JPS6310526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dielectric material containing barium titanate as a main component and having reduced temperature hysteresis of dielectric constant.

[Conventional technology]

BACKGROUND OF THE INVENTION With recent advances in electronic technology, that is, the discovery of new electronic materials and advances in circuit design technology, electronic devices are becoming smaller and lighter. The miniaturization of electronic devices has particularly encouraged the development of portable electronic devices. In other words, the development of crystal wristwatches, small communication devices, small calculators, etc. is remarkable. As these electronic devices become smaller, the influence of the surrounding environment has become impossible to ignore. Temperature changes, especially when carried, can be fatal to certain electronic devices. For this reason, methods have been sought to reduce the influence of device temperature on the device itself or a method for correcting it. For example, temperature correction using a crystal oscillator or thermistor having a zero temperature coefficient has been devised. In particular, quartz crystal resonators for quartz wristwatches or small communication devices have a zero temperature coefficient. As shown in these examples, there are electrical oscillation circuits in which changes in device characteristics due to temperature have a large effect on the function of the device itself. These are standard signal oscillation sources or filter circuits,
It is used as a modulation circuit and a pseudo-noise signal oscillation source. If their processing frequencies vary depending on the temperature, they will no longer perform their original functions. In the case of a quartz wristwatch, the quartz crystal oscillator used as a standard signal source exhibits frequency-temperature characteristics as shown in FIG. 1 in the case of a tuning fork-shaped bending oscillator. The horizontal axis is the temperature T (℃) and the vertical axis is the frequency f (KHz).
As shown in the figure, it is a quadratic curve with an apex near room temperature, approximately 24°C. The AT-cut thickness-shear resonator exhibits frequency-temperature characteristics as shown in Figure 2. Here, the horizontal axis shows the temperature T (° C.) and the vertical axis shows the frequency f (KHz). As shown in FIG. 2, it shows an almost cubic curve. Examples of surface acoustic wave elements used in radar signal processing, high frequency sources in car telephones, and spread spectrum code synchronization elements are shown in FIGS. 3 and 4. These are also used as high frequency filters. FIG. 3 shows a surface acoustic wave device using an ST-cut quartz plate, where the horizontal axis shows temperature T (°C) and the vertical axis shows frequency f (KHz).
FIG. 4 shows a surface acoustic wave device comprising a ZnO thin film on Pyrex, where the horizontal axis shows temperature T (°C) and the vertical axis shows frequency f (KHz).

Both are almost quadratic curves with a peak at room temperature around 24°C. This is an element having a so-called zero temperature coefficient, in which the temperature change becomes zero at these vertices.
It has been said that elements with such a zero temperature coefficient are practically the least susceptible to temperature effects, but even this assumes that the temperature is fixed near the peak temperature, and if the temperature shifts, the natural characteristics will change. The value will also fluctuate. An object of the present invention is to complete a circuit with even higher precision by correcting these fluctuations.

Although the thermistor was described above as a device for temperature correction of the device, a capacitive element can also be used in the same way.
Ceramic capacitors whose main component is titanium oxide are usually used, and a major reason for this is that the frequency changes little with temperature. In other words, the premise is that ordinary capacitors, like other elements, do not change their characteristics due to temperature. Ideally, a capacitance value that does not change over the entire temperature range of normally used temperatures, that is, around room temperature, is required. On the other hand, when attempting to correct an element that has frequency-temperature characteristics of a quadratic or cubic curve with a zero temperature coefficient as shown above, the first characteristic that the capacitor should have is that these characteristics should be maintained near room temperature. It must exhibit temperature characteristics that correspond to other elements.

