JPH036114A - surface acoustic wave device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device used as a filter, resonator, delay line, etc.

[Conventional technology]

Figure 7 shows 1, for example, the literature “8uvface Wave F
i-1ters'', H, Matthews, John
Wiley & 5ons.

FIG. 1 is a configuration diagram showing a conventional surface acoustic wave device shown in 1977, page 360. Here, a distributed delay line, which is one type of surface acoustic wave device, will be explained as an example. In the figure,
1) is a piezoelectric substrate 2 (2) and (3) are piezoelectric substrates (
1) The interdigital interdigital electrode for surface acoustic wave excitation and the interdigital interdigital electrode for surface acoustic wave reception using an avocized interdigital interdigital electrode using interdigital double electrodes formed on the interdigital interdigital electrode (2). ) and electrode fingers constituting (3), (5)
(6) is an electrode finger (4) and a pseudo-shaped dummy electrode provided in the same row and opposite to the electrode finger (4) in a part where adjacent electrode fingers (4) do not intersect; and the pad that binds the dummy electrode (5), (7a) and (?
b) are an input terminal and an output terminal for inputting and outputting electrical signals to and from the interdigital electrode for surface acoustic wave excitation (2) and the interdigital interdigital electrode for surface acoustic wave reception (3), respectively. FIG. 8 is an enlarged view showing the configuration of the surface acoustic wave excitation interdigital electrode (2) portion of the surface acoustic wave device shown in FIG. 7. In the figure,
(1), (21, (4), (5), (6),
(7a) is the same as that in FIG. 7, and the finely shaded portion in FIG. 92 indicates the dummy electrode (5). Electrode finger (
4) and dummy electrodes (5) are arranged as a set of two of the same length, and are connected by pads (6) to form a comb shape. finger (4)
The electrode fingers (4) of the lower pad (6) are crossed, and the length of the two crossings is changed. The configuration of the two surface acoustic wave receiving interdigital electrodes is also the same as that shown in FIG. 8 above. Here, 6. A double electrode is one in which two electrode fingers (4) of the same length are used in combination as described above, and the width of the five electrode fingers (4) is λ/8 (however, 8 λ is the width of the surface acoustic wave. Two electrode fingers (4) (indicating the wavelength at the electrode finger position) are arranged at an interval of λ/8. In addition, the avocized interdigital electrode is a device in which the intersecting length of the electrode fingers (4) is changed as described above, and weighting is performed so that the excitation or reception intensity of the surface acoustic wave is a function of the position, improving the two-frequency characteristics. ck! used to ! FIG. 7 shows the case of a chirp-shaped interdigital electrode, in which electrode fingers (4) constituting the interdigital electrode (2) for surface acoustic wave excitation
The arrangement pitch j2 changes sequentially so that it becomes narrower on the left side of the figure and wider on the right side. On the other hand, the arrangement pitch of the electrode fingers (4) constituting the 8-interdigital surface acoustic wave receiving interdigital electrode (3) changes l1i linearly so that it is wider on the left side of the figure and narrower on the right side.

Next, the action 0 effect will be explained.

Surface acoustic wave excitation sudah provided on the piezoelectric substrate (1)
When an electrical signal is input to the 7-shaped 1 [pole (2), surface acoustic waves are excited in the piezoelectric substrate (1) due to piezoelectric action. Since the arrangement pitch of the electrode fingers (4) of the interdigital electrode (2) for surface acoustic wave excitation is configured as described above, on the right side of the interdigital interdigital electrode (2) for surface acoustic wave excitation, there is an elastic surface with a low frequency. High frequency surface acoustic waves are efficiently excited on the left side of the interdigital interdigital electrode (2) for surface acoustic wave excitation. The surface acoustic waves excited in this manner propagate on the piezoelectric substrate (1) and reach the surface acoustic wave receiving interdigital electrode (3), where they are again converted into electrical signals and output. Here, since the arrangement pitch of the electrode fingers (4) of the interdigital electrode for surface acoustic wave reception (3) is configured as described above, on the left side of the interdigital interdigital electrode for surface acoustic wave reception (3), the elastic Surface acoustic waves are efficiently received.2 The interdigital interdigital electrode for surface acoustic wave reception (3) on the right side receives high frequency surface acoustic waves efficiently.

