Monday, August 13, 2012

OLEDs and Swords

At my undergraduate college, one of the first things you are given to do in materials science lab is to make a small version of a samurai sword. Though the student body is certainly smart enough and they understand the principles, no one ever makes one that works, at least not to my knowledge. Success depends on getting the edge of the sword to follow the water quenching curve on the diagram while the time-temperature-transformation profile of the back of the sword more resembles the air cooling curve. Of course, the entire sword has to be water quenched at once. There is a story about a samurai sword maker that cut off the hand o his apprentice when the apprentice stuck his hand in the quench water to see what temperature it was; the water temperature was a secret that the master was not ready to reveal. The diagram above is referred to as a Time-Temperature-Tansformation (TTT) curve.

The entire process is very dynamic and analysis of the end product does not necessarily tell you what went on. The problem with a student sitting down and figuring this all out is that there are multiple variables and the entire process is very non-linear; the difference between being very close and being a million mils away is not always apparent. Sometimes it does not matter how smart you are, you have to have the right recipe. That is why a number of companies have sprung up in silicon valley that offer a process for testing multiple micro-samples at once, to speed up the process of finding the right recipe. This differs substantially from a normal product development where all of the sub-components can be tested separately. A valley VC that specializes in materials based companies once told me that he never actually invests in a company that has yet to complete their materials development. This is in part, why there are so few technical glass companies in the world. A lot depends on their experience and catalog of recipes (glass chemistry, furnace chemistry, heat treating, etc.) that they have built up over time. Sometimes tramp chemical elements in the parts per billion range can have a dramatic effect on the product outcome. As semi-conductor makers are aware, softly whispering the word alkali in the fab can put enough sodium in the product to kill production. It was a parts per billion chemistry issue (with a phosphor poison) that originally put Westinghouse, the inventor of the active matrix LCD, out of the TV business.

OLED process development has exactly the same issues.


  1. A bit more on chemistry.... Glassmaking furnaces have to be periodically rebuilt. At one point, at the company where I was working, a newly rebuilt furnace came into production with the glass foaming (lots and lots of bubbles). Considerable effort was put into fixing the problem until someone decided to contact the furnace foreman, who had retired since the last rebuild. He said that he had no idea what was making the glass foam but that he traditionally threw a silver dollar into a rebuilt furnace for good luck.

    The issue that Westinghouse had with their TV production was that someone replaced a stainless steel washwater filter with a copper coated filter. It deposited just enough copper on the product so that their TV tubes would start going dark, after about 6 months in the field.

  2. At one point in time, Corning developed a glass razor blade; it never wore out. It was judged uneconomic to go into production because you could only ever sell one to each person.


Note: Only a member of this blog may post a comment.