  Recent studies on nanoscale field-effect sensors reveal the crucial
importance of the low frequency noise for determining the ultimate detection
limit. In this letter, the 1/f-type noise of Si nanoribbon field-effect sensors
is investigated. We demonstrate that the signal-to-noise ratio can be increased
by almost two orders of magnitude if the nanoribbon is operated in an optimal
gate voltage range. In this case, the additional noise contribution from the
contact regions is minimized, and an accuracy of 0.5% of a pH shift in one Hz
bandwidth can be reached.
