High-Density Flash Memory and Flash (1998), No. 4
Hitachi Review Vol. 47 Memory Card 148
High-Density Flash Memory and Flash Memory Card
Haruji Ishihara ABSTRACT: Flash memory is becoming a key component for mobile
computing and communication systems because of its nonvolatility, field
programmability, high density, and low cost. It is used as working memory
in applications such as cellular phones. It is also used as file memory in
applications such as flash cards. The flash card is a medium for transferring
data between two mobile PCs, or between a mobile PC and peripheral
equipment such as a digital still camera. Various types of data are stored in
flash cards; not only text data but also still picture, voice, and full-motion
video. These data require high-density storage media. Based on these needs,
Hitachi has developed high-density flash memory with Hitachi’s unique
“AND” cell structure and applied it to CompactFlash™* as small form-
factor flash card. The “AND” cell 64-Mbit flash memory and 45-Mbyte
CompactFlas are available now.
INTRODUCTION application: working memory and file memory, as
FLASH memory had been expected to replace dynamic shown in Fig. 1. Data in working memory is directly
random access memory (DRAM) and hard disk drive executed by a processor CPU, including code stored
(HDD) when it was introduced. The application of in a cellular phone. Therefore working memory must
flash memory is gradually expanding even though the have random access capability. Data in file memory
flash memory capacity is still less than that of DRAMs cannot be directly executed by a CPU. The data in file
and far from that of HDDs. Recently Hitachi memory must be transferred from file memory to main
introduced 45-Mbyte CompactFlah and 150-Mbyte memory for execution. This means that file memory
PC-ATA cards that incorporate Hitachi 64-Mbit flash does not require random-access capability, and serial
memory. These high-density flash cards will replace access may be sufficient.
low-density HDDs in industrial applications. Typical types of working memory are NOR- and
DINOR-cell flash memory that feature random-access
FLASH MEMORY STRUCTURES AND capability. Typical types of file memory are NAND-
FEATURES and AND-cell flash memory that feature high density
Flash memory is classified into two types by and low cost.
Application System Optimum flash
GPS: global positioning system
Working PC BIOS NOR
BIOS: basic I/O system
memory Cellular phone DINOR
HPC: handheld PC
Digital still camera
Direct execution by CPU GPS
as ordinary memory
Execution by CPU after
transfering data to RAM as HDD Fig. 1—Flash Memory Applications.
Flash card for
digital camera and Flash memory is classified into two
File HPC silicon disk NAND
types by application: working memory
and file memory.
* CompactFlash™ is a trademark of SanDisk Corporation and is licensed license it royalty-free to CFA members.
royalty-free to the CFA (CompactFlash™ Association) which in turn will
Hitachi Review Vol. 47 (1998), No. 4 149
NOR type AND type NAND type
Minimum erase unit Minimum erase unit Minimum erase unit
D1 D2 ... Dn D1 D2 ... Dn D1 D2 ... Dn
W0 W0 Select
Wm S S Select
Floating gate Word line
Word line (Control gate)
Fig. 2—Flash Memory Cell Structure.
AND-type flash memory cells eliminate contact hole so that die size can be reduced.
The cell structure of flash memory is shown in Fig. Data area area
2. The drain and source of all memory cells in NOR 512 byte 16 byte
and DINOR flash memory are connected to data lines Block 1 Sector 1
to provide random-access capability. The space for Block 2
connection between data lines and the drains and Block 3
sources of each memory cell increase the die size of Sector 4
flash memory. Sector 5
However, the drains and sources of all memory cells Sector 6
are not connected to data lines in AND and NAND Sector 7
flash memory. A drain and source of an entire block Sector 8
of memory cells are connected to a data line. This
means that the area for connection between data lines Block 2046
and drains and sources of memory cells is negligibly Block 2047
small, and smaller die size can be realized than for
NOR and DINOR flash memory. However only serial Fig. 3—Flash Memory Cell Array.
Write and erase unit of 64-Mbit AND flash memory is sector,
access is available because of this cell structure.
which has 512-byte data area and 16-byte control area.