This also requires very large changes depending on the corresponding element. Barium titanate ceramic capacitors have traditionally been used for crystal watches as capacitors for this purpose. Originally, as shown in Figure 5, when the horizontal axis is temperature T (℃) and the vertical axis is dielectric constant ε, the phase transformation point (Curie point) is around 120℃, and at this temperature, the dielectric constant ε When it has a maximum value, that is, below 120°C, it is a tetragonal system with a ferroelectric phase, and above 120°C, it becomes a cubic system with a paraelectric phase. Since the peak temperature is too high as it is, the Curie point can be moved to around room temperature by adding SrTiO ₃ , BaSnO ₃ , BaZrO ₃ or the like. Since the temperature characteristic shows a substantially quadratic curve, it has been considered effective as a temperature compensation capacitor for an element exhibiting the above-mentioned quadratic or cubic curve temperature characteristic. This characteristic is shown in FIG. Here, the horizontal axis is the temperature T (° C.), and the vertical axis is the dielectric constant ε. Any shape of this curve corresponding to the quadratic coefficient can be obtained depending on the additives or sintering conditions. This method has already been put to practical use in quartz wristwatches. In this case, a tuning fork-shaped flexural oscillator is used as the crystal oscillator, and BaTiO ₃ is used as a temperature compensation capacitor.
Those with BaSnO ₃ added are mainly used.
This made it possible to create a crystal wristwatch with better precision.

[Problem that the invention seeks to solve]

However, even with conventional methods, complete temperature compensation has not been possible. The reason for this is that, as is clear from FIGS. 5 and 6, variations in the dielectric constant-temperature characteristics are observed at temperatures lower than the Curie point. This phenomenon occurs because the characteristic shape is different when the temperature is increased from a low temperature side to a high temperature side and when the temperature is decreased from a high temperature side to a low temperature side. That is, it exhibits a temperature hysteresis phenomenon. Therefore, the dielectric constant at a constant temperature Tn takes a value from εH to εL.
If the amount (εH−εL)×100÷εL is defined as the hysteresis amount, this value indicates a value of 20 to 30% of the maximum value.
Therefore, even if temperature compensation is performed using this capacitor, the shape itself will not fit, and although this may not cause new errors, the compensation ability will be significantly reduced. Ta. The present invention eliminates the above-mentioned temperature hysteresis phenomenon and provides stable temperature characteristics, thereby achieving highly accurate temperature compensation. In other words, by almost eliminating the hysteresis phenomenon in the dielectric constant-temperature characteristics near the Curie point, we can (a) provide a highly stable temperature compensation capacitor, (b) provide a low-cost temperature compensation method, and (c) provide a highly accurate The purpose is to provide a stable signal oscillation source and (d) to provide a highly stable signal processing method.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve each object, the present invention incorporates La ₂ O ₃ , Sm into barium titanate or a barium titanate solid solution in which some of its constituent ions are replaced with Sr, Zr or Sn. _{2O3 ,}
0.1 of at least one selected from Gd ₂ O ₃ and Dy ₂ O ₃
It is characterized in that it is added in an amount of at least atomic % and within a range that does not change the crystal structure of the solid solution.

According to the present invention, the hysteresis phenomenon of dielectric constant temperature characteristics near the Curie point can be almost eliminated.
Barium titanate exhibits a cubic paraelectric phase above the Curie point, and exhibits a tetragonal strongly hyperelectric phase below the Curie point. No dipole efficiency occurs in the paraelectric phase. Therefore, each grain is uniform. However, in the ferroelectric phase, dipole efficiency occurs due to the displacement of Ti ions, which causes spontaneous polarization.
Ps generates. This spontaneous polarization Ps is divided into different directions for each domain within each grain. There are two types of directions: one with a 90° angle and one with a 180° angle to each other. This spontaneous polarization is the main cause of the temperature hysteresis phenomenon mentioned above. The present inventors have found that among this spontaneous polarization, the 90° domain is the main cause of temperature hysteresis.
Normally, when the grain size is reduced to 1 micron or less,
It is said that the 90° domain disappears, but when the grain size is reduced to that region, the temperature hysteresis almost disappears. In addition, the 90° domain disappears even when the size is less than 5 microns, even if it is not less than 1 micron, and the accompanying temperature hysteresis is reduced to 5%.
It became the following. This is thought to be because the grain boundary has a larger expansion coefficient during the cooling stage after sintering, so stress is applied to the grain, thereby preventing the presence of the 90° domain.

