The document presents a comprehensive overview of Static Random Access Memory (SRAM), detailing its design, fabrication, operational characteristics, and applications. SRAM is primarily used in microprocessors due to its speed and lower power consumption compared to DRAM, although it is more expensive and less dense. The future of SRAM includes developments in non-volatile SRAM, which offers faster write times and eliminates the need for backup batteries, positioning it for various applications including RAID controllers and network routers.

1. SRAM - Design
and Fabrication
Presented by-
Rinku (170002036)
Nishit Meena (170002038)
Sagar Rangari (170002039)

2. Outlines
● MOTIVATION
● INTRODUCTION
● SRAM CIRCUIT DESIGN
● EXPERIMENTAL FABRICATION
● FIGURE OF MERIT OF DIFFERENT GENERATION
● APPLICATIONS AND FUTURE SCOPE

3. MOTIVATION
❖ Recent day’s cache memory sizes are expanded with
advancements and they play an important role in
microchips
❖ SRAM Comprises 50% and more of modern designs
❖ For density, SRAM uses smallest possible devices and
therefore very sensitive to impact of manufacturing
variations
❖ With every era, the sizes of cache memory are increasing

4. INTRODUCTION
❖ SRAM - Static random access memory
❖ It is type of semiconductor random-access memory
❖ Uses a bistable latch circuit to store the logic
❖ Power consumption varies with frequency of operation
❖ SRAM can be used for high speed memory purpose in
microprocessors
Fig.1 A Static-RAM chip [1]

5. SRAM CIRCUIT DESIGN

6. MEMORY CLASSIFICATION
COMPUTER MEMORY
PRIMARY MEMORY SECONDARY MEMORY
HARD DISK
ROM
RAM CD PAN DRIVE FLOPPY DISK
DVD

7. Features Comparison Between Memory Types
SRAM DRAM
LOW LOW
2 Program voltage
1-8ns 8-50ns
3 Write/Erase time
8ns 50ns
4 Read time
YES
HIGH
10-30ms
0.1us
Hard disk
YES
YES
HIGH
50ns
1us1-
100ms
HIGH
10ms
0.1us
CD FLASH
NO NO
1 Non-Volatility

8. SRAM
❖ Hold data without external refresh
Fig.2 SRAM Memory Chip
[2]
❖ Simplicity : don’t require external refresh
circuitry
❖ Speed: SRAM is faster than DRAM
❖ Cost: several times more expensive than
DRAM
❖ Size: take up much more space than
DRAM
❖ Power: Consume less power than DRAM

9. Continued...
➢ A typical SRAM memory made up of six
MOSFETs. Each bit in SRAM is stored on 4
transistors(M1,M2,M3,M4) that forms two
cross- coupled inverter.
➢ This storage cell has two stable states which
are used to denote 0 and 1
➢ Two additional access transistors serve to
control the access to a storage cell during
read and write operation
Fig.3 6-Transistor SRAM Cell [3]

10. SRAM Read and Write Operation
● For write operation
● Data =1
● Datab=0
● Select=1
● For Read Operation
● Data=1
● Datab=1(Forcefully)
● Select=1
Fig. 4 Write Operation [4]
Fig. 5 Read Operation [4]

11. SRAM FABRICATION

12. ● 32,42 - Pull up
transistors
● 34,44 - Pull down
transistors
● 50,52 - NMOS
● 58 - Word line
● 54 - Bit line
● 56 - Complimentary
bit line
❏ Fig. 6 Shows the schematic diagram of one bit 6-T SRAM structure
❏ This structure is repeated over and over to form matrix of complex SRAM
IC’s
Fig. 6 [5]

13. ● 60,62,66,68 -
Masks used for
different
purpose, placed
over one
another
● 64 - One bit of
SRAM array
❏ Fig 7 and 8 shows the relative positions of mask to be placed over one
another
❏ Perfect positioning of masks is crucial to make better quality SRAM IC’s
Fig. 8 [5]
Fig. 7 [5]

14. ● 102 - Substrate
● 104 - Isolation
Region
● 106 - High-K gate
insulator (Hafnium
oxide)
● 108 - Another
Insulator (Titanium
Nitride)
● 110 - Dummy gate
electrode material
(Polycrystalline
silicon)
❏ Fig. 9 shows the relative positioning of one bit SRAM cell w.r.t. all masks
❏ Fig. 10 shows the cross sectional view taken along line X-X in Fig.7
❏ Basic steps of device fabrication such as oxidation, diffusion, ion implantation,
photolitiogyaphy etc are followed
Fig. 9 [5]
Fig. 10 [5]

15. ● 116 -
Insulator
(Silicone
nitride)
● 118 -
Insulator
(SiO2)
● 120 - Hard
mask
material
❏ Two different type of insulating materials are deposited (Fig. 11)
❏ Hard mask material is deposited over dummy electrodes for selective etching
(Fig. 12)
Fig. 11 [5] Fig. 12 [5]

16. ● 122 - Intergate
mask
● 124 - Spacer-cut
mask
❏ Intergate and Spacer-cut masks are used for patterning ‘Hard mask layer’, which
then can be used for selective etching
❏ Fig.14 shows the relative positioning of intergate and spacer-cut mask w.r.t original
arrangement
Fig. 14 [5]
Fig. 13 [5]

