JP2821263B2 - Surface acoustic wave device and communication device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention suppresses an unnecessary bulk wave which is excited together with a surface acoustic wave from an input electrode and travels mainly in parallel with a piezoelectric substrate, and suppresses out-of-band suppression. The present invention relates to a surface acoustic wave device suitable for improving the surface acoustic wave.

[Prior art] Conventionally, from an electrode for exciting a surface acoustic wave,
In order to suppress a bulk wave excited simultaneously with a surface acoustic wave, for example, Japanese Patent Application Laid-Open No. 54-13751 discloses that in a mode of a bulk wave, a slow-shear vibration appearing closest to the center frequency has a band. There is disclosed a technique of selecting a cutting direction of a substrate so that the propagation speed of the Rayleigh wave and the propagation speed of the slow shear mode substantially match each other.
This technique has an advantage that spurious components outside the high-frequency band near the pass band of the filter can be substantially suppressed.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology does not take into consideration the bulk wave mode other than the slow share, and suppresses the response of the bulk wave appearing out of the band in general. There was a problem that can not be done. Further, in the bulk wave mode, there is also a problem that the substrate that can be used is limited because the propagation speed depends on the substrate cutting angle depending on the substrate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave device suitable for suppressing an unnecessary bulk wave traveling parallel to a piezoelectric substrate and improving the degree of out-of-band suppression regardless of the characteristics of the substrate. .

[Means for Solving the Problems] To achieve the above object, a surface acoustic wave device according to the present invention comprises an input electrode for exciting a surface acoustic wave on a piezoelectric substrate, and a surface acoustic wave from the input electrode. An output electrode that converts a wave into an electric signal and outputs the signal, and a surface acoustic wave device in which the desired frequency is obtained by weighting the electrode finger intersection width in order to obtain characteristics; A first and a second bulk wave that are opposed to each other in a direction substantially perpendicular to the direction, and are configured so that bulk waves that travel in parallel to the surface of the piezoelectric substrate and are excited together with the surface acoustic wave from each other have phases opposite to each other. A second input electrode, the first and second
And a blocking means for blocking any one of the surface acoustic waves propagating from each of the input electrodes to the output electrode.

In order to cancel the bulk waves with each other, for example, one of the first and second input electrodes is shifted by half a wavelength of the surface acoustic wave at the center frequency of the device with respect to the other in the propagation direction of the surface acoustic wave. do it.

Further, the blocking means may include a sound absorbing agent applied to a surface acoustic wave propagation path of one of the first and second input electrodes and absorbing a surface acoustic wave,
The surface acoustic wave propagation path of one of the first and second input electrodes is formed obliquely to the propagation direction of the surface acoustic wave and has a depth of about the wavelength of the surface acoustic wave at the center frequency of the device. May be included.

Further, a groove having a depth of about the wavelength of a surface acoustic wave at the center frequency of the device may be formed between the first input electrode and the second input electrode.

[Operation] In the present invention, since the first and second input electrodes are configured such that the bulk waves excited from each of them have phases opposite to each other, the bulk waves generated from each input electrode can cancel each other. And unnecessary bulk waves can be suppressed. In this case, since the surface acoustic waves excited from each of the first and second input electrodes also have opposite phases, these surface acoustic waves cancel each other out at the output electrode. By providing a blocking means composed of a sound absorbing agent or a groove, for example, in one of the surface acoustic wave propagation paths of the second input electrode, only the surface acoustic wave propagating from the other input electrode reaches the output electrode. This prevents the surface acoustic waves from being offset by each other.

On the other hand, since the bulk wave is hardly cut off by the sound absorbing agent or the groove, the cutoff means hardly prevents the suppression of the cancellation between the bulk waves.

