Last updated: June 29, 2019.Your brain contains around 100 billion cells called neurons—the tiny switches that let you think and remember things.contain billionsof miniature 'brain cells' as well. They're called transistors andthey're made from silicon, a chemical element commonly found in sand.Transistors have revolutionized since they were firstinvented over half a century ago by John Bardeen, Walter Brattain, andWilliam Shockley. But what are they—and how do they work?Photo: An insect with three legs? No, a typical transistor on an electronic circuit board. Although simple circuits contain individual transistors like this, complex circuits inside computers also contain microchips, each of which might have thousands, millions, or hundreds of millions of transistors packed inside. What does a transistor actually do?Photo: Compact hearing aids were among the first applications for transistors—and this one dates from about the late 1950s or 1960s.

About the size of a pack of playing cards, it was designed to be worn in or on a jacket pocket. There's a microphone on the other side of the case that picks up ambient sounds. You can clearly see the four little back transistors inside, amplifying those sounds and then shooting them out to the little loudspeaker that sits in your ear.A transistor is really simple—and really complex. Let's start withthe simple part.

Then to summarise when using a Transistor as a Switch the following conditions apply: Transistor switches can be used to switch and control lamps, relays or even motors. When using the bipolar transistor as a switch they must be either “fully-OFF” or “fully-ON”. Transistors that are fully “ON” are said to be in their Saturation region. How to use a transistor a switch (work in progress) 1. Let’s assume you want to switch a motor or a light bulb. The first step is to determine the voltage and current of the load, the thing you are trying to control. In the case of the motor, if you know where it came from, you can look up the specifications on the manufacturers website.

A transistor is a miniature electronic component thatcan do two different jobs. It can work either as an or a switch:. When it works as an amplifier, it takesin a tiny at one end (aninput current) and produces a much bigger electric current (an outputcurrent) at the other.

In other words, it's a kind of current booster. That comes inreally useful in things like, one of the first thingspeople used transistors for. A hearing aid has a tiny in itthat picks up from the world around you and turns them intofluctuating electric currents.

These are fed into a transistor thatboosts them and powers a tiny,so you hear a much louder version of the sounds around you.William Shockley, one of the inventors of the transistor, once explained transistor-amplifiers to a student in a morehumorous way: 'If you take a bale of hay and tie it to thetail of a mule and then strike a match and set the bale of hay on fire,and if you then compare the energy expended shortly thereafter by themule with the energy expended by yourself in the striking of the match,you will understand the concept of amplification.' . Transistors can also work as switches. Atiny electric current flowing through one part of a transistor can make a much biggercurrent flow through another part of it.

In other words, the smallcurrent switches on the larger one. This is essentially how all computer chips work. Forexample, a chipcontains hundreds of millions or even billions of transistors,each of which can be switched on or off individually.

Since eachtransistor can be in two distinct states, it canstore two different numbers, zero and one. With billions of transistors, a chip can store billions of zeros and ones, andalmost as many ordinary numbers and letters (or characters, as we call them). More about this in a moment.The great thing about old-style machines was that you could takethem apart to figure out how they worked. It was never too hard, with abit of pushing and poking, to discover which bit did what and how onething led to another. But electronics is entirely different. It's allabout using electrons to control electricity. An electron is aminuteparticle inside an.

It's so small, it weighs just under0. The most advanced transistors workby controlling the movements of individual electrons, so you canimagine just how small they are. In a modern computer chip, the size ofa fingernail, you'll probably find between 500 millionand two billion separate transistors.

There's no chance of taking a transistor apart to find out how itworks, so we have to understand it with theory and imagination instead.First off, it helps if we know what a transistor is made from. How is a transistor made?Photo: A wafer of silicon.

Photo by courtesy of.Transistors are made from silicon, a chemical element found in sand, which does not normally conductelectricity (it doesn't allow electrons to flow through it easily).Silicon is a semiconductor, which means it'sneither really aconductor (something like a that lets electricity flow) nor aninsulator (something like that stops electricity flowing). Ifwe treat silicon with impurities (a process known as doping),we can make it behave in a differentway. If we dope silicon with the chemical elements arsenic, phosphorus,or antimony, the silicon gains some extra 'free' electrons—ones thatcan carry an electric current—so electrons will flow outof it more naturally. Because electrons have a negative charge, silicontreated this way is called n-type (negativetype). We can also dope silicon with other impurities such as boron,gallium,. Silicon treated this way has fewer of those'free' electrons, so the electrons in nearby materials will tend to flow into it.

We call this sort of silicon p-type (positive type).Quickly, in passing, it's important to note that neither n-type or p-type silicon actually has a charge in itself: both are electrically neutral. It's true that n-type silicon has extra 'free' electrons that increase its conductivity, while p-type silicon has fewer of those free electrons, which helps to increase its conductivity in the opposite way.

