GB831535A - Improvements in semi conductor switching devices and circuits therefor - Google Patents

Abstract

831,535. Transistors. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 22, 1956 [May 20, 1955], No. 15731/56. Class 37. [Also in Group XL (c)] A semi-conductor switching device comprises a body having a first region 2 of one conductivity type of thickness less than a diffusion length, adjoining a second thin region 3 of opposite conductivity type of lower resistivity than the first region, two spaced controlled electrodes 5 and 6 in contact with the first region and a control electrode 11 in contact with the second region, the arrangement being such that a potential gradient exists along at least one of the regions to control the respective rates of carrier injection across the PN junction at portions opposite the controlled electrodes. The controlled electrodes 5 and 6 may consist of point contacts or hook collectors, and are spaced at a distance greater than the diffusion length. Three ohmic electrodes 8, 9 and 10 may be applied to region 2 as in Fig. 2 which shows a switching circuit having one stable state (electrodes 5 and 6 both non- conducting), a second state with an output from collector 5 while a positive pulse is applied to electrode 10, and a third state with output from collector 6 while a negative pulse is applied to electrode 10. Normally batteries 18 and 23 reverse bias the whole of the PN junction, and no current flows through either of electrodes 5 and 6. The application of a positive potential to electrode 10 causes a potential gradient along N region 2 to forward bias the left half of the PN junction so that zone 3 acts as an emitter to collector electrode 5 while the right half of the PN junction is reverse biased preventing emitter action so that no current flows through electrode 6. A negative potential to electrode 10 similarly causes electrode 6 to conduct but not electrode 5. Electrode 11 maintains region 3 at uniform potential and holes are supplied by means of a connection to electrode 8 via resistor 26 which limits the cumulative action which takes place during operation. A modification is described in which electrode 9 is associated with a second input signal source, both inputs being applied through inductive coupling, to provide a trigger or a latch circuit. Electrode 8 may also be replaced by a point contact emitter source to supply zone 3 which is otherwise left floating. Fig. 5 (not shown) describes a modified two stable state arrangement in which earthed electrode 8 is shifted so that the arrangement is non- symmetrical and under no-signal conditions electrode 5 is conducting while electrode 6 is cut off. An alternative non-symmetrical arrangement is described (Fig. 5A) in which region 3 and electrode 11 are inclined with respect to the upper surface of region 2. Fig. 11 shows the device arranged as an amplifier for square-wave signals in which only one base electrode (43a) is used and the P zone 44 is floating; in this circuit, when the input signal to electrode 46 ceases this electrode becomes reverse biased to act as a collector to reduce hole storage effects and sharpen the output pulse. By connecting a resonant circuit between electrode 46 and 47 this circuit may be used as an oscillator the electrodes 46 and 47 operating alternately as emitter and then collector. In Fig. 14, the P region 118 which is of higher resistivity than before, is also provided with ohmic electrodes 64 and 65 so that a potential. gradient may also be provided along this region. The arrangement provides a trigger circuit in which under no signal conditions the left-hand side of the PN junction is reverse biased and the righthand side forward biased, so that electrode 121 and not electrode 120 conducts. A positive signal to electrodes 63 and 64 via terminal 67 reverses the position, which restores on cessation of the pulse or on the application of a negative pulse. This arrangement may also be converted into an oscillator by providing a resonant circuit between, electrodes 120 and 121.