Transistor: understand what it is and the importance of this component

Your brain contains about 100 billion cells called neurons – the tiny switches that let you think and remember things. Computers contain billions of miniature “brain cells” as well. They are called transistors and they are made of silicon, a chemical element commonly found in sand. Transistors have revolutionized electronics since they were invented more than half a century ago by John Barden, Walter Brattain e William shockley. But what is a transistor and how do they work?

What does a transistor do

A transistor is both quite simple and very complex. Let's start with the simple part: it's a miniature electronic component that can do two different jobs, work as an amplifier or a switch.

When functioning as an amplifier, it receives a small electrical current at one end (an input current) and produces a much larger electrical current (an output current) at the other. In other words, it's a kind of signal booster.

This is very useful in devices like hearing aids, one of the first things transistors were used for. A hearing aid has a tiny microphone that picks up sounds from the world around you and turns them into fluctuating electrical currents.

They're powered by a transistor that drives them and drives a tiny speaker, so you hear a much louder version of the sounds around you.

William Shockley, one of the inventors of the transistor, once explained transistor amplifier students in a more humorous way:

“If you take a bale of hay and tie it to a mule's tail and then hit a match with a bale of hay on fire, and if you compare the energy expended immediately afterwards by the mule to the energy expended by you on the beat of the match , you will understand the concept of amplification “.

William Shockley, one of the inventors of the transistor

Transistors can also function as switches. A small electrical current flowing through one part of a transistor can cause a much larger current to flow through another part of it. In other words, the small current connects the larger one.

This is essentially how all computer chips work. For example, a memory chip contains hundreds of millions or even billions of transistors, each of which can be turned on or off individually.

Since each transistor can be in two different states, it can store two different numbers, zero and one. With billions of transistors, a chip can store billions of zeros and ones, and almost as many common numbers and letters (or characters, as we call them).

The great thing about old machines was that you could take them apart to find out how they worked. It was never too difficult, with a little pushing here and fiddling there, figuring out which bit did what and how one thing led to another. But electronics is totally different.

Electronics studies the use of electrons to control electricity. An electron is a tiny particle inside an atom. It is so small that it weighs just under 0,000000000000000000000000000001 kg! The most advanced transistors work by controlling the movements of individual electrons – so you can imagine how tiny they are.

On a modern fingernail-sized computer chip, you are likely to find between 500 million and two billion separate transistors. There is no chance of taking a transistor apart to find out how it works, so we have to understand it with theory and imagination. First, we need to know what a transistor is made of.

How a transistor is made

Transistors are made of silicon, a chemical found in sand that does not normally conduct electricity (does not allow electrons to flow easily). Silicon is a semiconductor, which means it's not really a conductor (something like a metal that lets electricity flow), nor an insulator (something like plastic that stops the flow of electricity).

If we treat the silicon with impurities (a process known as doping), we can make it behave in a different way. If we use silicon with the chemical elements arsenic, phosphorus or antimony, the silicon gains some “free” electrons – the ones that can carry an electric current – ​​so the electrons will flow more naturally.

Because electrons have a negative charge, silicon treated in this way is called type n (negative type). We can also use silicone with other impurities such as boron, gallium and aluminum. Silicon treated this way has fewer of these “free” electrons, so electrons in nearby materials tend to flow into it. We call this kind of type p silicon (positive type).

However, it is also important to note that neither the silicon in the type n or type p actually has a charge in it: both are electrically neutral. It is true that n-type silicon has extra “free” electrons that increase its conductivity, while p-type silicon has fewer free electrons, which helps increase its conductivity in the opposite way.

In each case, the extra conductivity comes from adding neutral (uncharged) atoms of impurities to the silicon, which was neutral to begin with – and we can't create electrical charges out of air! A more detailed explanation would need me to introduce an idea called band theory, which is a bit beyond the scope of this article. All we need to remember is that “extra electrons” means extra-free electrons – those that can move freely and help carry an electrical current.

silicone sandwiches

There are two different types of silicon. If we layer them together, making sandwiches of p-type and n-type material, we can make different types of electronic components that work in all sorts of ways.

Suppose we join a piece of silicon type na to a piece of silicon type p and put electrical contacts on both sides. Exciting and useful things start to happen at the junction between the two materials.

If we turn on the current, we can make electrons flow across the junction from the n-type side to the p-type side out through the circuit. This is because the lack of electrons on the p-type side of the junction attracts electrons on the n-type side and vice versa.

But if we reverse the current, the electrons won't flow. What we've done here is called a diode (or rectifier). It is an electronic component that lets current flow in only one direction. It is useful if you want to transform alternating (two-way) electrical current into direct (unidirectional) current.

Diodes can also be made so that they emit light when electricity flows through them. These light-emitting diodes (LEDs) are already present in TV screens, monitors, smartphones and tablets and screens (and even in lamps), providing a higher quality image and generating much lower energy consumption than the technologies used. previously on these types of devices.

How transistors work in computers

In practice, you don't need to know anything about electrons and electronics in general, unless you 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 turn on an amplifier. But there's something else worth knowing: how does all this help computers store information and make decisions?

We can put some transistor switches together to make something called a logic gate, which compares various input currents and gives a different output as a result. Logic gates allow computers to make very simple decisions using a mathematical technique called boolean algebra.

Your brain makes decisions the same way. For example, using “entries” (things you know) about the weather and your appointments, you can make a decision like this: “If it is raining E I have an umbrella, I will go to the market”. This is an example of Boolean algebra using what is called a AND “operator” (the word operator is just a bit of mathematical jargon to make things look more complicated than they really are).

You can make similar decisions with other traders. “If it's windy OU it's snowing, so I'm going to put on a coat” is an example of using an operator OR. Or how about “If it's raining E i have an umbrella OU I have a coat, so it’s okay to go out.”

Using AND, OR, and other operators called NOR, XOR, NOT, and NAND, computers can add or compare binary numbers. This idea is the cornerstone of computer programs: the logical series of instructions that make computers perform all sorts of tasks.

Typically, a junction transistor is “off” when there is no base current and switches to “on” when base current flows. This means that an electrical current is required to turn the transistor on or off.

But transistors like this can be wired with logic gates so that their output connections go back to their inputs. The transistor stays on even when the base current is removed. Each time a new base current flows, the transistor “turns on” or off.

It remains in one of these stable states (on or off) until another current appears and flips the other way. This type of arrangement is known as a flip-flop, and it turns a transistor into a simple memory device that stores either a zero (when it's off) or a one (when it's on). Flip-flops are the basic technology behind computer memory chips.

Who could have imagined that such a small part would account for so much of our current technology? If it weren't for the simple yet powerful capability of transistors, you probably wouldn't be reading this text today.