JP3039117B2 - Multilayer type grain boundary insulating semiconductor ceramic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally functions as a capacitor to absorb low-voltage noise and high-frequency noise, while exhibiting a varistor function when a high voltage such as a pulse or static electricity enters. The present invention relates to a laminated type grain boundary insulated semiconductor ceramic capacitor used for protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity generated in the electronic devices.

[0002]

2. Description of the Related Art In recent years, semiconductor devices such as ICs and LSIs have been widely used for realizing multifunctional, lightweight, and compact electronic devices, and the noise immunity of the devices has been reduced accordingly. Therefore, in order to ensure noise immunity of such electronic devices, film capacitors, multilayer ceramic capacitors, semiconductor ceramic capacitors, and the like are used as bypass capacitors in power supply lines of various ICs and LSIs. However, these capacitors exhibit excellent performance in absorbing low-voltage noise and high-frequency noise, but these capacitors themselves have the function of absorbing high-voltage pulses and high-voltage static electricity. When a pulse having a high voltage or static electricity invades, a malfunction of a device, destruction of a semiconductor, and destruction of a capacitor are serious problems.

[0003] In such applications, SrTiO has been proposed as a new type of capacitor having a good noise absorption and being stable with respect to temperature and frequency, and also having a high pulse tolerance and excellent pulse absorption. A grain boundary insulated semiconductor ceramic capacitor having a varistor function in a ₃ series semiconductor ceramic capacitor (hereinafter, referred to as a ceramic capacitor with a varistor function) has been developed, and has already been disclosed in JP-A-57-27001 and JP-A-57-35303. It is provided by a gazette or the like.

The ceramic capacitor with a varistor function normally absorbs low-voltage noise and high-frequency noise as a capacitor, but functions as a varistor when a high voltage such as a pulse or static electricity enters, and is generated in electronic equipment. It has the feature of protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity, and their use has been increasingly expanded.

[0005] On the other hand, in the field of electronic components, lighter, thinner, smaller and higher performance has been increasingly promoted, and even with this varistor function-equipped ceramic capacitor, demands for smaller size and higher performance have been increasing. However, since the conventional ceramic capacitor with a varistor function is a single-plate type, if the size is reduced, the area of the electrode is reduced, and as a result, a problem is caused in that the capacity is reduced and the reliability is reduced. Therefore,
As a solution, it is anticipated that the application to lamination, which requires a large electrode area, will be promoted.

However, the ceramic capacitor with varistor function normally, an oxide is applied to the surface of the SrTiO ₃ based semiconductor device, since a step of insulating the grain boundary layer by thermal diffusion, BaTiO ₃ generally used It is very difficult to form a multilayer capacitor with a varistor function (hereinafter referred to as a multilayer ceramic capacitor with a varistor function) by firing the ceramic capacitor material with a varistor function at the same time as the internal electrode material, as compared with a system multilayer ceramic capacitor. Was considered.

To solve the problem of co-firing a multilayer ceramic capacitor material with a varistor function and an internal electrode material, Japanese Patent Application Laid-Open Nos. 54-53248 and 54-53250 are applied. A ceramic paste with a large amount of organic binder is printed on the part corresponding to the internal electrode, and a porous layer is formed on this part in the sintering process,
A method of injecting a conductive metal into the porous layer under appropriate pressure after sintering, or a method of forming an internal electrode by plating or melting to form a multilayer ceramic capacitor with a varistor function has been developed and provided. I have. But,
These are quite difficult in terms of process and have not yet reached the level of practical use.

In Japanese Patent Application Laid-Open No. Sho 59-215701, a heat diffusion material capable of insulating a grain boundary layer is mixed into a raw sheet made of powder calcined in a non-oxidizing atmosphere. A method of printing a conductive paste and sintering it in an oxidizing atmosphere. Further, Japanese Patent Application Laid-Open No. 63-219115 discloses a method in which a powder made into a semiconductor is used as a main component. There has been reported a method of firing a molded body in which raw sheets mixed with an agent and / or a diffusing agent containing a glass component and internal electrodes are alternately laminated in the air or in an oxidizing atmosphere.

