AMD has revealed that the 90nm processors it plans to ship in volume in the coming months will use strained silicon, reiterating claims the chipmaker made in April this year that it was planning to implement the technique.
The strained silicon process involves applying a separate material, such as Silicon Germanium, to silicon wafers. The SiGe's atoms are more widely spaced than those in the regular silicon crystal lattice, which 'strains' to align itself with the wider-spaced SiGe lattice. The upshot is more room for electrons to move between the lattice-locked nuclei, improving the semiconductor's electrical properties.
Intel already uses strained silicon for its 90nm processors, as does IBM. The two companies both use SiGe, but IBM also uses silicon-on-insulator technology, which it claims makes strained silicon easier to implement because it can apply the SiGe to the wafer, strain the silicon then remove the SiGe before fabrication. Removing the SiGe means IBM doesn't have to incorporate the material into the structure of its processors, as Intel has had to.
IBM calls its technique Strained Silicon Directly on Insulator (SSDOI). AMD is also an SOI supporter, but it has said it doesn't use the same approach as IBM. AMD staffers have said in the past that its straining is localised to specific components within the processor. That suggests that, unlike IBM's process, AMD's does not involve the removal of the SiGe. That may insulate it from the yield problems IBM has experienced with its 90nm PowerPC 970FX - aka 'G5' - processor, which are believed to centre on the materials used to make them.
The question remains: has AMD's longer 90nm implementation timescale given it the time to explore and solve the problems experienced by rivals who came to market with 90nm chips earlier than it did? Unfortunately, that question will only be answered when AMD's chips are available in the market. ®
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