JPH04810A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To more securely remove unnecessary reflected waves from a propagation path and to enlarge the amount of attenuating a block area by providing plural dummy electrode digits so as to incline a line connecting the ends of an electrode not only in an interdigital input electrode but on the both sides of the ground side electrode digit of an interdigital output electrode. CONSTITUTION:Paired piezoelectric substrates 1 are 128 deg. rotation Y cut LiNbO3 thin boards with 0.5mm thickness and 3mmX10mm size. For example, an interdigital input electrode 2 is composed of Al (or Al alloy), and equipped with the 128 pairs of comb-teeth as a weighted electrode so that a cross length can draw a prescribed envelope curve (shown by a dotted line in the figure). Then, a part inclined at 20 deg., for example, is formed obliquely to a cross electrode digit on the both sides of an input side electrode digit 21. For a dummy electrode digit 23, the 25 pairs of electrode digits, for example, are respectively formed on the both sides of a ground side electrode digit 22 of an interdigital input electrode 2 so that the line connecting the both ends of the electrode can be inclined at the same angle.

Description

[Detailed Description of the Invention] [Summary] Regarding the structure of a surface acoustic wave filter, the purpose is to improve the stopband characteristics of the surface acoustic wave filter. In the surface acoustic wave filter, in which a filter element formed so as to face each other is housed in a package having an insulated airtight terminal, electrode ends are provided on both outer sides of the ground-side electrode fingers of each of the comb-shaped input electrode and the comb-shaped output electrode. A plurality of dummy electrode fingers are provided so that the connecting lines are inclined, and a plurality of metal wires are provided between the connection bar terminal that connects each ground side electrode finger and each dummy electrode finger and the metal base of the package. Connect with wire to configure a surface acoustic wave filter.

[Industrial application field]

The present invention relates to a surface acoustic wave filter, for example, a structure of a comb-shaped electrode of a surface acoustic wave filter used for shaping a pulse waveform of a digital communication device, and a structure for taking out a ground side terminal.

[Conventional technology]

A surface acoustic wave filter is a three-terminal or four-terminal filter in which comb-shaped electrodes for input and output are provided on a piezoelectric substrate with a large electro-mechanical coupling coefficient, such as an artificial single crystal substrate such as LiTa0+ or LiNb0:+. It is a terminal type element.

The width of the comb teeth (L
), the space between the comb teeth (S), and the comb tooth pinch (P), where the wavelength of the surface wave is λ, are usually L = S - λ/4゜P =
Many have a design value of λ/2.

FIG. 4 is a diagram (part 1) showing an example of a conventional electrode pattern, in which the overlap of the most common comb-like electrode fingers, that is, the crossing length of the input electrodes is varied. The so-called weighting uses an electrode finger configuration, and the output electrode has a constant crossing length, so-called.
This uses a comb-shaped electrode with a regular electrode finger configuration. In the figure, 1 is the piezoelectric substrate, 2° is the comb-shaped input electrode, 21" is the input side electrode finger, 22" is the ground side electrode finger, 24" is the connection bar terminal on the input side, and 25" is the connection on the ground side. bar terminal, 3゛ is a comb-shaped output electrode, 31゛ is an output side electrode finger, 32゛ is a ground side electrode finger, 34' is an output side connecting bar terminal, 35'
is the connecting bar terminal on the ground side.

FIG. 5 is a diagram (part 1) showing an example of conventional element mounting, in which the filter element 10' shown in FIG. 4 is mounted in a package 10.
0 metal base 101 with an adhesive, for example, conductive A
G paste, and connect the respective terminals of the comb-shaped input electrode 2° and the comb-shaped output electrode 3′ to the inner end surfaces of the insulating and airtight terminal pins 102 implanted in the metal base 101 using metal wires 104, respectively. Thereafter, by hermetically sealing the cap 103 on the metal base 101, a metal base-mounted surface acoustic wave filter with an insulated airtight terminal is manufactured.

In a surface acoustic wave filter, a signal is input to an input electrode, a surface acoustic wave is excited and propagated through a piezoelectric substrate, and a signal is extracted from an output electrode. For example, the fourth
In the figure, I) is a surface acoustic wave that is excited and propagated from the comb-shaped input electrode 2', and if only this wave is received by the comb-shaped output electrode 3', the filter characteristics as designed can be obtained.

However, part of the initial surface acoustic wave pI is transmitted to the comb-shaped output electrode 3.
It is reflected by ゛.

Furthermore, there is a surface acoustic wave pz (reflected wave between input and output electrodes) that is reflected by the comb-shaped input electrode 2' and reaches the comb-shaped output electrode 3' again, which affects the filter characteristics, especially the stopband characteristics. May have adverse effects.

On the other hand, FIG. 6 is a diagram (part 2) showing an example of a conventional electrode pattern, in which the comb-shaped output electrode 3'' is of the regular type as in the conventional example (part I), but the input Electrode 2
"Input side electrode finger 21" in the area outside the weighted part is provided with an inclined part, and furthermore, along the extension line of the inclined part, that is, a plurality of electrode fingers are provided so that the line connecting the electrode ends is inclined. A dummy electrode finger 23' is provided. In addition, 4
is a shield electrode to prevent direct waves between input and output electrodes.

