What's the relationship between Vth and L valued in a MOS transistor?

[diemilio]

Hi everyone!!!

I know that there's an important dependence between Vth and the value of L in a MOS transistor. Choosing the right value of L in a design is critical for having small vth variations. Eventhought I know this, I haven't been able to find how are this to values related!!! Could someone explain this to me, or tell me where kind I find this information???

Thanks for your help,

diemilio

 

[dachuan315]

Re: vth dependence

you must run the Vth--L function by HSPICE.
because different model is different.

 

[diemilio]

Re: vth dependence

Hello dachuan315,

Thanks for your reply. I already did that and I also selected the Lmin I need to use in my design to minimize vth process variations. What I really want to know is: why does the vth vs L graph looks like it does!!!??? Why does vth decreases exponentially as L increases?? What's the physical explanation for this behaivour???

Thanks for your help,


diemilio

 

[srieda]

Re: vth dependence

Why does vth decreases exponentially as L increases??

i thought, vth decreases when L decreases!! This can be attributed to the DIBL (Drain Induced Barrier Lowering) effect.

 

[diemilio]

Re: vth dependence

Hi srieda,

Thanks for your post. I know that there's a region where Vth increases as L increases (due to short channel effects), but then it actually starts decreasing (figure w1). The really important part of the graph is when it decreases (and stabilizes) because at those points vth is less susceptible to process variations.

How can I explain this decreasing effect??

thank you,

diemilio

 

[al_valaee]

Re: vth dependence

Hi
you can find it in "analysis and design of analog integerated circuts"by gray,hursr,lewis,meyer