Results on studies of tunneling and conduction phenomena in thin metal-iron-oxide-metal sandwiches at helium temperature are described in this paper. Characteristic $I-V$ curves have been studied for both dc and ac applied voltage signals. The main features of interest are a voltage breakdown observed above certain critical currents, and a large negative-resistance region observed on the decreasing current leg of the $I-V$ curve. The breakdown phenomenon exhibits a delay time that is a function of the overvoltage applied to the junction, and comparison with nucleation theory has suggested that some type of phase transition is occurring. We suggest a model based on the order-disorder transition that is known to occur in magnetic iron oxide, ${\mathrm{Fe}}_3$${\mathrm{O}}_4$. We also discuss possible field ionization processes that could be playing a role in the transition. The sandwiches have been successfully utilized as amplifiers, and can also be set into self-oscillation under certain conditions. Examples of these features are included in the paper. The transition from high to low resistance observed in these sandwiches is similar to those observed in glassy semiconductors at higher temperatures, and certain comparisons may be useful in trying to understand the glassy-semiconductor behavior.

• Received 11 February 1969

DOI:https://doi.org/10.1103/PhysRev.184.565