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.