JPS62109419A - Thickness-shear vibrator - Google Patents

Abstract

PURPOSE:To prevent the secondary resonance produced by an inharmonious spurious mode by providing an additional film on an exciting electrode so that the integration value of an electric change distribution curve due to the displacement of vibration is equal to zero within the exciting electrode of an inharmonious spurious mode. CONSTITUTION:A vibration displcement distribution curve caused by an inharmonious spurious is changed by an additional film. At the same time, the quantity of electrification produced within an exciting electrode is approximately equal and offset as long as the amount of the vibration displacement produced within the exciting electrode by the inharmonious spurious mode is equal between the plus and minus sides. Thus the electrical resonance characteristics are never produced. In this connection, an additional film 7 is provided on the exciting electrode so that the integration value of the electric charge distribution curve produced by the displacement of vibration within the exciting electrode of an inharmonious spurious mode is equal to zero. This prevents the secondary resonance produced by the inharmonious spurious mode.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to a thickness-shear oscillator that can prevent the occurrence of sub-resonance due to anharmonic spurious mode of the thickness-shear oscillator and obtain good resonance characteristics. , is used as a filter element that prevents the guaranteed attenuation from decreasing outside the passband.

(Background of the Invention) Piezoelectric resonators made of single crystals, such as thickness-shear vibration mode crystal resonators, have traditionally been used as oscillating elements and filters in communication equipment because of their extremely high Q value, which determines the quality of their electrical characteristics. It has been used as an element. And in recent years,
Due to deterioration of communication conditions, for example, a thickness-shear oscillator is desired as an oscillation element without loss of frequency stability, and as a filter element, which fully satisfies the guaranteed attenuation amount outside the passband.

(Background Art) FIG. 5 is a diagram of a crystal piece constituting this type of thickness-shear resonator.

That is, this crystal piece 1 has the X-2 plane of the crystal axis XXy%z as the main surface, and the rotation axis is the y-axis, and the distance from the y-axis to the Z-axis is about 35.
It is usually called an AT cut and is rotated by 15 degrees.In the figure, the newly created axis after rotation is yも,
z′ is toshi. This crystal blank 1 has an excitation type i2 that excites thickness-shear vibration in the central part of the opposing amphiboid surfaces.
is formed, and extraction electrodes 3 extend from the excitation electrode 2 to the outer periphery of both ends. In reality, the outer peripheries of both ends of this crystal piece are electrically and mechanically connected by a holding device (not shown) and sealed in a container to form a thickness-shear oscillator.

FIG. 6 is an electrical resonance characteristic diagram of a thickness-shear resonator, with the horizontal axis representing frequency (f) and the vertical axis representing admittance (1/Ω). In other words, the electrical resonance characteristics of this thickness-shear resonator are such that, as shown in the curve in the figure, the main resonance frequency fO normally exhibits a sub-resonance fs at a frequency higher than the main resonance frequency fO. becomes. This sub-resonance occurs mainly due to the anharmonic spurious mode of the thickness-shear vibration mode or the contour-based spurious mode. Among these, sub-resonances fs1 and f due to anharmonic spurious modes whose energy is confined by electrodes are particularly important.
Since s2 has a low impedance level, e.g.
When used as a filter element, oscillation element, etc., this causes a reduction in the guaranteed attenuation amount, a frequency jump phenomenon, etc.

