JP3330099B2 - Piezoelectric oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pair of opposing vibration electrodes formed at the center of both main surfaces of a rectangular shape of a piezoelectric substrate, and electrically connected to the vibration electrodes, in a longitudinal direction of the piezoelectric substrate. And with a drawing electrode that is drawn out in the opposite side direction, and relates to a piezoelectric oscillator in which energy is confined in a vibrating portion sandwiched between a pair of facing vibrating electrodes, such as a resonator or a filter. The present invention relates to an applied energy trap type piezoelectric oscillator.

[0002]

2. Description of the Related Art Conventionally, an energy trap type piezoelectric oscillator used for a resonator or a filter has a frequency of several MHz.
Used in the frequency band from z to several tens of MHz.

For example, an energy trap type piezoelectric oscillator using a third overtone mode of thickness longitudinal vibration used for a resonator or the like is provided with a vibrating electrode on a part of one piezoelectric substrate polarized in the thickness direction. Has a structure
An alternating electric field is applied in the same direction as the polarization direction to utilize vibration in the thickness direction.

In other words, in the prior art, a thickness-longitudinal-vibration energy-trapping type piezoelectric oscillator has vibrating electrodes formed on a part of the opposing surface of a single piezoelectric substrate, and is sandwiched between a pair of opposing vibrating electrodes. A vibrating part and other non-vibrating parts were formed.

[0005] In such a piezoelectric oscillator, the vibration excited by applying an AC electric field to a pair of vibrating electrodes is confined in a vibrating portion between the vibrating electrodes.

When a piezoelectric oscillator is used as a resonator for a reference signal oscillator of a microcomputer, it is used by being incorporated in, for example, a Colpitts oscillation circuit. FIG. 5 shows a Colpitts-type oscillation circuit. The Colpitts-type oscillation circuit includes capacitors 11, 12, a resistor 13, an inverter 14, and an oscillator 15. Then, in order to generate an oscillation signal in the Colpitts oscillation circuit, it is necessary to satisfy the following oscillation conditions in relation to the loop gain and the phase shift amount.

The amplification factor of the amplifier consisting of the inverter 14 and the resistor 13 is α and the phase shift amount is θ _1. The feedback ratio of the feedback circuit consisting of the oscillator 15 and the capacitors 11 and 12 is β, and the phase shift amount is θ. _{When 2} , the loop gain needs to be α × β ≧ 1, and the phase shift amount needs to be θ ₁ + θ ₂ = 360 degrees × n (where n = 1, 2, 3,...).

In order to satisfy the condition of the amount of phase shift, it is important that there is no phase shift distortion due to spurious generation between and near the resonance frequency Fr and the antiresonance frequency Fa.

Further, in the Colpitts type oscillation circuit,
To obtain stable oscillation, the loop gain must be increased. Therefore, the P / V value of the oscillator that determines the gain of the feedback ratio β, that is, the resonance impedance R
It is necessary to increase the difference between o and the anti-resonance impedance Ra, and it is important that spurious is superimposed near the resonance frequency Fr and the anti-resonance frequency Fa, and the P / V value does not decrease.

As a method for reducing spurious, Japanese Patent Application Laid-Open No. 8-148767 discloses a method in which an organic polymer containing at least one powder particle selected from ceramics, glass and metal is applied to a piezoelectric resonator. Have been.

[0011]

However, in the conventional energy trap type piezoelectric oscillator, when the shape and size of the piezoelectric substrate are reduced in response to the demand for miniaturization of components, the shape of the piezoelectric substrate and the shape of the electrodes are reduced. Due to the temperature change, spurs that do not move due to temperature change are likely to occur, and the vibration excited by applying an AC electric field to a pair of vibrating electrodes of the piezoelectric substrate propagates to the non-vibrating part, and the vibration is not attenuated on the substrate end face. There is a problem that the end surface of the vibration is reflected because it is easy to reach, and spurs which largely move with the temperature change are induced.

