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1. KONDENZATORJI
18. In a multilayer ceramic capacitor, a
capacitance of more than 100µF can
be acquired through combined use
of the thin-layer technology in which
the thickness of a dielectric layer approaches
1um, and the multilayer technology
wherein hundreds to 1,000 layers
are exceeded.
As a result, a compact and high-capacitance
multilayer ceramic capacitor
has also been used for a decoupling capacitor,
for which an electrolytic capacitor
has been mainly used until now, or
power smoothing capacitor.
More effective decoupling performance
or power smoothing characteristics is anticipated
based on the excellent frequency
characteristics of a multilayer ceramic capacitor.
The application will be promoted
more and more in the future.
Acquired Capacitance Range
Fig.1 shows various capacitors mainly
used for general electronic equipment according
to the relation between the acquired
capacitance value and rated voltage.
In a capacitance range of less than
1µF, a type 1 (temperature compensating)
ceramic capacitor, a type 2 (high dielectric
constant) ceramic capacitor, and a film
capacitor are put into use.
An aluminum electrolytic capacitor
or tantalum electrolytic capacitor has
been mainly used in the high-capacitance
range exceeding 1µF. In recent years,
with the progress of the high-capacitance
technology in a multilayer ceramic capacitor,
the capacitance value per volume
has been rapidly expanded (Fig.2),
and a capacitance range of more than
100µF can be acquired even in a multilayer
ceramic capacitor.
Fig.3 shows the relation between the
acquired capacitance value and rated voltage
of a high-capacitance multilayer ceramic
capacitor exceeding 1µF for each
chip size. The relation between each chip
size and the maximum acquired capacitance
value indicates that a capacitance
value of up to 1µF can be acquired in 1005
size, that of up to 10µF can be acquired
in 1608 size, and that of up to 100µF can
be acquired in 3225 size. Moreover, the
rated voltage is lined up so that it is provided
up to DC 100V and widely used for
various applications. Judging from the
48 AEI October 2004
High-Capacitance Multilayer
Capacitor Delivers Better Performance
Fig. 1: Relation between capacitance value and rated voltage in each capacitor
Fig. 2: Transition of capacitance value per volume and dielectric thickness
Fig. 3: Range of capacitance value and rated voltage in each size
Copyright ? 2005 Dempa Publications, Inc.
relation of the chip size and the maximum
acquired capacitance value, the development
of a compact and high-capacity multilayer
ceramic capacitor will be promoted
more and more in future by the progress
of technology.
Frequency Characteristics
The structure of a multilayer ceramic
capacitor is shown in Fig.4. In the capacitor,
dielectric ceramics and electrodes
are alternately accumulated for formation.
A metal such as nickel is generally used
for electrode materials. Therefore, the electrode
resistance influencing the equivalent
series resistance (ESR) value or loss
of a capacitor is lower than for an electrolytic
capacitor by a few digits.
Fig.5 shows the comparison of the frequency
impedance characteristics of a
10µF high-capacitance multilayer ceramic
capacitor with those of an aluminum electrolytic
capacitor and tantalum electrolytic
capacitor. For the impedance characteristics
of an ideal capacitor, the impedance
decreases by one digit when a frequency
increases by one digit. As shown in Fig.5,
however, for the impedance characteristics
of an aluminum electrolytic capacitor,
the impedance value becomes constant
at approximately 10? and does not
decrease any longer when a frequency
reaches a few kilohertz or more. In a tantalum
electrolytic capacitor, the impedance
value does not decrease when a frequency
reaches some 10kHz or more. The
impedance value becomes constant at
some hundred milliohms.
In a multilayer ceramic capacitor, an
almost ideal impedance decrease is observed
until a self-resonance frequency
of approximately 1MHz is reached. The
impedance value at that time is a few milliohms.
When a frequency becomes
higher, an impedance value increases due
to the influence of an equivalent serial inductance
(ESL) term.
The value obtained when the impedance
of each capacitor is lowest is equivalent
to an ESR (equivalent serial resistance)
value. The ESR value of a multilayer
ceramic capacitor that uses a metal
lower in a resistance value than for an
electrolytic capacitor as the electrode of
a capacitor is low.
Fig.6 shows the relation between the
current value and capacitor surface temperature
occurring when a sine wave current
with a frequency of 100kHz flows
through each capacitor with a capacitance
value of 100µF. For the multilayer ceramic
capacitor whose ESR value is low,
the heat generation caused by a heavy current
is low and the increase in the surface
temperature is less than for other capacitors.
This indicates that the multilayer ceramic
capacitor is suitable for a heavycurrent
power smoothing capacitor.
Application to Decoupling Capacitor
In each circuit module or IC, a decoupling
capacitor is set in the power circuit
to secure the stabilized operation and function.
The decoupling capacitor is used to
remove or reduce the noise occurring via
a power line or the noise generated by its
own operation.
In the past, a high-capacitance electrolytic
capacitor and low-capacitance ceramic
capacitor were frequently used in
combination for a decoupling capacitor.
