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 replacetantalumnitride 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.
The
followingusesfor tantalum are gathered from a
number of sources as well as from anecdotal comments. I'd be delighted to
receive corrections as well as additionalreferenceduses (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.Semiconductorcircuits, 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.
Capacitors About half the tantalum consumed each year is used within the electronics industry, mainly as powder and wire for capacitors. As the market moves to greater miniaturization, the tantalum capacitor is favored in space-sensitive, high-end applications in telecommunications, data storage and implantable medical devices.
Semiconductors Tantalum is a critical component in the manufacture of state-of-the art semiconductors. Using the physical vapor deposition (PVD) process, tantalum is "sputtered" onto semiconductor substrates to form a thin film diffusion barrier to protect the copper interconnects. Tantalum sputtering targets are used in a variety of other products, including magnetic storage media, inkjet printer heads and flat panel displays.
Engine turbine blades The metal's high melting point and resistance to corrosion makes it suitable for alloying applications. Tantalum is used in nickel based superalloys where the principal applications are turbine blades for aircraft engines and land based gas turbines.
Chemical processing equipment Tantalum's high resistance to corrosion and high temperature makes the metal an ideal material of construction for liners in vessels, piping, valves and heat exchangers in the chemical and pharmaceutical industries.
Other applications Tantalum is used in a range of other applications requiring strength, ductility, toughness, corrosion resistance, thermal conductivity and high melting point:
Ballistics
Surgical implants and closures
Cemented carbides for cutting tools
Tantalum compounds for optical applications and sonic acoustic wave filters
The illegal trade of tantalum, tungsten, tin and gold from the Democratic Republic of Congo (DRC) and surrounding countries is fueling conflict in central Africa. Sales of these conflict minerals help fund arms for militias, ultimately leading to human rights abuses. Meanwhile, US companies that use these metals are facing growing pressure to find sources that are conflict-free. An Securities and Exchange Commission rule, scheduled to take effect June 2, would require the vast majority of US companies to disclose whether they use conflict minerals from the region.
Now the SEC rule has come under fire: A US appeals court last week ruled that part of the regulation – a provision requiring companies to state whether their products use conflict minerals – is unconstitutional. Some lawmakers are urging the SEC to move forward with the rest of the disclosure rule, but it's unclear how the commission will proceed, and ongoing litigation adds to the uncertainty about exactly how the conflict minerals rule will take effect.
The good news for companies is that compliance with these new regulations just got easier. In January, the Conflict Free Sourcing Initiative (CFSI) announced the existence of certified conflict-free smelters for all four of the conflict minerals. A key step in the supply chain, smelters turn rocks into purified metals for use in electronics. Tungsten was the last of the minerals to gain a verified smelter, and more smelters are expected in the coming months. As of 3 April, there were nearly 80 conflict-free smelters.
Some big name companies are taking their efforts a step further. Apple has started publicizing which of its suppliers may be sourcing minerals from conflict zones. The first list showed 104 smelters that were not yet verified as safe. The company also has vowed to go completely conflict-free by the end of 2014, meaning that all of its minerals will come from verifiable sources. Intel also recently announced that all of its microprocessors released in 2014 will be conflict-free.
Conflict minerals 101
Tantalum
Tantalum. Photograph: Wikimedia
Tantalum is a crucial ingredient in electronics manufacturing. In fact, half of all mined tantalum goes into electronics, and it is found in almost all electronic equipment, including mobile phones, laptops and hard drives. It is also used on an industrial scale, in jet engines, ships and missiles.
Tantalum can hold the highest electrical charge of any metal, which makes it an ideal component for a device called a capacitor, which stores and releases an electric charge. An average mobile phone only contains about 40mg of tantalum – a relatively insignificant amount, until one considers the hundreds of millions of devices in use.
According to the SEC, central Africa accounts for 15-20% of the world's tantalum supply, although some reports put the figure closer to 50%. The richest deposits of coltan, the naturally-occurring ore that tantalum is extracted from, are found in eastern Congo, where mining is done by hand.
In 2012, tantalum became the first mineral to gain a conflict-free smelter. And, according to the CFSI database, there are currently 26 conflict-free tantalum smelters, located predominantly in China and the US.
