JPH07106911A - Surface acoustic wave resonator/filter - Google Patents

Abstract

PURPOSE:To miniaturize both a surface acoustic wave resonator and a surface acoustic wave filter. CONSTITUTION:A surface acoustic wave resonator contains the input/output electrodes 3 and 4 which are provided on a piezoelectric substrate 1 for excitation of surface acoustic waves. Then a piezoelectric end face 5 which is set in parallel to the forming directions of both electrodes 3 and 4 and has the height (L1) approximately equal to at least the wavelength lambda is formed at a position apart from the center of an electrode finger 3a (4a) formed at the outmost edge of the electrode 3 (4) by a distance (L2) shown by an expression (n+1/2)lambda, where (n) shows an integer and lambda showing the length of the surface acoustic wave respectively.

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 resonator and a surface acoustic wave filter used as a high frequency device.

[0002]

2. Description of the Related Art Surface acoustic wave resonators and surface acoustic wave filters that utilize surface acoustic waves are currently widely used as high frequency devices. In recent years, not only the demand for TVs, VTRs, etc., but also the use thereof in mobile communication fields such as mobile phones and car phones has become popular.
Further, in these mobile communication fields, there is a strong demand for reliability and downsizing of devices, so that the surface acoustic wave resonator and filters using the same are required to have low loss and downsizing. It's coming.

For example, in a multi-electrode type surface acoustic wave filter, in order to reduce insertion loss, a grating reflector is provided in the vicinity of the electrode finger of the input electrode located at the outermost end, and resonance is provided. A similar reflector is also provided in the container to generate a standing wave. FIG. 6 is a schematic perspective view showing a conventional 1-port surface acoustic wave resonator, in which 30 is an input / output electrode and 31 is a reflector. FIG. 7 shows a surface acoustic wave resonator composite type filter using the surface acoustic wave resonator shown in FIG.
2 ... is a reflector.

[0004]

However, in the above grading reflector, there is a limit to miniaturization of the element, and some insertion loss cannot be avoided. Further, in the surface acoustic wave device shown in FIGS. 6 and 7, the number of reflectors is required to be about 100 to 200, and it is difficult to downsize the device.

In view of the above circumstances, it is an object of the present invention to downsize a surface acoustic wave resonator and a surface acoustic wave filter.

[0006]

In order to solve the above-mentioned problems, a surface acoustic wave resonator of the present invention has a surface acoustic wave resonance in which an excitation electrode for exciting a surface acoustic wave is arranged on a piezoelectric substrate. In the container, n is an integer and λ is the wavelength of the surface acoustic wave, and the distance from the center of the electrode finger formed at the outermost end of the excitation electrode is (n + 1/2) λ. Position, parallel to the direction of formation of the excitation electrode,
Further, it is characterized in that an end surface of the piezoelectric body having at least a height approximately equal to the wavelength λ is formed.

Further, the surface acoustic wave filter of the present invention has at least one set of the above surface acoustic wave resonators in which the resonance frequency and the anti-resonance frequency are matched with each other, and one resonator of each set is connected to the signal line. Is provided in series, and the other resonator is provided in parallel with the signal line.

Further, in the surface acoustic wave filter of the present invention, two or more input electrodes and one or more output electrodes for transmitting and receiving surface acoustic waves to and from each other on the piezoelectric substrate are alternately arranged on the same propagation path in an odd number as a whole. In the provided multi-electrode type surface acoustic wave filter, n is an integer, and λ is a wavelength of the surface acoustic wave, from the center of the electrode finger formed at the outermost end of the input electrode located at the outermost end to (n + 1 / 2) A piezoelectric end face that is parallel to the forming direction of the input electrode and has a height at least about the same as the wavelength λ is formed at a position separated by a distance represented by the formula λ. It is characterized by that.

[0009]

According to the above-mentioned first structure, the surface acoustic wave is reflected by the piezoelectric end face formed on the piezoelectric substrate, and this piezoelectric end face is the electrode formed on the outermost end as described above. Since it is formed at a position separated by a distance of (n + 1/2) λ from the center of the finger, the reflected wave resonates. Therefore, the conventional reflector is unnecessary, and the element is downsized by the area of the reflector.

The same applies to the surface acoustic wave filters having the above-described second and third configurations, and the size of the element can be reduced.

[0011]

(Embodiment 1) The present invention will be described below with reference to the drawings showing an embodiment thereof.

FIG. 1 is a schematic perspective view of a one-port surface acoustic wave resonator according to the present invention. In the figure, 1 is LiTa
A piezoelectric substrate made of O ₃ or the like, 3 is an input electrode, and 4 is an output electrode.

When the piezoelectric substrate 1 is made of LiTaO ₃ , the velocity of the surface acoustic wave propagating on the substrate 1 is 36.
413 with ° Y-X board (36 ° rotation Y-cut X-axis propagation)
It is required to be 4 m / s. Therefore, the center frequency is 83
When designing a 6 MHz filter, the wavelength at the center frequency is λ = 4134 m / s / 836 MHz =
Since the ratio between the electrode finger portion and the non-electrode finger portion is 1: 1 in this embodiment, the input / output electrode width and the width of the non-electrode finger portion are λ / 4 = 1.24 ( μm)
And As a result, only surface acoustic waves having frequencies near the center frequency 836 are propagated.