For example, in an energy trapping type resonator of the third overtone mode of thickness longitudinal vibration, the temperature change of the oscillation frequency is about +10 to 50 ppm / ° C.
The temperature change of the spurious frequency that moves greatly with the temperature change is large at about -100 to -300 ppm / [deg.] C., and the direction of the change is also different.

Therefore, at room temperature of 25 ° C., even if there is no spurious between and near the resonance frequency Fr and the antiresonance frequency Fa, when the temperature of the oscillator is changed, the spurious moves and the temperature at which the oscillation frequency and the spurious intersect is changed. At the crossing temperature, the phase shift is distorted due to the moved spurious, and the phase shift condition is not satisfied, and the anti-resonance impedance Ra is significantly reduced or the resonance impedance Ro is significantly increased, so that P / There is a problem that the V value becomes extremely small and oscillation stops.

For this reason, the shape of the piezoelectric substrate is limited to a size that does not induce spurious vibrations that largely move with a change in temperature, and there is a problem that the size of the piezoelectric substrate cannot be reduced.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 8-148767, an organic polymer containing at least one powder particle selected from ceramics, glass and metal is applied to a piezoelectric resonator. It has been found that at room temperature of 25 ° C. the spurious is reduced.

However, according to the method disclosed in this publication, an organic polymer containing at least one powder particle selected from ceramics, glass and metal is partially applied, and a spurious response is obtained by partially applying a mass load. Is effective in suppressing spurious vibrations that do not move due to temperature changes caused by the shape of the piezoelectric substrate and the shape of the electrodes, but it is particularly effective in piezoelectric resonators using the third-order overtone mode. In the case where the coating area or the coating thickness is small, it has been difficult to eliminate spurious vibration having a large temperature change due to the end face reflection.

Further, the application of an organic polymer containing powder particles has a problem that the P / V value is remarkably reduced, and has a sufficiently large P / V value. It has been difficult to suppress the generation of moving spurious.

In view of such a conventional problem, the present invention can reduce the size and size of the piezoelectric substrate, particularly the size in the width direction, to reduce the size, and can suppress the generation of spurious components that move with temperature changes. It is an object of the present invention to provide a piezoelectric oscillator having a large P / V value, and capable of obtaining a small-sized and stable oscillation in a wide temperature range.

[0019]

According to the present invention, there is provided a piezoelectric oscillator comprising:
[Claim 1] A piezoelectric substrate, a pair of opposing vibration electrodes formed at the center of both rectangular main surfaces of the piezoelectric substrate, and a longitudinal direction of the piezoelectric substrate electrically connected to the vibration electrodes. And a lead-out electrode that is pulled out in the opposite side direction of the piezoelectric vibrator, wherein energy is confined in a vibrating part sandwiched between the pair of opposing vibrating electrodes. One side of
Only on the surface , the thickness is 50 to 200 μm and the Young's modulus is 1 ×
An organic polymer of 10 ⁶ to 1 × 10 ¹⁰ Pa is provided, the length of the vibrating electrode in the longitudinal direction of the piezoelectric substrate is B ₁ , and the length of the organic polymer in the longitudinal direction of the piezoelectric substrate is B When L is satisfied, L / B ₁ ≧ 3 is satisfied .
Serial length W ₁ of the short sides of the rectangular main surface of the piezoelectric substrate is 1.5m
m or less .

Here, when the length of the short side of the rectangular main surface of the piezoelectric substrate is W ₁ and the length of the vibrating electrode in the short direction of the piezoelectric substrate is B ₂ , 0.2 ≦ B ₂ / It is desirable to satisfy W ₁ ≦ 0.9.

[0021]

[Action] In the piezoelectric oscillator of the present invention, on at least one side surface in the short direction of the piezoelectric substrate, a length of 3 times or more in length with respect to B ₁ of the vibrating electrode in the longitudinal direction of the piezoelectric substrate, and Young Since the organic polymer having a ratio of 1 × 10 ⁶ to 1 × 10 ¹⁰ Pa is provided, it is possible to eliminate the generation of spurious components which largely move with a change in temperature.

