Comparison of Multilayer Ceramic and Tantalum Capacitors

TECHNICAL
INFORMATION
COMPARISON OF MULTILAYER CERAMIC
AND TANTALUM CAPACITORS
by Jeffrey Cain, Ph.D.
AVX Corporation
17th Avenue South
Myrtle Beach, South Carolina 29578
[email protected]
Abstract:
Engineers now have a choice between ceramic and
tantalum when it comes to selecting capacitors
with values between 0.1 - 22µF. As the ceramic
material technology continues to advance, more
and more capacitance is realized in the same case
sizes compared to previous years. This paper will
examine what devices are available and the trade
off of using each of the technologies. The goal of
this work is to help in selecting the proper device
(tantalum versus ceramic) for a specific
application.
COMPARISON OF MULTILAYER CERAMIC AND
TANTALUM CAPACITORS
by Jeffrey Cain, Ph.D.
AVX Corporation
17th Avenue South
Myrtle Beach, South Carolina 29578
[email protected]
Although the construction techniques and materials
used to manufacture multilayer ceramic and tantalum
capacitors are completely different, the basic applications still remain the same. Capacitors in the 0.1 - 22µF
range are used mainly for digital circuit decoupling and
filtering. Acting as local supplies of charge, capacitors
assist power supplies in remaining at a constant DC
voltage despite the continuous switching of digital signal
circuitry. Capacitors also function as simple, single pole
filters and can be used in conjunction with other devices
(resistors and inductors) to create higher order filter
circuits.
As much as tantalums and ceramics are both capacitors, they do have many different properties. The case
sizes and capacitance values available will first be studied. The impedance curves, the parasitic inductance
(ESL) and equivalent series resistance (ESR) for each
of the technologies will also be outlined. Then the electrical performance under a variety of conditions, such as
temperature and DC bias, will be examined.
This work will focus on the surface mount versions of
both ceramics and tantalums only, with the knowledge
that the only real difference would be the added inductance form the leads themselves for the thru-hole
versions. The intent is to also limit the comparison
to devices of similar capacitance and size.
Products Available
The following table list the range of devices that
will be looked at in some detail. This list includes the
extended ranges of both the tantalum and ceramic
technologies.
Ceramics
0603 (1608M)
0805 (2012M)
1206 (3216M)
1210 (3225M)
Rated Voltage (V)
10 - 500
Dielectric
BaTiO 2
Capacitance Range
X7R - 0.0001 - 3.3
(µF)
Y5V - 0.022 - 22.0
Polarity
Bi-directional
DC Leakage Current
0.001µA max.
Case Sizes
Table 1
Tantalums
R - 0805 (2012M)
A - 1206 (3216M)
B - 1411 (3528M)
C - 2412 (6026M)
4 - 50
Ta2O 5
0.1 - 100
Polar
0.5 - 30µA Typical
The data shown in Table 1 warrants some comments.
First, one should keep in mind that there is a recommended 50% derating of the voltage for tantalum capacitors. That is a 5V application should use a 10 volt rated
part. Secondly there is a definite trade off in capacitance
and rated voltage for both technologies. On the tantalum side, for example, a C case device rated for 4 volts
has a maximum capacitance of 100µF, while a 50V rated
part has a capacitance of 1µF. A 10V, Y5V ceramic 1206
chip has a maximum capacitance of 10µF, yet a 50V part
has a max. cap of only 0.33µF. The X7R and Y5V
dielectrics were chosen because they are widely available and can achieve the capacitance ranges required.
Lastly, tantalums are polar devices so one must be careful how much reverse voltage gets applied as in a DC
blocking application.
Parasitics
The impedance curve of capacitors can tell a lot about
the performance of the device in an actual circuit. Every
capacitor has parasitic ESL and ESR, just simply
because of the physics involved in manufacturing the
devices. Both technologies have a finite length and
width of conductor in which the conduction currents
flow through, therefore they both have inductance
(ESL). The plates of the ceramic capacitor and the tantalum powder have some resistance (ESR). Impedance
implies real and imaginary parts, and today’s impedance
analyzers (such as an HP4194) measure both magnitude
and phase and from this one can calculate ESL and
ESR. Fig. 1 shows the magnitude of the impedance as
well as ESR for 4.7µF, Y5V, 1206, 16V ceramic and a
4.7µF, 16V, B case tantalum.