However, in one decoupling capacitor, a
high decoupling effect can be obtained
over a wide-range frequency by using a
Fig. 4: Structure of multilayer ceramic
capacitor
Fig. 5: Comparison of frequency and impedance characteristics in each capacitor
Fig. 6: Comparison of high-frequency current and surface rising temperature in each
capacitor
50 AEI October 2004
Copyright ? 2005 Dempa Publications, Inc.
high-capacitance multilayer ceramic capacitor
with excellent frequency impedance
characteristics.
As shown in Fig.7, the peak values of
waveforms obtained on the output side
are compared for each capacitor when a
peak value of 2V pulse wave, a frequency
of 100kHz, and 1MHz are supplied to the
circuit shown in Fig.7. The effect of noise
absorption is investigated in this case.
In a pulse wave of 100kHz, the peak
value when an aluminum electrolytic capacitor
with a capacitance value of 220µF
is used is 46 mVp-p. However, the peak
value decreases to 28 mVp-p at a capacitance
value of 1/4 (47µF) when a tantalum
electrolytic capacitor is used. When
a multilayer ceramic capacitor is used instead
of the tantalum electrolytic capacitor,
the peak value decreases to the almost
the same level as for the tantalum electrolytic
capacitor at a capacitance value
of 1/10 (22µF).
In other words, by using a multilayer
ceramic capacitor, a pulse absorption effect
equal to or of more than when using
these electrolytic capacitors is obtained
at the 1/10-capacitance value of an aluminum
electrolytic capacitor or the 1/2-
capacitance value of a tantalum electrolytic
capacitor.
Even in a pulse wave of 1MHz, similarly,
pulse absorption characteristics equal
to or of more than these electrolytic capacitors
can be obtained using a multilayer
ceramic capacitor with the capacitance
value that is 1/50 of an aluminum
electrolytic capacitor and 1/10 of a tantalum
electrolytic capacitor.
Fig.8 shows the block diagram of a
40W output class D power amplifier circuit.
Amultilayer ceramic decoupling capacitor
of 10µF is used for decoupling capacitors
C1 and C2 at the Vcc pin of IC.
Two aluminum electrolytic capacitors are
connected in parallel to decoupling capacitors
C3 and C4 in the power input
block on the board.
The power ripple voltage waveforms
when a multilayer ceramic capacitor is
used instead of aluminum electrolytic capacitors
C3 and C4 are shown in Fig.9.
A ripple voltage of 88 mVp-p in an aluminum
electrolytic capacitor becomes 71
mVp-p when two multilayer ceramic capacitors
of 10µF are used instead. By using
the multilayer ceramic capacitors, a
ripple reduction effect equal to or of more
than when using aluminum electrolytic
capacitor can be obtained even at a capacitance
value of 1/10.
51 AEI October 2004
Fig. 7: Comparison of noise absorption characteristic in each capacitor
Fig. 8: Block diagram of class D power amplifier circuit
Fig. 9: Comparison of power ripple voltage waveforms in aluminum electrolytic capacitor
and multilayer ceramic capacitor
Copyright ? 2005 Dempa Publications, Inc.
Application to Smoothing Capacitor
for DC/DC Converter
Fig.10 shows the block diagram of the
PWM DC/DC down-converter used for
notebook computers. Several multilayer
ceramic capacitors of 1 to 47µF are generally
used for decoupling capacitor C1
used for the input side. Several electrolytic
capacitors or multilayer ceramic capacitors
of ten to some hundreds of microfarad
are used for smoothing capacitor C2
on the output side. In the power circuit
that outputs a heavy current, multiple highcapacitance
capacitors are connected in
parallel to reduce a ripple voltage or the
heat generation of a capacitor and improve
the stability of load fluctuations.
Three polymer type aluminum electrolytic
capacitors of 470µF and 4V that
were used for C2 were replaced by three
multilayer ceramic capacitors of 100µF
and 6.3V. Fig.11 shows the output ripple
waveform when an output voltage is
1.35V and when a load current is 20A.
The ripple voltage in the polymer type
aluminum electrolytic capacitor is 36
mVp-p, and the ripple voltage in the multilayer
ceramic capacitor is 26 mVp-p.
Even in this case, by using the multilayer
ceramic capacitor, a ripple voltage reduction
effect equal to or of more than
electrolytic capacitors can be obtained at
an electrostatic capacity value of approximately
1/5.
Summary
As introduced above, the same performance
can be obtained at an electrostatic
capacity value of 1/2 to 1/3 as compared
with the conventional electrolytic
capacitor used when a multilayer ceramic
capacitor is employed as the decoupling
capacitor or smoothing capacitor of a
power circuit.
The multilayer ceramic capacitor is
lower in ESR or ESL value than other
capacitors because of its structure and
has the performance similar to a more
ideal capacitor. Therefore, the multilayer
ceramic capacitor is widely used
in electronic equipment such as the
power circuit or high-frequency circuit
introduced this time as well as general
electronic equipment. In future, Murata
Manufacturing Co., Ltd. will step up efforts
in expanding capacitance value and
in developing more compact multilayer
ceramic capacitors.
