About VT(threshold voltage) of MOS

[xhwubai]

Homework Statement

(1)what's the relationship between VT and channel length, width?
(2)In the formula of VT, when calculation of oxide capacitor voltage, namely, Vox=Q(inv)/Cox
, why Cox is per square capacitance?

Homework Equations

3. Thank you very much!

 

[runo]

1)-The relationship between Vt and the channel length is called short channel effect. If you search on the web you can find enough information. The third term in your equation needs a modification to see the relation between Vt and L.
2)- Cox's units can be modified depend on the units of the charges density. The aim is to get volts out of the devision.

 

[kerimek]

Regarding the threshold voltage (VT) of a metal-oxide-semiconductor (MOS) device, there are several important relationships to consider.

(1) The relationship between VT and channel length and width is known as the scaling effect. As the channel length decreases, the threshold voltage also decreases. This can be explained by the increased electric field in the channel due to the reduced distance between the source and drain. Similarly, as the channel width increases, the threshold voltage also decreases due to the increased number of carriers in the channel. This relationship is important in determining the performance and characteristics of MOS devices as they are scaled down in size.

(2) In the formula for VT, the oxide capacitance (Cox) is typically expressed as per square capacitance. This is because the oxide capacitance is dependent on the dimensions of the MOS device, particularly the area of the oxide layer. By expressing it as per square capacitance, it allows for easier comparison and analysis of different MOS devices with varying dimensions. Additionally, this allows for the use of scaling rules to accurately predict the performance of MOS devices as they are scaled down in size.

I hope this helps clarify the relationship between VT and channel length and width, as well as the use of per square capacitance in the formula for VT. Please let me know if you have any further questions.