JP2000281434A - Dielectric porcelain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dielectric porcelain having a temperature coefficient capable of compensating temperature coefficient of a piezoelectric resonator and having high folding endurance. SOLUTION: This dielectric porcelain has main crystalline particles 1 comprising perovskite type complex oxide containing at least Pb, Mg, Nb and Ti as metal elements and crystalline particles 2 comprising a bismuth layered compound which is present in grain boundary of the main crystalline particles 1. The bismuth layered compound is preferably at least one kind of compound among SrBi4Ti4O15, CaBi4Ti4O15 and PbBi4Ti4O15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a dielectric porcelain,
In particular, the present invention relates to a dielectric ceramic used as a capacitive element of an oscillator having a built-in load capacitance.

[0002]

2. Description of the Related Art In recent years, portable information communication devices have been widely used due to miniaturization of information communication devices, and various electronic components mounted on the devices have been reduced in size and height. Especially for oscillators built into information and communication equipment,
It is widely used as a reference signal for microcomputers, and there is a strong demand for a small, low-profile oscillator.

In an oscillation circuit, two load capacitance components C ₁ and C ₂ are connected between both ends of a piezoelectric vibrator 11 and a ground potential, as shown in an equivalent circuit shown in FIG. , The feedback resistor 15 and the inverter 16 are connected respectively. As described above, since the oscillation circuit needs the load capacitance components C ₁ and C ₂ , an oscillator having a built-in load capacitance is widely known in order to reduce the number of components and reduce the size and height.

A resonator having a built-in load capacitance has a structure in which, for example, a piezoelectric resonator and a load capacitance element are adhered to each other, fixed on an alumina substrate having high bending strength, and covered with a metal or ceramic lid. There is something. In this case, in order to reduce the height of the oscillator, it is necessary to reduce the thickness of the load capacitance element, which is one of the constituent members. The electrical characteristics required of the oscillator include temperature characteristics of the oscillation frequency.

The temperature characteristics of the oscillation frequency are described in
As described in Japanese Unexamined Patent Publication No. 7006 and the like, not only the temperature characteristics of the piezoelectric resonator but also the temperature characteristics of the capacitance of the load capacitance element are greatly affected. In particular, in the case of a PbTiO ₃ -based oscillator using a fundamental wave of thickness-shear vibration, the temperature characteristic of the oscillation frequency greatly changes due to the temperature change of the capacitance of the load capacitor. For this reason, in order to obtain an oscillator having a small change in the oscillation frequency in a wide temperature range, it is necessary to select an optimum load capacitance element and combine it with a piezoelectric resonator. Particularly, in recent years, it has been desired to reduce the temperature stability of the oscillation frequency, and it is necessary to control the temperature characteristics of the oscillator more strictly.

Conventionally, as a dielectric ceramic composition constituting a load capacitance element, Pb (Mg _1/3 Nb _2/3 ) O having a negative temperature coefficient of capacitance in a temperature range of -40 to + 150 ° C.
_A dielectric porcelain made of a perovskite-type composite oxide containing ₃ as a main component and at least PbTiO ₃ has been used.

[0007]

However, the above P
A dielectric porcelain composed of a perovskite-type composite oxide containing b (Mg _1/3 Nb _2/3 ) O ₃ as a main component and containing at least PbTiO ₃ has a transverse rupture strength of about 110 MPa and cracks during the polishing step. , The frequency of chipping is very high,
When the thickness of the porcelain was reduced to 200 μm to reduce the height, the resulting porcelain had a yield of only about 70% of the input amount.

Further, since the strength is low, there is a problem that cracking of the element and chipping of the end portion are apt to occur even in processing such as cutting out the element from the substrate. In addition, the built-in load capacitance type oscillator requires the piezoelectric resonator and the load capacitance element to be bonded together and fixed on an alumina substrate with high flexural strength. Since the load capacitance element may be broken due to the generation of stress due to the difference in thermal shrinkage, the thickness of the dielectric porcelain of the load capacitance element must be about 400 μm, and a low-profile type oscillator must be obtained. Could not.

