Murata’s Low-ESL Capacitors
Accommodate Changes in IC Features
F
unctional upgrading has recently
emerged as a trend not only in
CPUs and in other ICs for servers
and personal computers (PCs) but
also those for game machines and electronic equipment of automobiles. This
trend has led manufacturers to increase
the clock frequency, lower the operating
voltage, and increase the operating current of ICs for various applications. Meanwhile, the allowable ripple voltage has
been lowered extremely. As ICs evolve to
feature higher speeds and lower operating voltages, decoupling capacitors are
required to have lower inductance. This
article introduces the chip monolithic ceramic capacitors that have low equivalent
series inductance (ESL).
What Is a Low-ESL Capacitor?
Fig. 1 shows the equivalent circuit of
a monolithic ceramic capacitor, represented by a capacitance, an equivalent series resistance (ESR), and an equivalent
series inductance (ESL). Decreasing the
impedance of a capacitor circuit using a
high frequency requires lowering the ESL
component of the capacitor. Murata Manufacturing Co., Ltd. has already developed and marketed a series of monolithic
ceramic capacitors with the ESL lowered.
ous purposes. For
example, capacitors are used for
coupling to block
DC components or
bypassing to cut
off AC components or combined
with coils to form
a filter, resonant or
matching circuit.
To realize a lowESL capacitor, the
parasitic inductance (ESL) is reduced by forming Fig. 2: Structure of low-ESL capacitor
terminal electrodes
widthwise (reverse geometry) or increasage and can provide an increased decouing the number of terminal electrodes
pling effect when the capacitor is con(multi-termination) on a monolithic cenected between the power and ground
ramic capacitor. A low-ESL decoupling
lines of an IC. The low-ESL design also
capacitor can charge and discharge elecensures low impedance at high frequentricity at a higher speed than ever when
cies, and supports a good insertion loss
the capacitor is mounted in an IC packcharacteristic when the low-ESL capaci-
Functions of Low-ESL Capacitors
Capacitors are important parts of highfrequency circuits and are used for vari-
Fig. 3: Insertion loss characteristic
Table 1: Comparison of ESL between monolithic ceramic capacitors
Fig. 1: Circuit equivalent to a monolithic
ceramic capacitor
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AEI February 2006
Copyright  2006 Dempa Publications, Inc.
Table 2: Lineup of LL series low-ESL chip monolithic ceramic
capacitors
tor is used as a bypass capacitor in a highspeed transmission line in spite of increasing amounts of signals and data to
be processed by a chip set.
Table 1 shows the
comparison of ESL
values between a
3216-size, 2.2µF
general capacitor and
the low-ESL models
of 3216-size, 2.2µF
capacitor (reverse
geometry and multitermination [8- and
10-terminal] formats). The ESL of
the reverse geometry
is one-fourth of the
ESL of the general capacitor, and the
ESL of the multi-termination version is
one-eighth or less of the ESL of the general kind.
Kinds of Low-ESL Capacitors
Fig. 2 shows the three kinds of lowESL capacitors introduced by Murata.
The ceramic, internal electrode, and terminal electrode materials of the low-ESL
capacitors are the same as those of the
high-capacitance monolithic ceramic capacitors of the company.
Features of Low-ESL Capacitors
Insertion loss characteristic at high
frequencies
The low-ESL capacitors have better insertion loss characteristics at high frequencies in comparison with general
monolithic ceramic capacitors. The lowESL capacitors also show good noise re-
duction characteristics when they are used
as bypass capacitors (Fig. 3).
High-speed power supply characteristic
Fig. 4(a) shows a discharge circuit designed for a simulation using the ESL
and ESR values of various monolithic ceramic capacitors. Fig. 4(b) shows the
changes in the voltage across the 50 mΩ
load resistor as the result of the simulation in which the capacitor previously
charged with 1.5V discharges the electricity to the load resistor. The results indicate that both the reverse geometry and
multi-termination (8- and 10-terminal)
low-ESL capacitors discharge electricity
at higher speeds than the general (GRM
type) capacitor. These features enable a
low-ESL capacitor to work in the power
line for a high-speed IC to ensure steady
power supply.
Future Prospect
It seems that the IC market is driving
the trend toward higher clock frequency,
lower operating voltage, and higher operating current. The share of ICs is expected to expand in the conventional CPU
market as well as in the fields of game
machines and electronic equipment for
automobiles.
Amid this background, demands for
low-ESL capacitors are on the rise. Murata will beef up its lineup of capacitors
that have lower ESL to meet the requirements of the market.
About This Article
Fig. 4: Comparison of discharge characteristic between low-ESL and general capacitors
(simulated)
The author, Hideo Hirose, is Chief of
AS Capacitor at the Product Engineering Section I of Fukui Murata Manufacturing Co., Ltd.
AEI February 2006
Copyright  2006 Dempa Publications, Inc.
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