The Basic Facts About Sensitive Spacecraft Microelectronics and Space Radiation

What is a transistor?

Transistors are devices that behave as tiny switches in computer circuits and allow information to be stored and retrieved. There are several general types of transistors. One of these, shown in the image to the left, is called a field effect transistor (FET). FETs are composed of two semiconductor layers -- one above the other. Electrons flows through the lower layer which is called the channel from the source to the drain in response to an applied voltage. The direction of the current is defined to be opposite to the direction of the electron flow.

The upper layer is called the gate. The gate can be given a negative charge by allowing electrons to flow into the p-type semiconductor and fill some of the holes. If the gate is charged negative, electrons in the channel are repelled (like charges repel one another) and the current flow is stopped. In this way the transistor can be turned on or off. The semiconductor material is the key to making this device behave as a switch. Click here to see what would happen if the semiconductor were replaced by a conductor.

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