JPH0793224B2 - Ceramic capacitor and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic capacitor which has an excellent Q value at high frequencies, is small in size, and can have a large capacity.

2. Description of the Related Art As a conventional ceramic capacitor, one in which titanium oxide, barium titanate, strontium titanate, or a compound sintered body thereof is coated with Ag, Pt, Pd or another electrode material in the form of paste and baked Are known. Further, there is also one in which these dielectrics and electrodes are alternately laminated in several layers to achieve a small size and a large capacity.

These ceramic capacitors have excellent dielectric constants, small dielectric loss (tan δ), and excellent properties as capacitors. However, these ceramic capacitors also have a problem in their performance at high frequencies of 10 GHz or higher. The most problematic characteristic is an increase in loss at high frequencies, that is, a decrease in resonance Q value.
The Q value at a high frequency involves both the dielectric and the electrode, and the optimization of the combination is the most important. In particular, a monolithic ceramic capacitor having a large capacity cannot be obtained with a low loss at high frequencies due to various restrictions on its electrode material.

In recent years, as a high frequency transistor, a high mobility transistor using a two-dimensional electron gas has been developed, and the characteristics of this transistor are more excellent as the temperature is lower. Therefore, in applications such as satellite communication in which high-frequency and weak radio waves are handled, some measures have been taken to keep the entire system at a low temperature. However, in the conventional ceramic capacitor, the Q value of the high frequency is not significantly improved by this.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention has been made in view of the above points, and an object of the present invention is to provide a ceramic capacitor having an excellent Q value and a large capacity even at a high frequency and at a low temperature.

Means for Solving the Problems In order to solve the above problems, the present invention provides a binder for each of a perovskite structure oxide dielectric raw material and a layered perovskite structure type oxide superconductor raw material that can be sintered at 900 to 1100 ° C. , A plasticizer and a solvent are added to form a slurry, the slurry is processed into a sheet, and the perovskite structure oxide sintered body dielectric material sheets are stacked with the layered perovskite structure oxide superconductor material sheet sandwiched therebetween. After forming at least one layer of the structure, removing the binder, and sintering in an atmosphere containing oxygen at 900 to 1100 ° C., a perovskite structure oxide sintered body dielectric is formed into a layered perovskite structure type oxide. It is intended to provide a ceramic capacitor having at least one layer having a structure sandwiched by sintered superconductors.

Action The present invention can obtain a ceramic capacitor having a large Q value at high frequencies and a large capacity due to the structure described above.

Example (Example 1) Yttrium oxide (Y ₂ O ₃ ), barium carbonate (BaCO ₃ ) and copper oxide (CuO) were weighed so as to be included in a ratio of Y ₁ Ba ₂ Cu ₃ , and after mixing, 950 Bake for 5 hours in air at ℃. After crushing and mixing these again, 10 minutes in air at 950 ℃
Bake for hours. This is pulverized again to obtain fired powder particles.

Next, the sintered powder particles are mixed with a binder, a plasticizer, and a solvent to form a mixed slurry. Add 10 wt% polyvinyl acetate as a binder and 0.5 wt% dioctyl phthalate as a plasticizer. Add 60 wt% to the ceramic raw material.
A slurry was prepared by stirring and mixing with wt% methyl alcohol. This slurry, on a polyester film,
It is formed into a sheet by the doctor blade method and naturally dried to make a raw sheet. At this time, the thickness is set to 50 μm.

Next, PbO, Fe ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , and ZnO powders were mixed with Pb (Fe W) O.
-Pb (FeNb) O, Pb (FeW) O-Pb (ZnNb) O are pulverized and mixed, and baked at 900 ° C for 5 hours. This is pulverized and mixed again to obtain sintered powder particles.

Next, the sintered powder particles are mixed with a binder, a plasticizer, and a solvent to form a mixed slurry. Using this slurry, the thickness
Create a 50 μm raw sheet. The conditions for slurry preparation and green sheet preparation are the same as those for the Y-Ba-Cu oxide.

Next, two Pb-based oxide green sheets are stacked in a sandwich structure with two Y-Ba-Cu oxide green sheets, and pressed to form a laminated structure.

Next, this laminated material is subjected to binder removal at 600 ° C. for 24 hours. Then, it is baked in air at 950 ° C. for 3 hours, cooled, and cut into 1 mm square chips. The Q value of the ceramic capacitor thus obtained at 14 GHz is 77K
It was measured at. For comparison, the Q value was also measured for a conventional ceramic capacitor prepared by screen-printing an Ag-Pb alloy paste on both surfaces of the dielectric green sheet. As a result, with the conventional silver-based electrode, at 14 GHz, rather than dielectric loss,
The loss at the electrode was overwhelmingly large, and for all dielectric materials, the Q value almost corresponded to the loss at the electrode, and all were 100 or less. On the other hand, in this embodiment, 77K
Since the Y-Ba-Cu oxide electrode is in a superconducting state, the loss related to the electrode is much smaller than the loss of the dielectric, and the Q value corresponding to only the loss of the dielectric is obtained. A Q value of 500 or more was obtained for all materials. Dielectric and superconducting electrodes were examined by X-ray analysis and found to have a perovskite structure as the basis,
The superconductor electrode had a layered perovskite structure.

