Ultrafast metal-insulator varistors based on tunable Al 2 O 3 tunnel junctions

Ultrafast metal-insulator varistors have been fabricated using atomic layer deposition. A high-density matrix of micron-sized spherical Ni particles conformally coated with ∼ 7.5 - 22 nm Al 2 O 3 films exhibited transient response times ( ∼ 0.3 ns ) , capacitances ( ∼ 45 pF ) , leakage currents ( ∼ 33 pA ) , and nonlinearities ( α ∼ 380 ) which were all markedly improved over conventional metal oxide varistors. These characteristics result from the Fowler-Nordheim tunneling of electrons through uniform Al 2 O 3 tunnel junctions separating adjacent particles within the matrix.