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The first transistor developed was the junction transistor. Nearly all transistors today are classed as junction transistors.

Through the years there were developed new types of junction transistors that performed better and were easier to construct. When first introduced the junction transistor was not called that; it was the "cat's whisker" used in the first radio receivers in the 1920s. Shockley and his crew resurrected (возродить) it, a mere imposing name sounded much more scientific. The junction tran­sistor of 1948 was further modernized in 1951, with the develop­ment of the "grown" transistor. The technology for manufacturing transistors steadily improved until, in 1959, the first integrated cir­cuit was produced — the first circuit-on-a-chip.

The integrated circuit constituted another major step in the growth of computer technology. Until 1959 the fundamental logi­cal components of digital computers were the individual electrical switches, first in the form of relays, then vacuum tubes, then tran­sistors.

In the vacuum tubes and relay stages, additional discrete com­ponents such as resistors, inductors and capacitors were required in order to make the whole system work. These components were about the same size as packaged transistors. Integrated circuit technology permitted the elimination of some of these compo­nents and "integration" of most of the others on the same chip of semiconductor that contains the transistor. Thus the basic logic el­ement — the switch, or "flip-flop", which required two separate transistors and some resistors and capacitors in the early 1950s, could be packaged into a single small unit in 1960. That unit was half the size of a pea.

The chip was a crucial (важный) development in the acceler­ating pace of computer technology. With integrated circuit tech­nology, it became possible to jam (зд. размещать) more and more elements into a single chip. Entire assemblies or parts could be manufactured in the same time that it previously took to make a single part. Clearly, the cost of providing a particular computing function decreased proportionally. As the number of components on an integrated circuit grew from a few to hundreds, then thou­sands, the term for the chip changed to microcircuit.

 

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The two elements we can now concentrate on, as by far the most important semiconductors, are silicon and germanium. Silicon is one of the most plentiful elements in the world, but oc­curs in chemical compound such as sand (silica), from which it is difficult to extract pure silicon. The element can be isolated by the reduction of silica in an arc furnace. It then contains small quanti­ties of calcium, iron, aluminium, boron and phosphorus as princi­ple impurities. Alternatively, silicon can be prepared by the pyrolytic reduction of silicon tetrachloride and in this way the mate­rial can be obtained free from analytically detectable quantities of boron and phosphorus.

Germanium is comparatively rare but it is rather easier to re­fine. It should perhaps be mentioned that the list of semiconduc­tors given is not confined to elements; increasing attention is being paid to semiconductor compounds such as indium antimonide and other compounds of group Ш with group V elements.

 

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GaAs MESFETs Research

More than 40 years have passed since the bipolar transistor was invented by Shockley in 1948. Bipolar technology has highly matured today, and the structure of Si bipolar transistor has been improved almost to its physical limits. The upper frequency limit of its practical application is considered to be 4 GHz regardless of advances in technology.

In 1966, С.A.Mead demonstrated the possibility of a transistor with a very high cut-off frequency employing a GaAs field effect transistor with a Schottky barrier gate. Since then, GaAs MESFET research and development efforts have been made in many laboratories around the world. The main purpose of the de­velopment of GaAs MESFET is to obtain three-terminal mi­crowave semiconductor devices which can be used to develop mi­crowave amplifiers to replace the parametric low noise amplifiers and the travelling wave tube power amplifiers.

In the last several years, GaAs MESFETs have made remark­able progress in both low noise GaAs MESFET amplifiers, re­sulting in a substantial reduction in the cost of microwave com­munication systems. High power GaAs MESFETs replaced some TWTs, guaranteeing a much longer lifetime and a smaller size than the TWT.

 

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Materials for Multilayer Interconnections

As device dimensions are becoming increasingly smaller se­vere requirements are being imposed on the electrode material. The basic demand is conductivity because it can substantially im­prove the resistances and delay times of the electrical interconnec­tions lines used for VLIC structures.

Historically, metals like aluminum and gold have been used in bipolar and MOS IC's. With the advent of silicon-gate MOS tech­nology, polysilicon has been extensively used to form gate elec­trodes and interconnections. Refractory metals such as tungsten (W), molybdenum (Mo), titanium (Ti), and tantalum (Та) and their silicides are receiving increased attention as a replace­ment/compliment of polysilicon.

Silicides of W, Mo and Та have reasonably good compatibility with the IC fabrication technology. They have fairly high conduc­tivity, they can withstand all of the chemicals normally encoun­tered during the fabrication process.