JPH0558726A - Piezoelectric ceramics and surface mounting type piezoelectric parts - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric ceramics having a small changing rate of anti-resonance frequency for temp. and excellent heat resistance so that it can be used as a filter material mounted on vehicles or as piezoelectric parts mounted on substrates. CONSTITUTION:This piezoelectric ceramics essentially consists of Pb(Zr, Ti)O3, especially with >=0.93 molar ratio of Ti to Zr (Ti/Zr) and containing at least Mn by 0.85-2.0mol% in term of oxide. The ceramic features in that the inner bias electric field generating therein is larger than 0.15kV/mm and having tetragonal crystalline structure. This piezoelectric ceramic is used as piezoelectric parts mounted on substrates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic used for a filter or the like, and more particularly to a piezoelectric ceramic that can be mounted on the surface of a substrate having excellent heat resistance.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of communication information in video signals, audio signals, etc. and the diversification of communication terminals for mobile communication such as car telephones, a filter with high selection, low loss and high reliability. Therefore, development of a piezoelectric ceramic suitable for such a filter is desired. As such a piezoelectric ceramic, a Pb (Zr, Ti) O ₃ -based piezoelectric ceramic has been conventionally used to improve characteristics such as a dielectric constant, an electromechanical coupling coefficient Kp, and a mechanical quality coefficient Qm. Various improvements have been conventionally made in terms of composition.

[0003] In recent years, such a piezoelectric element is desired to be a ceramic filter or the like which can be surface-mounted on a substrate as electronic parts are made into chips, and its development is being advanced.

[0004]

However, when the conventional piezoelectric ceramic is applied to the surface mounting filter,
When the piezoelectric element is soldered to the substrate, it is exposed to a high temperature of 200 ° C. or higher, so that there is a problem that the piezoelectric ceramic is depolarized and the piezoelectric characteristic is lost.

Further, when applied to a filter of a vehicle-mounted communication device or the like, which undergoes drastic environmental changes, the set transmission / reception frequency fluctuates due to changes in the vehicle temperature, and stable transmission / reception cannot be performed. However, it is desired to develop a material having excellent heat resistance.

On the other hand, as a method for improving the heat resistance of the piezoelectric ceramic, the Curie temperature (T
Although the method of increasing c) is used, there is a problem that when the Curie temperature is increased, the relative dielectric constant decreases, and when applied to a filter, the amount of attenuation decreases, which is not an effective method. Is the current situation.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a piezoelectric ceramic and a surface mount type piezoelectric component which are excellent in heat resistance, prevent depolarization of the piezoelectric ceramic, and have a small frequency change due to heat. It is what

[0008]

The inventors of the present invention have selected Pb (Zr, Ti) O ₃ -based materials as piezoelectric ceramics, and have studied the thermal characteristics of such systems based on all factors. The heat resistance can be judged by the rate of change (fa drift) of the antiresonance frequency fa, and this fa drift is largely due to the internal bias electric field Ei of the piezoelectric ceramic, the crystallinity of the piezoelectric ceramic, and the amount of Mn added as a composition. It was found that the above objects can be achieved by controlling these.

That is, the piezoelectric ceramic of the present invention has a composition of Pb.
(Zr, Ti) O ₃ as a main component, containing at least Mn, and the content of Mn is 0.85 in all metal components.
The internal bias electric field Ei generated in the porcelain is 0.15 kV / mm or more, and the crystal structure is mainly tetragonal. By providing the surface-mounted piezoelectric component as a piezoelectric ceramic with a piezoelectric ceramic having an internal bias electric field Ei of 0.15 kV / mm or more, a highly reliable electronic component can be provided.

In evaluating the heat resistance of the piezoelectric ceramic, the frequency characteristics of the piezoelectric filter after the heat resistance test change in the center frequency and the pass band. This is due to a change in the resonance frequency of the piezoelectric resonator constituting the filter, and this change in the resonance frequency causes deterioration of the piezoelectric characteristics due to a change in the polarization state of the piezoelectric resonator. Therefore, the heat resistance of the piezoelectric ceramic can be evaluated by the change rate of the resonance frequency after the heat resistance test. Therefore, the piezoelectric ceramic can be judged by the fluctuation width (change width) of the anti-resonance frequency fa after the predetermined heat resistance test, that is, the fa drift.

According to the present invention, this fa drift greatly contributes to the internal bias electric field of the piezoelectric ceramic. Therefore, FIG. 1 shows the relationship between the internal bias electric field and the fa drift. According to FIG. 1, it is understood that the fa drift decreases as the internal bias electric field increases. According to the present invention, based on such a view, an excellent fa drift can be reduced by setting the internal bias electric field to 0.15 kV / mm or more, and as a result, the heat resistance of the porcelain can be increased. That is, when the internal bias electric field is smaller than 0.15 kV / mm, the fa drift becomes large and the frequency characteristic deteriorates. Since the dielectric constant tends to decrease when the internal bias electric field is too large, it is preferably 0.15 to 0.40 kV / mm.

