6. Two-Terminal Organic Memories with Metal or Semiconductor Nanoparticles

The rapid development of information technology has higher and higher demand for high-speed and high-density memory devices. In addition, flexible memories are required as the key units of flexible electronic systems that are regarded as the next-generation electronic systems. Two-terminal organic devices embedded with metal or semiconductor nanoparticles can exhibit resistive switches and stability in different resistance states. This electrical behavior renders them important application as memories. These organic memory devices can have high density and high mechanical flexibility, and the fabrication cost for them can be quite low. Several types of organic memory devices have been demonstrated. The first type of the devices has a triple-layer structure with a layer of metal nanoparticles sandwiched between two organic layers. The other types of the organic memories have a single-layer structure with metal or semiconductor nanoparticles or nanoparticle/polymer composites embedded in the single polymer layer. Several mechanisms have been proposed for the resistive switches, including the electric-field induced charge transfer between nanoparticles and another component, the charge trapping on nanoparticles, and electric-field induced polarization. In addition, a new type of organic memories was recently demonstrated, which explored the charge transfer between metal nanoparticles and bulk metal electrode. The organic memories can potentially solve technique bottlenecks in the present leading memory devices. Apart from the application as memories, organic memories can be used for other electronic systems. For example, the combination of organic memories with light-emitting diodes can give rise to electronic papers.