FIG. 7 is a diagram (part 2) showing an example of conventional element mounting, in which the filter element 10'' shown in FIG. The mounting is bonded with Ag paste, and the connecting bar terminal 25'' on the ground side of the comb-shaped input electrode 2'' and the connecting bar terminal 35'' on the grounding side of the comb-shaped output electrode 3'' are bonded to the metal base 101 using a metal wire 104. and comb-shaped input electrode 2″
Connect the connecting bar terminal 24'' on the input side of the comb-shaped output electrode 3'' and the connecting bar terminal 34'' on the output side of the comb-shaped output electrode 3'' with separate terminal pins
After connecting another terminal pin 104 and the metal base 101 by bonding with the metal wire 104, the cap 103 is sealed to the metal base 101 by, for example, thermocompression bonding. It is sealed to form a surface acoustic wave filter mounted on a metal base with an insulated airtight terminal.

In this case, the reflected wave p2 between the input and output electrodes shown in FIG.
is re-reflected at the inclined ends of the input electrode finger 21'' of the comb-shaped input electrode 2'' and the dummy electrode finger 23', and is bent from the propagation path of the signal surface wave. For example, it is absorbed by a sound absorbing material (not shown). By doing so, it is prevented from entering the comb-shaped output electrode 3'' and the stopband characteristics are improved.

Furthermore, since the ground-side electrode fingers of both comb-shaped electrodes are electrically connected to the wide metal base 101 on which the entire device is mounted and bonded, the grounding effect is also great.

[Problem to be solved by the invention]

Although the above conventional example (Part 2) has considerably improved the stopband characteristics5, in cases where even higher performance is required, for example, it is possible to reliably reduce the stopband attenuation of high and low frequencies to 30d.
There was a problem in that it could not be used for applications that required a B or higher, and a solution was needed.

[Means to solve the problem]

The above problem is solved by a package 100 having an insulated airtight terminal, in which a filter element 10 is formed on a piezoelectric substrate 1, at least a comb-shaped input electrode 2 and a comb-shaped output electrode 3 facing each other.
In the surface acoustic wave filter housed in the comb-shaped input electrode 2 and the comb-shaped output electrode 3, a plurality of wires are provided on both outer sides of the ground-side electrode fingers 22.32 of each of the comb-shaped input electrode 2 and the comb-shaped output electrode 3 so that the lines connecting the electrode ends are inclined. between the metal base 101 of the package 100 and a connection bar terminal 25.35 that connects each ground side electrode finger 22.32 and each dummy electrode finger 23.33. This problem can be solved by using a surface acoustic wave filter connected by a plurality of metal wires 104.

[Effect]

According to the present invention, a plurality of dummy electrode fingers 33 are provided not only on the comb-shaped input electrode 2 but also on both sides of the ground-side electrode fingers 32 of the comb-shaped output electrode 3 so that the line connecting the electrode ends is inclined. hand,
The ground side electrode fingers 22 of each of the input and output electrodes 2 and 3 further ensure the removal of unnecessary reflected waves from the propagation path.
．． 32 and each dummy electrode finger 23.33, and the metal base 101 of the package 100 are connected by a plurality of metal wires 104, so that the grounding resistance is sufficiently reduced. This makes it possible to obtain a surface acoustic wave filter with extremely large stopband attenuation.

〔Example] FIG. 1 is a diagram showing an example element of the present invention.

In the figure, 1 is a piezoelectric pair substrate, for example, 0.5 mm thick.
, 128° rotation Y cut L with size 3 mm x 10 mm
iNb0. It is a thin plate. 2 is a comb-shaped input electrode, for example, made of A1 (or Af gold alloy, for example, 1
It had 28 pairs of comb teeth, and was configured so that the crossing length drew a predetermined envelope curve (shown by a dotted line). The so-called weighting electrodes are formed on both sides of the input-side electrode fingers 21 with inclined portions at an angle of about 20 degrees, for example, with respect to the intersecting electrode fingers. Reference numeral 23 denotes dummy electrode fingers, which are placed on both sides of the ground-side electrode fingers 22 of the comb-shaped input electrode 2 along the extension line of the inclined portion, for example, with lines connecting the electrode ends of 25 pairs of electrode fingers at the same angle. It is formed to be slanted.

A comb-shaped output electrode 3 has 15 pairs of comb teeth having a constant intersection length and made of Al or An alloy with a thickness of 700 nm. This is a so-called regular type electrode. Reference numeral 33 denotes dummy electrode fingers, and like the dummy electrode fingers 23 of the comb-shaped input electrode 2, there are, for example, 25 pairs of electrode fingers on both sides of the ground-side electrode fingers 32 of the comb-shaped output electrode 3, and lines connecting the electrode ends. are formed to be inclined at a similar angle, for example.

