JPS6348448B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energy confinement type ceramic vibrator in which mechanical vibration energy is concentrated in a portion of the piezoelectric ceramic vibrator.

Ceramic vibrators using piezoelectric ceramic materials have many advantages such as being small, no adjustment, and no need for coils.
It is often used in intermediate frequency filters, etc. of wireless communication devices. Furthermore, due to the recent improvements in the performance of piezoelectric ceramic materials and their good compatibility with IC and LSI circuits, their uses will continue to expand in the future.

Conventional ceramic vibrators include those that utilize contour vibration such as spreading vibration of a disk, and energy confinement types that concentrate vibration energy in one part using thickness longitudinal vibration or thickness shear vibration of the plate. .

For a vibrator that uses contour vibration such as wide vibration of a disk, its resonant frequency is inversely proportional to the contour dimension, or in the case of a disk, its straight shape, so as the frequency increases, the vibrator size becomes smaller. However, since manufacturing is difficult, the practical frequency band is several hundred KHz or less. Furthermore, in a contour vibration vibrator, the entire vibrator vibrates, and the point where the vibration displacement becomes zero is a node, and in the case of wide vibration of a disk, the center of the disk is a node. Therefore, the vibrator is supported at the node. If the support at this node is strong, vibration energy will leak to the outside through the support, so a relatively soft support structure is usually adopted. As a result, reliability against external vibrations and the like is reduced.

FIG. 1a is a perspective view of a vibrator that utilizes the aforementioned spreading vibration of a disk, in which metal thin film electrodes 2 are formed on both sides of a piezoelectric ceramic plate 1 by vapor deposition or the like. This vibrator is supported as shown in Figures b and c. In Figure b, one end of a thin wire 3 is fixed to a metal support column 4 fixed to an insulating substrate, and the other end of a thin wire 3 is connected to a piezoelectric ceramic plate 1. It is fixed to the center of the metal thin film 2 on both sides with a conductive adhesive or the like. In addition, in FIG. 3c, the metal support 5 fixed to the insulating substrate is made of an elastic material
The tip of the piezoelectric ceramic plate 1 is connected to the center of the thin metal film electrodes 2 on both sides of the piezoelectric ceramic plate 1 to hold the vibrator.

On the other hand, a vibrator that uses thickness longitudinal vibration or thickness shear vibration of a piezoelectric ceramic plate has a resonant frequency that is inversely proportional to the plate thickness, and the vibration energy is trapped in the center of the plate, so the outer periphery of the piezoelectric ceramic plate is This means that it can be held firmly, making it highly reliable against external vibrations and the like. However, in order to improve the vibration energy confinement characteristics, the external dimensions of the vibrator are selected to be at least 30 times the plate thickness.

For example, a resonator with a frequency of 10MHz has a plate thickness of approximately 0.13
mm, the diameter is approximately 3 mm, but the frequency is 1 to 2 MHz.
In this case, the plate thickness would be 0.7 to 1.3 mm and the diameter would be 20 to 30 mm, making it impossible to achieve miniaturization, which is one of the characteristics of ceramic resonators. For this reason, only contour vibration ceramic resonators of several MHz or more have been put into practical use.

FIG. 2 is a perspective view of an example of a ceramic resonator using the above-mentioned thickness longitudinal vibration. Metal thin film electrodes 8 are formed on both sides of the piezoelectric ceramic plate 7 by vapor deposition or the like, and the peripheral edge of the piezoelectric ceramic plate 7 is covered with metal. It is held by a holder 9 and connected to the metal thin film electrode 8, and most of the vibration energy is trapped in the opposing portion of the metal thin film electrode 8.

As mentioned above, in the ceramic resonators that have been put into practical use in the past, in the range of several hundred KHz to several MHz, the resonator dimensions are either too small and difficult to manufacture, or too large and difficult to match with LSI circuits, etc. There was a drawback that it could not be removed and it would sag. Furthermore, contour vibration mode ceramic vibrators have not been put to practical use in high frequency bands due to low support reliability and other reasons.

SUMMARY OF THE INVENTION An object of the present invention is to provide an energy confinement type ceramic resonator that can operate at a frequency of several hundred KHz to several MHz, is easy to manufacture, and has high reliability. Examples will be described in detail below.

3 and 4 are a perspective view and a top view of an embodiment of the present invention, in which the piezoelectric ceramic plate 10 has a thickness t, a length l, and a width W, and the central portion is narrower than the width on both sides thereof. A recessed portion is formed to be W'. Again 1
1a to 11d are metal thin film electrodes formed by vapor deposition or the like, 12a and 12b are terminals, 13a and 13b are separation bands from which the metal thin films have been removed, and 14 is an arrow indicating the polarization direction. The narrow part of the piezoelectric ceramic plate 10 is the electrode 1
Terminal 1 is sandwiched between parts of 1b and 11c.
By applying voltage to 2a and 12b, electrode 1
Although the potentials between 1a and 11c and between electrodes 11b and 11d are equal, an electric field is applied to the narrow portion between electrodes 11b and 11c.

