**4.2 J-V characteristics of Ni/NiO/Ni QC devices**

In this section, we present current density-voltage (*J-V*) characteristics in Ni/NiO/Ni QC devices, which consist of NiO tunnel barriers sandwiched between two Ni thin films whose edges are crossed. First, we introduce the background of sub-micrometer scale tunnel junctions and the motivation for fabricating QC devices with tunnel barriers. Then, we show the derivation of a formula for *J-V* characteristics of QC devices with tunnel barriers and finally demonstrate experimental results of their *J-V* characteristics.
