JP2001185977A - Surface acoustic wave device and band frequency adjustment method thereof - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a surface acoustic wave device capable of eliminating a frequency deviation in a wafer or in a batch and a band frequency adjustment method thereof. SOLUTION: An input terminal electrode 3, an output terminal electrode 4, and a surface acoustic wave resonator 8 are respectively formed on a piezoelectric substrate 9, and between the input terminal electrode 3 and the surface acoustic wave resonator 8, and / or A surface acoustic wave device (S) characterized in that a linear conductor pattern (2) having a plurality of branches and having an inductance for performing band frequency adjustment is formed between a surface acoustic wave element (8) and an output terminal electrode (4). And

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. 8 shows an electric equivalent circuit of a conventional general surface acoustic wave device J, and FIG. 9 shows a specific plan view for explaining an electrode structure of the surface acoustic wave device J.

The surface acoustic wave device J has a ladder structure in which surface acoustic wave resonators are alternately cascaded in series and parallel on a piezoelectric substrate. Here, a series surface acoustic wave resonator 1a is connected between the input / output terminals 3 and 4 provided on the piezoelectric substrate 9 by two.
The figure shows an example of a 2.5-stage ladder-type structure in which three parallel surface acoustic wave resonators 1b are provided. 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. 10 shows the attenuation characteristic 106 of the surface acoustic wave device J constructed as described above, and FIG. 11 shows the impedance characteristics 108a and 108b of the surface acoustic wave resonator constituting the surface acoustic wave device J. .

The impedance characteristic 108a of the series surface acoustic wave resonator 1a is designed to be minimum in the pass band 7 of the filter, and the impedance characteristic 108b of the parallel surface acoustic wave resonator 1b is designed to be maximum in the pass band 7. are doing. That is, in the pass band 7, the series surface acoustic wave resonators are short-circuited, and conversely, the parallel surface acoustic wave resonators 1b are in an open state, and the signal coming from the input terminal 3 is not deteriorated to the output terminal 4 as much as possible. Designed to output in state.

[0006] In such a surface acoustic wave device (filter) for mobile communication, the allocated frequency bandwidth is insufficient due to intensifying high frequency and high density, and as a result, the transmission / reception band is contrary to the high carrier frequency. Has a problem that the distance between the two does not increase.

Factors controlling the attenuation characteristics of the surface acoustic wave device include the film thickness of the electrodes constituting the surface acoustic wave resonator, the pitch between the electrodes, the electrode line width and the duty ratio between the lines, and the like. And a method in which a piezoelectric substrate is etched and grooved by using a surface acoustic wave resonator electrode as a mask.

However, in the method of etching the surface acoustic wave resonator electrode, both the electrode film thickness and the duty are changed at the same time, so that not only the attenuation characteristics but also the pass band characteristics are changed. Becomes larger.

On the other hand, in the groove processing adjustment by etching the piezoelectric substrate using the surface acoustic wave resonator electrode as a mask, the electrode material mainly used is aluminum or an aluminum alloy. It requires a combination of etching gases that can provide a sufficient selectivity, and is applied exclusively to quartz substrates. In addition, for a useful piezoelectric substrate having a high electromechanical coupling coefficient, such as LiTaO3 or LiNbO3 single crystal, an etching gas that has a sufficient selectivity with an electrode of a surface acoustic wave resonator made of aluminum or an aluminum alloy has been discovered. Not applicable.

When a piezoelectric substrate having such a high electromechanical coupling coefficient is used, a method of adjusting the frequency on a wafer basis by using a method of etching a surface acoustic wave excitation electrode has been mainly adopted. However, it is not possible to eliminate the frequency deviation of the surface acoustic wave elements in the wafer or the band frequency deviation caused by batch processing of a large number of wafers by the etching method.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly reliable surface acoustic wave device capable of eliminating a frequency deviation within a wafer or a batch and a method of adjusting the band frequency thereof.

[0012]

To achieve the above object, a surface acoustic wave device according to the present invention comprises a piezoelectric substrate having an input terminal electrode, an output terminal electrode, and a surface acoustic wave resonator formed thereon. A surface acoustic wave device comprising a plurality of branch paths between an input terminal electrode and a surface acoustic wave resonator and / or between a surface acoustic wave element and an output terminal electrode for performing band frequency adjustment. It is characterized in that a linear conductor pattern having inductance is formed.

