Passive Electronic Components
Lecture 9
Page 1 of 25
26-May-2013
Capacitors 2
Lecture Plan
1.
2.
3.
4.
Common types of capacitors
Special types of capacitors
Typical applications
Selection guidelines
1. Common types of capacitors. The most commonly used today are MLCC, aluminum,
and tantalum capacitors.
Ceramic capacitors. Single-Layer and Multilayer Ceramic Capacitors (MLCC).
First HF electronic devices were built using mica capacitors. In 1940 a vitreous enamel was developed
in DuPont to replace mica in capacitors. Manufacturing processes for single-layer and multilayer
ceramic capacitors were developed in 1940s in USA. Common ingredients of ceramic dielectrics
include titanium dioxide, barium titanate, and strontium titanate. The exact formulas for the various
ceramics differ from one manufacturer to another.
The EIA standard (Electronic Industries Alliance, USA) classifies the ceramics into four classes (1,
2, 3, 4), and into types within those classes. The lower is the class number, the better are the overall
characteristics, but the larger is the size of the capacitor for a given capacitance. Types within each
class define:

temperature range [C],

temperature coefficient of capacitance (TCC) nominal value [ppm/K],

TCC tolerance [ppm/K].
Class 1 ceramic capacitors include the most temperature stable C0G capacitors (their old
designation is NP0), and temperature compensating capacitors. They are characterized by low content
of barium titanate.
EIA Codes For Temperature Slope of Class 1 Ceramic Capacitors.
Tolerance, ppm/K
Significant figure, ppm/K
Multiplier
at +25…+85C
C
0.0
0
-1
G
±30
B
0.3
1
-10
H
±60
L
0.8
2
-100
J
±120
A
0.9
3
-1000
K
±250
M
1.0
4
+1
L
±500
P
1.5
6
+10
M
±1000
R
2.2
7
+100
N
±2500
S
3.3
8
+1000
T
4.7
V
5,6
U
7.5
For example, C0G has TCC of 0.0±30 ppm/K in +25…+85C temperature range. P3K has TCC
-1500 ±250 ppm/K.
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Lecture 9
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In -55…+25C temperature range the negative tolerance is 1.25…4 times higher than the positive
depending on the "Significant figure" value. For example, C0G is ±30 ppm/K at +25 …+85C, but
-75…+30 ppm/K at -55 …+25C.
The industry commonly uses an "N/P" designation system in spite of its obsolescence because it is
more intuitive. "N" means a negative temperature coefficient, "P" - a positive coefficient.
Manufacturers use the both designation systems in their catalogs.
Some EIA and industry codes for commonly available Class 1 capacitors
Industry code P100 NP0 N030 N075 N150 N220 N330 N470 N750 N1500 N2200
M7G C0G B2G U1G P2G R2G S2H T2H U2J P3K R3L
EIA code
C0G capacitors are characterized by low temperature drift (limited to ±30 ppm/K over most of
their temperature range), insignificant aging effects, low voltage coefficient, almost frequency
independent capacitance, low leakage, and low dissipation factor.
The only problem with C0G capacitors is their size. 47 nF is about the largest through-hole
capacitor, and 27 nF is about the largest chip capacitor. Dielectric absorption is typically mediocre.
Temperature compensating capacitors are available in the range of +1000ppm/K…-5600ppm/K or
P1000…N5600. Tolerance on the temperature slope can vary from ±30 ppm/K for the lower slopes
(N30…N220) up to ±1000 ppm/K for N5600. Above N4200 the properties start to look more like
Class 2 than Class 1.
Both dissipation factor (DF) and dielectric constant  go up as the temperature slope of Class 1
ceramics goes more negative, thanks to the additives. It means that for example N1000 is more sizeefficient than C0G.
Advantages:
 Low and predictable TCC.
 Low dissipation factor (DF).
 Low Voltage Coefficient of Capacitance (VCC).
Shortcomings:
 Large size (low volumetric efficiency).
 Mediocre dielectric absorption.
Applications:
As a rule of thumb, Class 1 ceramics can be used in many common digital and analog electronics
applications including GHz range. The exceptions would be sample-and-hold circuits and integrators,
where mediocre dielectric absorption may be a problem.
Class 2, 3, and 4 ceramic capacitors
Class 2 and higher ceramic capacitors are typically based on ceramics with high content of barium
titanate (Ba2TiO3).
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Lecture 9
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EIA codes for non-temperature-stable ceramic capacitors (Class 2 and Higher)
Capacitance change over the
Low temp. limit, C:
High temp. limit, C:
rated temperature range, %:
X
-55
4
+65
A
±1.0
Y
-30
5
+85
B
±1.5
Z
+10
6
+105
C
±2.2
7
+125
D
±3.3
8
+150
E
±4.7
9
+200
F
±7.5
P
±10
R
±15
S
± 22
T
+22 -33
U
+22 -56
V
+22 -82
X7R, Z5U, and Y5V are the most common types.
For example, X7R is a capacitor that would be usable at -55…+125C and should change its
capacitance no more than ±15% in this temperature range with respect to capacitance value at 25C.
The capacitance of Class 2 and higher capacitors is affected by voltage. So the above temperature
drift limits are valid only if low voltage is applied across capacitor.
Advantages:
 Small size. (Comparable with electrolytic capacitors).
 Lower ESR than in electrolytic capacitors.
Shortcomings:
 Very high Temperature Coefficient of Capacitance (TCC).
 High Voltage Coefficient of Capacitance (VCC). It is different for AC and DC. That is
