June 26, 1948 - Patenting the Grown-Junction Transistor

On this day in engineering history, William Shockley filed a patent for the grown-junction transistor, the first bipolar junction transistor (BJT). The British-born researcher would later win a share of The Nobel Prize in Physics for his research on semiconductors and the discovery of the transistor effect.

Shockley's development of the grown-junction transistor was just one in a series of important discoveries at Bell Labs in New Jersey. In December 1947, the two men who would share the 1956 Nobel Prize with Shockley, John Bardeen and Walter Houser Brattain, had invented a point-to-point contact transistor that achieved amplification.

The Solid State Physics Group

In 1945, Bell Labs formed a special Solid State Physics Group to produce an alternative to vacuum tube amplifiers, devices which had played a critical role in the development of electronics. Made of glass and filled with gas, vacuum tubes produced an electrical signal by controlling the movement of electrons in a low-pressure space. They were easy to replace, but also fragile and short-lived.

As the head of the Solid State Physics Group, William Shockley labored alongside physicists John Bardeen, Walter Houser Brattain, and Gerald Pearson; chemists Stanley Morgan and Robert Gibney; and electronics export Hilbert Moore. Moore, the creator of a circuit where frequency of the input signal could be varied, worked well with Shockley and Pearson. Shockley's relationship with Bardeen and Brattain became strained, however, when Shockley was excluded from the duo's patent application.

The Sandwich Transistor

While arguing that he deserved credit for the point-to-point contact transistor, Shockley also sought to develop a different type of device. His first grown-junction transistor was made of a single crystal of germanium (a semiconductor material) with two PN junctions. Russell Ohl, another Bell Labs researcher who patented the first modern solar cell, had discovered PN barriers (as they were originally called) and how material impurities made some sections more resistant to electrical flow than others.

Grown-junction transistors are sometimes called "sandwich transistors" because a P-type semiconductor is sandwiched between two N-type layers (or vice versa). In Shockley's process, a seed crystal is pulled from a bath of molten semiconductor to produce a rod-shaped crystal called a boule. At specific times during the growth process, P-type and N-type dopants are applied.

William Shockley's patent for the grown-junction transistor (2,569,347) was issued on September 25, 1951. Although grown-junction transistors represented an important step in the development of solid-state technology, they were difficult to process and seldom effective at frequencies above the audio range.

Resources:

http://en.wikipedia.org/wiki/Grown_junction_transistor

http://en.wikipedia.org/wiki/William_Shockley

http://nobelprize.org/nobel_prizes/physics/laureates/1956/

http://en.wikipedia.org/wiki/Russell_Ohl

http://semiconductormuseum.com/PhotoGallery/PhotoGallery_M1752.htm