HITACHI AND FLASH MEMORY CELLS
Hitachi developed the 64-Mbit flash memory
HN29W6411 based on the AND cell structure for file ICs that have defect bits cannot be used and discarding
memory applications. One of the most important them increases costs.
factors for file memory is cost. Two new technologies The mostly-good memory technology is used for
are used to reduce cost. One is the AND cell structure solving this problem. The HN29W6411 memory array
mentioned above. The other is mostly-good memory is shown in Fig. 3. The minimum-size unit of a memory
technology. Generally speaking, memory ICs are not array is a sector that has a 512-byte data area and a
always perfect and they have defect bit(s). Memory 16-byte control area. A flag is raised in the control-
High-Density Flash Memory and Flash Memory Card 150
TABLE 1. 64-Mbit Flash Memory Features and Specifications (B¥/MO)
The 64-Mbit AND flash memory has sector erase function, and
provides fast and constant speed. 80
Penetration to consumer electronics
Memory cell structure Pseudo contactless 60 55
2 switch gates/128 cells
Power supply voltage 5-V and 3.3-V single
Random access time 5 µs HPC/PDA
Serial access time 50 ns
20 Dgital camera
Write unit 512 byte 12
Write time 1 ms typ./512 byte 3.5 6.3
Erase unit 512 byte
’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03
Erase time 1 ms Demand forecast by application
max. 443 kbyte/s (4-kbyte erase) Fig. 4—Flash Card Demand Forecast.
Write Flash card market is growing with demand for use in digital
transfer min. 57 kbyte/s (4-kbyte erase) cameras, HPCs and PDAs (personal digital assistance). Audio
rate and full-motion video applications are good candidates for
Sector erase 256 kbyte/s (512-byte erase)
byte area for every sector that is a perfect sector. The systems and 5-V systems. Table 1 shows the 64-Mbit
defective sectors that do not have a raised flag in the AND flash specifications and features.
16-byte control area are replaced by a good sector.
Based on this technology, mostly-good memory that TOTAL FILE STORAGE SOLUTION
has defect bits can be used. The HN29W6411 specifies Hitachi provides a total file storage solution that
mostly-good memory as a memory that has 98% or includes not only flash memory but also the flash
more good sectors out of 16,384 sectors. memory controller and flash card. The total solution
The write operation of HN29W6411 is done in provides three benefits: (1) The latest flash memory
sector units. The erase operation of HN29W6411 can can be used in a timely fashion because the controller
be done by either sector unit, or by a block unit that for the flash memory is available at the same time that
has 8 sectors. The sector erase function makes the flash the flash memory is introduced. (2) The optimum
memory controller simple because the erase unit is controller is provided because the flash memory
the same unit as the write unit. The rewrite speed with supplier knows the characteristics of the flash memory
sector erase is faster than with block erase when the better than others. (3) The knowhow that has been
number of rewrite sectors is 4 or less. It is a constant obtained through flash card development and business
256 kbyte/s. can be utilized for developing better flash memory for
The rewrite speed with block erase is faster than file storage.
sector erase when the number of rewrite sectors is 5
or more. Thus rewrite speed depends on the number FLASH CARD MARKET
of rewrite sectors. The peak speed is 443 kbyte/s. The demand forecast for flash cards is shown in
The serial read speed is very fast. The burst access Fig. 4. The present main applications are digital still
time is 50 ns even though the first byte access time is cameras and handheld PCs. The flash card for a digital
5 µs. Thus the average read speed is 17 Mbyte/s. The still camera stores a digital image of a photo. The data
HN29W6411 can operate at either 3.3 V or 5 V. This size of a digital photo image depends on resolution of
dual-voltage operation capability provides a flexibility the charge-coupled device (CCD) image sensor in the
of system design and compatibility between 3.3-V camera, color depth, and the compression ratio of the
Hitachi Review Vol. 47 (1998), No. 4 151
Fig. 5—CCD Resolution vs. Flash Bundle Option Compatible model
Card Capacity. CCD pixcel number card card
Megapixel cameras need higher
capacity flash cards such as 2M 15 Mbyte 30/45 Mbyte • Kodak DC210
8 M, 15 M, 30 M, 45 Mbyte. DC50
• Konica QM100
8 Mbyte 15/30 Mbyte • Casio QV700
1M 0.35 M • Canon PS350
1.4 M • NEC Picona
2/4 Mbyte 8/15 Mbyte
’96 ’97 ’98
Mbyte 30–60 Mbyte Compatible model
Flash card • Casio CASIOPEIA
45 • HP 200LX
15–30 Mbyte 320LX
30 • IBM PalmTop100
• NEC MobilePro400
MobileGear (MC-CS12) Fig. 6—HPC and PDA Memory
15 • Sharp Power Zaurus Trend.
