Biological synaptic function mimicked by memristor:
Spiking time-dependent plasticity (STPD)
Paired-pulse facilitation (PPF)
Excitatory postsynaptic current (EPSC)
Short-term plasticity (STP)
Long term plasticity (LTP)
Physical mechanism of memristor
Conductive filaments (CF)
mainly caused by ion migration and redox inside the material under external electric field
The Resistive switching (RS)
Can be by electrochemical metallization (ECM)
Use metals as top electrode (Ag and Cu)
When a positive voltage is applied to the TE, the active metal is oxidized to cation. This cation diffuses downward, passing through the functional layer driven by the positive field. The ions then reduced to metal at the bottom electrode, forming a CF. Thus the memristor switch to HRS to LRS.
When a negative voltage is applied, the memristor switch from LRS to HRS.
Selecting functional layer to control the formation and rupture of CF
Can be by valence change mechanism (VCM)
Metal oxide as a functional layer (for example), when electric field is applied, oxygen ion and oxygen vacancies (Vos) migrate. During SET process (i.e. switching from HRS to LRS), Vos accumulate toward the BE, resulting in the formation of CF of Vos. During the RESET process, Vos combine with Oxygen ions causing the CF to rupture.
Interface types
Mainly caused by the change of Schottky barrier at functional layer ()/insulator. The change of the barrier is usually accompanied by charge trapping/detrapping or anion migration at the insulating layer near the electrode.
