1.1ELECTRONIC DEVICES GENERATION GAPSIn1906, the first to show that silicon point-contact rectifiers in detection ofradio waves. The selenium and copper oxide rectifiers were developed,respectively.
The selenium rectifiers were heavily usedin the WWII in military communications and radar equipment. Point-contacttransistors were the first to be produced, but they were extremely unstable andthe electrical characteristics were hard to control. Thefirst grown junction transistors were manufactured in 1952. They were muchbetter when compared to their point-contact predecessor, but the production wasmuch more difficult. As a result of a complicated doping procedure the growncrystal consisted of three regions forming an n-p-n structure. Theprocess was difficult and could not be automated easily. Moreover, a lot ofsemiconductor material was wasted. In 1952 alloyed junction transistor wasreported (two pellets of indium were alloyed on the opposite sides of a sliceof silicon).
Its production was simpler and less material-consuming and couldbe automated at least partially.Thefirst diffused Ge transistor (diffusion was used to form the base region, whilethe emitter was alloyed) with a characteristic “mesa” shape was reported in1954. It was generally understood that for most applications silicontransistors would be better than germanium ones due to lower reverse currents.The first commercially available silicon devices (grown junction) weremanufactured in 1954. The first diffused Si transistor appeared in 1955. Toreduce the resistivity of the collector that limited the operation speedwithout lowering the breakdown voltage too much.
In 1960, the planar transistorwas proposed. The oxide that served as a mask was not removed and acted as apassivating layer. A built-in electric field could be introduced into the baseby means of graded doping.
Another way of introducing the electric field in thebase he thought of was grading the composition of the semiconductor materialitself, which resulted in graded band gap. This heterostructure concept couldnot be put to practice easily because of fabrication problems.In1958, the first integrated circuit was introduced where several devices were fabricated in onesilicon substrate and connected by means of wire bonding. This would be adisadvantage therefore in his patent he proposed formation of interconnects bymeans of deposition of aluminum on a layer of SiO2covering the semiconductor material. In order to find outhow high the base of a bipolar transistor could be doped before the injectionat the emitter junction, heavily dopedjunctions became inadequate. In 1957 and 1958, the first Ge tunneling diode andsilicon one were obtained.
The tunnel diode was extremely resistant to theenvironmental conditions due to the fact that conduction was not based onminority carriers or thermal effects. Moreover, its switching times were muchshorter than those of the transistor. The first bipolar transistors were quiteunreliable because semiconductor surface was not properly passivated.Duringthe course of this project a new concept of a field-effect transistor wasdeveloped and the actual device manufactured.
Unfortunately, the device couldnot match the performance of bipolar transistors at the time and was largelyforgotten. In 1963, the first CMOS circuit was proposed. Since polysilicon hadrelatively high resistance, gates made of silicides of refractory metals wereproposed. Silicon CMOS and the building block of CMOS known asthe MOS transistor or MOSFET (MOS field-effect transistor) is the semiconductorindustry’s driving force. The linear dimensions of transistors have decreasedby half every three years in order to remain with the frantic pace imposed byMoore’s law. In the early 1980s, the sub-micron dimension barrier wasovercomed.
Semiconductor manufacturers produced transistors with a 20nm gatelength on a regular basis in 2010. The first integrated circuit transistorswere fabricated on “bulk” silicon wafers.Moore’slaw has been a driving force for technological innovation and social change inthe late 20th and early 21st centuries. Moore’s law became the golden rule forthe 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 fitinto tiny spaces all at a lower cost for the end user. To conclude, the 20thcentury has been the century of electronics.The technologyroadmap is an ambitious document widely used as a guiding reference foradvanced semiconductor device research and manufacturing purposes. Based onresearch from the semiconductor industry and academia, the latest edition ofthe ITRS outlines the requirements and identifies the challenges which allowMoore’s law to be maintained over the next 15 years. In addition to thechallenges, it also outlines the possible solutions to some of the problemsthat the industry may face and highlights the specific areas that need urgentresearch.