Patent GB-887327-A (GB)
Title: Improvements in transistors
IPC: H01L29/00
Filed: 1958-05-30
Abstract: 887,327. Transistors. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 30, 1958 [May 31, 1957], No. 17334/58. Class 37. [Also in Group XL (c)] In a transistor comprising a body of semiconductor material of one conductivity type, the whole of one face of which is covered by a unipotential layer of material of the opposite conductivity type, a base electrode, and an emitter spaced more than the diffusion length from a plurality of current amplifying collector electrodes, are mounted on the opposite face of the body within a diffusion length of the layer. The base electrode is preferably situated between the collector electrodes, which may be of the hook type, and the emitter. Such a device may be made by the following steps: cutting a monocrystalline slice, the faces of which lie in 111 crystallographic planes from a 1 ohm/cm. P- type ingot, heating to 800 C. in arsenic vapour in a reducing atmosphere for 24 hours to provide an N-type layer over the entire surface, and removing the edges of the slice to provide a PNP body which is then subdivided into conveniently sized PNP elements. A blob of indium 12 (Fig. 6) is placed on one face of an element and heated for half an hour to alloy through the N-layer and form an ohmic connection to the P-type zone. An ohmic contact is then formed on the N-type layer by heating with a solder at 700‹ C. for 5 minutes and a pair of PN-junction connections 16, 16a by heating masses 12, 12a of indium on the N-layer in a similar treatment. A two collector device (Fig. 7) is formed from the resulting body by removal of the N-type layer between the electrodes by chemical or electrolytic etching or sandblasting, or by converting these parts of the layer into high resistivity material, and applying a solder electrode 5 over the whole of the opposite face. A similar device provided with a plurality of emitters and hook collectors, in which each emitter is more than the diffusion distance from any collector, as shown in Fig. 8, may be made by a similar process. The intrinsic amplification factors of the various collectors may be made different by variation of thickness of the N-type zones of the collectors. This is effected by forming the collectors individually using different treatment times in each case. Fig. 9 shows a logical circuit embodying such a device which operates as follows. When a single increment of current is applied through emitter 8A for instance, the floating N-type zone collects the current and re-emits at a point beneath the collector 12A of highest intrinsic α. On application of a second increment of emitter current via emitter 8B collector 12A saturates and the adjacent collector 12B which has a higher saturation current becomes conductive and robs collector 12A of its current. A further increment of emitter current from emitter 8C saturates collector 12B, thereby transferring all the collector current to collector 12C. An additional increment of current from emitter 8D saturates collector 12C and the preferred collector 12A again becomes conductive in addition to 12C. The robbing effect in this embodiment is critically dependent on the intercollector spacing as discussed in Specification 842,352. The uses of the circuit are further described in Group XL (c). Specification 814,896 also is referred to.