That is, when an AC electric field is applied to the vibrating electrode to excite it, the vibration generated in the vibrating portion sandwiched between the vibrating electrodes is not completely confined, and a part of the vibration propagates to the non-vibrating portion. .

If the area of the non-vibrating portion is reduced along with the miniaturization of the piezoelectric substrate, the propagated vibration reaches the end face of the piezoelectric substrate without being attenuated. Since it is absorbed by the organic polymer provided on the side surface in the hand direction, the reflection of vibration is eliminated, and the generation of spurious components that move significantly with a change in temperature can be eliminated.

In the piezoelectric oscillator of the present invention, when the length of the short side of the rectangular main surface of the piezoelectric substrate is W ₁ , and the length of the vibrating electrode in the short direction of the piezoelectric substrate is B ₂ , 0 .2 ≦ B
By satisfying ₂ / W ₁ ≦ 0.9, even at room temperature of 25 ° C., there is no spurious between and near the resonance frequency and the anti-resonance frequency, and the P / V value can be increased.

Further, the thickness of the organic polymer is set to 50 to 20.
By setting the thickness to 0 μm, it is possible to further suppress the generation of spurious components that move with a change in temperature, and to further increase the P / V value.

Therefore, even when the size of the piezoelectric substrate is reduced, the generation of spurious components that largely move with temperature changes can be suppressed, and the generation of spurious components between and near the resonance frequency and the antiresonance frequency is suppressed. Further, since the P / V value can be further increased, an energy-trap type piezoelectric resonator which is small and exhibits stable oscillation characteristics over a wide temperature range can be obtained.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, a piezoelectric oscillator according to the present invention has a piezoelectric substrate 1 having a rectangular main surface.
A pair of opposed vibrating electrodes 2 and 3 formed at the center of both rectangular main surfaces of the piezoelectric substrate 1;
And extraction electrodes 4 and 5 electrically connected to each other. The extraction electrodes 4 and 5 are extracted in the longitudinally opposed side surfaces of the piezoelectric substrate 1 (toward the short sides of the piezoelectric substrate 1). The portion sandwiched between the pair of opposing vibrating electrodes 2 and 3 is the vibrating portion 7, and the other portion is the non-vibrating portion 8, and energy is confined in the vibrating portion 7.

In the piezoelectric resonator of the present invention, one side surface in the short direction of the piezoelectric substrate 1 (one side surface on the long side)
In addition, an organic polymer 9 having a Young's modulus of 1 × 10 ⁶ to 1 × 10 ¹⁰ Pa is provided. The length L of the organic polymer 9
Is at least three times the length B ₁ of the vibration electrode in the longitudinal direction of the piezoelectric substrate 1.

That is, the length of the vibrating electrodes 2 and 3 in the longitudinal direction (long side direction) of the piezoelectric substrate 1 is B ₁ ,
When the length of the organic polymer 9 in the longitudinal direction is L, L / B ₁ ≧ 3 is satisfied. The organic polymer 9 is desirably formed on the side surface closest to the vibrating portion 7, and the formed length L is desirably wide so as to absorb vibration more. It is desirable to form over the entire long side surface from the viewpoint of absorbing vibration more.

The vibrating electrodes 2 and 3 are portions where the electrodes formed on both main surfaces of the piezoelectric substrate 1 overlap, and the length B ₁ of the vibrating electrode coincides with the width of the vibrating portion 7. Become.

The reason that the length L of the organic polymer 9 is set to be three times or more the length B ₁ of the vibrating electrode in the longitudinal direction of the piezoelectric substrate 1 is that a part of the vibration generated in the vibrating portion 7 is Since the length L of the organic polymer 9 is shorter than three times the length B _{1 of the} vibrating electrode, the organic polymer 9 is formed because the organic polymer 9 is isotropically propagated through the piezoelectric substrate 1. This is because reflection occurs at the non-existing portion, and spurious components that largely move with a change in temperature cannot be eliminated.

