hw15_solutions - ECE 440 Homework XV Solutions Spring 2006...

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ECE 440 Homework XV Solutions Spring 2006 1. Aluminum and polysilicon are commonly used as gate metals for the MOS structure in silicon. Assume that platinum is used as the gate metal. Reconstruct a diagram similar to Figure 6-17 showing the variation of the metal-semiconductor work function potential difference Φ ms with substrate doping concentration. The work function of Pt is 5.7 V and the electron affinity of silicon is 4.0 V. Show your work and draw to scale with accuracy. For n-type Si : Taking the difference between the metal work function and the semiconductor work function, we obtain: By diving both sides of the equation by the charge of an electron (q), the difference of the work functions can be expressed in terms of volts (as opposed to electron volts). For p-type Si : An identical procedure can be followed to find the difference in the work functions of the metal and p-type Silicon.
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Therefore, the final expression is and the corresponding plot is .
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2. (a) Find the voltage V FB required to reduce to zero the negative charge induced at the semiconductor surface by a sheet of positive charge Q ox located x’ below the metal. Here is a diagram of the situation: The positive charge located at x’ below the metal in the oxide induces negative charges at both the metal surface and the semiconductor surface. Needless to say, the negative induced
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This note was uploaded on 12/01/2011 for the course ECE 340 taught by Professor Leburton during the Spring '11 term at University of Illinois, Urbana Champaign.

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hw15_solutions - ECE 440 Homework XV Solutions Spring 2006...

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