elmer
It appears he's implying that yield numbers don't reflect the effects of intra-die variation as well as inter-die variation.
I did not understand him so. I believe where he was getting at is there is more and more dies basically functional, but not passing final checks anyway - for the reasons of intra-die variations which just do not allow to sell it.
I try to explain the little I believe to have understood of it for SRAM:
You need six transistors per cell. They might be all working, but you can only use them to store memory if variations of threshold-voltages of the six are within a tolerance. If they are all 0,5 plusminus 0,1, good. If they are all 0,6 plusminus 0,1, good as well. Good so far. But then you have an array of such cells, with maybe each cell working, but variation does not allow using the array because some cells are 0,6 +- 0,1 and some are 0,5 +- 0,1, because there is no common supply voltage to allow for reliable operation of all cells. I am mentioning this (very simplified) example because there was an article posted here today I did not read on after "SRAM is... easy to build" in the first paragraph. You know well threshold voltage is just one parameter. There is many more where variation is a problem.
Maybe Ali could further clarify if i missed where he was getting at.
Oh, and certainly you try to tackle these problems in dfm-conceptializations. :)
K.
|
