JP2903991B2 - Semiconductor porcelain composition and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strontium titanate-based semiconductor porcelain composition and a method for producing the same, and more particularly, to a strontium titanate-based semiconductor porcelain composition used as a noise absorbing element for an electric / electronic circuit mounted on a communication device, an audio device or the like. And a method of manufacturing the same.

[0002]

2. Description of the Related Art A grain boundary insulated semiconductor porcelain is obtained by thermally diffusing a metal oxide or the like into crystal grains of a sintered ceramic (ceramic) made into a semiconductor, thereby changing the crystal grain boundary layer into an insulating layer. The grain boundary insulated semiconductor porcelain obtained by insulating the grain boundary layer is used as a capacitive element. In addition, since the grain boundary insulating layer of the semiconductor porcelain formed by the above method is generally as thin as several nm, the capacitance element made of the grain boundary insulated semiconductor porcelain is compared with the capacitance element made of another type of porcelain. It is characterized in that it is smaller and can provide a larger capacitance.

In particular, strontium titanate (SrTi
The semiconductor porcelain element containing O ₃ ) as a main component is easy to have a grain boundary insulating structure due to the thermal diffusion of the above-mentioned metal oxide or the like, the electric characteristics are stable with respect to temperature and frequency, It has various advantages such as low loss, and can easily respond to recent demands for higher frequency of electronic devices and circuits and higher reliability in various application environments. For this reason, ceramic electronic component manufacturers are working on the development of high-performance and high-value-added capacitive elements containing strontium titanate as a main component.

As such a known example, for example, a metal oxide such as Bi, Mn, Cu, Pb, or Al is thermally diffused into a crystal grain boundary of a semiconductor ceramic mainly composed of strontium titanate to have a high dielectric constant. An example in which a grain boundary insulated semiconductor porcelain composition is manufactured (Japanese Patent Publication No. 62-42368), in which alkali metal is thermally diffused into the grain boundaries of a semiconductor porcelain in which calcium titanate and strontium titanate are dissolved, and a varistor function is obtained. Examples of producing the applied grain boundary insulating semiconductor ceramic composition (JP-A-58-91602) are given.

The above-mentioned grain boundary insulated semiconductor porcelain composition containing strontium titanate as a main component and having a varistor function has recently been used for a power supply noise filter, Its use is also expanding to noise absorbing elements and the like of semiconductor devices, and a capacitive varistor is a typical example of such a new use. This capacitive varistor is capable of absorbing several kV of noise or abnormal pulse voltage, and does not have the voltage nonlinearity and surge withstand capability of conventional ZnO-based varistors, but has the strontium titanate-based grain boundary insulation. Utilizing the high dielectric constant of the type semiconductor ceramic composition, there is an advantage that a rapidly rising pulse voltage can be absorbed without destroying the target protection element (various ICs, LSIs, etc.).

[0006]

However, recent ICs,
While the drive voltage of LSIs tends to be lower, the capacitive varistors used to protect them have higher voltage non-linearity and have lower voltage than conventional ones. There has been a problem that an element exhibiting a varistor function does not yet exist.

More specifically, the electrical characteristics required for the above-described capacitive varistor are described below in more detail.

The capacitance (C) must be large enough to absorb a high-speed pulse voltage. Varistor voltage (V
_1mA ) can be controlled freely. The voltage non-linear coefficient (α) must be sufficiently high to speed up the response to the pulse voltage. Even after a surge voltage (several tens of kV) is applied, the rate of change between the varistor voltage (V _{1 mA} ) and the voltage nonlinear coefficient (α) is small.

Further, as a specific example for the purpose of developing a grain boundary insulating semiconductor ceramic composition having such electrical characteristics, for example, a grain boundary oxidation type voltage nonlinear disclosed in JP-A-2-222502 is disclosed. There is a resistance element, but this element has a varistor voltage (V _{1 mA} ) as high as about 200 V, and is not suitable for use in ICs and LSIs in which the driving voltage has been reduced in recent years. was there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it has been proposed to control a strontium titanate-based semiconductor porcelain composition by controlling the chemical composition of the ceramic crystal grains and the grain boundary layer, thereby increasing the voltage. Has non-linearity,
It is an object of the present invention to provide a semiconductor ceramic composition having a high dielectric constant and a low dielectric loss capable of freely controlling a varistor voltage, and a method for manufacturing the same.

