Inventors of Radio: Julius Edgar Lilienfeld
December 1964 Radio-Electronics

December 1964 Radio-Electronics

December 1964 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

Here is yet more evidence of my oft-made claim that Germany might have dominated the world as a technological and financial superpower if it had not instigated two world wars. A huge amount of ingenuity and ability to convert ideas into reality has come out of Germany over the course of centuries. Oppressive and often inhumane government behavior caused a lot of that talent to emigrate to other countries, so the opportunity was lost. In this instance, I refer to Julius Edgar Lilienfeld, who not only produced the first sample of liquefied helium, but also is credited, according to this 1964 Radio−Electronics magazine article, for developing the first semiconductor devices for amplification. U.S. patent number US1745175A was awarded on January 28, 1930 (filed on October 8, 1926) for what was essentially a field effect transistor. Lilienfeld became a U.S. citizen in 1935. To be fair, I will also note that many of those fled-to countries are today as bad or worse than Germany was then.

Inventors of Radio: Julius Edgar Lilienfeld

Inventors of Radio: Julius Edgar Lilienfeld, December 1964 Radio-Electronics - RF Cafe

Julius Edgar Lilienfeld, inventor of the solid-state amplifier.

By Fred Shunaman

In the early days of the century, in Leipzig, Germany, Julius Edgar Lilienfeld attacked the problem of determining why hydrogen could not be liquefied. As one result of his research, Lilienfeld produced the first liquid hydrogen.

Thus began the career of the man who appears to have developed the first semiconductor devices for amplification. Working in the United States on electrolytic capacitors, Dr. Lilienfeld apparently learned much of the nature of conducting and semiconducting compounds, resulting in three patents covering solid-state electric amplifiers. His first patent (No. 1,745,175) describes a "Method and apparatus for controlling electric current." This device consisted of a substrate of glass or other material on top of which two conducting members, "gold, silver, or copper," called 11 and 12 in Fig. 1, a copy of his patent, were placed so that their edges would be very close together. Between the two edges, another electrode of metal foil (13) is juxtaposed in such a way that its upper edge lies flush with the upper surface of the glass. Over the conducting members and the glass between them a film of "copper and sulfur" (presumably cuprous sulfide) is deposited, either chemically or by sputtering or evaporation.

Lilienfeld's first solid-state patent - RF Cafe

Fig. 1 - Lilienfeld's first solid-state patent.

Representation of energy levels in the drawing - RF Cafe

Fig. 2 - Representation of energy levels in the drawing of Fig. 1.

Modification of the device for controlling electric current - RF Cafe

Fig. 3 - A later modification of the device "for controlling electric current."

The theory of the device, as given by the inventor, is that, if one of the connecting plates is held at a higher and the other at a lower voltage, there will be a voltage gradient across the semiconducting layer. As indicated in Fig. 2, a may be considered the voltage of Plate 11, b that of Plate 12, and c the drop across semiconducting layer 15. Varying the voltage on b (13 in Fig. 1) varies the impedance to the flow of electrons from 11 to 12, making it possible for the smaller amount of power in the circuit connected to element 13, which would nowadays be called the "base", to control the larger amount of power in the circuit connected to 11 and 12. The patent shows a radio set, with two of these devices hooked up as rf amplifiers, and two as af amplifiers, with a speaker output. We have found no evidence that such a set was ever constructed, and some doubt has been expressed as to whether the amplifier would work at radio frequency.

Another patent, No. 1,877,140, Sept. 13, 1932, is called "Amplifier for electric currents," and a third one, No. 1,900,008, Mar. 7, 1933, appears to be a refinement of the original one with the two conducting plates. A single plate of what is described in the patent as copper sulfide rests on a layer of aluminum oxide, which forms the surface of an aluminum substrate. A transverse notch, which, according to the patent, has to reduce the thickness of the top layer to a degree "approaching molecular thickness" is provided, and the "base" contact is simply made to the aluminum block (Fig. 3).

There is some doubt about just how these devices should be classified: as a kind of transistor, or some other type of solid-state amplifier? There is no doubt, however, that Dr. Lilienfeld did invent the first solid-state amplifier of record.

His wife, writing from the Virgin Islands, where Lilienfeld made his home after becoming a citizen of the United States in 1935, states: "His laboratory in Leipzig was a mecca for all interested in high-vacuum, low-temperature work. His X-ray tubes were the first anywhere to be used by the medical profession, and were manufactured in quantity by Koch & Stossel in Dresden."1

Before leaving Germany (apparently in the early 20's), he also made important discoveries in field emission. These were actual steps on the road toward the field electron microscope.2 One worker in that area3 believes the discoveries reflected a Lilienfeld influence on most field-emission work up to the present.

1 Science Fortnightly, P. Lorillard Research Laboratories, April 29, 1964

2 Müller, Dr. Erwin W., "Practical Field Electron Microscope," Radio-Electronics, September 1951, page 43

3 J. B. Johnson, "More on the Solid-State Amplifier and Dr. Lilienfeld," Physics Today, May 1964



Posted February 20, 2024