JPS6233301Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a multilayer ceramic capacitor. Demand for multilayer ceramic capacitors has been increasing in recent years as an essential component for making electronic devices and circuits faster and more compact with high reliability. The reasons for this are: 1 High-frequency multilayer ceramic capacitors with large capacitance values are superior to conventional tantalum capacitors,
It can be made smaller than other capacitors such as aluminum electrolytic capacitors and film capacitors. 2 Due to the structure of the electrode surface, internal inductance is smaller than other capacitors. For this reason, the series resonance frequency is higher than that of other capacitors (the equivalent circuit of a capacitor is shown in Figure 1,
It is expressed as a series combination of resistance R and inductance L, and the series resonance frequency is

It is given by the value of [Formula]. ), making it suitable for use in the high frequency range. 3. The equivalent series resistance of multilayer ceramic capacitors at high frequencies is smaller than that of other capacitors. For this reason, there is less voltage drop and less heat generation than when using other capacitors. Therefore, incorporating multilayer ceramic capacitors into electronic devices and circuits not only improves power efficiency, but also has fewer problems due to heat generation, so high reliability can be obtained even when mounted compactly. There are many advantages such as: However, there are cases where the equivalent series resistance value of the multilayer ceramic capacitor is too small, and in this case, it also acts as a drawback. For example, by connecting a multilayer ceramic capacitor and a resistance element in series, the equivalent series resistance value that is insufficient with the multilayer ceramic capacitor alone can be supplemented.
In some cases, the capacitor cannot be used unless the equivalent series resistance value is comparable to that of other capacitors. Below, we will explain a case where an unsatisfactory result is caused because the equivalent series resistance value is too small, and consider a solution. Feedback technology is indispensable for modern electronic circuits, and it is no exaggeration to say that the feedback concept is utilized in all electronic circuits to stabilize the circuit. The feedback circuit is normally constructed as shown in FIG. That is, the input signal V ₁ has a gain μ
(f) When trying to amplify with as little distortion as possible, the output
The circuit is configured to return a portion of the V ₂ signal to the input to the amplifier via a β circuit (usually an attenuator). This β circuit is usually called a feedback circuit. The circuit has a gain μβ and a phase angle arg
(μβ) is |arg(μβ)|≧180° and |μβ
It becomes unstable when the two conditions of |≧1 hold simultaneously. Therefore, the circuit design result is |μβ|=1 (i.e. odB) as shown by the broken line a in Figure 3.
If the phase exceeds -180° at frequency ₁ , where |μβ|=1, |arg(μ
It is necessary to compensate the amplitude characteristics or phase characteristics so that β)|<180°. One commonly used method for this compensation is e.g.
As shown in the figure, this method involves cascading a phase delay circuit into a μ circuit or a β circuit that has unstable characteristics. The voltage ratio of the phase delay circuit in Figure 4 is So, the amplitude characteristic is becomes.

[Formula] and when ω≪1/C(R ₁ +R ₂ ), |Vout/Vin|≒1. Also

[Formula] and 1/C (R ₁ + R ₂ )≪ω≪1/C
When R ₂ , |Vout/Vin|≒1/ωC (R ₁ +R ₂ ), which is a slope of -6 dB/octave. Also

