Low Power and Ultrafast Multi-State Switching in nc-Al Induced Al2O3/AlxOy Bilayer Thin Film RRAM Device

Low power and ultrafast multi-state storage resistive switching memory (RRAM) device had been developed based on Al/Al
₂
O
₃
/Al
_x
O
_y
/Al structure. Both of Al
₂
O
₃
and Al nanocrystal (nc-Al) induced Al
_x
O
_y
thin films were deposited by RF sputtering. The nc-Al Al
_x
O
_y
based RRAM device showed typical unipolar switching behavior which was due to conductive filaments (CFs) connected and broke in Al
₂
O
₃
/Al
_x
O
_y
layers. An additional 30 nm Al
₂
O
₃
thin film would deposit on Al
_x
O
_y
film to form bi-layer structure, in which the multi-state switching could be observed by applying different voltage pulses on it. In this study, a 15 V pulse with 600 ps width could trigger RRAM device switch from high resistance state(HRS)to next intermediate resistance state (IRS), the device could finally switch to LRS after continuous pulse simulation. Such switching from HRS to LRS was called “writing” process as data would be stored in RRAM device after this process. A longer but lower amplitude voltage pulse was required to make device switch from LRS to HRS which was called “erasing” process, as data would be eliminated after this process. The multi-state switching was corresponding internal switching between these IRSs during “writing” and “erasing” process. The multi-level resistances might be caused by partially formed CFs in Al
₂
O
₃
/Al
_x
O
_y
layers. The distribution of CFs could be controlled by controlling the shape of pulse voltage to achieve this multi-state storage. This bilayer structured RRAM device had good endurance and retention performances at both room and high temperatures.