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Quiz and Homework

Quiz

1. Which of the following  is NOT  true ?

A. QOX is a function of applied gate voltage
B. Threshold voltage is a function of tox.
C. P+Poly silicon gate is usually  used for n-MOS capacitor.
D. Once the threshold condition occurs, Qd (=the depletion charge) is  not  increased any more with Vgs.

2. Which of the following is correct ?

A. There is no electric field in the oxide in an equilibrated MOS capacitor.
B. For the threshold, Qch and Qd > 0 in an n-MOS capacitor.
C. In a flat-band condition, the surface potential Ys = 0
D. In accumulation, the depletion takes place in the silicon surface.

3. Which of the following is incorrect ?

An n-MOS (p-type) capacitor,

A. In  flat-band condition, |Qg| = |Qox|, Qch = 0
B. In threshold condition, |Qg| + |Qox| = |Qch + Qb|
C. In flat-band condition, Qb = 0, Qch = 0
D. In threshold condition, |Qg + Qox| = |Qch|, Qb = 0

Homework

1. Once the inversion condition occurs, there is no further increase of either the depletion layer width or the depletion charge. Explain the reason of this phenomenon.

2. In a MOS capacitor, the threshold is defined when Ys (surface potential) = 2YB (where YB is X= Ei-Ef value in the applet). (In fact, the condition is referred to as the strong inversion case in a MOS device. And thus, a threshold voltage for actual device has some deviation to that of a MOS capacitor, and commonly it is measured by given conditions from the manufacturer ). In an n-MOS capacitor (i.e. p-type MOS capacitor), if Na =1 x 1015cm-3 , and Al gate tox = 100A, ni = 1.45 x 10 10cm -3, calculate Ys & YB for the threshold. (Hint , Na= ni e (Ei-Ef)/kT at T = 300 K)

3. In an n-MOS capacitor, the depletion layer width is Wd = (2 esi Ys /qNa)1/2 . If the threshold condition occurs, the depletion layer width will reach its maximum value (Wdmax). Derive an equation for Wdmax at Ys = 2YB , and find the value for Wdmax using the same values for ni, Na and T in Question 2.