The role of avalanching in cold emission devices

Nonthermionic emission of electrons into a vacuum is observed in Malter effect emission, MgO cold-cathode type emission, and thin film metal sandwich emission. These cold-cathode effects possess certain similarities which appear to be the result of a common basic emission mechanism. MgO cold-cathode type emission has been the most extensively studied of these three cold-cathode effects. In MgO cold cathodes an electric field of the order of 10⁶v/cm is developed across a relatively thin (∼7000Å) oxide layer. This electric field is indirectly developed as a result of hole migration through the MgO layer. A similar process of field enhancement probably occurs in Malter effect emission, while in thin film metal sandwich devices the required electric field is developed directly. Study of the detailed characteristics of MgO cold-cathode emission suggests strongly that electron avalanching is the basic mechanism responsible for self-sustained emission. In the self-sustained region, the IV characteristics are those of a simple avalanche process. Furthermore, the observed electron velocity distribution and the temperature dependence of emission follow from the requirement that electrons which are emitted come from a highly energetic electron "gas," presumably the terminal result of an avalanching process. Similarities between this process and the mechanism producing emission from thin film metal sandwich devices with insulating layers of 250Å-16,000 Å thickness are discussed.