FAMILIAR friends can nevertheless sometimes surprise people. Such has been the case with a compound used to make the first solid-state batteries some 40 years ago. Researchers have now found that it can also be used to build transistors that are transparent and hence suitable for use in electronic books and head-up displays.
Sodium beta-alumina was discovered in the 19th century when the process of extracting aluminium from its ore, bauxite, was being developed. It is formed of alternating layers of aluminium oxide and sodium ions. In 1967 researchers at the Ford Motor Company discovered that it conducts these ions as though it were a liquid. That spawned the first solid-state batteries.
For two decades or so, the stuff was the darling of battery engineering. Then better ionic conductors and more promising designs emerged, and its popularity waned. Now a team of researchers led by Howard Katz of Johns Hopkins University in Baltimore, Maryland, has discovered that sodium beta-alumina has other interesting electrical properties which make it suitable for building transistors.
Transistors are the workhorses of electronics. They are switches that enable one electric current to control the passage of another. Linked together on the surfaces of silicon chips, they form the logic gates that do the calculations in computers, mobile phones, television sets and other electronic gadgets.
Dr Katz and his colleagues found that, although sodium ions flow readily in between adjacent aluminium-oxide layers of sodium beta-alumina, they cannot pass between them. By applying a small voltage at right-angles to the layers they found they could pull the ions towards the aluminium oxide, clamping them in place and thus controlling when the current flowed—the essence of a transistor. They report the result in the current issue of Nature Materials.
As a bonus that could help commercialise the technology, the technique that the team used to deposit the compound is relatively straightforward and cheap. The researchers worked with sodium beta-alumina in its liquid form, which enabled them to spread it easily onto a surface in precisely the pattern required for a printed circuit. When they heated it to 400°C, it turned into a solid, transparent film.
Dr Katz has now used sodium beta-alumina to build transistors on both glass substrates and flexible, plastic ones. His team thinks its new approach will be particularly suitable for use in portable devices, because it operates at low voltages. If so, an old flame may be rekindled.
Sodium beta-alumina was discovered in the 19th century when the process of extracting aluminium from its ore, bauxite, was being developed. It is formed of alternating layers of aluminium oxide and sodium ions. In 1967 researchers at the Ford Motor Company discovered that it conducts these ions as though it were a liquid. That spawned the first solid-state batteries.
For two decades or so, the stuff was the darling of battery engineering. Then better ionic conductors and more promising designs emerged, and its popularity waned. Now a team of researchers led by Howard Katz of Johns Hopkins University in Baltimore, Maryland, has discovered that sodium beta-alumina has other interesting electrical properties which make it suitable for building transistors.
Transistors are the workhorses of electronics. They are switches that enable one electric current to control the passage of another. Linked together on the surfaces of silicon chips, they form the logic gates that do the calculations in computers, mobile phones, television sets and other electronic gadgets.
Dr Katz and his colleagues found that, although sodium ions flow readily in between adjacent aluminium-oxide layers of sodium beta-alumina, they cannot pass between them. By applying a small voltage at right-angles to the layers they found they could pull the ions towards the aluminium oxide, clamping them in place and thus controlling when the current flowed—the essence of a transistor. They report the result in the current issue of Nature Materials.
As a bonus that could help commercialise the technology, the technique that the team used to deposit the compound is relatively straightforward and cheap. The researchers worked with sodium beta-alumina in its liquid form, which enabled them to spread it easily onto a surface in precisely the pattern required for a printed circuit. When they heated it to 400°C, it turned into a solid, transparent film.
Dr Katz has now used sodium beta-alumina to build transistors on both glass substrates and flexible, plastic ones. His team thinks its new approach will be particularly suitable for use in portable devices, because it operates at low voltages. If so, an old flame may be rekindled.