JPS6046889B2 - Edge mode ceramic resonator - 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 provides a ceramic resonator that is easy to support the resonator and to attach lead terminals to.

Conventionally, ceramic resonators use various vibration modes depending on the purpose, such as the resonant frequency and fractional bandwidth used.If the resonant frequency is less than a few, ring vibration of a circular plate or square plate, A vibration mode in which the entire resonator vibrates, such as length vibration of a rectangular plate, is used, and when the resonance frequency is from several MH2 to several tens of MH2, the vibration energy is locally concentrated in the center of the piezoelectric ceramic plate, so-called energy. Lock-in vibration mode is utilized.

Figure 1 shows 455k for intermediate frequency amplification circuits such as eyebrow radios.
This is an example of a ceramic resonator used in an HZ ceramic filter. Figure 1a shows a circular plate with a diameter of about 5m77L polarized in the thickness direction. It is a square plate with a length of about 4.7 Tnm.

Both the disk and square plate resonators shown in FIG. 1 vibrate in the ring with the center 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 10.7M pressure and a thickness of about 0.7M.
2Twt side length about 5? The center of the square plate has a diameter of approximately 1.5 mm.
? circular electrodes are formed facing each other, and external connection electrodes are drawn out from the circular electrodes on both sides to the ends 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, since conventional energy trapping resonators utilize a "thickness vertical mode" or "thickness vertical mode," the resonant frequency is determined by the thickness of the ceramic substrate. As the thickness increases, the external dimensions increase in proportion to this, so the lower limit of the resonant frequency is several MFI.
It was limited to z. The present invention is a conventional ceramic resonator as shown above! The present invention provides a ceramic resonator that is mainly used in the medium frequency band and is practical in terms of external dimensions and easy to support and attach lead terminals, excluding the drawbacks of
Vibration energy is concentrated only near the edges of a rectangular piezoelectric ceramic plate, and the resonant frequency is determined by the width of the piezoelectric ceramic plate.Using edge mode vibration, it is possible to cope with the distribution of areas where the areal strain due to vibration is large. The piezoelectric ceramic plate is characterized in that shaped drive electrodes are formed facing each other on both sides of the piezoelectric ceramic plate near the end thereof.

Hereinafter, the principle of the present invention will be explained in detail with reference to the drawings of embodiments. As is conventionally known, edge mode vibration is a mode related to a complex branch in a dispersion curve representing waves that undulate and attenuate in an infinite length strip, and was conventionally known as spurious vibration4.

In order to actively utilize this edge mode vibration, the present invention provides an electrode structure that effectively excites edge mode vibration. Is Figure 3 a sufficiently thin plate with polarization in the thickness direction? shows the coordinate system of a semi-infinitely long piezoelectric strip. An example of the dispersion curve of symmetric width vibration calculated for this porcelain strip is shown in FIG. The normalized frequency Ω is given by.

Here ω is the angular frequency, ρ is the density, ? is the plate width of the resonator, C
llP is the elastic constant when using the thin plate approximation, which is expressed as follows. Considering the frequency range below the stationary point Ω$ where the complex branch C1 appears, there are an infinite number of complex branches C1 in this region.
, C2...... and a real number branch representing one propagation mode! exists.

Edge modes do not couple with propagation mode L.

That is, it is assumed that the mode is a complete eigenmode with no energy loss, and further, only the first-order and second-order complex branches C1 and C2 are used from among the infinite number of complex branches. Complex branch C of each degree. There are four roots of wave number KH for →
Consider two complex branched CnC riddles with mutually conjugate wave numbers KH that give waves that decay to zero at +1. In other words, consider a total of four waves of first order and second order, express the solution by linear combination of these waves, and set the displacement components U1 and U2 in the X1 and X2 directions as follows ((EjO)t is omitted) where Kn =Krn+Jk
, n Song represents the complex conjugate. In the above equation, Kn ~ Almn ~ A2mn ~ αTTln is a constant representing the wave of the complex branch that satisfies the wave equation and the boundary condition at X1 = ±H, and An,, Bn is the equation = It is a constant determined by the boundary condition at the free end of 0.