For an electronics company looking to clean up its supply chain, tracing its tantalum is a good place to start. Apple, for instance, focused its initial supply chain cleanup efforts on tantalum, and announced in February 2014 that all of its tantalum smelters were validated as conflict-free.
"Tantalum is the one that has the biggest impact because it's in so many electronics," said Jess Kraus, chief executive of Source Intelligence, a company that helps businesses improve the transparency of their suppliers.
Tantalum is also the easiest to trace, because it is used in "very specific circumstances", Kraus said. By comparison, tin is "found in almost everything", from cellphones to toothpaste to pipes.
Tungsten
Tungsten. Photograph: Wikimedia
Tungsten, which is largely derived from wolframite or scheelite, has the highest melting point of any pure metal. Its conductivity, meaning its ability to hold an electric charge, makes it attractive to electronics manufacturers. Along with gold, it is commonly used to make computer chips.
However, only very small amounts of tungsten are used in electronics, which may be the reason that it was the last mineral to acquire a conflict-free smelter. "Tungsten is not as widely used as tin or tantalum or even gold," said Sasha Lezhnev, a senior policy analyst at the Enough Project, a non-profit organization that monitors conflict around the world.
More than 80% of tungsten ore comes from China; by comparison, Africa produces only about 1% of the world's supply. And the DRC's share is even smaller: According to the US Geological Survey, it was only responsible for around 0.5% of the world's supply in 2009.
The first conflict-free tungsten smelter came about largely thanks to Intel, Lezhnev said. Facing an internal deadline to produce a fully conflict-free product by the end of 2013, the company pushed the tungsten industry to look at conflict-free sourcing programs. "It was a pretty heavy negotiation, but they successfully convinced them," Lezhnev said.
Due to anti-trust regulations, the CFSI website will not list a smelter or refiner unless there are at least three validated smelters for a mineral. CFSI has only validated one conflict-free tungsten smelter so far, an Asia-based factory owned by US company Global Tungsten and Powder Corp. As of 1 April, CFSI listed on its website 10 smelters that are either being audited or have agreed to be audited within the next two years. Observers expect at least some of these smelters to be certified within the next couple of months.
Tin
Tin. Photograph: Wikimedia
Tin is extracted from an ore called cassiterite, which is commonly found alongside coltan, the rock that produces tantalum. It is present in virtually all electronics, and roughly half of all tin mined today is used as a solder in circuit boards in products like mobile phones and laptops.
While the DRC is Africa's largest tin producer, it only accounts for some 2.5% of the world's tin supplies. Indonesia is the largest exporter, and the country's Bangka Island is considered the world's tin capital. But illegal mining hasdevastated the island, causing environmental damage and dangerous conditions for miners.
The explosion in demand for devices like smart phones has increased the demand for tin. In 2013, it was the best performing metal on the London Metal Exchange. Unfortunately, this popularity makes regulation difficult: Tin is probably the hardest mineral to trace in a company's supply chain because it is "so ubiquitous", Kraus said.
"It's hard to even tell what it's in," he said. "The average company wouldn't know it's there."
There are currently 11 certified tin smelters, located primarily in South America and Asia. Soon after the US passed legislation requiring companies to report whether they used metals from central Africa, the majority of companies pulled out of the Congo completely. The country's tin production dropped dramatically, from 12,000 tons in 2009 to 2900 tons in 2011.
Gold
Gold mineral. Photograph: Flickr
Illicit profits from the 3T's (tantalum, tungsten and tin) have dropped by 65% since 2010, largely thanks to US legislation and pressure from technology companies. Rebel groups have since turned their attention to gold, which is now the most valuable mineral in the DRC, Lezhnev said. Thousands of unofficial mines operate throughout the country.
One of the main drivers of the illicit gold trade is the mineral's small size, which makes it is easy to smuggle across borders. Around $30,000 worth of gold can fit in a pocket and roughly $700,000 can be carried in a briefcase, according to a 2012 report from The Enough Project. By comparison, it would take 13 big trucks transporting 233 tons of tin ore to command the same value. According to the report, nearly four tons of gold were smuggled across the Congolese border to Uganda, Burundi and Tanzania in the first half of 2012. The illicit stocks were integrated in the local markets and then sold to international buyers.
A lot of the responsibility for gold now lies with the jewelry industry, which consumes about 50% of the world's gold, Lezhnev said. "It's really time for them to step up," he said.
