Ultrafast metal-insulator varistors based on tunable Al2O3 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 ∼7.5–22nm Al2O3 films exhibited transient response times (∼0.3ns), capacitances (∼45pF), leakage currents (∼33pA), 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 Al2O3 tunnel junctions separating adjacent particles within the matrix.