ink-jet printed film has a highly crystalline nature. Finally, 80-nm-thick Ag was
deposited on the Ag-PEO film as the top electrode, as shown in Fig. 10c. The
cross-section of the fabricated device is illustrated schematically in Fig. 10e.
The fabricated Ag/Ag-PEO/Pt device exhibited bipolar resistive switching characteristics under bias sweeping. Resistive switching could be repeated for more than
100 consecutive sweep cycles. The on and off resistances were of the order of 1 kΩ
and 100 MΩ, respectively, showing a high on/off resistance ratio of ~10
5 . Good
retention characteristics were also observed under atmospheric conditions.
The stability of the switching behavior was examined by bending the PEN
substrate [29]. To ascertain the bending amount, the bending radius was estimated
by a circular arc with a radius r, as illustrated in the inset of Fig. 11a. A smaller
bending radius implies a stronger bending of the substrate. Variations in the on/off
resistances and the turn-on/turn-off voltages are shown in Fig. 11a and b, respectively. In comparison with the flat substrate, there is no significant change in on and
on and off resistance states under substrate bending. The retention properties of the
device were also tested under substrate bending conditions. By keeping a certain
bending radius, a constant mechanical stress was applied to the device and sweeping
of the bias voltage was repeated up to 100 cycles. As observed in Fig. 11c, the on and
off states were very stable and reproducible. The on/off resistance ratio remained at
10
5 under bending. The switching characteristics were also examined with respect to
bending cycles, as shown in Fig. 11d. The device exhibited very stable on and off
resistance states. Due to high mechanical flexibility of the PEO film, the device
exhibited very stable switching behavior without any deterioration. This confirms
that neither the transport of Ag
+ ions nor the redox reactions at the electrode
interfaces are affected by bending the substrate. These results indicate that
SPE-based atomic switches have the potential to be developed into flexible switch/
memory devices.
6 Summary
In this chapter, we described the fabrication, characterization, and various functions
of SPE-based atomic switches. Similar to atomic switches based on inorganic solid
electrolytes, SPE-based atomic switches exhibit not only bi-stable resistive
switching but also quantized conductance. This is achieved by optimizing the device
structure, the fabrication method, and the measurement conditions. It is significant
that the high ionic conductivity of SPE enables us to directly observe filament
growth behaviors even in micrometer-scaled devices. Thus, we could investigate
how the filament growth processes are determined by kinetic factors such as the
redox reaction rates at interfaces, electric field strength, and ion mobility and
reduction sites in the polymer matrix. By combining with first-principles DFT
simulations, it was revealed that the observed quantized conductance originates
from the existence of a tunneling gap and the atomic rearrangement at an atomic
point contact. Furthermore, we succeeded in fabricating devices on a plastic
156
T. Tsuruoka et al.
deposited on the Ag-PEO film as the top electrode, as shown in Fig. 10c. The
cross-section of the fabricated device is illustrated schematically in Fig. 10e.
The fabricated Ag/Ag-PEO/Pt device exhibited bipolar resistive switching characteristics under bias sweeping. Resistive switching could be repeated for more than
100 consecutive sweep cycles. The on and off resistances were of the order of 1 kΩ
and 100 MΩ, respectively, showing a high on/off resistance ratio of ~10
5 . Good
retention characteristics were also observed under atmospheric conditions.
The stability of the switching behavior was examined by bending the PEN
substrate [29]. To ascertain the bending amount, the bending radius was estimated
by a circular arc with a radius r, as illustrated in the inset of Fig. 11a. A smaller
bending radius implies a stronger bending of the substrate. Variations in the on/off
resistances and the turn-on/turn-off voltages are shown in Fig. 11a and b, respectively. In comparison with the flat substrate, there is no significant change in on and
on and off resistance states under substrate bending. The retention properties of the
device were also tested under substrate bending conditions. By keeping a certain
bending radius, a constant mechanical stress was applied to the device and sweeping
of the bias voltage was repeated up to 100 cycles. As observed in Fig. 11c, the on and
off states were very stable and reproducible. The on/off resistance ratio remained at
10
5 under bending. The switching characteristics were also examined with respect to
bending cycles, as shown in Fig. 11d. The device exhibited very stable on and off
resistance states. Due to high mechanical flexibility of the PEO film, the device
exhibited very stable switching behavior without any deterioration. This confirms
that neither the transport of Ag
+ ions nor the redox reactions at the electrode
interfaces are affected by bending the substrate. These results indicate that
SPE-based atomic switches have the potential to be developed into flexible switch/
memory devices.
6 Summary
In this chapter, we described the fabrication, characterization, and various functions
of SPE-based atomic switches. Similar to atomic switches based on inorganic solid
electrolytes, SPE-based atomic switches exhibit not only bi-stable resistive
switching but also quantized conductance. This is achieved by optimizing the device
structure, the fabrication method, and the measurement conditions. It is significant
that the high ionic conductivity of SPE enables us to directly observe filament
growth behaviors even in micrometer-scaled devices. Thus, we could investigate
how the filament growth processes are determined by kinetic factors such as the
redox reaction rates at interfaces, electric field strength, and ion mobility and
reduction sites in the polymer matrix. By combining with first-principles DFT
simulations, it was revealed that the observed quantized conductance originates
from the existence of a tunneling gap and the atomic rearrangement at an atomic
point contact. Furthermore, we succeeded in fabricating devices on a plastic
156
T. Tsuruoka et al.