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Course: Class 12 Physics (India) > Unit 14
Lesson 1: Band theory of solidsIntro to semiconductors
Why are we obsessed with semiconductors? All our computers and digital devices are made from semiconductors. But what is so special about them? Why do we use them? In this video let's explore, what it is about semiconductors, that allows us to create all these awesome computing devices. Created by Mahesh Shenoy.
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Video transcript
- [Instructor] You may
have already learned that based on how
readily a material allows the flow of charges through it, we can divide or we can
classify materials as conductors, conductors, insulators, insulators, and semiconductors, semiconductors. And in this chapter, we'll be
focusing on semiconductors. But I always had a question in my mind, why do we talk about semiconductors? What kind of an application
would a semiconductor have?? I should think, well think of it this way, whereas conductors are
excellent at what they do, they allow the flow of electricity, or they allow the flow of charges. So where you require electricity,
we will use conductors. And insulators are good at what they do, they don't allow, or they
block the flow of electricity. So when we don't want electricity, or places where we don't want them, we can use insulating materials. So where would we use
these semiconductors? That was a big question
that always haunted me, why do we even talk about them? Well, the best way to think about this is by looking at a picture,
let's look at a picture over here. What do you see? You see a couple of men who
are pushing this huge thing into some room, and guess what this was, roughly about 60 years ago,
this was about 60 years ago. And what they're pushing was
one of the first hard drives that was ever made. And this hard drive, the
state of the art, back then, had an amazing capacity of 5MB. You heard it right. Let me just write it there, 5MB. And let me just show what we have today, I just clicked this picture,
this is a memory card that I use for my camera, that is 32GB, all right. This is where we are today. Today. And we're talking about 32GB. And let's just pause here for a while to try and sink this in. I mean, are you kidding me? This is just 5MB for this huge thing? That thing can't even store,
what's the max it can store? It can store maybe two or
three photos that we take today with our cameras, or cellphones. And this thing can store videos, games, and so many more, and
this is just 60 years ago. I don't know about you, but
this technological growth is inconceivable for me. And every time I talk about this, I get goosebumps, even
right now I'm getting them. So how is this even possible? And not just this, think
about all the computing stuff that we have, computers,
calculators, cellphone, all the electronic things that we have, they are amazing, they
have extraordinary capacity compared to what we used
to have a few years ago. So what's enabling all of this? Why is our computing technology
growing so exponentially, so rapidly, at such an incredible rate? Well, guess what? It's all due to the
advent of semiconductors. It turns out all this technology, even inside this memory card, it's made of semiconducting materials. But again, the question might be, why do we use semiconductors? And how semiconductors
allow us to do this, why can't we just do that using
conductors and insulators? So, let's explore a little bit
more into the detail of this. Let's start by asking the question, what's inside a computer? What do you think is the
most fundamental basic unit of a computer? What do you think it is? Well, you may have already
learned that computers are made up of ALU, CPU, RAM, and ROM, but what's the most basic thing? Just like how in living
beings, the most basic, fundamental unit of life is cells, what do you think is the most
fundamental unit over here? Well, when I first learned
this, I was shocked. It turns out the most
fundamental unit is a switch. That's right, a switch
that turns on and off, your computers are made primarily
of lots and lots and lots of switches. And here's a
simple way to think about it, the more switches you
put inside the computer, you get more computing power, you get more memory, that's it. But of course, the
difference between the switch that we're familiar with, and the ones inside your computer, is that the switches inside the computers have no moving parts. So unlike a regular switch, which is controlled mechanically, but pushing on and off, these
switches inside the computer are controlled by electricity,
by voltage or by current. We would say they are
electricity controlled. But again, the question could be, how do you built a switch
which has no moving parts? So we're now coming to
the meat of the stuff, we're talking about the
most, most fundamental thing that we require to build a computer, and that is, the secret over
here is to build a device. So you can build a device,
which only allows the flow of current in one direction,
so maybe this way, it allows the flow of
current in one direction, but it doesn't allow the flow of current in the opposite direction. You need to build something like this. So, basically it's a
conductor in one direction, but an insulator in
the opposite direction. If you can build a device like this, you can end up building a switch
which has no moving parts, and then you can go ahead and
end up building computers. Now earlier, in the early
1900s, we actually built them by just using conductors and insulators, and they look pretty much like this. This seems very
complicated, by don't worry, you don't have to worry about them, you're not gonna study them,
they're pretty ancient, they're pretty obsolete, they're only used for
some experiments today. But anyways, these were built
just by using conductors and insulators. And the problems with this device, so the problem with this, this is pretty old stuff, by the way, the problem with this was, that they worked on heating. That means you had to heat
this up to make it work, and that means if you were
to put a lot of these things inside a computer, your computer
would become extremely hot, and they were big devices,
that means your computers would be huge, you
would require big rooms, and they had to be
continuously cooled down. And since you're heating
it, it would require immense amount of power, and they were very bulky, and they were extremely
hard to manufacture, and they would go out in days,
so you had to replace them, very often. So this is an absolute
nightmare to think about, what we had before. But today, we can build these things just by using semiconductors. And the big ones, look somewhat like this. Yeah, these are the big ones, these are the ones that we have today, and they're built exclusively
using semiconductors. So the big ones look like this, and the beauty is, they
don't work on heat, you don't have to heat them, and that means they require
extremely low power, and so they are very efficient. And these are the big ones, the small ones are so tiny, that you
can fit a billion of them in your finger nail, they are that tiny. Which means our switch
has become extremely tiny, and so we can fit a lot
of them in our computers, making our computers awesome. So, long story short, why
do we use semiconductors for computing devices? Because with semiconductors,
you can build extremely tiny switches, and you can build
awesome computers out of them. And so in the future, we're gonna focus, and we're gonna learn exactly how, by exploring the properties
of semiconductors, we can build devices like this. And then eventually we're gonna learn how using these devices, how do we build switches
which have absolutely no moving parts, which are only electricity controlled.