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Transistor - Electronics .. Physics

Transistor

Semiconductor devices that have certain properties require the preparation of single crystals that are sometimes up to 15 cm long and 2.5 cm wide, and their purity reaches 99،99999999 percent. Then, amounts of impurities are added to these crystals, transforming them into one of the two types, S or M. This process is known as doping. By spreading doping media in different places of the semiconductor crystal, it becomes possible to create elements that contain a large number of semiconductor junctions.

The transistor contains only two of these junctions, arranged in the form M - S - M or S - M - S. The middle section is called the base Q and the two surrounding sections are called the emitter B where most of the carriers are formed and the collector M which is characterized by a large size that allows the charge carriers to disperse in it after crossing the base. It is worth noting that the function of the base in the transistor is very similar to the function of the network in the triode, and is limited to controlling the value of the current passing through the transistor.

(Above left) Types of transistors and their technical symbol.
(Above right) Alloy junction transistor. (Opposite page) Field effect transistor. (Left) and flat silicon transistor (Right)

This is because any change in the current passing between the emitter and the base, even if it is slight, is capable of creating large changes in the current passing between the emitter and the collector. For this reason, the transistor is used in amplification processes, and its use for this purpose is common in all electronic devices except for devices that require the use of valves or other specialized electronic devices. In addition, there is no difference between the M-S-M transistor and the S-M-S transistor in principle, but the availability of these two types has allowed and continues to allow for new starting points in the design of electronic circuits.

In addition to the alloy type, there are two other types of transistors, the first of which is known as the thin-film field effect transistor, and its control path is called the gate and is isolated from the emitter and collector, which are called in this case the source and filter. In this transistor, the changes that occur in the electric field around the control gate control the flow of current, knowing that the current entering it is of small value. This transistor is made by evaporating materials on glass on which separator masks are drawn that define each layer in it its designated area.

The flat silicon transistor uses a prepared silicon material in which doping media of both types are spread, creating M-regions and S-regions on which current-carrying connections are then fixed. The details of the diffusion process are given in the following section, and it is summarized by creating a layer of silicon oxide on the crystal in which holes are drilled by means of a photographic process, then exposing its area to the evaporated doping materials.