[ELI5] How do transistors work? What makes 3 chucks of silicon put together able to turn on and off?
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A transistor is a miniature semiconductor that regulates or controls current or voltage flow in addition amplifying and generating these electrical signals and acting as a switch/gate for them. Typically, transistors consist of three layers, or terminals, of a semiconductor material, each of which can carry a current.
Electrons repel each other. The three chunks are arranged in a special configuration with a thin layer of the middle chunk between the other two. When the voltage is high on the middle chunk, it repels the electrons that want to go between the outside chunks. When the middle chunk is grounded, current flows from the first chunk into it, and then on into the third chunk.
Its similar to a hall sensor. Some materials become conductive when a magnet is held close to it. Most Hall sensors are simply on/off, but a transistor is optimised so it can vary the conductivity. A transistor “can” be used as an on/off switch. Its also useful as an amplifier because as you vary the “tiny” signal, it allows more current to pass. In this way a small variable voltage signal can precisely adjust a large flow of current.
Study capacitance and inductance.
Let’s call the 3 “chunks” source, channel, and drain (in that order). The two ends (source/drain) have charge carriers available that allow current to flow through them if there’s a voltage. But the piece in-between, the channel, is depleted of charge carriers. If there are no charge carriers, there can’t be current flow. Since that’s what current flow is: the movement of charge carriers due to a voltage.
So let’s introduce a fourth piece: the gate electrode. It sits on top of the channel, but is separated from it by an insulator. And one more piece: the “bulk”. It’s kind of below the first three pieces.
If you put a voltage on the gate electrode, it can pull charge carriers up from the bulk into the channel. At that point, it can conduct electrical current, and the transistor is “on”. Conversely, put the opposite voltage on the gate and it will push the carriers out of the channel and turn the transistor “off”.
ELI5: When a voltage is applied to the middle silicon section, it pulls the ions to the side the middle lead is on creating a “channel” for electrons to flow from the two side bits of the transistor.
Most transistors these days are FETs, field effect transistors.
You take a lump of semiconductor, put an insulator on top and bottom and electrodes over that. Put an electric field here and all the charge carriers get repelled from one insulator: increase it and you create carriers of the other charge in a thin and properly conductive ‘inversion layer’. Contact to that layer at either side of your insulator with two more electrodes (‘source’ and ‘drain’) and it conducts electricity. Turn off the vertical field (‘gate field’) and the layer vanishes and the thing doesn’t conduct, giving you a voltage controlled switch.
Actually it turns out you can often get rid of the electrode on the bottom and create the gate field between the gate electrode and the source / drain only. Still works.
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