As we have seen earlier, there is an oxide layer below Gate terminal. Since oxide is a very good insulator, it contributes to an oxide capacitance in the circuit. Normally, the capacitance value of a capacitor doesn't change with values of voltage applied across its terminals. However, this is not the case with MOS capacitor. We find that the capacitance of MOS capacitor changes its value with the variation in Gate voltage. This is because application of gate voltage results in the band bending of silicon substrate and hence variation in charge concentration at Si-SiO2 interface. Also we can see (from fig.3.42 ) that the curve splits into two (reason will be explained later), after a certain voltage, depending upon the frequency (high or low) of AC voltage applied at the gate. This voltage is called the threshold voltage(Vth) of MOS capacitor.
curve splits into two (reason will be explained later), after a certain voltage, depending upon the frequency (high or low) of AC voltage applied at the gate. This voltage is called the threshold voltage (V
