Switching topological state off and on a step towards topological transistors.
In 2018, FLEET researchers achieved a world first: successfully ‘switching’ a topological material, via application of an electric field.
This success represented the first step in creating a functioning topological transistor – a key goal of FLEET’s Research theme 1.
In a topological insulator’s edge paths, electrons can only travel in one direction, which means there can be no ‘backscattering’, which is what causes electrical resistance in conventional electrical conductors.
Unlike conventional electrical conductors, these topological edge paths can carry electrical current with near-zero dissipation of energy, meaning that topological transistors could burn much less energy than conventional electronics. They could also potentially switch much faster.
Topological materials would form a transistor’s active ‘channel’ component, and would switch between open (0) and closed (1) to accomplish the binary operation used in computing.
The electric field induces a quantum transition from topological insulator to conventional insulator.
To be a viable alternative to current, silicon-based technology (CMOS), topological transistors must:
- operate at room temperature (without the need for expensive supercooling)
- ‘switch’ between conducting (1) and non-conducting (0)
- switch extremely rapidly, by application of an electric field.
While switchable topological insulators have been proposed in theory, this was the first time that experiments proved as material could switch at room temperature, which is crucial for any viable replacement technology.
Theoretical studies in 2021 confirmed that using topological insulators instead of conventional semiconductors to make transistors could reduce the gate voltage by half, and reduce transistor switching energy by a factor of four, ‘defeating’ Boltzman’s tyranny, which puts a lower limit on operating voltage.
The application of negative capacitance (via a ferroelectric material) connecting the topological material to the gate terminal allowed for significantly lower switching voltage.
The resulting device, the NC-TQFET (negative-capacitance topological-quantum field effect transistor) has been patented, and a spin-off company TQFET launched in 2024.
FLEET’s search for a viable room-temperature topological transistor was bold, at the outset of the Centre’s funding. However via combined efforts in materials, experimentation and theory across the Centre, the topological transistor is now a reality.
Topological electronics was added to the IEEE International Roadmap for Devices and Systems (Beyond CMOS chapter) in 2020, with FLEET’s efforts literally putting this technology on the map.
The inclusion of FLEET’s science in the Roadmap will ensure that the industrial R&D leaders in semiconductors are aware of this work, and will be able to consider FLEET’s breakthroughs among the potential solutions for future low-energy electronics, hence fulfilling the Centre’s mission.