Accordingly, an object of the present invention is to provide a dielectric ceramic having a temperature coefficient capable of compensating for the temperature coefficient of a piezoelectric resonator and having a high bending strength.

[0010]

According to the present invention, there is provided a dielectric porcelain comprising:
At least Pb, Mg, Nb and Ti as metal elements
And main crystal particles composed of a perovskite-type composite oxide containing the same, and crystal particles composed of a bismuth layer compound present at the grain boundaries of the main crystal particles. here,
The bismuth layer compound is SrBi ₄ Ti ₄ O ₁₅ , CaBi
₄ Ti ₄ O ₁₅ , BaBi ₄ Ti ₄ O ₁₅ and PbBi ₄
Desirably, at least one of Ti ₄ O ₁₅ is used.

The dielectric porcelain of the present invention comprises, as a main component, a perovskite-type composite oxide containing at least Pb, Mg, Nb and Ti as metal elements.
SrBi ₄ Ti ₄ O ₁₅ , CaBi ₄
Ti ₄ O ₁₅ , BaBi ₄ Ti ₄ O ₁₅ and PbBi ₄ T
It is desirable that at least one of i ₄ O ₁₅ be contained in an amount of 0.5 to 15.0 parts by weight.

Further, the perovskite-type composite oxide is
The composition formula is _expressed as Pb _1-a A _a ｛(Mg _1/3 Nb _2/3 ) _b (Co
_1/3 Nb _2/3 ) _c ｝ Ti _1-bc O ₃ (A is B
a, at least one of Sr and Ca),
b and c are 0.25 ≦ a ≦ 0.60, 0.60 ≦ b
≦ 0.80, 0.01 ≦ c ≦ 0.20, b + c <1.0
It is desirable to satisfy 0.

[0013]

According to the dielectric porcelain of the present invention, the perovskite-type composite oxide containing at least Pb, Mg, Nb and Ti as metal elements has a high dielectric constant, and the main crystal particles comprising the perovskite-type composite oxide In the grain boundaries of
The presence of crystal particles composed of the bismuth layered compound allows the ceramic strength to be improved while maintaining a high dielectric constant, and the temperature coefficient of capacitance to be -1000 to-
3000 ppm / ° C.

That is, by appropriately dispersing crystal particles of the bismuth layered compound having a large accept ratio in the grain boundaries of the main crystal particles, the stress in the porcelain can be effectively dispersed, and as a result, the mechanical strength is improved. be able to.

Further, at least Pb, M
The perovskite-type composite oxide containing g, Nb and Ti has a high dielectric constant, and can maintain high mechanical strength without lowering the dielectric constant by containing an appropriate amount of the bismuth layered compound.

Further, at least Pb as a metal element,
The perovskite-type composite oxide containing Mg, Nb and Ti has a large negative temperature coefficient of capacitance in a temperature range of −40 to + 150 ° C., and the bismuth layered compound has a temperature coefficient of −40.
The temperature coefficient of capacitance is 100 in the temperature range of
0 to 2000 ppm / ° C., and the dielectric ceramic of the present invention, which is a composite of these, has a temperature coefficient of capacitance of −1000 to −1000 without significantly changing the temperature coefficient of the main crystal grains. It can be in the range of -3000 ppm / ° C.

By combining with a piezoelectric resonator having a temperature characteristic of the oscillation frequency within ± 0.3% in a temperature range of −40 to + 150 ° C., the temperature characteristic of the oscillation frequency is corrected, and the load capacitance is incorporated. The temperature coefficient of the oscillation frequency of the type resonator can be almost zero.

Therefore, since the dielectric ceramic of the present invention has a high strength, the yield at the time of processing can be 99% or more even when the plate thickness is reduced to 200 μm, and the low-profile, low-level structure constituting the feedback circuit is realized. A dielectric ceramic for a load capacitance element of a type resonator can be obtained.

Further, the bismuth layered compound is XBi ₄ Ti
_{By using 4} O ₁₅ (X is at least one of Sr, Ca, Ba and Pb), the porcelain strength can be further improved.

