JPH04356809A - Surface acoustic wave device and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain the surface acoustic wave device improving the degree of freedom for design by arranging an oblique excitation part, which inclines a radiating direction from a main propagation axis, as well as a normal excitation part at an output electrode. CONSTITUTION:At an output electrode 3, an oblique excitation part 7 inclining a radiation direction B from a main propagation axis direction A is arranged as well as a normal excitation part 6, for which the radiation direction of surface waves is made equal to the main propagation axis direction A, composed of electrode fingers 3a and 3b. Thus, since the surface waves are radiated in the direction B different from the main surface wave propagation axis direction A, the surface waves are not transformed to a transformer arranged on the main propagation axis direction A but the surface waves are practically removed for the unit of a 0.5 excitation source. Therefore, the degree of freedom for designing the surface acoustic wave device can be improved, and satisfactory characteristics can be realized in the same chip sizes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface acoustic wave device having a high degree of design freedom and good characteristics, and a method for manufacturing the same.

[Prior Art] Conventionally, as a means for improving the frequency characteristics of a filter, such as increasing the degree of out-of-band suppression, a regular type electrode with a constant aperture has been proposed as described in Japanese Patent Application Laid-Open No. 50-40259. Methods such as removing the portion are known.

This conventional device has a plurality of electrode fingers constituting an electrode finger array, and each electrode finger is divided into two groups and connected to a common electrode so that the polarity changes alternately every two electrode fingers. has been done. Then, one of two mutually adjacent electrode fingers (electrode finger pair) having the same polarity is removed from the electrode finger array.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology focuses only on removing the electrodes, and does not give consideration to providing flexibility in the design of the surface acoustic wave device (7).

In other words, since two adjacent electrode fingers with the same polarity are removed as a unit, the excitation source of the surface acoustic wave that is formed between these electrode fingers and the adjacent electrode finger of another polarity is removed. , this was carried out only in pairs (two excitation sources with opposite signs), and the degree of freedom in design was small.

An object of the present invention is to provide a surface acoustic wave device in which excitation sources of surface acoustic waves are substantially removed in units of 0.5 pairs, and the degree of freedom in design is improved.

Furthermore, another object of the present invention is to provide a method for manufacturing such a surface acoustic wave device.

[Means for solving the problem] The above purpose is to radiate the surface acoustic waves generated from the location where 0.5 pairs of excitation sources are required to be removed in a direction different from the main propagation axis, or to radiate the surface acoustic waves generated from the location where 0.5 pairs of excitation sources need to be removed in a direction different from the main propagation axis, or to This is achieved by suppressing the response of

That is, according to one aspect of the present invention, at least one or more converters for converting an electric signal and a surface acoustic wave signal are disposed on the surface acoustic wave substrate, and at least one of the converters is , has a plurality of surface acoustic wave excitation sources, and has a portion where the polarities of adjacent excitation sources are substantially the same sign near the center frequency of the transducer on the main propagation axis of the surface acoustic wave, and , there is provided a surface acoustic wave device characterized in that its portions are arranged aperiodically.

A surface wave excitation aperture different from the excitation source is provided between the excitation sources of the same polarity, and the excitation aperture has a main radiation axis of the surface wave relative to a main propagation axis of the surface acoustic wave. It can be arranged in an inclined manner.

[Effect] As mentioned above, if the surface waves are radiated in a direction different from the main propagation axis of the surface waves, the surface waves will not be converted to the converter placed on the main propagation axis, and the surface wave will be substantially zero. .5 pairs of excitation sources can be removed. In addition, even when surface waves are radiated in the same direction as the main propagation axis, the conversion frequency characteristics at that point are
By reducing the efficiency near the filter center frequency, it is possible to substantially remove 0.5 pairs of excitation sources, and the design clarity can be improved compared to the case of 1 pair. can.

(The following is a blank space) [Example] Hereinafter, an example of the present invention will be described using FIGS. 1 to 12.

FIG. 1 schematically shows a first embodiment of the invention.

