BREAKDOWN OF Al/AlOx/Al TUNNELING JUNCTIONS

The breakdown of Al/AlOx/Al tunneling junctions is studied. Al (10 nm) /AlOx(approximately equals 2.5 nm)/Al (50 nm) tunneling junctions were fabricated on glass substrates by ion-beam mask sputtering. The sputtered Al film was oxidized in pure O2 gas for 4-40 h at RT. The AlOx barrier height evaluated from a fit to the Simmons-Schottky equation was 0.38-1.7 eV. The I-V characteristics were measured by the four-probe method. The breakdown of Al/AlOx/Al tunneling junctions can be classified into two types on the basis of I-V characteristics. Type 1 breakdown shows an abrupt increase in current and a decrease in resistance at the maximum applied voltage. This type of breakdown occurs at the voltage when the energy level of the AlOx valence band is equal to the barrier height. It is concluded that type 1 breakdown is caused by the Zener mechanism. Type 2 breakdown shows an erratic change of current and resistance. The average electrical resistivities of AlOx are 7.8x103 and 1.1x103 Wm for specimens showing type 1 and type 2 breakdowns, resp. It is considered that some defects in AlOx result in the low breakdown voltage for type 2 breakdown. 7 refs.