The composition of the piezoelectric ceramic of the present invention is Pb.
(Ti, Zr) O ₃ is a main component and at least Mn is contained, and Mn is 0.85 to all metal components.
It is important that the content is 2.0 atomic%. Mn
The amount was limited to the above range because Mn was 0.85 atomic%.
If it is less, the internal bias electric field becomes smaller,
This is because the mechanical quality factor Qm becomes smaller, and if it exceeds 2.0 atomic%, the relative permittivity εr and the electromechanical coupling factor Kp become smaller.

Further, the piezoelectric ceramic containing Pb (Zr, Ti) O ₃ as a main component has a perovskite type crystal structure, and rhombohedral type crystals and tetragonal type crystals are known as crystal phases. According to the piezoelectric ceramic of the present invention, it is important that the crystal structure is mainly tetragonal. This is because the tetragonal crystal has a higher internal bias electric field than the rhombohedral crystal, and the temperature dependence of the resonance frequency is good in terms of piezoelectric characteristics. This will be described with reference to FIG. 2. The length ratio of the c-axis length and the a-axis length of the crystal (c /
It means that the tetragonal crystal amount increases as a) increases, and that the internal bias electric field Ei tends to increase as the c / a value increases.
Therefore, according to FIG. 2, it is desirable that the c / a ratio is 1.017 or more. The crystal morphology of such a porcelain is also compositionally varied depending on the ratio of Zr and Ti forming the B site of the perovskite type crystal. In the present invention, the Ti / Zr molar ratio is 0.93 or more, particularly 1 or less. It is desirable to set it to 0.0 or more.

According to the present invention, the composition of the piezoelectric ceramic is not particularly limited except that it contains Pb (Zr, Ti) O ₃ as a main component and a predetermined amount of Mn, but in view of piezoelectric characteristics, for example, Chemical formula 1 and chemical formula 2 below

[0015]

Embedded image Pb _{[Zr x Ti y (Nb a Sb} b Mn c) z ] O ₃ wherein, 0.42 ≧ x ≧ 0.46,0.44 ≧ y ≧ 0.49 0.08 ≧ z ≧ 0.10 a = 1,0 ≧ b ≧ 0.45, 0.33 ≧ c ≧ 0.50

[0016]

Embedded image in Pb _{[Zr x Ti y (Nb a Mg} b Mn c) z ] O ₃ Formula, 0.425 ≧ x ≧ 0.46,0.44 ≧ y ≧ 0.475 0.08 ≧ z ≧ 0.10 a = 1,0 ≧ b ≧ 0.45, 0.33 ≧ c ≧ 0.50 As shown in the chemical formula, Nb, M as B site forming components
Piezoelectric ceramics having excellent piezoelectric characteristics and temperature characteristics of frequency can be obtained by adding g and Sb in a predetermined amount, and piezoelectric characteristics may be improved by adding Sn, Fe, Al and Cr. .. In the above composition formula, Pb
The characteristics can be improved by substituting 5 to 12 atomic% of the above with one or more elements selected from Ba, Ca and Sr.

Further, the piezoelectric ceramic of the present invention is suitable as a material for a surface mount type piezoelectric component, and a concrete example of the piezoelectric component is a ladder type filter shown in FIG.

As shown in FIG. 3, the filter 1 includes a piezoelectric ceramic 2 having an electrode formed by baking a paste such as Ag at about 550 ° C. on its surface, and a terminal electrode 3 sandwiching the central portion of the piezoelectric ceramic 2. And are housed in the envelope 4. Further, the end portion of the terminal electrode 3 is led out of the envelope 4. Then, this filter is applied to the wiring 6 on the surface of the substrate 5 by soldering Sn-Pb or the like 180-180.
It is bonded at 240 ° C and directly mounted on the surface of the substrate.

[0019]

According to the present invention, the fa bias, that is, the rate of change of the antiresonance frequency with respect to temperature, is reduced by satisfying the internal bias electric field Ei, Mn amount and crystal phase of the piezoelectric ceramic according to the present invention. Therefore, the heat resistance of the porcelain can be greatly improved.

Further, even when applied to a filter of a communication device mounted on a vehicle such as an automobile, the set transmission / reception frequency does not fluctuate due to the temperature change of the vehicle even when the environment changes drastically. Stable transmission / reception is possible.

Further, since it is excellent in heat resistance, it can be applied to a surface mount type piezoelectric component, and when it is mounted on the surface of a substrate by soldering or the like, depolarization does not occur even if it is heated. , The set piezoelectric characteristic does not fluctuate or deteriorate.

[0022]

EXAMPLES Pb ₃ O ₄ and Zr having a purity of 99.9% or more
O ₂ , TiO ₂ , Nb ₂ O ₅ , Sb ₂ O ₃ , MnO ₂ ,
Using each raw material powder of MgCO _3, the composition formula shown in Chemical Formula 1 above was weighed so that the x, y, z, a, b, and c values were in the ratios shown in Tables 1 and 2, and zirconia balls were used. Was wet mill mixed for 15 hours. Similarly, in the composition formula shown in Chemical Formula 2, the x, y, z, a, b, and c values were weighed so as to have the ratios shown in Tables 3 and 4, and mixed in the same manner. Then, mix each powder with 100
It is calcined at 0 ° C for 3 hours, the calcined product is crushed again by a ball mill for 24 hours, polyvinyl alcohol is added as a binder, and after granulation, a pressure of 1.5 ton / cm ² is applied to a diameter of 23 m.
A disc having m × thickness of 3 to 4 mm was formed.

