Microelectronic Circuits

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					Microelectronic Circuits
        An Overview
       L. K. Maheshwari
                     Topics
   Electronics
   Electronic Circuits
   Microelectronics and Microelectronic Circuits
   Microelectronic Devices and Models
   Circuit simulation with SPICE
   From paper to silicon
   Electronic Integrated Systems
                  Electronics
   Electronics is the study of the science and
    technology of carrier flow in vacuum, solids or
    gases
   Thus we have vacuum devices, semiconductor
    devices and gaseous devices
   The study of the science, technology and
    applications of these devices is the domain of
    electronics
              Microelectronics
   Microelectronics deals with fabricating
    components and devices within or upon a
    substrate and interconnecting them for a given
    circuit or system function
   Classification
        Microelectronic Circuits
   An interconnection of circuit components and
    devices on a single piece of silicon
   Examples of ICs
        Microelectronic Devices
   Bipolar Junction Transistors
   Metal Oxide Semiconductor Field Effect
    Transistors
       Modelling and Simulation
   The need for modelling and simulation
   Types
               History of BJT
   Discovered accidentally in 1947 by Bardeen and
    Brattain while trying to make the MOSFET,
    without understanding underlying physics
   Shockley (who was on a holiday at the time of
    the invention) deduced and wrote “Theory of
    Holes and Electrons in Semiconductors” to
    supplement the discovery
   Nobel Prize awarded to all three in 1956
       Salient features of the BJT
   Exponential transfer characteristics provide
    extremely high transconductance and hence high
    gain
   High fT of transistors provide high bandwidth
   Very fast switching speed when used as
    electronic switch
           History of MOSFET
   Julius Lilienfield proposed the operating
    principle of MOSFETs as early as in 1925
   In 1960, the Radio Corporation of America
    finally came up with the MOSFET
   In 1967, they came up with CMOS technology
    which offered faster operation and lower power
    dissipation than any other previous MOS
    families
    Salient features of the MOSFET
   Fabrication was essentially a surface-only
    technology and its ease and low cost provided a
    market viability not available with BJTs
   The proliferation of digital technology made the
    extremely high and extremely low “OFF” and
    “ON” resistances respectively, a very attractive
    feature for mass fabrication
   The ease of scalability of MOS technology
    helped create faster chips for new generations of
    microelectronic circuits
             CMOS technology
   Combines nMOS and pMOS transistors on the
    same chip
   pMOS devices used closer supply voltage and
    nMOS transistors used closer to ground provide
    ease of biasing, and hence pave the way for
    more versatile circuitry (in analog circuitry)
   Complementary operation actualises low power
    dissipation (in digital circuitry)
         Advantages of BiCMOS
   Combines high speed and gain, and low output
    resistance of BJTs with high input impedance of
    MOSFETs
   For digital circuits, this implies a simple low
    power logic family
   For analog circuits, this means that stages can be
    combined to provide high input and low output
    impedances of ideal voltage amplifier
         Drawbacks of BiCMOS
   Fabrication process not very mature
   Fine tuning of either BJTs or MOSFETs
    involved addition of further fabrication steps
   For high performance logic design, BiCMOS
    still has not been able to outdo pure CMOS
    technology, thus maintaining the latter as the
    choice for the mainstream industry
            Some other trivia…
   In 1959 Jack Kilby of Texas Instruments and
    Robert Noyce of Fairchild Semiconductors
    make first integrated circuit
   In 1962 Frederic Heiman and Stephen Hofstein
    created the first MOS IC
   In 1971 Intel produced the first microprocessor
    (the 4-bit 4004) with 2300 transistors on 3mm x
    4mm area and running at 108 kHz
   In 1999 Intel produced the 32-bit Pentium Pro,
    with 5.5 million transistors on 1cm x 1cm area
    using 0.13 µm technology and running at 1 GHz
           Microelectronics today
   In the early 21st century, AMD debuts its 64 bit
    processors which run at around 1.8 GHz, built
    with 90 nm technology. (Till date, AMD processors
    outperform any Intel processor of any number of bits, of
    any clock speed, of any process and of any number of
    transistors in its class)
   In 2005, ST Microelectronics became the first
    company in the world to demonstrate a 40 nm
    digital library prototype to the world. (The average
    diameter of the human hair is between 70 and 100 µm)
Analog and Mixed Signal Design
   Analog circuits form a small but absolutely
    indispensable part of today’s microelectronics. It
    is the front end for many electronic systems
   Understanding analog helps us deal with the
    basic units of voltage and current, and deepen
    our understanding for any form of circuitry,
    including digital
   Mixed signal ICs combine both analog and
    digital circuitry; e.g. data converters
    (ADC/DAC), PLLs, frequency synthesisers
              Circuit simulation
   The huge number of transistors in
    microelectronics circuitry, their fabrication costs
    and their level of miniaturisation make building
    test circuitry impossible in preliminary stages
   Simulation Program with Integrated Circuit
    Emphasis used to test circuits on computers
   SPICE uses numerical convergence techniques
    to use the computer to imitate the actual
    behaviour of circuits
                 From paper…
   After successful simulation of a circuit, a
    physical representation of the same is drawn by
    the designer. This is called a layout
   A layout corresponds to the top level view of
    actual physical placements of appropriately
    electronically treated silicon and its derivatives’
    layers for the integrated circuit
   With CAD tools the layout is converted into a
    circuit containing parasitics. This is resimulated
    with SPICE and readjustments are done as
    necessary
                   …to Silicon
   Once the desired electronic behaviour is
    obtained from the layout, masks are generated
   Each separate layer of the layout corresponds to
    a separate mask
   Then the layers of silicon and its derivatives are
    etched on to the substrate by using photolithography
A Piece of History
Birthplace of Silicon Valley

				
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