JPS6327888B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic resonator used in a ceramic filter or a ceramic oscillation circuit, and more particularly to a longitudinal effect type vertically vibrating resonator using frequency increasing type energy confinement.

Conventionally, ceramic resonators have been used in various vibration modes depending on the application, such as the resonant frequency and specific bandwidth used.When the resonant frequency is less than a few MHz, contour vibration of a circular plate, square plate, or rectangular plate is used. A vibration mode in which the entire resonator vibrates, such as length vibration, is used, and when the resonance frequency is from several MHz to several tens of MHz, the vibration energy is locally concentrated in the center of the piezoelectric ceramic plate, resulting in so-called energy trapped vibration. mode is used.

Figure 1 is for intermediate frequency amplification circuits such as AM radio.
This is an example of a ceramic resonator used in a 455kHz ceramic filter. Figure 1a shows a disk with a diameter of about 5 mm polarized in the thickness direction, and Figure 1b shows one side polarized in the thickness direction. It is a square plate with a length of approximately 4.7 mm. Both the disk and square plate resonators shown in FIG. 1 vibrate in contour with the central portion as the node of vibration. Therefore, the support of these resonators and the extraction of electrical terminals are carried out by pressing metal terminal plates on which minute protrusions are formed onto the vibration nodes, or by soldering thin lead wires to the vibration nodes. The former had reliability problems such as peeling of the electrode at the press-contact part and poor contact due to mechanical vibration, while the latter had the drawbacks of difficult soldering work and large variations in characteristics due to support. Figure 2 shows an example of the structure of an energy trapping resonator with a resonance frequency of 10.7MHz.A circular electrode with a diameter of about 1.5mm is formed facing the center of a square plate with a thickness of about 0.2mm and a side length of about 5mm. An external connection electrode is drawn out from the circular electrode to the edge of the substrate. In the energy confinement resonator shown in Figure 2, the connection to the lead terminals is made by soldering at the edge of the board, which has little effect on vibration, resulting in a highly reliable resonator with little variation in characteristics. can get. However, because conventional energy-containing resonators utilize a "thickness vertical mode" or "thickness shear mode," the resonant frequency is determined by the thickness of the ceramic substrate. The lower limit of the resonant frequency is a few
It was limited to MHz.

By the way, in a broad sense, this kind of "energy confinement mode" means that vibration energy is concentrated in a part of a vibrating body with a simple shape, and the vibration energy is concentrated in a part of the vibrating body that has a simple shape, and the vibration energy is concentrated in a part that hardly vibrates due to the dimensions and mechanical conditions. This can be said to be a resonant mode that is not affected by this phenomenon. As mentioned above, in general, resonators using an energy confinement mode have little spurious resonance response even though the maximum dimension is significantly larger than the wavelength, and there is a wide range where displacement and stress can be considered zero. , it has the advantage that it is easy to support the vibrator and attach lead wires without affecting the mode. The application of energy confinement in conventionally used resonators and filters is limited to plate thickness vibrations (particularly thickness vibrations with low-cut dispersion characteristics where the propagation constant kH is an imaginary number on the low frequency side below the cutoff frequency). Therefore, the applicable frequency is HF band of several MHz or more,
It was limited to the VHF band.

The present invention has been made in view of these problems, and it is a piezoelectric ceramic plate that is made smaller and can be applied to low frequencies of several MHz or less. By making it higher than that, the propagation constant of the peripheral part becomes an imaginary number at the frequency near the resonance point, realizing energy confinement.The vertical effect of the piezoelectric ceramic rectangular plate using so-called frequency increasing energy confinement. To provide a type wide vertical vibrating piezoelectric resonator.

The gist of the present invention is to provide an electrode on one side of the peripheral part of a piezoelectric ceramic rectangular plate polarized in the width direction, excluding the central part in the length direction, and to apply an electrode over the entire or almost the entire surface, and to apply a long electrode to the central part of the same surface. A width strip characterized in that a pair of strip-shaped drive electrodes are formed parallel to the width direction, each drive electrode is connected to one peripheral electrode on a different side, and each of the peripheral electrodes is used as a lead extraction terminal. This piezoelectric resonator utilizes vertical vibration, and furthermore, it utilizes vertical vibration characterized by having one or more strip-shaped floating electrodes provided in the middle in the width direction of a pair of drive electrodes in the same plane. It is a piezoelectric resonator.

Vertical vibration transmitted through a thin piezoelectric ceramic plate with a finite width exhibits a high-frequency cutoff type dispersion characteristic in most piezoelectric materials, and the energy confinement method is a frequency increase type. Piezoelectric ceramic plate 1 polarized in the width direction as shown in Fig. 3
A pair of electrodes 2 with width H ₁ on the surface of (width H, thickness t),
2' is formed, the dispersion curve of the longitudinal vibration transmitted through the piezoelectric ceramic plate 1 at this time becomes as shown in FIG.
In the figure, the solid line is the curve for no electrode, the broken line is for the entire surface electrode, and the chain line is the curve for the partial electrode (d/H=0.1, H ₁ /H=0.2). As can be seen from this figure, in vertical vibration, the ratio of the width and spacing of the electrodes provided on the plate surface to the plate width (d/H, H ₁ /H)
The cutoff frequency can be controlled by In the figure, the frequency Ωc that intersects the perpendicular line with a propagation constant of 0 is the cutoff frequency.