This molded sample was placed in an MgO sagger containing PZT calcined powder to prevent evaporation of the Pb component, sealed, and held in an electric furnace at each temperature between 1250 and 1320 ° C. for 2 hours. It was then fired.

The obtained sintered body is made to have a predetermined thickness (0.5 m
After polishing to m), Ag paste was applied to both surfaces and baked at 750 ° C. to form electrodes. For polarization,
A DC electric field of 5 KV / mm is applied for 10 minutes in insulating oil at 80 ° C, and then 25 to 220 ° C for stabilization of the polarization state.
The heat treatment was performed by holding each temperature for 1 hour. Next, 4.
An element for piezoelectric property evaluation was obtained by cutting a 3 × 4.3 × 0.5 mm square plate.

The piezoelectric characteristics are specific resistance ρ and relative permittivity ε.
r, Curie temperature Tc, and mechanical quality factor Qm were evaluated. The specific resistance ρ was measured after applying a DC voltage of 10 V for 30 seconds at room temperature. The relative permittivity εr was obtained by applying a signal voltage of 1 kHz and 1 Vrms using an impedance analyzer to obtain the capacitance, and calculating the permittivity from this.

Further, the electrostatic capacity was measured by the same method in the temperature range of 100 to 400 ° C., and the Curie temperature Tc was determined from the temperature showing the maximum value.

Next, the impedance characteristic in the range of 400 to 500 KHz was obtained by an impedance analyzer, and the mechanical quality factor Qm was calculated from the resonance frequency and the anti-resonance frequency determined by the impedance characteristic.

The heat resistance of the piezoelectric ceramic was evaluated by a test corresponding to surface mounting, that is, based on reflow soldering conditions. In the measurement, the fluctuation range of the anti-resonance frequency fa when passing the piezoelectric ceramic through the reflow furnace set to the temperature profile as shown in FIG. 4, that is, fa drift was measured to evaluate the heat resistance.

Further, the internal bias electric field Ei of the piezoelectric ceramic is measured by using the DE-E measured using the circuit of Sawyer Tower.
It was calculated from the hysteresis curve.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

According to Tables 1 to 4, according to the present invention, the fa drift value of the sample having the internal bias electric field Ei value of 0.15 KV / mm or more was 0.2% or less in absolute value. There is. The samples in Table 1 are sample No. Except for 20, the crystal phase was mainly tetragonal. Further, regarding the amount of Mn, sample No. 1, 2,
In Nos. 38 and 39, the internal bias electric field was small and the fa drift was large. On the contrary, the sample No. with a large amount of Mn. Both 7 and 53 had a low dielectric constant.

On the other hand, all of the products of the present invention achieved a relative dielectric constant of 900 or more, a Kp value of 45 or more, a Qm value of 1600 or more, and a fa drift of 0.2% or less (absolute value).

[0036]

According to the present invention, since the rate of change of the antiresonance frequency with respect to temperature is small, the heat resistance of the porcelain can be improved. As a result, it can be applied as a filter material to be mounted on a vehicle or the like which causes a drastic temperature change.
Further, since the piezoelectric characteristics do not deteriorate even under the condition of solder flow, it can be applied as a piezoelectric component mounted on a substrate.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an internal bias electric field Ei and fa drift.

FIG. 2 is a diagram showing a relationship between a ratio (c / a) of c-axis length / a-axis length of a porcelain and an internal bias electric field Ei.

FIG. 3 is a cross-sectional view of a surface mount piezoelectric filter.

FIG. 4 is a diagram showing a temperature profile of solder reflow in an example.

[Explanation of sign]

 1 Filter 2 Piezoelectric Ceramic 3 Terminal Electrode 4 Enclosure 5 Board 6 Wiring 7 Solder

Claims (3)

[Claims] 1. A piezoelectric ceramic containing Pb (Zr, Ti) O ₃ as a main component, containing at least Mn, and Mn being present in a proportion of 0.85 to 2.0 atomic% in all metal components. The internal bias electric field generated in the porcelain is 0.1
A piezoelectric ceramic excellent in heat resistance, which is characterized by having a crystal structure of tetragonal crystal as a main component, which is larger than 5 kV / mm. 2. A composition molar ratio of Ti to Zr (Ti / Z
The piezoelectric ceramic according to claim 1 in which r) is 0.93 or more. 3. A surface mount type porcelain containing Pb (Zr, Ti) O ₃ as a main component, comprising a piezoelectric ceramic having an internal bias electric field generated in the porcelain larger than 0.15 kV / mm. Piezoelectric component.