Sep 9, 2009
Ambient noise defeats quantization errors
Researchers in the US are making use of ambient noise to overcome quantization errors in a low-resolution, discrete measuring instrument. Typically, noise is a problem when making sensitive measurements, but in this case the random fluctuations are an asset and allow the team to characterize nanometre scale electronics in detail.
There is considerable interest in few electron systems and quasi-1D structures thanks to the rich nature of the change in various properties arising from lower dimensions and confinement.
Recent developments allow fabrication of extremely small-scale devices, but performing capacitance–voltage measurements to determine the number of carriers contributing to conduction in these nanometre scale structures has been a challenge.
The capacitance associated with charged carriers in nanometre scale devices are in the attoFarad (1 aF = 10–18 F) range. The parasitic capacitances in a typical electrical measurement setup are 100 million times larger, in the order of 100 picoFarads (1 pF = 10–10 F).
Ramping up the resolution
The team from Cornell University and the University of Connecticut has made use of ambient noise and the non-linear behaviour of field effect transistors to measure the capacitance associated with small-scale silicon transistors using a low-resolution, commonly available LCR meter. The noise in the environment provides sufficiently large fluctuations in the measuring instrument to enable very high precision through an averaging process.
The large amount of noise eliminates the quantization errors introduced by the discrete nature of the measuring instrument. The optimum level of noise, which would yield the highest precision with the smallest number of measurements is known as stochastic resonance. The non-linear nature of the capacitance–voltage characteristics of field effect transistors allows accurate determination of the parasitic contributions.
The researchers presented their work in Nanotechnology.
About the authors
This work was performed at Cornell University and the University of Connecticut. Ali Gokirmak and Hazer Inaltekin were PhD students at Cornell University and each served as postdoctoral research associates for one year at Cornell University. Sandip Tiwari is Charles N Mellowes Professor of Engineering at Cornell University with interests in the engineering and science of condensed matter and their applications. Ali Gokirmak is currently an assistant professor at the University of Connecticut studying semiconductor devices, electrical and thermoelectric phenomena, and phase-changes of materials at small scales. Hazer Inaltekin is currently a postdoctoral research associate at Princeton University studying wireless and social networks.