1.1 a result of a complicated doping procedure

1.1
ELECTRONIC DEVICES GENERATION GAPS

In
1906, the first to show that silicon point-contact rectifiers in detection of
radio waves. The selenium and copper oxide rectifiers were developed,
respectively. The selenium rectifiers were heavily used
in the WWII in military communications and radar equipment. Point-contact
transistors were the first to be produced, but they were extremely unstable and
the electrical characteristics were hard to control.

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The
first grown junction transistors were manufactured in 1952. They were much
better when compared to their point-contact predecessor, but the production was
much more difficult. As a result of a complicated doping procedure the grown
crystal consisted of three regions forming an n-p-n structure. The
process was difficult and could not be automated easily. Moreover, a lot of
semiconductor material was wasted. In 1952 alloyed junction transistor was
reported (two pellets of indium were alloyed on the opposite sides of a slice
of silicon). Its production was simpler and less material-consuming and could
be automated at least partially.

The
first diffused Ge transistor (diffusion was used to form the base region, while
the emitter was alloyed) with a characteristic “mesa” shape was reported in
1954. It was generally understood that for most applications silicon
transistors would be better than germanium ones due to lower reverse currents.
The first commercially available silicon devices (grown junction) were
manufactured in 1954. The first diffused Si transistor appeared in 1955. To
reduce the resistivity of the collector that limited the operation speed
without lowering the breakdown voltage too much. In 1960, the planar transistor
was proposed. The oxide that served as a mask was not removed and acted as a
passivating layer. A built-in electric field could be introduced into the base
by means of graded doping. Another way of introducing the electric field in the
base he thought of was grading the composition of the semiconductor material
itself, which resulted in graded band gap. This heterostructure concept could
not be put to practice easily because of fabrication problems.

In
1958, the first integrated circuit was introduced  where several devices were fabricated in one
silicon substrate and connected by means of wire bonding. This would be a
disadvantage therefore in his patent he proposed formation of interconnects by
means of deposition of aluminum on a layer of SiO2
covering the semiconductor material. In order to find out
how high the base of a bipolar transistor could be doped before the injection
at the emitter junction,  heavily doped
junctions became inadequate. In 1957 and 1958, the first Ge tunneling diode and
silicon one were obtained.The tunnel diode was extremely resistant to the
environmental conditions due to the fact that conduction was not based on
minority carriers or thermal effects. Moreover, its switching times were much
shorter than those of the transistor. The first bipolar transistors were quite
unreliable because semiconductor surface was not properly passivated.

During
the course of this project a new concept of a field-effect transistor was
developed and the actual device manufactured. Unfortunately, the device could
not match the performance of bipolar transistors at the time and was largely
forgotten. In 1963, the first CMOS circuit was proposed. Since polysilicon had
relatively high resistance, gates made of silicides of refractory metals were
proposed. Silicon CMOS and the building block of CMOS known as
the MOS transistor or MOSFET (MOS field-effect transistor) is the semiconductor
industry’s driving force. The linear dimensions of transistors have decreased
by half every three years in order to remain with the frantic pace imposed by
Moore’s law. In the early 1980s, the sub-micron dimension barrier was
overcomed. Semiconductor manufacturers produced transistors with a 20nm gate
length on a regular basis in 2010. The first integrated circuit transistors
were fabricated on “bulk” silicon wafers.

Moore’s
law has been a driving force for technological innovation and social change in
the late 20th and early 21st centuries. Moore’s law became the golden rule for
the electronics industry and a springboard for revolution as shown in Figure 1-1.
The two key drivers of technological growth are performance and cost.
Processing power raised and energy efficiency enhanced as more transistors fit
into tiny spaces all at a lower cost for the end user. To conclude, the 20th
century has been the century of electronics.

The technology
roadmap is an ambitious document widely used as a guiding reference for
advanced semiconductor device research and manufacturing purposes. Based on
research from the semiconductor industry and academia, the latest edition of
the ITRS outlines the requirements and identifies the challenges which allow
Moore’s law to be maintained over the next 15 years. In addition to the
challenges, it also outlines the possible solutions to some of the problems
that the industry may face and highlights the specific areas that need urgent
research.

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