In order to find the edge mode solution that satisfies the boundary condition T2 = T6 = 0 at formula = 0, we will use the variational method and introduce the lag radian L of the following formula.
．． -2 The resonant frequency can be obtained by setting the determinant regarding the coefficient of the condition giving the minimum of this Lagradian to zero.

Once the resonance frequency is determined, the displacements U1 and U2 are determined from equation (2), and the distribution of area strain Δ is determined from the following equation. Wa A
lVΔz FIG. 5 shows the edge mode vibration pattern obtained from the calculation results.

In addition, in order to see this displacement distribution in more detail, Fig. 6 shows the displacements U1 and U2 at X1=H and the displacement U at X1=0.
2 (U1 is always zero). The edge mode vibrates only near the end face, and as the equation increases, the displacement rapidly decreases, and at X2/2FI=1.5, the displacement is about several percent of the amplitude at the end face. Therefore, it can be seen that even if the portion where X2/2H>1.5 is fixed, the vibration is hardly affected. The present invention has a rectangular shape (length L, width T, thickness T), T
(2H) Vibration energy is concentrated only near the longitudinal ends of the piezoelectric ceramic plate polarized in the thickness direction, and the corners of the piezoelectric ceramic plate expand and contract in an arc shape, causing displacement within the piezoelectric ceramic plate. Two pairs of opposite-phase electrodes are formed on the upper and lower surfaces near the ends of the piezoelectric ceramic plate, respectively, and approximately semicircular drive electrodes are formed along the contour lines in areas where area distortion due to vibration is large. This is an edge mode resonator in which a portion at a distance X2/2H>1.5 from the end portion to which the electrode is attached is supported and fixed. FIG. 7 shows the calculation results of the areal strain distribution using contour lines.

The numerical values in the figure indicate relative values of areal strain. The present invention is characterized in that edge mode vibration is effectively vibrated by a drive electrode shaped to match the shape of the areal strain distribution by utilizing the fact that the induced charge due to vibration is proportional to the areal strain distribution.

FIG. 8 shows one embodiment of the present invention, in which a shows a front electrode and b shows a back electrode. Length (L) 20Tm
fn1 width (2FI) 2.4TwL1 thickness (T) 0.2?
After polarizing a rectangular piezoelectric ceramic plate 1 (Nepetic 6 material manufactured by Tohoku Metals Co., Ltd.) in the thickness direction, drive electrodes 3a and 3a'' were formed facing each other on both the front and back sides at the center of the end as shown in FIG. , and an external connection electrode 3 on the other end of the piezoelectric ceramic plate.
and 3" are pulled out. Drive electrodes 3a and 3a
The shape of `` is roughly semicircular in accordance with the shape of the portion with large area strain shown in FIG. Almost 0.
It is set at 3.

FIG. 9 shows the admittance characteristics of the resonator shown in FIG. 8. The resonator is fixed to the bake plate leaving a portion about 4wn apart from the end face. Therefore, the length of the piezoelectric ceramic plate is 6
It can be shortened to wn. In the characteristics shown in FIG. 9, the capacitance ratio Cd/C shows a small value of 33, which is sufficient to constitute a ceramic filter. In FIG. 9, a small spurious is seen near a frequency approximately 1.3 times the main resonant frequency.

This is due to vertical vibration in which the width direction vibrates uniformly, but it can be reduced by changing the electrode dimensions, and is often not a practical problem for general applications. FIG. 10 shows another embodiment of the present invention.
b indicates the front electrode and b indicates the back electrode.

