Scientists at the Forschungszentrum Jülich have developed a new type of transistor from a germanium-tin (A New Germanium-Tin Transistor developed as an Alternative to Silicon) alloy that has many advantages over conventional materials. Charge carriers can pass through the device more quickly than in silicon or germanium, allowing for lower operating voltages. The transistor thus appears to be a promising candidate for future low-power, high-performance chips, and perhaps also for the development of future quantum computers.
Over the past 70 years, the number of transistors on a chip has doubled approximately every two years – according to Moore’s Law, which still holds true today. The circuits have become a bit smaller, but the end of this development seems to be in sight.
“We have now reached a stage where the structures are only 2 to 3 nanometers in height. This is about the diameter of 10 atoms, which brings us to the limit of what is possible. It doesn’t get much smaller than that,” says Qing-Tai Zhao from the Peter Grünberg Institute (PGI-9) at the Forschungszentrum Jülich.
For some time, researchers have been looking for a substitute for silicon, which is the main material used in the semiconductor industry. The professor explains: “The idea is to find something with better electronics that can be used to do the same thing with a larger structure. The research focused in part on germanium, which has been used in the early days of computers. Electrons can travel faster in germanium than in silicon, at least in theory.
However, Qing-Tai Zhao and his colleagues have gone one step further. To improve the electronic properties even further, they introduced tin atoms into the germanium crystal lattice. This method was developed several years ago at the Peter Grünberg Institute (PGI-9) of the Forschungszentrum Jülich.
“The germanium-tin system we tested overcomes the weaknesses of silicon technology,” says Qing-Tai Zhao. In experiments, the germanium–tin transistor exhibits an electron mobility that is 2.5 times higher than a comparable transistor made of pure germanium.
Another advantage of the new material alloy is that it is compatible with the existing CMOS process for chip fabrication. Germanium and tin belong to the same head of the periodic table as silicon. Germanium-tin transistors can therefore be installed directly on silicon chips with existing production lines.
High power for the computer of the future
Besides classical digital computers, quantum computers can also benefit from germanium-tin transistors. For some time, efforts have been made to connect parts of the control electronics directly to the quantum chip, which operates in a quantum computer at temperatures close to absolute zero. Analysis shows that germanium-tin transistors will perform better under these conditions than silicon ones.
Qing-Tai Zhao says, “The challenge is to find a semiconductor that can still switch quickly at low voltages and high temperatures.” For silicon, this turning point drops below 50 Kelvin. Then, transistors need a high voltage and therefore a high power, which eventually leads to the failure of the soft quantum bits due to heating.
“Germanium-tin works best at these temperatures and measures up to 12 Kelvin, and it is expected that the material will be used at even lower temperatures,” says Qing-Tai Zhao. Qing-Tai Zhao says.
In addition, germanium-tin transistors are the next step for on-chip optical data transmission. Using light signals to transmit information has become the standard in many data networks because it is faster and more powerful than transmitting data through electrical conductors. In the field of micro- and nanoelectronics, however, data is often transferred electronically.
Colleagues in Jülich work Dr. Dan Buca has previously developed a germanium-tin laser that opens up the possibility of transferring data directly to silicon chips. Germanium-tin transistors, together with these lasers, offer a promising solution for the monolithic integration of nanoelectronics and photonics on a single chip.
Source: Forschungszentrum Jülich