Polyimide as a Tunneling Barrier in Single-Electron Tunneling Junctions

Yutaka Noghchi
National Institute of Information and Communications Technology, 588-2 Iwaoka, Nishi-ku, Kobe 651-2401, Japan
Single-electron tunneling junctions using polyimide (PI) spin-coat films (approx. 6 nm thick) as a tunneling layer were fabricated. A very small number of C60 or copper tetra-t-butylphthalocyanine (CuttbPc) molecules were dispersed in PI films, and films sandwiched between A1 and Au electrodes were used as the junctions. A Coulomb staircase behavior due to single-electron tunneling was clearly observed in the I (V) curves at a temperature of 16 K. These Coulomb staircases showed threshold voltage shift by photoirradiation, depending on the wavelength of incident light. This voltage shift was examined in conjunction with space charges formed at PI film-metal interface. Temperature dependence of the Coulomb staircase behavior was also examined, and it was well explained by taking into account the space charge behavior.