|(From top) Researchers at work in NCL, Pune , and a model of the barium titanate molecule
A bug found in your backyard soil may change your experience of computers in the not-so-distant future. A team of chemists at the Pune-based National Chemical Laboratory (NCL) has put to use the metallurgical capabilities of a fungus, otherwise known to destroy more than a hundred plants, to synthesise a material which is much sought after by the global microelectronics industry. The fungus, Fusarium oxysporum, not only produces barium titanate at room temperature and at a much cheaper cost but also retains most of its intrinsic properties at dimensions far smaller than can be achieved by conventional manufacturing processes.
Barium titanate belongs to a class of complex oxides known as ferroelectric materials. These materials use the orientation of their crystal atoms to store information. When an electric current is applied, atoms in these materials will align in a unique fashion which can be reversed only through application of another current. In the microelectronics industry, particularly in computers, this property is of immense value as these materials can store information and make it available as and when required, and hence act as “memory” materials. The global memory chip market is currently worth nearly $45 billion.
Have you ever wondered why your computer takes a minute or more before it can be used after being switched on' The type of memory chips we use in computers, what computer engineers call random access memory (RAM) chips, does play a role here. The present-day computers use DRAM or dynamic RAM as the computer’s main memory. When a computer is switched on, systems and application programs get loaded into the memory chip from the hard drive.
Wouldn’t that be better if the software were in the chip all the time' Yes, but unfortunately DRAM chips are volatile which means that they lose whatever is stored in them as soon as the power goes off.
“Ferroelectric materials like barium titanate are, however, different,” says Pankaj Poddar, an NCL researcher who along with three colleagues authored a paper in the September issue of The Journal of American Chemical Society. “It retains information as long as it has been asked to. Unless it has been instructed to reverse it, it holds on to data.”
To be sure, there are non-volatile memory chips on the market. A good example of this is flash memory cards. These store information as ones and zeros by holding electrons in insulated cells. They can be found in many portable gadgets such as MP3 players and digital cameras. But when it comes to its use in computers, flash memory has an inherent drawback: it cannot be re-written more than a hundred thousand times. On the other hand, DRAM and a ferroelectric memory can be read and re-written more than a million billion times.
FeRAM fits the bill
Ferroelectronic RAM or FeRAM has in a way been the holy grail of semiconductor memory technology. For more than 40 years, the electronics industry has been searching for a memory that is fast, flexible, scalable, low-power and non-volatile and cheap to make.
A good FeRAM fits the bill very well. Apart from being non-volatile, it is faster as it takes only 10 nanoseconds to store information versus 60 nanoseconds by DRAM. More importantly, it needs 85 to 95 per cent less battery power than a flash memory card.
However, FeRAM has a major drawback — materials like barium titanate lose their ferroelectric property when they are thinner than 40 nanometres (one nanometre is one billionth of a metre). This poses a huge challenge, particularly when the industry is geared towards further miniaturisation of things.
“But we seem to have been able to retain this property even in a barium titanate chip whose thickness is four to five nanometres,” claims the NCL scientist. The world over, firms specialising in memory chips are investing millions of dollars in ferroelectric memory products, but are still far away from a real breakthrough.
The NCL work is significant on two counts. First, the researchers have synthesised barium titanate using a commonly found microbe and that too at room temperature. Conventional fabrication methods in the semiconductor industry involve extreme temperatures and high pressure. The scientists fed the Fusarium oxysporum fungi with aqueous solutions of two chemicals, barium acetate and potassium hexafluorotitanate. After 24 hours, they could isolate barium titanate particles of four to five nanometre size from the fungal mycelial (vegetative part of a fungus) mass.
“However, the exact biochemical role played by the fungal proteins is yet to be unravelled,” says Absar Ahmad, who pioneered the fungi and plant extract-based nanosynthesis at NCL and is a co-author of the study. As compared with the production processes currently in use, this is eco-friendly as well as economically viable, the scientists argue.
The NCL researchers have also broken the barrier at which the material ceases to exhibit ferroelectric property. Their experiments using sophisticated equipment that can measure information stored at atomic levels demonstrates that the material retains information at least for tens of minutes.
Saluru Baba Krupanidhi, chairman of the Materials Research Centre at the Bangalore-based Indian Institute of Science, says the NCL work is very significant. Scientists have long been looking for a low-energy, low-temperature production process for making materials like barium titanate, he explains. “The NCL scientists seem to have achieved it.”
According to Ahmad and Poddar, the work might also have vital applications in strategic areas. Barium titanate is also a piezoelectric material (peizoelectricity is the voltage generated by the application of mechanical stress) and hence can be used as highly reliable sensors in guided missiles. “We intend to investigate whether the material will retain its piezoelectric property even at nano dimensions.”