[0011]

Means for Solving the Problems To achieve the above object, a semiconductor ceramic composition according to the present invention comprises (Sr)
_1-xy Ba _x C a _y ) _a (Ti ₁ -z Nb _z ) _b O ₃ (where x, y and z are respectively 0 <x ≦ 0.05, 0 <
y ≦ 0.25, 0.001 ≦ z ≦ 0.010, and a and b are 0.990 ≦ a / b <1.000
), Characterized in that Na and B are further segregated in the crystal grain boundary layer. (1) The method for producing a semiconductor porcelain composition according to the present invention is the method for producing a semiconductor porcelain composition according to the above (1),
The Na ₂ Ti ₃ O ₇ and B ₂ O ₃ in the strontium titanate-based sintered body, respectively 50mol% ≦ Na ₂ Ti ₃ O
_{7 ≦ 91mol%, 9mol% ≦} B 2 O 3 ≦ 50mol
%, And is coated and thermally diffused. (2)

[0012]

According to the semiconductor ceramic composition having the constitution described in the above (1), (Sr _{1 -xy} Ba _x C _{a y} ) _a
(Ti _1-z Nb _z ) _b O ₃ (where x, y and z are respectively 0 <x ≦ 0.05, 0 <y ≦ 0.25, 0.00
A value in the range of 1 ≦ z ≦ 0.010, and a and b are:
0.990 ≦ a / b <1.000), and Na and B are further segregated in the crystal grain boundary layer. A high dielectric constant and low dielectric loss grain boundary insulated semiconductor ceramic composition exhibiting a varistor function at low voltage.

In the above chemical formula, x and y indicate the amounts of Ba and Ca substituted for Sr at the A site, and when x is 0, the dielectric constant is small and the varistor voltage is too high. On the other hand, when x exceeds 0.05, dielectric loss and voltage non-linearity deteriorate, and the varistor voltage becomes too large. On the other hand, also when y is 0, dielectric loss and voltage non-linearity deteriorate, and the varistor voltage becomes too large. On the other hand, y is 0.2
If it exceeds 5, the voltage nonlinearity deteriorates, the dielectric constant becomes too small, and the varistor voltage becomes too large. Further, when z is less than 0.001, the dielectric strength is reduced, and breakdown occurs when a surge current flows. On the other hand, if z exceeds 0.010, the voltage nonlinearity deteriorates, the dielectric constant becomes too small, and the varistor voltage becomes too large. A / b is (S
The molar ratio of (r + Ba + Ca) / (Ti + Nb) is shown.
If a / b is less than 0.990, dielectric loss and voltage non-linearity deteriorate, the dielectric constant becomes too small, and the varistor voltage becomes too large. On the other hand, a / b is 1.000
Above this, the breakdown voltage is reduced, and the device is easily broken when a surge current flows.

According to the method for producing a semiconductor porcelain composition according to the above (2), there is provided the method for producing a semiconductor porcelain composition according to the above (1), wherein the strontium titanate-based sintered body is made of Na ₂ Ti _3. 50 mol each of O ₇ and B ₂ O ₃
% ≦ Na ₂ Ti ₃ O ₇ ≦ 91 mol%, 9 mol% ≦ B
_Since it is contained within the range of ₂ O ₃ ≦ 50 mol% and applied and thermally diffused, it has a high voltage non-linearity, and a particle having a high dielectric constant and a low dielectric loss capable of freely controlling the varistor voltage by its composition. A field insulating type semiconductor porcelain composition is manufactured.

If the proportion of Na ₂ Ti ₃ O _{7 in} the coating composition is less than 50 mol%, the voltage non-linearity deteriorates and the varistor voltage becomes too large. On the other hand, when the proportion of Na ₂ Ti ₃ O ₇ exceeds 91 mol%, the dielectric loss deteriorates and the dielectric constant becomes too small. Further, when the ratio of Na ₂ Ti ₃ O ₇ becomes 95 mol%, the dielectric strength decreases, and the device is destroyed when a surge current flows.

