GATE EC 2012 Set 1 Q50 — BJT and MOSFET Amplifiers

In the three dimensional view of a silicon n-channel MOS transistor shown below, $\delta=20\:nm$. The transistor is of width $1\: \mu m$. The depletion width formed at every p-n junction is $10\:nm$. The relative permittivities of $Si$ and $SiO_2$, respectively, are $11.7$ and $3.9$, and $\varepsilon_0=8.9 \times 10^{-12} \: F/m$.

The gate-source overlap capacitance is approximately