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Transistors

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It's useful if you want to turn alternating two-way electric current into direct one-way current. Diodes can also be made so they give off light when electricity flows through them. You might have seen these light-emitting diodes LEDs on pocket calculators and electronic displays on hi-fi stereo equipment. Now suppose we use three layers of silicon in our sandwich instead of two. We can either make a p-n-p sandwich with a slice of n-type silicon as the filling between two slices of p-type or an n-p-n sandwich with the p-type in between the two slabs of n-type.

If we join electrical contacts to all three layers of the sandwich, we can make a component that will either amplify a current or switch it on or off—in other words, a transistor. Let's see how it works in the case of an n-p-n transistor. So we know what we're talking about, let's give names to the three electrical contacts. We'll call the two contacts joined to the two pieces of n-type silicon the emitter and the collector , and the contact joined to the p-type silicon we'll call the base.

When no current is flowing in the transistor, we know the p-type silicon is short of electrons shown here by the little plus signs, representing positive charges and the two pieces of n-type silicon have extra electrons shown by the little minus signs, representing negative charges.

Another way of looking at this is to say that while the n-type has a surplus of electrons, the p-type has holes where electrons should be. Normally, the holes in the base act like a barrier, preventing any significant current flow from the emitter to the collector while the transistor is in its "off" state. A transistor works when the electrons and the holes start moving across the two junctions between the n-type and p-type silicon.

Let's connect the transistor up to some power. Suppose we attach a small positive voltage to the base, make the emitter negatively charged, and make the collector positively charged. Electrons are pulled from the emitter into the base—and then from the base into the collector.

And the transistor switches to its "on" state:. The small current that we turn on at the base makes a big current flow between the emitter and the collector. By turning a small input current into a large output current, the transistor acts like an amplifier. But it also acts like a switch at the same time. When there is no current to the base, little or no current flows between the collector and the emitter.

Turn on the base current and a big current flows. So the base current switches the whole transistor on and off. Technically, this type of transistor is called bipolar because two different kinds or "polarities" of electrical charge negative electrons and positive holes are involved in making the current flow.

We can also understand a transistor by thinking of it like a pair of diodes. With the base positive and the emitter negative, the base-emitter junction is like a forward-biased diode, with electrons moving in one direction across the junction from left to right in the diagram and holes going the opposite way from right to left.

The base-collector junction is like a reverse-biased diode. The positive voltage of the collector pulls most of the electrons through and into the outside circuit though some electrons do recombine with holes in the base. All transistors work by controlling the movement of electrons, but not all of them do it the same way. Like a junction transistor, a FET field effect transistor has three different terminals—but they have the names source analogous to the emitter , drain analogous to the collector , and gate analogous to the base.

In a FET, the layers of n-type and p-type silicon are arranged in a slightly different way and coated with layers of metal and oxide. Although there are extra electrons in the n-type source and drain, they cannot flow from one to the other because of the holes in the p-type gate in between them.

However, if we attach a positive voltage to the gate, an electric field is created there that allows electrons to flow in a thin channel from the source to the drain. This "field effect" allows a current to flow and switches the transistor on:. For the sake of completeness, we could note that a MOSFET is a unipolar transistor because only one kind "polarity" of electric charge is involved in making it work.

In practice, you don't need to know any of this stuff about electrons and holes unless you're going to design computer chips for a living! All you need to know is that a transistor works like an amplifier or a switch, using a small current to switch on a larger one.

But there's one other thing worth knowing: how does all this help computers store information and make decisions? We can put a few transistor switches together to make something called a logic gate , which compares several input currents and gives a different output as a result. Logic gates let computers make very simple decisions using a mathematical technique called Boolean algebra.

Your brain makes decisions the same way. For example, using "inputs" things you know about the weather and what you have in your hallway, you can make a decision like this: "If it's raining AND I have an umbrella, I will go to the shops".

That's an example of Boolean algebra using what's called an AND "operator" the word operator is just a bit of mathematical jargon to make things seem more complicated than they really are. You can make similar decisions with other operators. That idea is the foundation stone of computer programs : the logical series of instructions that make computers do things.

Normally, a junction transistor is "off" when there is no base current and switches to "on" when the base current flows. That means it takes an electric current to switch the transistor on or off. But transistors like this can be hooked up with logic gates so their output connections feed back into their inputs.