When [Formula] and when ω≫1/CR ₂ , |Vout/Vin|≒R ₂ /R ₁ +R ₂ , which is constant regardless of the frequency. Putting the above together, the amplitude characteristics and phase characteristics of the phase delay circuit are as shown in FIG. Therefore, by cascading a phase delay circuit into a μ or β circuit with unstable characteristics as shown in Figure 3a, |μβ|=1, as shown by the solid line b in Figure 3. The phase rotation at frequency ₁ is
It is possible to create a stable circuit where the angle is less than 180°. In this case, the constants R ₁ , R ₂ and C of the phase delay circuit can be appropriately selected according to the teachings of the prior art. This method performs compensation at the expense of some gain in the high frequency range, so it has the disadvantage that the bandwidth is narrower than before compensation, but it is often used because it is easy to design and operates stably. . It has been explained above that the phase delay circuit shown in FIG. 4 is an effective circuit in stabilizing the feedback circuit. As can be seen from the above explanation, in order to stabilize an electronic circuit using feedback technology combined with a phase delay circuit, as the frequency of the electronic circuit increases, the capacitance value C of the capacitor constituting the phase delay circuit It is necessary to select the resistance and capacitance so that the product with the resistance value R ₂ is smaller. Also, depending on the frequency range of the electronic circuit, by using the equivalent series resistance of a capacitor as _R2 , it is possible to form a phase delay circuit without separately preparing a resistance element called _R2 . I also understand that. The fact that the required phase delay circuit can be formed by replacing the equivalent series resistance of a capacitor without separately preparing a resistor element called R ₂ allows for high-density packaging and cost reduction of electronic circuits, which are rapidly required these days. This is a huge benefit in promoting the In other words, the resistance element
Not only does the mounting space for R ₂ become unnecessary, but the man-hours required for mounting can also be saved. However, as mentioned above, the equivalent series resistance value of multilayer ceramic capacitors is small, about a fraction of the equivalent series resistance value of other conventional capacitors. To replace the capacitor with a multilayer ceramic capacitor, the product of the capacitance value C and the resistance value R ₂ described above can be calculated as the capacitance value C and the resistance value R ₂ of other conventional capacitors.
In order to make it equivalent to the product of Circuit configuration must be performed. But in this case,
A multilayer ceramic capacitor is not preferable because it eliminates the advantage of being smaller than other capacitors. Furthermore, even if adding a correction resistor or capacitor poses no problem in terms of space, it is not desirable in that it increases the number of man-hours required to implement it. Considering the above circumstances comprehensively, it becomes necessary to develop a multilayer ceramic capacitor with a high equivalent series resistance value. By the way, it is known that in conventional laminated ceramic capacitors, the equivalent series resistance is mostly due to internal electrode resistance. Therefore, when changing the constituent material of the internal electrodes to one with a large specific resistance value as a means of increasing the equivalent series resistance, it is necessary to integrate the material with ceramic and sinter it (sintering temperature between 900°C and 1500°C).
It is necessary to choose a material that will not impair the original function of the capacitor by oxidizing or melting when exposed to temperatures (℃). Silver-palladium alloys, which have a relationship between composition and resistivity as shown in Figure 6, have been known as conductive materials that meet these conditions. You can change the value. However, since palladium is expensive, it is not desirable in terms of reducing the price of multilayer ceramic capacitors, and it is difficult to develop multilayer ceramic capacitors that use inexpensive metals as electrodes and have the required equivalent series resistance value. desired. The present invention was developed in response to such a need, and is characterized by having an internal electrode consisting of a plurality of regions partitioned by different constituent materials with different resistivities. Since it is a multilayer ceramic capacitor, the total number of internal electrodes is quite large, but it is not necessary that all the internal electrodes have the configuration of the present invention, and at least some of the internal electrodes must have the configuration like this. If so, it should be considered as implementation of the present invention. In addition, it is more convenient to use related materials as the above-mentioned constituent materials if possible, and it is even more convenient if the materials have the same composition and can significantly change the specific resistance by changing the composition ratio. . Furthermore, it is even better if the component that exhibits this effect most strongly is effective in a small amount, and if it is an expensive component, it is economically advantageous as described in the Examples. Hereinafter, the present invention will be explained in detail based on an example of implementation. Usually, a multilayer ceramic capacitor is composed of an outer electrode 1, an inner electrode 2, and a ceramic 3, as shown in FIG. 7, and the inner electrode 2 is arranged opposite to the adjacent inner electrode 2 with the ceramic 3 in between has an overlapping region 4 and a non-overlapping region 5. The non-overlapping region effectively functions to prevent the internal electrode from shorting with an adjacent internal electrode when the external electrode 1 is attached. The equivalent series resistance value R _E of a multilayer ceramic capacitor using n internal electrodes in which the resistance of the overlapping region 4 is R and the resistance of the non-overlapping region 5 is R _s is RE4/n×( R _s + R/3) = 4/nS (ρ _s l _s + ρl/3) …(1) l _s = Electrode length of the non-overlapping part l = Electrode length of the overlapping part ρ _s = Electrode length of the non-overlapping part It is known that the specific resistance ρ of the metal is expressed as: specific resistance S of the metal in the overlapping portion=cross-sectional area of the electrode. Therefore, in order to obtain the required equivalent series resistance while keeping the number of stacked layers n, electrode length, and electrode cross-sectional area constant, ρ _s and ρ can be appropriately selected. The purpose of the present invention is to propose a structure that can increase the equivalent series resistance, which has conventionally been too small and caused problems, by adjusting it to a desired value.
Moreover, it would be even more preferable if it became a means to achieve this objective at the lowest cost.
