Julius Edgar Lilienfeld proposed the basic principle behind the MOS field-effect transistor in 1925. Julius Edgar Lilienfeld was born on April 18, 1882 in Lemberg (now Lwow or Lviv, Ukraine), the capital of Galicia, then part of Austro-Hungary, where the population was about 110,000 (in 1880) including 30,000 Jews. His father, Dr. jur. Siegmund Lilienfeld, was a Jewish lawyer in Lemberg. His mother was Sarah Jampoler Lilienfeld. Julius Lilienfeld, who also gives in his vita, his religion as mosaic, attended the Oberrealschule (a sort of secondary school with preference of natural sciences) in the same town.
Lilienfeld did not go to the University of Lemberg, but started, in the winter term of 1899, his studies in mechanical engineering at thePolytechnic, Berlin – Charlottenburg. After one year of study and practical work in an engineering factory, he changed his mind, being aware of his prevailing interest in the natural sciences and left thePolytechnic in 1900. However, his engineering studies greatly helped his later work in science.
Julius Edgar Lilienfeld registered at the Friedrich-Wilhelms-Universitat, Berlin on 2, November, 1900. Up to the winter term of 1904, his favoritesubjects were philosophy, mathematics, physics and chemistry with special emphasis on experimental physics. He attended the lectures of van’t Hoff, M. Planck, E. Warburg and others. In his vita he mentions his first paper in a philosophical journal, Trial of a strict conception of mathematical probability (J. E. Lilienfeld, Versuch einer strengen Fassung des Begriffes der mathematischen Wahrscheinlichkeit, ZS. f. Philosophie und philosophische Kritik 1902, 119, 58-66).
From 1903 to 1904, he worked in the Physics Institute, under the guidance of Emil Warburg. Lilienfeld finished his studies in the winter term 1904 and received a certificate in which the lectures and exerciseshe attended are recorded.
Lilienfeld’s final certificate for studies at the Friedrich-Wilhelms-Universitat, Berlin, 1904
Lilienfeld received his Ph.D. on 18 February 1905, as printed on thedissertation (the examination took place on February 2, 1905). The examination accompanying the promotion was carried out by Warburg, Planck, Landolt and Dilthey with the result cum laude, i.e., with distinction.
The dissertation “On a very sensitive method for a quantitative spectral analysis of gas mixtures” got the note laudabile by Warburg and was published in 1905 (J. E. Lilienfeld, Uber eine allgemeine und hervorragend empfindliche Methode zur spektralen qualitativen Elementaranalyse von Gasgemischen, Ann. Physik 1905, 16, 931-942).
A satisfactory in Planck’s examination on the basic equations of Maxwell-Hertz electrodynamics, the Hamilton and d’Alembert principles, shows that Lilienfeld’s strength was not in theoretical physics. Also Landolt (chemistry) and Warburg (physics) recorded befriedigende Kenntnisse (satisfactory knowledge).
Ph.D. certificate of Lilienfeld obtained from Friedrich-Wilhelms-Universitat, Berlin, on 18 February 1905
In the winter term of 1905-1906, Lilienfeld joined the new Physics Institute of the University of Leipzig, built between 1901 and 1905 by Otto Wiener, who held the chair of experimental physics. Julius Edgar Lilienfeld soon published papers on properties of the glow discharge and on a mercury low pressure lamp with high output.
Investigations of glow discharges were not standard at Wiener’s Institute and might have been influenced by Lilienfeld’s time at Berlin. Nevertheless, Wiener obviously had no objections to these investigations and suggested financial support by the Royal Saxonian Society of Sciences in Leipzig. Lilienfeld, who never became a society member, delivered various papers (at first on glow discharges), which were presented by the member O. Wiener in the meetings and which were published in the society transactions. Several times Lilienfeld thanked the society for support.
In the autumn of 1908, Otto Wiener sent an application to the Saxonian ministry of education for equipment to produce liquid air and later on liquid hydrogen. In support of the request, the difficulties with constant supply and transportation of liquid air for several institutes of theuniversity were mentioned, and the use of a machine room of the Physical Institute suggested.
It was soon possible to buy a liquifier and Lilienfeld used it also for hydrogen. When some hydrogen leaked out of the machine, and apparently caused a small explosion, the institute became aware of the danger. Wiener sent (summer 1909) another application for a separate laboratory, which led to a larger building in the neighborhood of the institute. Lilienfeld worked on the installation (and further extension) of a plant for high pressures and low temperatures, air and hydrogen liquefaction, at the Leipzig Physics Institute.