Further, in the band frequency adjusting method of the present invention, the inductance is adjusted to a predetermined value by separating a part of the linear conductor pattern and reducing the number of branches connected to the linear conductor pattern. It is characterized by doing so.

[0014]

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

FIG. 1 is a schematic plan view of a surface acoustic wave device S according to the present invention. The surface acoustic wave device S is formed by forming at least an input terminal electrode 3, an output terminal electrode 4, and a surface acoustic wave resonator on a piezoelectric substrate, and a gap between the input terminal electrode 3 and the surface acoustic wave resonator. And / or a linear conductor pattern 2 having a plurality of branches and having an inductance for performing band frequency adjustment between the surface acoustic wave element and the output terminal electrode 4.

For example, as shown in FIG. 1, a surface acoustic wave device S includes a signal electrode 17 between input / output terminal electrodes 3 and 4 on a piezoelectric substrate 9 and a pair of surface acoustic wave resonators. Interdigital Transducer (hereinafter referred to as I
A linear conductor pattern 2 having a plurality of branched inductances is disposed between a bus bar 18 of a DT electrode) and the linear conductor pattern 2 is bent for each branch path. It is characterized by the following. Thus, a part of the linear conductor pattern 2 is separated, the path of the linear conductor pattern 2 connected to the surface acoustic wave resonator is reduced, and the inductance is adjusted to a predetermined value. I have.

More specifically, for example, aluminum or the like is placed on a piezoelectric substrate 9 made of, for example, a lithium tantalate single crystal, a lithium niobate single crystal, a lithium tetraborate single crystal, or a single crystal having a langasite-type crystal structure. The electrodes of the input terminal 3 and the output terminal 4 made of an alloy are arranged, and a surface acoustic wave resonator 1a made of a similar material is connected in series between them. IDT of a surface acoustic wave resonator 1b connected to a linear conductor pattern 2 having
The parallel surface acoustic wave resonator 1 is connected to the bus bar 18.
The other end of b is connected to the ground terminal electrode 5.

FIG. 6 is a detailed schematic plan view of the linear conductor pattern 2. The linear conductor pattern 2 has three base electrodes 2a, 2b and 2c branched into a plurality. The base electrodes 2a, 2b, 2c are formed in a meandering shape so as to have an inductance component. Then, projecting electrodes 10a, 10b, 10c are provided so as to project a part of the meandering base electrodes 2a, 2b, 2c from each. Dicing or laser cutting is performed in the vicinity of the protruding electrodes 10a, 10b, and 10c.
Is separated, and the number of branches connected to the linear conductor pattern 2 is reduced to adjust the inductance to a predetermined value, thereby adjusting the band frequency.

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 surface acoustic wave resonators are alternately cascaded in series and 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 band frequency adjustment of the attenuation characteristic of the surface acoustic wave device S, and FIG. 4 shows the frequency adjustment of the impedance characteristic of the parallel surface acoustic wave resonator 1b to which the linear conductor pattern 2 is connected. . The inductance of the linear conductor pattern 2 is appropriately separated from the state of the impedance characteristics 8a and 8b in FIG.
The damping characteristic 6 in FIG.
a and 6b can be adjusted like the attenuation characteristic 6c.

As can be seen from FIG. 4, by changing the resonance frequency without changing the impedance characteristic near the resonance frequency corresponding to the pass band 7, and adjusting the impedance gradient between the resonance and the anti-resonance frequency, It is possible to adjust the attenuation characteristic of the filter with as little influence as possible.

The width of the separated portion of the linear conductor pattern 2 to be adjusted is preferably 20 μm or more, and dicing or laser cutting is impossible if it is less than 20 μm. It goes without saying that the use of such a bent pattern facilitates adjustment by dicing or laser cutting.

[0023]

EXAMPLES Hereinafter, more specific examples of the present invention will be described.

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, linear conductor pattern 2, input / output terminals 3, 4
The fine electrode of the ground terminal electrode 5 was patterned by photolithography. Here, the electrode material is A
An alloy of 1-Cu 1% by weight was used 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, 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.

In the wafer state, non-defective and defective products are selected by
It can be determined by the correlation with the finished product, and 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 11 and 12.

