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VLSI

• What is VLSI?– “Very Large Scale Integration”

• Single Transistor-----------------------------1958• SSI – Small-Scale Integration (0-102)---1960• MSI – Medium-Scale Integration (102-103)---1967• LSI – Large-Scale Integration (103-105)---1972• VLSI – Very Large-Scale Integration (105-107)---1978• ULSI – Ultra Large-Scale Integration (>=107)---1989• GSI _ Giant Scale Integration (>=109)---2000

*Where these are given as no of transistors.

ENIAC - The first electronic computer (1946)

Digital Integrated Circuits © Prentice Hall 1995IntroductionIntroduction

Integration Level Trends

Obligatory historical Moore’s law plot

Example: Intel Processor Sizes

Source: http://www.intel.com/

Intel386TM DXProcessor

Intel486TM DXProcessor

Pentium® Processor

Pentium® Pro &Pentium® II Processors

1.5 1.0 0.8 0.6 0.35 0.25Silicon ProcessTechnology

Why monolithic Integration?

•Less area/volume, compact size

•Less power consumption

•Less testing requirement at sys level

•Higher reliability, due to improved on chip interconnects & elimination of soldered joints.

•Higher speed, reduced int length & abs of parasitic capacitance.

•Less cost and easy to handle

IC Products

• Processors– CPU, DSP, Controllers

• Memory chips– RAM, ROM, EEPROM

• Analog– Mobile communication,

audio/video processing• Programmable

– PLA, FPGA• Embedded systems

– Used in cars, factories– Network cards

• System-on-chip (SoC)

Images: amazon.com

What is an IC?

• It is a miniature, low cost electronic device consisting of active and passive components those are irreparably joined together on a single crystal chip.

What is “CMOS VLSI”?

• MOS = Metal Oxide Semiconductor (This used to mean a Metal gate over Oxide insulation)

• Now we use polycrystalline silicon which is deposited on the surface of the chip as a gate. We call this “poly” or just “red stuff” to distinguish it from the body of the chip, the substrate, which is a single crystal of silicon.

• We do use metal (aluminum) for interconnection wires on the surface of the chip.

• Integrated Circuits/MEMsHierarchy of various technology

Semiconductor process

Silicon GaAs

UnipolarBipolar UnipolarBipolar

ECL

TTL

NMOS PMOS

CMOS

• Selection of processing technology is a trade off among Operating speed, Chip area, Power dissipation.

• 1980------2mic.m tech-------64Kb per chip

• 1990------.5---------------------16Mb

• 1995------.25--------------------256Mb

• 2000------.18--------------------1Gb

• 2005------.15--------------------4Gb

• 2010------.08---------------------64Gb

VLSI Design Methodology

• Full custom Design style

• Semi custom Design style

• Frontend Designer

• Backend Designer

VLSI design flow--Y chart (D.GJASKI)

Top-down & bottom-up approach

n+n+S

GD

+

DEVICE

CIRCUIT

GATE

MODULE

SYSTEM

Digital Integrated Circuits © Prentice Hall 1995IntroductionIntroduction

FLOW CHART FOR VLSI DESIGN FLOW

Functional design

Fun verification

Logic design

Logic verification

Ckt design

Ckt verification

Layout design

Layout verification

Fabrication & Testing

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

Advancements over the years

• © Intel 4004 Processor

• Introduced in 1971• 2300 Transistors• 108 KHz Clock

• © Intel P4 Processor

• Introduced in 2000• 40 Million

Transistors• 1.5GHz Clock

Intel 4004 Microprocessor

Intel Pentium (IV) Microprocessor

System Design Pyramid

• Photo-litho-graphy: latin: light-stone-writing

• Photolithography: an optical means for transferring patterns onto a substrate.

• Patterns are first transferred to a photoresist layer.

•Typically a wafer is about 8-10 inches in diameter.

Individual ICs are placed inside it.

Photolithography and Patterning

Photoresist is a liquid film that is spread out onto a substrate, exposed with a desired pattern, and developed into a selectively placed layer for subsequent processing.

• Photolithography is a binary pattern transfer: there is no gray-scale, color, nor depth to the image.

Steps

• Photo resist Coating (covering)

A light sensitive organic polymer (plastic)

• Mask/ Reticle formation

• Exposure to light (UV/X-RAY/E-BEAM)

WHAT IS A PHOTOMASK?

Photomasks are high precision plates containing microscopic images of

electronic circuits. Photomasks are made from very flat pieces of quartz or glass with a layer of chrome on one side. Etched in the chrome is a portion of an electronic circuit

design. This circuit design on the mask is also called geometry.

The Resist

The first step is to coat the Si/SiO2 wafer with a film of a light sensitive material, called a resist.

A resist must also be capable of high fidelity recording of the pattern (resolution) and durable enough to survive later process steps

Solvent Evaporates

Photolithography

Energy - causes (photo)chemical reactions that modify resist dissolution rate

Mask - blocks energy transmission to some areas of the resist

Aligner- aligns mask to previously exposed layers of the overall design

Resist - records the masked pattern of energy

Energy

Mask + Aligner

PhotoresistWafer

Next Generation LithographyIn 1996, five technology options were proposed for the 130 nm gate length technology:

•X-ray proximity Lithography (XPL)

•Extreme Ultraviolet (EUV)

•Electron Projection Lithography (EPL)

•Ion Projection Lithography (IPL)

•Direct-write lithography (EBDW).

These options were referred to as the next generation lithography.

MOSFET Design Rules

• Lambda based design Rule

• Micron Rule

Minimum width and Spacing

Layer Value

Poly 2L

Active 3L

N select 3L

Metal 3L

Stick Diagrams

Metal

poly

ndiff

pdiffCan also drawin shades of

gray/line style.

• Wiring Tracks

• A wiring track is the space required for a wire– 4 width, 4 spacing from neighbor = 8

pitch

• Transistors also consume one wiring track

• Well spacing

• Wells must surround transistors by 6 – Implies 12 between opposite transistor

flavors– Leaves room for one wire track

Basic Circuit Layout

Gnd

VDD

x x

X

X

X

X

VDD

x x

Gnd

Stick Diagra

m

Stick Diagrams

Layout Diagrams

Gnd

VDD

x x

X

X

X

X

VDD

x x

Gnd

Stick Diagrams

Example: Inverter

MOSFET Arrays and AOI GatesA B C

yx

y

x

A B C

Parallel Connected MOS Patterning

x

y

A B

X X X

A B

x

y

Alternate Layout Strategy

A B

x

y

X X

X X

x

A B

y

MOSFET Arrays and AOI Gates

NAND2 Layout

Gnd

Vp

ba.

a b

Vp

Gnd

X X X

X X

a b

ba.

NOR2 Layout

Gnd

Vp

ba

a b

Vp

Gnd

X X

ba

X X X

a

b

Stick Diagrams

Power

Ground

B

C

OutA

Cells, Libraries, and Hierarchical Design

• Creation of a Cell Library

x

Gnd

xX

X

X

X

X

X

X

X

VDD

X x x

X X X

X X

a

b

X

X

X

X

VDD

x

Gnd

X

.a b

.a b

Gnd

X X

ba

X X X

a

b

X

X

X

X

VDD

x a b

• Cell Placement• System Hierarchy (MOSFET-Gates-F/Fs-

Registers-Networks-Systems)• Floorplans and Interconnect Wiring• Y= (# of Good Chips/Total No)*100%• Y=Yield• ‘Y’ depends on total area=A, and no of

defects=D,

• Y=e *100%AD

Interconnects• Place and Route Algorithm.

• Wiring Delay

• td=kl2

• l=length of inter connect.td