# About VT(threshold voltage) of MOS

• xhwubai
In summary, the relationship between Vt and channel length is known as short channel effect and can be found by researching online. Modification is needed to see the relation between Vt and L in the third term of the equation for Vox. Cox's units can be modified to obtain volts from the division, depending on the units of the charges density.
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!

#### Attachments

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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.

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.

## 1. What is VT (threshold voltage) of MOS?

The threshold voltage (VT) of a MOS (metal-oxide-semiconductor) device refers to the minimum voltage required for the device to start conducting current. It is typically measured between the gate and source terminals.

## 2. How is VT determined?

VT is determined by the properties of the materials used in the MOS device, such as the thickness and type of oxide layer and the doping levels of the semiconductor. It can also be affected by external factors such as temperature and applied voltage.

## 3. What is the significance of VT in MOS devices?

The threshold voltage is a critical parameter in MOS devices as it determines the device's on/off state and influences its performance. It also affects the device's power consumption and switching speed.

## 4. How does VT differ between NMOS and PMOS devices?

In NMOS (n-channel MOS) devices, the threshold voltage is typically positive, while in PMOS (p-channel MOS) devices, it is typically negative. This is due to the different types of doping used in the semiconductor material.

## 5. Can VT be adjusted?

Yes, the threshold voltage of a MOS device can be adjusted by changing the doping levels in the semiconductor material or by altering the properties of the oxide layer. This can be done during the manufacturing process or through external biasing techniques.

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