Memory-State Dependence of Random Telegraph Noise of $ \hbox{Ta}_{2}\hbox{O}_{5}/\hbox{TiO}_{2}$ Stack ReRAM

Memory-state [low-resistance state (
R
_L
) and high-resistance state (
R
_H
)] dependence of random telegraph noise (RTN) of Ta
₂
O
₅
/TiO
₂
resistive random access memory is investigated. The conduction mechanism of both memory states and a limit of resistance controllability are also investigated to clarify the difference in the RTN mechanism of both states. The boundary between the
R
_L
and
R
_H
states was found at 5-20 kΩ , and the conduction mechanism much depended on the memory state. The noise also depended on the memory state. The noise amplitude in the
R
_H
state was larger than that in the
R
_L
state. In the
R
_H
state, a tunnel barrier was generated to cut off a conduction path (filament), and traps inside the tunnel barrier were supposed to increase the noise amplitude. Moreover, the composition of the following degraded the noise distribution in the
R
_H
state: 1) capture and emission of charges with traps and 2) instability of these traps against the bias temperature stress.