In this example, the comb teeth of the comb-shaped electrode, that is, the width of the electrode fingers, the inter-comb tooth base S, and the comb tooth pitch P, are the center frequency f.
o = 70MHz, L = 7 μm, S = 7
When gmIP=14 μm and the wavelength of the surface acoustic wave is λ, P=λ/2.

Note that the same reference numerals are given to the same parts as those explained in the various aspects of the conventional example, and the explanation of the same parts will be omitted.

FIG. 2 is a diagram showing an example of the surface acoustic wave filter of the present invention in which the element is mounted, in which the filter element 10 is mounted on a metal base 101 having an insulated airtight terminal using, for example, Ag paste, which is a conductive adhesive. The connecting bar terminal 25 on the ground side of the comb-shaped input electrode 2 and the connecting bar terminal 35 on the ground side of the comb-shaped output electrode 3 are attached to the metal base 101 by a plurality of metal wires 104, for example, two metal wires 104 in the figure. The connecting bar terminal 24 on the input side of the comb-shaped input electrode 2 and the connecting bar terminal 34 on the output side of the comb-shaped output electrode 3 are directly bonded to separate terminal bins 102 using metal wires 104, and further After bonding and connecting another terminal pin 104 and the metal base 101 with the metal wire 104, the camp 103 is hermetically sealed to the metal base 101 by, for example, thermocompression bonding, thereby forming the metal base with an insulated airtight terminal of the present invention. Fabricate a mounted surface acoustic wave filter.

FIG. 3 is a diagram showing the filter characteristics of the embodiment of the present invention and the conventional example. The attenuation is plotted on the fir axis, and the frequency is plotted on the horizontal axis.

Each sample is mounted on a metal base with an insulated airtight terminal and hermetically sealed with a metal cap 103.A high frequency signal is applied to the comb-shaped input electrode 2, and a network analyzer is applied to the comb-shaped output electrode 3. was connected to measure the filter characteristics.

In the figure, ■ indicates the stopbands on both sides of the passband in the case of the embodiment of the present invention, and both showed good stopband characteristics of about 35 db. On the other hand, ■ is the case of the conventional example (part 2), and ■ is the case of the conventional example (part 1). It should be noted that the grounding configurations are each performed in the manner described above, and it can be seen that the stopband characteristics are all inferior to those of the uninvented embodiments.

In the above embodiment, a weighted electrode finger configuration was used for the comb-shaped input electrode 2, and a regular type electrode finger configuration was used for the comb-shaped output electrode 3.
Of course, the same effect can be obtained even when the configuration is reversed.

The embodiments described above are merely examples, and as long as they comply with the spirit of the present invention, the materials used, the number of electrodes, etc.
It goes without saying that any suitable shape, such as a shape in which the angle of inclination of the line connecting the electrode ends of each dummy electrode finger 23, 33 is weighted by two, or a combination thereof may be used.

[Effects of the Invention] As described above, according to the present invention, the line connecting the electrode ends is inclined not only on the comb-shaped input electrode 2 but also on both sides of the ground-side electrode fingers 32 of the comb-shaped output electrode 3. A plurality of dummy electrode fingers 33 are provided to further ensure the removal of unnecessary reflected waves from the propagation path.
．． A plurality of metal wires 104 are used to connect the connecting bar terminals 25, 35 connecting the terminals 33 and the metal base 101 of the pan cage I00 to sufficiently reduce the grounding resistance, so that the stopband attenuation can be reduced. becomes extremely large,
It greatly contributes to improving the performance 1 quality of surface acoustic wave filters.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example device of the present invention, FIG. 2 is a diagram showing an example of the element mounting state of a surface acoustic wave filter of the present invention, and FIG. 3 is a diagram showing filter characteristics of an example of the present invention and a conventional example. Figure 4 shows an example of a conventional electrode pattern (part 1), Figure 5 shows an example of conventional element mounting (part 1), and Figure 6 shows an example of a conventional electrode pattern. Figure (Part 2) and Figure 7 are (Part 2) showing examples of conventional element mounting. In the figure, 1 is a piezoelectric substrate, 2 is a comb-shaped input electrode, 3 is a comb-shaped output electrode, 4 is a shield electrode, 10 is a filter element, 21 is an input side electrode finger, 22.32 is a ground side electrode finger, 23 .33 is a dummy electrode finger, 25.35 is a connecting bar terminal, and 31 is an output side electrode finger.庬2 囔 1 区

Claims (1)

[Claims] At least a comb-shaped input electrode (
2) and a comb-shaped output electrode (3) facing each other, the filter element (10) is packaged with an insulated airtight terminal (
In the surface acoustic wave filter housed in the comb-shaped input electrode (2) and the comb-shaped output electrode (3), electrode ends are connected to both outer sides of the ground-side electrode fingers (22, 32) of each of the comb-shaped input electrode (2) and the comb-shaped output electrode (3). Multiple dummy electrode fingers (23,
33), and each ground side electrode finger (22,
32) and the connecting bar terminals (25, 35) connecting the respective dummy electrode fingers (23, 33) and the package (1).
00) is connected to a metal base (101) by a plurality of metal wires (104).