That is, among the excited surface acoustic waves, those with low frequencies are excited on the right side of the interdigital electrode (2) for excitation of surface acoustic waves (1) and received on the left side of the interdigital interdigital electrode (3) for receiving surface acoustic waves (2). For. The propagation distance on the piezoelectric substrate (1) is short, and the propagation time is also short.

Also, among the excited surface acoustic waves, those with high frequencies are 8
Since it is excited on the left side of the interdigital electrode for surface acoustic wave excitation (2) and received on the right side of the interdigital interdigital electrode for surface acoustic wave reception (3), the propagation distance on the piezoelectric substrate (1) is long. The night time is also long. In this way, the higher the frequency is, the longer the delay time becomes. A distributed delay line having so-called up-chirp dispersion characteristics is obtained. Although FIG. 7 shows an up-chirp distributed delay line, the electrode fingers (4) constituting the interdigital interdigital electrode (2) for surface acoustic wave excitation are shown in FIG.
The arrangement pitch of the electrode fingers (4) constituting the two surface acoustic wave receiving interdigital electrodes (3) is changed sequentially from wide on the left side of the figure to narrower on the right side of the figure. Varied distributed delay lines may also be used. In this case, the higher the frequency, the shorter the delay time.

A distributed delay line having a so-called down-chirp dispersion characteristic is obtained.

Further, as shown in FIG. 7, when the interdigital electrode 1 for excitation of surface acoustic waves (2) and the interdigital electrode for surface acoustic wave reception (3) are formed in an avocized shape.

Generally, a dummy electrode (5) is often used.

The function of the dummy electrode (5) is to ensure that the propagation velocity of the three surface acoustic waves does not differ between the intersecting part and the non-intersecting part of the electrode fingers (4).
Also, unlike the electrode fingers (4), they do not excite or receive surface acoustic waves. Furthermore, as shown in FIG. 7, the action of the double electrode is that of the adjacent electrode fingers (4) in the surface acoustic wave excitation interdigital electrode (2) and the surface acoustic wave reception interdigital electrode (3). Since the design is such that the phase difference of the reflected waves at the ends cancels each other out as a μ wave, the influence of reflection of surface acoustic waves by the 2N polar fingers (4) is reduced.

Next, the impulse response operation in the surface acoustic wave device, which is a problem in this invention, will be explained.

FIG. 9 shows the time response obtained from the output terminal (7I) when an impulse is input to the input terminal (7a) of the conventional surface acoustic wave device shown in FIG. FIG. 3 is a characteristic diagram showing experimental results. In Figure 9, the horizontal axis is time. The vertical axis represents the amplitude of the time response as a logarithm.

or. FIG. 10 schematically shows the interdigital electrode (2) for surface acoustic wave excitation and the barb-shaped electrode (3) for surface acoustic wave excitation of the surface acoustic wave device shown in FIG. 7 in Tables I to 7. 'C is an explanatory diagram, and the arrows in the figure indicate the propagation path of surface acoustic waves.6 In Figure 9, the amplitude peak indicated by symbol A is shown by the solid line in Figure 10.'': Urchin 9 Surface acoustic waves Interdigital electrode for excitation (
2) is the time response of the main signal generated by the surface acoustic wave that is excited and reaches the interdigital interdigital electrode (3) for direct surface acoustic wave reception. In FIG. 9, in addition to the time response of the main signal indicated by symbol A, the spurious time response indicated by symbol B appears. Results of investigation based on spurious generation time and surface acoustic wave propagation speed.

