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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.