why Class 2 and higher capacitors are normally characterized at no more than 1V AC or DC.
VCC is more dependent on the ratio of applied voltage to maximum rated voltage than on the
applied voltage itself. Therefore, the using of the highest rated voltage part of the given size is
beneficial.
 High voltage coefficient of dissipation factor. It is different for AC and DC. Dissipation
factor rises at the frequencies above 1 MHz.
 High frequency coefficient of capacitance. Commonly capacitance drops at the
frequencies above 1 MHz.
 Significant aging rate ( becomes lower as times goes by) because the original crystal
structure slowly transforms to another one. It can be reversed by annealing of capacitor for
several hours at +125…+150C. But after the heat treatment the aging process starts all over
again.
 High- ceramic capacitors show significant piezoelectric effect caused by barium
titanate. The higher is  the stronger is this effect. It may cause problems in low-level signals
circuitry making it vulnerable to mechanical shock and vibration. It is the reason to use Class 1
ceramics in analog circuitry.
The table below shows what happens to capacitance when DC voltage is applied to various types of
Class 2 capacitors.
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Lecture 9
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Relative capacitance versus applied DC voltage U
C0G
X7R
Z5U
1.00
1.05
1.20
U = 0.1 U rated
1.00
0.95
0.50
U = 0.5 U rated
1.00
0.70
0.30
U = 1.0 U rated
Applications.
 Value range 0.047…22 F. (In lower value range they are commonly replaced with C0G. For
higher values electrolytic capacitors are used).
 Coupling (DC blocking) and power supply bypassing.
For the best results: (a) use capacitors with the lowest  ; (b) apply a voltage that is significantly lower
that rated voltage).
Multilayer Ceramic Capacitors (MLCC)
The construction of ceramic capacitors has changed dramatically since its invention. Primarily a
common form of ceramic capacitor was a ceramic disk. A metal layer was screened and fired on each
side, and wires were soldered on. This construction is still good for pico- and nanofarad range of highvoltage capacitors. But with the decline of the vacuum tubes, demand for such parts has likewise
declined. Today's electronics requires more capacitance at lower voltage and in a smaller size.
Multilayer Ceramic Capacitor – MLCC matches these requirements and is manufactured now in huge
volumes.
MLCC manufacturing process is based on screen printing of very thin alternating layers of ceramic
dielectric and silver-palladium electrodes using respective inks. (Last time nickel and copper
electrodes were introduced). The resulting “sandwich” is fired to make a finished capacitor. The
dielectric layers may have thickness of 1.5…30 m. The end electrodes that connect the internal
electrodes are formed by dipping of two face sides of the capacitor into respective ink followed by
firing. It is silver ink if the internal electrodes are made of silver-palladium or copper ink if the internal
electrodes are made of copper or nickel. Finally the terminals of the parts are usually nickel plated and
solder-plated.
Leaded MLCC
MLCC chip
The internal electrodes were usually made of silver-palladium. The new tendency is using of base
metals electrodes (BME) made of nickel or copper.
There is the trade-off between metal electrode thickness and electrical performance. Thicker
electrodes ensure lower ESR but the additional thickness also increases the mechanical stresses in
electrode/dielectric interface and decrease volumetric efficiency. Consequently, thicker electrodes not
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Lecture 9
Page 5 of 25
only increase the cost of manufacturing by increasing the consumption of precious metals (silver,
palladium), they also increase the level of internal defects (like cracks and delaminations), resulting in
reduced product yields.
The thinner is the ceramic, the more is capacitance-per-volume or volumetric efficiency (it grows
inversely to a square of ceramic thickness). The limiting factor is a voltage breakdown.
At present, the top parameters of MLCCs are:
 up to 350 ceramic dielectric layers,
 dielectric layer thickness - 1.5m (6.3V rated voltage),
 electrode thickness - 1.5m.
Capacitors manufactured by Murata in 2008-2009 (X5R, 6.3V)
Case Size EIA Dimensions, mm Max. cap., µF
01005
0.01
0.40.2
0201
0.60.3
0.1
0402
1.00.5
2.2
0603
1.60.8
10
0805
2.01.25
22
1206
3.21.6
100
Special MLCCs
Because of wide range of applications MLCCs have diverged into a number of special types:
 Low profile (low height) capacitors for use in extremely thin products like smart cards,
or to be mounted under a RAM IC for power supply bypassing.
 High temperature operation capacitors. (At least +200C).
 High voltage capacitors. (Up to 10 kV for chip capacitors).
 Capacitors intended for gluing to PCB using conductive glue. Commonly they have
silver-palladium or gold terminals).
 Capacitors for microwave applications (lateral field capacitors).
 Low ESR capacitors (reverse-geometry MLCCs). Forming the terminal electrodes
along the long dimension of the device widens and shortens the current path between
terminations, thus reducing inductance and resistance.