17. ● 130 - Metal
Silicide
● 132 - Fill
material
(Poly-
crystalline
Si)
❏ After selective etching sharp-cornered structure is obtained (Fig.15)
❏ Implementation of metal silicide and polycrystalline Si
❏ After planarizing Fig.16 is obtained
Fig. 16 [5]
Fig. 15 [5]

18. ● 136 - Hard
mask layer
● 142 - Gate
electrode
material
● 150,152 -
Real Gate
electrodes
● 154 -
Source
drain
contacts
❏ Hard mask layer is patterned (Fig.17), which then used for selective etching
❏ Using this Hard mask layer various connections are established, e.g. -
common gate connection between pull-up and pull-down transistors
❏ After planarizing Fig.18 is obtained
Fig. 18 [5]
Fig. 17 [5]

19. CHARACTERISTICS
❖ SRAM is more expensive, but faster and significantly less power hungry than
DRAM
❖ It is therefore used where either bandwidth or low power ,or both, are
principal considerations
❖ SRAM is also easier to control and generally more truly random access than
modern types of DRAM
❖ Due to a more complex internal structure, SRAM is less dense than DRAM
and is therefore not used for high-capacity, low-cost applications such as the
main memory in personal computers

20. FIGURES OF MERIT OF
DIFFERENT GENERATIONS

21. ➢ The first solid state memory chip
➢ It is a 64-bit SRAM
➢ It applied the newly developed Schottky Bipolar technology
April 1969.
Fig. 19 Intel 3101 [6].

22. ➢ The first MOS memory chip
➢ A 256-bit SRAM
➢ Produced in with Silicon gate MOS technology
➢ It gave intel the edge it needed to produce high density memories
July 1969
Fig. 20 Intel 1101
[7]

23. Fig. 21 Intel Core 2 Duo E6300
Processor [8]
Fig. 22 Latest Intel Core i9-9900T
Processor ( 16M Cache, Up to 4.40 GHz )
[9]
➢ Modern SRAM’s are generally integrated inside microprocessors

24. Fig. 23 SRAM
Scaling Trend [10]
➢ SRAM trends shows cell area reduced by half every two years

25. APPLICATIONS AND
FUTURE TRENDS OF
WORK

26. Non Volatile SRAMs are the future of SRAMs for the following
reasons :-
➢ It provides write times as fast as 20ns .
➢ It provides unlimited write cycles .
➢ It instantly captures data on power loss .
➢ Eliminates the need for a backup battery .

27. Activities of Non Volatile SRAMs
➢ RAID Controller Cards: These are data storage devices used to manage and
improve the performance of hard disk drivers and solid-state drivers
➢ Programmable Logic Controllers (PLCs): These are computer control systems
used to automate industrial manufacturing equipment
➢ Network Routers: It uses nvSRAM to store critical configuration data so that
they can quickly recover after a power outage
➢ Electronic Gaming Machines: nvSRAM is replacing volatile memories in this
application to eliminate batteries and improve performance

28. Fig. 24 RAID Controller Card
[11]
Fig. 25 Programmable Logic
Controller [12]
Fig. 26 Network
Router [13]
Fig. 28 Electronic Gaming
Machine [14]

29. Random Transaction Rate (RTR) - Random Transaction Rate
(RTR) is the number of fully random read or write transactions
a memory can perform every second.
➢ Cypress's QDR-IV SRAM provides RTR up to 2132 MT/s
➢ This level of performance is critical to enable the next
generation of high performance systems
Fig. 29 RTR [15]. Fig. 39 QDR SRAM
[15].

30. FUTURE SCOPE
❏ To decrease the power dissipation
❏ Density of SRAMs in embedded application
❏ Reduction of leakage in a SRAM cell

31. Sources
● [1]https://en.m.wikipedia.org/wiki/Static_random-access_memory
● [2]
https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcTt6M5kR4jsgp9At1BE3orl2vgMXElW-ii
Cs-4blQYRSMQo2VP6
● [3]https://commons.wikimedia.org/wiki/File:6t-SRAM-cell.png
● [4]https://www.slideshare.net/tipusultan3150/sram-dram
● [5]http://www.freepatentsonline.com/20130193516.pdf
● [6]https://newsroom.intel.com/news/intel-at-50-intels-first-product-3101/
● [7]
https://commons.wikimedia.org/wiki/File:Intel_1101_1a.jpghttps://commons.wikimedia.org/wiki/File:Intel_1101_1a.
● [8]https://en.wikipedia.org/wiki/Conroe_(microprocessor)#Conroe
● [9]https://hexus.net/tech/news/cpu/133988-intel-core-i9-9900t-tested-multiple-times-geekbench-4/
● [10]https://fuse.wikichip.org/news/525/iedm-2017-isscc-2018-intels-10nm-switching-to-cobalt-interconnects/5/
● [11]https://www.esaitech.com/lsi-logic-ser523-6-port-raid-controllercard.html
● [12]https://images.app.goo.gl/p2bwpxSDR9uNsNuG6
● [13]https://www.lifewire.com/how-routers-work-816456
● [14]
http://www.emissourian.com/local_news/county/electronic-gaming-machines-in-use-in-franklin-county-not-regulated/

32. THANK YOU