Evolution of Digital IC Technologies :
The first “generation” of computers were relied on vaccum tube devices, after this
discrete semiconductor devices, followed by integrated circuits have been evolved. The first
integrated circuit was manufactured independently by two scientists: Jack and Kilby of Texas
Instruments in 1959. The first IC had small number of devices on a single chip then diodes,
transistors, resistors and capacitors, made it possible to fabricate one or more logic gates on a
single device. Digital integrated circuits are classified according to the number of transistors
integrated on a single chip. The different technologies involved in digital integrated circuits are
Small-scale integration (SSI) :
The first integrated circuits contained only a few transistors, called “Small-Scale
Integration” (SSI), they used circuits containing only 10s of transistors on single chip.
SSI circuits were crucial to early 1960 through 1963, and the integrated circuits
developed in this technology are basic logic gates.
Medium-scale integration (MSI) :
In 1960s new technology has been introduced in which the number of transistors
involved on the are hundred and named as “Medium-Scale Integration” (MSI). These
devices allowed more complex systems to be produced using smaller circuit boards, less
assembly work and a number of other advantages. The integrated circuits developed in
this technology are multiplexers and flip-flops. Using the multiplexer any combinational
logic can be implemented and using the D-FF any sequential circuit can be implemented
hence in order to design digital systems this technology was popular. This includes
encoders, decoders, counters, registers, arithmetic circuits, small memories, and others.
Large-scale integration (LSI) :
Further development driven by the economic factors such as time to market and cost
because by using MSI chips and bread boarding approach number of years and large
cost is required for designing complex digital systems e.g. microprocessor. This leads
to the “Large-Scale Integration” (LSI) in the mid 1970s, with tens of thousands of
transistors per chip. The devices produced in this technology are programmable logic
devices (PLDs) i.e. PAL, PLA and PROM are developed in this technology.
Very large-scale integration (VLSI) :
In the year 1980s new step has been developed in the development process that step is
the “Very Large-Scale Integration” (VLSI), in which more than 1000 transistors are
included on a single chip. This is the technology by which the first microprocessor has
been developed. In addition to this one megabit RAM chip has been developed which
contains million number of transistors. This developments in VLSI are mainly because
of design rules in CMOS technology, development of Complex Programmable Devices
(CPLD)s, Field Programmable Gate Arrays (FPGA) and the Electronic Design
Automation (EDA) tools.
Ultra large-scale integration (ULSI) :
It describes very large memories, larger microprocessors, and larger single-chip
computers. Complexities of 100,000 equivalent gates and greater are classified as ULSI.
Wafer-Scale Integration (WSI) :
Another technique used in IC industry is the wafer-scale integration (WSI), which uses
the complete uncut wafers for the development of processors and memory. The WSI step
was taken in 1980s by Gene Amdahl who is failed due to the semiconductor level
System-on- Chip (SOC) :
Although the WSI technique failed due to semiconductor level manufacturing issues, the
advanced tools in semiconductor manufacturing produces another thread on IC
complexity, which is known as System-on- Chip (SOC) design. In this SOC, the IC
blocks are manufactured as a various chips and have been integrated in a chip. In
addition, the printed circuit boards are developed to occupy the chip which involves
memory, microprocessors, peripheral interfaces, Input/Output logic control, data
converters etc. to develop electronic systems.