By the way, the vibration mode of thickness shear vibration is generally (
1, m, n). That is, in the mode symbol, l is the number of wavelengths in the thickness (y' axis) direction, that is, the overtone order, and m%n is the number of half wavelengths of the displacement distribution in the x and z' axis directions in each excitation electrode section. represent. For example, the fundamental wave is l = 1 and the overtone is 1 =
It is an odd order of 3.5.7. Now, if we consider the main vibration mode of the fundamental wave, its mode symbol is (1, 1, 1
), and the vibration displacement distribution curve (a) in Figure 7(a)
As shown in (b), with respect to the X and Z' axes, the maximum value is at the center of the excitation electrode, and it decreases like a cosine function on the excitation electrode, and decreases exponentially outside the excitation electrode. Further, at this time, the charge distribution induced on the electrode by the piezoelectric effect also has a shape almost similar to the displacement distribution. Then, the vibration displacement distribution curve of the anharmonic spurious mode, for example, the (1, 1, 2) mode, is
As shown in curves (C) and (D) in Figure (b), in the X-axis direction, the Z-axis is confined within the excitation electrode like a cosine function (towards the curve) like the main vibration. In the ' axis direction, the amount of change is O at the center of the electrode, resulting in a displacement distribution of a double angle sine function line (curve 2) in which two half wavelengths are placed on the electrode. At this time, since the charge distribution has opposite polarity and is symmetrical from the center of the electrode, the amount of charge generated at the excitation electrode is canceled out. Therefore, the anharmonic spurious mode in the 2'-axis direction is not electrically excited, and no electrical resonance characteristics occur. For the same reason, the anharmonic spurious mode is not electrically excited when m and n are even numbers. Next, the vibration displacement distribution curves (E) and (E) of the anharmonic spurious mode (1,113) shown in FIG. 7(c) are
In the axial direction, like the main vibration, it is confined in a cosine function (curve E) on the excitation electrode, whereas in the z'-axis direction, the maximum value is at the center of the excitation electrode, and the vibration is confined near both ends of the excitation electrode. It becomes a displacement distribution like a triple angle cosine function with a local minimum value. Since the charge distribution generated at this time has a similar shape to the displacement distribution, the polarity is reversed between the center part of the electrode and the side part of the electrode. Therefore, the charges collected on the excitation electrode are canceled out, so the amount of charge B generated? However, this anharmonic spurious mode is electrically excited and generated as electrical sub-resonance. Similarly, among the anharmonic spurious modes, those in which m and n are odd numbers sequentially occur as sub-resonances close to the main resonance frequency fo.

(Prior art) For this reason, in the conventional technology, for example, by reducing the diameter of the excitation electrode, or by reducing the amount of plateback of the excitation electrode, that is, the amount of reduction in frequency due to the excitation electrode, the anharmonic spurious vibration other than the main vibration is reduced. The mode was not confined to the lower part of the excitation electrode, and the sub-resonance level was lowered. In addition, as shown in Figure 8, by applying an additive 4 such as adhesive to the main surface of the crystal piece, only the anharmonic spurious mode is mechanically suppressed, and its influence on the main vibration mode is reduced. That's what I was doing. However, when the diameter of the excitation electrode is made small, not only does the crystal impedance in the main vibration mode increase, but also the inductance increases, which impairs the degree of freedom in design when used as a filter element. There were some drawbacks, such as: Furthermore, when the plateback amount of the excitation electrode is reduced, there is a limit to how thin the electrode film can be made due to manufacturing technology constraints, and when adding additives, not only the Q value decreases but also the aging characteristics deteriorate. There were other problems.

(Object of the Invention) An object of the present invention is to provide a thickness-shear oscillator that prevents the occurrence of sub-resonance due to anharmonic spurious mode.

(Points of Interest and Features of the Invention) The present invention is characterized in that the vibration displacement distribution curve due to the anharmonic spurious mode is changed by the additional film, and that the amount of vibration displacement between the + side and the one side is If they are equal, the amount of electrification generated within the excitation electrode is approximately equal and cancels each other out, that is, the integral value of the charge distribution curve due to vibration displacement within the excitation electrode becomes zero, so that no electrical resonance characteristics occur. Focusing on the point that it is possible to prevent the occurrence of sub-resonance due to this anharmonic spurious mode, we added a film on the excitation electrode so that the integral value of the charge distribution curve due to the vibrational displacement within the excitation electrode in the anharmonic spurious mode becomes zero. It is characterized by having undergone.