About This Article:
The author,Yukio Honda, is the Associate
Manager of the Technical Administration
Department at the Component
Division I of Fukui Murata
Manufacturing Co., Ltd. Fig. 10: Block diagram of PWM DC-DC down-converter
Fig. 11: Comparison of output ripple waveforms in polymer type aluminum electrolytic
capacitor and multilayer ceramic capacitor
52 AEI October 2004
Copyright ? 2005 Dempa Publications, Inc.
In a multilayer ceramic capacitor, a
capacitance of more than 100µF can
be acquired through combined use
of the thin-layer technology in which
the thickness of a dielectric layer approaches
1um, and the multilayer technology
wherein hundreds to 1,000 layers
are exceeded.
As a result, a compact and high-capacitance
multilayer ceramic capacitor
has also been used for a decoupling capacitor,
for which an electrolytic capacitor
has been mainly used until now, or
power smoothing capacitor.
More effective decoupling performance
or power smoothing characteristics is anticipated
based on the excellent frequency
characteristics of a multilayer ceramic capacitor.
The application will be promoted
more and more in the future.
Acquired Capacitance Range
Fig.1 shows various capacitors mainly
used for general electronic equipment according
to the relation between the acquired
capacitance value and rated voltage.
In a capacitance range of less than
1µF, a type 1 (temperature compensating)
ceramic capacitor, a type 2 (high dielectric
constant) ceramic capacitor, and a film
capacitor are put into use.
An aluminum electrolytic capacitor
or tantalum electrolytic capacitor has
been mainly used in the high-capacitance
range exceeding 1µF. In recent years,
with the progress of the high-capacitance
technology in a multilayer ceramic capacitor,
the capacitance value per volume
has been rapidly expanded (Fig.2),
and a capacitance range of more than
100µF can be acquired even in a multilayer
ceramic capacitor.
Fig.3 shows the relation between the
acquired capacitance value and rated voltage
of a high-capacitance multilayer ceramic
capacitor exceeding 1µF for each
chip size. The relation between each chip
size and the maximum acquired capacitance
value indicates that a capacitance
value of up to 1µF can be acquired in 1005
size, that of up to 10µF can be acquired
in 1608 size, and that of up to 100µF can
be acquired in 3225 size. Moreover, the
rated voltage is lined up so that it is provided
up to DC 100V and widely used for
various applications. Judging from the
48 AEI October 2004
High-Capacitance Multilayer
Capacitor Delivers Better Performance
Fig. 1: Relation between capacitance value and rated voltage in each capacitor
Fig. 2: Transition of capacitance value per volume and dielectric thickness
Fig. 3: Range of capacitance value and rated voltage in each size
Copyright ? 2005 Dempa Publications, Inc.
relation of the chip size and the maximum
acquired capacitance value, the development
of a compact and high-capacity multilayer
ceramic capacitor will be promoted
more and more in future by the progress
of technology.
Frequency Characteristics
The structure of a multilayer ceramic
capacitor is shown in Fig.4. In the capacitor,
dielectric ceramics and electrodes
are alternately accumulated for formation.
A metal such as nickel is generally used
for electrode materials. Therefore, the electrode
resistance influencing the equivalent
series resistance (ESR) value or loss
of a capacitor is lower than for an electrolytic
capacitor by a few digits.
Fig.5 shows the comparison of the frequency
impedance characteristics of a
10µF high-capacitance multilayer ceramic
capacitor with those of an aluminum electrolytic
capacitor and tantalum electrolytic
capacitor. For the impedance characteristics
of an ideal capacitor, the impedance
decreases by one digit when a frequency
increases by one digit. As shown in Fig.5,
however, for the impedance characteristics
of an aluminum electrolytic capacitor,
the impedance value becomes constant
at approximately 10? and does not
decrease any longer when a frequency
reaches a few kilohertz or more. In a tantalum
electrolytic capacitor, the impedance
value does not decrease when a frequency
reaches some 10kHz or more. The
impedance value becomes constant at
some hundred milliohms.
In a multilayer ceramic capacitor, an
almost ideal impedance decrease is observed
until a self-resonance frequency
of approximately 1MHz is reached. The
impedance value at that time is a few milliohms.
When a frequency becomes
higher, an impedance value increases due
to the influence of an equivalent serial inductance
(ESL) term.
The value obtained when the impedance
of each capacitor is lowest is equivalent
to an ESR (equivalent serial resistance)
value. The ESR value of a multilayer
ceramic capacitor that uses a metal
lower in a resistance value than for an
electrolytic capacitor as the electrode of
a capacitor is low.
Fig.6 shows the relation between the
current value and capacitor surface temperature
occurring when a sine wave current
with a frequency of 100kHz flows
through each capacitor with a capacitance
value of 100µF. For the multilayer ceramic
capacitor whose ESR value is low,
the heat generation caused by a heavy current
is low and the increase in the surface
temperature is less than for other capacitors.
This indicates that the multilayer ceramic
capacitor is suitable for a heavycurrent
power smoothing capacitor.
Application to Decoupling Capacitor
In each circuit module or IC, a decoupling
capacitor is set in the power circuit
to secure the stabilized operation and function.