[0016]

Examples and Comparative Examples Examples and comparative examples of the semiconductor porcelain composition according to the present invention and the method for producing the same will be described below.

First, a method for producing a strontium titanate-based semiconductor ceramic composition according to an embodiment of the present invention will be described.

As a raw material for synthesizing ceramics, S
rCO ₃ , BaCO ₃ , CaCO ₃ , TiO ₂ , Nb ₂
O ₅ was prepared, accurately weighed each raw material so that the main component composition shown in Tables 1-3 below. Next, the weighed raw materials are put into a pot mill together with appropriate amounts of cobblestone, a dispersant, and pure water, and wet-mixed for 24 hours. After that, the slurry-like raw material mixed in the above step is dehydrated and dried, and crushed. Next, the crushed powder is transferred into a firing crucible made of, for example, zirconia and calcined at a temperature of about 1170 ° C., thereby calcining and synthesizing a ceramic powder having a main component composition. Then, it was confirmed by X-ray diffraction and composition analysis that a predetermined solid solution was synthesized by the calcining synthesis.

Next, the powder calcined and synthesized in the above step is crushed, sized to a uniform powder of about 1.0 μm, and an organic binder or the like is added to the sized powder to reduce the diameter. 8m
m, a disk-shaped molded body having a thickness of 600 μm is prepared.

Further, the disc-shaped molded body is heated to about 1000 ° C.
The degreased body is filled into a baked crucible made of, for example, alumina, and the hydrogen concentration is 1 to 15 vol% and the nitrogen concentration is 85.
1380-1550 ° C in a reducing atmosphere of ~ 99 vol%
Then, firing is performed for 2.0 to 8.0 hours, and sintering of ceramics and conversion to a semiconductor are advanced.

Next, after sufficiently washing the obtained sintered body in an organic solvent and hot water, Na ₂ Ti ₃ O ₇ and B ₂ O ₃ were added to Tables 1 to ₃ to insulate the ceramic crystal grain boundaries. 3 is weighed so that the composition of the insulating agent is obtained, and these are combined with an organic vehicle material and kneaded to form a paste. The paste is converted to 20 to 50 m per 1 g of a sintered body.
It is applied to the surface of the sintered body at a ratio of about g. Next, the sintered body to which this paste has been applied is placed in the air at 1000 to 1350.
The grain boundary layer is insulated by baking at 0.5 ° C. for 0.5 to 4.0 hours. As the insulating paste, a compound other than the above may be used as long as it contains Na and B.

Next, a commercially available Ag paste for an electrode is printed on both surfaces of the semiconductor ceramic composition in which the grain boundary layer has been insulated by the above-described process, and the electrode is baked at about 650 ° C. to complete the device.

A method for evaluating the electrical characteristics of the thus obtained strontium titanate-based grain boundary insulating semiconductor ceramic composition will be described below. The electrical characteristics to be evaluated include capacitance (C value; nF), dielectric loss (D
F value;%), varistor voltage (V _{1 mA} ; V), voltage nonlinear coefficient (α;-), V _{1 mA} before and after the surge current flows and α
Is the rate of change (%).

First, the capacitance and the dielectric loss are measured using an impedance analyzer (4192A manufactured by YHP) at a frequency of 1 KHz, a measurement voltage of 1 V and a measurement temperature of 20 ° C. The varistor voltage is 0 V DC to the sample element.
DC constant voltage power supply up to 150V (YHP 414
0B), and a voltage between terminals (V _{1 mA} ) when a current of 1 mA flows through the element is displayed. The voltage nonlinear coefficient is a voltage between terminals (V) when a current of 10 mA flows.
_{10 mA} ) and calculate from the following equation (1).

[0025]

(Equation 1)

After measuring the varistor voltage and the voltage nonlinear coefficient,
Surge current between terminals (8 / 20μsec, 3000A /
cm ² ) several times, the varistor voltage and the voltage nonlinearity coefficient are measured again, and the rate of change of both values before and after the surge current is applied is determined. Thirty samples were manufactured for each composition by the above-described manufacturing method, and the electrical characteristics of all of them were determined by the above-described evaluation method, and the obtained values were averaged to obtain respective electrical characteristic values.

