VLSI Design Questions and Answers - Sheet Resistance of MOS Transistors and Inverters

1. Compute the sheet resistance of a 0.17 µm thick Cu wire if resistivity of Cu wire is 1.7 µΩ-cm.
a) 0.01 Ω/square
b) 0.001 Ω/square
c) 10.0 Ω/square
d) 0.10 Ω/square

Answer: d
Explanation: Sheet resistance of copper is = (1.7*10-8)/(0.17*10-6)=0.10 Ω/square.

2. For semiconductors doped through diffusion or through surface peaked ion implantation we derive the sheet resistance as ___________
a) Average resistivity of semiconductor/thickness
b) Resistivity/thickness
c) Conductivity/thickness
d) None of the mentioned

Answer: a
Explanation: For semiconductors doped through diffusion or through surface peaked ion implantation we derive the sheet resistance using the average resistivity of the material.

3. Sheet resistance of a semiconductor is ___________
a) Inherent property of the material
b) Function of thickness of the material
c) Also called as Specific Resistance
d) All of the mentioned

Answer: b
Explanation: Resistivity is the inherent property of any conducting material. It is also called Specific Resistance. Sheet resistance is function of thickness as resistivity for a material is fixed.

4. Sheet resistance of semiconductor is directly measured using ___________
a) Ohmmeter
b) Four point probe measurement
c) Non-contact eddy current based testing device
d) Any of the mentioned

Answer: b
Explanation: Sheet resistance of semiconductor is directly measured using Four point probe measurement.

5. The resistance of the semiconductor material is 800Ω. The sheet resistance if the dimensions of the material is 0.125µm wide and 1 mm long is?
a) 10 Ω/square
b) 0.01 Ω/square
c) 0.10 Ω/square
d) 1 Ω/square

Answer: c
Explanation: We know that R=Rs(L/W).
Therefore Rs=R x W/L
Substituting the values of R, W and L, Rs is found to be 0.10 Ω/square.

6. The typical values of sheet resistance for the n-well semiconductor is ____________
a) 1-5 KΩ/square
b) 10-50 KΩ/square
c) 1-5 Ω/square
d) 100-500 Ω/square

Answer: a
Explanation: The n-well semiconductors have high sheet resistance in the range of 1-5 KΩ/square.

7. The typical values of sheet resistance for polysilicon semiconductor is?
a) 15-30 Ω/square
b) 150-300 Ω/square
c) 1.5-3 KΩ/square
d) 0.15-0.3 Ω/square

Answer: a
Explanation: The typical values of polysilicon semiconductor is 15-30 Ω/square.

8. For λ based design, what is the standard unit of capacitance, (λ=5µm)?
a) 0.01pF
b) 0.0032pF
c) 0.0023pF
d) All of the mentioned

Answer: a
Explanation: 5 µm x 5 µm x 4 pF x 10-4/µm2 = 0.01pF.

9. If standard area is 2λ x 2λ, then the standard capacitance of a gate of length 30λ and width 6λ is?
a) 180oCg
b) 45oCg
c) 90oCg
d) 4oCg

Answer: b
Explanation: 30λ x 6λ/2λ x 2λ = 45 oCg.

10. Which of the following mainly constitutes the output node capacitance?
a) Inter electrode capacitance
b) Stray capacitance
c) Junction Parasitic capacitance
d) All of the mentioned

Answer: c
Explanation: Output node capacitance mainly consists of junction parasitic capacitance