Why does L changes as a function of frequency?
Physically L (inductance) should decrease as a function of frequency since at higher frequencies internal inductance decreases as the magnetic field is prevented from penetrating the volume of conductors reducing the inductance to its asymptotic external limit. But when you observe the pi parameters for a high Q inductor, you will notice that inductance increases near the self-resonant frequency before changing sign as you cross the self-resonant frequency. For a low Q inductor the inductance decreases monotonically. This effect is caused by the capacitance in shunt with the inductor. This capacitor has two components, a high-Q coupling capacitance through the air/oxide and a low-Q substrate capacitance. This capacitance eventually resonates the inductance and thus beyond self resonance the reactance becomes negative, or simply capacitive. Before self-resonance, though, the reactance of a high-Q structure peaks and close to self-resonance the imaginary part of the reactance divided by