The transistor then stays on even when the base current is removed. Each time a new base current flows, the transistor "flips" on or off. It remains in one of those stable states either on or off until another current comes along and flips it the other way. This kind of arrangement is known as a flip-flop and it turns a transistor into a simple memory device that stores a zero when it's off or a one when it's on.

Flip-flops are the basic technology behind computer memory chips. Artwork: The original design of the point-contact transistor, as set out in John Bardeen and Walter Brattain's US patent 2,, , filed in June about six months after the original discovery and awarded October 3, This is a simple PN transistor with a thin upper layer of P-type germanium yellow on a lower layer of N-type germanium orange.

The three contacts are emitter E, red , collector C, blue , and base G, green. You can read more in the original patent document, which is listed in the references below. The team, led by Shockley, had been trying to develop a new kind of amplifier for the US telephone system—but what they actually invented turned out to have much more widespread applications.

Bardeen and Brattain made the first practical transistor known as a point-contact transistor on Tuesday, December 16, Although Shockley had played a large part in the project, he was furious and agitated at being left out. Shortly afterward, during a stay in a hotel at a physics conference, he single-handedly figured out the theory of the junction transistor—a much better device than the point-contact transistor.

While Bardeen quit Bell Labs to become an academic he went on to enjoy even more success studying superconductors at the University of Illinois , Brattain stayed for a while before retiring to become a teacher. Shockley set up his own transistor-making company and helped to inspire the modern-day phenomenon that is "Silicon Valley" the prosperous area around Palo Alto, California where electronics corporations have congregated.

Two of his employees, Robert Noyce and Gordon Moore, went on to found Intel, the world's biggest micro-chip manufacturer. Bardeen, Brattain, and Shockley were briefly reunited a few years later when they shared the world's top science award, the Nobel Prize in Physics , for their discovery.

Their story is a riveting tale of intellectual brilliance battling with petty jealousy and it's well worth reading more about. You can find some great accounts of it among the books and websites listed below. All rights reserved. Full copyright notice and terms of use.

Please rate or give feedback on this page and I will make a donation to WaterAid. Woodford, Chris. Who invented the transistor? Sponsored links. Find out more On this website Computers: a brief history Flash memory Integrated circuits Logic gates Thyristors Other websites The Journey Inside : Intel's educational website, all about transistors and integrated circuits.

The Transistor : Learn about transistors in a fun way, with games and interactives on the Nobel Prize website. O'Reilly, A clear, well-illustrated primer for electronics beginners and a great place for a keen teenager to start. Experiment 10 begins the coverage of transistors.

Getting Started in Electronics by Forrest M. Mims III. Master Publishing, The circuit shown in diagram B is based on an NPN transistor. When the switch is pressed a current passes through the resistor into the base of the transistor. Transistors are an essential component in many circuits and are sometimes used to amplify a signal. Transistors can be regarded as a type of switch, as can many electronic components.

Transistors are manufactured in different shapes but they have three leads legs. Diagram 'A' shows an NPN transistor which is often used as a type of switch.

Transistor Options Beyond 3nm Complicated and expensive technologies are being planned all the way to , but it's not clear how far the. Transistor semiconductor history Texas Instruments RCA Bell Laboratories Western Electric General Transistor Fairchild Tung-Sol Sylvania Mullard Philips STC. Purdue University researchers have developed transistor technology that shows potential for improving computers and mobile phones.

An easy-to-understand introduction to transistors, including simple Flip-flops are the basic technology behind computer memory chips. Abstract: A complementary heterojunction field effect transistor technology based on the InAs/AlSb/GaSb system is proposed. The structure is formed by the. Transistor Technology Evokes New Physics. Read the Prize motivation: "for their researches on semiconductors and their discovery of the transistor effect.".

Purdue University researchers have developed transistor technology that shows potential for improving computers and mobile phones. Transistor semiconductor history Texas Instruments RCA Bell Laboratories Western Electric General Transistor Fairchild Tung-Sol Sylvania Mullard Philips STC. A transistor is a semiconductor device with at least three terminals for connection to an electric .. A history of Bell Laboratories and its technological innovations; Riordan, Michael; Hoddeson, Lillian (). Crystal Fire. W.W Norton & Company .

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