The increase in dielectric constant results in enhanced gate oxide capacitance and hence better gate control

Dear Sandeep Prabhu M sir,

I agree with you that increase in gate oxide capacitance will decrease off current but is there any mathematical relation which can be added as a proof.

Dear Sandeep Prabhu M sir,

I have one more doubt. Does increased gate oxide capacitance will increase the on-current or not?

Increased on-current

Thank you Sandeep Prabhu M sir.

Dear Amit Das ,

welcome!

Increasing the gate capacitance will increase both the on and off current of the transistor. The current in the transistor will not be equal zero at the threshold voltage because of the subthreshold current. As the capacitance increases the channel will be weakly inverted even before reaching the threshold voltage conditions where it is assumed that the full inversion will occur at a minority carrier concentration under inversion equal to the bulk majority concentration.

You need only to refer to the MOSFET theory under the threshold condition or the weak inversion. One of the major books is the semicondcutor devices physics by S M Sze.

Thank you Abdelhalim abdelnaby Zekry sir.

Can you please explain this line "As the capacitance increases the channel will be weakly inverted even before reaching the threshold voltage conditions"?

I mean how increase in capacitance will make the channel weakly inverted.

Dear Amit Das

The expression may not be very precise. May be more precise expression is that at any capacitance value the MOSFET will be weakly inverted before it reaches the condition of strong inversion assumed to occur at the on set of conduction at the cut off point. Therefore the cut off is some imposed condition which is not true since the transistor must pass through the weak and medium inversion before it reaches to the start of the strong inversion. Thereforeو there will be subthreshold current in any value of the capacitance.

But increasing the capacitance will increase the inversion charges at any inversion level. And therefore the transistor current will increase at any inversion level because of increasing the capacitance. In my previous statement there may may be overlap in the effects.

Thank you for your question.

You motivated me to precise my answer.

Got it Abdelhalim abdelnaby Zekry sir, thanks for the explanation.

The increase in dielectric constant results in better gate control due to increased gate oxide capacitance.

Sandeep Prabhu M Sir, can you please clarify the physics behind increase in gate capacitance with dielectric constant?

Increasing the gate capacitance will increase both the on and off current of the transistor. The current in the transistor will not be equal zero at the threshold voltage because of the subthreshold current. As the capacitance increases the channel will be weakly inverted even before reaching the threshold voltage conditions where it is assumed that the full inversion will occur at a minority carrier concentration under inversion equal to the bulk majority concentration.