Chip capacitor arrays comprise 2 or 4 capacitors and contribute in reduction of
mounting cost of circuit assembly. 4-capacitors array may be as small as 2.01.251.0
mm.
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Lecture 9
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4-capacitors arrays: ceramic multilayer (left) and film (right)

The X2Y Circuit Architecture (Syfer Technology Ltd.) is a patented technology. It is
characterized by presence of additional ground electrodes between the regular electrodes
and works both as an a single X capacitor (line to line decoupler) and as two Y capacitors
(line to ground filters) simultaneously. An application can use the X capacitor and the two
Y capacitors together or separately in a circuit. The needs of the circuit designer determine
the attachment or non-attachment of the appropriate corresponding ground terminations.
Advantages:
Applications:









Replaces 2 or 3 capacitors with one device
Matched capacitance line to ground on both lines
Low inductance due to cancellation effect
Differential and common mode attenuation
Reduces board area required for filtering
Effects of temperature variation eliminated
Effect of voltage variation eliminated
Effect of ageing equal on both lines
High current capability

Balanced lines
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Lecture 9
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


Twisted pairs
Broadband input/output filtering
EMI Suppression
Capacitors constructed in X2Y Circuit Architecture have extremely low internal inductance readings.
This minimal inductance characteristic is the result of the mutual cancellation of the opposing
magnetic fields within the architecture's physical layers of grounds and electrodes.

