The Transistor
A switch with no moving parts. AI is billions of them flipping.
How big?A few dozen nanometres. Thousands would fit across one human hair.
Real: What it looks like.
Keys: arrows rotate · + / − zoom · 0 reset · 1–4 views · S signal · T tour · L labels · Space spin. Models are stylised and built from code: proportions are honest, details are simplified.
What it is
A transistor is an electrical switch. Put a small voltage on the gate and a channel opens so current flows from source to drain; take it away and the channel closes. On = 1, off = 0.
Modern chips use a FinFET or newer gate-all-around design: the silicon channel stands up like a fin (or a stack of thin sheets) and the gate wraps around it, so it can shut the current off cleanly even when it is tiny.
Layers of copper wiring above connect the transistors into logic. Chain enough switches together and you can add, multiply and remember.
Why AI needs it
Every multiplication a neural network does is thousands of these switches flipping in a pattern. A big AI chip holds tens to hundreds of billions of transistors, each switching billions of times a second.
Every labeled part
- 1
Gate
The control. A small voltage here opens or closes the channel underneath, the way a finger presses a light switch.
- 2
Channel
The path current takes through the silicon fin. In X-ray it glows when the transistor is ON.
- 3
Source
Where electrons enter. The metal contact on top connects it to the wiring above.
- 4
Drain
Where electrons leave when the switch is on.
- 5
Fin
The silicon stands up like a shark fin so the gate can grip it on three sides. That's what lets tiny transistors switch off without leaking.
- 6
Copper wiring
Ten-plus layers of copper wires above the transistors connect them into circuits. Explode the view to see two of them lift off.
- 7
Silicon wafer
Everything is built on a polished slice of ultra-pure silicon. Silicon is made from sand.
Try it · concept lab
From a switch to a letter
Flip the gate, then flip eight switches to spell a character.
Eight switches = one byte. Tap to flip.
Number
65
As a letter
"A"
Big idea: Everything a computer does, AI included, is patterns of on/off switches. Eight make a byte; billions make a thought-shaped calculation.
Swap it: other ways to do the same job
Planar transistor
Flat channel, used until about 2011. Simpler, but leaks current once it gets very small.
Gate-all-around (nanosheet)
The newest design: the gate surrounds stacked sheets on all four sides. Better control, harder to manufacture.
Vacuum tube / relay
The original switches. A relay physically clicks and a tube glows. Room-sized computers were built from them.
Talk about it
- Q1
A transistor is just an on/off switch. What else in your house is an on/off switch?
- Q2
Early computers filled whole rooms with clicking switches. What would your day be like if computers were still that big?
- Q3
Switches keep getting smaller, but they can't shrink forever. What do you think people will try when they hit the limit?
For grown-ups: there are no right answers here. Ask a question, then ask "why do you think that?" The reasons matter more than the answer.
Printable question sheet (PDF)