The Young's modulus of the organic polymer 9 is 1 × 1
0 ^6-1 reasons in the range of × 10 ¹⁰ Pa, when the Young's modulus of the organic polymer material 9 is less than 1 × 10 ⁶ Pa, the organic polymer material 9 is too soft increases with the temperature change No effect on suppressing generation of moving spurious, 1 × 1
If the pressure exceeds 0 ¹⁰ Pa, the vibrations that have reached the end face of the piezoelectric substrate 1 cannot be completely absorbed, and some of the vibrations will be reflected. Because you can't.

The organic polymer 9 has a Young's modulus of 1 × 10 ^6.
An epoxy resin, a silicon resin, an acrylic resin, a urethane resin, or the like having a range of about 1 × 10 ¹⁰ Pa is used.

Further, the thickness of the organic polymer 9 is 50 to 2
Desirably, it is 00 μm. This is because, when the thickness of the organic polymer 9 is less than 50 μm, the vibration reaching the end face of the piezoelectric substrate 1 cannot be completely absorbed, and spurious components that move with a temperature change are easily generated. Conversely, if it exceeds 200 μm, the P / V value tends to decrease. The thickness of the organic polymer 9 is
For the above-mentioned reason, it is desirable that the thickness be 100 to 150 μm.

Further, in the piezoelectric resonator of the present invention, the length of the short side of the rectangular main surface of the piezoelectric substrate 1 is W ₁ , the vibration electrode 2 in the short direction of the piezoelectric substrate 1 (along the long side), when the third length was B _2, it is desirable to satisfy _{0.2 ≦ B 2 / W 1 ≦} 0.9.

The ratio of the length B ₂ of the vibrating electrode in the short side direction to the length W ₁ of the short side in the range of 0.2 ≦ B ₂ / W ₁ ≦ 0.9 is larger than 0.9. Or less than 0.2, spurs occur between and near the resonance frequency and the antiresonance frequency even at room temperature of 25 ° C., and P / V
This is because the value is significantly reduced.

The length W ₁ of the short side of the rectangular main surface of the piezoelectric substrate ₁ is 1.5 mm or less in order to achieve miniaturization.
Have been.

The piezoelectric substrate 1 is, for example, a piezoelectric ceramic substrate. Specifically, the piezoelectric substrate 1 is mainly composed of lead titanate (PT), and at least a part of Pb of lead titanate PbTiO ₃ is replaced by La. And a main component is an ABO ₃ -type perovskite-type composite oxide in which at least a part of Ti is replaced by Mn, and a B-site constituent element 1
When the number of moles of Pb to the mole is a and the total number of moles of elements other than Pb among the A-site constituent elements is b, a / (1
-B) is 0.92 to 0.99, a part of Pb is replaced by at least one of Sr, Ba and Ca, and a part of Ti is (Fe
_1/3 Sb _2/3 ), (Co _1/3 Sb _2/3 ), (Y _1/2 Sb
_1/2 ), (Yb _1/2 Sb _1/2 ), (In _1/2 Sb _1/2 )
And (Mg _1/3 Sb _2/3 ) substituted with at least one of them.

The vibrating electrodes 2 and 3 and the extraction electrodes 4 and 5 are formed by depositing a metal such as Cr, Ag, Cu, Pt, Ni, Au or the like individually or by sequentially combining them,
It is formed by vapor deposition or sputtering.

In the piezoelectric resonator configured as described above,
An organic polymer having a Young's modulus of 1 × 10 ⁶ to 1 × 10 ¹⁰ Pa on the side surface of the piezoelectric substrate 1 and having a length of at least three times the length B ₁ of the vibrating electrode in the longitudinal direction of the piezoelectric substrate 1. Since the number 9 is provided, it is possible to eliminate the occurrence of spurious components that move largely with a change in temperature. Further, compared to the conventional piezoelectric resonator, since the organic polymer does not contain powder particles,
/ V value can be significantly improved.

