EE2411UC Berkeley EE241 B. NikolicEE241 - Spring 2002Advanced Digital Integrated CircuitsLecture 28Flash MemoryBased on a talk by Ken Takeuchi, ToshibaUC Berkeley EE241 B. NikolicProject Reportsl Title of the project/ your names and e-mail addresses l Abstract (100 words) l Motivationl Problem statementl Possible solutions from literature (from midterm report)l Proposed comparison/solution. Discuss why did you select this particular one.l Conditions/assumptions of your designl Analysis: Does it work? Analytical analysis, simulation results.l Conclusion. What is this approach good for? What else could be done?l Referencesl Due on May 15, at 5pm (on the web)EE2412UC Berkeley EE241 B. NikolicHistory of Flash Memories84 85 86 87 91 92 93 … PRESENTSanDisk-typeDiNOR-typeSanDisk-typeNOR-typeNAND-typeDiNOR-typeAND-typeSST-typeXSST-typeXFile-StorageCode-StorageNOR-typeNAND-typeACEE-typeAND-typeSplit-gate-typeFLASH MEMORYInventionUC Berkeley EE241 B. NikolicFlash Memory Comparison- Code vs File Storage -Code StorageFile StorageApplicationsType of Flash memory PerformanceProgram storage for- Cellular Phone- DVD- Set TOP BoxBIOS for- PC and peripheralsSmall form factor card for- Digital Still Camera- Silicon Audio- PDA ... etcMass storage as- Silicon Disk DriveImportant :Acceptable :• High speed random access• Byte programming• Slow programming• Slow erasing • High speed programming• High speed erasing• High speed serial read• Slow random accessImportant :Acceptable :NOR • Intel / Sharp• AMD / Fujitsu / ToshibaDINOR • MitsubishiNAND • Toshiba / SamsungAND • Hitachi•SanDisk: NOREE2413UC Berkeley EE241 B. NikolicRequirements for File Storage Memoryl Low Bit Cost <$1/MBytel High Density >32MBytel High Speed Programming >2MByte/secand Erasing <3msec/blockl High Speed Serial Read l Low Power Consumptionl Good Program/Erase Endurance >1 million cyclesUC Berkeley EE241 B. NikolicDevice Technologiesl Low Bit Cost <$1/MBytel High Density >32MBytel High Speed Programming >2MByte/secand Erasing <3msec/blockl High Speed Serial Readl Low Power Consumptionl Good Program/Erase Endurance>1 million cyclesNAND Cell w. Self-Aligned STIUniform FN-FN Program/EraseEE2414UC Berkeley EE241 B. NikolicCell Array ComparisonSimplest wiringSmallest areaNOR SanDisk AND NANDErase gate(poly)Unit CellUnit CellWord line(poly) Word line(poly)Source line(Diff. Layer)Word line(poly)Bit line(metal)Source line(Diff. Layer)Unit CellContactSource line(Diff. Layer)Word line(poly)Bit line /Source line(metal)Unit CellSub Bit line (Diff. Layer)9F28F24F210F2UC Berkeley EE241 B. NikolicWord linesSelect transistorBit line contact Source line contactActive areaSTINAND Cell Array (Top view)EE2415UC Berkeley EE241 B. NikolicNAND Cell Array (Cross sectional view)Word lineWord lineBit lineSelect gateAA’AA’Source lineUC Berkeley EE241 B. NikolicCell Size Shrink by Self-Aligned STICurrent3Floating GateWord LineLOCOS_NAND : 6F2+aLOCOS_NAND : 6F2+aSTI_NAND : 4F2+aSTI_NAND : 4F2+aFFEE2416UC Berkeley EE241 B. NikolicNAND Cell Array (Cross sectional view)Word lineWord lineSTI1stfloating gate2ndfloating gateBB’BB’SiUC Berkeley EE241 B. NikolicStacked floating gateWord line(18V)1stfloating gate2ndfloating gateBB’Channel(0V)Effective Channel-FG voltage=18V*Cono/(Cono+Cox)à Large Cono is required.Floating gateWord line (18V)Channel (0V)ConoCoxEE2417UC Berkeley EE241 B. Nikolic0.15umTunnel Oxide1st poly-SiP-well0.4mm0.25mm 0.30mmSiNSTI2nd poly-SiMask SiNSpacer SiNMask SiNControl GateInter-poly(ONO)Self-Aligned STI ProcessUC Berkeley EE241 B. NikolicProgram / Erase MethodElectron Injection (Program)-Page program- Byte programHot ElectronProgram Current < 2-5mAS DVDVppChannel-FN tunnelingProgram Current< 1uAVppElectron Emission (Erase)- High Speed Erase( 3ms/Block )High VPE( 20v )VPEChannel-FN tunneling- Low Speed Erase(1s /Block)LowVPE( 12v )S DVPEEdge-FN tunneling- High Speed Erase(3ms/Block)HighVPE( 20v )S DPoly-FN tunnelingVPEEE2418UC Berkeley EE241 B. NikolicCell FunctionFN tunnelingEdge-FN tunnelingHot ElectronNOR SANDISK ANDPROG.ERASEProg. SpeedVth 0V20V20V 20V0V0V18V0V-8V6V0VOpen10V-8V-8V -8V10V0V0V 7V0V0V22V12V5V0VOpen0VF0V12V0.1MB/sec 0.5MB/secFN tunnelingFN tunnelingPoly-FN tunnelingEdge-FN tunnelingHot ElectronVth (V)Number Vth (V)NumberVccVth (V)NumberVccVth (V)NumberVcc00 00Access Mode2.0MB/secVery Fast2.5MB/secRandomSerialSerial SerialNANDUC Berkeley EE241 B. Nikolic+ Multi Level CellFloating GateLOCOSControl Gate3.5F3F2F3FNAND-type Cell(Contactless)2F2FSelf-AlignedSTI Cell2F2FSelf-Aligned STI CellFloating GateSTIControl GateCell Size 10-11F26-7F2 4-5F22-2.5F2Isolation LOCOS LOCOS SA-STI SA-STINOR-type CellNAND Cell TrendEE2419UC Berkeley EE241 B. NikolicNAND Flash Cell Size TrendStart of Mass ProductionJan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan-‘93 ‘94 ‘95 ‘96 ‘97 ‘98 ‘99 ‘00 ‘01 ‘02 ‘03 ‘040.110Cell Size ( um2 )1LOCOSSA-STIMLC0.01Multi Level CellFloating GateLOCOSTunnel OxideControl GateWSiONOControl Gate ONOFloating GateTunnel OxideSTIWSiSA-STI0.25um0.175um0.13um0.10umUC Berkeley EE241 B. Nikolic125mm21Gbit NAND Flash Memory10.7mm11.7mm2kB Page buffer & cacheCharge pump16896 bit lines32 word lines x 1024