However, in these two methods, the firing temperature is relatively low, ie, 1000 to 1200 ° C., and sintering of the ceramic is difficult to occur, so that the crystal particles are hardly brought into surface contact, and the completed element is a complete sintered body. Therefore, there is a disadvantage that the capacity is low, the voltage non-linear index α, which is a typical characteristic of a varistor, is small, the varistor voltage is unstable, and the reliability is poor. Furthermore, in the latter JP-A-63-219115, when a glass component is added as an additive, a glass phase is precipitated at a crystal grain boundary, and the above-mentioned electric characteristics are easily deteriorated, and the reliability is poor. Yes, and this is still less than practical.

Accordingly, the present inventors have disclosed in Japanese Patent Application No. Hei.
No. 7, as described in Japanese Patent Publication No.
₃ shows a ceramic composition based on a semiconductor component and a MnO ₂ —SiO ₂ base material and a method of manufacturing the same.
It is possible to develop a multilayer ceramic capacitor with a varistor function using t, Rh, Pd or Ni as an internal electrode. Furthermore, as described in Japanese Patent Application No. 3-152,991, an internal electrode composition in which at least one or more of low-valent Li, Na, and K atoms is dissolved in Ni or a compound containing Ni atoms. And a method for producing the same,
The development of a multilayer ceramic capacitor with a varistor function using i as an internal electrode has been made possible.

Further, as a patent relating to a multilayer varistor, there has already been disclosed in Japanese Patent Publication No. 58-23921,
A stacked voltage nonlinear element using O, Fe ₂ O ₃ , and TiO ₂ is disclosed. However, since this element has almost no capacitance, it exhibits excellent performance against pulses with relatively high voltage and absorption of static electricity, but against noise with low voltage below the varistor voltage and high frequency noise. Had the problem that it had little effect.

[0012]

However, the above T
The semiconductor component and MnO ₂ —SiO ₂ are added to i excess SrTiO _3.
-Based ceramic composition and low valence L
an internal electrode composition in which at least one of i, Na, and K atoms is dissolved in Ni or a compound containing Ni atoms;
Although the manufacturing method made it possible to develop a multilayer ceramic capacitor with a varistor function using Ni as the internal electrode, the composition of the external electrode was not studied as deeply as the internal electrode composition, and it could not be put to practical use. It had problems.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and normally functions as a capacitor to absorb low-voltage noise and high-frequency noise, while exhibiting a varistor function when a high voltage such as a pulse or static electricity enters. Regarding the multilayer ceramic capacitor with function, a multilayer grain boundary insulated semiconductor ceramic capacitor containing SrTiO ₃ as a main component, which uses Ni as an internal electrode and enables the simultaneous firing of the ceramic capacitor material and the internal electrode material in terms of process, has been proposed. It is intended to provide.

[0014]

According to the present invention, at least one of low-valent Li, Na and K atoms is contained in a grain boundary insulating semiconductor ceramic by Ni or Ni. Ni internal electrodes starting from an internal electrode paste solid-dissolved in a compound containing atoms are provided so as to alternately reach different edges, and Pd and Pt atoms are provided at both ends of the Ni internal electrodes. And at least one of the above is added to and mixed with Ni or a compound containing a Ni atom.

[0015]

With this structure, the oxidation resistance of the Ni internal electrode is improved by dissolving at least one of the low-valent Li, Na, and K atoms in Ni or a compound containing Ni atoms. The oxidizability of the crystal grain boundary portion of the ceramic element can be improved. Further, by adding and mixing at least one of Pd and Pt atoms to Ni or a compound containing Ni atoms as an external electrode, the contact between the Ni internal electrode and the external electrode is improved, and the oxidation rate is further reduced. Further, the oxidation of the external electrodes can be suppressed as much as possible, and a multilayer ceramic capacitor with a varistor function can be easily provided.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention will be specifically described below with reference to embodiments.