FIG. 7 shows the dielectric constant temperature characteristics according to the present invention.
Here, the horizontal axis shows the temperature T (° C.), and the vertical axis shows the dielectric constant ε.
Normally, when the grain size is reduced, the dielectric constant at the Curie point decreases and exhibits an almost constant dielectric constant, but in the case of the present invention, since SnTiO ₃ , BaSnO ₃ , BaZrO ₃ , etc. are added, the dielectric constant at the Curie point decreases. The rate decrease is small and is almost symmetrical with respect to the Curie point. In other words, it has a shape close to a quadratic curve. Therefore, it is suitable for temperature compensation of an element having a quadratic temperature characteristic, and is also effective for compensating a cubic curve. Also, by removing the 90° domain, the long-term change in characteristics, that is, the aging characteristics, is also improved.

FIG. 8 shows an example in which the present invention is applied to an oscillation circuit. 1 is a crystal resonator, and 2 is a temperature compensation capacitor using the present invention. A quartz wristwatch that uses a tuning fork-shaped bending oscillator has an accuracy of 10 seconds per year, while an AT-cut thickness-sliding crystal oscillator has an accuracy of within 5 seconds per year.
Circuits using this AT-cut crystal oscillator are also used in the oscillation circuits of mobile communication devices, enabling highly stable communication. Furthermore, FIG. 9 shows an example of application of the spread spectrum method to a communication method. 3 is a data source, 4 is a data modulator, 5 is a code generator, 6 is an oscillator,
7 is a filter, 8 is a VCO, 9 is a code generator,
10 is a baseband filter, and 11 is a data demodulator. a is the transmitting side, and b is the receiving side. 5,
Surface acoustic wave elements such as a code generator 9, an oscillator 6, and a filter 7 are used. By using the present invention to compensate for the temperature characteristics of these surface acoustic wave elements, it has become possible to realize a small portable communication device. In particular, this system can also be provided, for example, in the case of a wristwatch. It is also very effective as a car phone. The present invention is particularly effective for applications where the operating temperature environment fluctuates rapidly.

In order to carry out the present invention, hot pressing, sintering using fine raw materials, etc. are effective, but in the present invention, in particular, among La ₂ O ₃ , Sm ₂ O ₃ , Gd ₂ O ₃ , Dy ₂ O ₃ , By adding at least 0.1 atomic % of one or more of these, atomization occurred and a reduction in temperature hysteresis could be achieved. If the amount of addition is less than 0.1 atomic percent, not only will the effect of the addition not be exhibited, but addition of extremely small amounts may even cause semiconductor formation. The upper limit is about 5 moles because it causes distortion and segregation. Since these additives can cause semiconducting, special care must be taken to prevent semiconducting. Therefore, the sintering atmosphere and the cooling rate after sintering are important. Also, the amount added must be slightly adjusted depending on the purity of the main component. Particularly in the case of industrial raw materials, the amount added must be kept small. Also, by adding other additives, it is possible to prevent the material from becoming a semiconductor. For example, adding 0.3 mol % or more of SiO ₂ or adding 0.1 atomic % or more of an alkali metal element such as Na, K, Li, Rb, Cs, etc. within a range that does not cause vitrification reliably prevents semiconductor formation. Also 0.1
Fe ₂ O ₃ , MnO ₂ , and CuO in mole % or more were similarly effective, and the combination was effective in reducing temperature hysteresis. As a result of these treatments, the specific resistance of the dielectric of the present invention was 10 ⁸ Ω-cm or more.

Although the manufacture of these materials requires delicate control as described above, even better properties can be obtained when they are made into single crystals. In this case, it is thought that temperature hysteresis disappears because the entire crystal becomes a single domain. Single crystallization is performed by first creating a rod-shaped ceramic and then focusing infrared rays on it.

Furthermore, even when these compositions were used in the form of a thin film, a film without hysteresis was similarly obtained. In this case, high frequency magnetron sputtering was effective.

〔Example〕

Examples of the present invention will be described below.

Example 1 (Ba, Sr) obtained by coprecipitation of oxalate
TiO ₃ was fired, mixed with La ₂ O ₃ , press-molded, and sintered at 1350° C. for 3 hours. The average particle size was 2μ. A Pd-Ag electrode was installed on this and the specific resistance and dielectric constant temperature characteristics were investigated. The specific resistance was 10 ⁹ Ω-cm and the temperature hysteresis was 0.

