Mosfet equation: Qinv

[lufer17]

Hello everyone, according to the book SILICON-ON-INSULATOR TECHNOLOGY: MATERIALS TO VLSI 3rd Edition says the equation:

VG1=ΦMS1-((Qox1)/(Cox1))+(1+((Csi1)/(Cox1)))*Φs1-((Csi1)/(Cox1))*Φs2-((((1)/(2))*Qdepl+Qinv)/(Cox1))

Qdepl = - q*Na*tsi


As far as Qinv was not found on the internet, and in books the equation.
My question is - is this Qinv given (value entered in manufacturer, for example) or is there an equation?
If so, what is the equation?

 

[timof]

This equation expresses a general relationship between voltages, charges, capacitances, and other parameters of the MOS structure.
Qinv in the inversion layer charge. It depends on applied gate voltage, which is exactly reflected in this equation.

 

[dick_freebird]

Qdepl is how much charge to negate the doping at the surface.
That is a pretty straightforward thing.

Qinv is the additional charge to then invert the same region,
but how much? That's "squishier" and yet the more interesting,
as it goes right to channel conduction strength. Because it's
whatever you want it to be, good luck getting a simple answer.
It involves conditions that need specified to get a number, or
you have to carry the variable along with the formula until
-somebody- does.