The compositions of the main components of the semiconductor porcelain composition according to the examples, the composition of the insulating agent, and the measurement results of the electrical characteristics of the obtained grain boundary insulating semiconductor porcelain composition are shown in Tables 1 to 3 below. I have.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

As can be seen from the measurement results of the electrical characteristics shown in Tables 1 to 3, except for those corresponding to the comparative examples indicated by * in the remarks column, the semiconductor ceramic compositions according to the examples are as follows. And good electrical characteristics such as

That is, Na ₂ Ti ₃ O ₇ and B ₂ O ₃ were used as the insulating agents shown in Tables 1 to ₃ and the diameter was 6 mm.
When the element has a thickness of 500 μm, the capacitance (C) is 30 nF or more, and the dielectric loss (DF) is 1.0.
%, The varistor voltage (V _{1 mA} ) was 20 V or less, and the voltage non-linear coefficient (α) was 15 or more. The varistor voltage (V _1mA ) after the surge current (3000 A / cm ² ) was applied and the voltage nonlinear coefficient (α)
Were suppressed to -10% or less. The electrical characteristics of the semiconductor porcelain composition obtained by these examples have both excellent dielectric characteristics and voltage non-linearity (varistor characteristics) which are not present in the conventional semiconductor porcelain composition, and lower voltage. The varistor voltage can be controlled within the range of 20 V or less according to the purpose of the above, and the strontium titanate-based semiconductor ceramic composition of a specific composition can be sufficiently differentiated from other semiconductor ceramic compositions.

On the other hand, those corresponding to Comparative Examples indicated by * in the remarks column of Tables 1 to 3 sufficiently satisfy required electric characteristics such as deterioration of either dielectric characteristics or varistor characteristics. It does not.

In the above embodiment, an Ag paste is used as an electrode material. However, the electrode material is not limited to the Ag paste, and any other material that can form an electrode may be used. Absent.

[0035]

As described above in detail, in the semiconductor ceramic composition according to the present invention, (Sr _1-xy Ba _x)
Ca _{y) a} (Ti in _{1-z Nb z) b O} 3 ( wherein, x, y and z are, 0 <x ≦ 0.05,0 <y ≦ 0.2
5, a value within the range of 0.001 ≦ z ≦ 0.010, and a and b have a composition represented by the following relationship: 0.990 ≦ a / b <1.000) Further N in the grain boundary layer
Since a and B are segregated, it is possible to provide a grain boundary insulating semiconductor ceramic composition having high voltage non-linearity and exhibiting a varistor function at a low voltage and having a high dielectric constant and a low dielectric loss.

The method for producing a semiconductor porcelain composition according to the present invention is the method for producing a semiconductor porcelain composition according to the above (1), wherein the strontium titanate-based sintered body is made of Na ₂ Ti ₃ O. ₇ and B ₂ O ₃ each in 50 mol
% ≦ Na ₂ Ti ₃ O ₇ ≦ 91 mol%, 9 mol% ≦ B
_Since it is contained within the range of ₂ O ₃ ≦ 50 mol% and coated and thermally diffused, it has high voltage non-linearity and can control the varistor voltage freely, and has a high dielectric constant and low dielectric loss grain boundary insulation. Type semiconductor porcelain composition can be manufactured.

Claims (2)

(57) [Claims] (1) The inside of a crystal grain is (Sr _1-xy Ba _x C _ay )
_a (Ti _1-z Nb _z ) _b O ₃ (where x, y and z are respectively 0 <x ≦ 0.05, 0 <y ≦ 0.25, 0.0
A value within the range of 01 ≦ z ≦ 0.010, and a and b are:
0.990 ≦ a / b <1.000), wherein Na and B are further segregated in the grain boundary layer. 2. A strontium titanate-based sintered body containing Na
₂ Ti ₃ O ₇ and B ₂ O ₃ each in an amount of 50 mol% ≦
Na ₂ Ti ₃ O ₇ ≦ 91 mol%, 9 mol% ≦ B ₂ O
_The method for producing a semiconductor ceramic composition according to claim 1, wherein the composition is applied within a range of ₃ ≦ 50 mol% and applied and thermally diffused.