Focused ion beam process for formation of a metal/insulator/metal double tunnel junction

An improved method to fabricate a small lateral double tunnel junction which utilizes focused ion beam (FIB) etching and lift-off techniques is proposed. A double layer resist consisting of nitrocellulose and germanium layers was used. Narrow grooves with widths comparable to or narrower than the FIB diameter were formed in a ferromagnetic layer of Ni, and Ni/Ni-oxide/Au/Ni-oxide/Ni and Al/Al-oxide/Ni/Al-oxide/Al double junction structures were fabricated using the proposed method. The measured voltage and current characteristics of the latter structures indicated that double tunnel junctions with a barrier height of 0.61 eV were fabricated and suggest that this is a promising method to fabricate island structures for devices utilizing Coulomb blockade or spin blockade effects.