The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Modeling >> Semiconductor Devices >> Vt vs. Length of MOS
https://designers-guide.org/forum/YaBB.pl?num=1164621927

Message started by RDCam on Nov 27^th, 2006, 2:05am

Title: Vt vs. Length of MOS
Post by RDCam on Nov 27^th, 2006, 2:05am

I noticed the trend of Vt (threshold voltage) Vs. Length (um) for the low-vt nchannel MOS transistors in recent sub-micron technologies has changed. Previously the Vt for shorter channel lengths would be lower, but now it seems significantly higher cmopared to longer channel(>2u). The gradient of the Vt Vs L curve for L <~1.5u is very high. Are there any process experts who can explain this ? Will greatly appreciate any clarification on something that has been bugging me for a few months already!

Title: Re: Vt vs. Length of MOS
Post by ACWWong on Nov 27^th, 2006, 7:27am

Perhaps you are seeing the "Reverse-short-channel effect" which is an increasing vth with decreasing L to a peak, before vth again decrease at very short channels.... perhaps your vth vs L hump is just under 1.5um.

Try looking at something Tsividis "the MOS transistor" or googling it.

Title: Re: Vt vs. Length of MOS
Post by RDCam on Nov 28^th, 2006, 3:43am

The keyword RSCE is exactly what I was looking for. Once I could label the phenomenon I am able to find literature on it ! Thanks a lot.

Title: Re: Vt vs. Length of MOS
Post by Croaker on Nov 28^th, 2006, 8:36am

Basically it has something to do with the way the p-dopant diffuses, creating a higher Vth, even though Vth should be getting lower with channel-length.

Please post a link to any good explanatory page about this.