The experimental C-V characteristic shown in Figure 4 was observed under the fol

Question

The experimental C-V characteristic shown in Figure 4 was observed under the following conditions: The d.c. bias was changed very slowly from point (1) to point (2). At point (2) the VG sweep rate was increased substantially. Upon arriving at point (3) the sweep was stopped and the capacitance decayed to point (4). Qualitatively explain the observed characteristic.

The experimental C-V characteristic shown in Figure 4 was observed under the following conditions: The d.c. bias was changed very slowly from point (1) to point (2). At point (2) the VG sweep rete was increased substantially. Upon arriving at point (3) the sweep was stopped and the capacitance decayed to point (4). Qualitatively explain the observed characteristic. Figure 4

Explanation / Answer

Most likely these are the C-V characteristics of MOS Capacitor with n type substrate.

At point 1 positive bias is applied and the MOS Capacitor is in accumulation region. Now from point 1 to point 2 sweep rate was varied slowly. Now at slow sweep rate gate voltage is going from positve to negative, that means capacitor is going from accumulation to depletion region. Under slow bias the depletion charge will respond to the slowly varying potential, therefore there will not be suddent change in capacitance.

Now from point 2 to point 3 potential has been changed fastly and in this region Capacitor is under inversion region, therefore minority carriers in the channel will not respond to fast varying poteintial and Capacitance will degrade fast.

Now if bias is stoped at point 4 that means potential is not varying, that means all carriers shoul respond and capacitance shoul increse.

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