JPH07120921B2 - Piezoelectric resonator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an energy trap type three-terminal (dual mode) piezoelectric resonator using a second harmonic wave of thickness longitudinal vibration.

BACKGROUND ART FIG. 4 shows a conventional energy-trap type three-terminal (double mode) piezoelectric filter using thickness longitudinal vibration (hereinafter, referred to as TE mode). In this piezoelectric filter, the input electrode 53 and the output electrode 54 are arranged close to each other on the front main surface of the piezoelectric substrate 51 polarized in the thickness direction, and the back main surface is opposed to the input and output electrodes 53, 54. The ground electrode 52 is formed, and the structure is such that the TE mode fundamental wave is used. The arrow in FIG. 4 indicates the polarization direction.

[Problems to be Solved by the Invention] However, in the case of a piezoelectric filter using a TE mode fundamental wave, in order to realize energy trapping,
It was necessary to use a material having a Poisson's ratio of 1/3 or more as the material for the piezoelectric substrate. That is, in the case of the TE mode fundamental wave, as shown in FIGS. 5A and 5B, the dispersion curve changes depending on the Poisson's ratio of the piezoelectric substrate material. Fig. 5 (a) is the dispersion curve of the TE mode fundamental wave when the (effective) Poisson's ratio is 1/3 or more, and Fig. 5 (b) is the TE mode when the (effective) Poisson's ratio is 1/3 or less. It is a dispersion curve of the fundamental wave, and the vertical axis represents the frequency f and the horizontal axis represents the wave number k (the right half is the real number region of k, and the left half is the imaginary region of k). Also,
The solid line C shows the dispersion curve in the electrodeless part where the input / output electrode and the ground electrode are not provided, and the broken line d shows the dispersion curve in the electrode part where the electrode is formed on the surface. Due to the effect, the dispersion curve shifts to the low frequency side, and the cutoff frequency f ₁₁ of the fundamental wave at the electrode portion is lower than the cutoff frequency f ₁₀ of the fundamental wave at the electrodeless portion (f ₁₁ <f ₁₀ ).

As shown in FIG. 5 (a), when the Poisson's ratio is 1/3 or more, the wave number k in the electrode portion becomes a real number at a frequency higher than the cutoff frequency f ₁₁ , and at a frequency lower than the cutoff frequency f _10. Since the wave number k in the electrodeless part becomes an imaginary number, f
_At a frequency f in the range of ₁₁ <f <f ₁₀ , there is a vibration propagation mode in the electrode portion, but in the electrodeless portion, vibration is not transmitted and is attenuated, so that vibration energy is confined in the vicinity of the electrode portion.

In contrast, in the case of Poisson's ratio less than 1/3, as shown FIG. 5 (b), the wave number k becomes a real in the electrode portions at a frequency lower than the cut-off frequency f _11, than the cut-off frequency f ₁₀ At a high frequency, the wave number k in the electrodeless part becomes an imaginary number, and f ₁₁ <f _10. Therefore, in this case, there is no frequency region where the wave number is a real number in the electrode part and the wave number is an imaginary number in the electrodeless part. However, confinement of vibrational energy is impossible.

Therefore, in the piezoelectric filter using the TE mode fundamental wave, the PZ
Like T-based piezoelectric ceramics, the (effective) Poisson's ratio is 1/3
It is necessary to use the above piezoelectric materials, and the materials that can be used as the piezoelectric substrate are limited. Therefore, even if there is a preferable material for the piezoelectric substrate such as a piezoelectric material having good temperature characteristics, a material having a high Q, a low loss material, and a material having a large amount of attenuation, use it when the Poisson's ratio is 1/3 or less. However, it was difficult to obtain a filter having sufficient characteristics.

Further, in order to increase the frequency of use of the piezoelectric filter having the structure as shown in FIG. 4, it is sufficient to reduce the element thickness. However, if it can be used in a high frequency range, the element thickness becomes too thin, and the processing in the manufacturing process is increased. There was a problem that it became difficult to handle. Therefore, there is a limit to the frequency used.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and an object thereof is to provide an energy trap type three-terminal piezoelectric device having a structure capable of utilizing the vibration of the TE mode second harmonic. The object is to provide a resonator, thereby eliminating the drawbacks of the prior art.

[Means for Solving the Problems] Therefore, the piezoelectric resonator of the present invention is an energy trap type piezoelectric resonator utilizing a thickness longitudinal vibration mode,
A ground electrode is formed substantially in the center of the piezoelectric substrate in the thickness direction, and a first input electrode and an output electrode are formed on one main surface of the piezoelectric substrate so as to face the ground electrode. A second input electrode and an output electrode are formed on the other main surface, and the first and second input electrodes are electrically connected to each other and the first and second output electrodes are electrically connected to each other.

