The Franklin Institute Logo
Case Files logo

Invention of the Point Contact Transistor, 1954

Punching Holes

In building their transistor and creating this junction, Bardeen and Brattian realized that, when a small current came in through one gold contact, it changed the nature of the germanium semiconductor so that a larger, separate current began flowing across the germanium and out the second current. This little current altered the flow of a much bigger current, and thus when the current emerged from the transistor it was amplified. The "holes" punched into the semiconductor by the first current functioned in the same way as the metal grid which Lee De Forest had inserted into the vacuum tube to enable amplification earlier that century.

A semiconductor like germanium is extremely sensitive to how many extra or missing electrons it has inside. Each time the input signal punches more holes in the germanium, it changes the way current flows across the crystal. The output current varies with the input current. This sensitivity to changes in input current is what enables transistors to carry and amplify complex sounds like a human voice or an orchestra recording.

The Franklin Institute carefully arranged its Medal Day audience. You can access the seating chart created for the presentation of Bardeen and Brattain's Ballantine Medal by clicking on the thumbnails at right.