Point-contact transistor having two emitters. It became obsolete in the middle 1950s.
Modified grown-junction transistor or alloy-junction transistor having two connections at opposite ends of the base.[1] It achieved its high speed by reducing the input to output
capacitance. It became obsolete in the early 1960s with the development of the
diffusion transistor.
Diffused planar silicon bipolar junction transistor,[2] used in some
integrated circuits. This transistor, apart from the three electrodes (emitter, base, and collector), has a fourth electrode or grid made of conducting material placed near the emitter-base junction from which it is insulated by a silica layer.
^Wolf, Oswald; R. T. Kramer; J. Spiech; H. Shleuder (1966). Special Purpose Transistors: A Self-Instructional Programmed Manual.
Prentice Hall. pp. 98–102.
^U.S. patent 4,143,421 - Tetrode transistor memory logic cell, March 6, 1979. Filed September 6, 1977.