User:Panjasan/TN-Patent
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[edit] Twisted Nematic field effect (TN effect) - The patent story
The twisted nematic effect (TN-effect) in liquid crystals is claimed to be first discovered by James Fergason in 1970 at the International Liquid Xtal Company in Kent Ohio. Fergason patented his work in the USA in April 22, 1971 (see US patent 3,731,986). Hoffman-La Roche scientists Wolfgang Helfrich and Martin Schadt are listed as inventors in a patent application that was filed for the twisted nematic field effect in Switzerland on December 4, 1970 (Swiss patent No. 532 261). Fergason sued the company Hoffman-La Roche in the USA and he later sold the patent for $1 million in cash, half of all US royalties, and a smaller percentage of international royalties.
Here we present material about the competing patents, how it all happened and about the final status after many years.
[edit] The TN Patent
Translation of the article of Gerhard H. Buntz (Patent Attorney, European Patent Attorney, Physicist, Basel):"Twisted Nematic Liquid Crystal Displays (TN-LCDs), an invention from Basel with global effects", Information No. 118, October 2005, issued by Internationale Treuhand AG, Basel, Genf Zurich. Published in German, translation by panjasan.
"By the end of the sixties (1960s) the management of F.Hoffmann-LaRoche AG (Roche) decided a diversification into several new fields of business of which one was medical technology.
The appointed head of R&D of this field defined several points of focus for future research and development activities. One of these focal points was the use of improved displays for medical devices, among others the use of liquid crystal displays which, for some time already have been the objective of application research in some major companies manufacturing electronic components.
Liquid crystals (LCs) are organic substances combining physical properties of both liquids and of crystalline solid state materials. Their state of matter is liquid as the state of water and oil. Contrary to "real liquids" however, their molecules are not totally disordered but aligned in a certain orientational order with respect to each other. As a result of this ordering they exhibit e.g. anisotropic optical properties of "real crystals", like refraction and polarization, etc.
This hybrid nature of liquid crystal materials started to attract the attention of researchers early in the twentieth century. Their significance beyond strange anomalousness and their potential benefits for practical applications however yet remained to be recognized. The rapid development of digital electronics and the related search for suitable display devices soon moved liquid crystals into the center of attention.
All display devices with liquid crystals (i.e. liquid crystal displays, LCDs) share the same basic construction: a thin layer of liquid crystal material is formed between two flat glass plates which are coated with electrodes for application of an electric field across the layer. These substrate plates are either both transparent or one is transparent the other one reflective.
In the year1970 the state of development of a liquid crystal display device based on an effect called dynamic scattering (DS) was most advanced. The dynamic scattering of an otherwise clearly transparent liquid crystal layer is caused by turbulences induced by a current flow through the layer, becoming apparent by scattering of light. The development of the DS effect was advanced by the US company RCA, those days the leading company in the field of LCD research.
Even though LCDs based on the dynamic scattering effect were the first ones to hit the market as numeric displays for e.g. digital clocks, the drawbacks of this effect were obvious. Optical properties, life-time, energy requirements and transition times were inferior to other competing technologies.
The only serious alternative to the DS effect was a field-effect (i.e. an effect which is not based on a flow of electric current), the so called guest-host interaction. In this effect the dichroic dye molecules that are blended into the liquid crystal material are effecting the optical response.
By this time many electronics manufacturers around the globe frenetically started to search for better display devices based on liquid crystals. That research was focused on field-effects in a category of liquid crystals known as nematic.