Example 1 First, the average particle size was 0.5 μm.
Below 90% purity NiO with average particle size 0.5μm
When at least one of the following Pd powder and Pt powder was added, the powder was used as a starting material for an external electrode, and this powder was dispersed in a solvent together with an organic binder such as butyral resin to obtain an external electrode paste. Next, as shown in FIG. 3, SrTiO ₃ (Sr / Ti = 0.97) 97 m
ol%, Nb ₂ O ₅ : 0.5 mol%, Ta ₂ O ₅ : 0.5 mol
%, MnO ₂ : 1.0 mol%, SiO ₂ : 1.0 mol%, prepared by a doctor blade method or the like.
A raw sheet having a thickness of about μm is cut into a predetermined size, and NiO: 99.5 is placed on the cut raw sheet 1.
The internal electrode paste 2 having a composition of mol% and Li ₂ CO ₃ : 0.5 mol% was pattern-printed by screen printing according to a predetermined size. As is clear from FIG. 4, the inner electrode paste 2 containing Ni as a main component is not printed on the uppermost and lowermost raw sheets 1a to be ineffective layers. At this time, the internal electrode paste 2 mainly composed of Ni printed on the raw sheet 1 to be laminated in the middle is:
As is well known, printing was performed to alternate (different) edges. Thereafter, the raw sheets 1a are arranged on the upper and lower sides (usually, a plurality of layers are laminated). In the meantime, a plurality of layers of the raw sheet 1 on which the internal electrode paste 2 is printed are laminated and pressurized and pressed while heating. A molded body was obtained.

Next, an external electrode paste containing Ni as a main component is applied to both end surfaces of the molded body where the internal electrode paste 2 is alternately exposed at different edges, and the paste is applied at 1050 ° C. in air.
Degreasing and calcination were performed in air for 2 hours. Then, N ₂ : H ₂
= 1: 1 in a reducing atmosphere at 1250 ° C for 2 hours. After this calcination, it is reoxidized at 900 ° C. in the air, and further, at 400 ° C. and 30 ° C. in a reducing atmosphere of N ₂ : H ₂ = 99: 1.
The external electrodes were reduced again in minutes, and a multilayer ceramic capacitor with a varistor function shown in a partially cutaway perspective view in FIG. 1 was produced.
As shown in the figure, a plurality of internal electrodes 2a are provided in a ceramic element so that the internal electrodes 2a alternately reach different edges, and the ceramics electrically connected to these internal electrodes 2a. A multilayer ceramic capacitor 4 having a varistor function was obtained in which external electrodes 3a mainly composed of Ni were provided at both ends of the element.

The shape of the multilayer ceramic capacitor with a varistor function in this embodiment is represented by the symbol L × W × in FIG.
H is a 1.3 type of 1.60 × 3.20 × 1.20 mm, and the effective layer on which the internal electrode 2a is formed is 3
This is a stack of zero layers.

With respect to the multilayer ceramic capacitor with varistor function thus obtained, its capacitance, Tan
Various electrical characteristics such as δ, varistor voltage, voltage non-linear index α, and series equivalent resistance value ESR are described in the following (Table 1). The following measured values are described for various electrical characteristics.

(2) The capacitance C is measured at a voltage of 1.0 V and a frequency of 1.
Value at 0 kHz. ◇ Varistor voltage V _0.1mA is the value at the measured current 0.1mA.

◇ The voltage non-linear index α is measured current 0.1 m
From A and the value at 1.0 mA, it was calculated from the equation of α = 1 / log (V _{1 mA} V _{0.1 mA} ).

(2) The series equivalent resistance value ESR is calculated based on the measured voltage 1.
Resistance value at resonance point at 0V.

