ENEE 313, Spr. ’09 Quiz IX - May 6, 2009Name:1. In class we studied metal-oxide-semiconductor (MOS) structures with p-type semiconductors,which are used to m ake NMOS (n-channel) devices. For PMOS (p-channel) devices, an n-type bulk is used.The Figure shows the band diagram of a MOS system with the n-type bulk in equilibrium.We would need to apply some positive voltage between the metal and semiconductor sides(i.e. the metal side more positive) to obtain flat-band conditions in this case.(a) (5 pts.) Draw the band diagram of this systemin accumulation (majority carriers of the semi-conductor bulk are accumulated near the sur-face). Do we need to apply positive or negativepotential to the metal side relative to the bulk toobtain this condition? Hint: Identify majorityand minority carriers first.(b) (5 pts.) Draw the band diagram of this sys-tem in strong inversion (minority carriers ofthe semiconductor bulk become majority nearthe surface). What polarity potential should beapplied to the metal side relative to the semicon-ductor to obtain this condition?(Turn over for the last question.)12. The PMOS conducts current when there is a p-type channel between the p-type source andp-type drain.(a) (4 pts) In the device cross-section figure below, indicate the gate, gate oxide, source,drain and, the channel region. Mark the doping of the different regions if this device isa PMOS.(b) (3 pts) Which of the two conditions in Question 1 means conduction is possible betweenthe source and the drain?(c) (3 pts) Based on your answer to part 2.b), is the threshold voltage for a PMOS positiveor
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