6/23/00 - NEC's 288-Mbit Rambus device shaves cost
Jun. 23, 2000 (Electronic Engineering Times - CMP via COMTEX) -- TOKYO - NEC Corp. has
introduced what it claims is the first validated 288-Mbit Rambus DRAM, a development that may
lead to much-needed price reductions for the high-speed memories. The company is using a
0.18-micron process technology to shave die size and increase yields in a bid to lower RDRAM
costs.
Intel Corp. is counting heavily on DRAM makers to reduce RDRAM prices so that it can quickly
bring down the cost of PCs built on its next-generation Willamette processor. Scheduled for
introduction later this year, Willamette will rely on RDRAMs to give it sufficient memory
bandwidth for its quad-pumped processor bus.
NEC's move comes as most RDRAM makers are still struggling to bring down the cost of the
parts to no more than 20 percent above the cost of mainstream SDRAMs, which is Intel's goal.
However, even NEC is reluctant to say to what extent its latest cost savings will be passed on to
buyers of the chips.
NEC's 288-Mbit devices will carry a die overhead of less than 15 percent above a comparable
SDRAM, said Misao Higuchi, senior manager of technical marketing for NEC's memory
operations unit. That's better than the 20 percent die overhead for today's 128-Mbit devices, but it
still falls short of the 10 percent die-area premium that Rambus and Intel had promised several
years ago when the 16-bit-wide interface technology was introduced. The higher die overhead and
faster signaling frequency of RDRAMs have conspired to keep manufacturing yields low, which
has been a factor in RDRAM's high final cost.
With a 288-Mbit RDRAM ready for production on its 0.18-micron process technology, NEC
should be able to see yields pass 50 percent for the maximum, 800-MHz frequency, Higuchi
said. "For the 800-MHz speed grade, we expect 50 percent at 0.18 micron and then between 70
percent and 80 percent when we move to 0.15 micron, by the end of this year or early next year,"
he said.
Rising yields have emboldened Rambus to start thinking about upgrading the spec for higher
speeds. At the recent 2000 VLSI Circuits Symposium, Rambus officials said they would soon
announce a faster version of the spec as DRAM vendors shift to finer process technologies. They
noted that leading DRAM vendor Samsung Electronics claims it can increase Direct Rambus to
850 MHz at 0.21-micron process technology, 910 MHz at 0.19 micron and 1 GHz at 0.17
micron.
Higuchi expects the frequency boost to come after the shift to 0.18 micron, perhaps at the 0.15-
or 0.13-micron generation. "Maybe by 2001 or 2002, we'll see a new spec," he said.
Because initial 0.18-micron processes had shown poor yields at most DRAM companies, NEC
has until now produced its RDRAMs at 0.22 micron. Originally specified for 800 MHz, Rambus
DRAM now includes downgraded, 600- and 700-MHz speeds
With the new part, NEC will be able to introduce a "cut-down" RDRAM, essentially a 128-Mbit
DRAM made by dividing the 288-Mbit mask design in half. The lower-cost, 128-Mbit device will
likely be introduced when NEC switches to a 0.15-micron process, he said.
The company will also likely introduce a by-16 256-Mbit RDRAM when it moves to 0.15 micron.
Because the RDRAM address bus is fixed, a PC with a 64-bit-wide memory bus can use a
standard RIMM with four 256-Mbit RDRAMs instead of eight 128-Mbit devices.
For now, however, NEC will focus on 288-Mbit parts with error correction, a feature required for
the high-end systems the company is targeting in the early stages. Sampling now, the 288-Mbit
device will move into volume production this month. Rambus recently gave the part the stamp of
approval for meeting all RDRAM specifications, including timing, current, load capacitance and
inductance.
OEM prices have been as much as three times those of SDRAM, while aftermarket modules are
being priced at some 800 percent higher.
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