Example 2 Ti(OC ₅ H ₁₁ ) ₄ , Ba(OC ₃ H ₇ ) ₂ , Sr(OC ₃ H ₇ ) ₂ ,
When Sm(OC ₃ H ₇ ) ₃ was hydrolyzed and sintered, particles with a particle size of 1 micron or less and no temperature hysteresis were obtained.

Example 3 High purity BaCO ₃ 138g, SrCO ₃ 44g, TiO ₂ 80
After mixing 1.5 g of La ₂ O 3 and 1.5 g of La 2 O ₃ in a ball mill, 1100
It was calcined at ℃ for 2 hours. This raw material is further crushed by a grinder for 40
After being crushed for an hour, it was heat-treated at 900°C for 1 hour. This raw material was press-molded and then sintered at 1350°C for 4 hours. After cutting this out, we baked a Pd-Ag electrode and measured the dielectric constant temperature characteristics. It was an almost quadratic curve with a Curie point at 24°C. The powder diameter was 2 microns on average and there was no temperature hysteresis.

Example 4 Industrial BaTiO ₃ 186g, BaZrO ₃ 37g, Gd ₂ O ₅
After 0.7 g and 0.5 g of MnO ₂ were mixed in a ball mill for 24 hours, the mixture was press-molded into a plate shape and sintered at 1370°C for 3 hours. We obtained a dielectric constant-temperature characteristic that has a Curie point near 25℃ and a quadratic curve with no temperature hysteresis.

Example 5 High purity BaCO ₃ 197g, TiO ₂ 60g, SnO ₂ 38
g, Dy ₂ O ₃ 0.7 g, and Na ₂ CO ₃ 0.5 g were mixed in a mortar and then calcined at 1200° C. for 2 hours. Furthermore, it was crushed in a mortar, press-molded, and then sintered at 1370°C for 2 hours. After sintering, it was slowly cooled to 1000°C over 5 hours. This dielectric ceramic had no temperature hysteresis.

Example 6 BaTiO ₃ , SrTiO ₃ , Dy ₂ O ₃ and MnO ₂ were mixed in a crusher and then fired at 800° C. for 10 hours. This was placed in a rubber mold and molded into a rod shape using 3 tons of hydrostatic pressure. This was sintered at 1350°C for 3 hours. Furthermore, this rod-shaped sintered body was placed in an infrared furnace equipped with a spheroidal mirror, and the light from a halogen lamp was concentrated to create a partially molten zone, and by moving this molten zone, a solid solution single crystal was obtained. . There was no temperature hysteresis, and a particularly large rate of change in dielectric constant (ε) with respect to temperature (T) was obtained.

Example 7 High frequency magnetron sputtering was performed on a Virex glass substrate using targets containing BaTiO ₃ , SrTiO ₃ and La ₂ O ₃ . A thickness of about 20 microns was obtained in 10 hours. This thin film dielectric was free of temperature hysteresis.

A conventional technique, that is, a case in which some of the constituent ions of BaTiO ₃ are not replaced and an additive such as La ₂ O ₃ is not added is shown as a comparative example.

Comparative Example 1 After mixing 200g of industrial BaTiO ₃ in a mortar,
The mixture was calcined at 1350°C for 2 hours, ground again in a mortar, press-molded into a plate, and sintered at 1350°C for 2 hours.

When we measured the dielectric constant-temperature characteristics of this dielectric ceramic, it showed the characteristics shown in Figure 5, with a peak temperature of 123°C and a temperature hysteresis of 28°C at 100°C.
It was %.

Comparative example 2 High purity BaCO ₃ 138g, SrCO ₃ 44g, TiO ₂ 80
After mixing in a ball mill for 24 hours,
Calcined for an hour.

This raw material was further crushed in a crusher for 24 hours, then press-formed into a plate shape and sintered at 1350°C for 3 hours. When we measured the dielectric constant temperature characteristics of this dielectric ceramic, we found that
It exhibits the characteristics shown in Figure 6, with a peak temperature of 30
The temperature hysteresis at 10°C was 23%.

