[ELI5] How do transistors work? What makes 3 chucks of silicon put together able to turn on and off?

Question

[ELI5] How do transistors work? What makes 3 chucks of silicon put together able to turn on and off?

In: 18

Answer 1

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.