Lilienfeld’s low temperature laboratory and liquifier plant
Lilienfeld suggested also the use of compressors instead of pressurized gases and ordered various equipment according to his ideas.
Compressor from a factory in Wurzen near Leipzig used by Lilienfeld in his liquifier plant
Apparatus invented for the separation of gaseous mixtures, suitable of recovering oxygen and nitrogen from atmospheric air from a UK Lilienfeld patent (J.E. Lilienfeld, Improvements in and relating to the Separation of Gaseous Mixtures, UK Patent 22,930, A.D. application Oct. 17, 1911, accepted Oct. 10, 1912).
Lilienfeld worked with Count Ferdinand von Zeppelin on designing hydrogen-filled dirigibles. In a memorandum on the use of liquid hydrogen for airships, Lilienfeld explained the advantages of liquid hydrogen as a filling gas, which requires much less transport capacity than the much heavier steelflasks for gaseous hydrogen.
In addition, the hydrogen can be used as ballast or dead freight from the start and can replace gas losses during the journey. He also gives an estimate on the costs, if liquifiers were in continuous use at the airship base.
At that time, Lilienfeld also started work in a related field, looking for electrical conductivity in a highly evacuated tube. He described his investigations in his habilitation thesis (the habilitation is a postdoctoral qualification required at German universities to get promotion to professor) and other publications. Though his reputation was established, Lilienfeld had some difficulties with the Saxonian ministerial bureaucracy, because of a missing authorized leaving certificate of a grammar school or similar secondary school, but finally finished his habilitation dissertation (J.E. Lilienfeld, Die Elektrizitaitsleitung im extremen Vakuum, Leipziger Habilitationsschrift, March 15, 1910), which was soon published (J.E. Lilienfeld, Ann. Physik 1910, 32, 673-738). After giving his trial lecture Uber die Herstellung tiefer Temperaturen (On the production of low temperatures), Lilienfeld was awarded the Privatdozent position (unsalaried lecturer with an income being dependent on the students fees for subscribed lectures) at Wiener’s institute.
Lilienfeld started with lectures already in the winter term of 1910 on the liquefaction of gases and the areas of application of low temperatures. He often chose low temperature physics and technology, as the contents of his lectures, followed by X-rays and other radiation phenomena.
He did not, however, speak about his research areas, for instance, gas discharges, high vacuum or electrical conductivity in high vacuum or later on field emission. The average number of participants per lecture was about 12 the maximum was 30. These numbers appear normal for Lilienfeld’s specialized lectures. As usual the big lectures on experimental physics with demonstrations were held by Prof. Wiener, head of the Physical Institute. In the 1915 summer term, the lecture announced by Lilienfeld had to be canceled, because the students were recruited to the army.
Studying discharges in highly evacuated tubes led Lilienfeld to the construction of a new type of X-ray tube, soon called Lilienfeldrohre.
Scheme of an X-ray tube with circuitry described in an early USA patent of Lilienfeld (J.E. Lilienfeld, Process and apparatus for producing Roentgen rays, US Patent 1,122,011, filed Oct. 2, 1912, patented Dec. 22, 1914)
Lilienfeld developed an X-ray tube with a high vacuum by placing an additional filament as an electron source in a carefully chosen tube region (called tandem tube because the two discharge volumes were separated by the cathode).
Scheme of an X-ray tube with separated discharge volumes from a Lilienfeld UK patent J.E. (Lilienfeld, Improvements relating to the production of Rontgen rays, UK Patent 4097 A.D., application March 15, 1915)
Lilienfeld developed dosimetry of X-rays and worked with physicians on the improvement of X-ray diagnostics.
Scheme to measure the X-ray dose with collimator B, ionization chamber K, wire probe L and electrometer J (L. KUpferle, J.E. Lilienfeld, Die praktische Dosimetrie der Rontgenstrahlen Strahlentherapie, 1919, 19, 10-45)
Lilienfeld also used his X-ray tube to decide about the merits of Sommerfeld’s theory. (Bohr’s theory, which assumed that electrons moved in circular orbits, was extended by the German physicist Arnold Sommerfeld to include elliptic orbits and other refinements.)
