Abstract
Directly ion-beam deposited AlN films were used as insulating barriers for spin-dependent tunneling junctions, and the effect of the lead resistance on the measured ΔR/R was investigated. `Bow-tie' junctions with AlN thicker than 15 angstroms showed non-linear I-V characteristics with ΔR/R of 1.4%. Junctions with AlN films thinner than 12 angstroms showed small `negative' resistance with ΔR/R of -14%. The finite-element analysis was used to simulate the current flow and the measured resistance of the `bow-tie' structure with different resistance ratios of the tunneling junction to the lead. The result of simulation shows when the ratio is smaller than 0.077, the measured resistance becomes negative, and ΔR/R is significantly enhanced by the lead effect.