Fabrication of PNP Transistor in Integrated Circuit

Fabrication of PNP Transistor in Integrated Circuit:

There are different ways of Fabrication of PNP Transistor in Integrated Circuit. The important means of integrating PNP Transistor are

Vertical PNP transistor,
Lateral PNP transistor and
Triple Diffused PNP transistor.

Vertical PNP transistor:

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 PNP is called as Substrate PNP Transistor. The main drawback is that collector has to be held at a fixed negative potential.

Lateral PNP transistor:

The Lateral PNP transistor is formed without any additional process. The PNP transistor is formed simultaneously with NPN 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.

Triple Diffused PNP transistor:

If an extra p-type diffusion is added after n-diffusion then we can get PNP transistor starting for standard NPN transistor. The PNP Transistor thus obtained is called Triple Diffused PNP transistor. This Triple Diffused PNP 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.