Question

The capacitance of junction capacitor does not depend upon

(a) Impurity concentration of p-type epitaxial layer

(b) Impurity concentration of n-type epitaxial layer

(c) Area of the junction

(d) Voltage across the junction

The question was asked during an interview.

My query is from Active and Passive Components of IC in chapter IC Fabrication of Linear Integrated Circuits

Answer 1

Answer: (d) Voltage across the junction

Junction capacitance depends on:

- Impurity concentration of p-type epitaxial layer

- Impurity concentration of n-type epitaxial layer  

- Area of the junction

It DOES NOT fundamentally depend on the voltage across the junction as a primary parameter. While voltage affects the depletion width and thus influences capacitance, it is not a basic structural parameter like the others. The doping concentration and junction area are the primary determinants of junction capacitance in IC fabrication.