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How is Vth defined? (Read 2995 times)

fran2k5

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How is Vth defined?
Aug 07^th, 2007, 8:04am

Hi everybody,

recently I was performing some simple simulations of a single device in a 0.25um technology.
I wanted to check the variation of Vth with L keeping the same W.
I was quite surprised to notice that Vth decreases for longer transistors.
Could anybody help me out to interpret such results? I believe that the behavior should be opposite...
To check the Vth I use the "op" function of the calculator. How is this Vth defined? Does it correspond to the BSIM one?

Thank you very much,

fran2k5

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vivkr Community Fellow Offline Posts: 780	Re: How is Vth defined? Reply #1 - Aug 7^th, 2007, 11:10pm Hi Frank, Does the Vth first increase when you increase the channel length, and then start to fall off after a certain point? If yes, then you are seeing reverse short channel effect. If not, then I could not say what the cause might be. Try searching for reverse short channel effect on the web for more. Regards Vivek
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fran2k5 Junior Member Offline Posts: 29	Re: How is Vth defined? Reply #2 - Aug 8^th, 2007, 5:38am Thank you Vivek. I believe you are right. It seems that RSCE is predominant. The fact that the short-channel effect is evident in the sub-threshold Ids-Vds curves does not really mean that the threshold voltage has to decrease. Regards, frank
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