(Purpose and Effects of the Invention) The gist and effects of the present invention will be explained below with reference to the drawings. still,
For convenience of explanation, prevention of sub-resonance caused by an anharmonic spurious mode in one dimension of an AT-cut crystal piece will be explained as an example.

For example, assume that the sub-resonance generated in the crystal resonator is in the one-dimensional Z'-axis direction and is caused by an anharmonic spurious mode expressed by mode symbols (+, m, 3). In other words, the vibration displacement distribution curve of this anharmonic spurious mode is
As shown in FIG. 1(a), the excitation current ll12 has a maximum value at the center and a minimum value near both ends, similar to the triple angle cosine function described above. Therefore, the excitation of the charge distribution curve due to vibrational displacement The integral value on the electrode does not become zero, and charges corresponding to the difference in displacement between the + side and the one side are generated on the excitation electrode and excited.

FIG. 1(b) shows the displacement distribution when the additional film 5 is applied to the periphery of the excitation electrode 2 of the AT-cut crystal piece. That is, it is understood that due to the presence of the additional film 5, the position of one extreme value of the vibration displacement distribution curve at the end of the excitation electrode is further away from the center of the electrode. Therefore, this additional film 5
If is set to a predetermined condition, the integral value of the charge distribution curve within the excitation electrode due to the vibrational displacement of the anharmonic spurious mode can be made zero, so it is possible to prevent the occurrence of sub-resonance due to the anharmonic spurious mode. And additional film 5
But is it minimum in the main vibration mode and maximum in the anharmonic spurious mode? Since it is applied to the periphery of the H field, the vibration displacement due to the anharmonic spurious mode is more strongly affected than the main vibration mode, and this contributes to preventing the occurrence of sub-resonance due to the anharmonic spurious mode.

At the same time, due to the arrangement of its geometric displacement distribution, the integral value of the anharmonic spurious mode with a harmonic order of 5.7 approaches zero in the same way as when the harmonic order is 3. I can do it. If the additional film 5 is applied symmetrically to the electrode, the symmetric mode with harmonic order of 2.4.6, etc. will not lose the symmetry of the charge distribution, and will be different from when no additional film is applied. Similarly, it is not electrically excited. Therefore,
It is said that it is possible to suppress vibrations due to the anharmonic spurious mode of the thickness helical vibration mode and enhance vibrations due to the main vibration mode.

(Examples of the invention) Examples of the invention will be described below with reference to experimental data. In this embodiment, a third-order overtone, that is, a thickness-shear oscillator in which mode symbols (1, m, n) of 1 is set to 3, will be described in detail.

FIG. 2 is a diagram of an AT-cut crystal piece according to the spirit of the present invention. This crystal piece 6 has a polished approximately disk shape with a diameter a of 5 mnt, and its bidirectional surfaces have lengths in the x and z' axes directions of 1.65 mm and 1.09 mm, respectively.
5. An excitation electrode 7 made of, for example, silver and having a thickness of 2000 Å is formed, as well as extraction electrodes 8 extending in the 2' axis direction with a width d of 0.3 mm at both ends of the outer periphery. In this embodiment, an additional film 9 made of, for example, silver and having a width of 0.08 mm and a thickness of about 200 OA is applied to both edges of the excitation electrode B in the X-axis direction.

