A monolithic metal oxide semiconductor (MOS) non-polarized capacitor is a parallel plate capacitor with SiO₂ as the dielectric. A surface thin film of metal (aluminum) is the top plate. The bottom plate consists of the heavily doped n⁺ region that is formed during emitter diffusion. What is the typical value of capacitance for an oxide thickness of 500 Å of this MOS capacitor?

Take the permittivity of Dielectric (ϵ_r) as 4.

Question

Question

This question was previously asked in

ESE Electronics Prelims 2021 Official Paper

Answer 1

Concept:

The capacitance for a MOS capacitor is given by:

\(C_{ox}=\frac{\epsilon_{ox}}{t_{ox}}\) ---(1)

Calculation:

Putting on the respective given values in Equation (1), we get:

\(=\frac{4\times8.85\times10^{-14}}{500\times10^{-8}}=7.08\times10^{-8}\) F/cm²

1 cm² = \(\frac{10^8}{645}\) mil²

\(\rm C_{ox}=7.08\times10^{-8}\frac{F}{\frac{10^8}{645}\ mil^2}=4.5\times10^{-13}\) F/mil²

= 0.4 pF/mil²