Transistor

Transistor is a combination of  words ""transconductance" or "transfer" and "varistor". Transistor is semiconductor device having ability to change from conductor to insulator it can either allow the current or prohibit current to flow.

In 1906 Lee DeForest invents the triode vacuum which is the first electronic signal amplifier or work as switch.

Working of vacuum tube: 

Vacuum tube is amplify the signal in vacuum tube  there will two supplies Vplate and Vgrid and a vacuum is  present in which one side is anode and another side is cathode in which negative terminal of Vplate supply  as well as negative terminal of Vgrid connects with cathode and positive terminal of Vplate supply connected with anode and also positive terminal of Vgrid supply connected with control grid. By supplying the source the cathode is heated, and a positive voltage is applied to the anode the hole vacuum are heated  by which the electron flow from the cathode to anode and form  positive and negative polarity which make complete path, hence the principal of vacuum tube is thermionic emission phenomenon. 

                                 

                               

 John Ambrose Fleming took advantage of this effect to create the first vacuum tube device which called an oscillation valve.
 

Lee De Forest an American inventor who added a third electrode to the mix and develop the first triode tube and this third electrode known as the control grid.  

In between cathode and anode placed the control grid which is in the shape of a mesh. The number of electron flowing from the cathode to the anode it can be controlled by adjusting the voltage applied to the grid.  If increases the grid voltage then number of electron increases hence current is increases, in this mannare the triode works as an or on off switch for a circuit and also work as signal amplifier.

Features of control grid.

It is usually plating with gold and there are two posts made up of soft copper and it made up of tungsten or molybdenum wire welded  which have very high melting point  that means it tolerate the very high temperature.

The evolution of transistor comes from bell laboratory the former company of bell laboratory is American Telephone and Telegraph company services (AT&T). Alexander Graham Bell who started bell company  and also started the first time telephone research services.

The management of American Bell created in 1880 that would becomes AT&T long lines.

American Telephone and Telegraph company in 1885 created the nationwide long distance network starting from New York and reached Chicago in 1892. In 1907 AT&T was on financial crises then The founder of AT&T  Theodore Roosevelt was retired before the crises and the company request to rejoin and he again worked to raise the company.In 1915, the call was first enabled with the help of an amplifier from New York to San Francisco by Alexander Bell and gradually phone calls started expanding in streets very easily. 

In 1930 AT&T knew that if we have to expand the long distance calls then we have to solve vacuum tube problem. At that duration ,World War-2 broke and due to which Mervin kelly plan on hold. During World War-2, militaries uses the radar to detect the foreigner things. In Radar, by using Silicon and germanium  to make as a crystal  rectifier.

 Mervin kelly knew by using the silicon and germanium to invent the new thing regarding vacuum tube and he formed a research team of three people, William Bradford Shockley (physicist and inventor) , Walter Houser Brattain ( experimental physicist) and John Bardeen ( theoretical physicist) the trio scientist in 1947 created the world's first transistor at Bell Labs. The trio scientist were awarded with the Nobel Prize in 1956 for their discovery of the transistor.

Drawback of Vacuum Tube:

1: Tubes operates at higher voltages than transistors. 

2: The major disadvantages of tubes that it required bulky power supplies and high voltages can present an electric shock hazard.

3: Large in size.

4: Limited life.

5: Low reliability.  

An integrated circuit or monolithic integrated circuit is an electronics circuit on a small levelled  of semiconductor material that is normally silicon or germanium. The invention of the integrated circuit at Fairchild and Texas Instruments from 1957 to 1959.

Jean Hoerni at Fairchild developed the planar transistor then Jack Kilby and Robert Noyce at Fairchild developed the integrated circuit. 

 Now a days in a single chip of size 53*45mm there are 2.5 billion or above transistor are used, it means day by day the size of transistor will decreases.