JP2001345671A - Piezoelectric vibrator, piezoelectric filter, and mobile communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric vibrator and a piezoelectric filter that can suppress spurious waves and operate in high frequencies. SOLUTION: On a piezoelectric substrate 11, minimization is readily achieved by cutting an element in a shearing direction of a crystal. To avoid coupling on with spurious waves, a width-thickness ratio, which is conventionally set at 1.5 to 2.0, is set at 2 to 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a piezoelectric vibrator and a piezoelectric filter, and a mobile communication device including the same.

[0002]

2. Description of the Related Art In recent years, with the increase in the speed of information processing terminals and the digitization of communication, there has been a strong demand for small and high-frequency vibrators and small and wide-band intermediate frequency filters. Conventionally, energy-trapping piezoelectric vibrators and filters have been used for these vibrators and filters.
Further, there is a demand for a smaller and wider band. Quartz filters have been most widely used as energy trapping type piezoelectric filters, but when using quartz, it is difficult to construct a filter with a wide band because the electro-mechanical coupling coefficient of the material is small. It is.

For these purposes, piezoelectric single crystals and piezoelectric ceramics having a large electro-mechanical coupling coefficient are used. Among the piezoelectric single crystals, an X-cut LiTaO ₃ single crystal having a high vibration Q and excellent temperature characteristics is most often used.

[0004] LiTaO ₃ single crystal shows large piezoelectricity and is suitable for a wide band filter. For this, a thickness shear vibration having relatively small spurious is used, but it is difficult to design the element, and the spurious tends to be large.

A thickness-sliding piezoelectric vibrator using an X plate of LiTaO ₃ single crystal has the lowest resonance impedance when cut out in a direction of −50 ° ± 2 ° from the Y axis, and this direction is defined as a vibration displacement direction. ing. Such conventional LiT
FIG. 4 is a plan view showing an example of the aO ₃ piezoelectric vibrator.

Referring to FIG. 4, a conventional piezoelectric vibrator 1 comprises:
A piezoelectric substrate 2 made of LiTaO _3, and a pair of excitation electrodes 3 a and 3 b formed on one main surface and the other main surface of the piezoelectric substrate 2.
And In FIG. 4, the illustration of the extraction electrode is omitted. As shown in FIG. 4, in a conventional LiTaO ₃ vibrator, a vibrator in which an element is cut out to be long in the vibration displacement direction of thickness-shear vibration and an excitation electrode 3 is formed over the entire width of the piezoelectric substrate 2 is generally used. Was.

[0007] In order to avoid unnecessary vibrations related to the width, these vibrators need to be cut so that the width is several times the thickness. Since the width of the element is proportional to the thickness, the element becomes narrower as the thickness becomes thinner, that is, as the resonance frequency becomes higher. Therefore, if the cutting direction is significantly different from the cleavage direction of the crystal, when cutting at a narrow pitch, as shown in FIG. 4, cracks, cracks, and chippings 4 occur in the cleavage direction of the crystal, and the element is easily broken. There is a limit to subdivision. Further, if chipping occurs on the cut end face, this causes spuriousness. Therefore, it has been difficult to form a high-precision vibrator or filter operating at a high frequency.

For this reason, a piezoelectric vibrator using a piezoelectric substrate cleaved in the -57 ° direction from the Y axis is disclosed in Japanese Patent Laid-Open No. 6-30309.
No. 0 proposes this. Since the LiTaO ₃ single crystal X plate has a cleavage plane in the −57 ° direction from the Y axis, cutting along the cleavage plane can improve workability.

[0009]

However, even when a piezoelectric substrate cleaved in the -57 ° direction from the Y axis is used,
There is a problem that spurious characteristic of the element shape is apt to occur. Further, if the vibrator cut in the cleavage direction is not used in a region where the ratio of the thickness to the width (W / H) of the element is as extremely small as 1.5 to 2.0, spurious is generated in the band, and There was a problem that it was not possible to obtain the proper characteristics.

