1. VLSI Techniques
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2. VLSI Design
 What is VLSI?
 “Very Large Scale Integration”
 Defines integration level
 1980s hold-over from outdated taxonomy for integration levels
 Obviously influenced from frequency bands, i.e. HF, VHF, UHF
 Sources disagree on what is measured (gates or transistors?)
 SSI – Small-Scale Integration (0-102)
 MSI – Medium-Scale Integration (102-103)
 LSI – Large-Scale Integration (103-105)
 VLSI – Very Large-Scale Integration (105-107)
 ULSI – Ultra Large-Scale Integration (>=107)
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3. Moore’s Law
 In 1960 Gordon Moore predicted “the number of
components that can be integrated on a single chip
would increase at such a rapid rate that it will become
twice in every 18 months”.
 So by using Moore’s law we get an approximate
integration level trend at any time.
 But now moore’s law has reached its physical limit.
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4. Integration Level Trends
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5. Integrated Circuits/MEMs
 Today, VLSI refers to systems implementation with integrated
circuits
 Integrated circuit refers mostly to general manufacturing technique
 micro/nano-scale devices on a semiconductor (crystalline) substrate
 Formed using chemical/lithography processing
 What kind of devices / structures?
 transistors (bipolar, MOSFET)
 wires (interconnects and passives)
 diodes (junction, LEDs, VCSELs, MSM, photoconductor, PiN)
 MEMs (piezoelectric integration, accelerometers, gyroscopes,
pressure sensors, micro-mirrors)
 For CMOS digital design, we only use MOSFET transistors (used
as switches) and wires
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6. Chips
 Integrated circuits consist of:
 A small square or rectangular “die”, < 1mm thick
 Small die: 1.5 mm x 1.5 mm => 2.25 mm2
 Large die: 15 mm x 15 mm => 225 mm2
 Larger die sizes mean:
 More logic, memory
 Less volume
 Less yield
 Dies are made from silicon (substrate)
 Substrate provides mechanical support and electrical common point
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7. CMOS technique of IC fabrication
 Common metal oxide semiconductor for constructing
FET on wafer chip
 N-well technique of fabrication on doped silicon, poly
silicon, metal oxide and silicon oxide layer is
implemented.
 On this pattern of various layers Optical lithography
followed by photo resisting and etching is done.
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8. CMOS fabrication
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9. Chip Design styles
Design styles
Full custom Semi custom
Array based Cell based
Pre diffused like Macro cell like
gate arrays, sea PLA gate matrix
of gates etc etc
Pre wired like
Standard cell,
anti fuse based
hierarchical cell
memory based
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10. Phases of creating microelectronic
chips
 Design : Circuit representation is converted into
geometric representation
 Fabrication : involves method of deposition and
diffusion on wafer
 Testing : circuit is tested to meet design specifications
 Packaging : each circuit is packaged by establishing
interconnections.
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11. DESIGN FABRICATION TESTING PACKAGING
Modeling Slicing
Mask Tester 10000
fabrication 110011 111000
Synthesis and
Packaging
optimization
Wafer
fabrication Wafer
Validation Validation
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12. Concept of VLSI design
 Polygons represent layers deposited on the substrate
 More of an art than science
Scale:
approximately
10 um x 10 um
 One 2-input NAND gate with 4 transistors
 Typical microprocessor contains 50 – 200 million
transistors (10-50 million gates)
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13. Need of computerized design tools
 Manual layout of complex large scale design is obviously not practical
 Design complexity:
 Manually drawing layout for a billion transistors would take too long
 Even if we could… there are many problems like…
 How to verify (test) designs for functionality, speed, power, etc.?
 Complexity scales faster than actual design
 How to reuse designs?
 How to create human-readable designs?
 How to speed-up design process?
 These problems form a great deal of work
 Electronic Design Automation (EDA)
 a.k.a. CAD
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14. VLSI CAD
 Various software like synopsys , cadence etc. are used
by designers to synthesize highly efficient VLSI chips.
 Hardware description for IC is written in Verilog or
VHDL.
 It describes the hardware ,interconnection of circuit
blocks and functionality.
 VHDL(very high speed IC hardware design language)
is the C of VLSI technology.
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15. VLSI applications
 Basically three areas of application exist today for VLSI
 Analog : Small transistor count precision circuits such
as Amplifiers, Data converters, filters, Phase Locked
Loops, Sensors etc.
 ASIC: application specific IC a microchip to perform and
execute a particular task like digital signal processing,
image compression etc.
 SoC: systems on a chip are highly complex mixed signal
processors like a network chip or a wireless radio chip.
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16. Challenges to VLSI technology
 As integration increases VLSI chips somewhat suffer
from the challenges such as
 Power dissipation due to increasing components
 Noise delays due to capacitive or inductive coupling
 Decrease in clock frequency by skin effect on VLSI chip
 Improper scaling of wires for increasing components.
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17. Future of VLSI
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18. Parameter 1979 1999 2019
Gate length(um) 5 0.2 0.008
Gate delay(ps) 3000 150 7.5
Clock cycle(ns) 200 2.5 0.08
Wire pitch(mm) 15 1 0.07
Grid/chip 2 x 10^5 3 x 10^8 3 x 10^11
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19. Future of VLSI
 Technology is evolving everyday and VLSI is the most
progressing one it is moving to ULSI.
 It has been predicted that VLSI will develop more in
the coming decade.
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