Application Specific Integrated Circuits (ASIC)

Application Specific Integrated Circuits (ASIC)

Introduction:

1.1 Construction of ICs.

ICs are made on a thin (a few hundred microns thick), circular silicon wafer, with each
Wafer Holding hundreds of die (sometimes people use dies or dice for the plural of die).
The transistors and wiring are made from many layers (usually between 10 and 15
distinct layers) built on top of one another. Each successive mask layer has a pattern that is
defined using a mask similar to a glass photographic slide.
The first half-dozen or so layers define the transistors. The last half-dozen or so layers
define the metal wires between the transistors (the interconnect).

1.2 Physical Size of ICs.

The physical size of a silicon die varies from a few millimeters on a side to over 1 inch
on a side.

1.3 Measure of ICs

we measure the size of an IC by the number of logic gates or the number of transistors
that the IC contains.
As a unit of measure a gate equivalent corresponds to a two-input NAND gate (a circuit
That performs the logic function, F = A • B ). Often we just use the term gates instead of
gate equivalents when we are measuring chip size—not to be confused with the gate
terminal of a transistor.
For example, a 100 k-gate IC contains the equivalent of 100,000 two-input NAND gates.

1.4 Evolutions Of ICs.

The semiconductor industry has evolved from the first ICs of the early 1970s and matured
Rapidly since then.
Early small-scale integration ( SSI ) ICs contained a few (1 to 10) logic gates—NAND
gates, NOR gates, and so on—amounting to a few tens of transistors.
The era of medium-scale integration ( MSI ) increased the range of integrated logic
available to counters and similar, larger scale, logic functions.
The era of large-scale integration ( LSI ) packed even larger logic functions, such as
the first microprocessors, into a single chip.
The era of very large-scale integration ( VLSI ) now offers 64-bit microprocessors,
complete with cache memory and floating-point arithmetic units—well over a million
transistors—on a single piece of silicon. As CMOS process technology improves,
transistors continue to get smaller and ICs hold more and more transistors.
Some people (especially in Japan) use the term ultralarge scale integration ( ULSI ),
but most people stop at the term VLSI; otherwise we have to start inventing new words.

1.5 Technology Used In ICs.

The earliest ICs used bipolar technology and the majority of logic ICs used either
Transistor –transistor logic ( TTL ) or emitter-coupled logic (ECL). Although invented
before the bipolar transistor, the metal-oxide-silicon ( MOS ) transistor was initially
difficult to manufacture because of problems with the oxide interface. As these problems
were gradually solved, metal- gate n -channel MOS ( nMOS or NMOS ) technology
developed in the 1970s. At that time MOS technology required fewer masking steps, was
denser, and consumed less power than equivalent bipolar ICs. This meant that, for a given
performance, an MOS IC was cheaper than a bipolar IC and led to investment and growth
of the MOS IC market.

By the early 1980s the aluminum gates of the transistors were replaced by polysilicon
gates, but the name MOS remained. The introduction of polysilicon as a gate material
was a major improvement in CMOS technology, making it easier to make two types of
transistors, n -channel MOS and p -channel MOS transistors, on the same IC—a
complementary MOS ( CMOS , never cMOS) technology. The principal advantage of
CMOS over NMOS is lower power consumption.
Another advantage of a polysilicon gate was a simplification of the fabrication process,
Allowing devices to be scaled down in size

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