Silvaco -threshold voltage

[kalaiselvik]

Sir/Madam

This statement is used in design of dgmosfet tutorial -6 to find vt in silvaco tool (progrm in Enginering technology and society you tube channel)
Actually vt is the Vgs value at which device is on.from the graph device is on when vgs is 0.7v. (image attached)
but below statement is used to find vt & mentioned y.val=-7. i dont understand the statement & why y=-7
& why going to log scale.

extract name="vt1" x.val from curve ((v."gate") ,log10(abs(i."drain"))) where y.val=-7

can any one help me

Thank you

 

[dick_freebird]

There are multiple "VT" measurement methods.
The classical is the X intercept of sqrt(Id) but you
may also find current-per-square methods or
even simple arbitrary current ID@VG. Looks like
here the target is the last, on log scale (which is
irrelevant, it could as easily be looking for 1E-7
plain current).