Further, the dielectric porcelain of the present invention comprises, as a main component, a perovskite-type composite oxide containing at least Pb, Mg, Nb and Ti as metal elements, and 100 parts by weight of XBi ₄ Ti ₄ O ₁₅ (X is Sr,
At least one of Ca, Ba and Pb), that is, SrBi ₄ Ti ₄ O ₁₅ , CaBi ₄ Ti ₄ O ₁₅ , B
at least one of aBi ₄ Ti ₄ O ₁₅ and PbBi ₄ Ti ₄ O ₁₅ by containing 0.5 to 15.0 parts by weight, while maintaining a high dielectric constant, it is possible to improve the porcelain strength, static The temperature coefficient of the capacitance is -1000 to -3
000 ppm / ° C.

Further, the perovskite-type composite oxide is represented by a composition formula of Pb _1-a A _a ｛(Mg _1/3 Nb _2/3 ) _b (Co
_1/3 Nb _2/3 ) _c ｝ Ti _1-bc O ₃ (A is B
When at least one of a, Sr, and Ca), a, b, and c satisfy a predetermined range, the dielectric constant of the dielectric ceramic can be 500 or more.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a dielectric porcelain of the present invention has at least Pb, Mg, Nb as metal elements.
And main crystal particles 1 made of a perovskite-type composite oxide containing Ti and Ti, and crystal particles 2 made of a bismuth layered compound present at the grain boundaries of the main crystal particles 1. Al, Si and Zr are present at the grain boundaries of the main crystal grains 1.
May be present in a small amount.

Here, as the bismuth layered compound, B
i ₄ Ti ₃ O ₁₂ Bi ₃ Ti ₃ N ₆ O ₁₂ etc.
Bi ₄ Ti ₄ O ₁₅ (X is at least one of Sr, Ca, Ba and Pb) is desirable in that the strength can be improved.

The average particle size of the main crystal particles 1 is desirably 1.5 to 3.5 μm from the viewpoint of mechanical strength and relative permittivity, and the crystal particles 2 made of a bismuth layer compound enhance the mechanical strength. For this reason, the aspect ratio is 1.3 to 2.
Desirably, it is 0.

The dielectric porcelain of the present invention comprises, as a main component, a perovskite-type composite oxide containing at least Pb, Mg, Nb and Ti as metal elements, and 100 parts by weight of XBi ₄ Ti ₄ O ₁₅ (X is Sr, Ca, B
a and Pb) at 0.5 to 15.
It is desirable to contain 0 parts by weight.

This is mainly composed of XBi ₄ Ti ₄ O ₁₅ as a main component.
0.5 to 15.0 parts by weight with respect to 0 parts by weight is the reason why XBi ₄ Ti ₄ O ₁₅ is less than 0.5 parts by weight or more than 15.0% by weight. This is because the strength tends to decrease. As the amount of XBi ₄ Ti ₄ O ₁₅ , the temperature coefficient of the relative permittivity of the dielectric porcelain is −1000 to
From the viewpoint of being within the range of -3000 ppm / ° C,
It is particularly desirable that the amount be 1.0 to 7.0 parts by weight.

The compensation temperature range required for electronic components mounted on a vehicle is about twice as wide as the compensation temperature range for electronic components for electronic equipment. It is desirable that the temperature change rate of the oscillation frequency be within ± 0.1% with the oscillation frequency at the oscillation frequency of 25 ° C. as the reference frequency within the compensation temperature range of 150 ° C.

PbTiO as a ceramic oscillator material
The temperature change rate of the oscillation frequency in the case of using ₃ is -4.
Since it is about ± 0.5% at 0 to 150 ° C.,
In order to keep the temperature within 0.1%, the temperature coefficient of the capacitance must be −
Must be 1000-3000 ppm / ° C.
On the other hand, the bending strength is desirably 180 MPa or more. In addition, for miniaturization, the larger the relative permittivity, the better.
It is desired to be 500 or more.

The flexural strength of the dielectric porcelain is desirably 180 MPa or more. However, when the thickness of the dielectric porcelain is reduced to 200 μm in order to reduce the height, a yield of 99% or more is obtained. This is because it has the necessary strength.