[Z] Chip (AVX Corporation). It is discrete impedance-matching series
resistor/capacitor chip of 0603 size. The chip is used for line termination applications to
achieve maximum signal integrity by eliminating reflections and reducing DC power
consumption.
While resistor alone is still the prevalent method for matching impedance, the biggest problem with
this method is that when the signal line is high, DC current is drawn continuously. If a capacitor is
placed in a series with the resistor, the capacitor acts as a DC voltage/current block, allowing only
certain AC signals to pass to ground. More precise resistor values are necessary to minimize
reflections and reduce noise.
Sizes are 0603, 0805. Array 06034 is available. Capacitance values are 33, 47, 68, 100 and 150pF
with a tolerance of ±20%, and the resistor values are 22, 33, 47, 51, 100 and 150 Ohms with a
tolerance of ±10%. The DC rated voltage is 25V.
Aluminum capacitors.
1900 The capacitor using aluminum oxide as a dielectric material was revealed by Wheatstone and
Duff Durrentet. However, it was not used practically.
1908 Aluminum electrolytic capacitor using electrolytes was developed in General Electric
(USA).
Aluminum capacitors may have wet or solid electrolyte.
Wet electrolyte aluminum capacitors.
Aluminum electrolytic capacitor consists of:
 anode electrode (anode aluminum foil),
 cathode electrode (cathode aluminum foil plus electrolyte),
 dielectric - aluminum oxide layer formed on the anode foil surface that electrically
isolates the anode,
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Lecture 9
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 electrolytic paper that mechanically separates the anode foil from the cathode foil but
does not prevent the ions in the electrolyte from moving between the foils.
A very thin oxide layer formed by electrolytic oxidation (formation) of anode foil offers superior
dielectric constant and has rectifying properties. The thickness of the grown oxide film is nearly
proportional to the applied voltage (approximately 1.0…1.4 nm/V). When in contact with electrolyte,
the oxide layer possesses an excellent forward direction insulation property. Together with large
effective surface area attained by anode foil etching, a high capacitance in small sized capacitor
becomes available. Maximal capacitance of aluminum capacitors with wet electrolyte is 1 Farad.
By etching the surface of aluminum foil, the effective area of the foil as compared to the initial area
can be enlarged 80…100 times for low voltage capacitors and 30…40 times for middle and high
voltage capacitors.
Since the oxide layer has rectifying properties, a capacitor has polarity. If both the anode and
cathode foils have an oxide layer, the capacitor would be bipolar (non-polar).
A 0.05…0.11 mm thick anode foil and a 0.02…0.05 mm thick cathode foil are facing each other
and are interleaved with a paper and wound into a cylindrical shape. This is called a "capacitor
element." At this stage, it has configuration of a capacitor when the paper and the aluminum oxide
layer are dielectrics, however, the unit has negligible capacitance. But when this capacitor element is
impregnated with liquid electrolyte the electrolyte being electrically connected with cathode foil gets
in touch with oxide dielectric layer. A capacitor attains a high capacitance value after that. Electrolyte
is functioning as a cathode. The basic characteristics required from an electrolyte are:
 high electrical conductivity,
 forming property (healing of any flaws in the dielectric oxide of the anode foil),
 chemical stability with the anode and cathode foils, sealing materials, etc.,
 superior impregnation characteristics,
 low vapor pressure.
The standard capacitance tolerance is 20% (M); however, capacitors with a capacitance tolerance of
10% (K) are also manufactured for special usage. The capacitance of aluminum electrolytic capacitors
changes with temperature and frequency. The standard test conditions are 120Hz AC voltage and
+20C ambient temperature.
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Lecture 9
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Solid electrolyte aluminum capacitors.
Type of capacitor
Wet electrolytic
Solid electrolytic
Solid polymer electrolytic
Conductivity of wet and solid electrolytes
Type of electrolyte
Conductivity,
mS/cm
Electrolytic solution
3
Solid MnO2
30
Organic semiconductor (TCNQ complex salt)
300
Polymerized organic semiconductor
3,000
Resistivity,
mm
3,300
330
33
3.3
For comparison: resistivity of the best polymerized organic semiconductor (3.3 mm) is 2500 higher
than resistivity of so called "highly resistive metal alloy" nichrome (0.0013 mm).
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Construction of Vishay OS-CON capacitor
The principal advantage of solid aluminum capacitor when compared with wet one is very low ESR. It
permits for example filtering in a DC-DC converter with a fewer number of capacitors. Another
advantage is its safety (ignition free, open circuit failure mode).
Tantalum capacitors.
1930 Wet Foil Tantalum Capacitor was manufactured by Fansteel Metallurgical Corporation.
1955 A solid tantalum capacitor was developed in Bell Telephone Laboratories (USA).
1956 Sprague Electric started first-to-market solid tantalum capacitor based on its own patent.
Foil, Wet Slug and Solid Tantalum Capacitors.
Tantalum electrolytic capacitors are a step forward from aluminum capacitors. They come in a
number of types with different advantages, but in general, they have smaller size, lower leakage, lower
dissipation factor, lower ESR, more stable capacitance over temperature, and good service life.
The first tantalum capacitors were manufactured from tantalum foil with a sulfuric acid electrolyte.
Their construction resembles construction of aluminum capacitors. Foil tantalum capacitors are
manufactured for use at up to 300V voltage and up to 125C temperature. They are made in both
industrial and military styles but their usage is mostly military.
But the foil anode is a poor use of an expensive metal. Most of the modern tantalum capacitors are
"slug" capacitors. Tantalum powder is sintered into a porous yet strong slug together with a tantalum
wire. It constitutes the anode of the capacitor. The many small particles produce a very large surface
area. A layer of tantalum pentoxide (Ta2O5 with   27) is grown over the slug for the dielectric. In
one version of the capacitor, the electrolyte is gelled sulfuric acid. This is called a wet-slug capacitor.
It must be well sealed. Wet-slug tantalums are the capacitor of choice for some applications, especially
at very high temperatures (up to 200 °C). They are available with up to 125 V rated voltage.
Tantalum wet slug capacitor (see picture below) consists of:
 anode electrode (slug sintered from tantalum powder),
 cathode electrode (tantalum case plus gel electrolyte),
 dielectric - tantalum oxide layer formed on the anode electrode surface that electrically
isolates the anode,
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Lecture 9
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The vast majority of modern tantalum capacitors are "dry-slug" or "solid" capacitors. They consist
of:



