Chinese researchers have created the world’s smallest transistor gate

Why is it important: Moore’s Law has been on life support for a while, but it’s not dead yet. Chip makers are burning midnight oil to miniaturize transistor designs, and a team of researchers in China has created what is believed to be the smallest ever.

For several decades, scientists and engineers have reduced the size of transistors to such an extent that their smallest elements consisted of only tens of atoms. Since the advent of the first integrated circuits in the 1950s, the rate of progress in transistor miniaturization has followed Moore’s Law, which predicted that the density of active components in integrated circuits would double every two years.

As many of our readers know, progress in this direction has slowed down significantly in recent years. The main reason is that we are rapidly approaching the physical limits of existing materials and the most advanced manufacturing processes we have.

Image credit: Chakrabarti Laboratory

More precisely, we cannot make transistor gates that control the flow of current from source to drain much less than 5 nm due to what is called quantum tunneling what prevents them from doing their job. Materials such as graphene and carbon nanotubes may be vital to downsizing transistors due to their physical properties, but the transition from them to making functional devices will take some time.

in the newspaper released Chinese researchers explain this week that they have created the smallest gate length transistor ever reported. This milestone was made possible by the creative use of graphene and molybdenum disulphide and combining them into a two-step staircase design.

Side transistor structure: The dark blue part is the silicon dioxide base, the brown part is alumina coated with aluminum oxide, the thin light blue stripe is graphene, the yellow-black stripe is molybdenum disulfide, and below it is hafnium dioxide.

On the higher rung you have the source, and on the lower rung you have the sink. Both are made from an alloy of titanium and palladium, separated by a ladder surface that consists of a single sheet of semiconductor material called molybdenum disulfide, which itself rests on a layer of hafnium dioxide that acts as an electrical insulator.

The interior of the higher stage is literally a sandwich of alumina-coated aluminum that sits on top of a sheet of graphene — a single layer of carbon atoms. The aluminum oxide acts as an electrical insulator, except for a small gap in the vertical wall of the upper stage where the graphene sheet contacts the molybdenum disulfide. The entire structure of the stairs rests on a thick layer of silicon dioxide.

The trick to this design is that it uses the edge of the graphene sheet, which means that when the gate is set to the “on” state, it is only 0.34nm wide—essentially the width of the graphene layer itself. Another notable feature of this “sidewall transistor” is its negligible current leakage due to the higher on-state resistance. Manufacturers can use this quality for low power applications. Best of all, this would be relatively easy to do, although many of the prototypes required quite a bit of voltage to drive.

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Tsinghua University researcher Tian-Ling Ren co-authored the study and said it could be “the final knot for Moore’s law.” He also believes that a gate size smaller than 0.34nm is almost impossible.

Of course, the researchers of the new transistor only proved that a functional transistor could be made from materials one atom thick without inventing a new process for precisely positioning the required layers. Reliably building billions of such side transistors is still a distant dream, but it is an important step in this direction and holds out hope for faster, more power-efficient devices in the future.

Meanwhile, Samsung, Intel, and TSMC are hard at work developing universal gate transistors (GAA-FETs) and standardizing interconnects for chip designs.