JP2878671B2 - Surface acoustic wave device and surface acoustic wave filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device constituting a transversal surface acoustic wave filter, and more particularly to a floating electrode between electrode fingers of an interdigital transducer (hereinafter referred to as IDT). The present invention relates to an internal reflection type one-way surface acoustic wave device provided and a surface acoustic wave filter using the one-way surface acoustic wave device.

[0002]

2. Description of the Related Art A transversal type elastic surface of a type which transmits and receives (inputs and outputs) waves propagating in the left and right directions of an IDT electrode using a unidirectional surface acoustic wave device having an IDT electrode disposed on a piezoelectric substrate. In a wave filter, there is basically an insertion loss of 6 dB. Therefore, in order to reduce the insertion loss, various unidirectional surface acoustic wave devices have been conventionally proposed. These unidirectional surface acoustic wave devices can be roughly classified into the following three types: (a) three types of IDT electrode fingers having zero degree, 120 degree and 2 degree, respectively.
A three-phase unidirectional surface acoustic wave device for applying a signal having a phase difference of 40 degrees. (B) A groove type unidirectional surface acoustic wave device in which a meander line is provided by sewing between general IDT electrode fingers and grounded. (C) An aluminum IDT electrode finger is paired with a high-density metal electrode finger (for surface acoustic wave reflection) such as gold to excite the interval between the center of the surface acoustic wave and the center of reflection to be one of the wavelengths of the wave.
/ 8 internally reflected unidirectional surface acoustic wave device. There are three types. However, although the three-phase unidirectional surface acoustic wave device (a) maintains the unidirectionality of wave propagation over a wide frequency range,
The need to overbridge the electrode fingers extending from one of the busbars over the other busbar is extremely difficult to manufacture, which not only increases the manufacturing cost but also increases the complexity of the phaser. However, there is a disadvantage that the Further, the groove type unidirectional surface acoustic wave device (b) has a disadvantage that the total length of the meander line is long in the conventional structure, and the insertion loss of the filter due to the ohmic loss increases. In addition, although the phase shifter is not required for the internally reflected unidirectional surface acoustic wave device (c), it is necessary to separately deposit a gold electrode finger paired with the aluminum electrode finger, which complicates the process. There was a disadvantage.

[0003]

As described above, all of the conventional one-way surface acoustic wave devices are easy to manufacture.
Not all aspects of cost and performance were simultaneously satisfied. For this reason, the filter using the conventional one-way surface acoustic wave device has disadvantages in that the manufacturing process is complicated, the cost is high, and the insertion loss is large.
Therefore, the problem to be solved by the present invention is to solve the above-mentioned drawbacks of the conventional technology, and to produce a surface acoustic wave device that can be manufactured more easily and at lower cost than the conventional one, and a loss loss using the surface acoustic wave device. To provide a surface acoustic wave filter having a small size.

[0004]

According to a first aspect of the present invention, an IDT electrode is disposed on a surface of a piezoelectric substrate to receive or transmit a surface acoustic wave that has excited or propagated a surface acoustic wave. The IDT electrode includes a first positive electrode finger having an electrode finger width of λ / 8 and a second electrode having an electrode finger width of λ / 8, where λ is a wavelength at a basic operating frequency. Positive electrode finger, first short-circuited floating electrode having electrode finger width λ / 8, open floating electrode having electrode finger width λ / 8, second short-circuited floating electrode having electrode finger width λ / 8, electrode Finger width λ /
8 open-type floating electrodes, a first negative electrode finger having an electrode finger width of λ / 8, and a second negative electrode finger having an electrode finger width of λ / 8 are arranged in parallel with a gap width of λ / 8. And a unidirectional converter having, as a half-period electrode pattern, an electrode pattern formed by connecting a first short-circuit type floating electrode and a second short-circuit type floating electrode with a lead electrode. Features. The invention according to a second aspect is characterized in that the open floating electrode fingers constituting the surface acoustic wave device according to the first aspect are connected to each other. The invention according to claim 3 is characterized in that the surface acoustic wave device according to claim 1 or 2 operates at a higher harmonic. According to a fourth aspect of the present invention, a groove-type one-way converter or a one-way converter having different directions depending on the frequency is disposed at the center of the piezoelectric substrate, and has a direction in the center direction on both sides thereof. The present invention relates to a surface acoustic wave filter having a surface acoustic wave device disposed thereon, wherein the surface acoustic wave device receives an acoustic surface wave that has been excited or propagated by arranging an IDT electrode on the surface of a piezoelectric substrate. A first positive electrode finger having an electrode finger width of λ / 8, a second positive electrode finger having an electrode finger width of λ / 8, and a wavelength at a fundamental operating frequency being λ. A first short-circuit type floating electrode having an electrode finger width of λ / 8, and an electrode finger width of λ /
8, an open floating electrode having an electrode finger width of λ / 8, a second floating electrode having an electrode finger width of λ / 8, an open floating electrode having an electrode finger width of λ / 8, and a first negative electrode finger having an electrode finger width of λ / 8. , And a second negative electrode finger having an electrode finger width of λ / 8 are arranged side by side with a gap width of λ / 8, and a first short-circuit type floating electrode and a second short-circuit type floating electrode are connected to each other. It is a unidirectional converter having an electrode pattern interconnected by lead electrodes as an electrode pattern for a half cycle.

