Breakdown of Al/AlO_x/Al Tunneling Junctions

The breakdown of Al/Al_x,/Al tunneling junctions is studied. Al (10nm)/AlO_x(∼2.5nm)/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 room temperature. The AlO_x, barrier height evaluated from a fit to the Simmons-Schottky equation was 0.38-1.7 eV. The current-voltage characteristics were measured by the four-probe method. The breakdown of Al/AlO_x/Al tunneling junctions can be classified into two types on the basis of current-voltage 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 AlO_x 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 AlO, are 7.8×10 ³ and 1.17times;10³ Omega;m for specimens showing type 1 and type 2 breakdowns, respectively. It is considered that some defects in AlO_x result in the low breakdown voltage for type 2 breakdown.