The evolution of electronic circuits keeps on growing, with the objective of making available more speed in processing, advancing in miniaturization, and making possible a larger storage capacity for hundreds of types of equipment, from computers to cell phones and television sets. One of the paths in this evolution is the use of superconducting materials in the manufacture of these devices, as it is shown by a project prepared by the Glass and Ceramic Group of the Physics and Chemistry Department of the São Paulo State University (Unesp), in the town of Ilha Solteira, in the west of the state. Coordinated by Professor Cláudio Luiz Carvalho, the group produced a printed circuit with superconductor material instead of the copper traces that act to interlink the various components of an electronic board, such as transistors and capacitors, responsible for the functioning of a computer, for example.
Superconductivity is the capacity that certain materials, metal or ceramic, have for conducting electricity at extremely low temperatures without offering resistance or losses in conducting the electric current. “In superconducting material, the electrons move freely, without colliding, in a much more orderly way than in a common copper wire”, explains Carvalho, who has in his group the participation of Raphael Otávio Peruzzi and Rudi Solano, who are studying for a master’s degree,. In copper, for example, which works at room temperature, the collision of electrons causes loss of energy in the form of heat.
The superconducting technology is already used in coils of high performance motors, batteries or energy accumulators, electronic connectors and magnetic resonance equipment. In these cases, wires of superconductor are used, covered in liquid nitrogen, which keeps the temperature low. The expectation is that superconductor materials may also be used commercially for trains to levitate over the rails (by adopting powerful magnetic fields created with superconductor electromagnets), besides replacing electrical cables or systems, preventing the loss of electricity.
The researchers from Unesp developed an electric circuit made up of a ceramic compound that works at the temperature of 80 Kelvin (K), equal to minus 193° Celsius (C). “The greatest challenge for research groups all over the world is to increase the operating temperature of the superconductor materials”, Carvalho says. Commercial superconductor cables currently work at 77 K, or -196°C. In experiments, materials that work at 136K (-137°C) have been reached.
“Our greatest success was to make thin films that can be used in the manufacture of electronic circuits with a technique that was perfected by us”, Carvalho says. “This technique for the deposition of film called dip-coating (a chemical method using solutions) is much cheaper than others used by some industrial concerns, like Molecular Beam Epitaxy, or growth of the molecular layers (a physical method for the deposition of molecules until the film is formed). Here we do the whole process of getting thin semiconductor films at 80K, but we hope shortly to reach 100K (-173°C).” In Japan, thin superconductor films are now being used in the construction of supercomputers much faster than the present-day ones, but there they use much more expensive materials and equipment.
The material developed in Ilha Solteira is a ceramic produced with six chemical elements: Bismuth (Bi), Strontium (Sr), Calcium (Ca), Copper (Cu), Oxygen (O) and Lead (Pb). This compound is called superconductor oxide. Instead of cables or equipment, Carvalho’s team plans to make very thin films with this material and use them as superconductor material in electronic circuits. “We are now on the road to developing a device to be used in a chip.” To advance in the researches, the researchers want to form partnerships with companies that could manufacture these devices in the future.
The work of the researchers from Unesp was presented in April at the congress of the Materials Research Society (MRS), in the city of San Francisco, in the United States, which attracted participants from all over the world. “Many researchers have looked us up, particularly from countries that are investing a lot in superconductor technology, like China and Korea. We have received proposals to visit them and to develop or to teach the technique that we are using”, Carvalho says.
Superconductor devices: preparation and characterization
Regular Line of Research Grants
Cláudio Luiz Carvalho – Unesp
R$ 107,863.26 and US$ 17,775.00 (FAPESP)