CSE45435

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CSE45435 VLSI Design

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• Lecture 2
• Please note the change in Office Hours
• Office hours Monday 3.00 - 5.00
• Tuesday 11.30 - 1.00

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Trends in Microprocessor Technology
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Evolution in Complexity
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Silicon in 2010
Die Area 2.5x2.5cm Voltage 0.6
V Technology 0.07?m
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WHY MONOLITHIC INTEGRATION OF A LARGE NUMBER OF
FUNCTIONS ON A SINGLE CHIP?

• Demand for higher computing power
• Low cost
• Small size
• More circuitry ? more transistors
• Dense packing requirement with limited die size
  (less than 1.5cm on a side)

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Why build integrated Circuit?

• IC Technology is driving the whole innovative
  devices and systems which effected the way we
  live.
• Print a circuit, like printing a picture
• ICs are much smaller
• consume less power than discrete component
• easier to design and manufacture
• more reliable than discrete system
• can design more complex system
• cost no longer dependent on of devices
• Fast growth of electronic industry.

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VLSI applications

• Electronic system in cars
• Digital electronics control VCRs
• Transaction processing system, ATM
• Personal computers and Workstations
• Medical electronic systems
• Laptops, cellphones, PDAs
• etc.

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The advantages of digital ICs over discrete
components

• Size
• much smaller both transistor and wires.
• leads to smaller parasitic resistances,
  capacitances and inductances
• Speed
• communication within the chips are much faster
  than between the chips on a PCB
• High speed of circuits on-chip due to smaller
  size
• Power Consumption
• Logic operation within the chip consumes much
  less power
• Smaller size --gt smaller parasitic capacitances
  and resistance
• --gt require less power to drive the
  circuit

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Advantages of IC at System Level

• Smaller Physical Size
• can make small electronic appliances. ie.
  Portable TV, handheld cellular telephone
• Lower Power Consumption
• reduces total power consumption of a whole
  electronic circuit.
• cheaper power supply which leads to a simpler
  cabinet for power supply. Less heat, cooling
  fans may no longer be necessary.

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Advantages of IC at System Level (cont.)

• Reduced Cost
• Reduction in number of components.
• Power Supply requirement.
• Cabinets
• The cost of building a whole system is reduced
  eventhough ICs cost more.

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Integrated Circuit Manufacturing

• Technology
• Select technology to build a complex system in
  the fastest possible way.
• Economics
• IC plant is very expensive. 1billion or more.
• Is it worth to invest in IC business?

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Moores Law

• In 1960s,Gordon Moore Co-founder of INTEL
  predicted that the number of transistors would
  grow exponentially (Double every 18 months).
• Exponential improvement in technology is a
  natural trend steam engines, dynamos,
  automobiles etc.

ln
(dev)
good
year
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Good News

• Since the cost of the printing process (called
  wafer fabrication) was growing at a modest rate,
  it implied that the cost per function was
  dropping exponentially.
• At each new generation, each gate costs about
  1/2 what it did 3 years ago.
• Shrinking an existing chip makes it cheaper!

ln(cost/function)
die
cost
year
year
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Bad News

• Although the cost of manufacturing IC's remained
  approximately constant, the design cost did not.
  In fact, while designer productivity has improved
  with time, it has not increased at the same rate
  as the complexity of the chips.
• So the cost of the chip design is growing
  exponentially with the complexity of the circuit.
  Integrating a system on a piece of silicon has an
  attractive manufacturing cost, but frightening
  design cost and risk. Need to build very complex
  stuff.
• In addition, the number of custom IC designers
  was (and is) fairly limited. Even if you were
  willing to take the risk, where would you find
  the people to do the design?

ln(design cost/function)
y
ear
ln(design cost)
y
ear
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Design Technology
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VLSI Technology
1. Schottky TTL (Transistor-transistor logic)
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VLSI Technology
2. ECL (Emitter coupled logic)
NOR
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VLSI Technology
3. MOS (Metal Oxide semiconductor)
NOR
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VLSI Technology
4. CMOS (Complementary MOS)
NOR
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Most Prominent Technology - CMOS

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•    Smaller sized transistors
•   Lower power consumption
• Zero static power??
•   Dynamic power increases with switching
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• But SLOW compared to others
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• Compromise - BiCMOS Technology

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Manufacturing Steps

• 1.  Circuit schematic
• - transistor circuit diagram
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• 2.  Layout generation
• - rectangular patterns for transistors and
  interconnect
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• 3. Mask generation
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• 4. Chip fabrication

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Challenges faced

• Defects in wafer
•     use minimum die area
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• Reduce cost
•     use minimal layout area
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• Increase speed
•     use efficient interconnect patterns (
  long and winding paths reduce speed)
• Short design time
• High market competition

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Abstractions and Disciplines How to Deal with
109 Transistors?

• Partition the problem
• (Use hierarchy)
• Module is a box with pins
• apply recursively

• Digital abstraction
• signals are 1 or 0
• Switch abstraction
• MOSFETs as simple switches
• Gate abstraction
• Unidirectional elements
• Separable timing
• Synchronous abstraction
• Race free logic
• Function does not depend on timing

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Design Abstraction Levels
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What is on an Integrated Circuit?

• Actually only two types of things
• Conducting layers which form the wires on the IC.
  
• There are many layers of wires (used to have 1
  layer of metal, now advanced processes have 5-7
  metal layers). Wires have electrical properties
  like resistance and capacitance.
• (Requires insulators and contacts between
  layers.)
• Transistors (the free things that fit under the
  wires).
• There are a few kinds of transistors. In this
  course we will study MOS ICs, so we will work
  with MOS transistors. These transistors can be
  thought of as voltage controlled switches. The
  voltage on one terminal of the transistor
  determines whether the other two terminals are
  connected or not.

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MOSFET Fundamentals
N-channel Metal Oxide Semiconductor Field-Effect
Transistor
NMOS Transistor
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The MOS Capacitor
Negative Voltage To Metal
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The MOS Capacitor
Small Positive Voltage To Metal
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The MOS Capacitor
Less Positive
More Positive
Much More Positive
n
n ltlt Ions V lt VT
n gtgt Ions V gt VT
n ? Ions V ? VT
VT Minimum Voltage for Inversion
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NMOS Transistor
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PMOS Transistor