Embodiment FIG. 1 is a schematic plan view of a first embodiment of the present invention. As the piezoelectric substrate 1, a single crystal of lithium niobate that transmits a 128-degree rotated Y-axis and cuts an X-axis is used. On this substrate 1, input interdigital electrodes 2 and 3, output interdigital electrodes 4, and A grounded shield electrode 5 is provided. The input electrodes 2 and 3 have the same structure in terms of electrical and shape, and are shifted in the direction of the surface acoustic wave propagation axis 6 by half the wavelength at the center frequency of the device. Waveguides 7 and 8 are formed. Further, as shown by hatching in the figure, the sound absorbing agent 9
Waveguide 8 including both ends of piezoelectric substrate 1 and input electrode 3
Is applied on top. Input electrodes 2 and 3 are connected to input terminals 10 and 10 ', respectively, and output electrode 4 is connected to output terminals 11 and 11'.
It is connected to the. The input electrodes 2 and 3 have the same electrical and shape structure. Generally, bulk waves radiated from the respective electrodes are also excited under the same conditions, and bulk waves of the same mode have the same excitation intensity. Radiated in the direction. At this time, the excitation intensity of the bulk wave may slightly decrease due to the application of the sound absorbing agent. In such a case, the opening of the input electrode 3 is set so that the excitation intensity of the bulk wave of the electrode to which the sound absorbing agent is applied is equal to that of the electrode to which the sound absorbing agent is not applied.
It should be larger than that of. However, the input electrodes 2 and 3 are arranged along the surface acoustic wave propagation path 6 so as to be shifted by a half of the wavelength at the center frequency of the device, so that the bulk wave propagating from the input electrodes 2 and 3 is Are received in opposite phases to each other. At the same time, the bulk waves radiated from the input electrodes 2 and 3 are considered to propagate while canceling the phases in opposite phases. Can also suppress the effects of On the other hand, the surface acoustic wave propagating on the surface of the piezoelectric substrate 1 propagates from the input electrodes 2 and 3, and passes through the waveguides 7 and 8, respectively. However, since the sound absorbing agent 9 is applied to one of the waveguides 8, the surface acoustic wave propagating through the waveguide 8 is absorbed by the sound absorbing agent 9, and the surface acoustic wave reaching the output electrode 4 is 2
Only those that propagate from Therefore, it is possible to prevent the frequency characteristics from deteriorating due to the interaction between the input electrodes 2 and 3 designed to realize the desired frequency characteristics. Further, the sound absorbing agent 9 of the waveguide 8 also absorbs the surface acoustic wave diffracted from the input electrode 2 and obliquely travels, and has an effect of preventing the acoustic wave from traveling to the output electrode 4. The above can be said to be the same even if the input electrode and the output electrode are replaced because the filter device has a transversal configuration. As described above, the degree of out-of-band suppression was improved by suppressing the bulk wave and some of the diffracted waves.

In the first embodiment, the center frequency of the filter is 36.36M
Hz, the logarithm of the input IDTs 2 and 3 is 32.5 pairs, the maximum aperture length is 1800 μm, the logarithm of the output IDT 4 is 11 pairs, and the maximum aperture length is 2000 μm.

FIG. 2 is a schematic plan view of a second embodiment of the present invention. The configuration other than the input electrode 16 is the same as that of the first embodiment. The input electrode 16 is a common electrode portion 14 which is a common part of an electrode finger represented by an electrode finger 14 ′ connected to the input terminal 10, and an electrode finger represented by an electrode finger 15 ′ connected to the input terminal 10 ′ Are formed by two interdigital transducers which are electrically opposite in phase and are formed by a common electrode portion 15 which forms a common portion. That is, the two electrode finger intersections (openings) above and below the surface acoustic wave propagation axis 6 of the input electrode 16 have the same structure with respect to the geometric shape, and the surface acoustic wave propagation axis 6 of the input electrode 16 is the same. Up and down 2
Regarding the electrode fingers 14 'and 15' located at the same position in one opening, the electrode finger 14 'is connected to one input terminal 10 and the electrode finger 15' is connected to the other input terminal 10 '. Where the electrode finger
The electrode finger adjacent to and intersecting with the electrode finger 14 'is the electrode finger of the common electrode unit 15, is connected to the terminal 10', is adjacent to the electrode finger 15 ', and forms the intersection of the electrode finger. Fourteen electrode fingers are connected to the terminal 10. Therefore, the upper and lower openings of the surface acoustic wave propagation axis 6 are electrically opposite in phase. By using this electrode, the same effect as in the first embodiment of the present invention can be obtained. Further, according to the present embodiment,
Unnecessary excitation between the input electrodes 2 and 3, which has occurred in the first embodiment, can be eliminated, so that better characteristics can be obtained.