[0005] The invention according to claim 5 relates to a surface acoustic wave filter in which a plurality of surface acoustic wave devices having different frequency characteristics are arranged on the same piezoelectric substrate. A device for arranging an IDT electrode on a surface of a piezoelectric substrate to receive a surface acoustic wave excited or propagated by the surface acoustic wave;
Assuming that the wavelength at the basic operating frequency is λ, the DT electrode sequentially has a first positive electrode finger having an electrode finger width of λ / 8, a second positive electrode finger having an electrode finger width of λ / 8, and an electrode finger having a width of λ / 8. First short-circuit type floating electrode, open type floating electrode having electrode finger width λ / 8, electrode finger width λ /
8, a second floating electrode having an electrode finger width λ / 8, a first floating electrode having an electrode finger width λ / 8, and a second negative electrode having an electrode finger width λ / 8. Each of the electrode fingers has a gap width λ /
And a half-period electrode pattern in which a first short-circuit type floating electrode and a second short-circuit type floating electrode are connected to each other by a lead electrode. It is characterized by being a sex converter. According to a sixth aspect of the present invention, the open floating electrode fingers constituting the surface acoustic wave filter according to the fourth or fifth aspect are connected to each other. The invention according to claim 7 is characterized in that the surface acoustic wave filter according to claim 4 or 5 operates at higher harmonics.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. Before the description of the embodiments, the basic concept that led to the present invention will be described in order to facilitate understanding of the present invention. A general positive / negative IDT electrode is provided on a piezoelectric substrate, the interval between each electrode finger is set to λ / 2, and the frequency f =
When an AC electric field of v / λ (where v is the propagation speed of the wave to be excited) is applied, a surface acoustic wave substantially equal to λ is excited, and the excited surface acoustic wave moves along the substrate surface along the IDT electrode array. It is well known that the light propagates equally to the left and right. Here, as shown in FIG. 2, positive and negative IDT electrodes 2 and 3 are provided on a piezoelectric substrate (not shown), and widths L1 of IDT electrode fingers 2a and 3b extending from the IDT electrodes 2a and 3b and width L2 of a gap between these electrode fingers are provided. Is assumed to be, for example, λ / 8, and even if the floating electrode finger 4a having a width L1 electrically disconnected from any part is provided between the electrode finger gaps, the electrode is excited by the IDT electrode finger because of the symmetry of the electrode configuration. The reflection of the generated wave by the floating electrodes 4a, 4a is made equal to the left and right, so that the wave propagation of the device having such an electrode configuration is also equal to the left and right.
Therefore, if the symmetry of the electrode array in FIG. 2 is broken, the symmetry between the excitation wave and the reflected wave will be broken, and the wave energy propagating to one of the left and right sides of the IDT electrode array will be large.

