This was a liquid that showed long-range order, though only over a limited temperature range. On melting from the frozen state, the long-range order made the liquid cloudy, but as the temperature was increased, it became clear. The molecules of the liquid were long and thin, and the long directions followed an ordered pattern.
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Further research revealed three types of order. Smectic crystals are similar in their order to crystalline solids, in that the molecules form equally spaced layers, all pointing in the same direction, though with little positional order within a layer. Cholesteric crystals are layered, but the molecules lie along the layers, all those in a layer pointing in the same direction, with that direction changing gradually and regularly with distance, so that the director follows a helix.
Williams subsequently left the laboratory, but his lead was followed by George Heilmeier, who persuaded the RCA management to start an LC project. LCs are anisotropic in almost all their physical characteristics. The values of refractive index, dielectric constant, conductivity, elasticity and viscosity are very different when measured along the long molecular axis or the short axes. Because of the dielectric anisotropy, the molecule will turn in an electric field, and nematics divide into two classes, positive crystals, which align along the field, and negative crystals, which try to lie across it.
DSM can be generated in negative nematics, because charges build up along the molecules, giving rise to a field at right angles to the applied field. At higher fields, turbulence occurs. RCA publicized their discoveries in , and, amid some excitement, many companies set about exploiting liquid crystal displays LCD in digital watches and calculators.
Curiously, RCA was an exception. RCA had little interest in small instruments. Their display involvement was in CRTs, and here their position was almost unique. Harold Law and Al Schroeder had invented the shadow-mask tube some 10 years earlier, and this was now being made in quantity at plants in Lancaster, Pennsylvania, and Harrison, New Jersey Law , The company had early adopted the principle of licensing their inventions, and shadow-mask tubes were now produced worldwide. They were conscious of the problems of addressing, and unconvinced that the RCA invention of the TFT in Weimer a , b would be the solution.
Looking back, it is obvious that RCA held most of the assets needed to forge and preserve world leadership in flat-panel displays, but they opted out. In the next year they abandoned all work on LC TV, though some work on small displays continued until It would not be an overstatement to say that US industry lost its way on displays in the s. That laboratory had not been in the forefront of discovery on transistors and chips, relying mainly on licensing from Bell Telephone Laboratories BTL , but it had a proud record of innovation in vacuum tubes, culminating in the invention of the shadow-mask CRT.
RCA led in the early research on TFTs and LCDs, but the belief that flat-panel displays were against their long-term interests led them to withdraw from the field in The other potential industrial leader, BTL, had stayed curiously aloof from the frenzied search for novel display technology, partly because of their increased involvement in semiconductor lasers for communications, but also because senior figures in their laboratory were unconvinced that new displays were required. Prospects for new display technologies are clouded by the fact that there exists a device, the familiar CRT, that has long provided a versatile, elegant, functional, economical, and largely satisfactory solution.
In circumstances where industry was unwilling to lead in long-term research programmes, defence funding had previously filled the gap, and we have seen that this indeed happened in the UK.
The opposition was led, strangely, by the scientist who had contributed much to the earlier enthusiasm at RCA for LCs, George Heilmeier. He had left RCA in , and within two years was holding a senior post in the US DoD with responsibility for electronic device research contracts. How many realistic scenarios are there in which we win because we have a flat-panel, matrix-addressed display in the cockpit? We must feed on existing technologies.
It was not surprising then that in the s most of the important developments in this field came from Europe and Japan. There he suggested to Martin Schadt, the LC group leader, that he should work on a new display effect that exploited positive nematics. It was known that nematic molecules would lie down on a glass substrate that had been rubbed with a polishing cloth in one direction.
However, if a field was applied across that cell, the molecules would align themselves along the field, the twist would disappear, and light could pass. There were some curious features to this invention.
Such a rapid sequence of conception and construction is unusual. In fact, as Helfrich admitted 20 years later, he had thought of the TN effect in , and other ex-RCA staff confirmed this. However, he made little attempt to attract management interest, since, as he explained, he was there to help theoretical understanding, not to invent devices.
RCA made no attempt to invalidate the patent or to claim ownership, possibly because there were further legal complications Kawamoto James Fergason was a scientist who had worked on cholesteric LCs at Westinghouse in the early s, but left in to join Kent State University.
He made no attempt then to patent the concept, and was surprised, and probably irritated, when a colleague reported back after a visit to H-LR that Schadt and Helfrich had invented a new form of LCD.
