Tantalum is rarely used in elemental form.
Tantalum nitride (TaN) is often used as a resistor material in thin-film
networks for microwave hybrids (on alumina) as well as MMICs (on GaAs), due to
its high resistivity and stability over time and temperature. Tantalum
pentoxide (and other oxides) have been used as capacitor dielectrics in
electrolytic capacitors.
______________________________________________________
Jun 18, 2015 ... Resesarchers believe that graphene
could replace tantalum nitride within two chip generations.
The tantalum-nitride sheathing that is currently
used on copper wires in chips serves two functions. One is to help conduct
electricity and the other is to isolate the copper from the silicon on the
chip. Unlike the outer sheathing used in household copper wires, where the
wrapping prevents the wires from electrocuting us, the tantalum nitride ensures
that copper atoms do not contaminate the silicon transistors.
60% percent
of tantalum used in the U.S. is used in
capacitors.
Tantalum: uses
The
following uses for tantalum are gathered from a
number of sources as well as from anecdotal comments. I'd be delighted to
receive corrections as well as additional referenced uses (please use the feedback
mechanism to add uses).
Tantalum
metal has a number of important uses. It is used to make steels with desirable
properties such as high melting point, high strength, good ductility. These
find use in aircraft and missile manufacture. It is very inert and so useful in
the chemical and nuclear industries to line reactors. Tantalum wires were those
used first for light bulbs (now tungsten is preferred). The metal is immune to
body liquids and the body tolerates the metal well. Therefore, tantalum has
widespread use for surgical use. For instance, it can be used in sutures and as
cranial repair plates. The metal is used in the electronics industry for
capacitors.
The oxide is used to make
special glass with a high index of refraction for camera lenses.
Tantalum is a shiny, silvery metal which is soft when is pure. It
is almost immune to chemical attack at temperatures below 150 C. Tantalum is virtually
resistant to corrosion due to an oxide film on its surface.
Applications
Tantalum finds use in four areas: high-temperature applications,
such as aircraft engines; electrical devices, such as capacitors; sirurgical
impants and handling corrosive chemicals. It is rarely used as an alloying
agent because it tends to make metals brittle. Tantalum resist corrosion and is
almost impervious to chemical attack, for this reason it has been employed in chemical
industry, e.g. for heat exchanger in boilers where strong acids are vaporized.
Tantalum in the environment
Because tantalum oxide is very insoluble, there is almost no
tantalum to be found in natural waters. Few attemps have been made to measure
its level in soils, revealing a range from 0.1 to 3 ppm. Only tiny amounts of
tantalum are taken by plants: the amount in vegetation rarely exceeds 5 ppb.
The chief tantalum ores are tantalite, which also contains iron,
manganese and niobium, and samarskite, which contains seven metals. Another ore
which contains tantalum and niobium is pyrochlore. The main mining areas are
Thailandia, Australia, Congo, Brazil, Portigal and Canada. The demand of
tantalum is about 2300 tonnes a year. No assessment of total reserves of
extractable metal have been reliably calculated.
The primary use of tantalum metal is in making capacitors. A
capacitor is an electrical device similar to a battery. It can be
Tantalum
alloys are used to make artificial joints, such as an artificial hip shaft
(left) and socket.
given an electrical charge, which it then stores
until needed. Capacitors are essential parts of nearly all electrical circuits. Semiconductor circuits, like those used in transistors, require
tiny capacitors the size of grains of rice. Tantalum is one of the best metals
for this purpose. Different kinds of capacitors are made for many different
applications. They are used in military weapons systems, aircraft, space
vehicles, communication systems, computers, and medical applications. For
example, the smallest hearing aids are likely to have a tantalum capacitor.
Tantalum is also used in many different alloys. An alloy is made
by melting and mixing two or more metals. The mixture has properties different
from those of the individual metals. Tantalum alloys are used in laboratory
equipment, weights for very precise balances, fountain and ball point pen
points, and tools that have to operate at high speeds and temperatures.
Another application for tantalum alloys is in medical and dental
applications. The metal has no effect on body tissues. It is used in artificial
hips, knees, and other joints. Pins, screws, staples, and other devices used to
holds bones together are also made of tantalum alloys.