anode electrode (slug sintered from tantalum powder),
cathode electrode (MnO2 + graphite + silver paint),
dielectric - tantalum oxide Ta2O5 layer formed on the anode electrode surface that
electrically isolates the anode,
A layer of manganese dioxide (MnO2) is layered over tantalum pentoxide Ta2O5 followed by a layer
of colloidal graphite and a layer of silver paint. Manganese dioxide MnO2 layer is formed by pyrolysis
of manganese nitrate Mn(NO3)2 into manganese dioxide. Porous anode "slug" with oxidized surface is
dipped into an aqueous solution of manganese nitrate and after soaking is baked in an oven at
approximately 250°C to produce a MnO2 coat. The simplified chemical equation is
Mn(NO3)2  MnO2 + 2NO 2
The graphite layer between manganese dioxide and external silver coating is used to prevent the
silver layer coming into direct contact with the manganese dioxide. If this occurs a chemical reaction
would take place
Ag + 2MnO2  AgO + Mn2O3
The silver would be oxidized to high resistivity silver oxide, and the manganese dioxide reduced to
manganese (III) oxide, which has a high resistivity too.
With no liquid involved, solid tantalum capacitor can be sealed with just an epoxy dip, although the
better ones may have a molded body like in the picture below.
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Tantalum powder is characterized by “CV parameter” that indicates the product of capacitance and
rated voltage that is provided by 1 g of tantalum powder. It is measured in [FV/g]. CV of modern
powders approaches to 100,000. The powder is mixed with a suitable binder/lubricant to ensure that
the particles will adhere to each other when pressed to form the anode. The powder is then compressed
under high pressure around a Tantalum wire to make a Tantalum "slug". This is followed by sintering
at high temperature (typically 1500°C-2000°C) under vacuum. This causes the individual particles to
join together to form a sponge-like structure. This structure is of high mechanical strength and density,
but is also highly porous giving a large internal surface area. The next stage is the production of the
dielectric layer of tantalum pentoxide. This is produced by the electrochemical process of anodization.
The slugs are dipped into a very weak solution of acid, for example phosphoric acid, at an elevated
temperature, for example 85°C, and the voltage and current are controlled to form the pentoxide layer.
The dielectric thickness is controlled by the voltage applied during the formation process. Initially the
power supply is kept at a constant current until the required formation voltage has been reached.
The thickness of the oxide layer depends on the formation voltage, which is typically 3-4 times
higher than the rated voltage of the future capacitor. The oxide growth rate is 1.710-9 m/V.
Suppose that the oxide for 25V capacitor has to be built. Its thickness will be 1.710-9 m/V × 25 V ×
4 = 1.710-7 m. The electric field strength in this capacitor will be 25 V / 1.710-7 m ≈ 15 107 V/m.
Tantalum pentoxide is remarkable dielectric. That makes it possible to construct capacitors with small
dielectric thickness and therefore high capacity. However, the metal-metal oxide interface is
rectifying. That is, in one direction it is a good insulator, and in the other direction it is a conductor.
This is why tantalum capacitors are polar. Non-polar capacitor may be made by opposite (back-toback) series connection of to polar capacitors. Tantalum capacitors are available to several hundred µF
in voltage ratings to about 100V and to several thousand µF at low voltage (6…10V). Therefore their
maximum capacitance is significantly lower than in aluminum capacitors.
Effective area. Consider for example a 10F 25V tantalum electrolytic capacitor. Let us calculate
oxide film thickness:
d  NUv  4  25  1.7  10 9  0.2  10 6 m.
Here N – formation ratio (N = 4); U = 25 V rated voltage; v = 1.710-9 m/V (Ti2O5 growth rate).
Electrode surface area A may be evaluated supposing that  = 27:
10  10 6  0.2  10 6
A

