design of advanced erase mechanism for nor flash eeprom amit berman, june 2006 intel corporation
TRANSCRIPT
Design of Advanced Erase MechanismDesign of Advanced Erase Mechanismfor NOR Flash EEPROMfor NOR Flash EEPROM
Amit Berman, June 2006Intel Corporation
AgendaAgenda
Flash Memory Introduction Project’s Targets Current Erase Solution Proposed Methodology for New Mechanism Lab Results and Evaluation Conclusions Questions Session
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Flash Memory IntroductionFlash Memory Introduction
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Substratep-
Drain n+
Source n+
ToxFG
ONOGate
Bit-line
(Vd)
Control Gate
Wordline
(Vg)
--- -
--
Source
(Vs)
- -
What is Flash?- Non-Volatile Memory
- Examples: Cell-phone OS, PC BIOS
MOSFET with floating gate: Information is stored as electrons in the floating gate- Many Electrons – Logic ‘0’
- Few Electrons – Logic ‘1’
Best memory alternative: Low cost, Low power, High density and High speed.
High High DensityDensity
NonNon--VolatileVolatile
UpdateableUpdateable
ROMROMDRAM/DRAM/SRAMSRAM
EPROMEPROM
FlashFlashMemoryMemory
Flash Memory Introduction (2) Flash Memory Introduction (2)
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Id (A)
Vg (V)
E
5
01 2 3 4 5
R P
Substratep-
Drain n+
Source n+
ToxFG
ONOGate
Bit-line(Vd)
Control GateWordline
(Vg)
- -- ---
- ---- -
-- -
-
Source(Gnd)
- ---
Program - CHE Erase – FN tunneling Read – Sensing
Substratep-
Drain n+
Source n+
ToxFG
ONOGate
Bit-line(Float)
Control GateWordlineVg << 0
- - -- ---
Source(Float)
---
-- -- -
-Vwell=positive Vg
Substratep-
Drain n+
Sourcen+
ToxFG
ONOGate
Vread
Control GateVcc
--- -
--
Source
- -
SenseAmp Output
REF
SEN
Drain
I
I
Project’s TargetsProject’s Targets
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Speed-up Erase operation
(bottleneck 0.9sec per block) Improve product reliability by
reducing “Post Erase Repair” phenomena (DPM)
Reduce product test time
Current Erase SolutionCurrent Erase Solution
Channel Erase Pulses Block basis (shared bulk) Increasing pulse series
Erase Verify – Vt Measurement (read) until all block is erased
Disadvantages: Since not all cells are
similar ,some will be over-erased : always logic ‘1’.
Post erase repair – soft programming is needed.
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Proposed MethodologyProposed Methodology
Detect an “Optimum Point” on channel erase where fast and normal bits are erased but slow-erased bits are programmed.
Handle Slow-erased bits with “special care” – erase via drain. Reduce over-erased cells to minimum.
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Lab Results and EvaluationLab Results and Evaluation
We can identify slow-erased bit by constant charge loss in each erase pulse. Flash Vt will be briefly reduced.
Model for slow-erased bits: on erase pulse #10. Trade-off between reducing over-erased bits and erase speed. Erase operation speed is improved from 0.9sec per block to 0.7sec
per block.
PP project
60.00%
65.00%
70.00%
75.00%
80.00%
85.00%
90.00%
95.00%
100.00%
17 19 26 28 29 30 31 32 33 34 35 36 37
Pulse Number
% o
f Era
sed
Ce
lls
vVT 325.0
ConclusionsConclusions
Potential speedup: future implementation on embedded flash microcode and on test program platforms.
Quality and Reliability check is needed. Examine cost-effective trade-off with Q&R and device operation
speed.
PP project
Questions SessionQuestions Session
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