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How CPUs are Made (Page 2/5)

Posted: November 22, 2000
Written by: Tuan "Solace" Nguyen

Transistors @ Work

Adding certain types of impurities or other materials to the silicon in a transistor changes its crystalline structure and enables it to conduct electricity. Silicon containing boron is called p-type silicon - p for positive or having no electrons. Silicon containing phosphorus is called n-type silicon - n for negative or having electrons.


Transistors consist of three terminals -- the source, the gate and the drain. In the n-type transistor, both the source and the drain are negatively charged and sit on positively charged p-silicon. When positive voltage is applied to the gate, electrons in the p-silicon are attracted to the area under the gate forming an electron channel between the source and the drain. When positive voltage is applied to the drain, the electrons are pulled from the source to the drain. In this state the transistor is on and there is electrical flow. If the voltage at the gate is removed, electrons aren't attracted to the area between the source and drain anymore and the pathway is broken and the transistor is turned off.

Well, now that you know how a transistor works letís get to the real deal.

Getting Real Clean

The Clean Room

The clean room is a room where there are virtually zero dust particles. Class 1 clean rooms are the cleanest of all with only 1 speck of dust per cubic foot. Inside clean rooms is where you can find raw processors, without their packaging. One small speck of dust could damage thousands of transistors on a processor rendering it useless.

Clean rooms are 10,000 times cleaner than a hospital operating room. There are sophisticated air filtering systems which purify the air once every 10 minutes to keep the room incredibly clean. But keeping the room clean and having people entering in and out all the time is likely going to be disastrous. This is why the engineers that work inside a clean room must wear a clean suit or what Intel calls a bunny suit. Itís almost like working for the CDC (Center for Disease and Control). The suits are made out of special non-linting and non-static material that you wear over your everyday clothing.

Above is a picture of a tiny grain of salt that has damaged thousands of transistors on a microchip. If the city of New York was a processor die, then that grain of salt would be a football stadium slammed into the streets from nowhere. Imagine the damage that would cause.

Above is a picture of Intel engineers preparing to enter the clean room.

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