A regular type input electrode 2 and an output electrode 3 are provided on the surface acoustic wave substrate 1 as first and second converters that convert an electric signal and a surface acoustic wave signal, and electromagnetic coupling between input and output is eliminated. A diagonal electrode 4 is arranged for this purpose. Also, substrate 1
A sound-absorbing material 5 is placed on the end face to suppress reflection from the end face.
is coated.

The input electrode 2 is a non-weighted electrode with a constant aperture.

This input electrode 2 has a plurality of electrode fingers 2a and 2b, respectively. These constitute an electrode finger array. Further, each electrode finger 2a, 2b is arranged in two directions so that the polarity is alternately changed every two.
They are divided into groups and connected to common electrodes 2c and 2d, respectively.

Both electrode fingers 2a and 2b have a ribbon-like shape with two longitudinal sides parallel to each other.

The output electrode 3 is basically a non-weighted electrode with a constant aperture. This output electrode 3 includes, in addition to a normal excitation source part 6 in which the radiation direction of surface waves is the same as the main propagation axis direction A, an oblique excitation part 7 in which the radiation direction B is tilted from the main propagation axis A. Placed. Therefore, the output electrode 3 has a plurality of ribbon-shaped electrode fingers 3a, 3b whose two longitudinal sides are parallel, and a plurality of right-angled triangular electrode fingers 3e, 3f, respectively.
These electrode fingers 3a, 3b, 3e, and 3f constitute an electrode finger array.

Further, the electrode fingers 3a and 3b are located at a portion other than the portion adjacent to the electrode fingers 3e and 3f, that is, in the normal excitation source section 6,
Two of each are provided alternately.

The normal excitation source section 6 is composed of electrode fingers 3a and 3b. These electrode fingers 3a, 3b are provided so that two each are alternately provided in the portions other than the portions adjacent to the electrode fingers 3e, 3f.

Electrode fingers 3a and 3e are connected to a common electrode 3c, and electrode fingers 3b and 3f are connected to a common electrode 3d.

The oblique excitation section 7 is composed of electrode fingers 3e and 3f, and the opening thereof is arranged obliquely with respect to the main propagation axis A.

That is, the longitudinal direction of the two right-angled sides of the right-angled triangular electrode fingers 3e and 3f is arranged perpendicular to the main propagation axis A, and the side perpendicular to the longitudinal direction is arranged so as to be parallel to the main propagation axis A. They are arranged so that their hypotenuses face each other.

In FIG. 1, the diagonal excitation section 7 is provided at two locations.

Of course, it is not limited to this.

Further, these oblique excitation parts 7 have different inclination directions with respect to the main propagation axis A.

FIG. 2 shows the relationship between the output interdigital electrode 3 and the position of the excitation source.

A solid arrow 8 indicates a location where an excitation response exists when viewed in the direction of the main propagation axis A, and a broken arrow 9 indicates a location where there is no excitation response when viewed in the direction of the main propagation axis. The position of the excitation source is centered between the common electrodes 3c and 3d. Solid line and broken line arrows 8 and 9 correspond to the normal excitation section 6 and the oblique excitation section 7.

The impulse time response seen in the main propagation axis direction of the transducer shown in the upper part of the figure corresponds to the distribution of the excitation source shown in the lower part of the figure. Here, the code (upper and lower) of the excitation source indicates the location where the electrode is present in the order of the electrode finger connected to the common electrode 3c and the electrode finger connected to the common electrode 3d, as viewed from the input side interdigital electrode. (top), and the locations that exist in the reverse order are defined as - (bottom).

As shown in the figure, the arrangement of the excitation sources formed in this example is as follows:
In addition to the usual arrangement of excitation sources with different signs, there is also an arrangement of excitation sources with the same sign. Therefore, according to this embodiment,
It can be seen that removal of the excitation source (or impulse response) by 0.5 pairs is possible.

Note that, in the above embodiment, the number of pairs where there is no excitation response, that is, the number of missing excitation sources is 0.5, but the number is not limited to this. It may be in units of 0.5 pairs.

An example of an arrangement in which excitation sources having the same sign is arranged is, for example, a conventional split isolated electrode as shown in US Pat. No. 3,748,603. but,
In such an electrode, since the same pole portions are periodically arranged over the entire interdigital electrode, the effect of improving the f characteristic cannot be obtained.