The piezoelectric ceramic material used in ceramic resonators usually has a Poisson's ratio of 1/3 or less, and it is known that thickness longitudinal vibrations, etc., result in increased frequency energy confinement type resonators. There is. The relationship between the resonant frequency f ₀ of longitudinal vibration in the width direction of the ceramic vibrator and the vibrator dimensions is expressed by the following equation.

f ₀ =1/2·W ₀ ·v [Hz] ...(1) However, W ₀ is the width of the vibrator [m], and v is the longitudinal propagation velocity [m/s].

In the present invention, since the width W' of the central portion is smaller than the width W of both end portions, as can be seen from equation (1), the resonant frequency f ₁ of the longitudinal vibration in the width direction of the central portion is the width of both end portions. It becomes larger than the resonant frequency f ₂ of the directional longitudinal vibration. In addition, at both end portions, opposing electrodes 1
Since 1a, 11c and 11b, 11d are short-circuited, the elastic constant becomes small due to piezoelectric reaction, and the longitudinal propagation velocity v becomes small thereby, so that the resonance frequency f ₂ at both end portions further decreases. Therefore, when an alternating current voltage is applied to the terminals 12a and 12b, an alternating electric field is applied to the narrow width part at the center, and longitudinal vibration in the width direction is generated due to the piezoelectric transverse effect. Since the resonance frequency at both end portions is lower than the vibration excited at the end portion, the propagation constant becomes an imaginary number, and the vibration propagated to both end portions is attenuated. As a result, the vibration energy excited by the applied alternating current electric field is concentrated in the narrow central portion, resulting in a so-called energy-confined type vibrator.

As mentioned above, since the vibration energy is concentrated in the narrow part of the central part, the vibration displacement at the ends of both ends becomes zero, and the vibrator can be firmly held by these ends, so it is less susceptible to external vibrations etc. Reliability can be improved.

As a specific example, when the frequency is 2MHz, t=0.1
~0.3mm, l = 7~13mm, W1mm, W′0.9mm, and with these dimensions, manufacturing is easy, and the width W′ of the narrow part to obtain the desired resonance frequency is Since the desired value can be easily obtained by forming a recessed portion by grinding or the like, it is possible to easily manufacture a vibrator with a frequency of several hundred KHz to several MHz. Furthermore, since it is easy to process a plurality of piezoelectric ceramic plates 10 at the same time, it is also possible to reduce manufacturing costs.

FIG. 5 is a perspective view of an assembled configuration of an embodiment of the present invention, in which the same reference numerals as in FIGS. 3 and 4 indicate the same parts, 15 is an insulating substrate, 16a and 16b are conductive adhesives, 17a and 17b are metal supports. These supports 17a, 17b are the insulating substrate 15
The piezoelectric ceramic plate 10 is held by conductive adhesives 16a and 16b with the tip portions curved in a U-shape and connected to the electrodes 11a to 11d, and the terminals 12a and 12b in FIG. It is what it is. That is, since the vibration displacement at both ends of the vibrator becomes zero, it is possible to firmly hold the vibrator, and the U-shaped curved portion creates a short circuit between the opposing electrodes. It goes without saying that the support structure is not limited to the embodiment shown in FIG. 5, and other support structures may be adopted.

FIG. 6 is a perspective view of another embodiment of the present invention,
The same symbols as in FIG. 5 indicate the same parts, 18a, 1
8b is a damping material. As explained in the previous embodiment, longitudinal vibration in the width direction is excited by the alternating current electric field applied to the narrow width portion. in this case,
The piezoelectric ceramic plate 10 also expands and contracts in the length direction due to the piezoelectric transverse effect, and this vibration excites width bending vibration depending on the conditions at both ends, resulting in longitudinal vibration resonance in the width direction of the main vibration. Spurious occurs near the frequency.

Figure 7 shows the frequency response characteristics, A, B
indicates the spurious caused by the above-mentioned bending vibration. Damping materials 18a and 18b are provided to suppress such spurious,
without affecting the longitudinal vibration in the width direction of the main vibration.
Bending vibration can be suppressed.

FIG. 8 shows the frequency response characteristics of the embodiment in which damping materials 18a and 18b are provided, and the spurious signals A and B in FIG. 7 do not appear at all.

The damping materials 18a and 18b may be made of a material with a large acoustic loss, such as an epoxy resin. Further, damping materials can be provided not only at the upper portions but also at the lower portions of both ends of the piezoelectric ceramic plate 10. If damping materials are provided at the upper and lower portions, the effect of suppressing bending vibration will be further increased.

