Ultrafast metal-insulator varistors based on tunable Al2 O3 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 Al2 O3 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 Al2 O3 tunnel junctions separating adjacent particles within the matrix.