FIG. 1 is an electrode configuration diagram showing an example of an embodiment of a surface acoustic wave device according to the present invention constructed on the basis of the above-described concept. An IDT electrode 30 is arranged from the left end to the right end in the figure. It is assumed that the width of each of the constituent electrode fingers is set in order. In this example, the wavelength at the basic operating frequency is λ, and the first positive electrode finger 9 and the second positive electrode finger 10 having the electrode finger width λ / 8 connected to the positive electrode 3 are sequentially connected to the positive electrode 3. λ / 8 first short-circuit type floating electrode 11, electrode finger width λ / 8 open type floating electrode 14, electrode finger width λ / 8 second
, An open floating electrode 15 having an electrode finger width λ / 8, and an electrode finger width λ / 8 connected to the negative electrode 2.
The first negative electrode finger 16 and the second negative electrode finger 17 are arranged side by side on the piezoelectric substrate 1 with a gap width λ / 8 therebetween, and the first short-circuit type floating electrode 11 and the second The short-circuit type floating electrode 12 and the lead electrode 13 are connected to each other.
As a result, the electrode finger 9 of the positive electrode 3 and the electrode finger 17 of the negative electrode 2
An electrode pattern having a gap of approximately λ / 8 is formed between them, and a unidirectional converter structure having a half cycle of the electrode pattern is obtained. In such a structure, the excited wave energy propagates strongly in one direction. In this case, the electrode finger width and the gap between the electrode fingers do not necessarily have to be exactly these values, and may be any value as long as the phase of each wave becomes the same phase at the center frequency. Given the width, ±
A range of 80% is appropriate. In addition, an open floating electrode finger 1
By having a structure in which 4 and 15 are connected to each other, a surface acoustic wave device as a one-way converter having a large reflection coefficient can be obtained. The surface acoustic wave device can operate at any high frequency twice, three times,..., N times the basic operating frequency f0.

FIG. 3 is a schematic perspective view showing an example of an embodiment of a surface acoustic wave filter according to the present invention. As shown, the surface acoustic wave filter has center frequencies f1 and f2.
On both sides of the unidirectional converter 23 having different directions,
The surface acoustic wave devices 24 and 25 having the structure shown in FIG. 1 are arranged. The center frequency is not limited to two types of f1 and f2, but may be three or more types (f1, f2 f3,...). In the surface acoustic wave filter, by connecting the open floating electrode fingers (14, 15) of the surface acoustic wave devices 24, 25 to each other, a surface acoustic wave filter having a large reflection coefficient can be obtained. Also, the surface acoustic wave filter is twice, three times,..., N of the basic operating frequency f0.
It can operate at any high frequency. With the configuration described above, the surface acoustic wave device according to the present embodiment has an electrode finger extending from one of three bus bars as in the three-phase one-way surface acoustic wave device shown as a conventional technique. There is no need to overbridge on another bus bar, and it is not necessary to separately deposit a gold electrode finger paired with this aluminum electrode finger in addition to the aluminum electrode finger as in a conventional internal reflection unidirectional surface acoustic wave device. No, because electrode formation is possible with only one evaporation, exposure, etching process,
It can be manufactured simply and at low cost. In addition, the filter using the above surface acoustic wave device has an extraordinary factor that causes insertion loss, such as ohmic loss as in the filter using the groove type unidirectional surface acoustic wave device described in the related art. However, since the unidirectional converter inherently has little ripple based on TTE (triple transit echo), the insertion loss is extremely low. FIG.
9 shows the measurement results of the frequency characteristics in the electrode configuration shown in FIG. From this measurement result, the center frequency 41
It can be seen that a good value of 4.1 dB insertion loss is obtained at 5 MHz. In addition, in the example of FIG.
Is a negative electrode and the upper electrode 3 is a positive electrode, but it goes without saying that the lower electrode 2 may be a positive electrode and the upper electrode 3 may be a negative electrode.

[0009]

As described above, according to the present invention, a surface acoustic wave device which can be manufactured more easily and at lower cost than before, and a surface acoustic wave filter using this surface acoustic wave device and having a small insertion loss. Can be provided.

[Brief description of the drawings]

FIG. 1A is a plan view of an electrode configuration showing an embodiment of a surface acoustic wave device according to the present invention, and FIG. 1B is a cross-sectional view.

FIG. 2 is a plan view used for describing a process leading to the present invention.

FIG. 3 is a schematic perspective view showing an embodiment of a surface acoustic wave filter according to the present invention.

FIG. 4 is a diagram showing measurement results of frequency characteristics in the electrode configuration shown in FIG.

