Quasi‐Solid‐State Single‐Atom Transistors are 10,000 times smaller than conventional silicon transistors

Physicist Professor Thomas Schimmel and his Karlsruhe Institute of Technology (KIT) team have developed a single-atom transistor, the smallest transistor worldwide. This quantum electronics component switches electrical current by controlled repositioning of a single atom, now also in the solid state in a gel electrolyte. The single-atom transistor works at room temperature and consumes very little energy, which opens up entirely new perspectives for information technology.

Quantum electronics element enables switching energies smaller than those of conventional silicon technologies by a factor of 10,000.

They produced two minute metallic contacts. Between them, there is a gap as wide as a single metal atom. “By an electric control pulse, we position a single silver atom into this gap and close the circuit,” Professor Thomas Schimmel explains. “When the silver atom is removed again, the circuit is interrupted.” The world’s smallest transistor switches current through the controlled reversible movement of a single atom. Contrary
to conventional quantum electronics components, the single-atom transistor does not only work at extremely low temperatures near absolute zero, i.e. -273°C, but already at room temperature. This is a big advantage for future applications.

The single-atom transistor is based on an entirely new technical approach. The transistor exclusively consists of metal, no semiconductors are used. This results in extremely low electric voltages and, hence, an extremely low energy consumption. So far, KIT’s singleatom transistor has applied a liquid electrolyte. Now, Thomas Schimmel and his team have designed a transistor that works in a solid electrolyte. The gel electrolyte produced by gelling an aqueous silver electrolyte with pyrogenic silicon dioxide combines the advantages of a solid with the electrochemical properties of a liquid. In this way, both safety and handling of the single-atom transistor are improved.

Advanced Materials – Quasi‐Solid‐State Single‐Atom Transistors

The single‐atom transistor represents a quantum electronic device at room temperature, allowing the switching of an electric current by the controlled and reversible relocation of one single atom within a metallic quantum point contact. So far, the device operates by applying a small voltage to a control electrode or “gate” within the aqueous electrolyte. Here, the operation of the atomic device in the quasi‐solid state is demonstrated. Gelation of pyrogenic silica transforms the electrolyte into the quasi‐solid state, exhibiting the cohesive properties of a solid and the diffusive properties of a liquid, preventing the leakage problem and avoiding the handling of a liquid system. The electrolyte is characterized by cyclic voltammetry, conductivity measurements, and rotation viscometry. Thus, a first demonstration of the single‐atom transistor operating in the quasi‐solid‐state is given. The silver single‐atom and atomic‐scale transistors in the quasi‐solid‐state allow bistable switching between zero and quantized conductance levels, which are integer multiples of the conductance quantum G0 = 2e2/h. Source–drain currents ranging from 1 to 8 µA are applied in these experiments. Any obvious influence of the gelation of the aqueous electrolyte on the electron transport within the quantum point contact is not observed.

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