The Evolution of the Microprocessor

The Integrated Circuit:

The Evolution of an Electronic Miracle

The microprocessor evolved over the course of many years of research, and people all over the world enjoy the benefits of this electronic miracle. It is difficult to think of anything that has affected modern life more than this invention. Cellular phones, wristwatches, calculators, automobiles, stereos, televisions, and computers are just a few of the thousands of electronic devices that have a microchip at the heart of its operation. Over the years, three major breakthroughs occurred to accelerate the birth of the microprocessor: the vacuum tube, the transistor, and the integrated circuit.

The Vacuum Tube

American physicist Lee De Forest invented the vacuum tube in 1906. However, one must look back to 1879 when Thomas Edison first revealed the incandescent electric light bulb to understand how De Forest developed his idea. Edison’s invention consisted of a conducting filament mounted in a glass bulb. Electricity passing through the filament caused it to heat up and created a vacuum that prevented the filament from oxidizing and burning up. In 1883, Edison detected electrons flowing through the vacuum from the lighted filament to a metal plate mounted inside the bulb. This became known as the Edison Effect, but he did not develop this particular discovery any further. However, British physicist John Fleming found that the Edison Effect also detected radio waves and converted them to electricity. In 1904, Fleming first showed off his two-element vacuum tube known as the Fleming diode that converted an alternating current (AC) signal into direct current (DC) (Kuphaldt).

The Fleming diode consisted of an incandescent light bulb with an extra electrode inside. Electrons boiled off the surface of the metal plate and into the vacuum inside the bulb as the filament became white-hot. When the extra electrode became more positive than the filament, a direct current flowed through the vacuum proving that AC signals could be converted into DC. One of the first uses of the Fleming diode was to detect weak signals produced by the new wireless telegraph. Later, the diode vacuum tube was used to convert AC into DC for power supplies in electronic equipment (Kuphaldt).

Many inventors tried to improve the Fleming diode, but the only one who succeeded was American inventor Lee De Forest. In 1906, De Forest introduced a third electrode called the grid into the Fleming diode. (This grid was simply a bent wire between the plate and filament.) The grid changed (modulated) the current flowing from the filament to the plate when De Forest applied the signal from the wireless telegraph antenna to the grid instead of the filament. In 1907, he patented his bulb that had the same contents as the Fleming diode, except for the added electrode, and he is credited with the invention of the vacuum tube. This triode, called the Audion, was the first successful electronic amplifier that could also be used as a switch. Long distance communication became a reality as radio signals were amplified before they were transmitted, and receivers using the vacuum tubes amplified the incoming signal (Maxfield, Brown 1997)

The vacuum tube changed the way almost anything related to electricity or communications worked, especially in the area of digital computers. De Forest’s invention could control the flow of electrons inside the tube. This created the ability for electronic digital computers to use the zeros and ones of binary arithmetic to perform their operations. A zero could be represented by the absence of an electron current to the plate, and a small but detectable current served as a one (Sullivan et al, 1988). It was the beginning of today's huge electronics industry.

However, this revolutionary invention had its drawbacks. Tubes were bulky and generated much heat. Simple computers generated so much heat that cooling systems were needed to prevent overheating. Furthermore, the cooling systems consumed nearly as much power as the tubes themselves. The vacuum tubes were also unreliable, and they burned out like light bulbs. The practicality and reliability of computers built with vacuum tubes was directly related to how often the tubes failed. A computer having thousands of tubes might operate for as little as one hour between malfunctions (Sullivan et al, 1988). If large computers were to become possible, a replacement for the vacuum tube was a necessity.

The Transistor

William Shockley joined Bell Telephone Laboratories in 1936. In 1939, Shockley began searching for a way to convert certain substances into an amplifying device, but the war interrupted his work. He resumed his research in 1945 when Bell Labs established a group to develop a semiconductor to replace