The present invention is characterized by having an internal electrode consisting of a plurality of regions divided by different constituent materials with different resistivities, and it is up to each individual to decide which region the internal electrode should be divided into. This should be tailored to the actual circumstances of the implementation. Let us now consider that the internal electrode is divided into n regions and each region is made of a conductive material having the same composition but different composition ratios. Then, the correlation between the equivalent series resistance of the resulting multilayer ceramic capacitor and the amount of expensive elements required can be expressed by equations (2) and (3). ρ _s1 l _s1 +……+ρ _so l _so +1/3 (ρ ₁ l ₁ +……+ρ _o l _o )=ns/4R _E …(2) ρ _s1 pdl _s1 +……+ρ _so pdl _so +1/3 (ρ ₁ pdl ₁ +…+ρ _o pdl _o ) = amount of expensive element…(3) l _s1 +…+l _so = l _s …(4) l ₁ +…+l _o = l…(5) where ρ _s1 pd = amount of expensive element per unit length (non-overlapping part). ρ ₁ pd = amount of expensive element per unit length (overlapping area). ρ _so = specific resistance of the nth metal (non-overlapping part). l _s . _o = Length of the electrode formed from the nth metal (non-overlapping part). ρ _o = resistivity of nth metal (overlapping part). l _o = Length of the electrode formed from the nth metal (overlapping part). To simplify the discussion, we will discuss as an example the case where a silver-palladium alloy is used as the constituent material of the internal electrode and its composition ratio is varied. In this way, the highest equivalent series resistance value that can be taken by a multilayer ceramic capacitor constructed using only internal electrodes of the same standard formed using n silver-palladium alloys is the highest equivalent series resistance value for all ρ _so and ρ _o are equal. This is achieved when the region shown by A in FIG. 6 is composed only of metals having a weight composition of Pd (62%)-Ag (38%) exhibiting a resistivity of 42 μΩ-cm. Also, the minimum equivalent series resistance value is for all ρ _so and ρ
Pd (0%) where _o is equal and each region exhibits a resistivity of 1.6 μΩ-cm as shown by B in Figure 6.
This is achieved when it is composed only of metals with a weight composition of Ag (100%). However, these cases exhibiting the highest and lowest equivalent series resistances are meaningless cases. The present invention is meaningful when the required equivalent series resistance value is between the maximum and minimum values mentioned above. Furthermore, in this case, ρ _so , l _s are set such that the amount of the expensive element mentioned earlier (palladium in this case) is minimized and formulas (2), (4), and (5) are satisfied.
In principle, it is possible to select _o , ρ _o , l _o , ρ _so (pd), and ρ _o (pd). However, in reality, each internal electrode of a multilayer ceramic capacitor is desired to be formed by printing on a ceramic green sheet, so the composition of each internal electrode constituent material may be varied within one internal electrode, or ρ _so , l _so ,
If the amounts of ρ _o , l _o , ρ _so (pd), and ρ _o (pd) are too small, problems such as technical difficulty or excessive increase in man-hours will occur. Therefore, an appropriate value of n should be determined by comprehensively considering the amount of expensive elements to be saved, palladium in this example, the production volume of multilayer ceramic capacitors, the degree of increase in man-hours, the difficulty of printing technology, etc. It is necessary to select a material that can be used to manufacture capacitors. The present invention will be described in more detail below based on an example of implementation. A conventional multilayer ceramic capacitor with a capacitance of 200 μF and an equivalent series resistance of 1.2 mΩ requires 160 layers of internal electrodes measuring 13 mm x 11 mm x 5 μ, and the length of the non-overlapping portion of adjacent internal electrodes is was 0.5 mm, and its constituent material was 80% Ag-20% Pd by weight. In the laminated ceramic capacitor of this example, a material having a weight composition of 90% Ag-10% Pd, which is cheaper than the conventional composition, is used as the material for the overlapping parts which require a large area, and the non-overlapping parts which require a small area are used. As the constituent material, we used a material with a weight composition of 38% Ag-62% Pd, which contains a large amount of expensive Pd but has a higher resistivity. The printing technique was able to manufacture the electrodes by simply dividing one internal electrode into the two patterns described above and painting each pattern separately with conductive pastes having different material compositions. As a result of manufacturing a multilayer ceramic capacitor under almost the same manufacturing conditions as conventional multilayer ceramic capacitors, we were able to manufacture a multilayer ceramic capacitor with the same capacitance and equivalent series resistance as conventional multilayer ceramic capacitors. Furthermore, the multilayer ceramic capacitor of this example uses 40% more expensive Pd than conventional multilayer ceramic capacitors.
There weren't many. From this result, Ag38 with high resistivity
By increasing the area used for internal electrodes with a weight composition of %-Pd62% to within a range of about 5 times, the value of equivalent series resistance is further increased than before, and Pd
It is clear that it is possible to realize a multilayer ceramic capacitor that uses less amount of In the above description and examples of the present invention, only examples of silver-palladium alloys have been explained as the metals constituting the electrodes, but even in the case of other alloy electrodes, the resistance value changes depending on the composition. The laminated ceramic capacitor of the present invention having the required equivalent series resistance value can be formed by using any suitable material. For example, it is convenient to use a silver-palladium conductive material to which impurities such as copper, aluminum, silicon, titanium, etc. are added, since the specific resistance can be controlled simply by changing the content of each.

[Brief explanation of drawings]

Figure 1 is an equivalent circuit of a capacitor, Figure 2 is a block diagram of a feedback circuit, Figure 3 is an explanatory diagram of the gain and phase of the feedback circuit, Figure 4 is a basic configuration diagram of a phase delay circuit, and Figure 5 is a phase diagram. FIG. 6 is a diagram showing the gain and phase of a delay circuit, FIG. 6 is a diagram showing the correlation between the composition of a silver-palladium alloy and specific resistance, and FIG. 7 is a diagram showing the basic configuration of a multilayer ceramic capacitor. In the figure, 1 is an external electrode, 2 is an internal electrode, 3 is a ceramic, 4 is an electrode portion in a region that overlaps with an adjacent internal electrode via the ceramic, and 5 is an electrode portion in a region that does not overlap. There is.

Claims (1)

[Scope of utility model registration request] A multilayer ceramic capacitor characterized by having an internal electrode made up of a plurality of regions partitioned by different constituent materials having different specific resistances.