[Explanation of symbols]

Reference Signs List 1 piezoelectric substrate, 2 negative electrode, 3 positive electrode, 9 first positive electrode finger, 10 second positive electrode finger, 11 first short-circuit type floating electrode, 12 second short-type floating electrode, 13 lead Electrodes, 14 open floating electrodes, 15 open floating electrodes, 16 first negative electrode fingers, 17 second negative electrode fingers,
23 one-way transducer, 24 surface acoustic wave device, 2
5 Surface acoustic wave device, 30 IDT electrodes.

Claims (7)

(57) [Claims] 1. An interdigital digital camera on a surface of a piezoelectric substrate.
In a surface acoustic wave device in which a transducer electrode is arranged to receive a surface acoustic wave that excites or propagates a surface acoustic wave, the interdigital transducer electrode has a wavelength at a basic operating frequency as λ and an electrode finger width λ in order. / 8
A first positive electrode finger, a second positive electrode finger having an electrode finger width of λ / 8,
First short-circuit type floating electrode having electrode finger width λ / 8, electrode finger width λ
/ 8 open-type floating electrode, second short-circuit type floating electrode with electrode finger width λ / 8, open-type floating electrode with electrode finger width λ / 8, first negative electrode with electrode finger width λ / 8 A finger and a second negative electrode finger having an electrode finger width of λ / 8 are arranged in parallel with a gap width of λ / 8, and a first short-circuit type floating electrode and a second short-circuit type floating electrode are provided. A surface acoustic wave device comprising a unidirectional transducer having an electrode pattern formed by mutually connecting the electrode patterns by lead electrodes as an electrode pattern for a half cycle. 2. The surface acoustic wave device according to claim 1, wherein said floating floating electrode fingers are connected to each other. 3. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is operated with a harmonic. 4. A groove type one-way transducer or one-way transducer having different directions depending on the frequency is arranged at the center of the piezoelectric substrate, and a surface acoustic wave device having a directionality in the center direction is provided on both sides thereof. In the surface acoustic wave filter arranged, the surface acoustic wave device is a device that arranges an interdigital transducer electrode on a surface of a piezoelectric substrate and receives a surface acoustic wave that excites or propagates the surface acoustic wave. The interdigital transducer electrode has an electrode finger width of λ / 8, where λ is a wavelength at a basic operating frequency.
A first positive electrode finger, a second positive electrode finger having an electrode finger width of λ / 8,
First short-circuit type floating electrode having electrode finger width λ / 8, electrode finger width λ
/ 8 open-type floating electrode, second short-circuit type floating electrode with electrode finger width λ / 8, open-type floating electrode with electrode finger width λ / 8, first negative electrode with electrode finger width λ / 8 A finger and a second negative electrode finger having an electrode finger width of λ / 8 are arranged in parallel with a gap width of λ / 8, and a first short-circuit type floating electrode and a second short-circuit type floating electrode are provided. A surface acoustic wave filter having a one-way converter having an electrode pattern formed by mutually connecting the electrode patterns with lead electrodes for a half cycle. 5. A surface acoustic wave filter in which a plurality of surface acoustic wave devices having different frequency characteristics are arranged on the same piezoelectric substrate, wherein the surface acoustic wave device has an interdigital transducer electrode on a surface of the piezoelectric substrate. And a device for receiving a surface acoustic wave that has excited or propagated a surface acoustic wave, wherein the interdigital transducer electrode has a wavelength at a basic operating frequency as λ and an electrode finger width λ / 8 in order.
A first positive electrode finger, a second positive electrode finger having an electrode finger width of λ / 8,
First short-circuit type floating electrode having electrode finger width λ / 8, electrode finger width λ
/ 8 open-type floating electrode, second short-circuit type floating electrode with electrode finger width λ / 8, open-type floating electrode with electrode finger width λ / 8, first negative electrode with electrode finger width λ / 8 A finger and a second negative electrode finger having an electrode finger width of λ / 8 are arranged in parallel with a gap width of λ / 8, and a first short-circuit type floating electrode and a second short-circuit type floating electrode are provided. A surface acoustic wave filter having a one-way converter having an electrode pattern formed by mutually connecting the electrode patterns with lead electrodes for a half cycle. 6. The surface acoustic wave filter according to claim 4, wherein said floating electrodes are connected to each other. 7. The surface acoustic wave filter according to claim 4, wherein the surface acoustic wave filter is operated at a higher harmonic.