[0010] In order to solve the above problems, an object of the present invention is to provide a piezoelectric vibrator and a piezoelectric filter capable of suppressing unnecessary spurious components and increasing the frequency.

[0011]

In order to achieve the above object, a piezoelectric vibrator of the present invention comprises a piezoelectric substrate made of LiTaO ₃ single crystal, a first main surface of the piezoelectric substrate, and the first main surface. A pair of excitation electrodes formed on a second main surface facing the third main surface, and a third main surface of the piezoelectric substrate and a fourth main surface facing the third main surface. Is a plane substantially parallel to the cleavage plane of the LiTaO3 single crystal, and the thickness-to-width ratio (W / H) of the piezoelectric vibrator is 2-3.
It is characterized by being. With the above configuration, the device cut in the cleavage direction that is easy to process is a device that is wider than the device cut in the conventional cleavage direction,
An element having good characteristics can be manufactured.

In the above piezoelectric vibrator, the piezoelectric substrate is made of Li
An X plate of TaO ₃ single crystal, wherein the third main surface and the fourth main surface are at −57 ° ± 1 from the Y axis of the piezoelectric substrate.
It is preferable that the surface is ゜. According to the above configuration, a piezoelectric vibrator in which chipping during production is less likely to occur and spurs are particularly small can be obtained.

In the above-described piezoelectric vibrator, it is preferable that the third and fourth main surfaces of the piezoelectric substrate are surfaces cleaved by laser cutting. With the above configuration,
Since the occurrence of chipping and the increase in the surface roughness of the element end face can be prevented, a piezoelectric vibrator having good element characteristics can be obtained.

A piezoelectric filter according to the present invention includes a piezoelectric substrate made of LiTaO ₃ single crystal, an input electrode and an output electrode formed on a first main surface of the piezoelectric substrate, and a first electrode facing the first main surface. And a ground electrode formed on the second main surface of the piezoelectric substrate, wherein the third main surface of the piezoelectric substrate and a fourth main surface facing the third main surface are formed of the Li filter.
A plane substantially parallel to the cleavage plane of the TaO ₃ single crystal, wherein the ratio of the thickness to the width of the piezoelectric filter is 2 to 3. According to the above-described piezoelectric filter, a piezoelectric filter which is a wider element than the conventional one, can suppress unnecessary spurious components, and can operate at a high frequency can be obtained.

In the above piezoelectric filter, the piezoelectric substrate is L
an X plate of iTaO ₃ single crystal, wherein the third main surface and the fourth main surface are at −57 ° ±± with respect to the Y axis of the piezoelectric substrate.
Preferably, the plane is 1 °. According to the above-described configuration, a piezoelectric filter in which chipping hardly occurs at the time of manufacturing and spurious is particularly small can be obtained.

In the above-described piezoelectric filter, it is preferable that the third and fourth main surfaces of the piezoelectric substrate are surfaces cleaved by laser cutting. According to the above configuration, generation of chipping and increase in surface roughness of the cleavage plane can be prevented, so that a piezoelectric filter having good element characteristics can be obtained.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 An example of a piezoelectric vibrator will be described as a piezoelectric element according to Embodiment 1 of the present invention.
FIG. 1 shows a perspective view of the piezoelectric vibrator 10 of the first embodiment. FIG. 1 also shows the direction of the crystal axis of the piezoelectric substrate 10.

Referring to FIG. 1, piezoelectric vibrator 10 includes a pair of excitation electrodes 12a and 12b formed on piezoelectric vibrator 10. The excitation electrodes 12a and 12b have
Although not shown, the extraction electrodes are respectively connected. Note that the extraction electrode may be formed over the entire width of the piezoelectric substrate 11 as shown in FIG.

