There are two types of materials in this world conductors and insulators. A conductor has the ability to allow electric current to flow through it. An insulator cannot allow electric current to flow through it.

Under extreme conditions, an insulator can break down, thereby allowing current to flow. This usually has catastrophic consequences, though.

There are good conductors and poor conductors. The extent to which a material can conduct electricity is characterized by giving the material a value, called a resistance value. Some conductors have a very high resistance, so high that for all practical purposes they can be considered insulators.

Everything has some level of resistance. Here are some examples:

• Metal has low resistance great conductor, very poor insulator

• Air has high resistance poor conductor, fair insulator

• Skin has moderate resistance fair conductor, poor insulator

Likewise, in an Integrated Circuit (IC), every material used in the chip has its given resistance value. Some values are low. Some values are high, just as in the rest of the world.

Given a chip design project, then, the question becomes, "How do you make the resistors you want out of semiconductor materials used on the chip?"

To make the required resistive components from the materials available on a chip is a matter of learning to control values. Controlling values comes from the ability to calculate values. And that comes from measuring. The next section will show you how to measure resistance values.