100
Impedance & ESR (Ohms)
Introduction
10
TAJB475M016
1
Tantalum ESR
Ceramic Imp.
0.1
0.01
0.001
1E+3
Tant. Imp.
Ceramic ESR
1206YG475M
1E+4
1E+5
1E+6
1E+7
Frequency (Hz)
Fig. 1 - Impedance and ESR curves for 4.7µF tantalum
and ceramic capacitors.
Fig. 1 shows some interesting results. First, one can
tell they are the same capacitance value because the
impedance curves are the same at low frequencies, i.e.
at 1kHz. The ESR of the ceramics is also much lower
over most of the frequency spectrum. Lastly, by looking
at the upper end of the frequency spectrum, the ESL of
the ceramic package is also much lower. This is caused
mainly by the lead frames used in the packaging of surface mount tantalum capacitors. The following table lists
the measured parasitic inductance for a variety of tantalum and ceramic case sizes. It is interesting to note that
capacitance value has almost no effect on the change in
inductance. The governing properties are the path
length and aspect ratio that the current “sees” flowing
through the capacitor.
fairly close to the switching frequency of most power
supplies, while ceramics are typically not specified or
are given for resonant frequency only. The following
table shows the typical ESR at 100kHz and 1MHz for
some comparable ceramic and tantalum capacitors.
AVX
Part Number
TAJA105M016
1206YC105M
TAJA106M010
1206ZG106Z
TAJB226M010
1210ZG226Z
TPSC226M016
1210ZG226Z
'0603
'0805
'1206
'1210
R
A
B
C
Inductance (pH)
Ceramics
850
1050
1250
1020
Tantalum
1600
2200
2250
2800
Table 2
While ESL remains fairly constant with frequency,
ESR is very frequency dependent. Both tantalums and
ceramics have a dissipation factor (DF = ESR x (2␲fc)
that must be met at 120Hz and 1kHz respectively. The
following table lists the required maximum DF that
devices are allowed to meet before being able to ship to
a customer.
Tantalum
C <= 1.0µF
C > 1.0µF
Ceramic, X7R
50V and 100V
25V
16V
10V
Ceramic, Y5V
25V and 50V
26V
10V
DF
4%
6%
Test Frequency
120
120
2.5%
3%
3.5%
5%
1000
1000
1000
1000
5%
7%
10%
1000
1000
1000
Table 4
As this table demonstrates, ceramics typically
do have a much lower ESR, especially at higher
frequencies.
DC Bias Dependency
Ceramic capacitors are made with high K (permittivity) materials which exhibit a change in dielectric
constant with an applied DC voltage. Tantalum capacitors do not change capacitance with applied DC bias.
Since almost all capacitors are operated with a DC
voltage involved, this is a very important feature to
keep in mind when designing a circuit. Fig. 2 shows the
DC bias dependency for Y5V and X7R capacitors up to
rated voltage. This dependency is not really voltage
related, but rather is a phenomena caused by the electric field between the capacitor layers. A good rule of
thumb is a 15 - 20% loss for X7R at rated voltage and
75 - 80% for Y5V, regardless of the rated voltage. A
linear fit in between works quite nicely for a first order
approximation.
120
16V, X7R
100
% Capacitance
Case Size
[email protected] [email protected]
(mΩ)
(mΩ)
A case, 1µF, 16V
5000
1500
16V, 1µF, X7R
2200
25
A case, 10µF, 10V
1600
350
10V, 10µF, Y5V
600
20
B case, 22µF, 10V
1300
1000
10V, 22µF, Y5V
4
3
C case, 22µF, 10V
300
250
low ESR tant.
10V, 22µF, Y5V
4
3
Description
80
60
40
16V, Y5V
20
0
Table 3
0
4
8
12
16
DC Voltage (V)
Fig. 2 - % change capacitance vs. DC bias voltage for
Y5V and X7R ceramic capacitors.
Temperature Dependency
Unfortunately in the real world, most electronic circuits do not operate at 120Hz or 1kHz. Maximum ESR
for tantalum capacitors is specified at 100kHz, as this is
Once again, by their very nature ceramic and tantalum capacitors change capacitance over temperature.
