JPS6114194Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a surface acoustic wave device using unidirectional interdigital electrodes using a 90° phase shifter, and is particularly useful when a piezoelectric substrate is installed inside a plug-in type envelope, etc. Regarding the structure of the optimal electrode pattern.

When surface acoustic wave devices use normal interdigital electrodes, they are bidirectional, so there is a minimum
6dB insertion loss occurs. In order to reduce this insertion loss, a unidirectional interdigital electrode using a 90° phase shifter as shown in FIG. 1 has been proposed. The operation of this electrode will be described in detail in conjunction with the description of the embodiments, but it should be noted that the hot electrode lead-out portions 2 and 3 of this electrode are led out from the same side of the piezoelectric body 1.

On the other hand, Fig. 2 shows a state in which an element using the electrodes shown in Fig. 1 for input is mounted inside a plug-in type enclosure. In the figure, 5 is a bottom plate forming a part of the metal case, 6 and 7 are external input terminals, 8 and 9 are external output terminals, and 10 is an external earth terminal.
Only the earth terminal 10 is electrically connected to the case 5. These terminals 6, 7, 8, 9 and 10 are arranged circumferentially. One of the hot electrode lead portions 2 of the input electrode is connected to the terminal 6, and the earth electrode lead portion 4 is connected to the case 5 by a thin lead wire. The other hot electrode lead portion 3 is also connected to the terminal 7 by a thin lead wire, but since the hot electrode lead portion 3 and the terminal 7 are located on either side of the electrode, the thin lead wire crosses the electrode. As a result, there is a risk that fingers of the electrodes that cannot be connected will be short-circuited by the thin lead wire that crosses the electrode,
Another drawback is that the long thin lead wires increase stray capacitance and inductance.
The package is not limited to the plug-in type, and a pair of external terminals for input or output are arranged on both sides of the device to be mounted. When a package is used, the above-mentioned disadvantages always occur.
For convenience of explanation, the output electrodes are omitted.

The present invention was developed in view of the conventional situation described above, and allows an element using a unidirectional interdigital electrode using a 90° phase shifter to be installed in a plug-in type envelope without any hindrance. The gist of this is a surface acoustic wave device in which unidirectional interdigital electrodes using a 90° phase shifter are separated via a common electrode provided in the direction of surface acoustic wave propagation.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In Fig. 3, 11 is a piezoelectric material, which is usually
It is composed of materials such as piezoelectric ceramics such as PZT, piezoelectric thin films such as Zno, and single crystals such as LiNbO ₃ . Unidirectional interdigital electrodes are formed on the piezoelectric body 11 by patterning techniques such as photoetching. In this interdigital electrode, the phase of the surface wave excited from a pair of electrodes E1 and E2 is λ ₀ /
The electrode E1 is shifted by 4 in the direction of surface wave propagation.
E2 is arranged, and each electrode E1, E2
Common electrode 1 with earth potential provided in the direction of surface wave propagation
4 in the finger direction.
Here, λ ₀ is the wavelength of the surface acoustic wave at the center frequency.

In other words, 12 is λ in order to shift the phase of the surface waves excited from both electrodes E1 and E2 by λ ₀ /4.
It is a ground electrode with a width of _0/2 , and a plurality of ground side fingers 13 are arranged on both sides of this ground electrode 12 (in the left-right direction in the figure) with a center-to-center distance of λ ₀ .
are arranged sequentially. The electrode width of each finger 13 is λ ₀ /4. These fingers 13 are connected to each other by a common electrode 14 at a ground potential that extends near the center of each finger 13 in the surface wave propagation direction. Hot-side fingers 15 are inserted between the adjacent fingers 13, isolated from the common electrode 14, and on both upper and lower sides thereof. The distance between fingers 15 is λ ₀
The electrode width is /4. The finger 15 located on the left side of the earth electrode 12 connects to common parts 16 and 1 on the upper and lower sides of the common electrode 14, respectively.
7 is connected. These common parts 16, 17
are connected at the outermost finger 15a.
Further, the finger 15 located on the right side is connected to the finger 15 on the opposite side through common portions 18 and 19 on the upper and lower sides of the common electrode 14, respectively. These common parts 18 and 19 are connected by the outermost finger 15b. Earth electrode 1
The fingers 13 and 15 located on the left side of 2 constitute a first interdigital electrode E1, and the fingers 13 and 15 located on the right side constitute a second interdigital electrode E2. The first and second electrodes E1 and E2 have a λ ₀ /
By setting the distance between the centers of the fingers on both sides of the ground electrode 12 to (1+1/4)λ ₀ , the ground electrode 12 has a width of λ
They are separated by _0/4 . 20 is a first hot electrode lead-out part connected to the common part 16;
Reference numeral 1 denotes a second hot electrode lead-out portion connected to the common portion 19. The lead-out parts 20 and 21 may be connected to the common parts 17 and 18, respectively, and in short, a pair of hot electrode lead-out parts 20 and 21 may be arranged on opposite sides of the electrode. 22 is earth electrode 1
This is the ground electrode lead-out part connected to 2. Connection with an external circuit in this embodiment can be made by connecting a 90° phase shifter between the two hot electrode lead-out portions 20 and 21, as in the case of FIG.

