Presented by: Andrew Lints

& Dave Gooden

ALTERNATIVE RAM DESIGNS

AGENDA

1.Review of SRAM & DRAM as benchmarks2.MRAM (Magnetoresistive)3.TRAM (Thyristor)4.ZRAM (Zero-capacitor)5.Summary6.Questions

DYNAMIC RAM (DRAM)

Simple, low-cost, high-density, and Volatile

Consists of 1 transistor & 1 capacitor per memory cell

Digital value of cell is stored on the capacitor

As time passes, the capacitors are discharged, requiring constant refreshing (usually every <64ms) making this type of memory Dynamic.

DYNAMIC RAM (DRAM)

Due to the need to refresh each cell regularly, power consumption is fairly high

Due to the small cell size, scaling blocks to large capacity keeps speed high as shorter trace lengths keep latency down

STATIC RAM (SRAM) Volatile Typically uses 6-8 transistors Faster than DRAM Larger than DRAM Cache closer to CPU (L2/L3)

than DRAM No refresh required (less power!) Power can be less than DRAM

depending on frequency

MAGNETORESISTIVE RAM (MRAM) Non-volati le, sol id state - magnetic storage Built from two ferrous plates with an insulating layer One plate is kept charged at a constant level, the other is varied Reading occurs by sending a (small) test current through the cell (tunnel

magnetoresistance) Variety of write methods include a system similar to Core Memory (1960s)

Writes can be costly Density adds complexity & concerns

Write Operationhttp://low-powerdesign.com/article_MRAM_everspinhttp://low-powerdesign.com/article_MRAM_everspin

MRAM

h t t p : / / w w w . s c i e n c e d i r e c t . c o m / s c i e n c e / a r t i c l e / p i i / S 0 0 2 6 2 7 1 4 1 2 0 0 2 3 2 6

http://low-powerdesign.com/article_MRAM_everspin

Advertised size “pros” lead to cons Power & reliability correlate Power & size correlate

THYRISTOR RAM (TRAM) Volati le Sil icon on Insulator (SOI) pnpn thyristor 4x better density than 6T-SRAM Equal speed requires 2.5x higher density

Better active and standby power than 6T-SRAM

Fast Write with Thin Capacit ively Coupled Thyristor (TCCT-TRAM) Raises scalability concerns (high doping

precision) S and D T-RAM variants exist Compatible with FinFET and other

technologies

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7273751&tag=1

http://www.electronics-tutorials.ws/power/thyristor.html

ZERO-CAPACITOR RAM (ZRAM) Sil icon on Insulator (SOI) transistor body

produces capacitance in the transistor. Exploits “floating body effect” to store

information with only one transistor Eliminating the capacitor reduces on-chip

size, increasing memory density and access speed. Transistor and capacitor are essentially

stacked in the Z-plane, increasing density. Shorter trace distance decreases overall

latency despite having higher cell access time than SRAM

ZERO-CAPACITANCE RAM (Z-RAM) Speed increases over SRAM occur at larger memory block

sizes Writes occur using only gate and drain Writes occur during ON state (consumes power!) Licensed by AMD, though has not been brought into

production

COMPARISON SUMMARY

DRAM SRAM MRAM TRAM ZRAM Flash

Refresh Required Yes No No Varies Yes No

Density High 1T + 1C

Low6T

High~2T

High~3T

Very High1T

High1T

Volatile Yes Yes No Yes Yes No

Speed High Very High High High / Very High High / Very High Very Low

Scalability High Low Varies Varies / High High High

Power Less More Much Less Varies / Less More Much More

Cost Less More More More No Production (AMD) Much Less

Slide 11

1 for reference. can use this info, but make full tableAndrew Lints, 12/1/2016

SUMMARY Design is the pursuit of the “Holy Grai l” No one design fi ts every ideal , so design trade-of fs are required Key parameters Speed (Read & Write!) Power Reliability (Accurate read, write & maintenance of value) Volatility Die Size & Density Scalability Cache Level (on, off chip?)

Watch for the 3D stacked RAM project group!

QUESTIONS?

WORKS CITED h t t p : / / i e e e x p l o r e . i e e e . o r g / d o c u m e n t / 4 6 5 5 4 0 9 / ? a r n u m b e r = 4 6 5 5 4 0 9 ( Z R A M ) h t t p : / / w w w . h o t c h i p s . o r g / w p - c o n t e n t / u p l o a d s / h c _ a r c h i v e s / h c 1 9 / 3 _ T u e s / H C 1 9 . 0 5 / H C 1 9 . 0 5 . 0 2 . p d f

( T R A M ) h t t p : / / i e e e x p l o r e . i e e e . o r g / s t a m p / s t a m p . j s p ? a r n u m b e r = 7 2 7 3 7 5 1 ( T R A M ) h t t p : / / n v e . c o m / D o w n l o a d s / m r a m . p d f ( M R A M ) h t t p : / / l o w - p o w e r d e s i g n . c o m / a r t i c l e _ M R A M _ e v e r s p i n ( M R A M ) h t t p : / / w w w . s c i e n c e d i r e c t . c o m / s c i e n c e / a r t i c l e / p i i / S 0 0 2 6 2 7 1 4 1 2 0 0 2 3 2 6 ( M R A M ) h t t p : / / w w w . e m b e d d e d . c o m / d e s i g n / r e a l - t i m e - a n d - p e r f o r m a n c e / 4 0 2 6 0 0 0 / T h e - f u t u r e - o f - s c a l a b l e - S T T -

R A M - a s - a - u n i v e r s a l - e m b e d d e d - m e m o r y ( M R A M f o c u s , o t h e r s m e n t i o n e d / b e n c h m a r k e d ) h t t p : / / w w w . d i g i t i m e s . c o m / b i t s _ c h i p s / a 2 0 0 6 0 3 2 8 P R 2 0 2 . h t m l ( Z R A M ) h t t p : / / s e a r c h s o l i d s t a t e s t o r a g e . t e c h t a r g e t . c o m / a n s w e r / C o m p a r i n g - p e r f o r m a n c e - a n d - c o s t - o f - D R A M - v s -

N A N D ( F l a s h / D R A M ) h t t p : / / h e x u s . n e t / t e c h / n e w s / r a m / 9 8 0 3 5 - k i l o p a s s - d r a m - u s e s - v l t - t e c h - e l i m i n a t e - r e f r e s h - r e q u i r e m e n t /

( D R A M ) h t t p : / / w w w . d i g i t i m e s . c o m / b i t s _ c h i p s / a 2 0 0 6 0 3 2 8 P R 2 0 2 . h t m l ( Z R A M ) L e c t u r e b y D r . S h a a b a n ( h t t p : / / m e s e e c . c e . r i t . e d u / c m p e 5 5 0 - f a l l 2 0 1 6 / 5 5 0 - 1 1 - 1 4 - 2 0 1 6 . p d f ) ( S R A M &

D R A M ) h t t p : / / w w w . d i f f e n . c o m / d i f f e r e n c e / D y n a m i c _ r a n d o m - a c c e s s _ m e m o r y _ v s _ S t a t i c _ r a n d o m -

a c c e s s _ m e m o r y # P o w e r _ C o n s u m p t i o n ( D & S R A M ) h t t p s : / / p d f s . s e m a n t i c s c h o l a r . o r g / 7 e 4 1 / 2 e d 8 8 b b 7 8 5 5 6 0 0 a 6 3 f e 7 c 5 b 9 1 a f 7 b 1 6 1 0 7 2 6 . p d f ( S R A M )