18. MOS Capacitor a) Derive or state the gate-voltage relationship of the MOS capacity. b) In inversion we find two charge types on the semiconductor side, describe their origin. Which ones are fixed, which ones are mobile? Draw the band-diagram, and Charge- VS.-device cross-section. Draw qualitatively the amount and location (within the band-diagram) of these charges. c) Is the threshold voltage (Vt) above or below zero for an N-type silicon MOS capacitor? State at least 2 mechanisms how the Vt can be altered