Main memory • PSION Series-5 Flash card capacity for HPCs and
PDAs is increasing based on the
0 need for high-density main memory.
’97 ’98 ’99
TABLE 2. Small Form-Factor Flash Card
CompactFlash provides better compatibility and high-density capability.
Item Compact flash Miniature card Smart media
36.4 33.0 45.0
mm mm mm
Outline 42.8 38.0 37.0
mm mm mm
3.3-mm thickness 3.5-mm thickness 0.8-mm thickness
PC-ATA standard Flash memory NAND flash memory
Interface depended interface interface
Ensured controller which Depends on type of May depend on type of
Compatibility supports industrial standard flash memory and flash memory and
High Memories and controllers can be Limited by flash Limited by flash
density mounted as long as space is permitted. component density component density
digital image. The CCD sensor resolution was 250-k were 8 M to 15 Mbyte, because 50 k–100 kbyte is
pixels in 1996, then it increased to between 350-k and needed for each photo from a 250-kpixel CCD sensor.
1.4-M pixels in 1997, and it is expected to reach to 2- In 1997 the bundled card capacity was increased to 8
M pixels in 1998. Mbyte and the option card capacities became 15 M
The capacity of flash cards bundled with cameras to 30 Mbyte because 200 k–400 kbyte is needed for a
in 1996 was 2 M to 4 Mbyte and option card capacities 1-Mpixel CCD sensor. Thus in 1998 the bundled card
High-Density Flash Memory and Flash Memory Card 152
phones, pagers, and solid-state audio players as shown
Controller technology in Fig. 4. Full-motion video applications are also good
2-chip controller candidates for future flash card business.
1.0 1-chip controller
New controller HITACHI FLASH CARD
The Hitachi flash card family has two form factors:
64-Mbit flash PC-ATA (AT attachment) card and CompactFlash. The
0.1 64-Mbit A-mask PC-ATA card was standardized by PCMCIA (Personal
84-Mbit flash Computer Memory Card International Association)
256-Mbit flash and JEIDA (Japan Electronic Industry Development
Association), and all suppliers follow the standard.
1995 1996 1997 1998 1999 2000 However the small form-factor flash card market
segment is a different story. There are three major small
Fig. 7—Cost Reduction by New Technologies.
form-factor flash cards on the market. They are
Flash card cost will be continually reduced by new controller
technologies as well as flash technologies.
CompactFlash, Miniature Card, and SmartMedia —
as shown in Table 2. Hitachi selected CompactFlash
for its small form factor flash card for the following
capacity is expected increase to 15 Mbyte and the (1) Compatibility with PC related systems.
option card capacities increase to 30 M to 45 Mbyte (2) Compatibility with PC-ATA card.
in 1998 because 400 k -800 kbyte are needed for a 2- (3) Independence of flash memory variations.
Mpixel CCD sensor. Fig. 5 shows a chart of flash card CompactFlash maintains compatibility with an
capacity as a function of CCD sensor resolution. internal intelligent controller. This controller buffers
Other leading applications are handheld PCs and the flash memory variations and maintains the
PDAs. These portable PCs do not have HDDs or FDDs CompactFlash specification. But a disadvantage is the
due to space limitations, power consumption added cost of the controller. On the other hand, the
limitations, and mechanical shock considerations. User Miniature Card and SmartMedia do not have an
data and application programs are stored in DRAM internal intelligent controller. Therefore, it is difficult
main memory with battery backup. It is not reassuring to maintain compatibility among systems and the
for the user that user data is retained by battery backup interface depends on the flash variation. But lower cost
because reliability is problematic. is expected than for CompactFlash. Hitachi thinks that
Also, the computer speed slows down when the user compatibility is the most important factor for general
data and application programs occupy more than users even with added cost.
