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

as follows.

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

manufacturing issues.

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.