A few weeks ago I worked through the Altium
SMPS design course from FEDEVEL academy and that little project left me with an
unresolved question. Somehow I got the idea in the past few years that tantalum
capacitors are to be avoided, never really knowing why. Yet try to find a
330uF, 6.3V capacitor with ~4mOhm ESR and you’ll find that tantalum is
basically the only option. So I wanted to start a discussion about tantalum
caps with the main questions being:
- When and why to use
tantalum capacitors?
- Why avoid using tantalum
capacitors?
- Alternatives to tantalum
capacitors with pros and cons.
I did some quick research already and here’s
summary of what I’ve found so far
Why
and when to use tantalum capacitors?
Tantalum is used to create small sized
capacitors with ‘large’ capacitance. Compared to other materials the oxide
layer can be quite thin. So for all applications where pcb space is limited
(e.g. mobile phones) they are the to go to type of capacitor when ceramic
doesn’t cut it anymore.
Also tantalum capacitors can be created with
quite small ESR. This is why they are used a lot in (local) switched power
supplies as bulk capacitor. Ceramics have even lower ESR, but in power supply
regulators that might be too low for loop stability.
Why
avoid using tantalum capacitors?
From what I can find these are the main
reasons to avoid tantalum capacitors in your design:
Financial:
Tantalum capacitors are relatively expensive
even when supply and demand are balanced. Not too long ago prices went sky high
due to a shortage in raw materials.
Reliability:
There are numerous reports of tantalum
capacitors spontaneously combusting. I haven’t read into this any
further, but I take it some forum members can elaborate on this.
Moral:
Since some of the major tantalum ore
(columbite-tantalite / coltan) mines are located in conflict zones (e.g.
Democratic Republic of Congo) so one can argue that tantalum is a conflict
mineral. I’m not sure though to what extent that still counts today as there
are major mines elsewhere in the world too.
Tantalum is a heavy metal and as such toxic
and not really well for the environment. I did find a paper by AVX that
discussed ‘green’ tantalum technology though.
Alternatives
to tantalum capacitors and pros and cons?
Niobium
caps
Apart from being mentioned I haven’t been able
to find useful information yet, apart from that there is more Niobium ore
available which should make Niobium caps cheaper. On the other hand Coltan is
also used for mining Niobium so maybe the conflict argument could apply here
too?
(Wet)
Aluminum Electrolytic caps (Elco)
Specific low-ESR Elcos can be used. Larger
values, larger ripple current rating, larger voltage ratings are some benefits.
I must admit though that I realized that I haven’t seen SMT Elcos a lot outside
consumer gear. Did I miss something?
Polymer
(Solid) Aluminum caps
Used as in- or output bypass caps in SMPSs.
Larger values only available in small voltage ratings. I don’t know by how much
these must be derated though. Please tune in if you know more about this kind
of caps.
Monolytic
Ceramic caps
Larger voltage ratings, smaller derating, and
higher ripple current ratings are among its benefits compared to tantalum caps.
Since the ESR is much lower a small external resistance may be needed for loop
stability in SMPS designs.
Sources
Here is some of the info I found. There is a
lot to be found, and you'd have sift to get the info you want too. I included
the year of publishing when available, since a few years in our industry means
lots of changes.
AVX. (n.d.). Comparison of Multilayer Ceramic
and Tantalum Capacitors
AVX. (n.d.). “Green” Environmentally Friendly
Technology For Tantalum And Niobium Oxide Capacitors
Digikey. (n.d.). Tantalum Alternative Solutions by
Panasonic
EETimes. (2001). Tantalum capacitor options weighed
Kemet. (2008). Comparison of Ceramic and
Tantalum Capacitors
NIC Components. (1999). Alternates to surface
mount tantalum electrolytic capacitors
Wikipedia. (n.d.) Coltan
Related
Threads on the EEVblog
Tantalum caps
why we tend to not use electrolytics for
decoupling to gnd?
Output capacitor of a DC/DC converter
Tantalum capacitor options weighed