X7R and Y5V EIA are coding sequences that describe
40
% Capacitance
20
Tantalum
0
-20
X7R
-40
Y5V
-60
-80
-100
-60
-40
-20
0
20
40
60
Temperature °C
80
100
120
Fig. 3 - Typical temperature dependency for tantalum
and ceramic capacitors.
Ripple Current Capability
Power supply designers are often concerned about
the ripple current capabilities of capacitors on both the
input and output sides of converters. The biggest concern is the internal temperature rise caused by the I2R
power consumption of the capacitor. Since tantalums are
a polar device, this ripple should always be accompanied
by a DC bias. Since ESR is so dependent on frequency
and temperature, the power ratings listed should be
viewed as rules of thumb and not laws written in stone.
The tantalum capacitors have a published data set for a
10°C rise above the ambient. The experimental set-up
used to arrive at this number was emulated and done for
a series of ceramic capacitor chips. It should be noted
that different mounting techniques can alter the thermal conductivity greatly (see Ref. 1). The following
table lists the empirical data from this experiment.
Case Size
Tantalum
A
B
C
Ceramics
1206
'0805
1206
'0805
Dielectric
Max. power
dissipation (W)
for 10°⌬C
0.08
0.09
0.11
X7R
Y5V
Table 5
0.27
0.24
0.2
0.18
From table 5, the power handling of the ceramics is
typically much better than the tantalums. Keep in mind
that the ESR of ceramics is also typically lower (see
table 4), so more current can be driven through the
capacitor (P=I2R).
Microphonic Effects
Of much less concern, yet still important, especially
in audio applications, is the microphonic or piezoelectric
effect. Barium titinate which is the base ceramic
material for most dielectric systems will exhibit microphonic effects. It is not very difficult to take a Y5V
capacitor and put a DC bias with a small signal 1kHz
sine wave and get the capacitor to “sing”. Tantalum
capacitors exhibit no microphonic effects. The experiment done by AVX involved the opposite phenomena
whereby the part was shaken while under bias and the
resulting generated voltage was measured. This was
done for a series of 1µF devices and the results are
shown in Fig. 4. While this experiment does not give an
empirical number, the resulting relative voltage generation tells the story. This experiment confirms that the
higher the K of the ceramic capacitor, the worse the
microphonic effect becomes.
1000
Output (uV/ustrain)
how the capacitance changes over temperature. X7R
stands for ±15% change from -85°C to +125°C and Y5V
+22 to -82% from -30°C to +85°C. Fig. 3 shows the
change in capacitance for both tantalums and ceramics.
It should be noted that the temperature and DC
bias effects are cumulative and not exclusively
independent.
300
100
Y5V
30
10
X7R
3
1
Tantalum
0.3
0.1
0.03
0.1
0.3
1
3
DC Bias Voltage (V)
10
30
Fig. 4 - Microphonic effect of surface mount capacitors.
Conclusions
There is no simple answer to the question of when
one can replace a tantalum with a ceramic, or visa versa.
The parameters that the capacitor will see during its
lifetime need to be examined carefully. The benefits and
highlights are listed in the table below.
Important Parameter
ESR/Output ripple
Volumetric efficiency
Wide temperature range
Low inductance
DC bias
Microphonic
High frequency filtering
Tantalum
Ceramic
X
X
X
X
X
X
X
Table 6
One cannot just blindly replace one type of capacitor
technology with another and expect equal performance
offer all conditions. General knowledge of what the
circuit will see must be taken into consideration.
References
(1) I. Salisbury, “Thermal management of surface
mounted tantalum capacitors”, AVX Tech. Bulletin,
Nov. 1992.
(2) J. Cain, “Parasitic inductance of multilayer ceramic
capacitors”, AVX Tech. Bulletin, June 1997.
NOTICE: Specifications are subject to change without notice. Contact your nearest AVX Sales Office for the latest specifications. All statements, information and data
given herein are believed to be accurate and reliable, but are presented without guarantee, warranty, or responsibility of any kind, expressed or implied. Statements
or suggestions concerning possible use of our products are made without representation or warranty that any such use is free of patent infringement and are not
recommendations to infringe any patent. The user should not assume that all safety measures are indicated or that other measures may not be required. Specifications
are typical and may not apply to all applications.
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