FIG. 3 is a schematic plan view of a third embodiment of the present invention.
The configuration other than the sound absorbing agent 9 'applied to the waveguide 8 is the same as that of the second embodiment. In the present embodiment, as shown in FIG. 3, the sound absorbing agent 9 'is arranged so as to avoid the electrode finger crossing portion of the input electrode 16 located below the surface acoustic wave propagation axis 6, that is, the surface acoustic wave exciting portion. It has been applied. When the sound absorbing agent 9 'is applied in this manner, the change in the excitation intensity of the bulk wave due to the application of the sound absorbing agent on the surface acoustic wave exciting portion can be suppressed, and not only the design becomes easy, but also the design becomes easy. The electrode finger can be prevented from being disconnected due to the step of applying the sound absorbing agent on the surface acoustic wave excitation section, and the yield can be improved.

FIG. 4 is a schematic plan view of a fourth embodiment of the present invention. The electrode configuration of the present embodiment is the same as the electrode configuration of the second embodiment. About 2 mm of a sound absorbing agent 9 is applied to the upper surface of the piezoelectric substrate 1 on the side of the end surfaces 12 and 13. In addition, on the waveguide 8 between the input electrode 16 and the output electrode 4, a wavelength (3
A groove 17 having a depth of about 107 μm at 6.36 MHz) is provided obliquely with respect to the propagation axis 6 of the surface acoustic wave. In general, a surface acoustic wave propagates with its energy concentrated from the surface of a piezoelectric substrate within a range of a wavelength depth at a center frequency. Therefore, by providing the groove 17, the waveguide 8
Is reflected out of the waveguide 8 to prevent the surface acoustic wave from traveling to the output electrode. Therefore, the same effect as that of the second embodiment of the present invention can be obtained. Furthermore, since the influence of the bulk acoustic wave due to the application of the sound absorbing agent is eliminated, the bulk wave is more effectively canceled. Further, the step of applying the sound absorbing agent is simplified.

FIG. 5 is a schematic plan view of a fifth embodiment of the present invention. In this embodiment, the input electrode 16 and the output electrode 4 of the third embodiment are
Each of them is replaced with a split connect type input electrode 20 and output electrode 21. By doing so, in addition to the effect of the third embodiment of the present invention, it is possible to suppress reflection in the electrode and increase the degree of freedom in design.

FIG. 6 is a schematic plan view of a sixth embodiment of the present invention. In this embodiment, the input electrode 20 includes a common electrode portion 18 located on the waveguide 7 side, a common electrode 18 ′ located on the waveguide 8 side, and a common electrode 19 intersecting with an electrode finger extending therefrom.
Consists of The common electrode section 18 is connected to the input terminal 10,
The common electrode section 18 'is connected to the input terminal 10 via the 180-degree phase shifter 22.
Connected to Further, the common electrode section 19 is grounded. By doing so, the surface acoustic wave excitation section composed of the common electrode sections 18 and 19 and the surface acoustic wave excitation section composed of the common electrode sections 18 ′ and 19 excite surface acoustic waves of opposite phases. You. Therefore, an effect similar to that of the third embodiment of the present invention can be obtained.

FIG. 7 is a system block diagram of a seventh embodiment using the apparatus of the present invention as an intermediate frequency filter of a television receiver. The surface acoustic wave device 24 of the present invention includes a tuner block.
The signal of one channel is extracted (filtered) from the intermediate frequency signal sent from 23, and the extracted signal is
It is sent to the next detection block 25, and after detection, video signal output
26 and an audio signal output 27.

