VLSI Technology Evolution

Mr. A. B. ShindeAssistant Professor,Electronics Engineering, PVPIT, Budhgaonshindesir.pvp@gmail.com

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Before we start… Answer this What is VLSI ?

If your answers is other than…

V L S I = Very Large Scale Integration

then you are most welcome…

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Vacuum Tubes

Gas-filled Tube

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Early Computers

Courtesy: Intel Corporation

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Vacuum Tubes… A gas-filled tube is essentially a vacuum tube having a small

amount of some inert gas at low pressure.

Gas-filled tubes have two types: Cold-cathode type and Hot-cathode type.

Cold-cathode Hot-cathode

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Cold-Cathode Gas Diode

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Hot-Cathode Gas Diode

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Thyratron (Triode)

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Atomic Structure

Number of Electrons in orbit = 2n2Neils Bohr

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Energy Bands

larger the orbit of an electron, the greater is its energy and higher is the energy level.

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Energy Bands in Solids Valence band: The range of energies (i.e.

band) possessed by valence electrons is known as valence band.

Conduction band: The range of energies (i.e. band) possessed by conduction band electrons is known as conduction band.

Forbidden energy gap: The separation between conduction band and valence band on the energy level diagram is known as forbidden energy gap.

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Classification of Solids & Energy Bands

Insulators Conductors Semicondutors

1 eV is the amount of energy acquired by an electron when it is accelerated through a potential difference of 1 V.

energy gap is ≈ 15 eV Bands are overlapped energy gap is ≈ 1 eV

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Semiconductors Semiconductor has :

almost full valence band almost empty conduction band small energy gap (≈ 1 eV) between

valence and conduction bands.

Silicon atom

Germanium atom

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Commonly Used Semiconductors

Silicon Germanium

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Energy Band Description

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Effect of Temperature on Semiconductors At absolute zero: All the electrons are tightly held by the

semiconductor atoms. The valence electrons are engaged in co-valent bonding.

At this temperature, the co-valent bonds are very strong and there are no free electrons.

Hence, the semiconductor crystal behaves as a perfect insulator

Above absolute zero: Some of the covalent bonds in the semiconductor break due to the thermal energy supplied.

The breaking of bonds sets those electrons free therefore few free electrons exist in the semiconductor.

The resistance of a semiconductor decreases with the rise in temperature

It has negative temperature coefficient of resistance.

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Types of semiconductor Intrinsic Semiconductor: A semiconductor in an extremely pure form is known as an intrinsic

semiconductor It has little current conduction capability at room temperature

Extrinsic Semiconductor: The pure semiconductor must be altered so as to significantly increase

its conducting properties. This is achieved by adding a small amount of suitable impurity to a

semiconductor. The semiconductor with impurity is called as extrinsic semiconductor.

Further two types: n-type & p-type

(If Impurity is from 5th column) (If Impurity is from 3rd column)

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n-type Semiconductor When a small amount of pentavalent impurity is added to a pure

semiconductor, it is known as n-type semiconductor

Pentavalent impurities: arsenic (At. No. 33) &antimony (At. No. 51).

Such impurities which produce n-type semiconductor are known as donor impurities because they donate or provide free electrons

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p-type Semiconductor When a small amount of trivalent impurity is added to a pure

semiconductor, it is called p-type semiconductor.

Trivalent impurities:gallium (At. No. 31) & indium (At. No. 49).

Such impurities which produce p-type semiconductor are known as acceptor impurities because the holes created can accept the electrons.

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pn junction diode

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Transistor A transistor consists of two pn junctions formed by sandwiching either

p-type or n-type semiconductor between a pair of opposite types.

npn transistor

symbol 2 diode analogy

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Transistor

First transistor

1947: Bardeen, Brattain and Schokley at Bell laboratories built the first working point contact transistor (Nobel Prize in Physics in 1956)

The field of electronics shifted from vacuum tubes to solid-state devices

Courtesy: Texas Instruments

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Transistors To manufacture larger circuits the number of transistors required

will be more…ultimately large board space was required

Human mind never sits idle

They was continuously thinking “can we bring few transistors together…?

And the answer found in 1958… Yes IC was invented …!!!

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Integrated Circuit An integrated circuit (IC) is one in which circuit components such as

transistors, diodes, resistors, capacitors etc. are mounted on small piece of semiconductor i.e. first IC was developed.

On IC we can easily mount large number of components together.

IC Inventers: Jack Kilby & Robert Noyce

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Integrated Circuit

First integrated circuit

Courtesy: Texas Instruments

As 1958: Jack Kilby built the first integrated circuit flip flop at Texas Instruments (Nobel Prize in Physics in 2000)

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Integrated Circuit Cross Section: Internal View

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Integrated Circuit Growth

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Integrated CircuitAdvantages :1. Increased reliability due to lesser number of connections.2. Extremely small size3. Lesser weight and space requirement4. Low power requirements.5. Greater ability to operate at extreme values of temperature.6. Low cost 7. The circuit lay out is greatly simplified Disadvantages : 8. If any component in an IC goes out of order, the whole IC has to be replaced. 9. In an IC, it is neither convenient nor economical to fabricate capacitances

exceeding 30 pF.10. It is not possible to fabricate inductors and transformers 11. It is not possible to produce high power ICs (greater than 10 W).

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Integrated Circuit

But… remember “Human mind never sits idle …”

Continuous research goes on in the direction…

Can we increase the number of transistors…?

Answer is … Yes…!!!

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Integration Technology…

Year No. of Transistors

SSI 1964 1 to 20

MSI 1968 20 to 100

LSI 1971 100 to 1,000

VLSI 1980 1,000 to 10,000

ULSI 1984 10,000 and more

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VLSI Technology Design Stages: Abstraction Levels

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VLSI Technology

Programming Languages VHDL Verilog

Implementation Technology FPGA CPLD

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VHDL V = VHSIC H = Hardware D = Description L = Language

VHSIC = Very High Speed Integrated Circuit

We can describe any hardware (digital logic) using this language

c<= a and b;

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Implementation Technology FPGA = Field Programmable Gate Array

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Implementation Technology CPLD = Complex Programmable Logic Devices

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VLSI Design Flow