<P> where V GS (\ displaystyle V_ (\ text (GS))) is gate - to - source bias and V th (\ displaystyle V_ (\ text (th))) is the threshold voltage of the device . </P> <P> According to the basic threshold model, the transistor is turned off, and there is no conduction between drain and source . A more accurate model considers the effect of thermal energy on the Fermi--Dirac distribution of electron energies which allow some of the more energetic electrons at the source to enter the channel and flow to the drain . This results in a subthreshold current that is an exponential function of gate - source voltage . While the current between drain and source should ideally be zero when the transistor is being used as a turned - off switch, there is a weak - inversion current, sometimes called subthreshold leakage . </P> <P> In weak inversion where the source is tied to bulk, the current varies exponentially with V GS (\ displaystyle V_ (\ text (GS))) as given approximately by: </P> <Dl> <Dd> I D ≈ I D0 e V GS − V th n V T, (\ displaystyle I_ (\ text (D)) \ approx I_ (\ text (D0)) e ^ (\ frac (V_ (\ text (GS)) - V_ (\ text (th))) (nV_ (\ text (T)))),) </Dd> </Dl>

Mosfet can be used as voltage controlled capacitor