Metal–insulator–metal and metal–insulator structures as electron sources

Different types of M-I-M and M-I systems investigated in the past and at present and used as sources of electrons for vacuum electronic and solid-state devices are quoted and their main properties are compared. The problem of establishing the surface potential in M-I systems is emphasized. Physical processes determining electron emission are discussed. Three groups of system have to be distinguished, differentiated mainly by the thickness of the insulating layer. The importance of the inhomogeneous field distribution in this layer is pointed out. An idea is proposed explaining the conditions under which a transition can be effected from a cathode with 'normal’ characteristics to a formed system exhibiting 'anomalous’ characteristics. In such a way, it is possible to understand the emission phenomena of all the mentioned groups from the same point of view.