Further, the perovskite-type composite oxide of the dielectric ceramic according to the present invention has a composition formula of Pb _1-a A _a ｛(Mg
_1/3 Nb _2/3 ) _b (Co _1/3 Nb _2/3 ) _c ｝ Ti _1-bc
When expressed as O ₃ (A is at least one of Ba, Sr and Ca), the a, b and c are 0.25 ≦ a ≦
0.60, 0.60 ≦ b ≦ 0.80, 0.01 ≦ c ≦
It is desirable to satisfy 0.20, b + c <1.00.

This means that a representing the substitution amount with at least one of Ba, Sr and Ca is set to 0.25 ≦ a ≦ 0.
The reason why the temperature coefficient is set to 60 is that the temperature coefficient of the capacitance can be set to −1000 to −3000 ppm / ° C. within this range. On the other hand, when a is smaller than 0.25, the temperature coefficient tends to increase, and when a is larger than 0.6, the temperature coefficient tends to decrease.

The reason why the replacement amount b of Ti with (Mg _1/3 Nb _2/3 ) is set to 0.60 ≦ b ≦ 0.80 is that the relative dielectric constant should be 500 or more within this range. Because it can be. On the other hand, when b is smaller than 0.6, the relative permittivity tends to be too high, and when b is larger than 0.8, the relative permittivity tends to be low.

The reason why the substitution amount c of Ti with (Co _1/3 Nb _2/3 ) is 0.01 ≦ c ≦ 0.20 is that the relative dielectric constant should be 500 or more within this range. Because it can be. On the other hand, when c is smaller than 0.01, the specific permittivity tends to decrease, and when c is larger than 0.2, the specific permittivity tends to be too high.

[0034]

EXAMPLES First, PbO, MgCO ₃ ,
Nb ₂ O ₃ , Co ₃ O ₄ , SrCO ₃ , CaCO ₃ , B
Each raw material powder of aCO ₃ and TiO ₂ was weighed in a predetermined amount so as to have a composition as shown in Table 1, and was wet-mixed with a ball mill for 12 hours or more. Then, the mixture was dehydrated and dried.
After calcining at 000 ° C. for 3 hours, the mixture was pulverized to obtain a perovskite-type composite oxide powder.

On the other hand, Bi ₂ O ₃ , Ti
O ₂ , PbO, SrCO ₃ , CaCO ₃ , and BaCO ₃ are weighed in predetermined amounts and wet-mixed in a ball mill for at least 12 hours.
Next, the mixture was dehydrated and dried, calcined at 1000 ° C. for 3 hours, and then pulverized to obtain SrBi ₄ Ti ₄ O ₁₅ and CaBi.
₄ Ti ₄ O ₁₅ , BaBi ₄ Ti ₄ O ₁₅ , PbBi ₄ Ti
_A bismuth layered compound powder consisting of ₄ O ₁₅ was obtained.

Thereafter, a predetermined amount of a predetermined bismuth layer compound shown in Table 1 was added to the perovskite-type composite oxide powder, mixed for 5 to 8 hours by a ball mill, dried, mixed with an organic binder, and granulated. . 2 t / cm of the obtained powder
^Under pressure of ² , long side 34mm, short side 21mm, thickness 1.5m
It was press-formed into a square plate having a size of m. After degreasing, these compacts were sealed in a container made of MgO or the like, and fired in the atmosphere at 1200 to 1300 ° C for 2 hours. The obtained sintered body porcelain was polished to a thickness of 1 mm, and a silver electrode was baked and cut into 5 mm square to obtain a capacitive element.

For the evaluation of the capacitance element, the relative permittivity, tan δ, and the temperature characteristics of the capacitance were measured with an impedance analyzer. The relative permittivity is εr = C × t / (ε ₀ × S)
(Where C is the capacitance value, t is the capacitance part thickness, ε ₀ is the dielectric constant of vacuum, and S is the capacitance part electrode area). The temperature coefficient of the capacitance is C _TC = ｛(C (150 ° C.) − C (−4
0 ° C)) {C (25 ° C)} / 190 × 10 ⁶ (ppm /
° C). Furthermore, the bending strength is JISR1
601 evaluated the 4-point bending strength. Table 1 shows the results.

