processed into a variety of shapes and geometries, and the use of molecular design is
possible through chemical synthesis [2]. Polymer materials possess additional favorable properties, such as good mechanical stability, flexibility, and processability onto
various substrates [3]. Therefore, they should be a promising candidate for use in
future organic device applications. Many research groups have reported resistive
switching in polymer-based devices, and several charge-trapping mechanisms were
proposed to explain the observed switching behaviors [1, 3–5]. Despite that resistive
switching memories based on electrochemical reactions in polymer materials are
very attractive, a limited number of studies reported this type of polymer memory in
the second half of the 2000’s [6, 7]. Even in the research of atomic switches, only
inorganic solid electrolytes were used during that time period.
In 2008, we considered the possibility of realizing atomic switches using solid
polymer electrolytes (SPEs), which have used as the base materials for rechargeable
batteries, electrochromic windows, and light-emitting devices [8]. SPEs exhibited
high mechanical flexibility and stabilities up to their melting temperatures. Earlier
studies on SPEs were mostly related to alkali-metal (such as Li
+ and Na
+
) salt
complexes, which are developed for battery applications. However, alkali-metal
salt complexes are not suitable for electronic devices, because they easily react
with water under ambient conditions. In contrast, Ag
+
-salt complexes are expected
to be more stable under the same conditions. Thus, in 2009, we started development
of atomic switches using a Ag
+ -conductive SPE, and have attempted to demonstrate
resistive switching and the unique functions of these switches. In this chapter, we
describe the basic characteristics, the fundamental mechanism, and the novel functions of SPE-based atomic switches.
2 Invention of SPE-Based Atomic Switch
We selected polyethylene oxide (PEO) as the first polymer material. PEO was
discovered in 1973 by Wright and co-workers who studied the ionic conductivity
of alkali-metal salt complexes using PEO [9]. After the discovery, PEO came to be
recognized as the base material of rechargeable batteries, and the properties of PEO
and its derivatives have since been extensively investigated. In this section, we
describe the switching characteristics, operating mechanism, and memory properties
of an atomic switch based on a Ag
+
-conductive PEO.
2.1 Typical Switching Characteristics
The initial devices were fabricated with SPE films prepared by drop-casting from
PEO (M W ¼ 2 Â 10
6 ) and silver perchlorate (AgClO 4 ), which were dissolved in
water [10, 11]. The device has a cross-point structure with top Ag and bottom Pt
electrodes, as illustrated schematically in Fig. 1a. The Ag salt concentrations of the
140
T. Tsuruoka et al.
possible through chemical synthesis [2]. Polymer materials possess additional favorable properties, such as good mechanical stability, flexibility, and processability onto
various substrates [3]. Therefore, they should be a promising candidate for use in
future organic device applications. Many research groups have reported resistive
switching in polymer-based devices, and several charge-trapping mechanisms were
proposed to explain the observed switching behaviors [1, 3–5]. Despite that resistive
switching memories based on electrochemical reactions in polymer materials are
very attractive, a limited number of studies reported this type of polymer memory in
the second half of the 2000’s [6, 7]. Even in the research of atomic switches, only
inorganic solid electrolytes were used during that time period.
In 2008, we considered the possibility of realizing atomic switches using solid
polymer electrolytes (SPEs), which have used as the base materials for rechargeable
batteries, electrochromic windows, and light-emitting devices [8]. SPEs exhibited
high mechanical flexibility and stabilities up to their melting temperatures. Earlier
studies on SPEs were mostly related to alkali-metal (such as Li
+ and Na
+
) salt
complexes, which are developed for battery applications. However, alkali-metal
salt complexes are not suitable for electronic devices, because they easily react
with water under ambient conditions. In contrast, Ag
+
-salt complexes are expected
to be more stable under the same conditions. Thus, in 2009, we started development
of atomic switches using a Ag
+ -conductive SPE, and have attempted to demonstrate
resistive switching and the unique functions of these switches. In this chapter, we
describe the basic characteristics, the fundamental mechanism, and the novel functions of SPE-based atomic switches.
2 Invention of SPE-Based Atomic Switch
We selected polyethylene oxide (PEO) as the first polymer material. PEO was
discovered in 1973 by Wright and co-workers who studied the ionic conductivity
of alkali-metal salt complexes using PEO [9]. After the discovery, PEO came to be
recognized as the base material of rechargeable batteries, and the properties of PEO
and its derivatives have since been extensively investigated. In this section, we
describe the switching characteristics, operating mechanism, and memory properties
of an atomic switch based on a Ag
+
-conductive PEO.
2.1 Typical Switching Characteristics
The initial devices were fabricated with SPE films prepared by drop-casting from
PEO (M W ¼ 2 Â 10
6 ) and silver perchlorate (AgClO 4 ), which were dissolved in
water [10, 11]. The device has a cross-point structure with top Ag and bottom Pt
electrodes, as illustrated schematically in Fig. 1a. The Ag salt concentrations of the
140
T. Tsuruoka et al.