1. Information Storage and Spintronics 09
Atsufumi Hirohata
Department of Electronic Engineering
15:00 Monday, 29/October/2018 (J/Q 004)

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

3. 09 Flash Memory
NOR flash
NAND flash
TSV
Multiple value
SONOS

4. Performance Gap between HDD and DRAM* 4

5. Flash Memory In 1980, Fujio Masuoka invented a NOR-type flash memory :
1 byte high-speed read-out
Low writing speed
Difficult to integrate * ** 5

6. NOR-Flash Writing and Erasing Operation
Writing operation :
Erasing operation :
Positive
potential voltage
Negative
potential voltage
Control gate
Insulating layer
Floating gate
Drain
Source
Open
drain
Ground
Positive
Positive * 6

7. NAND Flash Memory
In 1986, Fujio Masuoka invented a NAND-type flash memory :
No 1 byte high-speed read-out
High writing speed
Ideal for integration
Flash erase for a unit block ( 1 ~ 10 kbyte ) only ! * 7

8. NAND-Flash Writing and Erasing Operation
Writing operation :
Erasing operation :
Positive
potential voltage
Ground
Control gate
Insulating layer
Floating gate
Drain
Source
Ground
Ground
Positive
Positive
Ground
Positive * 8

9. Reading Operation “0” state : “1” state :* 9

10. Cells, Pages and Blocks Flash memory blocks :* 10

11. Flash Memory Integration
NOR or NAND ? : * 11

12. 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 * 12

13. HDD vs Flash Memory Demand for flash memories :
Price of flash memories : * 13

14. Flash Memory Development
Intel flash memories :
130 nm (128 MB) in 2003
90 nm (512 MB) in 2005
50 nm (1 GB) in 2007
34 nm (4 GB) in 2009
25 nm (8GB) : 14

15. For Higher Recording Density ...
Through Silicon Vias　（TSV) :
Stacked flash :
Toshiba also demonstrated 16 GB flash.
Samsung demonstrated 16 GB flash. * ** 15

16. Recent Flash Memory 32 1-TB flash modules :
V-NAND architecture : 16 layers of flash memories to achieve 512Gb * 16

17. Latest Flash Memory Grade 3 : -40ºC ~ 85ºC Grade 2 : -40ºC ~ 105ºC
compatible with 64 layers * 17

18. Bit Cost vs Recording Capacity
Simple memory stack and BiCS memory :
Bit cost [arb. unit]
Layers
Simple memory stack
Memory capacity [bit]
BiCS flash memory
* H. Aochi, R. Katsumata and Y. Fukuzumi, Toshiba Review 66(9), 16 (2011). 18

19. Bit Cost Scalable (BiCS)
BiCS memory design :
Bit line
Upper selection gate
Control gate
Lower selection gate
Source line
String
* H. Aochi, R. Katsumata and Y. Fukuzumi, Toshiba Review 66(9), 16 (2011). 19

20. Multiple-Valued Flash Memory
Multiple electrons can be stored in the floating gate :
Conventional cells
Multiple-valued cells
“1”
“11”
“10”
Memory cell read-out threshold
Memory cell read-out threshold
“01”
“0”
“00”
Cell distributions
Cell distributions * 20

21. SONOS Si / SiO2 / SiN / SiO2 / poly-Si (SONOS) :
By replacing the poly-Si floating gate with SiN, i.e., Si9N10,
unbound dangling bonds can trap more electrons. * 21

22. 3-Dimensional Integration with Higher Density
Max Shulaker (MIT) proposed monolithic architecture : * * 22

23. Integration of Functionality
3D monolithic can be advantageous over TSV etc. : * * 23

24. Flash Memory vs DRAM Comparisons between flash memory and DRAM : *
Tunnel barrier
Floating gate
Principles
Transistor
Transistor
Condenser
Electron charges
are stored in the On On
Electrons are stored at the floating gate.
condenser.
Writing operation
Leakage from
the condenser.
Electrons cannot
tunnel through the
barriers.
Data volatility * 24