Stable analog resistance change of a molecular-gap atomic switch over a wide range

The development of hardware-based neuromorphic systems requires devices that change synaptic weight in an analog manner. Molecular-gap atomic switches exhibit higher on/off ratios compared to other, Redox-based, non-volatile memory devices, and also show analog change in resistance. However, several issues remain with these devices, such as those related to the stability and multiplicity of analog resistance. In this study, we employed Cu-doped Ta₂O₅ as an ionic transfer layer, since it was thought that the higher concentration of Cu in the Ta₂O₅ layer, from pre-doping, would stabilize the Cu atoms precipitated on the Ta₂O₅ layer even after removal of the bias application. The fabricated Pt/PTCDA/Cu-doped Ta₂O₅/Cu molecular-gap atomic switches showed analog change in resistance over a range of six (6) orders of magnitude, with high multiplicity. The stability of the analog resistance was also improved.