The decoupling capacitor is used to
remove or reduce the noise occurring via
a power line or the noise generated by its
own operation.
In the past, a high-capacitance electrolytic
capacitor and low-capacitance ceramic
capacitor were frequently used in
combination for a decoupling capacitor.
However, in one decoupling capacitor, a
high decoupling effect can be obtained
over a wide-range frequency by using a
Fig. 4: Structure of multilayer ceramic
capacitor
Fig. 5: Comparison of frequency and impedance characteristics in each capacitor
Fig. 6: Comparison of high-frequency current and surface rising temperature in each
capacitor
50 AEI October 2004
Copyright ? 2005 Dempa Publications, Inc.
high-capacitance multilayer ceramic capacitor
with excellent frequency impedance
characteristics.
As shown in Fig.7, the peak values of
waveforms obtained on the output side
are compared for each capacitor when a
peak value of 2V pulse wave, a frequency
of 100kHz, and 1MHz are supplied to the
circuit shown in Fig.7. The effect of noise
absorption is investigated in this case.
In a pulse wave of 100kHz, the peak
value when an aluminum electrolytic capacitor
with a capacitance value of 220µF
is used is 46 mVp-p. However, the peak
value decreases to 28 mVp-p at a capacitance
value of 1/4 (47µF) when a tantalum
electrolytic capacitor is used. When
a multilayer ceramic capacitor is used instead
of the tantalum electrolytic capacitor,
the peak value decreases to the almost
the same level as for the tantalum electrolytic
capacitor at a capacitance value
of 1/10 (22µF).
In other words, by using a multilayer
ceramic capacitor, a pulse absorption effect
equal to or of more than when using
these electrolytic capacitors is obtained
at the 1/10-capacitance value of an aluminum
electrolytic capacitor or the 1/2-
capacitance value of a tantalum electrolytic
capacitor.
Even in a pulse wave of 1MHz, similarly,
pulse absorption characteristics equal
to or of more than these electrolytic capacitors
can be obtained using a multilayer
ceramic capacitor with the capacitance
value that is 1/50 of an aluminum
electrolytic capacitor and 1/10 of a tantalum
electrolytic capacitor.
Fig.8 shows the block diagram of a
40W output class D power amplifier circuit.
Amultilayer ceramic decoupling capacitor
of 10µF is used for decoupling capacitors
C1 and C2 at the Vcc pin of IC.
Two aluminum electrolytic capacitors are
connected in parallel to decoupling capacitors
C3 and C4 in the power input
block on the board.
The power ripple voltage waveforms
when a multilayer ceramic capacitor is
used instead of aluminum electrolytic capacitors
C3 and C4 are shown in Fig.9.
A ripple voltage of 88 mVp-p in an aluminum
electrolytic capacitor becomes 71
mVp-p when two multilayer ceramic capacitors
of 10µF are used instead. By using
the multilayer ceramic capacitors, a
ripple reduction effect equal to or of more
than when using aluminum electrolytic
capacitor can be obtained even at a capacitance
value of 1/10.
51 AEI October 2004
Fig. 7: Comparison of noise absorption characteristic in each capacitor
Fig. 8: Block diagram of class D power amplifier circuit
Fig. 9: Comparison of power ripple voltage waveforms in aluminum electrolytic capacitor
and multilayer ceramic capacitor
Copyright ? 2005 Dempa Publications, Inc.
Application to Smoothing Capacitor
for DC/DC Converter
Fig.10 shows the block diagram of the
PWM DC/DC down-converter used for
notebook computers. Several multilayer
ceramic capacitors of 1 to 47µF are generally
used for decoupling capacitor C1
used for the input side. Several electrolytic
capacitors or multilayer ceramic capacitors
of ten to some hundreds of microfarad
are used for smoothing capacitor C2
on the output side. In the power circuit
that outputs a heavy current, multiple highcapacitance
capacitors are connected in
parallel to reduce a ripple voltage or the
heat generation of a capacitor and improve
the stability of load fluctuations.
Three polymer type aluminum electrolytic
capacitors of 470µF and 4V that
were used for C2 were replaced by three
multilayer ceramic capacitors of 100µF
and 6.3V. Fig.11 shows the output ripple
waveform when an output voltage is
1.35V and when a load current is 20A.
The ripple voltage in the polymer type
aluminum electrolytic capacitor is 36
mVp-p, and the ripple voltage in the multilayer
ceramic capacitor is 26 mVp-p.
Even in this case, by using the multilayer
ceramic capacitor, a ripple voltage reduction
effect equal to or of more than
electrolytic capacitors can be obtained at
an electrostatic capacity value of approximately
1/5.
Summary
As introduced above, the same performance
can be obtained at an electrostatic
capacity value of 1/2 to 1/3 as compared
with the conventional electrolytic
capacitor used when a multilayer ceramic
capacitor is employed as the decoupling
capacitor or smoothing capacitor of a
power circuit.
