Extraction of oxide trap properties using temperature dependence of random telegraph signals in submicron metal–oxide–semiconductor field-effect transistors

Abstract

Random telegraph signals (RTS) in the drain voltage of light-doped drain n-metal–oxide–semiconductor field effect transistors with W×L=0.5×0.35 μm2 were investigated in the 300–230 K temperature range. The mean capture and emission times were studied as a function of gate voltage as well as temperature in the RTS. A method was developed where several trap characteristics can be extracted, including the position, barrier energy for capture, enthalpy, and entropy associated with emission of an electron, as well as screened scattering coefficient for carrier mobility as a function of temperature. This article reports on a single trap as an example. The position of the trap in the oxide (Tox=70 Å) was found to be 12 Å and, as expected, independent of temperature. The mean capture and emission times exhibited an increase as the temperature is decreased, following a thermally activated process. Utilizing these observations and the temperature dependence of the drain current, the gate voltage dependence of the trap binding energy, and capture activation energy was evaluated. The capture cross-section prefactor (σ0) was calculated using temperature dependence of capture and emission times. These two independent calculations showed almost two orders of magnitude difference in σ0, which is unrealistic. In order to remedy this, the trap binding energy was resolved into entropy and enthalpy components, which were evaluated as a function of gate voltage using the RTS data. The relative contributions of charge carrier mobility and number fluctuations on RTS amplitude were studied as a function of temperature. The mobility fluctuations were found to dominate over number fluctuations over the whole temperature range, and this dominance was found to be more pronounced at higher temperatures. The scattering coefficient due to screened Coulomb scattering effect was computed from the measured RTS data as a function of channel carrier density.