Silicon, Circuits, and the Digital Revolution

Introduction to MOS Transistors and MOSFET Switches

CMOS is the industry standard logic used in consumer digital electronics. The CMOS NAND gate is the building block of the digital revolution; our goal over the next week is to understand the semiconductor origin of our digital world.

Here we examine the 'MOS' of CMOS, based on MOSFET transistors, where MOS stands for metal-oxide-semiconductor and FET stands for field-effect transistor. As studied in previous classes, the availability of n-type and p-type Silicon and compensation doping, which permits one type to be turned into the other type by adding additional dopants, is exploited to fabricate transistors.

In our previous class on binary counting, we found a way to represent numbers using just two digits, 0 and 1. One simple representation of a binary system is the electrical switch -- it is either on or off. Transistor circuits can be constructed to operate as miniature electrical switches, as we will see.

In addition, the state of a transistor switch may be controlled by the output of another transistor switch. Control of switches by other switches is the key idea behind using semiconductors in the form of transistor switches to carry out digital logic operations. The ease with which transistor switches can be used to store information in the form of binary numbers and their speed of execution in processing logic operations are essential ingredients in digital electronics.

Online Resources
      The Transistor from PBS
      How Transistors Work from the Education Programs at Intel

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Last updated May 2, 2000.
© George Watson, Univ. of Delaware, 2000.