In about September 1970 the researchers Wolfgang Helfrich and Martin Schadt, then working in the physics department of Roche, for the first time operated an LCD based on a new effect which they just had discovered. This effect, which later became known as the twisted nematic effect is based on a layer of nematic liquid crystals which are uniformly aligned on the substrate plates by a suitable treatment of their surfaces. The direction of alignment on both plates however is not parallel, but rather rotated by 90°. This effects a continuous quarter-circle rotation of the direction of molecular orientation across thickness of the LC layer, as known from spiral staircases and corkscrews. The polarization direction of linearly polarized light traveling through such a twisted structure of LC-molecules follows the rotation of the molecules and thus, the light leaves the LC-cell with the direction of polarization rotated by 90°. When such a layer is placed between crossed (linear) polarizers we observe the following: the light which is linearly polarized by the first polarizer is rotated by the LC-cell and thus transmitted by the second (crossed) polarizer which otherwise would block the light. Inversely, a pair of parallel polarizers now blocks the light rotated by the LC-cell which otherwise, i.e. without LC-cell in between them, would be transmitted.
This helical arrangement of liquid crystal molecules and its optical properties as described above were known at that time. Not known however and discovered by Helfrich and Schadt was the behavior of the LC-layer in an electric field. i.e. when a voltage is applied between the two electrodes. They noted that the capability of the twisted liquid crystal structure to rotate the polarization of light can be annihilated by a voltages as low as 2V. Considering again a TN-cell between crossed polarizers, but now with a voltage (> 2V) applied to the cell, the light is blocked just in the case of two crossed polarizers without a TN-cell between them. Inversely, an activated TN-cell (voltage > 2V) is transparent when placed between two parallel polarizers.
An arrangement of a twisted LC-layer sandwiched between two substrate plates coated with electrodes and located between two polarizers can be controlled via the applied voltage to be either transparent or opaque (i.e. blocking) light.
An important insight was given by the fact, that this effect is occurring at voltages that are far below those required for a complete unwinding of the helical structure formed by the liquid crystal molecules. It became obvious that it was sufficient to deform the central layer of the helical structure to interrupt the rotation of the polarization of light. This finding was highly surprising and in no way predictable.
This liquid crystal cell, internally named "Drehzelle" (twist-cell) in those days, was being tested by the company Brown Boweri Cie. (BBC) in Baden with the equipment available there for this purpose. By that time there was a contract of cooperation between both companies in the field of medical technology. The results of these tests confirmed, that the novel type of liquid crystal display featured impressive properties while avoiding all known drawbacks of DS-cells.
During the period in which these test have been carried out, a researcher from Kent State University (Kent, Ohio), himself involved in liquid crystal research there, had been visiting the BBC labs. Somehow, this visiting researcher came to know about what was being tested in the BBC laboratories and, being a highly experienced expert in the field himself, it was easy for him to immediately recognize the possible impact of that new type of liquid crystal display. One of his colleagues in Kent, J. L. Fergason by name, himself also a well known expert in the field of liquid crystals, some months ago just had established a company for development and production of liquid crystal displays under the name of ILIXCO ( International Liquid Xtal Company). With respect to the commercial interest of this company the leakage of information about the new LCD under test at the BBC labs was most threatening.
Right after Helfrich and Schadt found out about that incident they asked the department of intellectual properties to prepare and deposit a patent application for protection of the new liquid crystal cell in a minimum of time, since it seemed possible that ILIXCO would attempt a patent application itself. Within two weeks a patent application was finalized and filed at the national Swiss patent office in Bern on December 4, 1970.
Since patent applications are disclosed earliest 18 months after filing it was unclear for quite some time who of both parties could claim the earlier priority date. As it turned out later, Fergason indeed had filed a patent application for the identical invention in the USA however with the filing date indicated as April 22, 1971.
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to be completed ...
[edit] Sources
- Gerhard H. Buntz (Patent Attorney, European Patent Attorney, Physicist, Basel), "Twisted Nematic Liquid Crystal Displays (TN-LCDs), an invention made in Basel with global effects", Information No. 118, October 2005, issued by Internationale Treuhand AG, Basel, Genf Zurich. Published in Germa, translation by panjasan.
- Rolf Bucher, "Wie Schweizer Firmen aus dem Flüssigkristall-Rennen fielen", Das Schicksal von Roche- und BBC-Entwicklungen in 10 Abschnitten, Neue Zürcher Zeitung Nr. 141, 20.06.2005, Seite 56/B12.
- Martin Schadt, personal communication, 2006/2007
