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High-Density Flash Memory and Flash Memory Card
High-Density Flash Memory and Flash Memory Card
High-Density Flash Memory and Flash Memory Card
High-Density Flash Memory and Flash Memory Card
High-Density Flash Memory and Flash Memory Card
High-Density Flash Memory and Flash Memory Card
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High-Density Flash Memory and Flash Memory Card

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  • 1. 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 Flash 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 memory types by application: working memory AND 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
  • 2. 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 W1 W0 W1 W1 Wm Select Wm Wm S S Select S Metal layer Contact hole Floating gate Floating gate Word line Word line (Control gate) Embedded (Control gate) diffusion layer Fig. 2—Flash Memory Cell Structure. AND-type flash memory cells eliminate contact hole so that die size can be reduced. Control 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 Sector 2 connection between data lines and the drains and Block 3 Sector 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 Block 2048 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-
  • 3. 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 80 provides fast and constant speed. 80 Penetration to consumer electronics Item Specification Moving picture Memory cell structure Pseudo contactless 60 55 2 switch gates/128 cells Audio Power supply voltage 5-V and 3.3-V single 40 36 Random access time 5 µs HPC/PDA 25 Serial access time 50 ns 20 Dgital camera Write unit 512 byte 12 Write time 1 ms typ./512 byte 3.5 6.3 2 0 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. Block Write Flash card market is growing with demand for use in digital erase 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) further growth. 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
  • 4. 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 0.8 M • Konica QM100 – 2M QM3501 8 Mbyte 15/30 Mbyte • Casio QV700 1M 0.35 M • Canon PS350 PS600 – 1.4 M • NEC Picona 2/4 Mbyte 8/15 Mbyte 0.25 M 0 ’96 ’97 ’98 Mbyte 30–60 Mbyte Compatible model 60 Flash card • Casio CASIOPEIA 15–45 Mbyte 45 • HP 200LX 300LX 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 True-IDE standard Ensured controller which Depends on type of May depend on type of Compatibility supports industrial standard flash memory and flash memory and density density 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
  • 5. High-Density Flash Memory and Flash Memory Card 152 phones, pagers, and solid-state audio players as shown 3-chip controller Controller technology in Fig. 4. Full-motion video applications are also good 2-chip controller candidates for future flash card business. Relative cost/Mbyte 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 reasons. 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
  • 6. Hitachi Review Vol. 47 (1998), No. 4 153 4th generation 600 MB ... 1st 150 MB 150 MB ATA ... generation ... 75 MB 75 MB 75 MB Componet ... ... ... 15 MB 15 MB 15 MB 8 MB 64 Mbit 8 MB 84 Mbit 4th generation 256 Mbit 3rd 180 MB 2nd generation ... generation 45 MB 45 MB CF 1st 30 MB 30 MB 30 MB generation 20 MB ... ... 15 MB 15 MB 15 MB 15 MB 10 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 memory. 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: ishiharh@cm.musashi.hitachi.co.jp

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