As in this embodiment, by setting the actual dropout of the excitation source to 0.5 pairs of positions, and thereby realizing an arrangement of excitation sources of the same polarity and the same intensity as other locations, the non-weighted electrode The degree of freedom in design can be improved.

In this embodiment, since the frequency characteristic of the group delay time is flat, the 0.5 pairs of excitation sources are left and right symmetrically with respect to the center of the transducer (electrode).

In addition, since the excitation frequency characteristics were made symmetrical, the pitch of different polar excitation sources was set to (1/2+n)λo (n: integer, λo: surface wave wavelength at the center frequency), and the pitch of same polar excitation sources was mλo. (m: integer).

FIG. 3 shows the frequency characteristics of the first embodiment and the conventional filter.

The surface acoustic wave device used in this measurement actually has more excitation source pairs than shown in FIG. The performance of the filter of this embodiment and the conventional filter is compared using the same chip size (distance on the propagation axis). The solid line 10 is the characteristic of the conventional device, and the broken line 11 is the characteristic of the first embodiment. Due to the high degree of design freedom, the degree of out-of-band suppression is improved by approximately 10 dB. In this embodiment, the present invention is used to improve the degree of out-of-band suppression, but other performance improvements such as filter layer characteristics can be similarly performed.

FIG. 4 schematically shows a part of a second embodiment of the present invention. In this embodiment, the same components as in FIG. 1 are denoted by the same reference numerals.

In this embodiment, an input electrode 12 and an output electrode 13 are provided on a surface acoustic wave substrate 1 as first and second transducers that convert an electric signal and a surface acoustic wave signal, and electromagnetic coupling between input and output is provided. A diagonal electrode 4 for exclusion is arranged. In addition, on the end face of the substrate 1, in order to suppress reflection from the end face,
A sound absorbing material 5 is applied.

The input interdigital electrode 12 is an unweighted electrode with a gap of 0.5 pairs of excitation sources. This input electrode 2 has a normal excitation section 6 consisting of ribbon-shaped electrode fingers 2a and 2b arranged in parallel, and an oblique excitation section 7 consisting of right-angled triangular electrode fingers 2e and 2f.

The electrode fingers 2e and 2f are configured in the same manner as the electrode fingers 3e and 3f described above, and the hypotenuses of the right triangle are opposed to each other. Electrode finger 2
a, 2e are connected to the common electrode 2c, electrode fingers 2b, 2f
is connected to the common electrode 2d.

According to this embodiment, regarding the input interdigital electrode 12,
The degree of freedom in designing non-weighted electrodes is improved. On the other hand, the output interdigital electrode 13 is an aperture weighted electrode. This is because the design freedom of aperture weighted electrodes is greater than that of constant aperture transducers since the aperture can be varied. Therefore, in this embodiment, by using the non-weighted electrode and the aperture weighted electrode, the frequency characteristics can be controlled in more detail.

As described above, by using this embodiment, the degree of freedom in designing frequency characteristics can be further increased.

Next, an example in which the diagonal excitation section is different will be described.

FIG. 5 schematically shows a part of the third embodiment. Here, only the electrode pattern for one transducer is shown.

In this embodiment, an oblique excitation section 15 is provided within the output interdigital electrode 14.
is located. The excitation source is considered to be the center between the electrodes and is indicated by a dashed line in the figure. Further, the distance between one open end and the other open end in the main propagation axis direction is shown as Δ■ in the figure. Since the surface wave e propagating from each point of this oblique excitation source section in the main propagation axis direction is expressed as follows, (time term omitted, k0: wave number in the three propagation axis directions, z: propagation distance), the same received wave The integral value E of the wave in the direction of the main propagation axis received by the aperture (perpendicular to the main propagation axis, a certain z-coordinate part) is expressed as (s: line along the diagonal excitation part), so Assuming that A is approximately constant at each point, then. In order to set E to zero, it is sufficient that the value inside the parentheses in equation (4) is zero, so the following condition can be found. From equation (5), if λ is the wavelength at the frequency at which the response of the oblique excitation section is desired to be suppressed, the following equation is obtained. A case is obtained in which the above λ is close to the wavelength λo at the filter center frequency.