A piezoelectric step portion 2 is formed on the piezoelectric substrate 1. The piezoelectric body end face 5 in the piezoelectric body step portion 2 is separated from the center of the outermost electrode finger 3a (4a) of the input / output electrodes 3 and 4 by a distance L2 represented by the formula (n + 1/2) λ. Is formed in position. The above n is an integer, and λ is the wavelength of the surface acoustic wave. For example, if n is 1 and λ is 4.94 μm, the distance L2 is 7.41 μm.
m.

The end surface 5 of the piezoelectric body is formed in parallel with the forming direction of the input / output electrodes 3 and 4 and has an end surface height L1 of the wavelength λ or more. This is because about 90% of the total energy is included within the depth of one wavelength (λ) from the surface for the propagation of the surface acoustic wave.

Since the surface acoustic wave resonator of this embodiment has the above-mentioned structure, the surface acoustic wave 6 is reflected by the piezoelectric end face 5 formed on the piezoelectric substrate 1, as shown in FIG.
Since the piezoelectric end face 5 is formed at a position separated from the center of the outermost electrode finger by the distance of (n + 1/2) λ as described above, resonance of the reflected wave occurs. As a result, the conventional reflector becomes unnecessary, and the element is downsized by the area of the reflector.

Next, a method for manufacturing the surface acoustic wave resonator will be described.

First, as shown in FIG. 3 (a), LiTa
On the piezoelectric substrate 1 made of O ₃ or the like, aluminum (A
l) is deposited to form the input / output electrode pattern 10. Next, the piezoelectric substrate 1 is processed to form the piezoelectric step portion 2. This processing is based on FIB (Focused Io)
n Beam) device, as shown in FIG.
This is performed by irradiating the piezoelectric substrate 1 with an ion beam. In the above FIB apparatus, the irradiation ions are Ga ⁺ , the acceleration voltage is 25 keV, and the ion current is 2 A / cm ² . For example, if n = 1 and the center frequency is 900 MHz, then λ = 4.6 μm, and the ion beam irradiation position is
(N + 1/2) λ = 2.3 μm from the center of the outermost electrode finger
Position.

Since the piezoelectric body end surface 5 of the piezoelectric body step portion 2 is for reflecting the surface acoustic waves to resonate them, it is necessary to process the surface of the piezoelectric body 5 with high positional accuracy and smooth surface. The processing accuracy of the FIB device is ± 0.
Since it is 1 μm, the forming accuracy of the piezoelectric end face 5 is 2.3 ±.
Although it is 0.1 μm, it can be said that such an error has almost no effect on the resonance due to the reflection of the surface acoustic wave.
This can be confirmed by simulating that the distance between the electrode and the reflector is 0.5λ as 0.48λ to 0.52λ (corresponding to ± 0.1 μm). Further, the surface roughness of the end face can be controlled to 0.1λ = 0.46 μm or less in the FIB device.

After the piezoelectric body step portions 2 are formed on both sides of the piezoelectric body substrate 1 by the ion beam irradiation by the FIB device, both side surfaces of the piezoelectric body substrate 1 are cut by dicing as shown in FIG.

In the above manufacturing method, aluminum (Al) was vapor-deposited and then ion beam processing was performed. However, conversely, aluminum beam (Al) may be vapor-deposited and then Al vapor deposition may be performed. The method requires less effort than the above method. However, it can be said that it is inferior to the above method in terms of ensuring the accuracy of the piezoelectric body end surface 5.

In the above manufacturing method, the piezoelectric substrate 1 is processed by the ion beam. For example, the piezoelectric film is formed on the piezoelectric support substrate by vapor deposition and the piezoelectric step portion is formed by the lift-off method. Alternatively, the formed piezoelectric film may be dry-etched to form the piezoelectric step portion. For forming the piezoelectric film, a CVD method or MBE (Molecular Beam Epita) is used.
The xy) method or the like is used. In addition to the piezoelectric substrate made of LiTaO ₃ or the like, the piezoelectric supporting substrate may be S
A substrate such as i or sapphire is used. Then, when the piezoelectric layer is epitaxially grown on the piezoelectric support substrate to form a film, a piezoelectric end face with a uniform crystal orientation is formed, so that the surface acoustic waves can be reflected with high efficiency.

(Embodiment 2) Another embodiment of the present invention will be described below.

FIG. 4 is a schematic perspective view showing a surface acoustic wave filter using the surface acoustic wave resonator described in the first embodiment. In the figure, 12 and 13 are surface acoustic wave resonators of the first embodiment, of which the resonators 12 and 12 are provided in series with the signal lines 15 and 16 by a bonding wire 14. On the other hand, the resonators 13 and 13 are provided in parallel with the signal line, and one end side is grounded.