In the inspection of a surface acoustic wave device in a wafer state, as shown in FIG.
It is possible to adjust the band frequency of an element that does not satisfy the standard 11 of the attenuation band characteristic or the surface acoustic wave element having the frequency characteristic of 13 that does not satisfy the standard 12 of the pass band frequency. The protruding electrode 10a is separated and the number of bent inductance branches connected to the protruding electrode 10a is reduced so that a frequency characteristic of 14 is obtained.

As shown in FIG. 6, the linear conductor pattern 2 has three base electrodes 2a, each of which is branched into a plurality of about 10 μm wide.
2b, 2c, the base electrodes 2a, 2b, 2c have the inductance of an electrode wire meandering at a pitch of 4 μm and a width of 60 μm.

The meandering base electrodes 2a, 2b,
Projecting electrode 10 so that a portion of 2c protrudes from each
a, 10b, and 10c were formed so that the inductance ratio of these meandering electrode wires was 1: 2: 3 (may be changed as appropriate). When the protrusion electrode 10a of the linear conductor pattern 2a is cut off at the dicing position 15a,
The inductance of the branch path 2a does not contribute to the inductance of the on-line conductor electrode 2.

When the cut is made at the dicing position 15b, the inductance of the branch path 2b does not contribute to the inductance of the on-line conductor electrode 2.
That is, it is possible to adjust the value of the inductance that goes in series with the series surface acoustic wave resonator.

FIG. 7 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 outer shape 16 of the element after dicing. The appearance when the protruding portion 10a is cut off at the dicing position indicated by 15a in FIG. 6 is shown.

Thus, in the present embodiment, the band frequency can be adjusted by controlling only the dicing position without changing the outer shape of the chip after dicing.

[0033]

As described above in detail, according to the surface acoustic wave device of the present invention, the cutting position of the linear conductor pattern is changed according to the average frequency of each element on the wafer and the frequency characteristic of each element. It is possible to appropriately adjust the inductance of the conductor pattern. Thereby, the filtering characteristics of the surface acoustic wave device can be easily adjusted,
In addition, it is possible to provide an excellent surface acoustic wave device capable of eliminating a band frequency deviation in a wafer or a batch and a band frequency adjusting method thereof.

[Brief description of the drawings]

FIG. 1 is a plan view schematically illustrating an electrode configuration on a piezoelectric substrate in 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 band frequency adjustment of the surface acoustic wave device according to the present invention.

FIG. 4 is a characteristic diagram before and after band frequency adjustment of the surface acoustic wave resonator according to the present invention.

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

FIG. 6 is a schematic plan view showing an example of a linear conductor pattern according to the present invention.

FIG. 7 is a schematic plan view showing a pattern layout and a dicing position of a surface acoustic wave element formed on a wafer.

FIG. 8 is an equivalent circuit diagram of a conventional surface acoustic wave device.

FIG. 9 is a schematic plan view of a conventional surface acoustic wave device.

FIG. 10 is a characteristic diagram showing electric characteristics of a conventional surface acoustic wave device.

FIG. 11 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: Linear conductor pattern 3: Input terminal electrode 4: Output terminal electrode 5: Ground terminal electrode 6, 106: Electrical characteristics of surface acoustic wave device 7, Pass band 8, 108: Elasticity Impedance characteristics of surface acoustic wave resonator 8, 108: surface acoustic wave element 9: piezoelectric substrate 10: protruding electrode 11: attenuation characteristic standard 12: pass band standard 13: electric characteristic of defective surface acoustic wave device 14: surface acoustic wave 15: Dicing position 16: Chip outer shape after dicing 17: Signal electrode between input / output terminal electrodes 18: IDT bus bar S: Surface acoustic wave device

Claims (2)

[Claims] 1. A surface acoustic wave device in which an input terminal electrode, an output terminal electrode, and a surface acoustic wave resonator are respectively formed on a piezoelectric substrate, wherein the input terminal electrode and the surface acoustic wave resonator are disposed between the input terminal electrode and the surface acoustic wave resonator. And / or a linear conductor pattern having a plurality of branches and having an inductance for performing band frequency adjustment is formed between the surface acoustic wave element and the output terminal electrode. Wave device. 2. A part of the linear conductor pattern is separated,
2. The band frequency adjustment method for a surface acoustic wave device according to claim 1, wherein the number of branches connected to the linear conductor pattern is reduced to adjust the inductance value.