According to Julie Schindall, director of communications and stakeholder engagement at the Electronic Industry Citizenship Coalition, which oversees the CFSI, convincing the jewelry industry to clean up its supply chain is a "long, ongoing conversation".
"We're all aware gold continues to be a problem. It's very much an area we continue to collaborate on," she said.
Lezhnev said that clamping down on the trade in conflict gold requires a two-pronged strategy: praising the companies leading the charge against illegal mining, and sanctioning illicit gold traders.
There are bright spots on the horizon. Of the 82 conflict-free smelters, 42 work with gold. And it's getting harder for unregulated gold producers to hide their wares. Professional services firm Ernst & Young recently discovered that a gold refiner in Dubai was hiding illegally mined gold from the Congo.
"The more that happens", Lezhnev said, "the better system we'll see getting put in place."
In today’s market there is an increasing need for stable voltage in countless applications but especially for the computers and digital equipment that use powerful microprocessors, such as CPU, ASIC and LSI. These processors deal with massive volumes of data and require large scale integration and faster clock speeds which call for more load current and in turn, lower operating voltages. Additionally, the market is seeing current ramp at the start of LSI operations (di/dt) becoming faster and faster.
The components industry is under pressure to provide solutions that manage the risk of unstable power. Various capacitor technologies are employed in voltage regulators such as tantalum capacitors, aluminum capacitors, and for low ESR (equivalent series resistance), polymer capacitors and multi-layer ceramic capacitors (MLCC).
The Unstable Supply of Rare Tantalum Ore
The first technology mentioned, Tantalum capacitors, uses a rare metal (tantalum) as its primary material and because of its scarcity it suffers from cyclical shortages. Our industry has seen such shortages in 1997, 2000, and 2008. To solve this cyclical shortage of material, other types of capacitors found their way into applications which typically used Tantalums, for instance, MLCC’s replaced the smaller capacitance tantalums, larger capacitance tantalums were replaced by aluminum capacitors and, in the low ESR arena, polymer aluminum capacitors are regarded as an excellent substitute. Looking ahead it appears that another shortage is coming due to the instable supply of tantalum ore, according to industry sources. This will inevitably lead to a shortage in supply and an increase in the cost of tantalum capacitors.
Conflict Minerals
"The Wall Street Reform and Consumer Protection Act," which became effective on July 21, 2010 discourages the use of conflict minerals including gold (Au), tantalum (Ta), tungsten (W) and tin (Sn). These metals were produced from the mines in the Eastern region of the Democratic Republic of Congo (DRC) and surrounding countries which are controlled by non-government military groups, or unlawful military factions. Illegal mining profits by local military groups in the Eastern DRC leads to human rights abuses, environmental travesties, and theft from the Country’s citizens. This is another consideration for increased on tantalum capacitors.
Breaking Away from Tantalum Capacitors
Tantalum capacitors have a strong foothold in the North American market, especially when compared to their use throughout the rest of the world. In the past, tantalums were chosen because there was a lack of other options available and the industry’s complacency despite its notable weakness of mandatory voltage derating (in order to prevent failures). With the potential shortage and inevitable price increase; now is the time to contemplate how to break away from the tantalum trap. With an abundant supply of material, Aluminum Capacitors are one viable option; with products that include aluminum polymer capacitors and surface mount aluminum capacitors. Polymer aluminum capacitors use polymer as a solid electrolyte. They boast ESR values as low as 3mohm (@100KHz). This is because polymer offers 10,000 times better conductivity than the electrolyte found in wet aluminum technology, and 1,000 times more than MnO2 used in tantalum technology. Polymer Aluminum Capacitors have available capacitance ranges from a few microfarads to 560uF. In addition, they also offer stable capacitance against frequency and temperature changes.
Surface Mount Aluminum Capacitors cover an extensive CV range from 6.3V to 450V / 0.1uF to 6800uF, and are available for general purpose to low impedance. State-of-the-art SMT aluminum capacitors use high-conductivity electrolyte, achieving 60mohm (100KHz) ESR which surpasses regular tantalums. If we can rethink the entrenched use of tantalum capacitors and view capacitor selection from a new perspective, we will be able to achieve better designs and reduce costs at the same time.
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.