 0.0084 m 2  8.4  10 3 mm 2 .
12
 0
8.85  10  27
Cd
 
10F 25V conformal coated 595D Vishay tantalum capacitor has 7.13.22.5 (mm) dimensions. His
external surface area is approximately
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27.1  3.2  2.5  3.2  7.1  2.5  97mm2
That is almost 100 times less than the surface area of its porous anode.
The Ta2O5 layer is prone to defects, and the key to the solid tantalum capacitor's reliability is that the
MnO2 provides self-healing phenomenon. If a flaw in the Ta2O5 layer develops, the leakage will cause
localized heating in the MnO2 and convert it at 450°C to much less conductive Mn2O3 sealing off the
flaw. The important condition of the self-healing is a current limiting. If the current reaches
approximately 1A the temperature goes higher and at 500°C amorphous Ta2O5 dielectric turns into
conductive crystalline form that results in further current increase. Finally a tantalum anode may be
ignited. It burns very fast consuming oxygen that was released as a result of MnO2 decomposition.
The dominant failure mode in this case is “short-circuit”.
Maximal rated voltage in solid tantalum capacitors usually does not exceed 50V because the
tantalum particle size limits the Ta2O5 thickness that can be grown. Maximal temperature rating is
commonly 85…125C.
A rarely mentioned characteristic of solid tantalums is their rapid decline in leakage current. When
both aluminum and tantalum electrolytic capacitors are powered up, their leakage current starts high,
but declines over time. For aluminums, the leakage takes minutes to decline to a stable value. For
tantalums, this occurs in seconds.
Even though "dry-slug" tantalums are not wet-chemistry devices, they are still polarized. But
sometimes the failure of tantalum capacitors installed backwards may occur after more than a year of
circuit use.
One of the ways to decrease ESR of Ta capacitors is use of multi-anode construction (parallel
connection of several pellets in the same package).
Conductive polymer in Ta capacitors. Tantalum resistivity is 13cm. MnO2 resistivity is
approximately 2cm or 5 orders of magnitude more! Therefore MnO2 resistivity is the main
part of ESR. Some years ago MnO2 was replaced by almost 100 times more conductive
substance – conductive polymer. It possesses self-curing property too (decomposes at 280300°C in the locality of dielectric breakdown). The shortcomings of these capacitors when
compared with MnO2 devices are lower maximal working temperature (105°C versus 125°C)
and higher leakage current (0.1CV A versus 0.01CV A).
Niobium and niobium oxide (NbO) capacitors (new products). They are very similar to Ta capacitor
but have less weight, lower risk of ignition (NbO), and are expected to be cheaper. They are intended
to compete with ceramic and Ta capacitors in low voltage (no more than 16V) range.
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Film capacitors.
Various polymer films are used as dielectric in the film capacitors: polyester, polypropylene,
polycarbonate, polyphenylene sulfide, teflon. Film thickness may be as low as 0.9-1.2 m.
Polyester (mylar) capacitors are very popular, because they are inexpensive. Even though most of
their characteristics are very good, capacitance varies drastically with temperature about as badly as in
aluminum electrolytic capacitors.
Polypropylene capacitors also have a very low dissipation factor and a good stability but lower
operating temperature (up to +100°C). They are ideal for AC applications, high current and pulse
applications.
Polycarbonate capacitors have a higher temperature range up to +125°C, low dissipation factor and a
very low change of capacitance with temperature. Commonly they are used as precision capacitors.
Polyphenylene sulphide (PPS) capacitors have a higher temperature range up to +150°C, low
dissipation factor and a very low change of capacitance with temperature and presently being offered
as replacement for polycarbonate capacitors.
Teflon capacitors have very low dielectric absorption, high insulation resistance, low dissipation
factor, high temperature capability. But they are expensive. Commonly they are used as precision
capacitors.
Film capacitors are subdivided into: (a) metallized, (b) foil (see picture below).
The electrodes in a foil (non-metallized) design are separate sheets of metal foil wound with
interlayer sheets of dielectric film material. These foil electrodes extend alternately out of each
end of the capacitor roll beyond the dielectric. This provides a mass of metallic material to
which leads are attached by welding or soldering. Their disadvantage is short circuit failure
mode. So they should not be used in across the line applications.
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In the metallized type of construction the foil electrodes are replaced with a thin layer of
99% pure aluminum vapor-deposited directly onto the dielectric film. It greatly reduces the
physical size of the capacitor. Provisions are made, by means of masking, to provide each
dielectric with a margin. The two sheets of metallized dielectric are positioned properly
relative to a right and left margin and wound into a roll. Since the dielectric material itself is
present at each end of the wound capacitor along with the metal electrode material, direct
attachment of the leads is not done. The end terminations of the metallized unit are
accomplished by application of a fine molten metal spray. The spray makes contact with the
electrode material resulting in the plate contact. The lead wires attached to this metal spray.
The metallized capacitor offers a distinct advantage over the non-metallized unit: self-healing
feature. It results from the extreme thinness of the metallized electrode material. Whenever a
flaw or weak spot in the dielectric results in a short condition, the dissipated heat vaporizes
away the small pattern of the electrode film around the point of the short. As a result of the
vaporization, the short condition is removed and the capacitor is again operational. This
phenomenon is known as a "clearing" or self-healing process (see picture below).





Advantages of a metallized capacitor in comparison with non-metallized capacitor:
The self-healing feature.
The volumetric efficiency is higher.
Weight savings is in direct proportion to the volumetric efficiency.
The cost in the higher capacitance ratings (above 0.1 F) is less.
Failure mode is open circuit.




Disadvantages of a metallized capacitor in comparison with non-metallized capacitor:
The dissipation factor is higher.
The insulation resistance is lower.
The maximum current limitation is lower.
The maximum AC voltage-frequency capability is less.
Passive Electronic Components
Lecture 9
Page 16 of 25
Properties of film capacitors versus X7R and Z5U ceramic capacitors
Commonly upper rated temperature in film capacitors does not exceed 100°C. But in polyester,
polycarbonate film capacitor it is +125°C, and in polyphenylene sulfide film capacitor it may reach
+150°C.
Electric double-layer capacitor (EDLC).
EDLCs fill gap between aluminum electrolytic capacitors and galvanic batteries. They are capable of
several hundred thousands charge – discharge cycles and can be combined in power modules by series
and parallel connections. The components available on the market have a capacitance in 0.01 F…2700
F range, an energy density of 4.9Wh/kg, and a power density of 4.5kW/kg at 2.5V voltage rating.
Possibility of carbon activation is 2000 m2/g. “Dielectric” thickness is 2…5 nm. Within the group of
carbon-based EDLCs, two concepts can be distinguished:
 aqueous systems with low ESR (1.2 cm at 300 K for 30 % sulfuric acid) and a
maximum cell voltage of about 1.2 V,
 organic systems with relatively high ESR (>40 cm at 300 K) and a maximum voltage
of about 2.5 V. Surge voltage should not exceed 2.7V. Operation temperature should not exceed
+65C.
EDSL capacitance depends on two parameters: Co and K. Co is a basic capacitance which is
independent of the voltage while K is coefficient of linear dependence on the voltage:
C  C 0  KU ;
q  C 0  KU U  C 0U  KU 2 ;
i (t )  C 0  2 K U
 dU ;
dt
2
4