Lilienfeld tried to produce a very high vacuum, especially to investigate the discharge current in glass tubes. He thoroughly degassed all metal parts of the tube as well as the glass tube up to the softening temperature, to reduce any gas release during the operation of the discharge tube, which he ran with some ten thousand volts.
The vacuum was not only produced by conventional vacuum pumps, such as the Gaede pump, but by the gas adsorption of cooled charcoal. He started with liquid air, but after obtaining the technical means, he also tried liquid hydrogen. When finally a cryostat was finished in the institute, he even used solid hydrogen, obtained by pumping off the hydrogen.
On 1 August 1916, the Saxonian ministry promoted J.E. Lilienfeld to an extra budget, extraordinary professor (equivalent to associate professor). The award of such a professorship can be explained by the fact that he was not a successor of somebody who had died or left, leaving a budget, so indeed a new position was necessary for Lilienfeld and he was given it despite of the war times.
Lilienfeld, always eager to apply scientific results, obtained several patents on field emission devices originating from his research of current in vacuum tubes, but with no obvious technical applications at that time. Lilienfeld suggested the use of cold emission to produce charge carriers. Later on, he applied for patents in which he described devices, which show a closer similarity to a field-emission gun.
In a patent application of 1922 for an autoelectric device, Lilienfield clearly states that “the invention relates to an electron releasing device embodying an autoelectronic effect, that is to say, a release of electrons due solely to an electric field”. He suggested the use of electropositive metals, such as the alkali and alkaline earth metals (e.g. cesium, rubidium, sodium and lithium).
Autoelectronic device with a field emission tip which can be cleaned by electron bombardment and covered with distilled substances to change emission properties from Lilienfeld’s USA patent (J.E. Lilienfeld, Autoelectronic Device, US Patent 1,578,045, Application tiled January 28, 1922, patented March 23, 1926).
Lilienfield applied for another field-emission device patent in 1928, named the authoeletronic triode device, where an additional magnetic field was necessary. The device could be used for X-ray generation, as well as a generator of alternating current [then] “the tube may operate as an externally excited, or a self-excited, device to generate suitable oscillations”.
Scheme of the autoelectronic mode device from Lilienfeld’s USA patent (J.E. Lilienfeld, Autoelectronic mode device, US Patent 1,979,275, application October 3, 1928, patented November 6, 1934).
In 1921 Lilienfeld traveled to the United States to lecture and to pursue his patent claims, particularly those relating to General Electric’s X-ray tubes, and to attempt to regain rights to his U.S. patents, which had been seized by the Alien Property Custodian in 1919.
By 1922 he was spending a large portion of his time in the United States. In 1926 he resigned his faculty position at Leipzig to stay in the United States (he decided to immigrate due to the increasing persecution of Jews in Germany). Lilienfeld held a series of temporary appointments during this period. When Lilienfeld first came to USA, he did some work at New York University on a temporary appointment for a year or two.
In 1928 Lilienfeld took a research and development position with Amrad, Inc., a manufacturer of radios and radio parts, in Malden, Massachusetts. He began work on the electrochemistry of anodic aluminum oxide films and their application in the manufacture of electrolytic capacitors, essential components in much electronic equipment. His detailed studies between 1928 and 1932 of the anodization process and of the structure of the resulting films have received subsequent confirmation.
His 1931 patent describing a method for producing stable crystalline anodic films remained the basis for the manufacture of electrolytic capacitors into the twenty-first century. There is some evidence that his capacitor work may have led to the transistor discovery/invention as Lilienfeld patented the first solid state electrolytic capacitor (#1,906,691, filed on March 28, 1928) and a solid state rectifier in 1926 (patent #1,611,653). Julius Edgar Lilienfeld gave a 49 page paper on electrolytic capacitors before the Electrochemical Society in 1930, with two shorter papers in 1932 and 1935.
The fundamental theories and practice laid out in these papers remains in use to the present day for aluminum capacitors (a $6,000,000,000/year business world wide). He developed and patented other improvements even after his Malden laboratory, then known as Ergon Research Laboratories of Magnavox Corporation, closed its doors in 1935.
