What Is A Semiconductor? - By Lumos Learning
Transcript
| 00:05 | hold here . I have a circuit with a battery | |
| 00:09 | light bulb and gap . If I fill this gap | |
| 00:13 | with a metal , the light comes on . If | |
| 00:15 | I fill this gap with glass , the light stays | |
| 00:18 | off . You probably already know this because metal is | |
| 00:22 | an electric conductor and glass is an insulator . But | |
| 00:25 | what happens when I fill this gap with a silicon | |
| 00:28 | wafer ? The light stays off , so you might | |
| 00:34 | think the silicon is an insulator . But what if | |
| 00:36 | I heat it up ? Thank you . It lights | |
| 00:49 | up . The silicon is insulating at room temperature but | |
| 00:56 | conducts electricity when it's very hot . It's a semi | |
| 01:00 | conductor whose conductivity changes based on the environment . This | |
| 01:08 | special ability makes semiconductors the perfect brains for electronic devices | |
| 01:12 | . Circuits of small semiconductor switches called transistors are at | |
| 01:16 | the heart of computer chips and enable them to do | |
| 01:19 | math and run programs . Semiconductors have enabled electronics to | |
| 01:23 | become smaller , faster and more reliable . But what | |
| 01:26 | is it exactly about these semiconductors that allow them to | |
| 01:29 | either conduct or insulin in a single atom ? Electrons | |
| 01:35 | can occupy specific energy levels when multiple atoms bond the | |
| 01:39 | electrons are shared between them . But because the atoms | |
| 01:42 | are now interacting the energy level . Shift around in | |
| 01:45 | a solid trillions and trillions of atoms interact with each | |
| 01:48 | other , their individual energy levels smear into energy bands | |
| 01:52 | . For a material to conduct , the electrons must | |
| 01:55 | be able to jump from lower energy states to higher | |
| 01:57 | ones . The spacing of these energy levels and how | |
| 02:00 | they're filled with electrons determines if the material is a | |
| 02:02 | conductor , insulator or semiconductor . If there's a huge | |
| 02:06 | gap between the lower energy levels and the higher ones | |
| 02:08 | , it's hard for electrons to jump to the higher | |
| 02:10 | ones so current can't flow . And it's an insulator | |
| 02:13 | like this . Glass metals have no gap at all | |
| 02:17 | . Electrons can move to the higher energy levels with | |
| 02:19 | no problem . Current can flow . Semiconductors fall somewhere | |
| 02:24 | in the middle . They have a medium sized band | |
| 02:26 | gap . So technically , I can make this glass | |
| 02:28 | conduct electricity if I added enough energy through heat to | |
| 02:32 | push the electrons into a higher band . But that | |
| 02:40 | amount of heat would either melt or break the glass | |
| 02:43 | before it actually conducts . This is true of most | |
| 02:47 | insulators . The amount of energy needed to make them | |
| 02:49 | conduct is just too high . But in a semiconductor | |
| 02:53 | , the band Gap is small enough that electrons can | |
| 02:56 | jump into the higher energy band so that current can | |
| 02:58 | flow . The amount of heat we apply determines how | |
| 03:01 | many electrons jump into the higher band and how much | |
| 03:04 | current flows . And he isn't the only way to | |
| 03:07 | change the conductivity and a semiconductor . We can also | |
| 03:09 | use light electric currents in a computer electric fields . | |
| 03:14 | As I've said , computers are made up of semiconductor | |
| 03:17 | switches called transistors , that switch between conducting and insulating | |
| 03:21 | . Computers use electric fields because heat is slow and | |
| 03:25 | would burn too much energy . We can turn this | |
| 03:28 | way for into computer chip by printing a circuit of | |
| 03:31 | transistors on it , using a process called photolithography . | |
| 03:35 | Here in the photo room , we cover the wafer | |
| 03:37 | with a light sensitive material and expose it to light | |
| 03:40 | that we shine through a pattern mass . Then we | |
| 03:43 | developed the waiver like film and photography , which leaves | |
| 03:46 | behind a pattern that becomes the circuit . Printing . | |
| 03:50 | The transistors at once lets you make circuits that are | |
| 03:53 | smaller and cheaper than if you built them from individual | |
| 03:56 | parts . Transistors make up the logic elements , the | |
| 04:00 | memory components and the communication modules that let computers talk | |
| 04:04 | to each other With semiconductors , you can cheaply add | |
| 04:07 | transistors to almost any device you can think of , | |
| 04:10 | from spaceships to servers to maybe even your toaster . | |
| 04:13 | Semiconductors have enabled the technological revolution , the Internet , | |
| 04:18 | the computer and the cell phone . No semiconductors , | |
| 04:21 | no information age . I'm Jamie . And thanks for | |
| 04:28 | watching this episode of science out loud . Be sure | |
| 04:30 | to check out some of our other videos , including | |
| 04:32 | mine , on how computers compute . Check out our | |
| 04:35 | website for more information , and I'm just like |
Summarizer
DESCRIPTION:
Semiconductors are in everything from your cell phone to rockets. But what exactly are they, and what makes them so special? Find out from Jamie, a Ph.D. student in Electrical Engineering and Computer Science at MIT.
OVERVIEW:
What Is A Semiconductor? is a free educational video by Lumos Learning.
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