In each case, the extra conductivity comes from having added neutral (uncharged) atoms of impurities to silicon that was neutral to start with—and we can't create electrical charges out of thin air! A more detailed explanation would need me to introduce an idea called, which is a little bit beyond the scope of this article. All we need to remember is that 'extra electrons' means extra free electrons—ones that can freely move about and help to carry an electric current. Silicon sandwichesWe now have two different types of silicon. If we put them togetherin layers, making sandwiches of p-type and n-type material, we can makedifferent kinds of electronic components that work in all kinds ofways.Suppose we join a piece of n-type silicon to a piece of p-typesilicon and put electrical contacts on either side. Exciting and usefulthings start to happen at the junction between the twomaterials.

If we turnon the current, we can make electrons flow through the junction fromthe n-type side to the p-type side and out through the circuit. Thishappens because the lack of electrons on the p-type side of thejunction pulls electrons over from the n-type side and vice-versa. Butifwe reverse the current, the electrons won't flow at all.

What we'vemade here is called a (or rectifier).It's an electroniccomponent that lets current flow through it in only one direction. It'suseful if you want to turn alternating (two-way) electric current intodirect (one-way) current. Diodes can also be made so they give offlight when electricity flows through them. You might have seen theselight-emitting diodes (LEDs) on pocket and electronicdisplays on hi-fi stereo equipment.

How a junction transistor worksNow suppose we use three layers of silicon in our sandwich insteadof two. We can either make a p-n-p sandwich (with a slice of n-typesilicon as the filling between two slices of p-type) or an n-p-nsandwich (with the p-type in between the two slabs of n-type).

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

When nocurrent isflowing in the transistor, we know the p-type silicon is short ofelectrons (shown here by the little plus signs, representing positivecharges) 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 asurplus of electrons, the p-type has holes where electronsshould be. Normally, the holes in the base act like a barrier, preventing anysignificant current flow from the emitter to the collector whilethe transistor is in its 'off' state.A transistor works when the electrons and the holes start movingacross the two junctions between the n-type and p-type silicon.Let'sconnect the transistor up to some power. Suppose we attach a smallpositive voltage to the base, make the emitter negatively charged, andmake the collector positively charged. Electrons are pulled from theemitter into the base—and then from the base into the collector. Andthe transistor switches to its 'on' state:The small current that we turn on at the base makes a big currentflow between the emitter and the collector. By turning a small inputcurrent into a large output current, the transistor acts like an amplifier. Butit also acts like a switch at the same time.

When there is no current tothe base, little or no current flows between the collector and theemitter. Turn on the base current and a big current flows. So the basecurrent switches the whole transistor on and off. Technically, thistype of transistor is called bipolar becausetwo different kinds (or 'polarities') of electrical charge (negative electrons andpositive holes) are involved in making the current flow.We can also understand a transistor by thinking of it like a pair of diodes. With thebase positive and the emitter negative, the base-emitter junction is like a forward-biaseddiode, with electrons moving in one direction across the junction (from left to right inthe diagram) and holes going the opposite way (from right to left). The base-collectorjunction is like a reverse-biased diode.

The positive voltage of the collector pullsmost of the electrons through and into the outside circuit (though some electrons do recombine with holes in the base). How a field-effect transistor (FET) worksAll transistors work by controlling the movement of electrons, butnot all of them do it the same way. Like a junction transistor, a FET(field effect transistor) has three different terminals—but theyhave the names source (analogous to the emitter), drain(analogous to thecollector), and gate (analogous to the base).

In a FET, thelayers ofn-type and p-type silicon are arranged in a slightly different way andcoated with layers of metal and oxide. That gives us a device called aMOSFET (Metal Oxide Semiconductor FieldEffect Transistor).Although there are extra electrons in the n-type source and drain,they cannot flow from one to the other because of the holes inthe p-type gate in between them. However, if we attach a positivevoltage to the gate, an electric field is created there that allowselectrons 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 unipolartransistor because only one kind ('polarity')of electric charge is involved in making it work. Getting over it with bennett foddy speedrun.

How do transistors work in calculators and computers?In practice, you don't need to know any of this stuff aboutelectrons and holes unless you're goingto design computer chips for a living! All you need to know is that atransistor works like an amplifier or a switch, using a small currentto switch on a larger one. But there's one other thing worth knowing:how does all this help computers storeinformation and make decisions?We can put a few transistor switches together to make somethingcalled a, which compares severalinput currents and gives a different output as a result. Logic gates let computers makevery 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 inyour hallway, you can make a decision like this: 'If it's raining AND Ihave an umbrella, I will go to theshops'. That's an example of Boolean algebra using what's called an AND'operator' (the word operator is just a bit of mathematical jargon tomake things seem more complicated than they really are). You can makesimilar decisions with other operators. 'If it's windy OR it's snowing,then I will put on a coat' isan example of using an OR operator.

