1 Consiglio Nazionale delle Ricerche (CNR)-Istituto per la Microelettronica e Microsistemi (IMM), Sezione di Catania, Stradale Primosole, 50, 95121 Catania, Italy.
We report a sharp threshold at 4 V in the growth rate of breakdown spots in thin films of SiO2 on silicon. This provides some of the first information concerning the electronic structure of the breakdown spot.