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Unformatted text preview: ECE 440 Homework XIII Fall 2008 Due: Monday, Dec. 08, 2008 1. Other than aluminum, polysilicon is another common gate metal for the MOS structure in silicon. By incorporating heavy doping during chemical vapor deposition of polysilicon one can greatly increase the conductivity of the polysilicon metal. Accidentally our engineer has made a mistake and heavily doped the polysilicon to be p-type. Reconstruct a diagram similar to Figure 6-17 showing the variation of the metal-semiconductor work function potential difference ms with substrate doping concentration for p + poly-Si. Assume that the Fermi level of p + polysilicon is at the edge of valence band. Show your work and draw to scale with accuracy. 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 both the metal surface and the semiconductor surface....
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- Spring '09