FIG. 8 shows a comparison between the filter frequency characteristic (solid line) 28 of the first embodiment of the present invention and the frequency characteristic (dashed line) 29 of the conventional surface acoustic wave filter. This filter is for TV / IF for West Germany
Targeting a filter. According to the present invention, it is possible to suppress the response of the bulk wave that appears outside the conventional high-frequency band, and the degree of suppression of the out-of-band by about 5 dB is improved.

FIG. 9 is a schematic plan view of an eighth embodiment of the present invention. This embodiment has an electrode configuration similar to that of the fifth embodiment shown in FIG. 5, and is obtained by screen-applying APB-50 (polybutadiene resin) as a sound absorbing agent. This sound absorbing agent has an advantage that it is easy to produce and excellent in mass productivity because it is of an ultraviolet curing type in addition to having an excellent sound absorbing effect.

FIG. 10 is a schematic plan view of a ninth embodiment of the present invention.
In this embodiment, a groove (cut) 31 having a depth equal to or greater than the wavelength of the device center frequency is provided between the input electrodes 2 'and 3'. By providing this notch 31, the waveguides 7, 8
No interaction occurs in the propagation process of the bulk wave propagating through, and a better effect can be obtained.

FIG. 11 is a schematic plan view of a tenth embodiment of the present invention. The input electrodes 32 and 32 ′ have an axially symmetric shape with respect to an axis perpendicular to the surface acoustic wave propagation axis 6, and are arranged at L and L ′ away from the electrode end of the output electrode 4, respectively. In the figure, the upper common electrode section is connected to the input terminal 10, and the lower common electrode section is connected to the input terminal 10 '. Note that the arrangement is such that | L−L ′ | = half wavelength (at the center frequency of the device). The ends 12 'and 13' of the piezoelectric substrate 1 are cut obliquely. Input electrode
Bulk waves propagated from 32 and 32 'are received by the output electrode 4 in the opposite phase, and surface acoustic waves propagated from the input electrode 32' are absorbed by the sound absorbing agent 9. Furthermore, since the bulk waves traveling from the input electrodes 32 and 32 'to the substrate ends 12' and 13 'are reflected out of the waveguide, the same effects as in the ninth embodiment can be obtained.

FIG. 12 shows an input electrode of a surface acoustic wave device according to an eleventh embodiment of the present invention.
FIG. 33 is a schematic plan view of a part of No. 33. The input electrode 33 cancels the bulk wave excited by the excitation unit at a position separated by a half (or an odd multiple thereof) of the wavelength at the device center frequency from the excitation unit represented by each of the electrode finger intersections 34. To this end, an excitation unit having a sound absorbing agent applied to the surface represented by each of the electrode finger intersections 35 is provided. Thus, the same effects as those of the first and second embodiments can be obtained, and the chip size can be reduced.

[Effects of the Invention] As described above, according to the present invention, regardless of the characteristics of a piezoelectric substrate, it is possible to satisfactorily suppress a bulk wave that travels mainly in parallel to the substrate surface and improve out-of-band frequency characteristics. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a first embodiment of the present invention, FIG. 2 is a schematic plan view of a second embodiment of the present invention, and FIG.
FIG. 4 is a schematic plan view of a fourth embodiment of the present invention, FIG. 5 is a schematic plan view of a fifth embodiment of the present invention, and FIG. 6 is a sixth embodiment of the present invention. FIG. 7 is a system block diagram of a seventh embodiment in which the device of the present invention is used as an intermediate frequency filter of a television receiver, and FIG. 8 is a filter frequency characteristic of the first embodiment of the present invention and a conventional device. FIG. 9 is a schematic plan view of an eighth embodiment of the present invention, FIG. 10 is a schematic plan view of a ninth embodiment of the present invention, and FIG. FIG. 12 is a schematic plan view of a tenth embodiment of the present invention, and FIG. 12 is a schematic plan view of a part of an input electrode of a surface acoustic wave device according to an eleventh embodiment of the present invention. 1 .... Piezoelectric substrate, 2, 3, 16, 20, 32, 32 ', 33, 3
5, 37 ... interdigital electrode, 4, 21, 38 ... output interdigital electrode, 5 ... shield electrode, 6 ... propagation axis of surface acoustic wave, 7, 8 ... surface acoustic wave propagation path, 9 , 9 ', 30 ...
Sound absorbing agent, 10, 10 '... input terminal, 11, 11' ... output terminal, 12, 13, ... piezoelectric substrate end face, 14, 15, 18, 18 ', 19
... Input common electrode section, 14 ', 15' ... Electrode finger, 17 ...
Groove, 22 ... 180 ° phase shifter, 23 ... Tuner block, 24
…… the surface acoustic wave device of the present invention, 25 …… Detection block, 26…
... video output terminal, 27 ... audio output terminal, 28 ... filter frequency characteristics of the first embodiment of the present invention, 29 ... frequency characteristics of a conventional surface acoustic wave device filter.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Nogami 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Hiroaki Ikeda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Home Appliance Research Laboratory (56) References JP-A-51-32244 (JP, A) JP-A-51-78967 (JP, A)

