Forum › Category: Layout › What is Channel length and Channel Length Modulation?
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AvatarVLSI Master asked 5 months ago
I learned that the channel length in a MOSFET is the distance between the source and drain junctions under the gate. You see, it determines how the device performs. Channel length modulation happens when the channel length changes slightly due to high drain voltages. This affects the current flow and can cause the MOSFET to behave differently than expected. Channel-length modulation, also known as the Early effect, is an important phenomenon in Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). What is channel length
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AvatarDigitalWorld answered 5 months ago

You can think of the channel length as the distance electrons travel from the source to the drain in a MOSFET. Channel length modulation occurs when this distance changes due to high drain voltages. I noticed that this effect makes the current increase a bit more than expected, even when the MOSFET is supposed to be in saturation.

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AvatarTechGuru answered 5 months ago

We often look at the channel length as the critical dimension in a MOSFET. It's the part under the gate that allows current to flow from the source to the drain. With channel length modulation, the effective length shortens when you have a high drain voltage. This shortening makes the current increase slightly, which can alter the expected behavior of the MOSFET in the saturation region.

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Avatarsemiconductor answered 5 months ago

What is the effect of channel length modulation?

When we see a decrease in the effective length of the channel in a MOSFET, the resistance of the channel also decreases. This causes an increase in the drain current (Ids). Because the resistance is proportional to the length of the channel, you will notice that the output resistance of the NMOS device is marginally decreased as well. You can see this effect clearly in the drain current equation for a MOS device in the saturation region. The reduction in the channel length leads to a higher current. This equation can be rearranged using the parameter lambda (λ), making the transconductance (gm) equation more complex. We consider channel-length modulation a "short-channel effect." It becomes more relevant with new advanced nodes that have shorter MOSFET lengths. Channel-length modulation intensifies when the source-to-drain separation is shorter, the drain junction is deeper, and the oxide insulator is thicker.