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Unformatted text preview: ENGRI 1110 Homework #2 Due Monday, September 29, 2008 NOTE: In order to make grading the homework assignments of such a large class manageable, please start your answer to each new question on a new page. In order to minimize the waste of paper, feel free to use scrap paper that has already been printed on one side. 1. A p-n junction is formed using p-doped and n-doped silicon. a) Draw the shape of the band diagram (showing both the conduction and valence bands) from one side of the junction to the other with no applied bias. b) Show the direction of electron flow when the junction is forward biased. c) Discuss BRIEFLY how the shape of the bands is important to changes in the electron flow when the temperature increases during forward bias. (5) a) no bias (5) b) forward bias (5) c) The slope of the bending between the bands (connecting the p and the n type regions) decreases when the junction is in a forward bias. This decrease in barrier height, along with increased energy (from higher temperature), allows easier flow of electrons. However the total current in forward bias depends also on how many of the electrons flowing over the barrier recombine with holes as they do so, and it turns out that the increase in total current with increasing temperature is not that large. 2. (10) Describe the pros and cons of various metals used in interconnects. Metal Pros Cons Silver Good Conductivity Electromigration, Diffuses into Si Aluminu m Good Conductivity Electromigration Tungsten High Melting Temp- Stable High Resistance Copper Excellent Conductivity Diffuses into Si 3. (10) A metal line needs to be fabricated on top of a silicon wafer using photolithography....
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