FIGS. 3(a) and 3(b) are resonance characteristic diagrams with frequency on the horizontal axis and admittance on the vertical axis, which were measured with a network analyzer by inserting a thickness-shear oscillator into a π-type circuit. Curve A in Figure 3(a) shows the resonance characteristics before the additional film 9 is applied on the excitation electrode of the crystal piece, and the crystal impedance value due to the main vibration mode (3, 1, 1) at 58.0925 MHz is set to 75Ω by OdB. The level difference between main resonance fO1 and main resonance EO from this main resonance fO to +135KHz is -
14.5dB anharmonic spurious mode (3,3,1)
, and an anharmonic spurious mode (3,1,3) with a level difference of 113 dB at +242.5KHz, and +37
Anharmonic spurious mode (3, 3, 3) with a level difference of approximately -16 dB at 7 KHz, +393 KH
, (3,5,1) sub-resonance fs(fsl, fs2,
fs3, fs4) are occurring. That is, as mentioned above, these sub-resonances fs are caused by + of the charge distribution curve due to vibrational displacement within the excitation electrode of each anharmonic spurious mode.
This occurs because the distribution amounts on one side and the other side are different, and the integral value thereof is large. The curve (b) in FIG. 3(b) is a resonance characteristic diagram of the crystal piece with the additional film 9 applied on the excitation electrode, and the crystal impedance value of the main resonance fO is approximately the same as when the additional film 9 is not applied. It is 75Ω. On the other hand, the level difference between the sub-resonance fsl due to the anharmonic spurious (3,3,1) mode and the main resonance fO is -16.7 dB, which is an increase of about 2 dB compared to when the additional film 9 is not applied. are doing. As is clear from the figure, the magnitude of the spurious itself, that is, the level modulation from the resonance point a to the anti-resonance point, and the sub-resonance fsl due to the anharmonic spurious mode (3, 3, 1), is approximately 3 dB. The sub-resonance fs3 and fs4, whose level is about 1 dB due to the anharmonic spurious modes (3, 3, 1) and (3, 5, 1), have disappeared. That is, due to the additional film 9, the extreme values of the vibrational displacement distribution curve move inside the electrode, so that the displacement amounts on the + side and the one side almost match, and the integral value of the charge distribution curve due to the vibrational displacement within the excitation electrode becomes zero. This is because it was close to. In this example, sub-resonance occurs in the spurious mode (3, 1, 3) at approximately the same level as when no additional film is applied.
The reason for this is that because the additional film is applied only to both ends of the square electrode in the X-axis direction and not in the Z''-axis direction, the extreme value of the vibration displacement distribution curve in the Z'-axis direction does not shift to an extreme. It is.

Therefore, in this embodiment, due to the presence of the additional film 9, the crystal impedance value of 75Ω of the main resonance fs is kept approximately constant, and the anharmonic spurious modes (3, 3, 1) and (3, 3, 3) are This shows that it was possible to reduce the resonance level difference with respect to the main resonance of (3, 5, 1), and also to reduce the resonance level itself. For this reason, the additional film 9 can be easily formed on the excitation electrode by, for example, vapor deposition, so as mentioned above, it is possible to reduce the diameter of the vJJJ vibration pole or the plate back area, or apply an additive such as an adhesive. There is no need to do so, there is no reduction in Q, there is no deterioration of aging characteristics, and there are no extreme restrictions on design freedom or manufacturing. For example, when used as a filter element, the amount of compensation attenuation outside the pass band is sufficiently satisfied, and when used as an oscillator, the frequency stability will not be impaired due to jump phenomena or the like.

(Other embodiments of the present invention) FIG. 4 is a diagram showing another embodiment based on the gist of the present invention.

≠), FIGS. 4(a) and (b) show that an additional film is applied to the outer periphery of the rectangular electrode in the x-, z'-axis direction in the above example,
xSz where m1n of mode symbol (1, m, n) is an odd number
The charge distribution curve due to the vibrational displacement of the spurious mode generated in the two-dimensional axial direction is made so that its integral value becomes zero within the excitation electrode, and the same or better effect as described above is obtained.

2), Figures 4 (C) and (d) show that the crystal piece is rectangular, the excitation electrode is circular, and the excitation electrode is divided (C) or continuous along the outer circumference of the excitation electrode in the (d) in the same figure provided with the additional film produced the same effect as in the previous section 1, indicating that the present invention can be achieved regardless of the shape of the crystal piece and the excitation electrode.

