Introduction to VLSI

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• •IC: Integrated circuits: many transistors on one chip.

• •Very Large Scale Integration (VLSI): very many• •CMOS :Complementary Metal Oxide

Semiconductor• –Fast, cheap, low power transistors• •Today: How to build your own simple CMOS

chip (you can have your own company)• –CMOS transistors: control performance• –Building logic gates from transistors (AND, OR,

NOT, XOR)• –Amplifier, adder, Flip Flop System level design:• –Transistor layoutand fabrication

1. 1958: First integrated circuit–Flip-flop using two transistors

2. Built by Jack Kilby at Texas Instruments3. 2003–Intel Pentium 4 mprocessor (55 million

transistors)4. –512 Mbit DRAM (> 0.5 billion transistors)5. 53% compound annual growth rate over 45 years6. –No other technology has grown so fast so long•7. --Driven by miniaturization of transistors–Smaller is

cheaper, faster, lower in power!

• •1018 transistors manufactured in 2003–100 million for every human on the planet05010015020019821984198619881990199219941996199820002002

• •Integration:Levels

• •SSI:10gates/ chip: Small signal integration

• •MSI:1000gates/ chip: Medium Signal Integration

• •LSI:10,000 gates/chip: Large Signal Integration

• •VLSI:higher that 10K gates/ chips

• •In 1971, minimum dimensions of 10 um in 4004• •In 2003, minimum dimensions of .18um in

Pentium4.• •Scaling down forever ? (No, transistors cannot

be less than atoms)• •Many predictions of fundamental limits to

scaling have already proven wrong• •We believe that scaling will continue for at least

another decade.• •What is the future?

• •Silicon is a semiconductor

• •Pure silicon has no free carriers and conducts poorly

• •Adding dopants increases the conductivity

• •Group V(Arsenic): extra electron (n-type)

• •Group III(Boron): missing electron, called hole (p-type)

• •Four terminals: gate, source, drain, body• •Gate –oxide –body stack looks like a

capacitor• –Gate and body are conductors• –SiO2(oxide) is a very good insulator• –Called metal –oxide –semiconductor

(MOS) capacitor• –Even though gate is no longer made of

metal

• •Body is commonly tied to ground (0 V)

• •When the gate is at a low voltage:

• –P-type body is at low voltage (substrate)–Source-body and drain-body diodes are OFF

• –No current flows, transistor is OFF

• •When the gate is at a high voltage:

• –Positive charge on gate of MOS capacitor

• –Negative charge attracted to body

• –Inverts a channel under gate to n-type

• –Now current can flow through n-type silicon from source through channel to drain, transistor is ON

• •Similar, but doping and voltages reversed

• –Body tied to high voltage (VDD)

• –Gate low: transistor ON

• –Gate high: transistor OFF–Bubble indicates inverted behavior

• Power Supply• •GND = 0 V• •In 1980’s, VDD= 5V• •VDD has decreased in modern processes –

High VDD would damage modern tiny transistors

• –Lower VDDsaves power • •VDD= 3.3, 2.5, 1.8, 1.5, 1.2, 1.0,• •Dimension of the transistors decrease.

•Gate delay/ Propagation delays

•Rise Time

•Fall Time

--control the performance of the gate/ system

•Fast/ slow/Loading effect

•BiCMOS: Bipolar CMOS (Faster low power loss)