Unit Opener

Electronics has become part of everyday life -- it underlies mobile phones, computers, televisions, air conditioners, microwave ovens, washing machines, medical diagnostic equipment, and even the ATMs that handle money, alongside its central role in communication systems. This chapter opens with the historical evolution of the field: J.A. Fleming's 1897 vacuum diode, followed by Lee De Forest's vacuum triode (and later tetrode and pentode tubes) that made it possible to control electrical signals, then the transistor era launched by Bardeen, Brattain and Shockley's 1948 bipolar junction transistor (Nobel Prize, 1956), whose popularity grew once germanium and silicon became the semiconductor materials of choice. From 1958 onward, integrated circuits packed thousands of components onto a single chip -- first analog, then digital -- culminating in Intel's 1969 microprocessor. This same miniaturization drove a parallel computer revolution: the room-sized ENIAC of the 1940s (built 1943-46, weighing about 50 tons, occupying roughly 1800 square feet, and using 18,000 vacuum tubes) has given way to desktops, laptops, palmtops and, at the extreme, chip-scale computers no bigger than a grain of rice. Electronics is defined here as the branch of physics that designs circuits using active components -- transistors, diodes, integrated circuits, sensors -- which are capable of adding power to a circuit, working alongside passive components -- resistors, inductors, capacitors, transformers -- which cannot. This particular chapter narrows in on the semiconductor side of that story: p-n junction diodes, bipolar junction transistors, and the logic circuits built from them.