Claims (10)

(57) [Claims] An input electrode for exciting a surface acoustic wave and an output electrode for converting a surface acoustic wave from the input electrode into an electric signal and outputting the signal are formed on a piezoelectric substrate. In the surface acoustic wave device weighted with the electrode finger intersection width to obtain the input electrodes, the input electrodes are arranged to face each other in a direction substantially orthogonal to the propagation direction of the surface acoustic wave, and are excited together with the surface acoustic wave from each of the input electrodes. And a first and a second input electrode configured to make the bulk waves traveling parallel to the surface of the piezoelectric substrate have opposite phases to each other.
A surface acoustic wave device provided with a blocking means for blocking any one of the surface acoustic waves propagating from each of the input electrodes to the output electrode. 2. The method according to claim 1, wherein the first and second input electrodes are each composed of interdigital electrodes, and have an opening length such that the amplitudes of the bulk waves excited from these input electrodes are equal to each other. The surface acoustic wave device according to claim 1, wherein: 3. An arrangement in which one of the first and second input electrodes is displaced from the other by a half wavelength of the surface acoustic wave at the center frequency of the device in the direction of propagation of the surface acoustic wave, whereby each of the first and second input electrodes is displaced. 2. The surface acoustic wave device according to claim 1, wherein the bulk waves excited from the electrodes are canceled out of phase with each other. 3. 4. The method according to claim 1, wherein the blocking means is applied to a surface acoustic wave propagation path of one of the first and second input electrodes.
The surface acoustic wave device according to claim 1, further comprising a sound absorbing agent that absorbs surface acoustic waves. 5. The surface acoustic wave device according to claim 4, wherein the sound absorbing agent is applied to a surface acoustic wave propagation path other than an electrode finger intersection of the input electrode. 6. The center of the device, wherein the blocking means is formed on one of the first and second input electrodes in a surface acoustic wave propagation path obliquely to a propagation direction of the surface acoustic wave. 2. The surface acoustic wave device according to claim 1, further comprising a groove having a depth about the wavelength of the surface acoustic wave at a frequency. 7. The surface acoustic wave device according to claim 1, wherein the input electrode and the output electrode are interdigital electrodes each having a split connector type electrode finger. 8. A groove formed between the first input electrode and the second input electrode and having a depth about the wavelength of a surface acoustic wave at a center frequency of the device. 2. The surface acoustic wave device according to 1. 9. An input electrode for exciting a surface acoustic wave and an output electrode for converting a surface acoustic wave from the input electrode into an electric signal and outputting the signal on a piezoelectric substrate, and having a desired frequency characteristic. In the surface acoustic wave device weighting the electrode finger intersection width in order to obtain, the input electrode is constituted by a first electrode finger intersection, and travels in parallel with the surface acoustic wave and the surface of the piezoelectric substrate. A first excitation source configured to excite a bulk wave; and a second excitation source configured by a second electrode finger intersection, configured to cancel only the bulk wave excited by the first excitation source. A surface acoustic wave device characterized by the above-mentioned. 10. A communication device using the surface acoustic wave device according to claim 1.