A computer chip can process and store information using two different devices. If these devices could be combined into one or put next to each other, there would be more space on a chip, making it faster and more powerful. Engineers have developed a way that the millions of tiny switches used to process information (transistors) could also store that information as one device.
The method accomplishes this by solving another problem: combining a transistor with higher-performing memory technology than is used in most computers, called ferroelectric RAM. Researchers have been trying for decades to integrate the two but issues happen at the interface between a ferroelectric material and silicon, the semiconductor material that makes up transistors. Instead, ferroelectric RAM operates as a separate unit on-chip, limiting its potential to make computing much more efficient. The new technology uses a semiconductor that has ferroelectric properties. This way, two materials become one material without interface issues.
The result is a so-called ferroelectric semiconductor field-effect transistor, built in the same way as transistors currently used on computer chips. The material, alpha indium selenide, not only has ferroelectric properties but also addresses the issue of a conventional ferroelectric material usually acting as an insulator rather than a semiconductor due to a wide bandgap, which means that electricity cannot pass through and no computing happens. Alpha indium selenide has a much smaller bandgap, making it possible for the material to be a semiconductor without losing ferroelectric properties.
Alpha indium selenide was built into a space on a chip, called a ferroelectric tunneling junction, which engineers could use to enhance a chip's capabilities. In the past, researchers hadn't been able to build a high-performance ferroelectric tunneling junction because its wide bandgap made the material too thick for electrical current to pass through. Since alpha indium selenide has a much smaller bandgap, the material can be just 10 nanometers thick, allowing more current to flow through it.
More current allows a device area to scale down to several nanometers, making chips denser and energy efficient. A thinner material — even down to an atomic layer thick — also means that the electrodes on either side of a tunneling junction can be much smaller, which would be useful for building circuits that mimic networks in the human brain.