Reference STATE OF THE ART Stan Augarten

ISBN 0-89919-195-9

Photo of
Resistor - Transistor Logic
The 907


Two years after the introduction of the first planar IC, a resistor-transistor logic (RTL) chip know as a flip-flop (p. 10), Fairchild produced the much more sophisticated RTL chip shown on the right, the 907. Its layout clearly demonstrates the advances in IC technology that had been made in the intervening period. Not only did the 907 have many more components than its predecessor, laid down in a way that greatly increased the chip's performance, it also contained isolation channels and buried layers - features that were to become commonplace in ICs.

  Isolation channels are narrow strips of silicon used to separate, or isolate, one transistor from another; isolation channels are doped with either positive ions or electrons and are easily distinguished from the top of the chip. Buried layers, on the other hand, are embedded directly under the transistors' collectors and can't be seen. Unlike isolation channels, buried layers are made of antimony or arsenic, which are highly conductive. This cuts down on the resistance to electron flow inherent in collectors. Working in conjunction with isolation channels, buried layers greatly enhance a transistor's performance, allowing ICs to be turned on much faster and with much lower voltage than would otherwise be the case.

The 907 consists of two logic gates, each composed of four transistors and an equal number of resistors. The transistors are the small green boxlike features with the overlapping beige bars (within the two inner boxes encircled by the dark red lines); the resistors are the perpendicular green bars. A large fifth resistor lies at the bottom. The dark red lines are the visible edges of isolation channels, while the beige features are aluminum conductors. Actual size: 0.038 x 0.048 inches. Photo of


©Copyright Stan Augarten
This book is provided for general reference. The National Museum of American History and the Smithsonian Institution make no claims as to the accuracy or completeness of this work.

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