Further, the ratio of the length B ₂ of the vibrating electrode in the short direction to the length W ₁ of the short side of the rectangular main surface of the piezoelectric substrate 1 is set to 0.2 ≦ B ₂ / W ₁ ≦ 0.9. By doing, 2
Even at a room temperature of 5 ° C., there is no spurious between and near the resonance frequency and the anti-resonance frequency, and the P / V value can be increased.

The thickness of the organic polymer 9 is set to 50 to 20.
By setting the thickness to 0 μm, it is possible to further suppress the generation of spurious components that move with a change in temperature, and to further increase the P / V value.

In the above example, the organic polymer 9 formed on the side surface of the piezoelectric substrate 1 has an elliptical shape. However, in the present invention, the shape of the organic polymer 9 is not particularly limited.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the dimensions of the piezoelectric substrate 1 are set to (long sides 3.0 to 3.0).
2.0 mm, the short side W ₁ 1.52~0.5mm, thickness 0.
(Pb _0.85 ) _0.97 La _0.1 Sr _0.05
A piezoelectric substrate 1 made of (Fe _1/3 Sb _2/3 ) _0.02 Mn _0.02 Ti _0.96 O ₃ was produced.

Cr and Ag were sequentially deposited on both main surfaces of the piezoelectric substrate 1 and polarized at a temperature of 80 ° C. and 2 kV DC for 30 minutes. After that, the dimensions of the electrodes for simultaneously forming the extraction electrodes 4 and 5 electrically connected to the vibration electrodes 2 and 3 are changed, and a resist is printed on a rectangular portion corresponding to the electrodes, and the non-vibration portion is printed. After removing the electrode at the portion corresponding to No. 8 by etching, the resist was removed to obtain an energy confined ceramic resonator using a third overtone of thickness longitudinal vibration corresponding to an oscillation frequency of 33.86 MHz.

Further, an epoxy resin having a Young's modulus shown in Table 1 is applied to the side surface of the piezoelectric substrate 1 with a length L and a thickness t shown in Table 1 to form an organic polymer 9. A piezoelectric resonator as shown in FIG.

The ratio (L / B ₁ ) of the length L of the organic polymer 9 in the longitudinal direction of the piezoelectric substrate 1 to the length B ₁ of the vibrating electrode in the longitudinal direction of the piezoelectric substrate 1, rectangular main surface short side of length W _1, and the ratio of the length of B ₂ in the widthwise direction of the vibrating electrode to the length W ₁ of the short side of (B ₂ / W _1), the organic polymer material 9 The thickness was set to t, and these were changed as shown in Table 1.

Regarding the characteristics of the piezoelectric oscillator, the presence or absence of spurious was confirmed by impedance characteristics at 25 ° C., and the temperature was changed from −40 ° C. to + 150 ° C., and two items of impedance characteristics and oscillation characteristics were evaluated.
As the impedance characteristics, the impedance waveform (anti-resonance impedance Ra and resonance impedance Ro) of the third overtone of thickness longitudinal vibration and phase shift were measured by an impedance analyzer. For the oscillation characteristics, the oscillation frequency was measured using the inverter oscillation circuit shown in FIG. Table 1 shows the results. P / V value is P / V
= 20 x Log (Ra / Ro).
In addition, sample No. Reference numerals 6 and 8 indicate reference samples.

[0049]

[Table 1]

From Table 1, it can be seen that in the piezoelectric oscillator of the present invention,
The P / V value is as high as 55 or more, and the resonance frequency Fr and the anti-resonance frequency F are not only affected by spuriousness at 25 ° C. (room temperature) but also by temperature change from −40 ° C. to + 150 ° C.
There was no spurious during and near a, and no generation of moving ripple and no oscillation stop were observed. Sample N
25 ° C and 115 ° C of energy confinement type oscillator of o.3
FIG. 3 shows the impedance characteristics at.

