Thin film structures

摘要

1,010,575. Tunnel devices. SPERRY RAND CORPORATION. June 6, 1963 [June 8, 1962], No. 22639/63. Drawings to Specification. Heading H1K. A thin film device, suitable for tunnelling comprises a film of vapour deposited aluminium oxide between two films of conductive material, one at leash of which is not aluminium; the aluminium oxide being " formed " by a prolonged application of a suitable voltage to increase the current density which it is capable of handling. One or both of the metal films may be of Au, Ag, Pt, Pa, Cu, Zn, Cd, Cr, Fe, Ni, Pb, Mg, Ti, Ta, Va, Co, W, Bi, and one of the films may be of Al. The deposition of the metal films either on a substrate in the first instance, or finally on the aluminium oxide film may be effected by vapour deposition. The aluminium oxide deposition is also effected by vapour deposition, pure aluminium being vaporized in an atmosphere of oxygen in which the deposition takes place. In one embodiment a 5000 Š film of Pb is evaporated on to a glass slide, followed by a 350 Š film of Al 2 O 3 followed by a further 5000 Š film of Pb, in the form of strips having various areas. On applying voltages of less than 12 V only small currents are obtained, but on reaching this voltage the current grows for a period of 45 sees. after which it remains constant and of the order of Ima. This is the " forming " process referred to above. After this process the current densities obtained are much larger and correspond to an " unformed " film of about 1/ 7 th the thickness. If the film is left without impressed voltage for about an hour, then it requires to be reformed, although the process takes a shorter period. The effect is suggested to be due to the formation of a positive ionic space charge which drifts towards the cathode and lowers the work function thereat. The current is also stated to be temperature dependent, rising sharply with temperature above 250‹ K. An experiment is described for observing the relaxation of the space charge referred to above. A device in which gold is used for the outer films is also described in which the edges of the structure may be coated with SiO, or other insulating material.