Therefore, if Δ■ satisfies equation (7), it becomes possible to sufficiently suppress the response from the oblique excitation part in the direction of the main propagation axis.
It becomes possible to get the value closer to the design value.

In this example, only waves propagating in the direction of the main propagation axis were treated, but in reality they are affected by waves propagating obliquely, so Δ
There may also be cases where (2) is shifted from equation (7).

As described above, by using this embodiment, it is possible to sufficiently suppress the response from the oblique excitation section in the direction of the main propagation axis.
．． Since the omission of the five pairs of excitation source parts can be set to substantially zero, it is possible to get closer to the design value, and the characteristics are also improved.

FIG. 6 is a diagram schematically showing a part of the fourth embodiment.

In this embodiment, the diagonal excitation part 1 in the input interdigital electrode 16 is
A diagonal floating electrode 18 was placed at position 7. In the first to third embodiments, each of the diagonal excitation sections had one excitation source, but in this embodiment, the number of excitation sources is increased by arranging floating electrodes between the electrodes. This increases the radiation directivity of the surface waves in the oblique direction, making it possible to further suppress radiation in the main propagation axis direction.

As described above, by using this embodiment, it becomes possible to further suppress the response from the oblique excitation section in the direction of the main propagation axis, and the degree of agreement with the design value is further improved.

FIG. 7 schematically shows a part of the fifth embodiment.

In this embodiment, an oblique excitation section 20 is provided within the input interdigital electrode 19.
are placed. The diagonal excitation section 20 is bent multiple times in the opening direction, and has a plurality of radiation axes, with the opening direction alternately changing for each side. Since the angle between the main radiation direction B' and the main propagation axis direction A in the oblique excitation section 20 can be made larger, the surface waves radiated in the main propagation axis A direction can be further suppressed.

As described above, by using this embodiment, it is possible to further improve the degree of agreement with the design values.

FIG. 8 is a diagram schematically showing a part of the sixth embodiment.

In this embodiment, an arcuate excitation section 22 is arranged within the input interdigital electrode 21 . By making the missing parts of the 0.5 pairs of excitation sources arc-shaped as shown in the figure, the frequency characteristics of the radiation can be made into a smooth function (fewer poles) (because the radiation directivity becomes smooth). This makes it possible to consider the characteristics of the 0.5-pair excitation source dropout portion to be substantially constant near the center frequency, making it easy to correct them.

As described above, if this embodiment is used, it becomes easy to correct the 0.5 pair excitation source missing portion, and more accurate design becomes possible.

FIG. 9 is a diagram schematically showing a part of the seventh embodiment.

In this embodiment, 0.5 pairs of substantial parasitic portions 24 are provided within the input interdigital interdigital electrode 23. The intersection is made in the direction perpendicular to the main propagation axis direction as usual, but the distance g between the electrodes is set as follows using the wavelength λo at the center frequency.

The radiation characteristic R of the interdigital electrode is determined by the metallization ratio (electrode width/
IE3 Trans, SU-22, P395 (197
5) 12, H. As shown by Engan et al.

In order to set R=0, it is sufficient to use the following equation, and if λ is set near the center frequency, the formula (8) is obtained.

In this way, when g is defined as in equation (8), the response in the main propagation axis direction can be substantially reduced considerably.

As described above, if the present invention is used, it is not necessary to use oblique or curved electrodes, and thus the electrode pattern can be easily designed.

In each of the above embodiments, the surface acoustic wave substrate 1 includes, for example,
A piezoelectric substrate made of short crystals of lithium niobate with a 128° Y-axis cut is used, and the propagation direction of surface acoustic waves is set as the X-axis. Other materials may also be used.

FIG. 10 schematically shows a part of the steps of an embodiment of a method for manufacturing a surface acoustic wave device.

In manufacturing the surface acoustic wave device of this embodiment, first, interdigital electrodes are formed on the surface acoustic wave substrate 1, and then the electrodes are trimmed.

