Patent GB-983879-A (GB)
Title: Solid state devices
IPC: H01L27/00
Filed: 1962-05-16
Abstract: 983,879. Superconductive devices. RADIO CORPORATION OF AMERICA. May 16, 1962 [May 31, 1961], No. 18944/62. Heading H1K. A solid state device comprises a member 27 capable of becoming superconducting at temperatures near absolute zero, a thin insulating layer 23 through which tunnelling can occur and an electrode 25 which may or may not be capable of superconduction. Fig. 3 illustrates (in the case where electrode 25 is not capable of superconduction) the energy conditions prevailing when no bias (V T  from battery 33) exists. Areas 61, 63 represent allowed states for the superconducting electrons and the thermally stimulated normal charge carriers respectively, and 57 represents the Fermi level. Owing to the absence of allowable states in E 1 , no tunnelling current flows. When bias V T  is applied the Fermi level for 25 rises to permit tunnelling from 25 to the allowed states 63 and the current characteristic thus is that shown at 51, Fig. 2. If current I c  is caused to flow through the semi-conductor 27, the gap E 1  narrows, so that tunnelling occurs at lower values of V T  (curves 53, 54). On further increase of I c  to a critical value, superconductivity ceases and the energy gap E 1  disappears, so that tunnelling takes place for all values of T and the characteristic becomes a straight line 55. If material 25 is also superconducting the energy diagram with I c  zero is as shown in Fig. 6. Current is small until V T  approaches   E 1 -E 2 /2 in which the upper edges of the band   gaps are level. Energy states just above these edges have a high density so that the tunnel current becomes large. On further increase of V T  the lower edge of 63 comes opposite the gap E 2  and the current thus falls. As V T  E 1 +E 2  further increases to the upper edge 2 of 67 comes opposite the lower edge of 63 and travelling again takes place to provide a sharp rise in current. This characteristic is shown at 71, Fig. 5. If control current I o  is provided, this narrows both energy gaps to produce curve 73. When eventually 25 ceases to be superconducting the curve becomes similar to 54 of Fig. 2. Finally, when neither 25 or 21 is superconducting a straight line characteristic obtains as before. The device can be used as an amplifier by operating on the rising parts of the curves (load line 77), or as a bi-stable device (load line 78). The device shown in Fig. 1 comprises an aluminium member 27, with a thin insulating layer 23 which may be obtained by oxidizing the aluminium in air, or by depositing a monomolecular layer of barium or chromium stearate. Other superconducting materials such as niobium, tin, lead, or alloys such as niobium stanide or niobium vanadium stanide may be used. If the electrode 25 is not to be capable of superconductivity it may be of silver, copper or gold. In a further embodiment, Fig. 7, the members 21, 25 may take the form of strips, the latter being coated with the insulating material, mounted on a borosilicate substrate having platinum electrodes 27, the members being deposited by vapour deposition using masking techniques. In further embodiments having crossed conductors as described above an additional conductor may be provided, either as a strip passing through the central axis, or as an arcuate member, having its centre on the axis, for providing an additional control magnetic field, Figs. 8-11 (not shown).