The above spurious. As shown by the broken line in FIG. 10, after being excited by the 9 interdigital interdigital electrodes for surface acoustic wave excitation (2), the ends (a) of the 9 interdigital interdigital electrodes for surface acoustic wave excitation (2) or the 1 elastic surface The wave is reflected at the end of the receiving interdigital electrode (3). Curved electrode for surface acoustic wave reception (3
) was found to be caused by surface acoustic waves that reach and are received.

Incidentally, the surface acoustic waves reflected at the end (b) or end 0 have little effect on the reception level.

The above reflection is. Nothing is provided on the piezoelectric substrate (1) outside the surface acoustic wave interdigital electrode (1) outside the surface acoustic wave excitation interdigital electrode (2) and the surface acoustic wave reception interdigital electrode (3). Due to the difference in propagation speed between the surface acoustic waves that propagate in a wide area where the piezoelectric substrate (1) It is thought that this was caused by Even in a general surface acoustic wave device in which the arrangement pitch of the electrode fingers (4) constituting the reception interdigital electrode (3) is constant, when the number of electrode fingers (4) increases, 8 spurious waves occur due to the same reason as mentioned above. occurs.

[Problem to be solved by the invention]

In conventional surface acoustic wave devices, as mentioned above, reflection of surface acoustic waves occurs due to acoustic impedance mismatch at the boundary between the end of the interdigital electrode and the piezoelectric substrate, resulting in spurious response of one hour. There was a problem.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to obtain a surface acoustic wave device that can reduce spurious response in a two-hour response.

[Means to solve the problem]

The surface acoustic wave device according to the present invention has a transducer for excitation of surface acoustic waves on a piezoelectric substrate in the vicinity of the ends of the pole and transducer for surface acoustic wave reception which are far from the other transducer. A metal film is provided which is connected to the pad of the electrode and has an edge at one end close to the electrode finger and an edge at the other end which is inclined with respect to the electrode finger.

[Effect]

C2. Surface acoustic wave device invented by Jin. By providing the metal film as described above, the uneven acoustic impedance at the end of the interdigital electrode for surface acoustic waves propagating through the interdigital electrode is alleviated, and most of the surface acoustic waves are transmitted to the end of the interdigital electrode. and proceed to the metal film without being reflected.

The reflection direction of the surface acoustic wave reflected at the edge of the metal film is the electrode finger (
Alternatively, since the C and E2 are not perpendicular to each other and are directed outward from the electrode finger, the influence of the reflected wave is reduced and the spurious response of the time response is reduced.

[Embodiments of the invention]

FIG. 1 is a block diagram of a surface acoustic wave device which is an embodiment of the present invention, and will be explained using a distributed delay line as an example, as in the conventional example. In addition, in the embodiment, a metal film is provided at the end of the interdigital electrode.

In order to eliminate additional reflections at the electrode finger portions that do not intersect, this shows a practical front side in which a metal film is provided that connects to the pad so that the metal film is also filled in the electrode finger portions that do not intersect. . In fig. (1) to (6), (7a),
(7b) is the same as the conventional device shown in FIG.
(8a) is a metal film provided on the end side of the piezoelectric substrate O) of the interdigital electrode (2) for surface acoustic wave excitation; (sb) is the metal film provided on the end side of the piezoelectric substrate (O) of the interdigital electrode (3) for surface acoustic wave reception; ), (9s) and (9b) are metal films (9s) and (9b), respectively, which are formed by the portions that are inclined with respect to the electrode fingers (4).
sa) slope of (8b), (10a) (xoh)
are metal film extensions indicating extensions of the metal films (8a) and (8b) filling the portions where the electrode fingers (4) do not intersect, respectively. Electrode fingers (4) 7 The dummy electrodes (5) were the same as in the conventional example, and the arrangement pitch of the electrode fingers (4) was also the same as in the conventional example. or. In this embodiment, the inclined portions (9a) (9b
3 is an inclined line having a constant inclination angle with respect to the electrode finger (4), and is arranged in a convex shape.

Here, in the above embodiment, the surface acoustic wave excitation and reception 8 and the operations and effects of the distributed delay line are the same as in the conventional example, and therefore their explanation will be omitted.