In fact, it was as a result of this inadvertent disclosure that H-LR had rapidly taken the patenting and publishing actions. Fergason himself set about composing patents and, after an abortive attempt in February, submitted in April a patent, which was granted in Fergason No mention was made in this patent of his earlier publications. He therefore had good grounds for contesting the H-LR patent, and after protracted legal proceedings this was withdrawn.
A compromise agreement shared royalties amicably between all the interested parties except RCA.
Though the way was now legally clear for companies to exploit TN displays, the commercial position was unclear. A number of companies had taken licences from RCA to exploit dynamic scattering, and they were reluctant to adopt an untested technology. However, problems soon arose because of the LC material. It became apparent that there was no stable LC available, and LCDs were acquiring a poor reputation for reliability.
Now events took a curious turn, because a politician became involved.
He was surprised to hear that royalties to RCA on the shadow-mask tube cost the UK more than Concorde, and after overnight deliberation authorized the Director of RRE, Dr later Sir George Macfarlane, to start a programme on flat-panel electronic displays. Surprised at this rapid decision, and informed by senior staff that there was no expertise within RRE to mount a meaningful development programme, he set up a committee to study the field.
This recommended in December that the UK Government should fund research on flat-panel electronic displays, with LCs as the first priority Hilsum Though formal approval of this recommendation would normally have taken some months, and, indeed, was never granted, RRE had anticipated approval, and justified their action on the urgent need for displays for the portable radar sets they had invented.
The Plessey Research Laboratory at Caswell were also involved, specializing in electrophoretics. This trust was rewarded manifold. Gray was given the task of finding a stable LC, because RRE, schooled in defence requirements for reliable components, appreciated that consumers also would not tolerate short-lived equipment.
All available LCs had serious shortcomings. The solution did not come immediately.
Hull worked first on carbonate esters, then on sulphonate and carboxylic esters. All efforts were leading nowhere, and Gray was now becoming frustrated. He decided to take a step back and see if the materials had a common fragile feature. Gray realized that one common feature was the central linking group.
It would be possible to have a biphenyl structure, but this was unlikely to give a practical working temperature range. The proposed structure was.
They left with some reluctance, for their recently qualified PhD graduate, Ken Harrison, was ready to attempt the preparation of pentyl-cyano-biphenyl 5CB and pentyloxy-cyano-biphenyl 5OCB. They returned to a scene of great excitement, for both materials had been made and found to be LCs.
Even more exciting were the results of stability tests at Malvern. They needed to design complicated eutectic systems, but it would have taken far too long to plot eutectic diagrams for all promising combinations.
He realized that the Schroeder—Van Laar equation for binary eutectics might be extended to predict mixture properties from thermodynamic data for the individual materials. However, the accuracy was not high enough, and Raynes then developed a more accurate semi-empirical method, which proved ideal.
This was so useful commercially that it was not put into print for some years Raynes Raynes predicted that no mixture of biphenyls would operate well below zero. Gray then reasoned that adding a terphenyl component would give a wider range mixture, and though terphenyls were difficult to make, they proved to be the solution. Meanwhile, production processes of pure biphenyls had been perfected at Poole, where Ben Sturgeon, the Technical Director of BDH, had made inspired contributions, and before long BDH was selling biphenyl eutectics widely, for though their temperature range was not ideal, their stability was very attractive.
Using cyan and magenta phosphors, a reasonable limited-color image could be obtained. Filed 22 January. It is recommended if this is your current configuration that you do not update to version 7. Production was extremely limited, and no advertisements for it were published in New York nor Washington newspapers. Sziklai G. He has authored over 35 research papers and has over 25 issued patents in the areas of organic LEDs, lasers, photodetectors, memories, and nanostructured devices.
E7 could be said to be the saviour of the LC industry, for it was invented at a time when LCDs were suspected of being inherently unreliable, and it remained the preferred material for many years. Rapidly they dominated the market. Less than five years earlier, the company had never made an LC.
I should not give the impression that the biphenyls had no rivals. The German company Merck Chemicals had made LCs for academic users since , had increased production to meet commercial demand in , and commanded the market before biphenyls appeared. They did not remain idle. Darmstadt was stimulated by the competition, and they conceived their own stable family, similar to alkyl-cyano-biphenyls, but with a cyclohexane ring substituted for one phenyl ring.
There are many physical parameters of LCs that control the electro-optical behaviour, but the most important for displays are the elastic constants and the rotational viscosity. The threshold voltage for switching, V T , is given by 4. It can be seen that V T is independent of the viscosity and the cell thickness d , but the time constants depend on both. Since , a rapid switch-on is readily available at higher voltages. The visual appearance of a TN cell depends strongly on the angle of view, and both the viewing angle and the contrast ratio came under criticism as the possibility of major markets became apparent.