Attenuation band standard 15: Dicing position 16: Chip outer shape after dicing 51: Damping of defective product Characteristic 52: Damping characteristic of good product S: Surface acoustic wave device

Claims (3)

[Claims] 1. A surface acoustic wave resonator and a comb-shaped conductor pattern having an electrostatic capacitance whose one end is connected to a terminal of the surface acoustic wave resonator are provided on a piezoelectric substrate. Surface acoustic wave device. 2. The surface acoustic wave device according to claim 1, wherein the other end of the comb-shaped conductor pattern is bent. 3. The surface acoustic wave device according to claim 1, wherein a part of the comb-shaped conductor pattern is divided, and the number of comb teeth of the comb-shaped conductor pattern connected to the surface acoustic wave resonator. Wherein the capacitance is adjusted to a predetermined value by reducing the capacitance of the surface acoustic wave device.