Patent GB-844078-A (GB)
Title: Improvements in or relating to circuit arrangements including semi-conductor devices
IPC: H03K3/45
Filed: 1957-06-14
Abstract: 844,078. Semi-conductor circuits. SIEMENS & HALSKE A. G. June 14,1957 [June 14, 1956; Aug. 10, 1956], No. 18905/57. Class 40(6). [Also in Groups XVIII and XXXVI] In a circuit arrangement including a semiconductor device consisting of an elongated semi-conductor body having a non-rectifying base electrode at each end and a rectifying emitter electrode located between the ends wherein a potential difference is maintained between the two base electrodes and the emitter electrode is reversely biased with respect to that portion of the semi-conductor body in the immediate vicinity of the emitter electrode, a magnetic field is produced in at least a part of the semiconductor body in such a way that the potential of the said portion of the semi-conductor body is reduced to an extent such that the emitter electrode is caused to be forwardly biased with respect to the said portion. The semi-conductor device is thus controlled by the field and not by the emitter current alone as in prior arrangements. In the arrangement shown, a strip n of n-type semiconductor material is provided at each end with non-rectifying base electrodes B1 and B2 respectively and on one of the narrower sides with a rectifying emitter electrode D of p-type material which is positively biased so that current is just prevented from flowing across the junction. If current flows between the base electrodes B2 and B 1 the equi-potential surfaces are as shown in full lines in the Figure. The semi-conductor body shows the Hall effect, so if a magnetic field is applied perpendicular to the plane of the Figure so that the Hall voltage UH makes the side of the strip on which the electrode D is located negative with respect to the other side, the equi-potential surfaces assume an oblique position as shown by the dotted lines, and the potential in the semiconductor body near D is reduced to such an extent that the p-n junction becomes conductive. A resistor may be connected in series with the emitter electrode of such a value that the current is interrupted when the magnetic field is removed. To aid switching, the resistor may consist of a semi-conductor material, particularly an A<SP>111</SP> B<SP>v</SP> compound, and may be located within the range of the magnetic field so that the value of the resistance is increased when the field is present. If no resistor is used the flow of current may continue when the field is removed and must then be interrupted by separate means such as a control-field acting in opposition to the primary field, or an external voltage variation e.g. at the emitter electrode, or a circuit interruption at the base electrodes. A ferrite or iron plate may be arranged on one or both sides of the semi-conductor body to increase the mechanical strength of the crystal and/or to increase the strength of the field. The field may be applied to only a part of the body and has the effect of increasing the resistance of that part, or the body may be in two parts, one of which carries a rectifying emitter electrode and the other is subjected to the magnetic field and operates like a magnetically controlled resistor. One or more p-n or n-p-n junctions may be arranged in the part to which the field is applied to produce an exponential dependence of the resistance on field strength, and a magnetic blocking layer may be set up by roughening one of the narrower sides of the semi-conductor body to provide additional means of switching the device. An alternating magnetic field may be provided, e.g. by a permanent magnet suspended over the semi-conductor body, so that the device is switched in dependence on the direction of the field, such an arrangement having possible uses in an electric clock or as a storage element, or for controlling electro-mechanical relays. A plurality of emitter electrodes and/or collector electrodes may be provided at suitable points on the semi-conductor body to provide an additional control by means of carrier injection.