Characterization of Multistep Electron Charging and Discharging of a Silicon Quantum Dots Floating Gate by Applying Pulsed Gate Biases

Abstract

Electron charging and discharging operations for a silicon quantum dots (Si-QDs) floating gate with discrete charged states were characterized in n-metal–oxide–semiconductor field-effect-transistors (MOSFETs) by applying single-pulsed gate biases Vg with pulse widths ranging from 10 ns to 100 ms. The drain current levels for charged states increase stepwise with Vg pulse width, which indicates multistep electron charging in the Si-QDs floating gate due to quantization energy and electron charging. The gate voltages required to minimize the time for charging and discharging the Si-QDs floating gate are limited by the leakage current through the control oxide, which partially compensates the charging or discharging current through the tunnel oxide in the high-gate-voltage region. The transient variation of the drain current at zero gate bias, after the application of pulsed gate biases for the dot floating gate to be charged, shows that a critical transition from an unstable charged state to a stable one occurs, depending on the pulse height or width. This suggests the redistribution of electrons in the floating gate during the metastable state, which involves a reduction in the effective charging energy and the resultant elimination of the Coulomb blockade.