Next, the operation when this embodiment is used for input will be described. The surface waves excited by the electrodes E1 and E2 propagate in both left and right directions. Focusing on the surface waves propagating to the right, electrode E
The surface wave A due to the electrode E1 has a phase lead of λ ₀ /4 (π/2) with respect to the surface wave C due to the electrode E1. On the other hand, regarding the surface waves to the left, the surface waves B caused by the electrode E2 are λ ₀ /
The phase is delayed by 4 (π/2). Further, regarding the signal that excites the surface wave, the signal applied to the electrode E2 is delayed by π/2 with respect to the signal applied to the electrode E1. Therefore, surface waves A and C become in-phase waves and strengthen each other, and surface waves B and D
The wave becomes a wave with the opposite phase and cancels out. As a result, the surface waves propagate only to the right, making them unidirectional.

The above also applies to the lower part of the common electrode 14, and also to the one shown in FIG. In other words, compared to the conventional example shown in FIG. 1, this example has almost the same characteristics, but
The difference is that the hot electrode lead-out portions 20 and 21 can be arranged on opposite sides of the interdigital electrode.

FIG. 4 is a plan view showing this embodiment installed in a plug-in type envelope. Since the description of the envelope is the same as in the case of FIG. 2, the same reference numerals will be used and the description will be omitted. The lead-out part 20 is connected to the terminal 6, the lead-out part 21 is connected to the terminal 7, and the lead-out part 22 is connected to the case 5 by thin lead wires, and none of the thin lead wires straddles the electrode.

In the above embodiment, the electrodes obtained can be used for both input and output, and the electrode width of each finger is not limited to λ ₀ /4, but may be narrower than λ 0 /4, and the fingers may be of a split type. may be configured. Moreover, the ground electrode 12 has a diameter of λ ₀ /2
It may be made narrower or may be deleted in some cases. Furthermore, the outermost fingers 15a, 15b
It is preferable to form the fingers wider than the other fingers in order to prevent voltage supply from becoming impossible due to cutting of the electrodes. Furthermore, the electrode pattern is not limited to the regular type, and may be weighted in various ways.

In particular, as a counterpart electrode of the electrode according to the present invention,
When using a two-stage electrode configured using an even-odd design method to obtain arbitrary frequency characteristics and phase characteristics, there is no loss due to the two-stage configuration.
The present invention becomes even more effective.

As explained above, according to the present invention, there is no need to attach a thin lead wire across the interdigital electrode, unnecessary contact between electrode fingers due to the thin lead wire during use is eliminated, and floating due to the thin lead wire being drawn around is eliminated. Capacitance and inductance due to the thin wire itself are reduced, and the connection (bonding process) of the lead thin wire becomes easier.

[Brief explanation of the drawing]

Figure 1 shows a conventional surface acoustic wave device, Figure 2 shows a conventional surface acoustic wave device.
The figure shows the device of FIG. 1 installed in an envelope, FIG. 3 shows an embodiment of the surface acoustic wave device according to the present invention, and FIG. 4 shows the device of this embodiment installed in an envelope. It is a diagram showing a state where the interior is installed.

Claims (1)

[Claims for Utility Model Registration] An input-side interdigital electrode that excites surface acoustic waves in cooperation with a piezoelectric body, and an output-side interdigital electrode that also receives surface acoustic waves, and at least one of these is provided. The interdigital electrodes of the excitation or reception surface waves are mutually λ
It consists of a pair of electrode parts placed close to each other along the surface acoustic wave propagation direction with a ground electrode between them so that the phase shift is _0/4 , and a phase shift of π/2 is applied to these electrode parts. In a surface acoustic wave device for supplying or extracting an electrical signal, an interdigital electrode constituted by the pair of electrode portions is provided with a common electrode continuous to the ground electrode, which is provided in the surface acoustic wave propagation direction. separated through
A surface acoustic wave device characterized in that hot side fingers of separated electrode portions on both sides are interconnected by an outermost finger. λ ₀ : Wavelength of surface wave at center frequency