Threshold voltage of the transistor. Why is it different?

Dear all,

I have some quesitons about the threshold voltage of the CMOS. I hope anyone could answer it. Thanks first. :)

For the same circuit configuration (common source) and under same bias voltage and same aspect ratio of the two NMOS (one is 10/1 and second one is 100/10), why the threshold voltage of the 100/10 is higher than 10/1 ? Actually, there Vsb = 0 in two case.

Thanks

wccheng

Reason of Channel-Body voltages are different so Vt are different of two transistor.For more information look at page 106-111 in the book of Yannis Tsividis, Operation And Modelling of MOS Transistor, 2nd Edition.