dana@gmu90x.UUCP (J Dana Eckart) (07/30/88)
I have long been interested in liquid crystal displays (LCDs). However, "acceptable" displays have only recently (in the past 2 years?) become available. The three major difficulties, as I understand it, are: 1) the slow response which makes for a slow refresh (although they have gotten much faster), 2) individual pixels must be have a relatively large separation distance to prevent activating adjoining pixels, and 3) the more pixels per panel, the greater the likelyhood that one will be bad (thus compromising the entire panel). It occurs to me that all three of these problems can be circumvented by layering several (4) panels. Consider the following panel section, where different numbers correspond to different panels. [Gosh! An application of four coloring. :-)] 3 4 3 1 3 4 3 1 3 2 1 2 4 2 1 2 4 2 3 4 3 1 3 4 3 1 3 2 1 2 4 2 1 2 4 2 3 4 3 1 3 4 3 1 3 The benefits of such a layout are: 1) pixels on individual panels are separated by greater distances than if fewer panels were used (to get the same pixel density), 2) the entire display can be refreshed in 4 parallel sections (although whether or not this could truly be done in parallel depends upon the controlling hardware), and 3) each panel, having fewer pixels, should be more reliable to produce. The use of multiple layers is possible because the principle behind an LCD is that light be transmitted through nonoccluded pixels. In fact, I think that multiple layers is the technique used for developing color LCDs. The basic idea is to achieve a more pleasing display (with all the benefits of low power consumption, works well in bright light, small and flat, etc.) without requiring fundamental breakthroughs in technology. Using multiple layers of LCDs seems to accomplish this. In fact, this technique allows you to construct a display that has NO BLANK SPACE between pixels! In fact, some quick calculations give a bit more information. Suppose that we wanted a 12" square display with 1024 x 1024 pixels. Then in order to have no blank spaces between pixels, each pixel must be about .012" square. This also means that the nearest pixel is also .012" away. Do these figures fall into realm of possibility? If not, what's the highest resolution one could hope for with this method given current technology? The above numbers give about 85 pixels/inch. How many pixels/inch could using layered panels give (using current technology)? I feel certain that I must be overlooking something rather obvious, otherwise wouldn't this have already been done? I am curious about what it is that I must have overlooked. I welcome any comments. Curiosity continues to kill the cat ... J Dana Eckart UUCP: ...!(gatech | pyrdc)!gmu90x!dana INTERNET: dana@gmu90x.gmu.edu SNAIL: P.O. Box 236/Fairfax, VA 22030-0236
mlj@mit-amt.MEDIA.MIT.EDU (Mary Lou Jepsen) (07/31/88)
In article <1240@gmu90x.UUCP>, dana@gmu90x.UUCP (J Dana Eckart) writes: > This also means that the nearest pixel is also .012" away. Do these figures > fall into realm of possibility? If not, what's the highest resolution one > could hope for with this method given current technology? The above numbers > give about 85 pixels/inch. How many pixels/inch could using layered panels > give (using current technology)? > > I feel certain that I must be overlooking something rather obvious, otherwise > wouldn't this have already been done? I am curious about what it is that I > must have overlooked. I welcome any comments. I thnk that you might have overlooked some things, but there might be a way to eliminate the problems that I see: 1. Liquid Crystal are normally deposited in sheets of large area; not into individual small pixels. It is necessary to align liquid crystal molecules, this is easier to do if it you have a thin film, rather then a pit for a blob of crystals and then a lot of space and then another pit for the crystals... And, it is especailly difficult to align the super-twisted nematic liquid crystals. 2. So then you say, ok, let's use four homogeneous layers of crystals; none of this pit'o'crystals then open space then pit'o'crystals stuff. You, of course, plan on using etched transparent lines of ITO (Indium tin oxide -- a transparent conductor)so that you don't obstruct the view of layers further away from the ITO lines. The problem is that an ITO line carrying information intended for a pixel either instead or also, "turns on" the area of the sheet of liquid crystals above the ITO line. 3. To solve this problem you further complicate the already complex design, you etch your lines while keeping you pixel areas covered (with photoresist or something) then you fill this area with indexed-matched optical epoxy (Norland makes some good stuff) and take out the photoresist with something that won't damage the epoxy (acetone won't work -- but there is probably something). Then you need to fill the areas left with a conductor that is the opposite color of the activated crystal (black or white depending of the kind of crystal). I think that this will work. Hopefully, you could fit a CCD array in this area underneath the active liquid crystal area. That would yield greater contrast. 3. Check the SID digests (Society For Information Display) their conferences always feature the most up-to-date info. I think that the spacing problem hasn't been deemed as important as the resolution and contrast problems. Therefore it hasn't been addressed in the detail that the other problems have. It sounds like a good way to me though. I think that you should pursue it (but it is four times as expensive as a solution that would simply reduce the spacing requirement between the pixels ). Mary Lou Jepsen mlj@media-lab.media.mit.edu