PNP Transistor

PNP Transistor:

There are different ways of fabricating PNP Transistor in integrated circuits. The important means of integrating PNP Transistor are (i) vertical p-n-p, (ii) lateral p-n-p and (iii) triple diffused p-n-p.

In vertical pnp transistor, the p type substrate is used as p-type collector while the n-epitaxial layer is used as base. Obviously the next diffusion layer of p-type is used as an emitter. This type of p-n-p is called as substrate p-n-p transistor. The main drawback is that collector has to be held at a fixed negative potential.

The lateral p-n-p transistor is formed without any additional process. The p-n-p transistor is formed simultaneously with n-p-n transistor. Here n-epitaxial layer is used as base simultaneously two p-regions are diffused to form emitter and corrector ring as shown in the Fig. 1.19.

PNP Transistor

If an extra p-type diffusion is added after n-diffusion then we can get p-n-p transistor starting for standard n-p-n transistor. The p-n-p transistor thus obtained is called triple diffused p-n-p transistor. This type of transistor is fabricated only if there is a special need because of complicated process calculations and increase in cost due to addition in fabrication process.

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