Question

Which of the following transistor has the limitation, due to the requirement of additional fabrication steps and design consideration?

(a) Vertical pnp transistor

(b) Lateral pnp transistor

(c) Triple diffused pnp transistor

(d) Substrate pnp transistor

This question was posed to me during an online interview.

This intriguing question comes from Active and Passive Components of IC in section IC Fabrication of Linear Integrated Circuits

Answer 1

Right answer is (c) Triple diffused pnp transistor

Simplify with an easy explanation: In triple diffused pnp transistor fabrication process, an extra p-type diffusion is added to a standard npn-transistor after the n-diffusion to obtain a pnp transistor. However, the usefulness of such a structure is not used due to its limitation.