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Design >> Analog Design >> Why Vth decrease with larger channel length in modern CMOS?
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Message started by neoflash on Mar 26^th, 2013, 10:35pm

Title: Why Vth decrease with larger channel length in modern CMOS?
Post by neoflash on Mar 26^th, 2013, 10:35pm

If we plot the Vth versus channel length, we will notice Vth first increase when channel length is close to Lmin, then Vth slowly decreases with larger L.

Why Vth will get smaller with larger L?

Title: Re: Why Vth decrease with larger channel length in modern CMOS?
Post by raja.cedt on Mar 27^th, 2013, 12:45am

Hello,
this indeed depends on the foundry and will not be consistent for all. According to short channel effect when channel length getting smaller and small amount of charge will be created from drain and source diffusion, due to this Vth reduced. So smaller length smaller the vth. To combat this Vth reduction people use pocket hollows in the channel. Ideally this should make Vth flat across all the lengths but some time it might over compensate also, means Vth slightly increase with channel length up to some extent .

Thanks,
Raj.