hw_6_sol - Homework 6 Solutions 7.3. For the transistor of...

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Homework 6 Solutions 7.3. For the transistor of Figure P7.1, by how much should the gate voltage be changed to produce inversion? Threshold? Assume half the applied voltage appears across the oxide and half across the semiconductor. If the device in the figure is at equilibrium, is this an enhancement or a depletion FET? We need to bend the bands in the Si by an additional 0.1 eV to just invert the surface, meaning the gate voltage should be increased by 2 × 0.1=0.2V. To produce threshold, the surface should be inverted by 0.3 eV, requiring another 0.3eV of band bending or 0.6V. Thus the change in gate voltage required to reach threshold if 0.6+0.2=0.8V. As no channel exists at equilibrium, this is an enhancement device. 7.4. For each of the transistors of Figure 7.10, a) What is the polarity of the threshold voltage V T ? b) What is the polarity of V DS that should be used? c) When V GS =0 (equilibrium), is the transistor on or off? d) Is the current I D carried by electrons or holes? e) For V GS > V T , is the current I D carried primarily by drift or diffusion? Enhancement NFET Enhancement PFET Depletion NFET Depletion PFET V T Positive Negative Negative Positive V DS Positive Negative Positive Negative V GS =0 Off Off On On Carriers Electrons
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This note was uploaded on 01/11/2012 for the course ECE 432 taught by Professor Lu during the Fall '08 term at Ohio State.

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hw_6_sol - Homework 6 Solutions 7.3. For the transistor of...

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