[Operation] In the present invention, the ground electrode is formed in the center of the piezoelectric substrate, and the first input / output electrode and the second input / output electrode are formed on both main surfaces of the piezoelectric substrate. The distance between the input / output electrode and the ground electrode and the distance between the second input / output electrode and the ground electrode are both half the element thickness, and it is possible to excite the TE mode second harmonic vibration in the three-terminal piezoelectric resonator. It became so.

In the case of the TE mode fundamental wave, it was necessary to use a piezoelectric material with a Poisson's ratio of 1/3 or more as a condition for realizing energy confinement. No restrictions. Therefore, because the Poisson's ratio is 1/3 or less, it is now possible to use piezoelectric substrate materials that could not be used in the past, and it is now possible to select piezoelectric substrate materials from a wider range of piezoelectric materials than before. Become. Therefore, it is possible to use a material for a piezoelectric substrate having a higher Q and a better temperature characteristic than the materials used so far, and a three-terminal piezoelectric resonator having a better temperature characteristic, a low loss and a large attenuation amount. Will be able to manufacture.

In addition, when the second harmonic mode is used, the operating frequency can be doubled without reducing the element thickness, so that the strength of the substrate is increased and the manufacturing and processing of the high frequency three-terminal piezoelectric resonator is facilitated.

Further, in the piezoelectric resonator of the present invention, a three-terminal piezoelectric resonator including a first input / output electrode and a ground electrode and a three-terminal piezoelectric resonator including a second input / output electrode and a ground electrode are connected in parallel. The structure is equivalent to the one described above, and the bandwidth of the resonator can be widened.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a piezoelectric resonator according to an embodiment of the present invention. The piezoelectric substrate 1, which is a fired product of piezoelectric ceramics,
A polarization process is applied to the whole in the thickness direction (the polarization direction is indicated by an arrow P), and thickness longitudinal vibration is excited by applying a signal to the electrodes. A ground electrode 2 is formed on the central layer in the thickness direction inside the piezoelectric substrate 1, and an input electrode 3 and an output electrode 4 are provided on the front main surface of the piezoelectric substrate 1 so as to face the ground electrode 2, and An input electrode 5 and an output electrode 6 are provided on the main surface so as to face the ground electrode 2. The input electrode 3 and the output electrode 4 on the front main surface are separated from each other by a certain distance, and the input electrode 5 and the output electrode 6 on the back main surface are also separated from each other by a constant distance. Face each other, and the output electrodes 4 and 6 on the front and back main surfaces also face each other. Furthermore, the input electrodes 3 and 5 on the front and back main surfaces are electrically connected to each other and connected to an external input terminal. Similarly, the output electrodes 4 and 6 on the front and back main surfaces are electrically connected to each other and connected to an external output terminal.

Since this piezoelectric resonator is an energy trap type resonator, the ground electrode 2 and each of the input / output electrodes 3, 4, 5 and 6 have a smaller area than the main surface of the piezoelectric substrate 1, It is provided so as not to reach the edge (see FIG. 2).
Further, since the input / output electrodes 3, 4 or 5, 6 have the same electrode area as each other and are separately arranged symmetrically, the dual mode in which the vibration of the symmetric mode and the antisymmetric mode is excited It is a resonator. Further, since the ground electrode 2 is formed in the central layer of the piezoelectric substrate 1 in the element thickness, the second harmonic vibration having the wavelength of the fundamental wave 1/2 is excited.

FIG. 3 shows an outline of the dispersion curve for the second harmonic wave in the TE mode. The vertical axis represents the frequency f, the horizontal axis represents the wave number k (the right half of the horizontal axis is the real number region, the left half is the imaginary number region), and the solid line a is the dispersion curve in the region where the electrodes of the piezoelectric resonator are not provided, and the broken line. B is the dispersion curve in the region where the electrodes are provided. In TE mode second harmonic, unlike TE mode fundamental wave,
Similarly, when the Poisson's ratio is 1/3 or less and 1/3 or more, it is represented by the dispersion curve as shown in FIG. Therefore, in the case of TE mode second harmonic, the frequency f between the cut-off frequency f ₂₀ of the second harmonic in the cut-off frequency f ₂₂ of the second harmonic and the non-electrode portion of the electrode portion _{(f 22 <f <f 20} ) Then, the wave number k at the electrode
Becomes a real number, and the wave number k becomes an imaginary number in the electrodeless part,
Containment of wage energy is realized regardless of the Poisson's ratio. Therefore, a piezoelectric material with a Poisson's ratio of 1/3 or less, which could not be used conventionally (for example, PbTiO ₃ , LiTaO ₃ , L
iNbO ₃ , Li ₂ B ₄ O ₇ etc.) can be used,
It is possible to select a material suitable for the application from many materials, for example, it becomes possible to use a material with a high Q or a material with good temperature characteristics, and to improve the temperature characteristics of the piezoelectric resonator. You can Further, it is possible to select a piezoelectric material having a lower loss or a piezoelectric material capable of increasing the amount of attenuation in the stop band.

