Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2002-12-02
2004-07-20
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S303000, C361S306100, C361S310000
Reexamination Certificate
active
06765781
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer capacitor capable of greatly reducing the equivalent serial inductance (EBL) and capable of controling the equivalent serial resistance (ESR).
2. Description of the Related Art
In recent years, the central processing units (CPUs) used for data processing apparatuses have remarkably increased in operating frequency due to higher processing speeds and higher integration. On the other hand, reduction of the power consumption has resulted in a remarkably reduction in the operating voltages.
Therefore, in power sources for supplying power to CPUs, there are sharp, large fluctuations due to the load current. It has become extremely difficult to keep fluctuations in the voltage accompanying this to within tolerances of the power source.
Therefore, sometimes a decoupling capacitor is connected in parallel between the power source and CPU. A conventional decoupling capacitor is comprised of a two-terminal structure multilayer ceramic capacitor. At the time of a transient fluctuation in the quickly changeable load current, current in supplied from this multilayer ceramic capacitor to the CPU or other integrated circuit by quick charging and discharging to suppress fluctuation of the power source voltage and stabilize the power source.
Note that in a conventional multilayer ceramic capacitor able to be used for a decoupling capacitor, the internal conductors connected to the external terminal electrodes are stacked via ceramic layers. The directions of currents flowing through the internal conductors have therefore been the same.
Along with the increasingly higher operating frequencies of today's CPUs, however the fluctuations in the load current have become faster and larger. Therefore, the parasitic part of the ESL of the multilayer ceramic capacitor itself obstructs the charge and the discharge, so that it effects on fluctuations of the power source voltage. The effect due to the multilayer ceramic capacitor is therefore becoming insufficient.
That is, in a conventional multilayer ceramic capacitor, since the ESL is high, fluctuation of the power source voltage V easily becomes greater in the same way as above along with fluctuations at the time of charging and discharging accompanying fluctuations in the load current
1
. This is because the fluctuations in voltage at the time of transition of the load current are approximated by the following equation 1 and therefore the level of the ESL is related to the magnitude of fluctuation of the power source voltage. Further, from equation 1, reduction in the ESL can be said to be linked with stabilization of the power source voltage.
dv=ESL·di/dt
(1)
where, dV is transitory fluctuation of voltage (V),
i is the fluctuation of current (A), and
t is the tire of fluctuation (sec)
Further, in a multilayer ceramic capacitor, the ESR is smaller and the high frequency characteristics are better than with an electrolytic capacitor, but advances in materials technology and thick film forming technologies have lad to remarkable advances in reducing the thickness of layers of dielectrics and increasing the number of layers in recant years. As a result, large capacity multilayer ceramic capacitors having large electrostatic capacities comparable with those of aluminum electrolytic capacitors and tantalum electrolytic capacitors have been appearing.
Further, the much greater number of layers of multilayer ceramic capacitors in recent years has not only increased the electrostatic capacity, but also caused a tendency for a further drop in the ESR. That is, the ESR at the time of high frequency fluctuation of the current is predominately due to the electrical resistance of the internal conductors, so when the greater number of layers causes an increase in the density of the internal conductors of the multilayer ceramic capacitor, the ESR is further reduced.
That is, in the equivalent circuit of the multilayer ceramic capacitor, the equivalent resistance of the internal conductors themselves laminated via the ceramic layers are formed at both sides of the capacitor circuit. When the greater number of layers causes an increase in the capacitance of the capacitor circuit, the whole resistance decreases and the ESR is further reduced in inverse proportion to the number of layers.
On the other hand, a large capacity capacitor is mainly used for flattening the output of a switching power source. If using a capacitor with a small ESR, however, while this is effective for reducing the output ripple voltage, when the ESR is overly small, the control system of the switching power source suffers from unstable output voltage or a susceptibility to abnormal oscillation. This in because when using a capacitor with an overly small ESR, the phase easily becomes delayed in the feedback circuit of the control circuit and the control circuit can no longer function normally.
Therefore, in the past, for applications such as flattening the output of the switching power source, often an electrolytic capacitor having a large ESR is used instead of a multilayer capacitor.
As opposed to this, from the standpoints of reducing costs and reducing size, it is desirable to use a multilayer capacitor for such applications as well. A further increase in layers of the multilayer capacitor in pursuit of greater capacity in the future, however, may invite a greater reduction in the ESR and therefore an overly small ESR.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a multilayer electronic device able to greatly reduce the ESL.
A second object of the present invention is to produce a multilayer capacitor able to be used for various applications by controling the ESR.
To attain the first object, according to a first aspect of the present invention, there is provided a multilayer capacitor comprising at least two of a first internal conductor and a second internal conductor formed in flat shapes, at least two of a first polarity conductor and a second polarity conductor formed in flat shapes, a dielectric body formed by stacking a plurality of dielectric sheets with dielectric sheets sandwiching each of the conductors, a first terminal electrode arranged at an outside of the dielectric body so as to be able to be connected to an external circuit and connected to the first internal conductor, a second terminal electrode arranged at the outside of the dielectric body so as to be able to be connected to the external circuit and connected to the second internal conductor, a first linkage electrode for connecting the first internal conductor and the first polarity conductor at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along a stacking direction become opposite to each other, and a second linkage electrode for connecting the first internal conductor and the first polarity conductor at the outside of the dielectric body while creating portions where the directions of currents between the conductors adjoining each other along the stacking direction become opposite to each other.
According to the multilayer capacitor according to the first aspect of the present invention, the dielectric body is formed by stacking a plurality of dielectric sheets with each dielectric sheet sandwiched between two first and second internal conductors and two types of first and second polarity conductors formed in flat shapes. Two first and second terminal electrodes arranged at the outside of the dielectric body so as to enable connection to an external circuit are connected to the first and second internal conductors.
The first internal conductor and first polarity electrode are connected by a first linkage electrode and become the same polarity. Further, the second internal conductor and second polarity electrode are connected by a second linkage electrode and become the own polarity. Further, portions where the directions of the current become opposite between these conduc
Dinkins Anthony
Oliff & Berridg,e PLC
TDK Corporation
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