Lilienfeld found, however, in 1927, employment as director of the Ergon Research Laboratories in Malden, Massachusetts, and lived nearby in 239, Forest St. Winchester, Mass. In a letter to Albert Einstein, Lilienfeld wrote that he did some work in his own laboratory for a few branches of industry, more or less of the consulting kind. In the Ergon Research Laboratories his interest focused on electrolytic condensers, which might be due to the profile of this institution. Different patents of Lilienfeld concern the improvement or measurement of electrolytic condensers.
While at the Ergon Research Laboratories, Lilienfeld obviously had suppressed his interest in strong electric fields and had worked as a chemical physicist, looking primarily at interfaces between electrolytes and salts or other substances, Finally he returned again to higher fields and invented devices, which affect our present life in countless applications.
There are several patents of Lilienfeld, which contain new ideas for devices. One would expect that he tried to improve the electron tube, being acquainted with the technology of X-ray tubes and the ultra-high vacuum (UHV) techniques. Lilienfeld, however, thought about a totally different device with no external or internal similarity to a radio receiver tube.
In a letter to Otto Wiener on October 16, 1926, he writes “I had much pleasure doing research on a phenomenon which is known though ignored by physicists and which can be investigated with relatively small means”. He continues “The practical use is a rectifier that delivers up to 3 Amps and can be used for charging of accumulators and many other purposes where low voltages are required”.
It is known, that Walter Schottky wrote in his extensive article on cold and hot electron discharges (W. Schottky, Uber kalte und warme Elektronenentladungen, Z. Physik 1923, 14, 63-106) a section on rectifying contacts, and this might have influenced Lilienfeld.
Residing in Brooklyn, New York, Lilienfeld applied for a patent on a rectifying apparatus for alternating current, which seems to be the starting point for his patents on more important solid-state devices. He refers to dry-cell rectifier patents by Pawlowski and others, and suggests a powdered compound of copper and sulfur, which is precompressed and, to insure the contact throughout the life of the cell, he suggests, as a novel feature, a pressure above the minimum required, which is realized by a special holder and spring.
A rectifier apparatus for alternating current, scheme from the Lilienfeld patent (J.E. Lilienfeld: Rectifying apparatus for alternating current, US Patent 1,611,653, application filed March 27, 1926, patented December 21, 1926)
Lilienfeld’s construction appears simple, but the use of a solid compound opens in fact an avenue to solid-state devices. Similar to his idea with field-emission devices, where he totally left behind the classical thermionic diode or triode vacuum tube, he again thought about a different principle, now even more radical in thought, by focussing his undivided attention on the conductivity modulation of a solid by a transverse field. Starting 1926, in Brooklyn, N.Y., Lilienfeld applied for three patents.
The first two, from 1926 and 1928, describe what we now call a field-effect transistor (FET) structure. The first patent (J.E. Lilienfeld, Method and apparatus for controlling electric currents, US Patent 1,745,175, application filed October 8, 1926, granted January 18, 1930) gives a MESFET or metal/semiconductor FET. The second patent (J.E. Lilienfeld, Device for controlling electric current, US Patent 1,900,018 application filed March 28, 1928, patented March 7, 1933) is derived from the first, and gives a depletion mode MOSFET.
The n-type Metal – Oxide – Semiconductor Field – Effect – Transistor (nMOSFET) consists of a source and a drain, two highly conducting n-type semiconductor regions, which are isolated from the p-type substrate by reversed – biased p-n diodes.
A metal or poly – crystalline gate covers the region between source and drain. The gate is separated from the semiconductor by the gate oxide. The basic structure of an n-type MOSFET and the corresponding circuit symbol are shown in the Figure.
As can be seen on the figure the source and drain regions are identical. It is the applied voltages, which determine which n-type region provides the electrons and becomes the source, while the other n-type region collects the electrons and becomes the drain. The voltages applied to the drain and gate electrode as well as to the substrate by means of a back contact are referred to the source potential, as also indicated in the Figure.
The main technological problem was the control and reduction of the surface states at the interface between the oxide and the semiconductor. Initially it was only possible to deplete an existing n-type channel by applying a negative voltage to the gate. Such devices have a conducting channel between source and drain even when no gate voltage is applied and are called “depletion-mode” devices. A reduction of the surface states enabled the fabrication of devices, which do not have a conducting channel unless a positive voltage is applied. Such devices are referred to as “enhancement-mode” devices. The electrons at the oxide-semiconductor interface are concentrated in a thin (~10 nm thick) “inversion” layer. By now, most MOSFETs are “enhancement-mode” devices.