certain amount of main memory. For these reasons the Cost reduction is one of the keys to expanding flash
user wants to use flash cards as mass storage for user card applications and markets. Hitachi is endeavoring
data and application programs. In general, the user to continuously reduce costs of controller technology
needs flash cards that have twice the capacity of main and flash memory technology, as shown in Fig.7. When
memory. Fig. 6 shows the trends of main memory Hitachi introduced the first-generation flash card in
capacity and flash card capacity. In 1998, 15 M- to 1996, the controller consisted of three chips: a
45-Mbyte flash cards will be needed. microcontroller, gate array, and 4-Mbit DRAM. Then
The flash card market will be enlarged by audio- the number of controller chips was reduced to two in
related applications such as voice recorders, cellular the 2nd-generation card by eliminating the DRAM
Flash memory Fig. 8—Double Density Packaging
2-layer TCP technology Technology.
Hitachi TCP technology facilitates
doubling CompactFlash card density
up to 45 Mbyte.
TQFP package 2-layer TCP technology TQFP: thin quad flat package
controller flash memory TCP: tape carrier package
Hitachi Review Vol. 47 (1998), No. 4 153
1st 150 MB 150 MB
75 MB 75 MB 75 MB
15 MB 15 MB 15 MB
8 MB 64 Mbit
8 MB 84 Mbit
4th generation 256 Mbit
3rd 180 MB
generation 45 MB 45 MB
CF 1st 30 MB
30 MB 30 MB
generation 20 MB
15 MB 15 MB 15 MB 15 MB
8 MB 8 MB 8 MB
1996 1997 1998 1999 2000
Fig. 10—Hitachi Flash Card Road Map.
It is expected that 180-Mbyte CompactFlash and 600-Mbyte
Fig. 9—Hitachi Flash Card. PC-ATA card will become available with 256-Mbit flash
chip in 1997. The 3rd-generation card was introduced capacity is shown in Fig. 10. It is expected that a 180-
with a 1-chip controller by using micro CBIC Mbyte CompactFlash and a 600-Mbyte PC-ATA card
technology in November 1997. will be available with 256-Mbit flash memory in the
Flash memory chips now dominate the cost of flash 2nd half of 1998.
cards, especially for high capacity cards. The 2nd-
generation 64-Mbit flash memory is under development CONCLUSIONS
to reduce the die size and enhance performance. Then High-density flash memory and flash cards will be
84-M and 256-Mbit flash memory chips will be popularly used not only for mobile computing and
introduced for further cost reduction in the 2nd half of communication systems but also for industrial
1998. applications such as file storage because of advantages
Based on digital still camera and handheld PC trends, such as high portability, low power consumption, high
Hitachi is focusing on high-capacity flash cards. Two reliability and reasonable cost. Hitachi will continue
key technologies are used to implement high-capacity to focus on high-density flash technology for leading-
flash cards. One is high-density flash memory chips edge file storage applications.
as mentioned above.
The other is packaging technology. Fig. 8 shows
the cross section of CompactFlash. There are 4
positions for mounting controller and flash memory
chips. The 1-chip controller occupies one position and
flash memory chips occupy 3 positions. A 24-Mbyte
card is the maximum capacity when conventional
packaging technology is used with 64-Mbit flash
memory. ABOUT THE AUTHOR
However tape carrier packages facilitate stacking
two 64-Mbit flash memory chips at one position so Haruji Ishihara
that six 64-Mbit flash memory chips can be mounted. Joined Hitachi, Ltd. in 1972. Belongs to the Memory
Product Marketing Dept. at the Semiconductor &
Based on this technology, Hitachi introduced a 45- Integrated Circuits Div. Currently working on product
Mbyte CompactFlash and a 150-Mbyte PC-ATA card marketing for flash memory and flash card.
as shown in Fig. 9. The further expansion of flash card E-mail: firstname.lastname@example.org