It's all in the cards
By Keri Allan & Chris Edwards
Electronics Times
(23/07/01 11:09 AM GMT)
After several years of shortage that saw companies sign up
supply agreements to guarantee deliveries, the Nor flash
business has gone into decline. The Nikkei Market Access survey
has revealed that the market will have declined by 2% to 456
million units in Q2 this year compared with the previous quarter.
Nikkei reckons the decline is only temporary and has been
caused by the inventory that built up at cellphone manufacturers
at the start of this year. Nikkei has predicted that demand will
start to surge ahead for the rest of the year to more than 550
million devices in Q4.
But International Data Corporation (IDC) reckons the real growth
in the next few years will be in Nor's competitor, the Nand flash
device. Driven by demand for digital audio players and cameras,
IDC claims the flash memory card market will see a compound
annual growth rate of almost 50%, from $717m in 1999 to
$5.3bn in 2004. Most flash memory cards currently in use are
based on Nand rather than Nor flash.
Xavier Pucel, manager of IDC's semiconductor research programme, said: "Users needing a way to
store, archive, transport and easily transfer content from the Web will drive flash card volume, which
in turn will reduce costs."
Doug Kellam, vice-president of marketing for card and card reader supplier Lexar Media, said: "More
and more consumer, business and industrial devices are beginning to use flash memory for digital
cellphones, digital cameras, personal digital assistants, lan switches, PC cards, set-top boxes,
embedded controllers and other devices. Sales of these devices may slow over the coming months
but we anticipate a healthy, regulated rise in flash for the market."
Card formats
The issue is: which type of card? There are three main formats currently in use with more on the way
as the Internet audio market develops. Until a few years ago, the main battle was between
CompactFlash, developed by SanDisk, and Toshiba's SmartMedia. Sony then joined in, using its
position in the consumer electronics market to push the chewing gum-sized Memory Stick.
NPD Intelect Market Tracking grabbed the largest
market share in the digital still camera business and
now reckons that Memory Stick's share has climbed
from 5% in 1999 to just under 30% by the end of
2000. John Reimer, president and CEO of Lexar
Media, said: "The Memory Stick format has shown
impressive growth."
Sony has tried to promote Memory Stick as a
standard, signing up some 120 companies in the
electronics, telecoms and automotive industries.
Compared with CompactFlash, the stick's capacity is
limited. Currently it can take 64Mbyte of memory but
128Mbyte sticks are now appearing on the market,
putting it into the same bracket as SmartMedia.
CompactFlash cards are larger and currently range in
capacity up to 512Mbyte.
But CompactFlash has itself been splintered into
smaller variants such as the MultiMediaCard (MMC)
and the Secure Digital (SD) card. MMC appeared first
but the SD card has picked up backing from 225
vendors that intend to build support for it into digital
audio players, organisers and camcorders. Sandisk
has said that it intends to go into production with a
128Mbyte SD card by the end of September, having started production in conjunction with Toshiba
of a 512Mbit Nand flash device.
Connie Wong, director of special services at Semico Research, said: "The availability of higher
capacity cards makes them much more feasible for applications such as digital video camcorders,
which require considerable storage."
SD cards adds support for the Secure Digital Music Initiative (SDMI) rights protection system. It is not
the only way in which these cards are getting additional functions. Hitachi is working with Infineon
Technologies on a variant of MMC intended for mobile phones that will contain the subscriber
identity information normally contained on a separate smartcard chip.
The WIM-MMC sees the SIM chip combined
with secure flash memory storage so that it
can hold larger amounts of personal data. And
it is not the only way that Nand flash is moving
into the mobile phone. Helmut Schock, senior
manager for memories at Toshiba Electronics
Europe, says the move towards multichip
packages for the memory in mobiles is carving
a path for Nand that could supplant at least
some of the Nor capacity.
"The cost for Nand flash is about 50¢/Mbyte
and that is under hard pressure at the
moment," said Schock. That compares with
$2/Mbyte for Nor: "We see a trend for cost
reasons for moving towards Nand flash."
In the past, Nand's main problem in
supplanting Nor as non-volatile system
memory is that Nand memory has to be accessed in blocks. Nor supports random accesses so that
it can be used by a processor for code storage.
Toshiba has developed a three-chip stack that combines both Nor and Nand flash chips with an
SRAM die. Schock says one customer design, for a third-generation handset, is underway with the
device that has a total of 224Mbit of memory, more than half of it in the form of Nand flash:
"[Manufacturers] will use more and more Nand flash with smaller Nor for cost reasons."
The idea behind combining Nor with Nand is to put the critical OS code into the Nor flash and then
use Nand for applications code and data that can be paged into the SRAM. The company has
opted for pseudo-SRAM to boost the amount of storage needed to handle that approach up to
32Mbit.
Schock says the biggest issue with the multichip packages will be predicting which capacity
combinations will be used by phone manufacturers.
To get capacities up to 1Gbit, Nand flash manufacturers are using a technique originally used by
Intel in its Nor-based Strataflash product line. By varying the programming time, it is possible to store
different amounts of charge in the floating gate of a flash memory cell. Intel used this to store four
discrete states, allowing 2bit to be stored per cell.
Hitachi, which developed the And technology
as a competitor to Nand, is developing a 1Gbit
memory using a similar multi-level cell (MLC)
technology, again storing 2bit/cell. Toshiba
intends to use MLC in both its Nor and Nand
products with a 1Gbit device expected by the
end of the year.
Although it is possible to store more states,
there is a trade-off in the sense amplifier part of
the memory that tries to work out the stored
value. The more bits stored, the longer it takes
to get a reliable reading. Because of this, says
Schock, eight-level cells are possible but the
technology is unlikely to go much further.
So, for further improvements in density, the
memory manufacturers will continue to rely on
die shrinks. With 4Gbit on the way in 2004,
AI