U
E (U )   C 0  K U 
.
3

 2
EDLC sometimes referred by trade names “Supercapacitor”, Nippon Electric Company (NEC) and
“Ultracapacitor” Pinnacle Research Institute (PRI).
Passive Electronic Components
Lecture 9
Page 17 of 25
Manufacturing of EDLC
Examples of EDLC:
 EPCOS B49300 UltraCap. Capacitance - 2700F. Voltage rating - 2.3V. Stored energy - 9522J.
Maximal current - 200A. Weight - 650g. Volume - 0.59 liter.
 Seiko Instruments Inc. Chip-type 3.2 x 2.5 x 0.9 mm. Capacity: 14mF (30 times more electric
capacity compared with a similar sized tantalum capacitor). Charge voltage: 2.6V.
Application: backup for memory, clock function and power management ICs for mobilephones and most other portable electronic devices.
Passive Electronic Components
Lecture 9
Page 18 of 25
3. Typical applications of capacitors
BLOCKING: A capacitor is used to block or prevent DC voltage from circuit output. To
block the DC voltage, the capacitor is placed in series with the load.
The major characteristics for the capacitor are insulation resistance, ESR, and voltage rating.
COUPLING: A coupling capacitor is used to pass only the AC signal from one circuit stage to
another. The capacitor is connected in series between the stages just like in blocking application.
The major characteristics are insulation resistance, ESR, and voltage rating.
BYPASS (DECOUPLING): A bypass capacitor is used to keep the AC portion of an input
signal from reaching a load. The capacitor is placed in parallel with the load to produce a low
impedance path across the load.
The impedance of the capacitor should be 10% of the input impedance of the load.
The main characteristics for the capacitor are insulation resistance and ESR.
TIMING: A capacitor is used to store a charge until a specific amount of time has elapsed.
The major capacitor characteristics are insulation resistance/leakage current, capacitance
stability, ESR and dielectric absorption.
SAMPLE AND HOLD: The capacitor is used to store a charge until a sample is taken. The major
capacitor characteristics are similar to a timing application.
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Lecture 9
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FILTERING: A filter capacitor is used to smooth the DC pulses after rectification. The
capacitors store charge and deliver it to the load when the rectified or pulsating DC voltage
decreases below the peak of the DC voltage signal.
The major capacitor characteristics are capacitance, ESR, and ripple current rating.
ENERGY STORAGE: Capacitors in energy storage applications are used to deliver a high
energy, short duration pulse of energy.
Major capacitor characteristics in this application are: ESR, pulse rating and voltage rating.
EMI SUPPRESSION. Capacitors in EMI Suppression are used to suppress noise pulses that
could damage the circuit elements. EMI filters are commonly capacitors or capacitor/resistor
networks mounted across the input of a device. Mains capacitors connected between two phases, or
between a phase and neutral must comply with the X capacitor requirements of EN 60384-14
standard. Capacitors connected between the primary circuit and protective earth must comply with the
Y capacitor requirements of EN 60384-14.
Passive Electronic Components
Lecture 9
Page 20 of 25
ARC SUPPRESSION (SNUBBER). A capacitor/resistor network is used to suppress arcs
across relay or switch contacts to prevent their damage.
POWER FACTOR CORRECTION. (Power Factor is the ratio of the active power to the apparent
power). Capacitors are used to bring the phase angle of the circuit back to unity. Failure to do so will
result in a penalty charged by the power companies:
P.F . 
W - Active Power, VA - Apparent Power
W
.
V A
EDLC capacitor applications
All-weather quick start applications
- The current car battery is geared up to meet peak power needs during engine startup even in coldest
weather conditions that impair battery performance. EDLC can supply the seconds-long peak power
unaffected by the weather and permit the battery to be downsized and its useful life extended.
- The current catalytic converter in cars sends untreated exhaust gas into the environment for a few
minutes until it is warmed up and begins functioning. EDLC can quickly pre-heat the catalytic
converter and enable it to function immediately.
Load-leveling and Uninterruptible Power Systems (UPS)
- Because the EDLC has much less energy storage capability, it is not a viable substitute for the
battery in Uninterruptible Power Systems as a long-term power source. However, as a short-term
support for Uninterruptible Power Systems, its rapid response capability means that it can act as a
temporary bridge until an alternative power source kicks in.
- Moreover, the EDLC in the Uninterruptible Power System serves a load -leveling function by
absorbing power surges and spikes and then releasing clean quality power essential for precision hightech equipments.
No-maintenance applications
- Many buoys in sea lanes emit light during night-time using the energy captured from the sun and
