Case Study 1: Chip Fabrication Cost

Concepts illustrated by this case study

 

· Fabrication Cost

· Fabrication Yield

· Defect Tolerance through Redundancy

 

There are many factors involved in the price of a computer chip. New, smaller technology gives a boost in performance and a drop in required chip area. In the smaller technology, one can either keep the small area or place more hardware on the chip in order to get more functionality. In this case study, we explore how different design decisions involving fabrication technology, area, and redundancy affect the cost of chips.

 

1.1Below table gives the relevant chip statistics that influence the cost of several current chips. In the next few exercises, you will be exploring the effect of different possible design decisions for the IBM Power5.

 

a) What is the yield for the IBM Power5?

b) Why does the IBM Power5 have a lower defect rate than the Niagara and Opteron?

 

1.2It costs $1 billion to build a new fabrication facility. You will be selling a range of chips from that factory, and you need to decide how much capacity to dedicate to each chip. Your Woods chip will be 150 mm 2 and will make a profit of $20 per defect-free chip. Your Markon chip will be 250 mm 2 and will make a profit of $25 per defect-free chip. Your fabrication facility will be identical to that for the Power5. Each wafer has a 300 mm diameter.

 

a) How much profit do you make on each wafer of Woods chip?

b) How much profit do you make on each wafer of Markon chip?

c) Which chip should you produce in this facility?

d) If your demand is 50,000 Woods chips per month and 25,000 Markon chips per month, and your facility can fabricate 150 wafers a month, how many wafers should you make of each chip?

 

Chip	Die size (mm2)	Estimated defect rate (per cm2)	Manufacturing size (nm)	Transistors (millions)
IBM Power5	389	.30	130	276
Sun Niagara	380	.75	90	279
AMD Opteron	199	.75	90	233

 

 

1.3Your colleague at AMD suggests that, since the yield is so poor, you might make chips cheaper if you placed an extra core on the die and only threw out chips on which both processors had failed. We will solve this exercise by viewing the yield as a probability of no defects occurring in a certain area given the defect rate. Calculate probabilities based on each Opteron core separately (this may not be entirely accurate, since the yield equation is based on empirical evidence rather than a mathematical calculation relating the probabilities of finding errors in different portions of the chip).

 

a) What is the probability that a defect will occur on no more than one of the two processor cores?

b) If the old chip cost $20 dollars per chip, what will the cost be of the new chip, taking into account the new area and yield?