they are not turned on/off so often. That the new structure can be easily formed in
metal wiring layers is also advantageous for the application.
Although the deposition and dissolution of Cu atoms occur with the smaller gate
bias such as 0.1 V, this does not cause any degradation in the nonvolatility and
reliability of the device. This is because a Cu filament is thick enough to be stable
and a bias application is needed to dissolve a filament.
2.2 Nucleation Controlled Type
Another type of three-terminal atomic switch has been developed based on the
nucleation control of metal clusters. In the gapless-type atomic switches, there are
four elemental processes in their SET process [6]. (1) Oxidation of metal atoms of an
active electrode, (2) Drift of metal cations introduced from an active electrode,
(3) Nucleation of a metal cluster at a counter inert electrode, and (4) filament growth
of the nucleus. When we use sulfide, e.g., Cu 2 S, as an ionic transferring material,
oxidation and reduction of metal atom easily occur with a smaller bias, as shown in
the former sections and chapters, resulting in that the rate limiting process is the drift
of metal cations traveling in an ionic transfer layer. Since metal cation’s drift is an
Fig. 2 Initialization free three-terminal atomic switch formed in a metal wiring layer. (a) Schematic
cross section of the switch, (b) A scanning electron microscopic image of the switch, (c) Change in
drain current (I D ) on a log scale and (d) change in drain (I D ), source (I S ) and gate (I G ) currents while
sweeping the gate bias. (Reproduced with permission from Ref. [5])
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metal wiring layers is also advantageous for the application.
Although the deposition and dissolution of Cu atoms occur with the smaller gate
bias such as 0.1 V, this does not cause any degradation in the nonvolatility and
reliability of the device. This is because a Cu filament is thick enough to be stable
and a bias application is needed to dissolve a filament.
2.2 Nucleation Controlled Type
Another type of three-terminal atomic switch has been developed based on the
nucleation control of metal clusters. In the gapless-type atomic switches, there are
four elemental processes in their SET process [6]. (1) Oxidation of metal atoms of an
active electrode, (2) Drift of metal cations introduced from an active electrode,
(3) Nucleation of a metal cluster at a counter inert electrode, and (4) filament growth
of the nucleus. When we use sulfide, e.g., Cu 2 S, as an ionic transferring material,
oxidation and reduction of metal atom easily occur with a smaller bias, as shown in
the former sections and chapters, resulting in that the rate limiting process is the drift
of metal cations traveling in an ionic transfer layer. Since metal cation’s drift is an
Fig. 2 Initialization free three-terminal atomic switch formed in a metal wiring layer. (a) Schematic
cross section of the switch, (b) A scanning electron microscopic image of the switch, (c) Change in
drain current (I D ) on a log scale and (d) change in drain (I D ), source (I S ) and gate (I G ) currents while
sweeping the gate bias. (Reproduced with permission from Ref. [5])
130
T. Hasegawa et al.