FIG. 1 shows an embodiment of the structure of the present invention.
In FIG. 1, reference numeral 1 is an oxide sintered body dielectric, and 2 is a layered perovskite structure type oxide superconductor electrode.

FIG. 2 shows the components of the crystal structure of the electrode superconductor of this example. This shows a perovskite structure.
In the figure, 3 contains Cu, 4 contains O, 5 contains Y or Ba, and these constituent elements are stacked in layers with a certain period. In an actual superconductor, this structure is considered to be an oxygen-deficient structure in which oxygen is appropriately removed.

FIG. 3 shows that the dielectric layer is composed of two layers, and in between and above and below,
It shows an example of a structure sandwiching a superconductor electrode layer. In FIG. 3, 6 is a terminal electrode connected to the upper and lower two electrode layers and the intermediate electrode layer, respectively. Since the area of the terminal electrode 6 is overwhelmingly smaller than that of the electrode 2, the influence on the characteristics is small. Therefore, after laminating and sintering, a conventional silver-based electrode paste may be applied to each end face so as not to cause a short circuit and baked. In order to prevent short-circuiting, the sheets may be laminated and fired so that the portions without the electrode green sheet at the edges are alternately produced at the time of laminating the sheets.
By increasing the number of layers, the capacitance can be increased, and with such a structure, a small-sized and large-capacity capacitor can be obtained.

Example 2 Lanthanum oxide (La ₂ O ₃ ), barium oxide (BaCO ₃ ) and copper oxide (CuO) were weighed so as to be contained in a ratio of La _1.84 Ba _0.16 Cu ₁ and mixed, and then In the same manner as in 1, sintered powder particles, slurry and green sheet are obtained. The dielectric green sheet is the same as in Example 1.

Next, using this raw sheet, the same process as in Example 1 was performed to form a ceramic capacitor. The Q value of the obtained ceramic capacitor was measured at 30K, and the result was compared with that of a conventional silver-based electrode. As a result, the same result as in Example 1 was obtained. That is, also in this case, the electrode was a superconductor, and the electrode loss was extremely low in this example, and a good Q value was obtained.

The electrode has a layered perovskite structure as in Example 1.

(Example 3) Rare earth oxides (oxides of Yb, Er, Ho and Dy), barium carbonate (BaCO ₃ ) and copper oxide (CuO) were used, and the ratio of rare earth oxides and barium oxide was 0.3 per 1 copper oxide. And variously weighed so as to be 0.7, and after mixing, in the same manner as in Example 1, sintered body powder particles, slurry and green sheet are obtained. The dielectric green sheet is the same as in Example 1.

Next, using this raw sheet, a ceramic capacitor was formed through the same process as in Example 1. The Q value of the obtained ceramic capacitor was measured at 50K, and the result was compared with that of a conventional silver-based electrode. As a result, the same result as in Example 1 was obtained. That is, also in this case, the electrode was a superconductor, and the electrode loss was extremely low in this example, and a good Q value was obtained.

The electrode has a layered perovskite structure as in Example 1.

As described above, according to the method of the present invention, high-frequency Q
A ceramic capacitor with a large value can be obtained.

FIG. 2 shows the crystal structure of Example 1. The layered perovskite structure of Examples 2 to 3 was used in each Example instead of Y and Ba. It is replaced by the elements other than Cu and O.

In the structure of this embodiment, both the dielectric material and the electrode material are oxides. Therefore, sintering can be performed in an atmosphere containing oxygen, for example, air, and can be produced without impairing the superconducting properties as an electrode and the dielectric properties as a dielectric. Conversely, in an oxygen-free atmosphere, good dielectric properties,
Superconducting properties cannot be obtained. Therefore, it is necessary to fire in an atmosphere containing oxygen.

Further, in this embodiment, both the dielectric and the superconductor electrode are based on the oxide perovskite structure. Therefore, it is very well-suited as a crystal, and there are no problems such as a decrease in the superconducting critical temperature of the electrode and a decrease in the Q value due to peeling or deformation during firing. This is especially important when laminated in layers. If it is not familiar, so-called delamination occurs and the characteristics of the capacitor are significantly deteriorated. From this, the effect of the present embodiment is obtained by the combination of the perovskite structure oxide dielectric and the layered perovskite structure type oxide superconductor, and conversely, for any combination of these materials, It is applicable.

