EE245 Homework 2

Due 9/16/01


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  1. How small a diameter of silicon wire will support your weight? (note- if you don't feel comfortable revealing your weight on a homework assignmnet: lie).  Assume E=150GPa and a strain limit of 1% 
  2. Spider silk has a Young's modulus of around 60 GPa, and a strain limit of nearly 30%.  What diameter of silk will support the weight of a 1 gram spider?.
  3. Your 1 gram spider extrudes a silk thread with a 1 square micron cross-section (actual spider silk varies from around 1 to 10 microns in diameter). If she uses ten percent of her body volume (assume a body volume of 10mm^3, a pretty small spider) to make silk, how long of a thread can she make before she runs out?
  4. How long of a thread can you hang in a 1 gravity field before it breaks under its own weight?  Write your answer in terms of material properties. 
  5. Go to the MEMS Clearinghouse at ISI (mems.isi.edu).  Click on "materials" and find the Young's modulus of bulk aluminum and the range of the modulus thin film aluminum.
  6. A MEMS accelerometer has a polysilicon strain gauge with a gauge factor of -20 used in a Wheatstone bridge with only one active resistor.  Assuming that the polysilicon will break at a strain of +/-1%, and that there is a 1 volt excitation on the bridge, calculate the minimum and maximum possible output voltage from the bridge.
  7. A MEMS accelerometer has a capacitive readout used in a one-active Wheatstone bridge with a 1 volt excitation.  Assuming that there are travel limits that constrain the accelerometer to move no more than half the initial gap in each direction, calculate the min and max output voltage.
  8. Calculate the sheet resistance of a 1 micron thick aluminum layer.  Calculate the resistance of a 1 mm long, 1 micron wide wire on this layer.
  9. Estimate the total length of wire on a modern microprocessor, assuming dense wiring, 10 levels of wiring, and half-micron line/space on each layer.
  10. Download sugar and run it using the info here.  How long did it take you, and did you have any trouble? 


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(K. Pister)