stored in the battery. But, the battery needs replacing every couple years, and the servicing of these
widely scattered buoys is an expensive undertaking. The light buoys can be made practically
maintenance-free if EDLC are used instead of batteries to store solar energy.
- Construction sites and road hazards need to be warned of by lighted signs and markers at night-time.
By using a solar panel and EDLC in the same housing, maintenance-free signs and markers can be
produced. These can be quickly set up in field conditions whenever needed without going through
expensive and time-consuming wiring process.
Peak pulse power applications
- Unlike analog equipment that draws a steady current, a digital wireless communications device loads
the battery with short, heavy current spike during its transmit mode. If an EDLC is added to the
system, then it can take over the task of providing the intermittent pulse power while the battery
Passive Electronic Components
Lecture 9
Page 21 of 25
functions only as a supplier of steady current. Users benefit from longer talk-time between charges
and from the extension of battery-life.
Quick charge applications
- EDLC can be charged in seconds whereas batteries require hours of charging time. Wireless power
tools with an EDLC can be charged just before use without waiting time. Moving toys such as
miniature racing cars are also applications that can benefit from quick charge properties of the EDLC.
Memory back-up applications
- Already widely used in consumer electronics products, small-size EDLC protect user data and clock
information from being lost during short-period power outages or, in case of portable devices, during
replacement of batteries. For this use, the EDLC is better than the battery because it is cheaper and
requires no replacing during the lifetime of the application device.
Automotive applications and Electric Vehicles
- The use of EDLC for generative braking can greatly improve the fuel efficiency of cars under stopand-go urban driving conditions. Only EDLC have both storage capacitance and high current handling
capability to capture and store large amount of electrical energy generated by braking within a short
time and to release it again for re-acceleration. The generative braking has the potential to be one of
the biggest applications for large-size EDLC in the medium term.
- EDLC can enhance the performance and competitiveness of an electric vehicle. It permits faster
acceleration; extends the range by generative braking; and extends battery life by freeing it from
stressful high power tasks.
Though some applications of EDLC such as memory back-up applications are already in widespread
use, most applications described above are just in the beginning phase of being adopted. Moreover,
EDLC are friendly to environment, help conserve energy, and enhance the performance and portability
of consumer devices.
4. Selection guidelines
There are following factors that have to be taken into consideration when selecting a capacitor:
1) Capacitance and capacitance tolerance.
2) Capacitance change versus temperature.
3) Capacitance change versus DC bias.
4) Rated voltage.
5) Acceptability of short circuit condition.
6) Acceptability of acoustic noise.
Typical Characteristics of Different Types of Capacitors
Characteristics
MLCC
C0G
1pF –
0.01F
MLCC
X7R
1pF –
2.2F
MLCC
Z5U
1000pF
- 27F
Polystyrene
film
100pF –
0.03F
Min. tolerance, %
Standard tolerance, %
0.5
5
5
10
20
+80 -20
0.5
5
Rated voltage range, V
50 200
-55…
50 200
-55…
50 100
+10…
Capacitance range
Temperature range, C
Al
Ta
0.5F
– 1F
0.1F –
1000F
Doublelayer
5F –
3600F
5
20
+30 -10
100-600
20
+100 10
3-500
6-125
2.3
-55…
-40…
-55…
-30…
Passive Electronic Components
Lecture 9
Page 22 of 25
D.F. at 1 kHz, %
D.A., %
Frequancy response
9 – best
2 – poorest
Polarity
+200
+125
+85
+70
+105
(wet)
+125
(solid)
+150
(solid)
+175
(wet)
0.1
0.6
9
2.5
2.5
8
3.0
NA
8
0.1
0.05
6
8
NA
2
8-24
NA
5
NP
NP
NP
NP
P
P
+70
P
Passive Electronic Components
Lecture 9
Page 23 of 25
Applications
UHF applications
Precision analog circuits
Power line blocking and filtering
High temperature applications
High energy storage
Types of capacitor
(in descending order of performance)
MLCC C0G
Film, MLCC C0G
Ta, MLCC Z5U, Al + MLCC;
MLCC, Ta
Double-layer, Al, Ta
Capacitors' cost versus capacitance
-Impedance comparison between MLCC and electrolytic capacitors
Passive Electronic Components
Lecture 9
Page 24 of 25
Performance comparison between MLCC and low ESR electrolytic capacitors
Lower ESR of the MLCC structure allows to employ devices with smaller capacitance ratings than the
tantalum (or aluminum) alternative:
Tantalum capacitor
nom. value, µF
1
2.2
4.7
10
22
47
100
220
Nom. value of possible
MLCC alternative, µF
0.1 to 0.47
0.22 to 1
0.47 to 2.2
1 to 4.7
2.2 to 10
4.7 to 22
10 to 47
22 to 100
Capacitor Technology CV Diagram
(Source – AVX Technical Information ”Tantalum and niobium technology roadmap”)
Passive Electronic Components
Lecture 9
Page 25 of 25