The excitation electrode 12a is formed on the first main surface 11a of the piezoelectric substrate 10, and the excitation electrode 12b is
Is formed on the second main surface 11b opposite to the main surface 11a. The excitation electrode 12a and the excitation electrode 12b are formed approximately symmetrically and substantially symmetrically with the piezoelectric substrate 11 interposed therebetween. That is, the excitation electrode 12a is formed at a position facing the excitation electrode 12b.

The piezoelectric substrate 11 is made of a single crystal of LiTaO ₃ X.
It is a board. (Including those cut by a plane inclined several degrees from the X plate. The same applies to the following embodiments.)
First main surface 11a and second main surface 11 of piezoelectric substrate 11
b is an X cut plane and a −X cut plane, respectively. In addition, of the principal surfaces of the piezoelectric substrate 11,
The fourth main surface 11d opposed to the main surface 11c and the third main surface 11c is a plane substantially parallel to the cleavage plane of the LiTaO ₃ single crystal.

Specifically, for example, the third main surface 11c
And the fourth main surface 11d is a piezoelectric substrate 11 (LiTaO
(X plate ₃ ) is preferably −57 ° ± 1 ° from the Y axis. That is, the third main surface 11c and the piezoelectric substrate 11
Is preferably −57 ° ± 1 °. Note that the cleavage plane of the LiTaO ₃ single crystal is a plane substantially at −57 ° from the Y axis, but if the deviation is about ± 1 °, chipping at the time of cutting can be made sufficiently small (in the following embodiment, Is the same).

The thickness of the piezoelectric substrate 11 is determined by the resonance frequency. For example, to obtain a resonance frequency of about 40 MHz, the thickness becomes about 50 μm and the length becomes about 1.0 μm.
mm (about 20 times the thickness) and a width of about 125 μm (2.5 times the thickness, W · H = 2.5). This range is preferably in the range of 2.0 to 3.0.
Note that the third main surface 11c and the fourth main surface 11d are preferably surfaces cleaved by a laser in order to minimize chipping.

In the conventional LiTaO ₃ vibrator, when the width of the piezoelectric substrate is cut to around 100 μm, remarkable chipping occurs on the end face or the element itself is cracked. there were. Further, even when the element can be manufactured, the surface roughness of the end face affects the characteristics of the vibrator, and the production of a vibrator of about 30 MHz is the limit.

However, in the piezoelectric vibrator 10 of the present invention, since the cutting direction of the piezoelectric substrate 11 and the cleavage direction of the crystal substantially coincide with each other, the substrate can be divided more accurately and the surface roughness of the end face is minimized. You. For this reason, the piezoelectric vibrator 10 of the present invention
According to this, it is easy to increase the frequency of the element and the production yield is improved. For this reason, it is difficult to excite unnecessary vibrations, and a piezoelectric vibrator that does not generate large spurious components can be obtained.

By optimizing the ratio of the width and the thickness of the element at this time, the spurious is reduced. In the region where the ratio of the width and the thickness of the element is 2 to 3, the spurious is not in the band, and is separated from the resonance. Thus, a piezoelectric vibrator having good characteristics was obtained in such a manner that the piezoelectric vibrator slightly existed on the low frequency side and the high frequency side. Further, if the device is manufactured in a region having an element width of 2 or less, it becomes difficult to manufacture a high-frequency device (thin thickness). Conversely, in the region where the ratio of the thickness to the width of the element is 2 or more, the distance between the spurious on the low frequency side and the high frequency side approaches the bandwidth or less, and there is no region where the spurious does not enter the band. . As can be seen from the figure, the relationship between the thickness and the width of the element is 2 to
It can be seen that by setting the value of 3, a piezoelectric vibrator having good characteristics in which the band of the spurious and the main vibration caused by the width is sufficiently separated.

An example of a method for manufacturing the piezoelectric vibrator 10 shown in the first embodiment will be described below. FIGS. 2A to 2C are plan views of each step. FIG. 2 (A)
FIGS. 2D to 2F are cross-sectional views taken along line AA ′ of FIG.

