# VLSI Questions and Answers – Submicron CMOS

This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “Submicron CMOS”.

1. Submicron CMOS technology is
a) faster
b) slower
c) large
d) slow and large

Explanation: Submicron CMOS technology is faster small and device dimensions are closely interrelated.

2. In CMOS devices, which has slower performance?
a) n-transistor
b) p-transistor
c) all of the mentioned
d) none of the mentioned

Explanation: In CMOS devices, p-transistors have inherently slower performance than similar n-transistors and this is due to lower mobility of holes compared with that of the electrons.

3. As the channel length is scaled down, influence of mobility
a) increases
b) decreases
c) remains the same
d) does not affect

Explanation: As the channel lengths are scaled down, the influence of mobility starts to diminish as the effects of velocity saturation begin to be felt.

4. Current drive is ______ to mobility.
a) directly proportional
b) inversely proportional
c) logarithmically proportional
d) exponentially proportional

Explanation: Current drive is directly proportional to mobility and inversely proportional to the channel length L.

5. When velocity saturation occurs, Idsat is ______ to Vsat.
a) inversely proportional
b) directly proportional
c) logarithmically proportional
d) not related

Explanation: When velocity saturation occurs, drive current saturation Idsat is directly related to saturation velocity. It is given as Idsat = W*Cox*Vsat*(Vgs-Vt).
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6. Current is dependent on ________ when saturation velocity occurs.
a) mobility
b) channel length
c) saturation velocity
d) transconductance

Explanation: When saturation velocity occurs, current becomes independent of mobility and the channel length and it is dependent on only saturation velocity.

7. Transconductance is independent of
a) channel width
b) channel length
c) material
d) channel depth

Explanation: Transconductance is a constant and it independent of the channel length. Current is independent of mobility and channel length.

8. Velocity saturation occurs at
a) lower electric field strength in n-devices
b) higher electric field strength
c) intermittent electric field strength
d) lower electric field strength in p-devices

Explanation: Velocity saturation occurs at lower electric field strengths in n-devices owing to their higher mobility when compared with p-devices.

9. When dimensions are scaled down ______ tends to a constant value.
a) current drive from p-transistors
b) current drive from n-transistors
c) voltage drive from p-transistors
d) voltage drive from n-transistors

Explanation: When dimensions are scaled down, current drive from n-transistors tends to a constant value independent of channel length.

10. At ______ length, the holes start to run into velocity saturation.
a) shorter
b) larger
c) all of the mentioned
d) none of the mentioned

Explanation: At shorter length, the holes start to run into velocity saturation and the current drive from p-transistors does not tend to a constant value.

11. ______ technology is used to provide for faster devices.
a) silicon based FET technology
b) silicon based MOS technology
c) gallium arsenide based MOS technology
d) gallium arsenide based VLSI technology

Explanation: Gallium arsenide based VLSI technology is used to provide for the faster devices which will be required as the sophistication of our system design capabilities.

12. Silicon logic is faster than gallium arsenide.
a) true
b) false

Explanation: Silicon logic has speed limitations that are becoming apparent in the state-of-the-art fast digital system design.

13. ________ is used with silicon to satisfy the need for very high speed integrated technology.
a) gallium oxide
b) gallium arsenide
c) silicon dioxide
d) aluminium

Explanation: Gallium arsenide is used in conjunction with silicon to satisfy the need for very high speed integrated technology (VHSI) in many new systems.

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