Which of these statements are true (multiple)? 1. At equilibrium, in an ideal MO

Question

Which of these statements are true (multiple)?

1. At equilibrium, in an ideal MOS structure, the bands within a semiconductor are always flat.
2. The sum of all the charges across the MOS capacitor is always equal to zero.
3. The effect of a surface charge sheet layer in oxide, if present at the Gate-Oxide interface would be much more pronounced than if the surface charge layer present at the Oxide-semiconductor (substrate) interface.
4. At high frequencies, the minority charge carriers do not have enough time to drift up to the inversion layer and thus the depletion layer remains devoid of mobile charges and the capacitance remains at a minimum.
5. If ms is greater than zero, then the bands with the semiconductor bend downwards at thermal equilibrium assuming no interface charges.
6. The surface potential (band bending) reaches a maximum at 2fp or 2fn. Thereafter, the minority carrier concentration increases exponentially as a function of applied bias on the gate.
7. The presence of interface charges Qss’ preferentially lowers the threshold voltage of PMOS as compared to that of NMOS.
8. The maximum depletion layer charge increases as square root of the doping concentration of semiconductors.
9. The inversion charge density is a function of the gate oxide capacitance and the “excess” gate voltage above the threshold value.
10. It is possible to determine the mobility of the carriers by plotting ID as a function of VGS. However, VDS needs to be very small.
11. The effect of source substrate biasis to increase the stored charge in the inversion layer and therefore increase the threshold voltage. Depending upon the polarity of the applied bias the threshold voltage can increase or decrease.
12. Current can flow between the source and the drain for electric fields slightly less than the threshold voltage. Such current is found to an exponential function of VGS.
13. Channel length modulation arises due to the depletion regions of the source and drain overlapping in the channel region and therefore the current begins to increase as a function of drain voltage.
14. Short channel effect results in the lowering of the threshold voltage once the transistors channel length is less than 2 m. It is most significant in highly doped substrates.
15. Threshold voltage shift due to short channel effect can be minimized by using very shallow junctions for the source and the drain regions.
16. Velocity saturation occurs because carriers in the semiconductor approach thermal velocity at which point the mobility becomes a meaningless concept.

Explanation / Answer

1- True( Since in Ideal MOS Cap Metal Substrate Work Function Difference is 0).

2- True( Since No conduction current flows, Sum of charges will be 0)

3- True

4- True

5- False( Bands will bend upwards)

6- True

7- True

8- True

9- True

10- True( From Maximum Transconductance mobility can be extracted).

11- True( Body Effect)

12-True( Subthreshold Current)

13- True

14-False( True for channel length less than 90 nm)

15- True

16- True.

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