GE-108
MOS-CAP and MOSFET-Tutorial
IIT Ropar
1. Solve problem 16.7, 16.9 (a-e) of RF Pierret.
2. Solve problem 16.11 (a-b) of RF Pierret.
3. Practice solved exercise 16.3 (pg. 583) of RF Pierret.
4. Plot the C-V of MOS-CAP with p-substrate and n-substrate at high and low frequency, as-
sume the flat-band condition at equilibrium.
5. In a MOS capacitor take a p-type semiconductor with (i) ϕm > ϕs and (ii) ϕs > ϕm . Plot the
band diagram in equilibrium, accumulation and strong and weak inversion in both the cases.
Now take a MOS-CAP with n-type semiconductor for (iii) ϕm > ϕs and (iv) ϕs > ϕs . Plot
the band diagram in equilibrium, accumulation, strong and weak inversion specifying the gate-
voltage (V g) polarity in each case.
6. For the MOSFET shown below, metal gate is replaced with the highly doped poly-Si gate,
whose Fermi level is 0.1 eV above the conduction band edge. Let W=L=5µm, TOX =300 Å and
µn =550 cm2 /V − s.
(a) Calculate VF B .
Figura 1: Device schematic of the MOSFET.
(b) Calculate threshold voltage VT .
(c) Plot the C − V curve of the device qualitatively.
(d) Draw the C − V curve if the gate material is changed from n+ to p+ (i.e Fermi level is 0.1
eV below the valence band edge) keeping the substrate material p . Also calculate the VT
and VF B .
(e) Draw the C − V curve if the substrate material is changed from n to p type with same
doping concentration keeping the gate as n+ . Also calculate the VT and VF B .
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GE-108
MOS-CAP and MOSFET-Tutorial
IIT Ropar
(f) Draw the band diagram of the device at the flat-band condition.
Hint: Electron affinity of poly-si and si are same. Take band-gap of Si 1.1ev. and T=300K.
7. Explain using the band-diagram how the threshold voltage of a MOSFET shall change when a
body-source voltage VBS is applied to MOSFET. Also derive the expression of threshold voltage
in the presence of VBS . Assume the necessary parameters and state them in the your answer.