The multilayer ceramic capacitor is
lower in ESR or ESL value than other
capacitors because of its structure and
has the performance similar to a more
ideal capacitor. Therefore, the multilayer
ceramic capacitor is widely used
in electronic equipment such as the
power circuit or high-frequency circuit
introduced this time as well as general
electronic equipment. In future, Murata
Manufacturing Co., Ltd. will step up efforts
in expanding capacitance value and
in developing more compact multilayer
ceramic capacitors.
About This Article:
The author,Yukio Honda, is the Associate
Manager of the Technical Administration
Department at the Component
Division I of Fukui Murata
Manufacturing Co., Ltd. Fig. 10: Block diagram of PWM DC-DC down-converter
Fig. 11: Comparison of output ripple waveforms in polymer type aluminum electrolytic
capacitor and multilayer ceramic capacitor
52 AEI October 2004
Copyright ? 2005 Dempa Publications, Inc.
28. 1.2.1 Capacitor winding technology
In the conventional production process, the capacitors are made by individually rolling the metallized
films or the film/foils into cylindrical rolls and then covering them with an insulating sleeve or
coating.
In the MKT, MKP and MFP type series, our production range includes capacitors with space-saving
flat wound bodies with insulating coatings or in plastic cases, as well as cylindrical wound capacitors.
Flat windings are produced by compressing the cylindrical rolls before they are placed in the
casings, so that the casing form is optimally used.
1.2.1 Capacitor winding technology
In the conventional production process, the capacitors are made by individually rolling the metallized
films or the film/foils into cylindrical rolls and then covering them with an insulating sleeve or
coating.
In the MKT, MKP and MFP type series, our production range includes capacitors with space-saving
flat wound bodies with insulating coatings or in plastic cases, as well as cylindrical wound capacitors.
Flat windings are produced by compressing the cylindrical rolls before they are placed in the
casings, so that the casing form is optimally used.
29. 1.2.2 Stacked-film technology
In stacked-film production technology, large rings of metallized film are wound onto core wheels
(with diameters of up to 60 cm). In this way, the “master capacitors” are produced under well-defined
and constant conditions.
As a result, the capacitor production lots obtained when the rings are sawed apart to produce the
actual stacked-film capacitor bodies are especially homogenous.
The pulse handling capabilities of stacked-film capacitors are of particular advantage. Since each
individual layer acts as a separate capacitor element, any damage to the contacts due to overloading
is restricted to the respective capacitor element and does not affect the entire capacitor, as is
the case for wound capacitors.
1.2.2 Stacked-film technology
In stacked-film production technology, large rings of metallized film are wound onto core wheels
(with diameters of up to 60 cm). In this way, the “master capacitors” are produced under well-defined
and constant conditions.
As a result, the capacitor production lots obtained when the rings are sawed apart to produce the
actual stacked-film capacitor bodies are especially homogenous.
The pulse handling capabilities of stacked-film capacitors are of particular advantage. Since each
individual layer acts as a separate capacitor element, any damage to the contacts due to overloading
is restricted to the respective capacitor element and does not affect the entire capacitor, as is
the case for wound capacitors.
32. Capacitors with metallized plastic film have a decisive advantage over capacitors with metal foil
electrodes: they have self-healing properties.
These self-healing properties permit utilization of the full dielectric strength of the dielectric materials
of metallized film capacitors, whereas metal-foil electrode capacitors must always be designed
with a safety margin to allow for any possible faults in the dielectric.
Metallized types thus have a distinct size advantage, which is particularly apparent with the larger
capacitance ratings.
With metallized-film designs, it is also possible to implement even complicated capacitor arrangements,
e.g. multiple internal series connection to cope with high dc voltages coupled with
high ac load capabilities.
The combination of metal foils, metallized and plain film used in MFP and MFT capacitors gives
an extremely high current carrying capability together with self-healing properties.
1.2.5 Self-healing
The metal coatings, which are vacuum-deposited directly onto the plastic film, have a thickness of
only 20 … 50 nm. If the dielectric breakdown field strength is exceeded locally at weak points, at
pores or impurities in the dielectric, a dielectric breakdown occurs. The energy released by the arc
discharge in the breakdown channel is sufficient to totally evaporate the thin metal coating in the
vicinity of the channel. The rapid expansion of the plasma in the breakdown channel causes it to
cool after a few microseconds, thus quenching the discharge. The insulated region thus resulting
around the former faulty area will cause the capacitor to regain its full operation ability.
Since the absence of any form of pressure in the individual dielectric layers and a good homogeneity
improves the self-healing properties, stacked-film capacitors have better self-healing properties
than wound capacitors.
Note:
At low voltages, anodic oxidation of the metal coatings leads to an electrochemical self-healing
process.
Capacitors with metallized plastic film have a decisive advantage over capacitors with metal foil
electrodes: they have self-healing properties.
These self-healing properties permit utilization of the full dielectric strength of the dielectric materials
of metallized film capacitors, whereas metal-foil electrode capacitors must always be designed
with a safety margin to allow for any possible faults in the dielectric.
Metallized types thus have a distinct size advantage, which is particularly apparent with the larger
capacitance ratings.
