I’m a senior research manager in charge of plastic electronics. You’re going to ask me what plastic electronics is and so let me set the context by saying that all the products that we carry around these days increasingly are all user interface. So if you have a cellphone, if you have a tablet, if you have a laptop, most of what you see is either a screen or keyboard or a combination of the two.
Increasingly the physical product is dominated by those components. The screen; the touch elements, possibly a keyboard if you have one.
If you take a laptop screen, it is quite a chunky element. It’s made of lots and lots of stuff and it’s quite a weight. It’s a lot of expensive double glazing. It is two sheets of glass, which is fragile and the way that these displays are made they are essentially like making a giant silicon chip.
They take even larger sheets of glass and cover them with transistors, by quite an expensive process. It’s a process of putting layers of exotic materials down, at high temperatures and often in a vacuum chamber, and then those materials are patterned by putting a resist everywhere, exposing the bits you don’t want, etching the resist away, etching the exotic material away and then washing off the resist.
You only want a few wires or lines or dots, they get left behind. Everything else has been put on and then etched away, rinsed, thrown away and put down the drain.
Laptop screens are heavy and expensive and are also not very efficient. With today’s displays 90 per cent of the light that goes into the backlight is thrown away. They are inefficient and not very green as a product. It impacts on your battery life, you need a bigger battery and it makes the product bigger and heavier.
What could we do about that? We started looking at this a number of years ago. The first thing we thought was if you didn’t have to continually refresh the display maybe you could make the whole display much simpler. Today’s displays are painting the image 60 times a second. That’s, for a complex display, quite a fast data rate and speed usually means power, so that’s another drain on power. The image was written some years ago and it’s not actually not plugged in but it keeps its image. So it’s not burning power, unless you are updating. Not only that, it is made on plastic. I can take you through the manufacturing process. We have gone to what we call printed, or plastic electronics where we are trying to pattern things rather than subtractively, the way I described before, much more towards how a printing system would do it, additively. You only put what you want where you want it. This saves on a lot of expensive, exotic materials.
The magic behind this display, to give it its memory, every pixel remembers its state, is that it has this bumpy surface. It’s expensive double glazing, it’s a liquid crystal display, with a thin layer of liquid between two layers of glass. The liquid is exotic, it has a grain like wood and that would normally just lie in one position. With a normal display you put a field on it and you re-orientate that grain to line up with the electric field. In this case with a bumpy surface that angles that grain up so that there are two places where it wants to stay when there is no power.
This is a very tiny structure, it’s like the size of the dimples on the back of a CD or DVD. Traditionally you would make that with lithography and here’s one we made earlier on a piece of glass. If you had to do that for every display, it’s a bit of an exotic process. What we did instead was to take a copy of that like a printing plate, on flexible plastic. It’s a copy of the original structure , made by casting a copy or imprinting a copy, and we metallised it so that we just have a window through the bit that we are interested in. we can then use that as a printing plate to make multiple copies almost on a continuous basis.
Here I have one of those copies made on a piece of plastic and you can see them same diffractive structure. We can also use that to pattern other structures in the system. So this is a thin piece of metal foil and we have imprinted structures that control where thin metal electrodes go, where RGB colour filters go by then depositing into channels. So we made a complex structure there. You can just see, contact positions with very fine metal lines that go along and this coloured area is the RGB filter colour array.
It’s easier to see on this. You make that and then transfer it off on to a transparent substrate and you can see now this is the colour filter area and these are the contacts and this is the thing we printed previously and our display is really a sandwich of those two put together with the thin layer of the liquid crystal in between it.
That results in the display you see here and here’s an earlier version. As you can see this is done here at our lab here in Bristol, it’s effectively made by hand, Blue Peter style with sticky tape because we are trying to do the research we then put that into industry. One of the other things that’s appealing about plastic electronics, a lot of these processes are potentially ten times cheaper to make in terms of the investments you have to make to build a factory. So it’s an area where new manufacturing technologies can come along and there may be much more potential for starting to make at least elements of this in Europe, in the UK and so there’s a potential commercial benefit to the UK here an we’re trying to encourage that as much as we can.
So what will this actually mean in terms of the displays on our phones and our laptops?
So this is what we did, we did this some years ago. We were trying to save power so that you would have a longer battery life, you could have more complex images, you would simplify some of the electronics by only having to incrementally update, rather than repaint the whole screen continually. If you are just reading a page of text you only update it when you want to change certain things.
When we completed this work, people made the obvious link that we would save a lot of power in driving the display but you still have to have a light behind it. Almost all colour displays today are effectively stained glass windows with red, green and blue sub-pixels that filter out the light and so you just let in the red, or the red and the green or red green blue if you want white through. That still burns a lot of power because you still need to have a lot of light. The red, green and blue filters throw away two thirds of the light. The rest of the optics to make it work throw away another 50 per cent at least. And also you can’t have a completely open pixel, you have to have a border around it and so forth and that throws away even more. That’s what gives you a net result of only 10 per cent, or much less sometimes coming through the display.
So we were then asked to look at, well if you are really going to have much lower power portable batteries that have much better battery life, thinner, lighter, cheaper can you fix that problem and just use ambient light rather than carry a light around with you?