First, as shown in FIGS. 2A and 2D, a 50 μm thick piezoelectric substrate 11 serving as the piezoelectric substrate 11 is formed.
Are formed such that the parallelism of the opposing main surfaces is good. The outer size of the piezoelectric substrate 11 at this time is selected according to the substrate thickness. Generally, the thickness of the piezoelectric substrate 11 is 5
In the case of about 0 μm, the size of the substrate is preferably set to 2 inches or less in consideration of the yield. With this size, a thin plate of about 50 μm can be handled.

Next, as shown in FIGS. 2B and 2E, the excitation electrode 12 is provided on one main surface and the other main surface of the piezoelectric substrate 11.
A metal film to be a and 12b is formed. FIG. 2 shows a case where the lead line is formed over the entire width of the element in the width direction.

Finally, as shown in FIGS. 2C and 2F, by cutting the piezoelectric substrate 11 in a direction parallel to the cleavage plane of the piezoelectric substrate 11 (the direction of the dotted line in the figure), the piezoelectric vibration is reduced. The child is obtained.

In the step shown in FIG. 2C, it is preferable to use excimer laser for cutting the piezoelectric substrate 11. Excimer lasers have short wavelengths and allow for high precision cutting. By using this technique,
Unlike cutting with a normal dicing saw or diamond cutter, chipping of an end face and deterioration of surface roughness can be prevented, and deterioration of element characteristics can be prevented. Cracks caused by heat are resolved by taking the cutting direction in the cleavage direction.

In addition, by using laser cutting in which a stress (thermoelastic force) is selectively grown in the cleavage direction by heating with a laser and the latest gas cooling, there is no cutting margin, little chipping, and almost material cutting. 100% can be used as elements.

Further, the piezoelectric vibrator of the present invention, in which the cleavage direction and the division direction match, is also suitable for mechanical processing. Specific examples include ultrasonic processing, sand blasting and processing. All of these processes are difficult to process unless the width is at least twice as large as the thickness, but the area of the present invention has a large ratio (thickness) to the thickness as compared with the range that was conventionally optimal. This method is suitable for this method.

Embodiment 2 In Embodiment 2, an example of a dual mode piezoelectric filter will be described for the piezoelectric filter of the present invention. The same parts as those of the piezoelectric vibrator 10 of the first embodiment will not be described again. Also,
Leader lines are omitted.

FIG. 3 is a plan view of the piezoelectric filter 40 according to the second embodiment. FIG. 3 shows the piezoelectric substrate 4
The direction of the 0 crystal axis is also shown.

In the figure, a piezoelectric filter 40 according to the second embodiment includes a piezoelectric substrate 11 and a first main surface 1 of the piezoelectric substrate 11.
1a, an input electrode 41 and an output electrode 42,
A ground electrode (not shown) formed on the second main surface opposite to the first main surface. The ground electrode is formed on the second main surface at a position corresponding to the input electrode 41 and the output electrode. The piezoelectric filter 40 functions as a band-pass filter that passes a certain frequency band.

The piezoelectric substrate 40 is the same as that described in the first embodiment, and is an X plate of LiTaO ₃ single crystal. The first main surface 11a and the second main surface 11b of the piezoelectric substrate 40 are an X-cut surface and a −X-cut surface, respectively. Further, among the main surfaces of the piezoelectric substrate 11, the third main surface 11c, which is a cut surface, and the fourth main surface 11d facing the third main surface 11c are substantially parallel to the cleavage plane of the LiTaO ₃ single crystal. Plane. Specifically, for example, the third main surface 1
1c and the fourth principal surface 11d are provided on the piezoelectric substrate 11 (LiT
It is preferably a cleavage plane of (aO ₃ X plate). That is, the angle α between the third main surface 11c and the Y axis of the piezoelectric substrate 11 is preferably −57 ° ± 1 °.

As the piezoelectric substrate 11 having a length of 2.5 mm, a width of 0.125 mm, and a thickness of 50 μm cleaved in the −57 ° direction from the Y axis, a center frequency of 4
A bandpass filter of about 0 MHz is obtained.

