RRAM Device Characterizations and Modelling
349
The physical mechanism of Forming process is similar to SET process. The
intrinsic defect in the fresh samples is usually few. While in the beginning of SET
process, there are still some V O in the resistive switching layer and a remaining defectrich region near the bottom electrode after RESET process. Hence, the Forming
voltage is larger than SET voltage and the conductance after RESET is generally
larger than the conductance of fresh state. Often, the remaining defect-rich region is
referred to as the virtual electrode [26].
Unipolar
The resistive switching mechanism of unipolar Ox-RRAM is similar to the bipolar
type as shown in Fig. 3. The difference is the material storing the dissociated O
2− .
In the unipolar Ox-RRAM, the dissociated O
2− will be absorbed and released from
the easily-reduced oxide clusters which are closely neighbored with the conductive
filament consisting of V O . In more details, there are more than one phase of oxide
co-exists in the resistive layer [27]. One type of oxide phase is oxygen-rich phase.
The oxygen-rich clusters can release O
2− due to the thermal decomposition when
the local temperature reaches a threshold temperature [27]. The released O
2− will
recombine with the V O and rupture the CF. So the device can switches from the
LRS to HRS. During SET process, the generation of V O is the same with bipolar
Ox-RRAM. But the dissociated O
2− will be absorbed by the around oxygen-rich
phase rather than drifting to the top electrode.
Fig. 3 Comparison between resistive switching mechanism of the unipolar and bipolar Ox-RRAM.
For bipolar RESET, the O 2− is released by the O 2− reservoir assisting by electrical field together
with heat. For unipolar RESET, the O 2− is released by Joule heating induced thermal decomposition
of O 2− from the easily-reduced oxide clusters or grains in the capture section region. Reprinted
from [14]
349
The physical mechanism of Forming process is similar to SET process. The
intrinsic defect in the fresh samples is usually few. While in the beginning of SET
process, there are still some V O in the resistive switching layer and a remaining defectrich region near the bottom electrode after RESET process. Hence, the Forming
voltage is larger than SET voltage and the conductance after RESET is generally
larger than the conductance of fresh state. Often, the remaining defect-rich region is
referred to as the virtual electrode [26].
Unipolar
The resistive switching mechanism of unipolar Ox-RRAM is similar to the bipolar
type as shown in Fig. 3. The difference is the material storing the dissociated O
2− .
In the unipolar Ox-RRAM, the dissociated O
2− will be absorbed and released from
the easily-reduced oxide clusters which are closely neighbored with the conductive
filament consisting of V O . In more details, there are more than one phase of oxide
co-exists in the resistive layer [27]. One type of oxide phase is oxygen-rich phase.
The oxygen-rich clusters can release O
2− due to the thermal decomposition when
the local temperature reaches a threshold temperature [27]. The released O
2− will
recombine with the V O and rupture the CF. So the device can switches from the
LRS to HRS. During SET process, the generation of V O is the same with bipolar
Ox-RRAM. But the dissociated O
2− will be absorbed by the around oxygen-rich
phase rather than drifting to the top electrode.
Fig. 3 Comparison between resistive switching mechanism of the unipolar and bipolar Ox-RRAM.
For bipolar RESET, the O 2− is released by the O 2− reservoir assisting by electrical field together
with heat. For unipolar RESET, the O 2− is released by Joule heating induced thermal decomposition
of O 2− from the easily-reduced oxide clusters or grains in the capture section region. Reprinted
from [14]