3) Figure 4(e) shows a case in which two rows of additional films are applied to the outer periphery of a rectangular excitation electrode on a circular or rectangular crystal piece, and the same effect as the previous item is obtained, and the present invention is This shows that there is no damage due to the parallel arrangement of additional films.

(Other Matters) In the detailed explanation of the present invention, the main resonant frequency of the thickness-shear oscillator was explained as a third-order overtone with a harmonic character number of 3, but the fundamental wave with the harmonic character number as 1 was explained. However, the same effect can be achieved.

In this embodiment, the charge distribution curve due to vibrational displacement is made to have an integral value of zero within the excitation electrode due to the t-addition film applied on the excitation electrode, but this is not the case in the present invention. Examples include, but are not limited to, deleting a part of the excitation electrode, applying an additional film on the extraction electrode, and further processing the external shape of the crystal piece, such as bevel or convex. It goes without saying that the charge distribution curve due to vibrational displacement may be changed, and the point is that the integral value of the charge distribution curve due to excitation vibrational displacement becomes zero within the excitation electrode.

Furthermore, the present invention is not limited to the additional film of the above embodiment, but can be applied, for example, by controlling the material, thickness, width, and position of the additional film within the electrode, thereby reducing vibrational displacement within the excitation electrode. Needless to say, it is possible to reduce the integral value of the charge distribution curve to zero and prevent the occurrence of sub-resonance, as well as other publications such as "An analysis method for square electrode energy confinement type resonators", Transactions of the Institute of Electrical Communication Engineers, AXJ 63-A, 8, pp530-53
2 (Sho 5S-OS)>, z, etc. can be applied to advantageous use and easy implementation, and the present invention can be modified as appropriate without departing from the spirit thereof.

(Effects of the Invention) As explained above, the present invention provides an additional film on the excitation electrode so that the integral value of the charge distribution curve due to vibrational displacement within the excitation electrode in the anharmonic spurious mode becomes zero. It is possible to provide a thickness-shear oscillator that prevents the occurrence of sub-resonance due to anharmonic spurious mode.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are vibration displacement distribution curve diagrams explaining the present invention, FIG. 2 is a plan view of a crystal piece showing an embodiment of the present invention, and FIGS. 3(a) and (b). 4 is an admittance characteristic diagram illustrating the effects of one embodiment of the present invention, FIG. 4 is a plan view of a crystal blank showing another embodiment of the present invention, and FIG. 5 is a crystal blank illustrating a thickness-shear oscillator. , Figure 6 is an admittance characteristic diagram of a thickness-shear oscillator, Figure 7 is a displacement distribution diagram explaining the vibration mode of a thickness-shear oscillator, and Figure 8 is a diagram showing the conventional technique for preventing sub-resonance due to anharmonic spurious mode. FIG. 3 is a plan view of a crystal piece. 6 crystal piece, 7 excitation electrode, 8 extraction electrode, 5.9
・Additional membrane. 1st country (Q) 1 1st country (b) 1 Fig. 2 No. 31!1 ((1) 11 ÷ f Fig. 3 (b) -1 ÷ f Fig. 4 No. 51!l 6th

Claims (2)

[Claims] (1) An excitation electrode that excites the main vibration mode of thickness shear vibration is formed on the piezoelectric plate where thickness shear vibration is excited, and an anharmonic that occurs with respect to the main vibration mode of thickness shear vibration is formed. 1. A thickness shear resonator characterized in that when a charge distribution curve due to vibrational displacement within an excitation electrode in a spurious mode is integrated, the integral value becomes zero. (2) In the claim set forth in item 1, when the charge distribution curve due to the vibration displacement in the excitation electrode of the anharmonic spurious mode generated with respect to the main vibration mode of thickness shear vibration is integrated, the integral A piezoelectric vibrator characterized in that an additional film is provided on the excitation electrode so that the value becomes zero.