FIG. 9 is a perspective view of still another embodiment of the present invention,
20 is a piezoelectric ceramic plate, 21a, 21b are electrodes, 23
24 is an arrow indicating the polarization direction, 25 is an insulating substrate, 26a and 26b are conductive adhesives, 27
a and 27b are metal supports. Piezoelectric ceramic plate 2
0 has concave portions a and b formed at the top and bottom, and the central portion is a narrow portion. Further, the electrodes 21a and 21b correspond to the electrodes 11a and 11b of the above-mentioned embodiment, and the electrodes 1
Electrodes corresponding to 1c and 11d are provided on the opposite side. Since the piezoelectric ceramic plate 20 has a symmetrical structure, the vibrations due to longitudinal expansion and contraction become pure expansion and contraction vibrations and no bending vibrations occur because of the formation of the recesses a and b. As a result, there is no spurious response due to bending vibration in the vicinity of the longitudinal vibration frequency in the width direction of the main vibration, and the frequency response characteristic becomes almost the same as the characteristic shown in FIG. 8. Note that, as in the embodiment shown in FIG. 6, a damping material may be provided to suppress residual bending vibration components based on errors in the recesses a and b.

As explained above, the present invention provides the piezoelectric ceramic plates 10 and 20 which are entirely polarized in the thickness direction and have a narrow portion in which the width W' of the central portion in the longitudinal direction is smaller than the width W of both end portions. Electrodes 11a to 11d are formed by forming metal thin films on one side surface and the other side surface of a piezoelectric ceramic plate by vapor deposition or the like, and are separated by separation bands 13a and 13b so as to sandwich the narrow portion at different positions in the length direction. , comprising electrodes 11a, 11c facing each other at both ends in the length direction, and terminals 12a, 12b connecting electrodes 11b, 11d to each other,
By applying an alternating current voltage to the terminals 12a and 12b, an alternating electric field is applied to the narrow width part, causing longitudinal vibration in the width direction, and even if the longitudinal vibration generated in the narrow width part propagates, it is attenuated in both side parts. Therefore, both ends can be firmly held, and the terminals 12a and 12b can be used as supports.

The resonant frequency is determined by the width W' of the narrow part, and the dimensions are easy to manufacture even for use in the hundreds of KHz to several MHz bands, and the support of the vibrator can be strengthened, making it inexpensive and This makes it possible to provide a highly reliable ceramic resonator.

In addition, if bending vibration occurs due to end conditions of the piezoelectric ceramic plate, damping materials 18a and 18b are provided to suppress the bending vibration and to suppress spurious waves occurring near the longitudinal vibration frequency in the width direction of the main vibration. I can do it. Therefore, the restrictions imposed by the selection of the dimensional ratio of the piezoelectric ceramic plate and the selection of the supporting means are relaxed.

Furthermore, the above-mentioned bending vibration can be suppressed by symmetrically forming concave portions at the upper and lower portions of the central portion in the longitudinal direction of the piezoelectric ceramic plate to create a narrow portion. This results in a stretching vibration and no bending vibration.

[Brief explanation of drawings]

Figures 1 a to c are a perspective view of a conventional vibrator that uses spreading vibration of a disc and a side view showing a holding means; Figure 2 is a perspective view of a conventional vibrator that uses thickness longitudinal vibration; 3 is a perspective view of one embodiment of the present invention, FIG. 4 is a top view, FIGS. 5, 6, and 9 are perspective views of different embodiments of the present invention, and FIGS. 7 and 8.
The figure is a frequency response characteristic curve diagram. 10, 20 are piezoelectric ceramic plates, 11a to 11d, 2
1a and 21b are electrodes, 12a and 12b are terminals, 1
3a, 13b, 23a are separation bands, 14, 24 are arrows indicating the polarization direction, 15, 25 are insulating substrates, 16
a, 16b, 26a, 26b are conductive adhesives, 1
7a, 17b, 27a, 27b are supports, 18
a and 18b are damping materials.

Claims (1)

[Claims] 1. A piezoelectric ceramic plate that is entirely polarized in the thickness direction and has a narrow portion in which the width of the center portion in the longitudinal direction is smaller than the width of both end portions, and one side surface of the piezoelectric ceramic plate and electrodes formed on the other side of the piezoelectric ceramic plate and separated by a separation band so as to sandwich the narrow portion at different positions in the length direction; and counter electrodes at both ends of the piezoelectric ceramic plate in the length direction. A ceramic resonator characterized in that it is equipped with terminals that are interconnected. 2. A piezoelectric ceramic plate that is entirely polarized in the thickness direction and has a narrow portion in which the width of the central portion in the longitudinal direction is smaller than the width of both end portions, and a piezoelectric ceramic plate that is polarized on one side and the other side of the piezoelectric ceramic plate. A terminal in which the formed metal thin film is interconnected with electrodes separated by separation bands so as to sandwich the narrow portion at different positions in the length direction, and opposing electrodes at both ends of the piezoelectric ceramic plate in the length direction. 1. A ceramic vibrator comprising: a damping material provided on at least the upper portion of both lengthwise ends of the piezoelectric ceramic plate to suppress spurious waves. 3. A piezoelectric ceramic plate that is entirely polarized in the thickness direction and has a narrow portion formed by a recess between the upper and lower parts such that the width of the center portion in the length direction is smaller than the width of both end portions; Metal thin films formed on one side surface and the other side surface are connected to electrodes separated by a separation band so as to sandwich the narrow width part at different positions in the length direction, and to both ends of the piezoelectric ceramic plate in the length direction. 1. A ceramic resonator characterized by comprising terminals in which opposing electrodes are connected to each other.