JPH09181555A - Piezoelectric resonator - Google Patents

Abstract

(57) [Abstract] [Problem] There is a problem that the temperature characteristic of the resonance frequency is deteriorated, and when a filter is formed by using a piezoelectric resonator, the pass band is changed due to a change in operating temperature. A square partial electrode is formed on one surface of a piezoelectric ceramic substrate formed by cutting out four corners of a sintered body having a square planar shape, and a full surface electrode is formed on the other surface of the piezoelectric ceramic substrate. When the length of the partial electrode in the diagonal direction is y ₁ and the length of the full surface electrode in the diagonal direction of the partial electrode is y ₂ ,
It satisfies 0.4 ≦ (y ₂ −y ₁ ) / y ₁ ≦ 1.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric resonator using a spreading vibration mode, and more particularly to a piezoelectric resonator used in mobile communication such as car stereos, cordless telephones and pagers.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of communication information such as video signals and audio signals and the diversification of communication terminals such as car phones and mobile communications, a filter with high selection, low loss and high reliability is required. Development of a piezoelectric ceramic suitable for such a filter is desired.

Conventionally, Pb (Z
(r, Ti) O ₃ -based piezoelectric ceramics are used, and various improvements in composition are conventionally made in order to improve characteristics such as relative dielectric constant, electromechanical coupling coefficient Kp, and mechanical quality coefficient Qm. ing.

In recent years, such a piezoelectric element can be surface-mounted on a substrate with the development of electronic component chips. In mobile communication, as a means for compensating for a shortage of channels, a digital transmission system is used instead of an analog system. Multiplex of
A ceramic filter which performs time division and has good group delay time characteristics is desired, and its development is being promoted.

Conventionally, when a piezoelectric resonator is used as a kHz band ceramic filter, the center frequency is adjusted depending on its shape and dimensions, or four corners of a square piezoelectric resonator are cut off to form cut portions, thereby forming a center portion. The frequency is adjusted (see Japanese Utility Model Laid-Open No. 63-12191).

[0006]

Generally, in a piezoelectric first resonator of a ceramic filter for mobile communication such as a cordless telephone and a pager, the resonance frequency is low in the capacitance range and the operating temperature range. Must have good temperature characteristics. Here, in order to further reduce the electrostatic capacitance, it is necessary to use the electrodes on one surface of the piezoelectric vibrator as partial electrodes. However, when a resonator is formed by using one surface as a partial electrode, there is a problem that the temperature characteristics of the resonance frequency deteriorate in the operating temperature range. Therefore, when a filter is formed by using the above-mentioned piezoelectric resonator, there is a problem that the pass band changes due to a change in operating temperature.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a piezoelectric resonator having a small capacitance and a good temperature characteristic of a resonance frequency in an operating temperature range. .

[0008]

According to the present invention, there is provided a piezoelectric resonator comprising:
A piezoelectric resonator in which a square partial electrode is formed on one surface of a piezoelectric ceramic substrate formed by cutting out four corners of a sintered body having a square planar shape, and an entire surface electrode is formed on the other surface of the piezoelectric ceramic substrate. Where y _{1 is} the length of the partial electrode in the diagonal direction and y ₂ is the length of the full surface electrode in the diagonal direction of the partial electrode, 0.4 ≦ (y ₂
-Y ₁ ) / y ₁ ≦ 1.0 is satisfied.

[0009]

In the piezoelectric resonator of the present invention, the capacitance can be made smaller by forming the partial electrodes, the four corners of the square-shaped vibrator are cut off, and the diagonal of the square-shaped partial electrode is further cut. When the length in the direction is y ₁ and the length of the entire surface electrode in the diagonal direction of the partial electrode is y ₂ ,
Since 0.4 ≦ (y ₂ −y ₁ ) / y ₁ ≦ 1.0 is satisfied, the temperature characteristic of the resonance frequency can be improved. It is considered that this is because the asymmetry of stress generated in the low temperature region on the upper and lower surfaces of the piezoelectric ceramic substrate can be minimized.

Further, in the piezoelectric resonator of the present invention, the changes of the resonance frequency Fr and the anti-resonance frequency Fa become small, and the position of the ripple (abnormal resonance point) is lowered from the frequency band to be used, for example, near the 455 kHz band. By moving to the frequency side, it is possible to further reduce the spurious due to the short side vibration.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the piezoelectric resonator of the present invention, when the diagonal length of the partial electrode is y ₁ and the full length electrode of the partial electrode in the diagonal direction is y ₂ , 0.4 ≦ (y ₂ -
y ₁ ) / y ₁ ≦ 1.0 is satisfied.

As described above, (y ₂ −y ₁ ) / y _{1 is set} to 1 or less because when this value is larger than 1, the difference between the resonance frequency on the low temperature side and the resonance frequency on the high temperature side is large. This is because the temperature characteristics of the resonance frequency deteriorate. From the viewpoint of improving the temperature characteristics of the resonance frequency, 0.4 ≦ (y
₂₋ y ₁ ) / y ₁ ≦ 0.8, particularly 0.4 to 0.
7 is desirable.

Further, the piezoelectric ceramic substrate of the present invention preferably contains, for example, Pb (Zr, Ti) O ₃ as a main component. For example, Pb (Zr, Ti) O ₃ Pb, Z
A part of r, Ti is substituted with an alkaline earth metal such as Ba, a group 5a element of the periodic table such as Nb, a rare earth element such as Y, or a group 6a element of the periodic table such as Cr is used. .

