Characterization of scaled MANOS nonvolatile semiconductor memory (NVSM) devices

We have modeled and characterized scaled Metal–Al2O3–Nitride–Oxide–Silicon (MANOS) nonvolatile semiconductor memory (NVSM) devices. The MANOS NVSM transistors are fabricated with a high-K (KA = 9) blocking insulator of ALD deposited Al2O3 (8 nm), a LPCVD silicon nitride film (8 nm) for charge-storage, and a thermally grown tunneling oxide (2.2 nm). A low voltage program (+8 V, 30 μs) and erase (−8 V, 100 ms) provides an initial memory window of 2.7 V and a 1.4 V window at 10 years for an extracted nitride trap density of 6 × 1018 traps/cm3 eV. The devices show excellent endurance with no memory window degradation to 106 write/erase cycles. We have developed a pulse response model of write/erase operations for SONOS-type NVSMs. In this model, we consider the major charge transport mechanisms are band-to-band tunneling and/or trap-assisted tunneling. Electron injection from the inversion layer is treated as the dominant carrier injection for the write operation, while hole injection from the substrate and electron injection from the gate electrode are employed in the erase operation. Meanwhile, electron back tunneling is needed to explain the erase slope of the MANOS devices at low erase voltage operation. Using a numerical method, the pulse response of the threshold voltages is simulated in good agreement with experimental data. In addition, we apply this model to advanced commercial TANOS devices.