This has no light on behind it. It’s a plastic display which is about a millimetre thick. It’s just mounted on this to keep it secure because it’s a made by hand prototype and it’s cycling through. This is not a full blown display at this point. It’s the HP logo as a segmented display so we’re driving the whole HP logo shape as one giant pixel as you like we are driving each of the coloured segments. This was to test the total colour range. So the only displays that currently use just ambient light are things like the e-books, which are black and white. There are just beginning to come out some colour ones. But they have the same problem that if they have red, green, blue colour filters on the front they throw most of the light away so you either end up with a very dark display or very pale colours to compensate for it. This is, just like printing, is a cyan, yellow, magenta layered display so we are controlling each of those colours by subtractive colour rather than additive colour which is what a normal display does.
So again, a plastic display potentially made by the same kind of techniques, now with much better optics, much, much more efficient optically so you can get away with just using ambient light. It is actually quite bright colours.
Ambient light is all very well during daylight hours, what about when it’s dark?
You can of course, like you would with a magazine, book or piece of paper, you turn the light on. If you need a bit of additional light it’s much more efficient given that this is very optically efficient, you don’t need a very bright light to make it work. That’s the problem with the more traditional displays is that you need 10 times the amount of light to match ambient and that’s in office conditions. If you take your backlit display outside when it’s sunny you are trying to compete your backlight against the sun with a lot of inefficiency and it just doesn’t make sense. So that this will get better as the lights get brighter. Yes if you were in very dark conditions you might want some supplementary light but that would be just as you would if you were to read a magazine or a book. Or you could build in some really low power front lighting. Some of the monochrome eBooks are doing that now. They have simple glow light, an LED that illuminates it enough in dark conditions. 90 per cent of the time people have enough light for them to see what they are doing.
So what I just showed you, if you put a display that is showing yellow light cyan light and magenta light they are actually absorbing red, green and blue. That’s why I said that they were working the opposite way around – subtractive rather than additive. We are effectively turning blue absorption off in the yellow layer. If you therefore have to stack those layers together you still have a loss problem that you have to go through a lot of layers, a lot more layers, three times as many as in a normal display and you still lose some things. It’s very easy for the colours to become muddy. So the innovation, what enabled us to actually have that bright colour that you saw there, is that the blue light only goes through the top layer, it doesn’t go through the bottom layers. We have magic mirrors that return the light as soon as they possibly can.
On a black background you can see very bright red, green, blue colours. The slightly magic thing is that they look perfectly diffused like they are perfectly bright coloured paper. This is an ordinary diffuser next to it that looks a lot less bright. If you look through it, it’s not diffused any longer whereas the diffuser still is, that’s why we say that there’s a kind of magic element.
This enables the blue light comes in, gets processed by the yellow ink layer if you like and then immediately returned by this and it’s returned in a nice scattery way as it would be from a scattery piece of paper. But the light that carries on to be processed by the red and green absorbing layers, the cyan and the magenta layers of the display is undisturbed so it doesn’t get messed up before it gets processed. We have found a nice cheap way of doing it. You can do it in a rather expensive, exotic way but to make a low cost display you have got to make it simpler. Here we have put all that together and we’ve made it pixelated. We worked with some people in the US to make a cyan, yellow, magenta display on plastic with transistors to drive the pixels and put the whole thing together and you can see that this is cycling through, with the HP logo spinning and quite good colour. There is a little colour reference, this is a colour standard for simple printing and we are using it as a sort of reference point to compare.
So this is a plastics display, made using plastic electronics techniques, no backlight, just using ambient light. It’s probably the most efficient colour display in the world at the moment I would say.
In terms of power consumption, what are we talking about it, in comparative terms?
In comparative terms if you take a tablet display these days that might be consuming 5 watts, it’s on a 1-10 watt range depending on exactly what technology is being used. This could be 10 or a hundred times better than that because most of the power goes into the backlight and that’s gone completely. So it’s significantly less.
And in terms of resolution of displays?
As you try to get higher and higher resolutions the optical efficiency is more and more challenging to get because there is less room to squeeze in all the circuitry and so forth. I don’t think this will hit very high resolution immediately, like all technologies, there will be a maturity where we start with the lower resolution one, where it’s easier to do, and then roll it out. There’s a bit of a win we have because to do any particular resolution a standard display has red, green and blue side-by-side. So in one dimension it has already three times the resolution and so we only need a whole single pixel, we just have them stacked on top of each other. So we have a little bit of a win there in resolution terms. But it would probably start off in the sort of just under 100 pixels per inch range to get the kind of optical efficiency and the colour and then as the manufacturing technology matures, we would hope to pus that towards the higher resolutions. It would start not in the front of screen, main screen, in its first product, hitting the market. It would start with secondary displays and other applications where you are less critical with higher resolution. If you think of electronic white boards for example. You write on a white board with a pen, the nib is several millimetres across, so to do an electronic version of that you wouldn’t need super-high resolution to start with you might want it eventually but you wouldn’t need it initially.
And in terms of timeframe, when do you perceive that these sort of things will be on the market?
We will maybe be able to get some early versions out in the next year or two, that’s something we are actively working on, we can’t give a definite timeframe. What we are hoping to do is work with HP’s partners and supply chain because this involves a lot of people doing a lot of interesting technology to get it together and that’s something we are actively working on now.
