<Dd> φ F = (k T q) ln ⁡ (N A N i) (\ displaystyle \ phi _ (F) = \ left ((\ frac (kT) (q)) \ right) \ ln (\ left ((\ frac (N_ (A)) (N_ (i))) \ right))) </Dd> <P> where φ F (\ displaystyle \ phi _ (F)) is half the contact potential, k (\ displaystyle k) is Boltzmann's constant, T (\ displaystyle T) is temperature, q (\ displaystyle q) is the elementary charge, N A (\ displaystyle N_ (A)) is a doping parameter and N i (\ displaystyle N_ (i)) is the intrinsic doping parameter for the substrate . </P> <P> We see that the surface potential has a direct relationship with the temperature . Looking above, that the threshold voltage does not have a direct relationship but is not independent of the effects . This variation is typically between − 4 mV / K and − 2 mV / K depending on doping level . For a change of 30 ° C this results in significant variation from the 500 mV design parameter commonly used for the 90 - nm technology node . </P> <P> Random dopant fluctuation (RDF) is a form of process variation resulting from variation in the implanted impurity concentration . In MOSFET transistors, RDF in the channel region can alter the transistor's properties, especially threshold voltage . In newer process technologies RDF has a larger effect because the total number of dopants is fewer . </P>

Why do p channel enhancement mode mosfet required threshold voltage