Researchers from NTT in Japan have demonstrated what they hope will be that company's contribution to the definition of a new ampere: single electron transfer in silicon, at relatively high speed in a charge-confining trap.
The accurate transfer of electrons in one direction provides a high-accuracy measurement of current flow, which is an important part of the long, ongoing international effort to find a more accurate standard of the ampere.
As readers of The Register will be aware, international efforts to tie down our measurement units to basic physical units have been going on for some time, with the kilogram's silicon globes also key to a better standard.
As NTT writes, “In the new SI units, the value of the elementary charge e, which has so far been determined from measurements, is fixed and the ampere is set from the fixed value. It is therefore desirable to realise the current standard using single-electron transfer because it directly connects e to the ampere”.
The NTT researchers are particularly pleased that they've been able to handle single-electron transfers at frequencies up to 3.5 GHz, since trying to count off enough electrons for an ampere one-at-a-time would take an unfeasibly long time. Achieving the feat at 17 Kelvin is a plus as well, and NTT believes it's going to be able to achieve an error rate below 10 -8, which would also satisfy the gods of international standards.
The company hit the mark by fabricating two transistors with fine gate electrodes on a silicon nanowire. Applying a negative voltage to the gates forms a “single-electron island”, and the clock signal is used to control the release of single electrons from the gates. ®