Department of Electronics Advanced Information Storage 11 Atsufumi Hirohata 16:00 11/November/2013 Monday (P/L 002)

Quick Review over the Last Lecture Shingled write recording : * Bit patterned media (BPM) : ** Discrete tracks : *** *** ** Conventional recording Conventional BPM Discrete tracks for BPM Nano-holes Tracks * S. Matsuo, H. Uwazumi and N. Hara, Fujidenki Gihou 85, 316 (2012);

11 Flash Memory NOR flash NAND flash TSV Multiple value SONOS

Performance Gap between HDD and DRAM *

Flash Memory In 1980, Fujio Masuoka invented a NOR-type flash memory : ** * 1 byte high-speed read-out ×Low writing speed ×Difficult to integrate

NOR-Flash Writing and Erasing Operation Writing operation : Erasing operation : * Positive potential voltage GroundPositive Open drain Negative potential voltage Control gate Floating gate Source Insulating layer Drain

NAND Flash Memory In 1986, Fujio Masuoka invented a NAND-type flash memory : * High writing speed Ideal for integration ×No 1 byte high-speed read-out ×Flash erase for a unit block ( 1 ~ 10 kbyte ) only !

NAND-Flash Writing and Erasing Operation Writing operation : Erasing operation : * Positive potential voltage Ground Control gate Floating gate Source Insulating layer Drain Ground Positive Ground Positive

Reading Operation “0” state : “1” state : *

Cells, Pages and Blocks Flash memory blocks : *

Flash Memory Integration NOR or NAND ? : *

Solid State Drive with Flash Memory Solid state drive (SSD) started to replace HDD : pureSi introduced 2.5” 1-TB SDD in 2009 : Data transfer speed at 300 MB/s  Slow write speed For example, a system with a units of 2kB for read / out and 256 kB for erase : in order to write 1 bit, the worst case scenario is 128 times read-out 1 time flash erase 128 times re-write *

HDD vs Flash Memory Demand for flash memories : Price of flash memories : *

Flash Memory Development Intel flash memories : nm (128 MB) in nm (512 MB) in nm (1 GB) in nm (4 GB) in nm (8GB) :

For Higher Recording Density... Through Silicon Vias （ TSV) : Stacked flash : * Samsung demonstrated 16 GB flash. Toshiba also demonstrated 16 GB flash. ** memories-and-transistors

Bit Cost vs Recording Capacity Simple memory stack and BiCS memory : * H. Aochi, R. Katsumata and Y. Fukuzumi, Toshiba Review 66(9), 16 (2011). Memory capacity [bit] Bit cost [arb. unit] Layers Simple memory stack BiCS flash memory

Bit Cost Scalable (BiCS) BiCS memory design : * H. Aochi, R. Katsumata and Y. Fukuzumi, Toshiba Review 66(9), 16 (2011). String Bit line Upper selection gate Control gate Lower selection gate Source line

Multiple-Valued Flash Memory Multiple electrons can be stored in the floating gate : * Conventional cells Multiple-valued cells Memory cell read-out threshold Cell distributions Memory cell read-out threshold “1” “0” “11” “00” “01” “10”

SONOS Si / SiO 2 / SiN / SiO 2 / poly-Si (SONOS) : * By replacing the poly-Si floating gate with SiN, i.e., Si 9 N 10, unbound dangling bonds can trap more electrons.

Flash Memory vs DRAM Comparisons between flash memory and DRAM : * Flash memory Transistor Condenser Transistor Tunnel barrier Floating gate On Electrons are stored at the floating gate. Electron charges are stored in the condenser. Leakage from the condenser. Electrons cannot tunnel through the barriers. Principles Writing operation Data volatility