Integrated Injection Logic

Integrated injection logic (I²L) offer a number of advantages over conventional ICs. For one thing, they permit a very high scale of integration. For another, the supply voltage may be as low as 0.5 to 0.9 V. A mere 10^-12 J of energy is enough to do the necessary switching.

Figure 8.10a shows the structure of an n₁-p₂-n₂ planar I²L transistor which is a unit cell of an I²L chip. The n₁ -type substrate in this transistor acts as an collector. In contrast to conventional planar transistor, the device in our case is used in the inverse mode. In addition to the transistor, there is also a p₁ -region called the injector(I). Together with the n₁ -type collector and the p₂ -type base of the n₁-p₂-n₂ transistor (VT2), the injector makes up a p_i-n_l-p₂ transistor (VT1), where the injector operates as an emitter.

Fig. 8.10. Planar I²L transistor

Let a forward voltage be applied to the injector junction from a supply source, E_I. The applied forward voltage causes holes to move from the injector into the n₁ -type collector region, while the excess charge due to holes injected there under the influence of E_I is neutralized by in-coming electrons. The excess electrons and holes diffuse through the region n₁ to the n₁ - p₂ collector junction which is enriched with charge carriers so that its potential barrier is brought down, and its resistance decreases. Holes and electrons diffuse farther through the p₂ -type base to the p₂-n₂ emitter junction and likewise reduce its potential barrier and resistance.

In this way, the resistance of both junctions in the n₁-p₂-n₂ transistor is reduced, and the transistor VT2 operates close to saturation, that is, similarly to a closed switch. If we now short-circuit the base to the emitter by closing the switch S, the voltage across the collector junction will fall to zero, no more carriers will be able to arrive at the р₂ — п₂ emitterjunction, and its resistance will go up abruptly. Thus, the transistor VT2 will move to a state close to cutoff, and this corresponds to an open switch.

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