On the other hand, the sample No. 11 having a small Young's modulus is too soft and has no effect on suppressing the spurious movement due to the temperature change, and the Young's modulus is 1 × 10 ¹⁰
In sample No. 16 exceeding Pa, some vibrations were reflected without being able to absorb the vibrations that reached the end face of the piezoelectric substrate,
Spurious that moves with the temperature change occurred.

Further, in Sample No. 21, where no organic polymer was formed, spurious was generated at 25 ° C., and when the temperature was increased from 25 ° C. to 114 ° C., the sample moved from the higher frequency side. The ripple was superimposed on the anti-resonance frequency, causing phase distortion and a decrease in the P / V value, and the oscillation was stopped. FIG. 4 shows the impedance characteristics at 25 ° C. and 115 ° C. at this time.

Sample No. 22 was obtained by applying a coating obtained by adding Al ₂ O ₃ particles to an epoxy resin. In this case, the P / V value was low, and spurious components that moved with a temperature change were generated. Occurred.

[0054]

As described in detail above, in the piezoelectric oscillator of the present invention, on at least one side in the short direction of the piezoelectric substrate, in the longitudinal direction of the vibrating electrode of the piezoelectric substrate with respect to the length B ₁ 3 More than double length, Young's modulus is 1 × 10 ⁶ to 1 × 10 ¹⁰
Since the organic polymer of Pa is provided, it is possible to eliminate the occurrence of spurious components that largely move with a change in temperature.

The ratio of the length B ₂ of the vibrating electrode in the short direction to the length W ₁ of the short side of the piezoelectric substrate is set to 0.9 ≧ B ₂ / W
By setting ₁ ≧ 0.2, even at a room temperature of 25 ° C., there is no spurious between and near the resonance frequency and the antiresonance frequency, and the P / V value can be increased.

Further, the thickness of the organic polymer is set to 50 to 20.
By setting the thickness to 0 μm, it is possible to further suppress the generation of spurious components that move with a change in temperature, and to further increase the P / V value.

[Brief description of the drawings]

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

FIG. 2 is a side view of FIG.

FIG. 3 is a schematic diagram showing a Colpitts type oscillation circuit.

FIG. 4 shows the piezoelectric oscillator of Sample No. 3 at + 25 ° C. and +115.
It is the impedance characteristic of ° C.

FIG. 5 shows + 25 ° C. and +11 of the piezoelectric oscillator of Sample No. 21.
This is an impedance characteristic at 5 ° C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2, 3 ... Vibration electrode 4, 5 ... Extraction electrode 7 ... Vibration part 8 ... Non-vibration part 9 ... Organic polymer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-3612 (JP, A) JP-A-8-1448967 (JP, A) JP-A-3-123214 (JP, A) JP-A-50- 104886 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/17 H03H 9/02

Claims (2)

(57) [Claims] 1. A piezoelectric substrate, a pair of opposing vibration electrodes formed in the center of both rectangular main surfaces of the piezoelectric substrate, and electrically connected to the vibration electrodes and in a longitudinal direction of the piezoelectric substrate. And a lead-out electrode that is pulled out in the opposite side direction of the piezoelectric vibrator, wherein energy is confined in a vibrating part sandwiched between the pair of opposing vibrating electrodes. One side of
Only on the surface , the thickness is 50 to 200 μm and the Young's modulus is 1 ×
An organic polymer of 10 ⁶ to 1 × 10 ¹⁰ Pa is provided, the length of the vibrating electrode in the longitudinal direction of the piezoelectric substrate is B ₁ , and the length of the organic polymer in the longitudinal direction of the piezoelectric substrate is B When L is satisfied, L / B ₁ ≧ 3 is satisfied .
Serial length W ₁ of the short sides of the rectangular main surface of the piezoelectric substrate is 1.5m
m or less . 2. The length of the short side of the rectangular main surface of the piezoelectric substrate is W
_1, wherein when the length of the vibrating electrode in the lateral direction of the piezoelectric substrate was B _2, the piezoelectric oscillator according to claim 1, characterized by satisfying the _{0.2 ≦ B 2 / W 1 ≦} 0.9 Child.