The manufacturing method of this embodiment differs from the conventional manufacturing method in the electrode trimming step, and the formation of the interdigital electrode itself is the same as the conventional method. Therefore, the trimming process will be explained here.

Laser trimming is performed on the excitation source missing portions of the input interdigital electrodes 25 in units of 0.5 pairs. That is, as shown in FIG. This is done by irradiating the laser spot while watching.

Next, the trimming spot 28 is made to meander as shown in FIG. do.

As described above, if this embodiment is used, trimming can be performed while testing characteristics, which is effective in improving yield.

Typical applications of the surface acoustic wave device of the present invention including the above-mentioned embodiments include, for example, filters, oscillators, and the like. Application examples of the surface acoustic wave device used as a filter will be described below.

FIG. 11 is a block diagram showing the configuration of an embodiment of a television receiver using the surface acoustic wave device of the present invention.

The television receiver of this embodiment includes an antenna 30, a tuner block 31, a surface acoustic wave device 32 functioning as a filter, and a demodulation block 33.

In such a configuration, a signal input from the antenna 30 is converted into an intermediate frequency signal by the tuner block 31, a signal for one channel is extracted by the surface acoustic wave device 32, and a video and audio signal is converted by the demodulation block 33. is played back and output to the video output terminal 34 and audio output terminal 35, respectively.

The surface acoustic wave device 32 uses the technology of the present invention to improve the degree of out-of-band suppression, prevent interference from adjacent channels and others, and obtain a good image signal.

As described above, according to this embodiment, it is possible to improve characteristics such as adjacent interference.

FIG. 12 is a block diagram showing the configuration of an embodiment of a satellite broadcasting receiver using the surface acoustic wave device of the present invention.

The satellite broadcasting receiver of this embodiment includes a parabolic antenna 36,
It includes an outdoor unit 37 and an indoor unit 38. The indoor unit 38 includes a down converter section 39, a surface acoustic wave device 40 functioning as a filler, and a demodulation system 41.

In such a configuration, the signal received by the parabolic antenna 36 is transmitted by the outdoor unit 37 at approximately 1 GHz.
is converted into a 1st IF signal and sent to the indoor unit 38. In the indoor unit 38, the down converter section 39
The signal is further converted into a 2nd IF signal in the 400 MHz band, the surface acoustic wave device 40 extracts the signal for one channel, the demodulation system 41 reproduces the video and audio signals, and the video and audio signals are output to the video output terminal 42 and the audio output terminal 43, respectively. is output to.

The surface acoustic wave device 40 has improved shoulder characteristics using the present invention, and has obtained good S/N characteristics.

As described above, by using this embodiment, it is possible to improve the S/N characteristics of a communication device.

[Effects of the Invention] As described above, according to the present invention, the degree of freedom in designing the surface acoustic wave device is improved, so good characteristics can be achieved with the same chip size, and the performance of the device is improved.

Furthermore, if the surface acoustic wave device of the present invention is used in a communication device,
It is possible to improve the performance of the set at low cost.

[Brief explanation of the drawing]

FIG. 1 is a plan view schematically showing the configuration of a first embodiment of the surface acoustic wave device of the present invention, FIG. 2 is an explanatory diagram showing the relationship between the interdigital electrodes and the excitation source position, and FIG. A graph showing the frequency characteristics of the embodiment and the conventional surface acoustic wave device, FIG. 4 is a plan view schematically showing a part of the configuration of the second embodiment of the present invention, and FIGS. 5 to 8 are the diagrams of the present invention. A plan view schematically showing a part of the electrodes constituting the third to sixth embodiments of the surface acoustic wave device;
FIG. 9 is a plan view schematically showing a part of the electrode constituting the seventh embodiment of the surface acoustic wave device of the present invention, and FIG. An explanatory diagram showing the trimming process, FIG. 11 is a block diagram showing the configuration of an embodiment of a television receiver using the surface acoustic wave device of the present invention, and FIG. 12 is a block diagram showing the configuration of an embodiment of a television receiver using the surface acoustic wave device of the present invention. FIG. 1 is a block diagram showing the configuration of an embodiment of a satellite broadcast receiver. 2, 12, 14, 16, 19, 21, 23, 25... Input interdigital electrode, 3, 13... Output interdigital electrode, 7, 15
, 17, 20... Oblique excitation part, 22... Arc-shaped excitation part, 2
4, 27...Substantial non-excitation part, 32, 34...Surface acoustic wave device. Applicant Hitachi, Ltd. Representative Patent Attorney Kazuko Tomita