Comparative example 3 High purity BaCO ₃ 197g, SnO ₂ 38g, TiO ₂ 60g
After mixing in a mortar, the mixture was calcined at 1200°C for 1 hour, ground again, formed into a plate, and sintered at 1370°C for 3 hours.

When the dielectric constant-temperature characteristics of this dielectric ceramic were measured, it also showed the characteristics shown in FIG. 6, with a peak temperature of 26°C and a temperature hysteresis of 23% at 6°C.

Comparative Example 4 186 g of industrial BaTiO ₃ and 37 g of BaZrO ₃ were mixed in a ball mill for 24 hours, then press-molded into a plate shape.
It was sintered at 1370°C for 2 hours.

When the dielectric constant-temperature characteristics of this dielectric ceramic were measured, it also showed the characteristics shown in FIG. 6, with a peak temperature of 27°C and a temperature hysteresis of 24% at 7°C.

As described above, it can be seen that according to the above configuration of the present invention, temperature hysteresis can be eliminated.

〔Effect of the invention〕

As described above, according to the present invention, (a) the dielectric constant temperature hysteresis phenomenon of the beryllium titanate solid solution near the Curie point can be almost eliminated; (b) the spontaneous polarization caused by the displacement of Ti ions can be eliminated; It was discovered that an angle of 90° causes temperature hysteresis, and barium titanate 2 has some of its constituent ions Sr, Zr, and Sn.
La, barium titanate solid solution substituted with
Temperature hysteresis could be reduced by adding at least one of the oxides of Sm, Gd, and Dy. (c) Normally, to eliminate the 90° domain, the grain size should be reduced to 1 micron or less. (d) By adding at least one kind of alkali metal such as SiO ₂ or Na, K, Li, Rb, or Cs, or by adding Fe ₂ O ₃ or MnO ₂ By adding at least one of , CuO, etc., and combining them, La,
It has characteristics not found in other examples, such as being effective in preventing the tendency to become semiconducting due to the addition of oxides such as Sm, Gd, Dy, etc. and reducing temperature hysteresis, and has practically stable temperature characteristics. The effect of supplying the body is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the frequency-temperature characteristics of a tuning fork type bent crystal resonator. FIG. 2 is a diagram illustrating the frequency-temperature characteristics of an AT-cut crystal resonator. FIG. 3 is a diagram showing the frequency-temperature characteristics of a surface acoustic wave device using an ST-cut quartz plate. FIG. 4 is a diagram showing the frequency-temperature characteristics of a surface acoustic wave device comprising a ZnO thin film on Pyrex. FIG. 5 is a diagram showing the dielectric constant temperature characteristics of barium titanate. FIG. 6 is a diagram showing the dielectric constant temperature characteristics of a conventional temperature compensation capacitor. FIG. 7 is a diagram showing the dielectric constant temperature characteristics of the present invention. FIG. 8 is a diagram illustrating an example in which the present invention is applied to an oscillation circuit. 9th
The figure is a diagram illustrating an example in which the present invention is applied to a spread spectrum communication system. 1...Crystal resonator, 2...Temperature compensation capacitor,
3... Data source, 4... Data receiver, 5... Code generator, 6... Oscillator, 7... Filter, 8... VCO,
9...Code generator, 10...Baseband filter, 11...Data demodulator.

Claims (1)

[Claims] 1. Some of the constituent ions of barium titanate are Sr,
At least one selected from La ₂ O ₃ , Sm ₂ O ₃ , Gd ₂ O ₃ , and Dy ₂ O ₃ is added to a barium titanate solid solution substituted with Zr or Sn in an amount of 0.1 atomic % or more and the crystal structure of the solid solution is A dielectric material characterized by the addition of additives within a range that does not change. 2. The dielectric material according to claim 1, wherein the average grain size is 5 microns or less. 3. The dielectric material according to claim 1 or 2, wherein 0.3 mol% or more of SiO ₂ is added. 4. The dielectric material according to claim 1 or 2, wherein at least one of Na, K, Li, Rb, and Cs is added in an amount of 0.1 atomic % or more and within a range that does not cause vitrification. 5. The dielectric material according to claim 1 or 2, wherein at least 0.1 mol% of one or more of MnO ₂ , Fe ₂ O ₃ , and CuO is added.