[0024]

[Table 1]

When the above (Table 1 is explained, the data number marked with * is a comparative example, which is outside the scope of the present invention.
If the external electrode is highly oxidized and does not have both the function of absorbing low voltage noise and high frequency noise as a capacitor and the function of absorbing high voltage such as pulse and static electricity as a varistor, etc.) It has a large series equivalent resistance value ESR and poor frequency characteristics. Therefore. These samples are not suitable as ceramic capacitors with a varistor function for protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity generated in electronic devices.

On the other hand, the samples of the present invention indicated by the other sample numbers have a large capacitance, a large voltage non-linear index α, and a small series equivalent resistance value ESR. It has both the function of absorbing high-frequency noise and the function of absorbing high voltage such as pulse and static electricity as a varistor.The capacitance temperature change rate and the varistor voltage temperature coefficient are small, and the reliability and electrical characteristics are low. It has a characteristic that is not easily affected by temperature. Therefore, these samples are suitable as ceramic capacitors with a varistor function for protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity generated in the electronic devices.

Further, Pd, NiO as an external electrode material are used.
In a multilayer ceramic capacitor with a varistor function manufactured by adding at least one or more of Pt atoms, oxidation of an external electrode is suppressed, and tan δ and a series equivalent resistance value E are reduced.
A decrease in the SR value was confirmed. It is considered that this is because the added Pd acts as a reducing agent to suppress the oxidation of the surface layer of the external electrode and reduce the resistance value of the electrode.

(Embodiment 2) Next, as a second embodiment of the present invention, Ag or Ag-
An example in which a Pd-based external electrode is formed will be described.

The internal electrode paste 2 of the laminated molded product obtained by using the internal electrode composition and having the same ceramic material composition as that of the above-mentioned Example 1 was alternately exposed to different edges. , Pt is coated with an external electrode paste in which at least one or more of them is added and mixed.
Degreasing and calcination were performed at 050 ° C. for 2 hours in the air. Then, at 1250 ° C. in a reducing atmosphere of N ₂ : H ₂ = 99: 1,
Baking was performed for 2 hours. After firing, an Ag-Pd system (Pd: 10
The external electrode paste is applied on the external electrode 3a containing Ni as a main component and baked at 900 ° C. in air to form a partially cut-away perspective view in FIG. A plurality of layers of internal electrodes 2a are provided so that the internal electrodes 2a alternately reach different edges, and Ni is a main component at both ends of the ceramic element electrically connected to these internal electrodes 2a. To obtain a multilayer ceramic capacitor 4a with a varistor function, in which an external electrode 3a to be formed and an Ag or Ag-Pd-based external electrode 3b were provided thereon. FIG. 5 shows a manufacturing process of this embodiment.

With respect to the multilayer ceramic capacitor having the varistor function thus obtained, the capacitance, tan
Various electrical characteristics such as δ, varistor voltage, voltage nonlinearity index α, and series equivalent resistance value ESR are described in the following (Table 2) and (Table 3).

[0031]

[Table 2]

[0032]

[Table 3]

When the above-mentioned Example 2 is explained, in Tables 2 and 3, those marked with * in the material number are comparative examples, which are outside the scope of the present invention. (Table 2)
The Ag external electrode shown in Table 3 is better when the Ag external electrode shown in Table 3 is formed.
-The value of the series equivalent resistance value ESR was slightly lower than that of the sample in which the -Pd-based external electrode was formed. This is considered to be because the non-resistance value of Pd is slightly higher than the non-resistance value of Ag.

When a multilayer ceramic capacitor with a varistor function was prepared by adding and mixing at least one of Pd and Pt to NiO, reductions in tan δ and series equivalent resistance value ESR were confirmed. At this time, when Pd was not added, it was observed that a layer having relatively high resistance was formed at the boundary between the lower Ni external electrode 3a and the upper Ag or Ag-Pd-based external electrode 3b. ,
It was confirmed that a boundary layer was not formed when Pd was added to the lower layer external electrode paste. That is, it is considered that Ni and Ag or Ag-Pd form an alloy through Pd. However, this phenomenon was effective only when Pd was added to the lower external electrode paste, and no effect was obtained even when Pd was added to the upper external electrode paste.
And it was confirmed that this addition effect was obtained not only for Pd but also for Pt or a mixture of Pd and Pt.