Both resonators 12 and 13 have double resonance characteristics, and their impedances have two resonance frequencies of 0 and infinity. Here, the frequency at which the impedance becomes 0 is called the resonance frequency, and the frequency at which the impedance becomes infinite is called the anti-resonance frequency. When the resonance point of the resonator 12 and the anti-resonance point of the resonator 13 coincide with each other, the resonator 12 is in the ON state and the resonator 13 is in the OFF state in the vicinity of the frequency, so that it is in the pass band. on the other hand,
Since the resonator 12 is in the OFF state at the anti-resonance point, an attenuation pole is generated on the high frequency side of the pass band, and the resonator 13 is in the ON state at the resonance point, so that even in the low frequency side of the pass band. An attenuation pole will be generated, and it will function as a bandpass filter.

Since the surface acoustic wave filter having the above-described structure is provided with a plurality of resonators of the first embodiment which do not require the grating reflector as described above, the size can be further reduced.

(Embodiment 3) Another embodiment of the present invention will be described below.

FIG. 5 is a schematic perspective view showing a multi-electrode type surface acoustic wave filter. In the figure, 21 is a piezoelectric support substrate, 22 is a piezoelectric support substrate 2 by a lift-off method.
1 is a piezoelectric film formed with a step portion 2 '. Reference numeral 19 is an input section formed on the piezoelectric film 22, and 20 is an output section. The input section 19 has two or more comb-shaped input electrodes 19a formed thereon, and the output section 20 has one or more comb-shaped output electrodes 2a formed thereon. The comb-shaped input / output electrodes 19a and 20a are alternately arranged on the same propagation path.

The piezoelectric end surface 5'forming the step portion 2'is defined by the formula (n + 1/2) λ from the center of the electrode finger formed at the outermost end of the input electrode 19a located at the outermost end. It is formed at a position separated by the distance (L2) shown. Further, the piezoelectric end surface 5'is provided with the input / output electrodes 19a,
It is formed parallel to the forming direction of 20a and has an end face height L1 of the wavelength λ or more.

Also in the above configuration, as in the first embodiment,
Since the grating reflector is unnecessary, the surface acoustic wave filter can be downsized.

[0031]

As described above, according to the present invention, it is possible to miniaturize the surface acoustic wave resonator and the surface acoustic wave filter.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a one-port surface acoustic wave resonator of the present invention.

FIG. 2 is an enlarged cross-sectional view near a piezoelectric step portion of the present invention.

FIG. 3 is a cross-sectional view showing the method of manufacturing the surface acoustic wave device of the present invention in the order of steps.

FIG. 4 is a schematic perspective view showing a surface acoustic wave resonator composite type filter of the present invention.

FIG. 5 is a schematic perspective view showing a multi-electrode surface acoustic wave filter of the present invention.

FIG. 6 is a schematic perspective view of a conventional 1-port surface acoustic wave resonator.

FIG. 7 is a schematic perspective view showing a conventional surface acoustic wave resonator composite type filter.

[Explanation of symbols]

 1 Piezoelectric Substrate 2 Piezoelectric Step 2'Step 3 Input Electrode 4 Output Electrode 5 Piezoelectric End Face 5'Piezoelectric End Face 6 Surface Acoustic Wave 19 Input 20 Output 21 Piezoelectric Support Substrate 22 Piezoelectric Membrane

Front Page Continuation (72) Inventor Kosuke Takeuchi 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Inventor Kenichi Shibata 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A surface acoustic wave resonator in which an excitation electrode for exciting a surface acoustic wave is arranged on a piezoelectric substrate,
From the center of the electrode finger formed at the outermost end of the excitation electrode to (n + 1), where n is an integer and λ is the wavelength of the surface acoustic wave.
/ 2) A piezoelectric end face that is parallel to the direction in which the excitation electrode is formed and that has a height that is at least about the same as the wavelength λ is formed at a position separated by a distance represented by the formula λ. A surface acoustic wave resonator characterized by the above. 2. A surface acoustic wave resonator according to claim 1, wherein the resonance frequency and the anti-resonance frequency are matched with each other, and one or more sets of the surface acoustic wave resonators are provided in series with respect to a signal line. ,
A surface acoustic wave filter, wherein the other resonator is provided in parallel with a signal line. 3. A multi-electrode type surface acoustic wave in which two or more input electrodes and one or more output electrodes for transmitting and receiving surface acoustic waves to and from each other are alternately arranged on the same propagation path on the piezoelectric substrate in a total number of an odd number. In the filter, n is an integer and λ is the wavelength of the surface acoustic wave, and is expressed by the formula (n + 1/2) λ from the center of the electrode finger formed at the outermost end of the input electrode located at the outermost end. A surface acoustic wave filter characterized in that a piezoelectric end face that is parallel to the formation direction of the input electrode and has a height at least about the same as the wavelength λ is formed at a position separated by a certain distance. .