Jun 25, 2014
Real-time monitoring of electrons
Originating from the Brownian motion of electrons, thermal noise is a fundamental yet unavoidable type of noise in all electronic devices. Thermal noise was reported first by Johnson and Nyquist in 1928 and their model of thermal noise based on a fluctuation-dissipation theory is still used in a range of fields. Reporting in Nanotechnology, a team from NTT basic research laboratories in Japan examines the model with single-electron resolution using a nanometre-scale dynamic random access memory (DRAM). Here a nanometre-scale transistor slows down electrons going in and out of a tiny capacitor and electrons are counted in real time by a charge sensor.
Noise in transistors is widely investigated to guarantee precise operation in electronic circuits. Three types of noise have been identified: shot, flicker and thermal. Thermal noise originates from the thermal agitation of massive electrons in an electronic device. It has the potential to degrade circuit performance and this problem may become more serious as transistors shrink in alignment with Moore’s law. For that reason, the researchers have employed a DRAM to investigate it.
The real-time monitoring of single-electron motion proves the robustness of the well known thermal-noise model. This includes the occupation probability, the law of equipartition of energy, a detailed balance and the law of kT/C. It also reveals that the individual electron motion follows the Poisson process. This means that while the statistical distribution of the fluctuation of electrons is based on thermal noise, individual electron motion is "microscopically" based on the Poisson process, which is the form shot noise should take.
The real-time monitoring of single-electron motion has already been reported in other papers. However, these demonstrations were carried out at a low temperature and in special conditions where the law of equipartition of energy is not available. This means that the experimental conditions were far from those in currently used electronic devices.
On the other hand, this time, all demonstrations were achieved in circumstances familiar to all readers, i.e. a transistor operated at room temperature. This means that the results can be fully shared for all electronic devices. Additionally, the DRAM promises new logic circuits utilizing single electrons for low power consumption and high functionality.
More information about the research can be found in the journal Nanotechnology 25 275201 (IOPselect article).