Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2002-06-27
2003-08-12
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S310000, C361S303000, C361S306200
Reexamination Certificate
active
06606237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multilayer capacitors, wiring boards, decoupling circuits, and high frequency circuits, which include the multilayer capacitors. More particularly, the present invention relates to multilayer capacitors that are very effective in high frequency circuits. In addition, the present invention relates to wiring boards, decoupling circuits, and high frequency circuits including the multilayer capacitors.
2. Description of the Related Art
Most conventional multilayer capacitors are formed of ceramic dielectric materials. In addition, each of these conventional multilayer capacitors has a main body including a plurality of laminated dielectric layers, and a plurality of pairs of first and second internal electrodes opposing each other via specified dielectric layers and alternately arranged in a direction in which the dielectric layers are laminated to form a plurality of capacitor units. First external terminal electrodes are located on the first end surface of the main body, and second external terminal electrodes are located on the second end surface thereof. The first internal electrodes are extended onto the first end surface of the main body to be electrically connected to the first external terminal electrodes. In addition, the second internal electrodes are extended onto the second end surface of the main body to be electrically connected to the second external terminal electrodes.
In the multilayer capacitor, for example, currents flow By from the second external terminal electrodes to the first external terminal electrodes. In this case, the currents flow from the second external terminal electrodes to the second internal electrodes and, then, flow from the second internal electrodes to the first internal electrodes passing through the dielectric layers. After this, the currents pass through the first internal electrodes to the first external terminal electrodes.
The equivalent circuit of a capacitor is shown as a circuit in which a capacitance (C), an equivalent series inductance (ESL), and the resistance (R) of an electrode are connected in series. In this case, R is referred to as an equivalent series resistance (ESR).
In the equivalent circuit, a resonant frequency f
0
is determined by an equation f
0
=1/[2&pgr;×(L×C)
½
]. The capacitor cannot function at a frequency higher than the resonant frequency. In other words, when the value of L, that is, the value of ESL is small, the resonant frequency f
0
becomes high, so that the capacitor can be used at the higher frequency. It is considered that copper may be used as the material of internal electrodes to reduce the value of ESR. However, in order to use the capacitor in a microwave band, the capacitor must be capable of reducing ESL.
In addition, the reduction of ESL is required for a capacitor used as a decoupling capacitor connected to a power source circuit for supplying a power source to a MPU chip of a micro processing unit (MPU) of a workstation, a personal computer, or other suitable device.
Regarding this case,
FIG. 16
is a block diagram illustrating an example of a connecting structure including a MPU
1
and a power source unit
2
.
In
FIG. 16
, the MPU
1
has a MPU chip
3
and a memory
4
. The power source unit
2
supplies a power source to the MPU chip
3
. A decoupling capacitor
5
is connected to a power source circuit located between the power source unit
2
and the MPU chip
3
. In addition, a signal circuit is located between the MPU chip
3
and the memory
4
.
The decoupling capacitor
5
used in the MPU
1
, like a typical type of decoupling capacitor, is used to smooth noise absorption and fluctuations in the power source. Moreover, recently, the operational frequency of the MPU chip
3
has been designed to be over 1 GHz. Thus, the MPU chip
3
needs to have high-speed performance. In order to satisfy this requirement, a quick power supply function is necessary. This is a function in which power is supplied in a few nanoseconds from the capacity of electricity charged in a capacitor, when power for starting-up is suddenly needed.
Thus, an inductance component provided in the decoupling capacitor
5
used in the MPU
1
is required to be as low as possible, for example, to be a few pH or lower. That is, a capacitor having lower inductance is desired.
More specifically, in the MPU chip
3
, a DC current voltage of approximately 2.0V is applied, and a consumed power is approximately 24W. That is, a current of approximately
12
A flows through the chip. In this case, there is provided an arrangement for reducing the consumption of power. When the MPU
1
is not operating, the MPU
1
is in a sleep mode, in which the amount of the consumed power is reduced to 1W or lower. When converted from the sleep mode to an active mode, it is necessary to supply power required for the active mode to the MPU chip
3
in a significantly short time, as shown below. At the operational frequency of 1 GHz, when converted from the sleep mode to the active mode, power needs to be supplied in 2 to 4 nanoseconds.
However, since the power source unit
2
cannot supply the power in such a short time, electrical charge accumulated in the decoupling capacitor
5
near the MPU chip
3
is released until the power source is supplied from the power source unit
2
to the MPU chip
3
.
In the case of an MPU having an operational clock frequency exceeding 1 GHz, in order to perform the above function, the ESL of the decoupling capacitor
5
disposed near the MPU chip
3
needs to be a few pH or lower.
However, since the ESL of the above-mentioned conventional multilayer capacitor ranges from approximately 500 pH to 800 pH, this hardly satisfies the above necessary condition of being a few pH or lower. Regarding an inductance component occurring in the multilayer capacitor, magnetic flux, having a direction that is determined by the direction of a current flowing though the multilayer capacitor, is induced to produce a self-inductance component.
Under the aforementioned background, examples of the structures of multilayer capacitors capable of reducing .ESL are provided in Japanese Unexamined Patent Application Publication No. 2-256216, U.S. Pat. No. 5,880,925, Japanese Unexamined Patent Application Publication No. 2-159008, Japanese Unexamined Patent Application Publication No. 11-144996, and Japanese Unexamined Patent Application Publication No. 7-201651.
The ESL is reduced by cancellation of magnetic flux induced in the multilayer capacitor. For the cancellation of magnetic flux, the direction of a current flowing through the multilayer capacitor is diversified. In order to diversify the direction of the current, the number of terminal electrodes provided on the external surface of the main body of the capacitor is increased, thereby increasing the number of leading internal electrodes extended to be electrically connected to the terminal electrodes. Additionally, the leading internal electrodes are oriented in some directions.
For example, in each of Japanese Unexamined Patent Application Publication No. 2-256216, U.S. Pat. No. 5,880,925, and Japanese Unexamined Patent Application Publication No. 2-159008, there is provided a structure in which lead internal electrodes are extended onto two opposing side surfaces of the main body of a multilayer capacitor, which is a first conventional art.
In addition, Japanese Unexamined Patent Application Publication No. 11-144996 provides a structure in which leading internal electrodes are extended onto four side surfaces of the main body of a multilayer capacitor, which is a second conventional art.
Furthermore, Japanese Unexamined Patent Application Publication No. 7-201651 provides a structure in which leading internal electrodes are extended onto a main surface of the main body of a multilayer capacitor, which is a third conventional art.
When a focus is put on the reduction of ESL in the first to third conventional arts, in general, the second conventional
Figueroa David G.
Hioki Takashi
Holmberg Nicholas L.
Hori Haruo
Kuroda Yoichi
Dinkins Anthony
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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