In this phone, there are nearly 100 million transistors,
in this computer there’s over a billion.
The transistor is in virtually every electronic device we use:
TV’s, radios, Tamagotchis.
电视机 收音机 电子宠物
But how does it work?
Well the basic principle is actually incredibly simple.
It works just like this switch, so it controls the flow of electric current.
It can be off, so you could call that the zero state
or it could be on, the one state.
And this is how all of our information is now stored and processed,
in zeros and ones,
little bits of electric current.
But unlike this switch, a transistor doesn’t have any moving parts.
And it also doesn’t require a human controller.
Furthermore, it can be switched on and off
much more quickly than I can flick this switch.
And finally, and most importantly it is incredibly tiny.
最后 也是最重要的一点 它极其微小
Well this is all thanks to the miracle of semiconductors
or rather I should say the science of semiconductors.
Pure silicon is a semiconductor,
which means it conducts electric current better than insulators
but not as well as metals.
This is because an atom of silicon has four electrons in its outermost or valence shell.
This allows it to form bonds with its four nearest neighbours.
-Hidey ho there! -G’day.
-嗨 各位！ -你好
So it forms a tetrahedral crystal.
But since all these electrons are stuck in bonds,
few ever get enough energy
to escape their bonds and travel through the lattice.
So having a small number of mobile charges is what makes silicon a semi-conductor.
Now this wouldn’t be all that useful without a semiconductor’s secret weapon —
You’ve probably heard of doping,
it’s when you inject a foreign substance in order to improve performance.
Yeah it’s actually just like that, except on the atomic level.
没错 其实就像那样 只不过是原子层面
There are two types of doping called n-type and p-type.
To make n-type semiconductor, you take pure silicon
and inject a small amount of an element with 5 valence electrons,
This is useful because Phosphorous is similar enough to silicon
that it can fit into the lattice, but it brings with it an extra electron.
So this means now the semiconductor has more mobile charges
and so it conducts current better.
In p-type doping,
an element with only three valence electrons is added to the lattice.
Now this creates a ‘hole’ —
a place where there should be an electron, but there isn’t.
But this still increases the conductivity of the silicon
because electrons can move into it.
Now although it is electrons that are moving,
we like to talk about the holes moving around —
because there’s far fewer of them.
Now since the hole is the lack of an electron,
it actually acts as a positive charge.
And this is why p-type semiconductor is actually called p-type.
The p stands for positive —
it’s positive charges, these holes, which are moving and conducting the current.
Now it’s a common misconception that n-type semiconductors are negatively charged
那么 就有一个常见的误解 认为n型半导体带负电
and p-type semiconductors are positively charged.
That’s not true, they are both neutral
because they have the same number of electrons and protons inside them.
The n and the p actually just refer to the sign of charge that can move within them.
So in n-type, it’s negative electrons which can move,
因此 在n型半导体中 可以移动的是负电子
and in p-type it’s a positive hole that moves.
But they’re both neutral!
A transistor is made with both n-type and p-type semiconductors.
A common configuration has n on the ends with p in the middle.
一种常见的配置是 n型在两端 p型在中间
Just like a switch,
a transistor has an electrical contact at each end
and these are called the source and the drain.
But instead of a mechanical switch, there is a third electrical contact called the gate,
which is insulated from the semiconductor by an oxide layer.
When a transistor is made, the n and p-types don’t keep to themselves —
electrons actually diffuse from the n-type,
where there are more of them into the p-type to fill the holes.
This creates something called the depletion layer.
What’s been depleted?
Charges that can move.
There are no more free electrons in the n-type — why?
Because they’ve filled the holes in the p-type.
Now this makes the p-type negative thanks to the added electrons.
现在 p型半导体由于电子增多 呈负电性
And this is important because the p-type will now repel any electrons
that try to come across from the n-type.
So the depletion layer actually acts as a barrier,
preventing the flow of electric current through the transistor.
So right now the transistor is off, it’s like an open switch, it’s in the zero state.
现在晶体管是断开状态 就像断开的开关 处于0状态
To turn it on, you have to apply a small positive voltage to the gate.
This attracts the electrons over
and overcomes that repulsion from the depletion.
It actually shrinks the depletion layer
so that electrons can move through and form a conducting channel.
So the transistor is now on, it’s in the one state.
现在 晶体管是闭合的 处于1状态
This is remarkable
because just by exploiting the properties of a crystal
we’ve been able to create a switch that doesn’t have any moving parts,
that can be turned on and off very quickly just with a voltage,
and most importantly it can be made tiny.
Transistors today are only about 22nm wide,
which means they are only about 50 atoms across.
But to keep up with Moore’s law, they’re going to have to keep getting smaller.
Moore’s Law states
that every two years the number of transistors on a chip should double.
And there is a limit
as those terminals get closer and closer together,
quantum effects become more significant
and electrons can actually tunnel from one side to the other.
So you may not be able to make a barrier high enough to stop them from flowing.
Now this will be a real problem for the future of transistors,
but we’ll probably only face that another ten years down the track.
So until then transistors, the way we know them, are going to keep getting better.
因此 在那之前 我们所认知的晶体管将会越来越好
Once you have, let’s say, three hundred of these qubits,
then you have like two to the three hundred classical bits.
Which is as many particles as there are in the universe.
In this phone, there are nearly 100 million transistors,