As described above, the multilayer ceramic capacitor with a varistor function can be easily manufactured by the structures described in the first and second embodiments. The multilayer ceramic capacitor with a varistor function thus obtained is very large. Because of its capacitance, large voltage non-linear index α, small varistor voltage, series equivalent resistance value ESR, and excellent temperature, frequency, and noise characteristics, it usually has low voltage noise and high frequency noise as a capacitor. When a high voltage such as a pulse or static electricity enters, it exhibits a varistor function, and exhibits excellent response to abnormal voltages such as noise, pulses, and static electricity. It is expected to replace monolithic ceramic capacitors and semiconductor ceramic capacitors.

Further, the multilayer ceramic capacitor with a varistor function of the Ni internal electrode according to the present invention is small in size, has a large capacity, and has high performance as compared with a conventional single-plate type ceramic capacitor with a varistor function. Applications for mounting components are also expected. Furthermore, compared to a multilayer ceramic capacitor with a varistor function using a noble metal such as Pd or Ag as an internal electrode, the use of low-cost Ni as an internal electrode is expected to reduce raw material costs.

[0037]

As described above, the ceramic capacitor with a varistor function according to the present invention has both a capacitor function and a varistor function, and usually functions as a capacitor to absorb low-voltage noise and high-frequency noise. When a high voltage such as noise or static electricity enters, it performs a varistor function, so noise, pulses,
It has the function of protecting semiconductors and electronic devices from abnormal voltages such as static electricity.It has a small size, large capacity, and high performance compared to conventional single-plate type ceramic capacitors with varistor function. It is also expected to be applied to a great extent, and its practical effect is extremely large, for example, it can be used as an element for high-density mounting of video cameras, communication devices, and the like.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a multilayer ceramic capacitor with a varistor function obtained according to a first embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view showing a multilayer ceramic capacitor with a varistor function obtained according to a second embodiment of the present invention.

FIG. 3 is a manufacturing process diagram of the multilayer ceramic capacitor with a varistor function according to the first embodiment of the present invention.

FIG. 4 is an exploded perspective view of a multilayer ceramic capacitor with a varistor function for explaining the shape of the raw sheet to be laminated and the internal electrode paste printed thereon according to the first embodiment of the present invention.

FIG. 5 is a manufacturing process diagram of a multilayer ceramic capacitor with a varistor function according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 1a Raw sheet 2 Internal electrode paste 2a Internal electrode 3a Lower layer Ni external electrode 3b Upper layer Ag or Ag-Pd-based external electrode 4,4a Multilayer ceramic capacitor with varistor function

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-40210 (JP, A) JP-A-2-248015 (JP, A) JP-A-4-251908 (JP, A) JP-A-5-205 36561 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01G 4/12

Claims (2)

(57) [Claims] 1. A ceramic green sheet provided with a Ni internal electrode starting from a paste in which at least one of low-valent Li, Na, and K atoms is dissolved in Ni or a compound containing Ni atoms. Of the Pd and Pt atoms such that the Ni internal electrodes are electrically connected to the opposed end faces of the molded body laminated in such a manner that a plurality of the Ni internal electrodes alternately contact different end faces opposite to each other. A multilayer grain boundary insulated semiconductor ceramic capacitor comprising an external electrode formed by adding at least one of Ni and Ni to a compound containing Ni atoms. 2. The laminated type grain boundary insulated semiconductor ceramic according to claim 1, wherein the external electrode is a lower layer external electrode, and an upper layer external electrode of Ag or Ag-Pd is further formed on the lower layer external electrode. Capacitors.