Next, the impulse response operation in the above embodiment will be explained.

Figure 2 shows that when an impulse is input to the input terminal (7B) of the surface acoustic wave device as shown in Figure 1, the output terminal (
7h) A characteristic diagram showing the experimental results of the time response obtained.The horizontal axis is time, and the vertical axis is the logarithmic amplitude of the time response. 2 schematically shows the interdigital electrode (2) and metal film (8a) for surface acoustic wave excitation and the interdigital electrode (3) and metal film (8b) for surface acoustic wave reception of the surface acoustic wave device shown. It is an explanatory diagram, and arrows in the diagram indicate propagation paths of surface acoustic waves.

In FIG. 2, the amplitude peak indicated by black is K, which is the same as in conventional surface acoustic wave devices of this type.

This is the time response of the main signal generated by the surface acoustic wave as shown by the solid line in FIG. , [7 However, in the characteristic diagram shown in FIG. 2, spurious as shown at point B in FIG. 9 does not appear. As shown by the dotted line in FIG.
The surface acoustic wave that reached the end of the metal film (8a) (3)
This is because the light is reflected obliquely to the outside of the interdigital electrodes (2) and (3) at the inclined portion (sa) ('9b) of 8h) and is not received by the interdigital interdigital electrode (3) for surface acoustic wave reception. Furthermore, the time response of the main signal shown by point A in FIG. 2 shows the same characteristics as the time response of the main signal shown in black in FIG.
The influence on the time response of the main signal due to the formation of
I can see that there isn't.

As described above, in the surface acoustic wave device according to the present invention, the effect of reducing the spurious of the one-hour response without affecting the main signal is obtained. FIG. 4 shows another embodiment of the present invention. 1 is a configuration diagram showing a certain surface acoustic wave device. In the embodiment shown in FIG. 1, the shape of the inclined portions (9a) (9b) on the end side of the piezoelectric substrate (1) of the metal film (8a) (ab) is set at a constant level with respect to the electrode (4) as shown in the figure. A case is shown in which the inclined lines have an inclination angle and are arranged so as to be inclined in the same direction. Since the direction of reflection of the surface acoustic waves reflected by the inclined portions (9a) (9b) is toward the outside of the electrode finger (4) or obliquely to the electrode finger (4), the same effect as described above can be obtained.

FIG. 5 is a configuration diagram showing a surface acoustic wave device according to still another embodiment of the present invention, in which the piezoelectric substrate (8a) (8b) of the metal film (8a) (8b) in the embodiment shown in FIGS. 1)
Still another embodiment of the shape of the end-side sloped portions (9a) and (9b) is shown. In the figure, the oblique part (9a) is an example of a shape made of a combination of straight lines with an appropriate inclination to the electrode finger (4), and the sacro-oblique part (9b) is an example of a shape made of a curved line. . In this embodiment as well, the 2″″
The same effects as in the above embodiments can be obtained.

In addition, for 8 or more, this invention C has a lateral surface wave device! The embodiment of the metal film (sa) (8d) at t is shown in three examples; however, the slopes (9a) (9b) of the metal film (8a) (8b) ) The metal film on the excitation side (8
The metal film (8b) on the receiving side may be symmetrical. or. The metal film extensions (10a) and (10h) are separate from the means for solving the problems of the present invention, and do not need to be provided. FIG. In the figure, (2) is a diagonal electrode for surface acoustic wave reception using a regular-sized diagonal electrode in which the intersecting length of the electrode fingers (4) accommodated by the double electrode is uniform, and is similar to the above. Aggchirp distributed delay line is shown. In a surface acoustic wave device configured in this way, the number of electrode fingers (4) is generally small on the side of the interdigital electrode (2) for surface acoustic wave excitation, and the metal film is avoidized because the influence of reflection at the end is small. It is formed only on one surface acoustic wave receiving electrode (3) configured in the shape of

The same effect as described above is exhibited for reflection at the end of the electrode (3). It goes without saying that the shape of the metal film (8b) in FIG. 6 can also be the same variation as described above, such as the shape shown in FIG. 4 or FIG. 5. or,
The metal film extension (xob) may not be provided.