Based on these results, as shown in FIGS. 5 to 7, a piezoelectric ceramic rectangular plate 1 polarized in the width direction
(Width H, length l ₀ , thickness t) A drive electrode is formed at the center, and peripheral electrodes are applied over the entire surface or almost the entire surface on the left and right peripheral regions excluding the central region in the length direction. Then, the cutoff frequency at the center becomes higher than the cutoff frequency at the periphery, and it is possible to trap the energy of increasing frequency of longitudinal effect width vertical vibration in the drive electrode section at the center. Figure 5 shows the case where the peripheral electrode and drive electrode are provided only on one side of the plate, Figure 6 shows the case where the peripheral electrode and drive electrode are provided on both sides of the plate and short-circuited, and the drive electrode is provided on one side. A configuration example is shown in which drive electrodes are provided on both surfaces, peripheral electrodes are short-circuited, and drive electrodes are opposed to both surfaces.

In the figures, a, b, and c indicate side, front, and back views, respectively. As shown in each figure, if the central drive electrode is connected to the left and right peripheral electrodes, the left and right peripheral electrodes can be used as lead wire extraction terminals. Furthermore, since the vibration energy is concentrated in the center, the resonance characteristics are not affected even if lead wires are soldered to the peripheral electrodes or the peripheral parts are supported and fixed.

Next, an example will be shown in which PbTiO ₃ porcelain is used for the piezoelectric ceramic rectangular plate.

Each dimension of the resonator in Fig. 7 is H
= 1.05mm, l ₀ = 10mm, t = 0.2mm, d = 0.1mm, g =
0.3mm, l=3.35mm, H ₁ /H is 0.45, 0.18, 0.11
Instead, the admittance characteristics measured for the resonator are shown in FIG.

It has been shown that by reducing the width of the central drive electrode and therefore reducing H ₁ /H to about 0.2 or _less , unnecessary vibrations near the resonance frequency can be removed and sharp and clean resonance characteristics can be obtained. There is.

Similar characteristics have been confirmed not only in the configuration shown in FIG. 7 but also in the configurations shown in FIGS. 5 and 6.

In order to obtain the same frequency (approximately 2MHz) as this resonator, if the resonator is constructed using the energy confinement of conventional thickness-shear vibration, the plate thickness will be approximately
It is quite large, with a diameter of about 20mm on a 0.7mm plate. It has been clarified that the present example is extremely compact compared to such a conventional device, and also has superior characteristics.

In the above embodiment, two drive electrodes are provided symmetrically with respect to the center of the piezoelectric ceramic plate in the width direction, but a floating electrode 8 may be provided between these drive electrodes as shown in FIG. This floating electrode 8 and the drive electrodes 2 on both sides
By aligning the center of the gap with 2' and 2' to a position where the stress distribution in the width direction of the 3rd width mode becomes 0, as shown in FIG. 2(c), the resonance response of the 3rd width mode can be suppressed.

FIG. 10 shows an example in which the resonance response of the third-order width mode is suppressed in this manner, and shows that the third-order width mode is almost completely suppressed. However, in FIG. 10, a shows the characteristics without a floating electrode, and b shows the characteristics when a floating electrode is provided.

In the above embodiments, only the PbTiO ₃ porcelain plate was explained, but similar effects can be obtained with piezoelectric single crystals and PZT ceramics.

As described above, the present invention has been described. By utilizing the frequency-increasing energy confinement of vertical vibration of the piezoelectric effect type, the dimensions of the resonator can be significantly reduced, and it can be closed even at low frequencies in the MF band (03 to 3MHz). Embedded resonators are now applicable. The resonator of the present invention is effective as a ceramic filter or a ceramic oscillation circuit resonator, and its effects are remarkable.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional ceramic resonator used in a 455kHz ceramic filter, Figure 2
The figure is a perspective view of a conventional energy-trapped ceramic resonator for 10.7MHz, Figure 3 is a perspective view of a piezoelectric plate for vertical vibration for explaining the present invention, and Figure 4 shows the electrode width of Figure 3. Figures 5 to 7 show examples of piezoelectric resonators according to the present invention, respectively, and a is a side view, b is a front view, c is a back view, and Figure 8 is a diagram showing the dispersion characteristics when changed. Figure 7 shows the admittance characteristics when the width of the drive electrode is changed, and Figure 9 shows a side view and a plan view of another embodiment of the present invention having a floating electrode, as well as the position of the gap between the floating electrode and the drive electrode. FIG. 10 is a diagram showing the admittance characteristics of the present invention with and without floating electrodes. In the figure, 1...piezoelectric ceramic plate, 2, 2', 7,
7'... Drive electrode, 3, 3', 5, 5'... Peripheral electrode,
4, 4'...Lead extension wire terminal.

Claims (1)

[Claims] 1. Electrodes are applied to the entire or almost the entire surface of a piezoelectric ceramic rectangular plate polarized in the width direction, except for the central portion in the length direction, and electrodes are applied to the center portion in the longitudinal direction. Utilizes vertical vibration characterized by forming a pair of parallel strip-shaped drive electrodes, connecting each drive electrode to peripheral electrodes on different sides, and using each of the peripheral electrodes as a lead extraction terminal. piezoelectric resonator. 2. Piezoelectric resonance utilizing vertical vibration according to claim 1, characterized in that one or more strip-shaped floating electrodes are provided in the widthwise middle of a pair of drive electrodes in the same plane. Child.