With metallized-film designs, it is also possible to implement even complicated capacitor arrangements,
e.g. multiple internal series connection to cope with high dc voltages coupled with
high ac load capabilities.
The combination of metal foils, metallized and plain film used in MFP and MFT capacitors gives
an extremely high current carrying capability together with self-healing properties.
1.2.5 Self-healing
The metal coatings, which are vacuum-deposited directly onto the plastic film, have a thickness of
only 20 … 50 nm. If the dielectric breakdown field strength is exceeded locally at weak points, at
pores or impurities in the dielectric, a dielectric breakdown occurs. The energy released by the arc
discharge in the breakdown channel is sufficient to totally evaporate the thin metal coating in the
vicinity of the channel. The rapid expansion of the plasma in the breakdown channel causes it to
cool after a few microseconds, thus quenching the discharge. The insulated region thus resulting
around the former faulty area will cause the capacitor to regain its full operation ability.
Since the absence of any form of pressure in the individual dielectric layers and a good homogeneity
improves the self-healing properties, stacked-film capacitors have better self-healing properties
than wound capacitors.
Note:
At low voltages, anodic oxidation of the metal coatings leads to an electrochemical self-healing
process.
38. The ability of a capacitor to withstand a continuous (sine-wave) alternating voltage load Vrms or
alternating current Irms is a function of the frequency and is limited by three different factors (refer
to figure 13):
Region : Limit at which corona discharges start to occur, VCD:
Below a certain frequency limit f1 the applied ac voltage Vrms should not exceed the threshold voltage
VCD at which corona discharges (partial discharges) would start to occur with some intensity in
air pockets in the capacitor and thus eventually endanger its dielectric strength. The following relation
must be taken into consideration:
Vrms = VCD i.e. Irms = VCD 2? f C
This voltage limit is determined, above all, by the internal construction of the capacitors (which determines
the field strength at the edges); it also depends, to a lesser extent, on the thickness of the
dielectric. This voltage limit can be raised, in particular, by using internal series connection
designs.
Region : Limit due to thermal power dissipation:
Above the frequency limit f1 the permissible alternating voltage load must be reduced with increasing
frequency in order to keep the power dissipation PE resulting in the capacitor body:
PE = Vrms
2 2? f C tan d
below the power PA which can be dissipated in the form of thermal energy by the surface area A of
the capacitor:
PA = a A T
where: a = heat transfer coefficient.
In order to prevent permanent damage to the capacitor, the steady-state overtemperature T
attained at the hottest part of the capacitor surface in relation to the surrounding atmosphere must
not exceed a certain value.
By equating the power generated and the power that can be dissipated as thermal energy:
PE = PA
the conditions for the maximum permissible alternating voltages and alternating currents in this
region can be deduced as:
This can be simplified by the following close approximation:
The frequency limit f1 is the maximum frequency at which the full permissible ac voltage Vac may
be applied to the capacitor without the maximum permissible power dissipation being exceeded.The ability of a capacitor to withstand a continuous (sine-wave) alternating voltage load Vrms or
alternating current Irms is a function of the frequency and is limited by three different factors (refer
to figure 13):
Region : Limit at which corona discharges start to occur, VCD:
Below a certain frequency limit f1 the applied ac voltage Vrms should not exceed the threshold voltage
VCD at which corona discharges (partial discharges) would start to occur with some intensity in
air pockets in the capacitor and thus eventually endanger its dielectric strength. The following relation
must be taken into consideration:
Vrms = VCD i.e. Irms = VCD 2? f C
This voltage limit is determined, above all, by the internal construction of the capacitors (which determines
the field strength at the edges); it also depends, to a lesser extent, on the thickness of the
dielectric. This voltage limit can be raised, in particular, by using internal series connection
designs.
Region : Limit due to thermal power dissipation:
Above the frequency limit f1 the permissible alternating voltage load must be reduced with increasing
frequency in order to keep the power dissipation PE resulting in the capacitor body:
PE = Vrms
2 2? f C tan d
below the power PA which can be dissipated in the form of thermal energy by the surface area A of
the capacitor:
PA = a A T
where: a = heat transfer coefficient.
In order to prevent permanent damage to the capacitor, the steady-state overtemperature T
attained at the hottest part of the capacitor surface in relation to the surrounding atmosphere must
not exceed a certain value.
By equating the power generated and the power that can be dissipated as thermal energy:
PE = PA
the conditions for the maximum permissible alternating voltages and alternating currents in this
region can be deduced as:
This can be simplified by the following close approximation:
The frequency limit f1 is the maximum frequency at which the full permissible ac voltage Vac may
be applied to the capacitor without the maximum permissible power dissipation being exceeded.
54. High voltage power capacitors KLV
Advanced technology of KLV capacitors is
based on construction of ALL-FILM capacitor
sections, improved electrical and mechanical
connections between sections and
impregnation with environmentally
compatible insulating oil.
Application
KLV capacitors are designed for reactive power
compensation of electrical networks and
industrial plants. When required voltages are
higher then rated voltage of individual capacitor,
units are integrated into banks by means of
series connection. Fusing is provided according
to national requirements.
