Tuesday, March 25, 2003

Back to my normal programming

This article (via slashdot) discusses the fact that the world's first 20 inch colour screen based on Organic Light Emitting Diodes (OLEDs) is about to go into production. This is a large WXGA (1280x1024) colour screen, good for laptops or other applications such as flat screen televisions. This is quite exciting.

But what does this mean? Well, as I have mentioned before, flat panel displays presently come in two types. The most common are Liquid Crystal Displays, such as those on laptops, mobile phones, and flat panel televisions with smaller screens. These consist of arrays of pixels, each made of a material that varies from being transparent to opaque depending on the size of the electrical voltage you apply to it. Each of these pixels has a red, green, or blue filter placed over it, and a light is shone from behind the screen. Therefore it is possible for any image in any combination of colours to appear on the screen. These screens are strong and robust, and have very stable images, making them excellent for computer screens. However, for televisions they leave a little to be desired, for several reasons.

Firstly, LCD displays are an example what are called transmissive displays. This means that the light coming from the front of the screen is not being generated by screen itself, but is being shown from behind the screen and through the screen. Transmissive displays have two problems. They have limited viewing angles - meaning that they are best viewed from directly in front of the screen rather than from one side. They are not all that bright, and these types of screen are not very good in environments where there is a lot of background light. (Rear projection televisions, which were the most common type of large screen set until recently, are also a transmissive display, and also have both of these problems). These problems can be reduced by making the screen itself as thin as possible,LCD displays specifically have another problem, which is that they have slow response times. Rapid moving action on LCD screens tends to blur.

None of these problems are huge issues for computer screens, which we look at from straight in front and on which we generally do watch fast moving action. (The exceptions are when we watch DVDs on out laptops, and when we play games). For this reason, and due to the fact that billions of dollars have been spent on designing LCD screens that are both thiner and which have faster response times, LCD screens have been moving from merely being used on laptops to being used on many desktop PCs as well. (The exception is high end gaming machines, for which LCD resonse times are still clearly too slow). There has also been a move towards producing LCD based flat panel television screens for domestic use, but these leave something to be desired.

These are one of two common flat panel technologies for television screens. The other is plasma displays. A plasma display essentially consists of a large number of tiny neon lights, in a mixture of red, green, and blue, each of which is controlled individually. Together they can produce a picture. Plasma displays (like conventional CRT televisions) are an emissive display. The light is actually generated on the surface of the display. These are very bright, can be viewed from any angle, and have fast response times. However, it is not possible to build individual display elements below a certain size. This means that images on plasma screens are often a little grainy, and that plasma screens cannot be made less than about 32 inches in diagonal. Also, plasma displays are very heavy, fragile, and use a lot of power, whereas LCD displays are light, robust, and use relatively little power.

Therefore, the flat panel display market presently consists of two technologies. LCD is predominant for displays up to about 30 inches (although the largest in existence is 40 inches) and plasma is predominant for screens from about 40 inches (although the smallest is 32 inches), with some overlap between 30 and 40 inches.

What would be good is another display technology that is emissive and hence bright and can be viewed from any angle, uses low power consumption, allows small pixels and so does not lead to grainy displays, and is not heavy and not fragile. OLEDs may potentially be able to fill this niche. The little flashing lights on the front of your computer are Light Emitting Diodes (LED), but these are solid state light emitting diodes made from semiconductors like Gallium Arsenide and Gallium Nitride. These cannot be made very small, and so are only useful for making very large screens. (However, they have revolutionised the technology behind very large screens like stadium scoreboards). However, it turns out that it is also possible to make LEDs out of organic molecules - that is those consisting of chains of carbon atoms. If this can be done, these can be used for building screens These can be much smaller than conventional LEDs, and a great deal of effort has been spent on developing them to the level where an array of them can be put together to create a screen. Conceivably, OLED displays will lack virtually all of the limitations of LCDs and plasma displays, and if they fulfil their potential they will probably supersede both.

This is why the article I quote at the start of the post is so interesting. Apparently Chi Mei Optoelectronics Corporation or Taiwan in collaboration with IBM Japan have actually done this, and they have a 20 inch OLED display on the market. I haven't actually physically seen one of these, but it would be interesting to do so. Still, it sounds good. What is also interesting is that the large keiretsu based Japanese consumer electronics companies like Toshiba and Hitachi are again absent. (Sharp and Seiko Epson appear to be doing work in the area though - these companies also pioneered LCDs 25 years ago). This new development is another invention of the parallel consumer electronics industry that has sprung up in Taiwan, Korea, and southern coastal China (with American expertise) initially to provide low cost components essentially for the PC industry but which has subsequently broadened.

In any event, this is big news. You are going to see OLED displays everywhere within a small number of years. (For a little more information on OLEDs, there is quite a good article here).

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