While a minimum requirement for amplification of electrical signals is power gain, one finds that a device with both voltage and current gain is a highly desirable circuit element. The MOSFET provides current and voltage gain yielding an output current into an external load which exceeds the input current and an output voltage across that external load which exceeds the input voltage.
The current gain capability of a Field-Effect-Transistor (FET) is easily explained by the fact that no gate current is required to maintain the inversion layer and the resulting current between drain and source. The device has therefore an infinite current gain in DC. The current gain is inversely proportional to the signal frequency, reaching unity current gain at the transit frequency. The voltage gain of the MOSFET is caused by the current saturation at higher drain-source voltages, so that a small drain-current variation can cause a large drain voltage variation.
The third patent (J.E. Lilienfeld, Amplifier for electric currents, US Patent 1,877,140, application filed December 8, 1928, granted September 13, 1932) describes two other transistor structures, the Metal Base Transistor or the Semiconductor/Metal Semiconductor Transistor (SMST) and the Schottky-Barrier-Collector Transistor or MSMT.
J.E. Lilienfield-US Patent 1,877,140. First known patent describing the Metal Base Transistor or the Semiconductor/Metal Semiconductor Transistor (SMST) and the Schottky-Barrier-Collector Transistor or MSMT.
No one really knows whether Lilienfeld ever tried to build his device. Even if he did, the device would not have worked well, if at all, since the production of high quality semiconductor materials was still decades away. Thus, in the 1920s and 1930s, Lilienfeld’s solid-state amplifier ideas had no practical value to the radio industry. Like so many patents, Lilienfeld’s went into obscurity. Nevertheless, his ideas embody the principles of the modern-day, field-effect transistor (FET).
The word transistor had its beginning in 1946 in work at Bell Telephone Laboratories that used high-purity germanium to create a solid-state amplifying device. Re-invention of transistors some twenty years after the Lilienfeld’s work earned Bell Telephone Laboratories three Nobel Prizes, but they were forced to abandon all patent claims to the field-effect transistor (which dominates modern electronics) because of Lilienfeld’s “prior art.” Practical field-effect transistors date from applications of single-crystal silicon in 1960.
Lilienfeld also developed many other, though less spectacular inventions, such as a loudspeaker (patent #1,723,244), a spark plug (patent #2,015,482), vacuum tube seals (patent #2,015,483 and #2,015,484), a pupillograph for eye examinations (patent #2,445,787), motion picture camera for industrial use (patent #2,521,734), elastic fabrics and garments (patents #2,570,352, #2,659956, #2,627,603, #2,659,957, #2,700,317, and #2,880,730), fabric furniture (patents #2,891,603 and #2,907,376), and many improvements in electrolytic capacitor construction, electrolytes, foil anodizing methods, and assembly techniques.
Though Lilienfeld must have worked hard in 1926, applying for his first transistor patent, he found an American wife, Beatrice Ginsburg. They were married in New York City on May 2, 1926, and lived in Winchester, Mass., for some time, when Lilienfeld was director of the Ergon Research Laboratories in Malden, Mass. Lilienfeld became a U.S. citizen in 1934.
In 1935 he and his wife built a house in St. Thomas in the U.S. Virgin Islands in the hope of escaping an allergy associated with wheat fields from which Lilienfeld had suffered for most of his life. Lilienfeld frequently traveled between St. Thomas and various mainland locations and continued to test new ideas and patent the resulting products.
In his lifetime Lilienfeld obtained fifteen German patents and sixty U.S. patents. He fought for his patent claims until his death in St. Thomas. Even on the Virgin Islands, he made some experiments and had scientific correspondence with Albert Einstein.
Julius Edgar Lilienfeld died in Charlotte Amalie in the Virgin Islands on 28 August, 1963 at the age of 82. Although Lilienfeld’s work on high-vacuum X-ray tubes and on field-effect transistors came at the wrong times to bring him fame and although his leading role in capacitor technology is barely known, he deserves recognition as a talented if eclectic scientist and as a prolific inventor. In 1988 the annual Julius Edgar Lilienfeld Prize of the American Physical Society was established through a bequest by Beatrice Lilienfeld to recognize “outstanding contributions to physics by an individual who has exceptional skills in lecturing to audiences of non-specialists.”