In the piezoelectric filter 40 of the present invention, since the cutting direction of the piezoelectric substrate 11 and the cleavage direction of the crystal substantially coincide with each other,
The division can be performed more accurately, and the surface roughness of the end face is minimized. Therefore, according to the piezoelectric filter 40,
A piezoelectric filter that is easy to manufacture, has a low insertion loss, and can easily operate at a high frequency can be obtained.

The piezoelectric filter 40 of the third embodiment
Can be manufactured by a method similar to the method described with reference to FIG.

Although the embodiments of the present invention have been described with reference to the examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention. it can.

For example, the present invention can be applied to a ladder / grating type filter in which a plurality of transducers are connected in series and parallel or a filter in which a plurality of multimode transducers are connected. Needless to say, an effect can be obtained.

[0043]

As described above, according to the piezoelectric vibrator or the piezoelectric filter of the present invention, a piezoelectric device having a lower spurious and higher frequency can be obtained as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a piezoelectric vibrator of the present invention.

FIG. 2 is a diagram showing an example of a method for manufacturing the piezoelectric vibrator of the present invention.

FIG. 3 is a diagram showing an example of the piezoelectric filter of the present invention.

FIG. 4 is a diagram showing an example of a conventional piezoelectric vibrator.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric vibrator 2 piezoelectric substrate 3a, 3b excitation electrode 4 chipping 10 piezoelectric vibrator 11 piezoelectric substrate 11a first main surface 11b second main surface 11c third main surface 11d fourth main surface 12a, 12b excitation electrode 40 piezoelectric filter 41 input electrode 42 output electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsunori Morikiki 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. F term (reference) 5J108 AA01 AA07 BB03 CC04 CC12 JJ01

Claims (7)

[Claims] 1. A piezoelectric substrate comprising a LiTaO ₃ single crystal, and a pair of excitation electrodes formed on a first main surface of the piezoelectric substrate and a second main surface opposite to the first main surface. A piezoelectric vibrator, wherein a third main surface of the piezoelectric substrate and a fourth main surface opposed to the third main surface are formed of the Li substrate.
A plane substantially parallel to the cleavage plane of the TaO ₃ single crystal;
A piezoelectric vibrator, wherein the ratio of the width to the thickness of the TaO ₃ single crystal substrate is set to 2 to 3. 2. The piezoelectric substrate is an X plate of LiTaO ₃ single crystal, and the third main surface and the fourth main surface are −57 ° ± 1 ° from the Y axis of the piezoelectric substrate. 2. The piezoelectric vibrator according to 1. 3. The piezoelectric substrate according to claim 1, wherein the third and fourth main surfaces of the piezoelectric substrate are surfaces cleaved by laser cutting.
3. The piezoelectric vibrator according to claim 1. 4. A piezoelectric substrate made of LiTaO ₃ single crystal, an input electrode and an output electrode formed on a first main surface of the piezoelectric substrate, and a second main surface opposed to the first main surface. And a third main surface of the piezoelectric substrate and a fourth main surface opposed to the _third main surface are substantially the same as the cleavage plane of the LiTaO ₃ single crystal. A piezoelectric filter having parallel surfaces, wherein the ratio of the width to the thickness of the LiTaO ₃ single crystal substrate is set to 2 to 3. 5. The piezoelectric substrate according to claim 4, wherein the piezoelectric substrate is a LiTaO ₃ single crystal X plate, and the third main surface and the fourth main surface are surfaces at −57 ± 1 ° from the Y axis of the piezoelectric substrate. The piezoelectric filter according to any one of the preceding claims. 6. The piezoelectric substrate according to claim 4, wherein the third and fourth main surfaces are surfaces cleaved by laser cutting.
3. The piezoelectric filter according to item 1. 7. A mobile communication device comprising the piezoelectric vibrator according to claim 1. Description: