April 6, 1993 RM
NEC sampling 64-Mbit DRAM made with production photolithography
Following its prompt release of the R4400 microprocessor, NEC has
underscored its current mastery of process technology by starting to
sample 64-Mbit dynamic RAMs. The company presented its 64-Mbit prototype
at the Integrated Solid-State Circuits Conference a little over a year
ago, and samples might ordinarily be expected in 1994. Contrary to some
expectations, the current samples are not laboratory devices made with
direct-writing electron beams or other exotic process. Rather, they
demonstrate a cutting-edge production process.
Fabrication is i-line optical lithography without phase-shift
photomasks, with 0.35-micron feature size. This results in a 0.85 x 1.
69-micron cell and a 10 x 21-mm die. Such a die would have been a
laboratory curiosity a few years ago, but current processes control defect
densities much better than in the past, or modern microprocessors as well
as memories would be impractical. The parts will be completely in the
low-voltage world, running from 3.3-V supplies and featuring LVTTL
interface. Initial organizations are 4, 8, and 16 bits wide. Page mode is
standard, and self-refresh an option. The 16-bit-wide parts come in
54-pin thin small-outline packages (TSOPs). The others come in 34-pin, 500
x 875-mil SOJ or TSOP packages. Initial production prices will be around
$600 ea/10,000. If NEC's production projections are close, 4-, 16-, and
64-Mbit generations will all be produced simultaneously. Obviously, only the
most space-sensitive and least price-sensitive applications will pay the
premium for the 64-Mbit devices. Current PCs accommodate 32 or 64 Mbytes
on the motherboard, using 4-Mbyte SIMMs, supposedly enough to run Windows
NT. On the other hand, something like an Iris Indigo subnotebook would
need the densest parts. Eventually, as with all DRAM generations, the
price will come down and 256-Mbyte main memories will be essential. For
more information, call NEC's Literature Hotline, 800-366-9782 or circle
xxx. –Rodney Myrvaagnes
CAPTION:
A chip as large as this 10 x 21-mm 64-Mbit DRAM would not have been
producible a few years ago, even with much grosser features.
Advertisement
