A four-terminal P-N-P-N switching device

A four-terminal germanium p-n-p-n switching transistor is described. In an appropriate circuit the device has useful switching gain for both the turn-on and turn-off operations. A pulse of one polarity turns the switch on, and a pulse of the opposite polarity turns it off. In the absence of triggers, the state is maintained. Equivalence to a pair of complementary conventional transistors in a direct-connected, common-base emitter-follower regenerative circuit is shown. The collector junction is common to both transistor sections so that saturation is simultaneous. Saturation current is kept small in one section, and the switch is turned off by withdrawing the small saturation current. Expressions are derived for switching gain, and requirements on device parameters are obtained. Common-emitter gain for one transistor section must exceed the ratio of load current to off-trigger current. Device structure is described. A combination of alloy, diffusion, and post-alloy diffusion techniques is used for fabrication. One transistor section with a thin base has high common-emitter gain, and the other has moderate gain. Switching performance data are given. A load current of 20 ma at 20 volts is switched with 2-ma pulses. Trigger pulse durations of the order of the switching time are required. Switching times of about 100 nsec are obtained.