OLEDS and Why Your Old CRT TV still Works

Two stories about TV, not directly about OLED, that I will tie together down below. This note is about OLEDs. Although you can not buy a LCD TV that was made in the US, the active matrix LCD was actually invented in the US, in Pittsburgh by Westinghouse. Westinghouse was a prominent TV brand that was developing new technology. Westinghouse did not survive in the TV business long enough to capitalize on their invention because they had a problem at their factory. It seems a worker replaced a steel mesh filter in their water reclaim system with a copper coated steel mesh filter. That put just enough copper into the wash water and just enough wash water residue was left on the TV screen to serve as a phosphor poison. The TV tubes that the Westinghouse factory was making would go dark after about 6 months of use. The resultant recall of half a year’s production put Westinghouse out of the TV business. Parts per billion of copper put them out of business.

Another major brand of TV in those times was General Electric (GE). Although GE made glass for things such as light bulbs and such, GE bought their glass for CRT tubes from others. In addition to making glass, GE had an array of materials technologies including silicones and polycarbonate. At one point, in order to put downward pressure on glass prices, GE threatened to develop a polycarbonate CRT bulb. The glassmakers looked at the threat and determined that although such a product was possible and did have some advantages relative to glass, the product would only last about a year before there was enough inward migration of atmospheric gas to render the polycarbonate CRT non-functional.

The point of both stories is that emissive technologies tend to be sensitive to the most minute amount of contaminants. That is why some of the companies developing OLED technology concentrate on an ultra-clean manufacturing environment. It is also why the other key to OLED’s future is hermaticity. In a CRT, glass provided an absolute hermetic environment. The CRT was made in a clean environment, the inside of the tube, where the phosphors were, was maintained in high vacuum. Further a sacrificial barium “getter” was deposited on the inside of the tube to bind any stray oxygen that was left over from manufacture.

So, the phosphors did their thing in an absolutely pristine environment that was maintained as long as the tube continued to hold its vacuum, which is tantamount to forever for a consumer product. In terms of product chemistry, the environment virtually eliminated any alternative pathways that could be formed between the phosphor in its elevated state and when it drops back down to its base state by emitting a photon. The industry employed other tricks, such as moving to higher and higher voltage phosphors. This brought the product to the point where the phosphor aging was no longer the primary aging limitation but metallization of the glass from decades of electron bombardment.

The high voltage architecture may have some relevance to OLED design as well. But certainly, cleanliness and hermaticity are the key to making OLED technology work.

Big Surprise

The iPhone 6 does not us sapphire. Apparently Ray Soneira, agrees with me; this is from his DisplayMate website, "The use of sapphire to make the iPhone screens scratch proof was one of the most talked about rumors over past year as a result of Apple’s $578M investment with GT Advanced Technologies to build a factory in Arizona. The likelihood of sapphire appearing on the iPhone 6 was close to zero because it will probably take at least another year for everything to come together. It is important to note that sapphire has some downsides over and above its much higher cost and manufacturing complexity. The most important issue for display performance is that sapphire has almost double the screen Reflectance of glass (due to principles of optics), so it will be harder to read sapphire screens in high ambient light. That might be one reason why the recently announced Apple Watch Sport edition has a cover glass rather than sapphire like the other models – because it is much more likely to be used unshielded in high ambient light outdoors. Another reason is that while sapphire is very hard it is also brittle and is likely more prone to impact breakage, which is more common in sports situations. So, if given the choice, I personally would choose a cover glass with its better screen visibility and breakage protection. Others may find the scratch protection more important."

There is commonly confusion over display specifications. Many people do not understand the difference between color gamut and color resolution. And it is understandable that a non technical person might not understand the difference between hardness and toughness or the difference between an isotropic glass and an anisotropic transparent crystal. However, a display being fundamentally an optical device, when the discussion turns to a new material in the optical chain, it is amazing that the new material's optical performance could be so widely ignored. In GTAT's promotional literature, they did publish its "index of refraction", for all to see (... that particular page seems to have been removed from the web site. "Oops!.. Sorry about that. The page you requested cannot be found.") However the format of the publishing indicated that "more is better" even though a higher index is exponentially more surface reflection. In "More is Better, " I detail the problems mobile displays have with surface reflections; how that is the limiting factor on current mobile LCD performance. The amazing hype regarding sapphire leading up to the iPhone 6 announcement just goes to prove that no one actually reads specs.

Update 10/8/14 GTAT filed for chapter 11 on 10/6/14 The stock is now selling below $2 and had been as high as over $20. Its market cap is now just under $240 Million.

Smart Watch Formats

In the Sep 20, 2009 edition of “Touch Panel,” in an article that I published titled, “The case for a flexible touch panel keyboard” I made this statement regarding mobile devices at that time, “This limitation in screen information content has produced a number of “unbalanced” designs where the computing power of the device addresses too few pixels to adequately support the intended functions of the device.” Of course that statement was shortly followed, in June of 2010, with Apple’s retina display where they effectively pushed pixel density to the limit. It has subsequently been followed by numerous large phone designs where screen sizes have grown from 3.5” to well over 5” with the actual screen now constituting almost the entire front of the device rather than 70%. And makers continue to add to the pixel density even though the retina display theoretically started already at the resolution limit of the human eye. Full HD resolution is now available giving 2 megapixels, about 13.5 times the number of pixels as the Apple 3G. Given this journey of the past few years, mobile device makers may be planning to start over, not with low resolution displays but with smaller displays in a watch format with the consequent reduction in pixel count proportional to the reduction in screen area.

Some time ago one of my cousins described a technique for flight simulator displays where the direction the pilot was looking was monitored. The center of his field of view was generated in high resolution while things in the pilot’s peripheral were generated in much lower resolution. An observer watching the pilot in the simulator could clearly see the high and low resolution areas of the screen. However, to the pilot, it appeared that the entire screen was in high resolution. This technique was adopted to maximize the use of limited computing power in rendering an image for the pilot. Although a smart watch may not have the same computing power limitations, it would seem that the screen area limitations could be addressed by a similar technique.

The current generation of motion sensors is very small and very precise. They could be used to create virtual screen area to compensate for very small screens. This is standard in “near to eye” applications but could also be useful on a wrist mounted device. But there is no real substitute for just using a larger display. The first wrist watches were pocket watches with a wrist band. They kept pretty-much the same size although they were eventually engineered to be much thinner. Given their single function, there was never much of a point to making them bigger. That is not the case with a smart watch. A large cylindrical display with the virtual screen area enhancement would have interesting 3D effects as well.