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how does a transistor work as a switch
One Nvidia H-one-hundred chip holds 80 billion transistors, each one a switch with no moving parts. So what is the finger that flips them?
The finger is a voltage. Put a voltage on the middle terminal, called the gate, and electrons are allowed through the other two or blocked.
Slice one open. The common kind has a source and a drain, two islands of silicon, a gate on top, and a razor-thin glass insulator between them.
Gate at zero volts: the silicon between source and drain is the wrong kind for carrying electrons, so no path exists. The switch is off.
Now raise the gate voltage. Its electric field reaches through the glass and pulls electrons up under the gate, forming a thin conducting channel.
The channel only forms above a threshold voltage, and no current flows into the gate, because the glass blocks it. A field does the work, not a current.
So a gate voltage opens or closes a path, and that path is a one or a zero. Chips stack billions of these, flipping billions of times a second.
Every click, every pixel, every answer on your screen is billions of tiny paths opened and closed by voltage.