Re: You seem to think that just because Intel is not using their version of SOI at the 130nm node, but they are using it at the 65nm node (and possibly the 90nm node), that they missed the boat, and now have to integrate it at a later time.
I think it is obvious that Intel got caught with its pants down.
Here's what Intel's director of process architecture and integration said last year at the same time AMD, IBM, Motorola, and the Taiwan foundries were already developing SOI processes. Following are additional comments from Intel senior engineer Kaizad Mistry on the results of Intel research into SOI processes and their conclusions:
"Good for them," said Mark Bohr, director of process architecture and integration at Intel's Hillsboro, Ore., facility, when presented with the growing list of companies adopting SOI for their high-end processors. "I don't want to change their minds," he said, adding that SOI may prove "very painful" for Intel's competitors....
Intel now acknowledges that at the 0.18-micron generation, SOI circuits run faster than bulk CMOS devices, largely because SOI effectively eliminates junction capacitance. However, as CMOS scales to 130 nm, 100 nm and beyond, SOI's performance edge will diminish, the company maintains, largely because junction capacitance will decline relative to total parasitic capacitance. Capacitance at the gate and in the interconnects will dominate at the 100-nm technology node and beyond, Intel holds....
Even as more companies gravitate toward SOI, others, including Intel, argue that simply scaling bulk CMOS brings an equal payback for the effort expended. And for high-volume, cost-sensitive products, the added wafer costs of SOI are significant, this camp holds....
Moreover, switching to SOI would require new EDA tooling, circuit models and training in "a tough design methodology," he said. Despite those difficulties, Intel would surely make the switch if convinced of the performance gains, said Intel senior engineer Kaizad Mistry. However, in what surely will be a much-debated paper, Mistry argued at the VLSI Technology Symposium that whatever speed advantages SOI technology may have at the 0.18-micron generation will diminish over time.
Intel created 0.18-micron SOI circuits, the "best reported to date" for 0.18-micron design rules, he said. Mistry's team in Portland, Ore., built test circuits using Intel's bulk 0.18-micron CMOS process and compared them to circuits adapted to SOI wafers. Mistry reported a 16 percent performance gain for SOI for an inverter with a fanout of 1, an 8 percent gain for an inverter with a more typical fanout of 4 and a 20 percent improvement for a three-input NAND.
That 15 percent gain was countered somewhat by the need to create a "guardband" for the so-called "history effect," reducing the net gain to only 10 percent, Mistry said. SOI transistors typically switch more slowly after an initial "on" state because the body is "floating" — that is, not connected to a grounded substrate. Since it is impossible to predict which transistors are suffering from the history effect, the circuit designer must create a guardband of 5 to 7 percent to ensure a predictable transistor performance on an MPU with millions of transistors, said Mistry.
The performance gain at 0.18-micron design rules might have tempted Intel, except that the wafer and design infrastructure was woefully lacking. The Intel team forecast that at the 0.13-micron generation, the performance gains stemming from the lack of junction capacitance in an SOI technology would diminish.
Intel believes that it is well ahead of other silicon vendors in terms of reducing junction capacitance in its bulk CMOS process. As scaling proceeds, and junction capacitance plays a smaller role vis-à-vis gate capacitance, the SOI advantage in terms of parasitics in the junction regions will fade to insignificance, the company contends.
Bottom line, by Mistry's accounting: By the 100-nm generation, SOI's advantage is only 3 percent. And that ignores the interconnect load, which erodes the SOI gain even further, Mistry said. For all of those reasons, SOI has no appeal to Intel, he concluded. |
