Hi friends… one more article is in front of you. This article is quite essential for every student of ECE and EEE, because it is unavoidable fact that if we want to make advancements in electrical and electronics field… we need to start with the basic components i.e., the transistors, diodes etc… If we only know about these components operation we can try new designs… so without wasting much time let us know about the TRANSISTOR. I am sure it will be interesting.

INTRO :

              If cells are the building blocks of life, transistors are the building blocks of the digital revolution. Without transistors, the technological wonders you use every day –cell phones, computers, cars would be vastly different, if they existed at all.

 

Before transistors, product engineers used vacuum tubes and electromechanical switches to complete electrical circuits. Tubes were far from ideal. They had to warm up before they worked (and sometimes overheated when they did), they were unreliable and bulky and they used too much energy. Everything from televisions, to telephone systems, to early computers used these components, but in the years after World War II, scientists were looking for alternatives to vacuum tubes. They’d soon find their answer from work done decades earlier.

In the late 1920’s, Polish American physicist Julius Lilienfeld filed patents for a three-electrode device made from copper sulfide. There’s no evidence that he actually created the component, but his research helped develop what today is a field effect transistor, the building block of silicon chips.

Twenty years after Lilienfeld filed his patents, scientists were trying to put his ideas to practical use. The Bell Telephone System, in particular, needed something better than vacuum tubes to keep its communications systems working. The company assembled what amounted to an all-star team of scientific minds, including John Bardeen, Walter Brattain and William Shockley, and put them to work researching vacuum tube substitutes.

In 1947, Shockley was director of transistor research at Bell Telephone Labs. Brattain was an authority on solid-state physics as well as expert on nature of atomic structure of solids and Bardeen was an electrical engineer and physicist. Within a year, Bardeen and Brittain used the element germanium to create an amplifying circuit, also called a point-contact transistor. Soon afterward, Shockley improved on their idea by developing a junction transistor.

The next year, Bell Labs announced to the world that it had invented working transistors. The original patent name for the first transistor went by this description: Semiconductor amplifier; three-electrode circuit element utilizing semi conductive materials. It was an innocuous-sounding phrase. But this invention netted the Bell team the 1956 Nobel Prize for Physics, and allowed scientists and product engineers far greater control over the flow of electricity.

It’s no exaggeration that transistors have enabled some of humankind’s biggest leaps in technology. Keep reading to see exactly how transistors work, how they altered the course of technology, and in the process, human history, too.

WHAT IS A TRANSISTOR?

  •  Transistors are the devices that control the movement of electrons, and consequently, electricity. They work something like a water faucet  not only do they start and stop the flow of a current, but they also control the amount of the current. With electricity, transistors can both switch or amplify electronic signals, letting you control current moving through a circuit board with precision.

The transistors made at Bell Labs were initially made from the element germanium. Scientists there knew pure germanium was a good insulator. But adding impurities (a process called doping) changed the germanium into a weak conductor, or semiconductor. Semiconductors are materials that have properties in-between insulators and conductors, allowing electrical conductivity in varying degrees.

The timing of the invention of transistors was no accident. To work properly, transistors require pure semiconductor materials. It just so happened that right after World War II, improvements in germanium refinement, as well as advances in doping, made germanium suitable for semiconductor applications.

Depending on the element used for doping, the resulting germanium layer was either negative type (N-type), or positive type (P-type). In an N-type layer, the doping element added electrons to the germanium, making it easier for electrons to surge out. Conversely, in a P-type layer, specific doping elements caused the germanium to lose electrons, thus, electrons from adjacent materials flowed towards it.

Place the N-type and P-type adjacent to each other and you create a P-N diode. This diode allows an electrical current to flow, but in only one direction, a useful property in the construction of electronic circuits.

Full-fledged transistors were the next step. To create transistors, engineers layered doped germanium to make two layers back to back, in a configuration of either P-N-P or N-P-N. The point of contact was called a junction, thus the name junction transistor.

With an electrical current applied to the center layer (called the base), electrons will move from the N-type side to the P-type side. The initial small trickle acts as a switch that allows much larger current to flow. In an electric circuit, this means that transistors are acting as both a switch and an amplifier.

These days, in place of germanium, commercial electronics use silicon-based semiconductors, which are more reliable and more affordable than germanium-based transistors. But once the technology caught on, germanium transistors were in widespread use for more than 20 years.

Article  By

Ravi Teja

(3/4 ECE MGIT)

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