Owing to high partial discharge inception voltage,
KLV capacitors are suitable for installation in
networks with higher harmonics and transient
voltages. Low temperature-dependent
capacitance change makes them particularly
suitable for filter circuit installations.
Element fuses can extend the service life of a
power capacitors and thus avoid interruptions of
operation. However, the fuse mechanism is only
intact as long as there is a sufficient number of
elements connected in parallel - when the
capacitors grow older, eventually the point of time
will come at which the fuses of the remaining
elements will no longer melt. For this reason is
recommended to measure capacitance every one
or two years. Besides, each capacitor bank
should be monitored by means of an unbalance
protection device or a phase comparison
protection device. External fuses can also be
used when internal fuses can not be used due to
higher rated voltage or smaller rated output of
capacitor.
Pressure switch with terminal cap (on
demand):
Used for protection of capacitor units and banks,
without unbalance protection.
In case of a capacitor failure increased pressure
may occur inside the container which finally might
High voltage power capacitors KLV
Advanced technology of KLV capacitors is
based on construction of ALL-FILM capacitor
sections, improved electrical and mechanical
connections between sections and
impregnation with environmentally
compatible insulating oil.
Application
KLV capacitors are designed for reactive power
compensation of electrical networks and
industrial plants. When required voltages are
higher then rated voltage of individual capacitor,
units are integrated into banks by means of
series connection. Fusing is provided according
to national requirements.
Owing to high partial discharge inception voltage,
KLV capacitors are suitable for installation in
networks with higher harmonics and transient
voltages. Low temperature-dependent
capacitance change makes them particularly
suitable for filter circuit installations.
Element fuses can extend the service life of a
power capacitors and thus avoid interruptions of
operation. However, the fuse mechanism is only
intact as long as there is a sufficient number of
elements connected in parallel - when the
capacitors grow older, eventually the point of time
will come at which the fuses of the remaining
elements will no longer melt. For this reason is
recommended to measure capacitance every one
or two years. Besides, each capacitor bank
should be monitored by means of an unbalance
protection device or a phase comparison
protection device. External fuses can also be
used when internal fuses can not be used due to
higher rated voltage or smaller rated output of
capacitor.
Pressure switch with terminal cap (on
demand):
Used for protection of capacitor units and banks,
without unbalance protection.
In case of a capacitor failure increased pressure
may occur inside the container which finally might
58. Carbon nanotubes and polymers, or carbon aerogels, are practical for supercapacitors. Carbon nanotubes have excellent nanoporosity properties, allowing tiny spaces for the polymer to sit in the tube and act as a dielectric. Polymers have a redox (reduction-oxidation) storage mechanism along with a high surface area. MIT's Laboratory of Electromagnetic and Electronic Systems (LEES) is researching using carbon nanotubes[1].
Supercapacitors are also being made of carbon aerogel. Carbon aerogel is a unique material providing extremely high surface area of about 400-1000 m2/g. Small aerogel supercapacitors are being used as backup batteries in microelectronics, but applications for electric vehicles are expected[2].
The electrodes of aerogel supercapacitors are usually made of non-woven paper made from carbon fibers and coated with organic aerogel, which then undergoes pyrolysis. The paper is a composite material where the carbon fibers provide structural integrity and the aerogel provides the required large surface.
The capacitance of a single cell of an ultracapacitor can be as high as 2.6 kF (see photo at the beginning).Carbon nanotubes and polymers, or carbon aerogels, are practical for supercapacitors. Carbon nanotubes have excellent nanoporosity properties, allowing tiny spaces for the polymer to sit in the tube and act as a dielectric. Polymers have a redox (reduction-oxidation) storage mechanism along with a high surface area. MIT's Laboratory of Electromagnetic and Electronic Systems (LEES) is researching using carbon nanotubes[1].
Supercapacitors are also being made of carbon aerogel. Carbon aerogel is a unique material providing extremely high surface area of about 400-1000 m2/g. Small aerogel supercapacitors are being used as backup batteries in microelectronics, but applications for electric vehicles are expected[2].
The electrodes of aerogel supercapacitors are usually made of non-woven paper made from carbon fibers and coated with organic aerogel, which then undergoes pyrolysis. The paper is a composite material where the carbon fibers provide structural integrity and the aerogel provides the required large surface.
The capacitance of a single cell of an ultracapacitor can be as high as 2.6 kF (see photo at the beginning).
59. Nano World: Carbon Nanotube Capacitors File photo of carbon nanotubesby Charles Q. Choi New York (UPI) Feb 03, 2006 Carbon nanotubes could help release and hold electrical energy, for potential use in everything from microchips to hybrid cars, experts told UPI's Nano World.
The nanotube devices are known as capacitors. While a battery stores compounds known as electrochemicals, a capacitor is made of a pair of electrodes separated by an insulator that each stores an opposite charge. Batteries release energy by reacting electrochemicals together, while capacitors do so when they are hooked into circuits. While capacitors might not be capable of storing as much energy as batteries of the same size, they could be much better at delivering more energy over a short time, explained researcher Gehan Amaratunga, an electronic engineer at Cambridge University in Britain.