Further, in the present embodiment, specific values were used as the thickness of the dielectric and the thickness of the oxide superconductor for an electrode, but each thickness is arbitrary.

In addition, in the present example, as a result of X-ray analysis of the crystal structure of the superconducting oxide sintered body powder in any of the examples, the powder state already had a layered perovskite structure, and the magnetic susceptibility From the measurement, diamagnetism was observed, and it was already powder particles in a superconductor state.

The oxide superconductor used in this example exhibits superconducting properties only when fired at 900 to 1100 ° C. Therefore, those which can be used in combination as a dielectric are still 900 to 1
It must be capable of firing at 100 ° C. The Pb-based perovskite structure oxide dielectric used in this example is a typical one.

The ceramic capacitor of the present invention has an extremely excellent Q value at high frequencies at low temperatures, and by using it at low temperatures in combination with a high-frequency transistor using a two-dimensional electron gas, a high mobility transistor, and the like, It is possible to configure amplifiers, oscillators, etc. with extremely good performance. In addition, they can be stacked, which facilitates miniaturization and large capacity.

In this embodiment, specific values were used as the amounts of the binder, plasticizer, and solvent, but it is sufficient if the raw sheet can be processed successfully.
It is not limited to this value.

As described above, according to the present invention, a binder, a plasticizer, and a solvent are added to each of the perovskite structure oxide dielectric raw material and the layered perovskite structure type oxide superconductor raw material that can be sintered at 900 to 1100 ° C. To prepare a slurry, at least one or more layers are formed by processing the slurry into a sheet and stacking the perovskite structure oxide sintered body dielectric raw material sheet by sandwiching the layered perovskite structure oxide superconductor raw material sheet. Then, after removing the binder, by sintering in an atmosphere containing oxygen at 900 ~ 1100 ℃, perovskite structure oxide sintered body dielectric,
It is intended to provide a ceramic capacitor having at least one layer having a structure sandwiched between layered perovskite structure type oxide sintered body superconductors.

[Brief description of drawings]

FIG. 1 is a sectional view of a ceramic capacitor of one embodiment of the structure of the present invention, and FIG. 2 is a schematic view of a perovskite structure which is a constituent element of a layered perovskite structure which is a crystal structure of an oxide superconductor used in the present invention. FIG. 3 is a sectional view of a ceramic capacitor according to another embodiment of the structure of the present invention. 1 ... Oxide sintered body dielectric, 2 ... Layered perovskite structure type oxide superconductor electrode, 3 ... Cu, 4 ... O, 5 ...
… Y or Ba, 6 …… Terminal electrode.

Claims (8)

[Claims] 1. A structure in which a perovskite structure oxide sintered body dielectric which can be sintered at 900 to 1100 ° C. is sandwiched between layered perovskite structure type oxide sintered body superconductors is at least 1.
A ceramic capacitor having at least two layers. 2. A-Ba-Cu oxide (provided that A is a powder of a layered perovskite structure type oxide superconductor sintered body powder particle)
Is a Y, a rare earth element), and the ceramic capacitor according to claim (1). 3. The ceramic capacitor according to claim 2, wherein La, Yb, Er, Ho, Dy is used as the rare earth element. 4. A Pb-Fe-W-Nb oxide or Pb-Fe-W-Zn-N as a perovskite structure oxide sintered body dielectric.
A ceramic capacitor according to claim (1), characterized in that a b oxide or a compound thereof is used. 5. A binder, a plasticizer, and a plasticizer for each of the perovskite structure oxide dielectric raw material and the layered perovskite structure type oxide superconductor raw material which can be sintered at 900 to 1100 ° C.
A slurry is prepared by adding a solvent, the slurry is processed into a sheet shape, and the perovskite structure oxide sintered body dielectric raw material sheet is sandwiched between the layered perovskite structure oxide superconductor raw material sheets and stacked, at least. After forming one or more layers and removing the binder, 900-1100 ℃
2. A method for manufacturing a ceramic capacitor, comprising sintering in an atmosphere containing oxygen. 6. An A-Ba-Cu oxide (provided that A is a powder of layered perovskite structure type oxide superconductor sintered body powder particles).
Is a rare earth element), and the method for manufacturing a ceramic capacitor according to claim (5). 7. The method for producing a ceramic capacitor according to claim 5, wherein La, Yb, Er, Ho and Dy are used as the rare earth element. 8. A Pb-Fe-W-Nb oxide or Pb-Fe-W-Zn- as a dielectric of a perovskite structure oxide sintered body.
The method for producing a ceramic capacitor according to claim (6), characterized in that Nb oxide or a compound thereof is used.