Claims (17)

[Claims] 1. At least one transducer for converting an electric signal and a surface acoustic wave signal is disposed on a surface acoustic wave substrate, and at least one of the transducers is configured to excite a surface acoustic wave. has a plurality of sources, and has a portion where the polarities of adjacent excitation sources have substantially the same sign near the center frequency of the transducer on the main propagation axis of the surface acoustic wave, and
A surface acoustic wave device characterized in that its portions are arranged aperiodically. 2. The surface acoustic wave device according to claim 1, wherein the non-periodically arranged excitation source has a substantially constant aperture. 3. The surface acoustic wave according to claim 1, wherein the excitation source locations having the same signs are located symmetrically with respect to the center of the transducer in the propagation direction of the surface wave. Device. 4. The converter has a portion where adjacent excitation sources have opposite polarities, and the excitation source pitch at that portion is (1/1).
2+n)λo (n: integer, λo: wavelength of the surface wave at the center frequency), and the excitation source pitch at the point with the same sign is mλo(
4. The surface acoustic wave device according to claim 1, wherein λo is constant within the transducer. 5. In addition to the one transducer, there is another transducer, and the transducer is a transducer having aperture weighting. The surface acoustic wave device described. 6. A surface wave excitation aperture different from the excitation source is provided between the excitation sources of the same polarity, and the excitation aperture has a main radiation axis of the surface wave that is a main propagation axis of the surface acoustic wave. 6. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is arranged at an angle with respect to an axis. [Claim 7] The distance Δ■ between the opening ends of the openings tilted with respect to the main propagation axis, as seen in the direction of the main propagation axis of the surface acoustic wave, is set as Nλo (N: integer). The surface acoustic wave device according to claim 6, characterized in that: 8. Claim 6, wherein a floating electrode is arranged between the electrodes of the opening tilted with respect to the main propagation axis.
The surface acoustic wave device described. 9. The surface acoustic wave device according to claim 6, wherein the aperture tilted with respect to the main propagation axis has a plurality of radiation axes. 10. The surface acoustic wave device according to claim 6, wherein the opening inclined with respect to the main propagation axis has a shape that is bent several times with respect to the opening direction. 11. The surface acoustic wave device according to claim 1, wherein the surface wave aperture between the excitation sources of the same polarity has a curved shape. 12. The elastic surface according to claim 1, wherein the distance g between the electrodes of the surface wave aperture between the excitation sources of the same polarity is M/2·λo (M: integer). wave device. 13. At least one transducer for converting an electric signal and a surface acoustic wave signal is disposed on the surface acoustic wave substrate, and at least one of the transducers has a longitudinal direction parallel to the transducer. 1. A surface acoustic wave device comprising a row of ribbon-shaped electrode fingers, the ribbon-shaped electrode finger row including a pair of electrode fingers whose aperture direction is inclined from the main propagation axis. 14. The transducer according to claim 1, wherein the transducer is composed of interdigital electrodes operated by piezoelectric effect.
, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13. 15. A row of ribbon-shaped electrode fingers whose longitudinal directions are parallel to each other, and a pair of electrode fingers included in the ribbon-shaped electrode finger row whose aperture direction is inclined from the main propagation axis. The surface acoustic wave aperture is trimmed while observing the frequency characteristics of the surface acoustic wave device with respect to a pair of electrode fingers provided on a surface wave substrate, the aperture direction of which is inclined from the main propagation axis. A method for manufacturing a surface wave device. 16. A filter comprising the surface acoustic wave device according to claim 1. 17. A communication device characterized by using the filter according to claim 16.