[0014]

1 and 2 show a piezoelectric resonator of the present invention. In FIG. 1, reference numeral 1 indicates a piezoelectric ceramic substrate containing Pb (Zr, Ti) O ₃ as a main component. This piezoelectric ceramic substrate 1 is formed by cutting four corners of a sintered body 2 having a square planar shape as shown in FIG. 3 in equal amounts (a). A square partial electrode 4 similar to the planar shape of the sintered body 2 is formed on one surface of the piezoelectric ceramic substrate 1, and a full surface electrode 5 is formed on the other surface.

In the piezoelectric resonator of the present invention, as shown in FIG. 4, the diagonal length of the partial electrode 4 is y ₁ , and the full length electrode 5 of the partial electrode 4 in the diagonal direction is y. _When it is set to ₂ , 0.4 ≦ (y ₂ −y ₁ ) / y ₁ ≦ 1.0 is satisfied.

In order to confirm the effects of the present invention, the present inventors have measured the size of the piezoelectric ceramic substrate 1 (the size 1 of the sintered body 2), the cut amount (t) of the sintered body 2, and the size of the partial electrode 4. (B) and (y ₂ −y ₁ ) / y ₁ are changed,
The temperature characteristics of capacitance and resonance frequency were investigated.

First, as starting materials, commercially available PbO and T having a purity of 99.5% or more and an average particle size of 1.0 to 3.0 μm are used.
iO ₂ , ZrO ₂ , Nb ₂ O ₅ , Y ₂ O ₃ , Cr ₂ O ₃
A predetermined amount of each powder of BaCO ₃ and BaCO ₃ was weighed, wet mixed in a ball mill, dried, and calcined. After wet pulverizing this with a ball mill, an organic binder is added and pressure molding is performed, and this molded body is fired in an oxidizing atmosphere to obtain a composition formula (Pb _0.97 Ba _0.03 ) (Nb _0.525 Cr _0.285 Y _0.190 )
_A sintered body having a square planar shape represented by _0.05 Ti _0.494 Zr _0.456 O ₃ was produced.

This was ground to a thickness of 0.5 mm, and a square partial electrode having a length b shown in Table 1 and a thickness of 10 μm was formed on one surface, and a full-scale electrode having a thickness of 10 μm was formed on the other surface.

For the electrodes, a paste made of Agj glass was applied, dried and then baked at 520 ° C. to form the electrodes. Immerse this in insulating oil at 80 ° C and apply 3k to both end surfaces.
A DC voltage of V / mm was applied for 30 minutes for polarization treatment. Then, heat treatment was performed at 220 ° C. for 1 hour to stabilize the polarization stable state.

Next, this piezoelectric ceramic was cut into a square plate having a square planar shape with a side length l of 4.6, 4.8 and 5.0 mm as shown in Table 1, A sample of the piezoelectric resonator was obtained.

Then, the four corners of the sample were obliquely cut by equal amounts (t) as shown in Table 1 to form cut portions. The cut amount t of the cut portion is the distance from the square-shaped apex angle in FIG.

After that, the electromechanical coupling coefficient Kp of each piezoelectric resonator was calculated from the values of the resonance frequency and the anti-resonance frequency measured at a measurement frequency of 350 to 550 kHz by an impedance analyzer (4194A). The capacitance was measured with an impedance analyzer (4194A) at a measurement frequency of 1 kHz. Furthermore, 25 ℃ and -30 ℃
, The resonance frequency at 25 ° C. is f (25), and the resonance frequency at −30 ° C. is f (−3).
0). In addition, f (2
5) -f (-30) was calculated. Table 1 shows the results.

[0023]

[Table 1]

From Table 1, in the samples within the range of the present invention, the capacitance is small and the temperature characteristic f (2) of the resonance frequency is
5) It can be seen that -f (-30) has excellent characteristics of less than 1 kHz.

[0025]

As described in detail above, the piezoelectric resonator of the present invention has a small capacitance and a good temperature characteristic of the resonance frequency in the operating temperature range, and the resonance frequency Fr,
The change in the anti-resonance frequency Fa becomes small, and the position where the ripple (abnormal resonance point) occurs is determined by the frequency band used, for example
It is possible to move from the vicinity of 55 kHz band to the low frequency side and further reduce the spurious due to vibration in the short side direction, which is most suitable for the piezoelectric first resonator of the ceramic filter for mobile communication such as cordless telephones and pagers. A piezoelectric resonator can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a piezoelectric resonator of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a plan view showing a square piezoelectric ceramic substrate.

FIG. 4 is a plan view of the piezoelectric resonator of the present invention.

[Explanation of symbols]

 1 ... Piezoelectric ceramic substrate 2 ... Sintered body 4 ... Partial electrode 5 ... Full surface electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Fukuda 1-4 Yamashita-cho, Kokubun-shi, Kagoshima Inside Kyocera Stock Company Research Institute (72) Inventor Katsuhiko Onizuka 1-4-4 Yamashita-cho, Kokubun-shi, Kagoshima Kyocera Corporation Shikisha Research Institute

Claims (1)

[Claims] 1. A square-shaped partial electrode is formed on one surface of a piezoelectric ceramic substrate formed by cutting four corners of a sintered body having a square planar shape, and a full-scale electrode is formed on the other surface of the piezoelectric ceramic substrate. When the length of the partial electrode in the diagonal direction is y ₁ and the length of the full surface electrode in the diagonal direction of the partial electrode is y ₂ ,
A piezoelectric resonator characterized by satisfying 0.4 ≦ (y ₂ −y ₁ ) / y ₁ ≦ 1.0.