Transistor

What is a transistor?
Basically, a transistor is an electronic switch. Think of it as working like one of those dimmer switches for lights. the dimmer can do two things: turn the light on and off (switching), and make the light brighter, dimmer, brighter, dimmer (modulation).

A transistor does the same thing with an electric current - turns it on or off, lets it run high/low. But while you use your hand to control the light switch, a transistor is controlled by something different, an electric signal.

What is the advantage of a transistor?
One of the big advantages of a transistor is that it needs so little power (electricity) to operate it. In 1953, scientists worked out that one flea, jumping once a minute, would supply enough energy to run a transistor!

How much does a transistor cost to build?
In the 1950s, when transistors were new, each one cost between $5 and $45 United States dollars to build. Today, the transistors on the microchip in, say, a computer, cost less than one-hundredth-thousandth of a cent each! Thatís as close to being free as youíll get.

What came before the transistor?
Before transistors, glass vacuum tubes performed the same task. But they were big. For example, it has been calculated that a digital mobile phone - if it used vacuum tubes instead of transistors - would fill abuilding about the size of the George Washington monument in Washington, DC!!




	A vacuum tube




	An early transistor (1948)



		This type of desktop computer would be impossible without transistors

The very first electronic computer had 18 000 vacuum tubes, would filled an average house, and weighed about 36 tonnes. Today, your digital watch has roughly the same computing power.

If a modern notebook computer was made using vacuum tubes, the tubes, power system, wiring and cooling equipment would fill an entire skyscraper.


	The Washington Monument - or the worldís largest mobile phone??

The history of the transistor
Before the transistor could be invented, humans had to learn how to control electricity. It was the work of scientists such as Maxwell, Hertz, Farday and Edison during the 1800s that made this control of electricity possible. These people were quickly followed by others, such as Braun, Marconi, Fleming and DeForest, who applied this newly-found knowledge to developing useful inventions, such as the radio (wireless).

At the Bell Labs in America, scientists set up a team to investigate ways to use this knowledge to make practical devices for improving communication. Three of the scientists in this team were John Bardeen, Walter Brattain and William Shockley. They conducted experiments with a greyish-white element called germanium, using it as a semiconductor, to switch and modulate electric currents. They discovered the transistor effect and developed the first device in December 1947. For their work, they were awarded the Nobel Prize in physics in 1956.

The first transistor was very simple - a paper clip, two tiny slivers of gold and a chunk of germanium resting on a crystal plate. Following its first demonstration, the scientists wrote in their notebook, ... this circuit was actually spoken over and by switching the device in and out, distinct gains in speech level could be heard ....

The first appplications for the new transistor were for country telephone carriers and in headset amplifiers for telephone operators. In 1954, the transistor became an essential part of the electronic telephone switching system, and a key part of many other devices, such as portable radios, computers and radar.

In the 50+ years since that first demonstration, the transistor has become an essential part of daily business and human life.

What is a semiconductor?
This is a unique material, somewhere between a conductor (like aluminium) and an insulator (like glass). Germanium was the semiconductor used in the first transistors, but it has been replaced today by silicon.

What is a vacuum tube?
A vacuum tube did the same job as transistors do today. But it had some problems: it was expensive to manufacture, large, hot and not very reliable. The first computers used vacuum tubes, but they had a tendency to burn out quickly. Because the tubes actually glowed and gave off light, they attracted moths and other bugs, which caused short circuits. Scientists would have to shut the computer down to clean out the bugs. Ever since then, fixing computer problems has been called debugging.

The vacuum tube was used in radios, telephone equipment, television and computers. However, as these devices became faster, smaller and more powerful, scientists realised something would be need to replace the vacuum tube - and the search for the transistor began.


	What is silicon? This gray, crystal-like element, the most popular semiconductor material in the world is made from - believe it or not - sand (or sandstone). What is germanium? Germanium is a greyish-white element with a brilliant metallic shine and a crystal-like structure. Although it was used in the first transistors, it has now been replaced with silicon, which is much more readily available. Did you know ... ? More than half a billion transistors are manufactured every second The first electronic computer was the size of some suburban homes, and used 18 000 vacuum tubes - to do the same basic mathematical calculations the transistors in a wristwatch do today. The are an estimated 200 million billion transistors in the world; thatís about 40 million for every man, woman and child on earth. By the end of the century, microcircuits will contain one billion transistors on a chip the size of a fingernail. The circuit patterns on these chips will be as complicated as a road map of the entire planet