Charge Loss Mechanisms of Nitride-Based Charge Trap Flash Memory Devices

Investigation on the origin of the anomalous tail bits on nitrided charge trap flash memory

“…90°C and above, the time to failure data points are fitted well and activation energy, Ea of 1.1456 eV is obtained. This value corroborates well with the typical Ea for NBCTF memory [1][2][3]. However, as shown in Fig.…”

“…This indicates the defects density induced by the extensive repeated cycles charge injections in P/E cycling intensifies the underlying CL mechanism of nitrided NBCTF memory. With the implementation of FN tunneling as charge injection mechanism, extensive P/E cycling will typically result in defects such as bulk oxide traps and charge trapping (CT) interface states [1][2][3][4]. As shown in Fig.…”

“…The silicon nitride layer acts as the designated charge trap layer which is sandwiched between the top silicon oxide layer and tunnel silicon oxide layer. The intrinsic defects in silicon nitride layer which surrounded by oxide layers inherently trap injected charges during P/E operations [1][2][3][4]. The top and tunnel silicon oxide layers provide sufficient protection to prevent charge leakage due to direct tunneling of charges from silicon nitride layer.…”

“…Nevertheless, there are three critical limitations that prevent further technology scaling on FG flash memory, i.e. (1) severe stress induced leakage current (SILC) triggered if the tunnel oxide layer is scaled to less than 8 nm; (2) gate coupling ratio of minimum 0.6 has to be met in order for control gate of FG flash memory to properly exert control to FG and the channel; (3) severe cellto-cell interference [1][2][3][4][5][6][7][8]. As compared to FG flash memory, NBCTF memory enables better downscaling of the tunnel oxide layer while still preserving overall good data retention performance.…”

“…Tunnel oxide nitridation (TON) is one of the approaches applied together with the downscaling of tunnel oxide layer in order to enhance the immunity of NBCTF memory to Fowler-Nordheim (FN) stress induced damages in tunnel oxide layer. By implementing various wet or dry nitridation processes, TON is done by incorporating nitrogen content into the tunnel oxide layer to achieve larger memory window and better hardening towards the damages due to extensive program/erase P/E) cycling stress through FN injection [1][2][3][4][5][6][7][8][9][10]. Nevertheless, TON was also found to result in several critical reliability issues such as Fermi-level defects and mid-gap defects.…”