Further, according to such a structure of the piezoelectric resonator, the bandwidth of the resonator is widened, and a wideband second-harmonic resonator can be manufactured. This is formed by the piezoelectric resonator having an element thickness of 1/2 formed by the input / output electrodes 3 and 4 on the front main surface and the ground electrode 2, and the input / output electrodes 5 and 6 on the back main surface and the ground electrode 2. It is considered that this is because the structure is equivalent to connecting in parallel a piezoelectric resonator whose element thickness is 1/2.

Moreover, if the second element is used and the element thickness is the same,
A piezoelectric resonator having a double resonance frequency can be manufactured, and the element thickness can be doubled if the resonance frequency is the same, so that a high frequency piezoelectric resonator can be easily realized, and it can be processed in the manufacturing process. Cracks and chips are less likely to occur,
In addition, the green sheet can be easily handled and the manufacturing can be easily performed.

FIG. 2 shows an example of a method for manufacturing the piezoelectric resonator. First, the electrode paste 9 is applied to the upper surface of one of the two green sheets 7 and 8 of piezoelectric ceramics formed by the ordinary doctor blade method or the like.
Is printed to form the electrode patterns 3a and 4a which will be the input electrode 3 and the output electrode 4, the electrode pattern 2a which will be the ground electrode 2 will be formed on the upper surface of the other green sheet 8, and the input electrode will be formed on the lower surface of the green sheet 8. 5 and the electrode patterns 5a and 6a to be the output electrodes 6 (in FIG. 2, they are projected and shown in the frame of the broken line showing the lower surface of the green sheet 8). After that, the electrode patterns 2a to 6a are aligned with each other, and the green sheets 7 and 8 are laminated in the state shown in FIG. 2, pressure-bonded, fired, and further polarized to polarize the whole in the element thickness direction. Produce a piezoelectric resonator.

The above-mentioned piezoelectric resonator is in the element state, and when it is used as an electronic component, it is a chip-type component in which protective substrates are attached to both surfaces to form external electrodes, or lead terminals are attached. It is packaged with a package resin. Further, in FIG. 1, the input / output electrode and the ground electrode are shown as being externally connected, but the electrode portion for soldering the lead-out electrode and the lead terminal for connection with the external electrode is Generally, it is formed integrally with the input / output electrodes on the surface of the piezoelectric substrate. Further, in the above-mentioned embodiment, the electrode pattern is formed by printing the electrode paste, but it may be formed by a method such as sputtering or vacuum deposition.

Further, the piezoelectric resonator of the present invention can be appropriately modified in addition to the above-mentioned embodiment, and although not shown, the polarization directions of the piezoelectric substrate may be reversed above and below the ground electrode. Furthermore, the input electrode and the output electrode may face each other on the front and back of the piezoelectric substrate.

[Advantages of the Invention] According to the present invention, it has become possible to manufacture an energy trap type three-terminal piezoelectric resonator using a TE mode second harmonic. For this reason, it is possible to use a material having a Poisson's ratio of 1/3 or less as the material for the piezoelectric substrate, and to select a material suitable for the application from more materials, and to obtain the temperature characteristics of the three-terminal piezoelectric resonator. It is possible to improve, reduce loss, increase attenuation, and the like. Further, the limit frequency of the three-terminal piezoelectric resonator can be increased, and the high frequency resonator can be easily manufactured. Moreover, according to the present invention, it has a structure equivalent to that of connecting two double-harmonic piezoelectric resonators in parallel, the bandwidth of the resonator can be widened, and the second-harmonic wave for wideband can be used. Piezoelectric resonators can be manufactured.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a perspective view showing a manufacturing process of the same, and FIG. 3 is a schematic view showing dispersion curves of an electrode portion and an electrodeless portion of the same. The figure is a cross-sectional view of a conventional example, and FIGS. 5 (a) and 5 (b) are schematic diagrams showing respective dispersion curves when the Poisson's ratio of the piezoelectric resonator is larger than 1/3 and smaller. 1 ... Piezoelectric substrate, 2 ... Ground electrode 3,5 ... Input electrode 4,6 ... Output electrode P ... Vector showing polarization direction

Claims (1)

[Claims] 1. An energy trap type piezoelectric resonator utilizing a thickness longitudinal vibration mode, wherein a ground electrode is formed substantially at the center of the piezoelectric substrate in the thickness direction, and one main surface of the piezoelectric substrate is opposed to the ground electrode. A first input electrode and an output electrode, and a second input electrode and an output electrode are formed on the other main surface of the piezoelectric substrate so as to face the ground electrode, and the first and second input electrodes are connected to each other. A piezoelectric resonator, wherein the first and second output electrodes are electrically connected to each other and are electrically connected to each other.