In addition. In the embodiments described above, the case is shown in which the electrode fingers (4) having a double electrode or υ are used.

In addition, in the two or more embodiments, a case is shown in which a dummy electrode is provided in the avocized interdigital electrode, but the present invention can also be applied to a case where a dummy electrode is not used regardless of this.

Further, the present invention can be applied to either a regular type or an abodied type electrode, or a chirped type or a non-chirp type, and the same effects as described above can be obtained.

Incidentally, although the above embodiments have been described using a distributed delay line as an example of a surface acoustic wave device, it is obvious that the present invention can be used in other surface acoustic wave devices.

〔Effect of the invention〕

As explained above, in this invention, since the metal film is provided close to the end of the interdigital electrode, reflection of 8 surface acoustic waves at the end of the interdigital electrode can be reduced, and the end of the metal film can be 1. Tilt against the electrode.

Since it is formed in a six-fold shape, the direction of the reflected wave reflected at the edge of the metal film is not perpendicular to the electrode, but instead goes outside the electrode finger, resulting in spurious time response due to the influence of zero reflection. can be reduced.

[Brief explanation of drawings]

Fig. 1 shows the configuration of a surface acoustic wave device which is an embodiment of the present invention. Fig. 2 shows the output terminal obtained when an impulse is input to the input terminal of the surface acoustic wave device shown in Fig. 1. Figure 3 is an explanatory diagram schematically showing the surface acoustic wave device shown in Figure 1. Figure 4 is a surface acoustic wave which is another embodiment of the invention. Fig. 5 is a structural diagram showing a surface acoustic wave device according to another embodiment of the present invention. Fig. 6 is a structural diagram showing a surface acoustic wave device according to another embodiment of the present invention. 7 is a configuration diagram showing a conventional surface acoustic wave device, and FIG. 8 is an enlarged view showing the configuration of the interdigital electrode part for surface acoustic wave excitation of the surface acoustic wave device shown in FIG. 7. 9 is a characteristic diagram showing the experimental results of impulse response in the conventional surface acoustic wave device shown in FIG. 7, and FIG. 10 is an explanation schematically showing the surface acoustic wave device shown in FIG. 7. It is a diagram. In the figure, (1) is a piezoelectric substrate, (2) is an interdigital electrode for surface acoustic wave excitation, (3) is an interdigital electrode for surface acoustic wave reception, (4) is an electrode finger, and (5) is a dummy electrode. . (4) is the electrode finger 2 (5) is the dummy electrode, (6) is the pad, (7a) is the input terminal, (7b) is the output terminal,
csa) (811) is a metal film, (9a) (9b
) are the inclined parts of the piezoelectric substrate (fork) end side of the metal films (8a) and (8b), respectively, and (xoa) and (1ab) are the metal film extension parts that are the extension parts of the metal films (sa) and (8b), respectively. be. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A transducer-shaped electrode for surface acoustic wave excitation and a transducer-shaped electrode for surface acoustic wave reception each have a configuration in which strip-shaped electrode fingers connected by pads and arranged in a comb shape are arranged in an interdigital shape on a piezoelectric substrate. In the surface acoustic wave device, at least one of the surface acoustic wave excitation interdigital electrode and the surface acoustic wave reception interdigital electrode is disposed on the piezoelectric substrate near the ends of the interdigital electrodes that are far from the other interdigital electrode. A metal film is provided, each of which is connected to each pad of the interdigital interdigital electrode, one edge of which is close to the electrode fingers connected by each of the pads, and the other edge of each metal film is connected to the electrode finger. What is claimed is: 1. A surface acoustic wave device characterized in that the surface acoustic wave device is formed in a shape consisting of a portion inclined with respect to the surface of the acoustic wave device.