[0038]

[Table 1]

From Table 1, it can be seen that in Sample No. to which no bismuth layered compound was added. In No. 1, the relative dielectric constant was 610 and the transverse rupture strength was 130 MPa. However, in the sample of the present invention, the relative permittivity was almost unchanged even though the bismuth layered compound was added to improve the transverse rupture strength to 180 MPa or more. They were equivalent, and the temperature coefficient was -1000 to -3000 ppm / ° C.

Then, the perovskite-type composite oxide satisfies a predetermined composition, and the amount of the bismuth layered compound added is 0.1.
The dielectric porcelain of the present invention in the case of 5 to 15 parts by weight has a temperature characteristic of capacitance of −1000 to −3000 ppm / ° C.,
It has a relative dielectric constant of 500 or more and a bending strength of 180 MPa or more, and has a bending strength about 1.5 times higher than that of a conventional Pb (Mg _1/3 Nb _2/3 ) O ₃ dielectric ceramic composition. And a thin capacitive element.

FIG. 2 shows the relationship between the amount of the bismuth layered compound obtained in the present invention and the bending strength. From FIG. 2, it is clear that the dielectric porcelain of the present invention can improve the bending strength.

[0042]

As described above, the dielectric porcelain according to the present invention has a flexural strength of the conventional Pb (Mg _1/3 Nb _2/3 ) O.
_{It is} about 1.5 times higher than the _3- PbTiO ₃ dielectric ceramic composition, has a relative dielectric constant as large as 500 or more, has a temperature coefficient of relative dielectric constant of −1000 to −3000 ppm / ° C., and has a stable temperature of the oscillation frequency. It can be seen that this is suitable as a resonator element having excellent characteristics.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a dielectric porcelain of the present invention.

FIG. 2 is a graph showing the relationship between the amount of a bismuth layered compound added and the transverse rupture strength.

FIG. 3 is a Colpitts type oscillation circuit diagram.

[Explanation of symbols]

 1 ・ ・ ・ Main crystal particles 2 ・ ・ ・ Crystal particles

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4G031 AA03 AA04 AA05 AA06 AA11 AA14 AA22 AA32 AA35 BA09 CA01 5E001 AB01 AE00 AE01 AE02 AE03 AE04 5G303 AA10 AB06 AB11 AB12 AB20 BA12 CA01 CB03 CB05 CB17 CB06

Claims (4)

[Claims] 1. At least Pb, Mg, N
1. A dielectric porcelain comprising: main crystal particles composed of a perovskite-type composite oxide containing b and Ti; and crystal particles composed of a bismuth layered compound present at a grain boundary of the main crystal particles. 2. The bismuth layered compound is XBi ₄ Ti ₄ O ₁₅
(X is at least one of Sr, Ca, Ba and Pb
2. The dielectric porcelain according to claim 1, wherein the dielectric porcelain is a seed. 3. A metal element comprising at least Pb, Mg, N
and a perovskite-type composite oxide containing Ti and XBi ₄ T with respect to 100 parts by weight of the main component.
i ₄ O ₁₅ (X is Sr, Ca, at least one of Ba and Pb) according to claim 1 or 2, wherein the dielectric ceramic is characterized in that it contains 0.5 to 15.0 parts by weight. 4. The perovskite-type composite oxide has a composition formula of Pb _1-a A _a ｛(Mg _1/3 Nb _2/3 ) _b (Co _1/3 Nb)
_2/3 ) _c ｝ Ti _1-bc O ₃ (A is Ba, Sr
And at least one of Ca), a, b and c are represented by the following formula: 0.25 ≦ a ≦ 0.60 0.60 ≦ b ≦ 0.80 0.01 ≦ c ≦ 0.20 b + c <1.00 4. The dielectric ceramic according to claim 1, wherein the dielectric ceramic is satisfied.