Amaratunga and his colleagues have developed nanoscale capacitors made from multi-walled carbon tubes roughly 70 nanometers or billionths of a meter wide. These nanotubes were grown vertically from nickel catalyst dots on niobium films. The scientists went on to cover this nanotube forest and its niobium floor with a silicon-nitride layer and then an aluminum film. The resulting capacitor is made from niobium and aluminum electrodes separated by an insulating silicon-nitride layer and carbon nanotubes.
The nanotubes dramatically boost the amount of surface, and thus electrical charge, that each metal electrode can possess. The potential for smaller and more powerful capacitors might prove crucial in developing microchips with ever denser circuitry, Amaratunga said, which need high power "in the minimum area possible." Developing the kind of nanoscale capacitors needed for such ultra-dense circuitry has until now proven very complicated or unreliable.
Moreover, such nanoscale capacitors might help improve the development of compact and cost effective supercapacitors, which has direct bearing on "electric or hybrid electric vehicles such as the Toyota Prius," Amaratunga said. These supercapacitors could help reduce the amount of battery weight these vehicles carry, thus improving their fuel consumption or performance or both, he explained.
The researchers are currently pursuing supercapacitors for portable electronics "such as PDAs, where the optimization of battery weight and lifetime remains a significant issue," Amaratunga added. He and his colleagues published their findings in the journal Applied Physics Letters.
The nanoscale capacitors might also serve in advanced memory chips, said Manish Chhowalla, a materials scientist at Rutgers University in Piscataway, N.J., who did not participate in this study. He noted that nanocapacitor conductance was high when they stored charge and low when they did not, which could serve as the equivalent of zeroes and ones "that are the basis of any memory device." The advantage nanotube capacitors might have over competing memory storage methods is the fact that they take up most of their space vertically, allowing more of them to be packed together onto a surface.
In the future, Amaratunga hopes to move away from electron beam lithography, their current method of placing the nickel catalyst dots on the niobium films, to other techniques more viable for larger surfaces. He anticipated it would take six to eight years before their nanoscale capacitors are use in products. Their work is sponsored by Samsung, who "will guide the commercialization of the research," Amaratunga said. Nano World: Carbon Nanotube Capacitors File photo of carbon nanotubesby Charles Q. ChoiNew York (UPI) Feb 03, 2006Carbon nanotubes could help release and hold electrical energy, for potential use in everything from microchips to hybrid cars, experts told UPI's Nano World.
The nanotube devices are known as capacitors. While a battery stores compounds known as electrochemicals, a capacitor is made of a pair of electrodes separated by an insulator that each stores an opposite charge. Batteries release energy by reacting electrochemicals together, while capacitors do so when they are hooked into circuits. While capacitors might not be capable of storing as much energy as batteries of the same size, they could be much better at delivering more energy over a short time, explained researcher Gehan Amaratunga, an electronic engineer at Cambridge University in Britain.
Amaratunga and his colleagues have developed nanoscale capacitors made from multi-walled carbon tubes roughly 70 nanometers or billionths of a meter wide. These nanotubes were grown vertically from nickel catalyst dots on niobium films. The scientists went on to cover this nanotube forest and its niobium floor with a silicon-nitride layer and then an aluminum film. The resulting capacitor is made from niobium and aluminum electrodes separated by an insulating silicon-nitride layer and carbon nanotubes.
The nanotubes dramatically boost the amount of surface, and thus electrical charge, that each metal electrode can possess. The potential for smaller and more powerful capacitors might prove crucial in developing microchips with ever denser circuitry, Amaratunga said, which need high power "in the minimum area possible." Developing the kind of nanoscale capacitors needed for such ultra-dense circuitry has until now proven very complicated or unreliable.
Moreover, such nanoscale capacitors might help improve the development of compact and cost effective supercapacitors, which has direct bearing on "electric or hybrid electric vehicles such as the Toyota Prius," Amaratunga said. These supercapacitors could help reduce the amount of battery weight these vehicles carry, thus improving their fuel consumption or performance or both, he explained.
The researchers are currently pursuing supercapacitors for portable electronics "such as PDAs, where the optimization of battery weight and lifetime remains a significant issue," Amaratunga added. He and his colleagues published their findings in the journal Applied Physics Letters.
The nanoscale capacitors might also serve in advanced memory chips, said Manish Chhowalla, a materials scientist at Rutgers University in Piscataway, N.J., who did not participate in this study. He noted that nanocapacitor conductance was high when they stored charge and low when they did not, which could serve as the equivalent of zeroes and ones "that are the basis of any memory device." The advantage nanotube capacitors might have over competing memory storage methods is the fact that they take up most of their space vertically, allowing more of them to be packed together onto a surface.
In the future, Amaratunga hopes to move away from electron beam lithography, their current method of placing the nickel catalyst dots on the niobium films, to other techniques more viable for larger surfaces. He anticipated it would take six to eight years before their nanoscale capacitors are use in products. Their work is sponsored by Samsung, who "will guide the commercialization of the research," Amaratunga said.
