A new type of transistor!

Roberto Saracco July 22, 2017 Blog 865 Views

A graphene nanoribbon (GNR) is created by unzipping (opening up) a portion of a carbon nanotube (CNT) (the flat area, shown with pink arrows above it). The GRN switching is controlled by two surrounding parallel CNTs. The magnitudes and relative directions of the control current, ICTRL (blue arrows) in the CNTs determine the rotation direction of the magnetic fields, B (green). The magnetic fields then control the GNR magnetization (based on the recent discovery of negative magnetoresistance), which causes the GNR to switch from resistive (no current) to conductive, resulting in current flow, IGNR (pink arrows) — in other words, causing the GNR to act as a transistor gate. The magnitude of the current flow through the GNR functions as the binary gate output — with binary 1 representing the current flow of the conductive state and binary 0 representing no current (the resistive state). Credit: Joseph S. Friedman et al./Nature Communications

A transistor is a component that is able to make an electron current flow depending on the presence or absence of a signal. Think about a faucet: you open the faucet (the signal) and water flows. You close it and water stops.
Transistors are made of silicon (even though the first one was made in germanium) because silicon is a semiconductor, it may act like a resistance (stopping the flow of electrons) or as a conductor (hence letting the flow of electrons go through).

Since 1947, when it was invented, researchers have created different types of transistors perfecting the use of silicon to make it ever more efficient. This has resulted in a tremendous growth in performance (and decrease in cost) – the Moore’s law. Now we have reached the end of the line and researchers are looking for alternatives.

Researchers at Northwestern University, University of Texas, University of Urbana- Champaign and University of Central Florida have come up with a radically new approach to create a transistor.

They are using 3 carbon nanotubes (CNT) the central one split open (see figure). The two lateral CNT are the ones carrying the signal: its presence generate a magnetic field that makes the central CNT conductive or insulating. Hence it becomes possible to regulate the flow of electrons in the central CNT depending on the signal present in the lateral ones.

The interesting part is that the flow of electrons in the lateral CNT (as in the central one) is facing basically no resistance, hence this transistor would consume very little power (the researchers estimate a 100th of the one needed by a normal transistor) and the speed of switching -based on spintronic- (the time it takes to move from being an insulator to being a conductor) is in the order of THz, that is some 250 times faster than today best commercial transistors.

Clearly the gap between making one transistor and making billions of them squeezed within a single chip is huge. Hence it will take some years before some usable chips will become available and even more before we can replace current silicon transistors with these. Yet, it is good to see there are more ways that can be explored.