In 1906 the American physicist Lee De Forest invented the vacuum tube triode which was the first three terminal device and enabled amplification and switching of electrical signals.
The vacuum tube helped push the development of telephony, radio and computers forward a great deal. However, the metal that emitted electrons in the vacuum tubes burned out. The tubes were too big, not reliable and required so much power that big and complicated circuits took too much energy to run. In the late 1940's, big computers were built with over 10,000 vacuum tubes and occupied over 93 square meters of space.
The problems with vacuum tubes lead scientists and engineers to think of other ways to make three terminal devices. Instead of using electrons in vacuum, scientists began to consider how one might control electrons in solid materials, like metals and semiconductors.
Already in the 1920's, scientists understood how to make a two terminal device by making a point contact between a s