Traps identification in silicon nanocrystals memories by low noise technique

Abstract

This work reports the extraction of oxide traps properties of n-metal–oxide–semiconductor field-effect transistors with W × L = 0.5 × 0.1 μm 2 using random telegraph signals (RTS) techniques. RTS study of nc-Si has been performed on thin tunnel oxides from 0.8 to 2.0 nm. RTS signals were two or more levels switching events observed on the drain current of transistors with and without nc-Si. The simple two levels RTS 1 noise was observed on samples without nc-Si. On transistors with nc-Si we distinguish two different RTSs (RTS 2 and RTS 3). RTS signal variations with temperature have shown that there's three slow interfacial traps located at E c — 0.26 eV (trap1), E c — 0.23 eV (trap2) and E c — 0.2 eV (trap3). The spatial localization of traps 1, 2 and 3 from the Si–SiO 2 interface are determined using numerical simulations ( x Trap1 ≈ 0.6 nm, x Trap2 ≈ 0.8 nm and x Trap3 ≈ 0.4 nm). RTS noise observed on these devices is attributed to traps localized precisely at the interface thermal oxide/deposited control oxide. (RTS 1) noise is attributed to trap1 and (RTS 2, RTS 3) to traps 2 and 3. From RTS analysis in frequency domain, we extract the power spectrum density of the drain current noise (PSD). From these PSDs we have measured the cut-off frequencies of a single trap even at very low frequencies (for RTS 1 noise f c = 5 Hz (trap1) and for RTS 2 noise f c1 = 2 Hz (trap2), f c2 = 130 Hz (trap3)). These results are in good agreement with those obtained by analysis in time domain and confirm the localization of each trap from the Si–SiO 2 interface.