Or how about 'If it's raining AND Ihave an umbrella OR I have a coat then it's okay to go out'. Using AND,OR, and other operators calledNOR, XOR, NOT, and NAND, computers can add up or compare binary numbers.That idea is the foundation stone of computer programs: the logicalseries of instructions that make computers do things.Normally, a junction transistor is 'off' when there is no basecurrent and switches to 'on' when the base current flows. That means ittakes an electric current to switch the transistor on or off. Buttransistors like this can be hooked up with logic gates so their outputconnections feed back into their inputs. The transistorthen stays on even when the base current is removed. Each time a newbasecurrent flows, the transistor 'flips' on or off. It remains in one ofthose stable states (either on or off) until another currentcomes along and flips it the other way.

This kind of arrangementis known as a flip-flop and it turns atransistor into a simplememory device that stores a zero (when it's off) or a one (when it'son). Flip-flops are the basic technology behind chips. Who invented the transistor?Artwork: The original design of the point-contact transistor, as set out inJohn Bardeen and Walter Brattain's US patent (2,524,035), filed in June 1948 (about six months afterthe original discovery) and awarded October 3, 1950.

Find out more On this website.Other websites.: Intel's educational website, all about transistors and.: A PBS website about Bardeen, Brattain, Shockley, and the history of the transistor.: Learn about transistors in a fun way, with games and interactives on the Nobel Prize website.Archived via the Wayback Machine.Books Technical and practical. by Charles Platt. O'Reilly, 2015. 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. by Forrest M. Master Publishing, 2003. Dependable introduction with lots of example circuits to try. by Paul Horowitz, Winfield Hill. Cambridge University Press, 2015. This is a much more detailed undergraduate textbook—and the one I used myself at college.

by B.S. Cambridge University Press, 1998. A relatively easy-to-follow, mostly non-mathematical introduction to solid-state physics; in effect, it explains how solids really work from the inside.

Chapter 10 explains electric currents and semiconductors.Historical. by J.B. Springer, 2017. A wide-ranging review of how electronics has changed our lives over the last century or so. by Michael Riordan and Lillian Hoddeson.

Norton & Co., 1998. A very readable history of transistors and integrated circuits.Articles Technical. by David Schneider. IEEE Spectrum, 16 January 2019. How perovskite crystals can be 'painted' onto a substrate to make field-effect transistors. by Samuel K.

IEEE Spectrum, 14 December 2017. How and why Qualcomm settled on devices called nanorings as potential new kinds of transistors. by Dexter Johnson. IEEE Spectrum, 7 Oct 2016. Are nanotransistors, made from carbon nanotubes, the future?.

by Wendy M. Scientific American, 22 July 2014. Memristors, not transistors, could lie at the heart of tomorrow's computers.

by Jin-Woo Han and Meyya Meyyappan. IEEE Spectrum. June 23, 2014. Partly vacuum tube, part transistor, it could work 10 times faster than silicon, NASA Ames researchers claim. by Charles Arthur, Guardian, 4 May 2011.

Making 'three-dimensional' transistors allows engineers to cram even more of them into the same space. byJohn Markoff.

The New York Times, 31 August 2009. What kinds of devices might replace transistors?. by Alexis Madrigal, Wired, April 17, 2008. Announcements about a new 'smallest transistor' happen every couple of years!Historical.: BBC News, 15 November 2007. Photos of the transistor pioneers, early transistors, and circuits. by Michael Riordan.

IEEE Spectrum, 30 April 2004.Patents.: The original point-contact transistor patent filed by John Bardeen and Walter Brattain on June 17, 1948 and awarded in October 1950.: This was Shockley's furious follow-up to the original patent, filed on June 26, 1948 (about 10 days after the original Bardeen/Brattain patent) and awarded on September 25, 1951.: Another of Shockley's patents, filed in September 1948 and awarded in April 1950.Videos Technical.: An excellent, easy-to-follow, 9-minute intro to transistors from Collin Cunningham of MAKE. Explains the difference between low-power (signal) transistors and high-powered devices, why transistors were better than vacuum tubes, and what we can use transistors for. There's also a very good explanation of the original Bardeen and Brattain point-contact transistors.HistoricalWe're fortunate to have some surviving archive footage of the three transistor pioneers!.: Shockley explains how transistors came to be invented and the part he played.: A 23-minute documentary about Bardeen's life and work.: Watch Dr Brattain explaining the theory of semiconductors and solid-state physics (29 minutes).Also from the archives, you might like these:.: How electron tubes made possible amplification of long-distance telephone calls. Transistors were the next logical step and were originally developed for exactly the same purpose.: This 1953 documentary explores the likely social impact of transistors.