Patent GB-805207-A (GB)
Title: Electric circuit devices utilizing semiconductor bodies and circuits including such devices
IPC: H03K17/56
Filed: 1956-06-08
Abstract: 805,207. Semi-conductor devices. WESTERN ELECTRIC CO. Inc. June 8, 1956 [June 20, 1955], No. 17784/56. Class 37. [Also in Groups XIX and XL (c)] A semi-conductor device, particularly a multistable state counter or switching device, comprises a semi-conductor body with a series of sections each comprising an emitter, and means for concentrating the emitter current to that portion of each section which is adjacent the next section, so that in operation, the sections conduct in succession. In Fig. 1, a high resistivity N-type body 11 of germanium, silicon or AIII BV compound, is provided with ohmic contacts 12 and 13 to enable an electric field to be applied across the body. P-type zones 14, 15, 16 and 17 are provided on the surface of the body, arranged end to end, each zone having an ohmic connection at one end. Alternate zones are connected through series resistors 21-24 to a common terminal and switch means 34 so that a positive potential may be applied via resistor 33 to either the even or the odd numbered zones. The forward biasing of each PN - junction depends on the potential of the N-type body region adjacent the junction. Emission of minority carriers from a P-zone effects conductivity modulation of that region of the body lying between the zone and electrode 13, thus tending to increase the forward bias and emitter current. Moreover, due to the potential drop along the P- zone, which is thin enough to have significant resistance, most of the emission flows from that portion .of the P-zone adjacent its ohmic concontact. If zone 15, for example, is assumed to be conducting, a positive potential being supplied to zones 15 and 17 and an earth potential to zones 14 and 16, that region of body 11 between the ohmic contact and of zone 15 and electrode 13 will be of relatively low resistance. If switch 34 is then operated to apply positive potential to zones 14 and 16, and earth potential to zones 15 and 17, only zone 16 will emit and become conducting, since (due to hole storage) that region of zone 16 lying adjacent the ohmic contact end of zone 15 is provided with a larger forward bias than any other zone. Once started, the emission spreads through zone 16 until, as in zone 15, it becomes concentrated around the ohmic contact region. When one zone is conducting, the potential drop across resistor 33, evectively reverse biases the remaining P-zones. Successive operation of switch 34 thus results in each of the P-zones 14-17 becoming conducting in turn. A batterv 43 associated with the first P-zone 14 ensures that zone 14 becomes conducting when the first positive pulse is applied to the series of zones which includes zone 14. Alternatively, zone 14 may be displaced so that it has one portion nearer to electrode 13, than any other P-zone. Modifications are described in which the P-zones are arranged to slightly overlap each other, or are in the form of a closed ring round a cylindrical body, as shown in Fig. 6. The ring may also be provided between electrodes of different radius (Fig. 7, not shown) so that an increased electric field is obtainable adjacent the inner electrode. In a further modification, an additional and separate series of ohmic contacts are provided on the ends of each P-zone opposite to the first ohmic contacts, so that the stepping can take place in either direction. In another embodiment (Fig. 9), a second series of P-zones also having ohmic contacts at one end, are provided on the surface of a thin body of N-type material opposite to that bearing the first series, thereby providing a reversible stepping arrangement. Fig. 10 shows an arrangement comprising in effect a series of junction transistors with hook collectors and a common base region 101. Ohmic contacts 109, 112 are provided at one end of the emitter zone 102, and to a region of the base zone adjacent each emitter. By considering the effect of α 1  and α 2'  the current amplification factors for the emitter and hook collector junctions, and of the resistor 112 in the base lead, it is shown that the collector-emitter current voltage characteristic has a negative resistance region which provides conducting and non-conducting stable states. The application of successive positive pulses to the leads 25H and 26H connected to alternate collectors then results in a stepping operation as described for the previous examples. In an alternative arrangement, the base zone is shaped so that portions of this zone effectively replace resistors 112, and in a further example both emitter and collector zones are provided with a second series of ohmic contacts at the other end so as to provide bi-directional stepping. The arrangement may utilize zener or avalanche effects, or surface leakage effect to provide the necessary two stable states. The P-zones may be provided by heating on indium strips in contact with an N-type semi-conductor body, etching away the indium remaining on the surface and then applying indium dots at one end of each strip. Alternatively, aluminium can be evaporated on the surface through masks, and then diffused. The ohmic electrode to the P-region may be provided by alloying indium or bonding a gold lead doped with gallium thereto. The ends of the P-zones may be tongued and grooved to increase the influence of one zone or the other. The NPNP body may be produced by diffusing aluminium and antimony simultaneously into an N-type body. Specifications 700,231, 753,013, 790,387 and 803,887 are referred to.