In FIG. 10, anti-phase drive electrodes are formed to suppress spurious waves caused by the vertical vibration. That is, in the figure, the piezoelectric ceramic plate 1 has the same dimensions and is made of the same material as the above embodiment, and after polarization treatment in the thickness direction, first, as shown in the figure, the piezoelectric ceramic plate 1 is polarized along the longitudinal direction of the piezoelectric ceramic plate, with the front and back sides of the center portion facing each other, as shown in the figure. Arc-shaped drive electrodes 3a and 3a'' reaching a position 0.3) times the width in the direction are formed.Next, the areal strain shown in FIG. Corresponding to the portion where the relative value is large, anti-phase driving electrodes 2a are provided opposite to both the front and back surfaces of both sides near the end of the piezoelectric ceramic plate.
2a'' and 4a, 4a'' are formed. Furthermore, on the back side, the drive electrode 3a'' and the opposite phase drive electrodes 2a'', 4
a'' is electrically connected and serves as a floating electrode, and on the surface there are a drive electrode 3a and opposite phase drive electrodes 2a, 4a.
3 from each end in the longitudinal direction of the piezoelectric ceramic cover plate.
External connection electrodes 3, 2, and 4 are drawn out with fixed positions. FIG. 11 shows the admittance characteristic of a resonator in which external connection electrodes 2 and 4 of the resonator shown in FIG. 10 are connected, and this and external connection electrode 3 are used as two terminals. As in the previous embodiment, the resonator is fixed to the baking plate, leaving a portion about 4 TWL away from the end face. In the characteristics shown in FIG. 11, the spurious noise seen in FIG. 9 is completely suppressed, and it can be seen that the anti-phase driving electrodes have a great effect in suppressing spurious noise. Therefore, anti-phase drive electrodes are effective especially when requirements for spurious characteristics are severe. Furthermore, in the case of FIG. 10, the fact that the external connection electrodes are on the same surface is advantageous for constructing a filter by connecting a plurality of resonators. In Fig. 11, the capacitance ratio is 43, which is larger than that in Fig. 9, but this is due to the line capacitance of the lead line, the capacitance between the drive electrode and the anti-phase drive electrode, and the capacitance between them. This can be improved by changing the electrode shape within a range that does not significantly affect the vibration characteristics, or by narrowing the width or shortening the length of the lead line, and this change does not limit the present invention in any way. do not have. As mentioned above, in the edge mode resonator of the present invention, the vibration energy is concentrated near the end of the rectangular piezoelectric ceramic plate, so if the part of the edge mode resonator of the present invention is fixed at a distance of 1.5 times the width of the plate or more from the end of the drive electrode, Supporting the resonator and attaching lead terminals, which have almost no effect on the resonator characteristics, are also facilitated, and a highly reliable resonator with less variation in characteristics due to support can be obtained.
In addition, the shape of the drive electrode is determined according to the areal strain distribution4.
Therefore, a practical capacitance ratio can be obtained, and even if a ladder type ceramic filter is constructed using these, a practically sufficient fractional bandwidth can be obtained. The above explanation was about piezoelectric ceramics, but instead of piezoelectric ceramics, L
It goes without saying that similar resonance can be obtained using a piezoelectric single crystal such as iTaO3 or other piezoelectric materials.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional ceramic resonator used in a 455k pressure ceramic filter. FIG. 2 is a perspective view of a conventional energy trapping type 10.7 MHZ ceramic resonator. FIG. 3 shows coordinate axes for vibration analysis of a semi-infinitely long piezoelectric ceramic strip to explain the present invention. Figure 4 is an example of dispersion curve calculation, Figure 5 is the displacement distribution of edge mode vibration, and Figure 6 is X1=O and X1=
Distribution of displacements U1 and U2 at H, FIG. 7 is a calculation result of area strain distribution, and FIG. 8 is a structural diagram showing an embodiment of the present invention.
9 shows the admittance characteristic of the resonator shown in FIG. 8, FIG. 10 shows the structure of another embodiment, and FIG. 11 shows the admittance characteristic of the resonator shown in FIG. In the figure, 1...piezoelectric ceramic, 2, 3, 3''94...external connection electrode, 3a, 3a''
... Drive electrode, 2a, 2a'', 4a, 4a''・
...An electrode for anti-phase drive.

Claims (1)

[Claims] 1. An edge mode vibration resonator in which vibration energy is concentrated only in the vicinity of the longitudinal ends of a rectangular piezoelectric ceramic plate polarized in the thickness direction, and the corners of the piezoelectric ceramic plate are displaced in an arc shape within the plane, An arc-shaped drive electrode is provided at a distance from the end of the piezoelectric ceramic plate to a distance 0.3 times the width of the piezoelectric ceramic plate, and in a part where area strain due to vibration is large centered on the center in the width direction, and the end part An edge mode ceramic resonator characterized in that a point located at a distance of more than 1.5 times the width of the piezoelectric ceramic plate is supported and fixed.